BCAST always promotes collaborations among individual academics, industry, and international partners. We are proud of our researchers who are carrying out world leading high quality fundamental and applied research. All our researchers are actively engaged in a number of projects.
1. TARF-LCV: Towards Affordable, closed-loop Recyclable Future Low Carbon Vehicle structures
Z Fan, G Scamans, I Stone, X Yang, W Yang We believe that the future low carbon vehicle (LCV) will be achieved by a combination of multi-material concepts with mass-optimised design approaches through the deployment of advanced low carbon input materials, efficient low carbon manufacturing processes and closed-loop recycling of end of life vehicles (ELVs). Advanced materials will include aluminium (Al), magnesium (Mg) and polymer matrix composites (PMCs) which are all supplied from a recycled source. A holistic and systematic mass-optimised design approach will be used not only for mass reduction and high performance during vehicle life, but also for facilitating reuse, remanufacture and closed loop recycling at end of vehicle life. Novel manufacturing processes will be used to reduce materials waste and energy consumption, shorten manufacturing steps and facilitate parts integration and ELV recycling.
Fully closed loop ELV recycling will be facilitated by new materials development, novel design approaches, advanced manufacturing processes and efficient disassembly technologies, all of which will be effectively guided by a full life cycle analysis (LCA).
2. (LiME) - Industrial Sponsorship: Siemens VAI Metals - Development towards industrialisation of the melt-conditioned twin roll casting process for light metals
Z Fan, K Al-Helal,
In recent years BCAST has developed the melt conditioned twin roll casting (MC-TRC) process for production of high quality light alloy strips. This project aims to further develop the MC-TRC process for both magnesium and aluminium alloy strip. Processes used within this project include melt conditioning process and TRC process
3. ExoMet - Physical processing of molten light alloys under the influence of external fields 'RTD/Innovation' account
D Eskin, H Nadendla, Z Fan, S Vadakke Madam, J Tamayo, E Djan This project revolves around innovative liquid metal engineering and the application of external physical fields, in order to significantly influence the microstructures and properties of light alloys, such as aluminium and magnesium. Three types of external fields will be explored, namely electromagnetic, ultrasonic and intense mechanical shearing.
To meet the future EU challenges of lightweighting and pollution reduction, especially relevant in transportation, it is necessary to improve the castability of light alloys to enhance grain and eutectic refinement in monolithic alloys and to develop new high strength nanocomposites using nano-reinforcers which have only recently become available.
4. UltraMelt - Fundamental Study of Cavitation Melt Processing: Opening the Way to Treating Large Volumes
D Eskin Ultrasonic cavitation treatment offers sustainable, economical and pollution-free solutions to melt processing of conventional and advanced metallic materials with resulting significant improvement of quality and properties. However, the transfer of this advanced and promising technology to industry has been hindered by difficulties in treating large volumes of liquid metal as required by processes such as continuous casting.
Current knowledge cannot answer a seemingly simple question: how long does it take to treat a certain volume of liquid with an ultrasonic source for minimum energy input, cost and complexity? This research aims to answer this question paving the way to extensive industrial use of ultrasonic melt processing with the benefit of improving the properties of lightweight structural alloys, simultaneously reducing the need for degassing and grain refinement additives - polluting (Cl, F) and expensive (Zr, T, B, Ar) - and eliminating complicated processing steps such as fluxing and rotary degassing.
This project aims to respond to the challenge of efficiently treating large liquid volumes by: (1) developing a comprehensive numerical model that couples various multi-scale and multiphysics phenomena occurring inside and outside the cavitation region and by (2) changing emphasis from conventional static batch treatment to processing in continuous liquid flow.
5. Processing of bulk MgB2 superconductor
H Nadendla, A Bhagurkar Studentship project focusing on conventional solid state reaction between Mg and Boron can result MgB2 superconducting phase.
The potential area of application will be magnetic shielding and high power handing mircrowave filters.
This is a collaborative research project between BCAST and Bulk Superconducting Materials Group at The University of Cambridge. Microstructural feature of these bulks will be initially characterised at Brunel.
6. Development of biodegradable nanocrystalline beta-TCP/Mg alloy composites (exchange with Prof Minfang Chen, China)
Y Huang The project aims to develop a novel technology for fabricating biodegradable nano beta-TCP reinforced Mg matrix composites with tailored properties for orthopaedic applications. The technology is based on a combined high-shear solidification and severe deformation processing route and will be optimised to obtain a dispersion of true nano beta-TCP particles in the matrix. The fabricated composites will be characterised and evaluated in terms of microstructure, mechanical properties and in-vitro performance. Mechanisms of strengthening and toughness enhancement and mechanisms that govern the degradation rate of the material in the human fluid environment will be investigated. The project outcomes are expected to have a strong impact on the development of a new generation of biomaterials.
7. Ballistic resistant lightweight hybrid metal matrix nano-composite structures
H Nadendla, R Davenport
Increased function in modern defence equipment and significant weight to these systems. As a result there is a constant demand for developing lightweight materials. The objective is to demonstrate processing of low-cost lightweight (1.5-2.2g/cc) hybrid, metal matrix nano-composites, with tailored mechanical properties of ballistic resistance, facture toughness, ductility and strength.
8. CASE studentship: Improved brazing processes for joining ceramics to metals to enhance structural integrity of the assembly
H Nadendla The properties of ceramics makes them a highly attractive industrial material, particularly in severe operating conditions. In order to get the most out of them it is a common requirement to join them to metals. Whilst this can be done in many ways, the common industrial method is often brazing since this give high strength, reliable joints. However, it introduces two problems, wetting and mismatch in coefficient of thermal expansion.
This ground breaking research will aid understanding of ways in which the braze filler metal reacts with the ceramic and metal surfaces during the brazing process. This project aims to build on existing in this field by developing a fundamental understanding of the ways in which the braze filler interacts with the metallic and ceramic surfaces at the molecular level.
9. HardAlt - new generation of protective coatings alternative to hard chrome
The total annual estimated direct cost of corrosion, not including wear damage, in the worlds is estimated at about 3.1% of the world’s Gross Domestic Product (GDP). Protective coatings serve to prevent wear and corrosion and thus reduce the total loss from corrosion and wear. Hard chromium plating is one of the most widely used techniques for production of such coatings. However, hard chromium faces many problems: EU restrictions due to use hexavalent chromium, health issues for the plating industry personnel due to cancers events, functional defects of the coatings and low current efficiency. Thus, there is an urgent need to substitute chrome plating with an alternative one that could provide the same or even enhanced benefits that chrome has, without causing the above problems. The target of the project is to eliminate the use of hard chromium plating in European electroplating industry by delivering a suitable alternative.
10. DOSHORMAT - Degassing machine for aluminium casting process based on ultrasound
D Eskin, K Al-Helal
Taking advantage of previous results achieved by ULTRAGASING (FP7-SME-2011-1), DOSHORMAT intends to optimise and develop two ready-to-market ultrasonic degassing machines for aluminium foundries that represent efficiency solutions for degassing molten aluminium. The degassing technology is one of the main components of quality assurance in casting industry.
The aim of DOSHORMAT is to improve and optimise the previous prototypes from ULTRAGASSING, adapting them to all the market needs, by developing one equipment specifically designed for HPDC and Gravity Casting and another for degassing much larger volumes, suitable for LPDC and, in general, for any casting activity. DOSHORMAT will improve the melt quality, reducing the gas content and removing the oxides, highly enhancing the quality and mechanical performance of the components produced (e.g. transport applications), while meeting the present and future environment regulations.
11. Ultra-Cast - Development of efficient and scalable ultrasound-assisted solidification technologies for manufacturing advanced metallic alloys
D Eskin, I Tzanakis
12. RecycAl - High Shear Processing of Recycled Aluminium Scrap for Manufacturing High Performance Aluminium Alloys
Z Fan, I Stone, J Lazaro Nebreda
The EU wrought aluminium industry is based on the use of primary aluminium. Primary aluminium production is both energy and carbon intensive and EU production is rapidly declining. Secondary aluminium (post-consumer scrap) is either downgraded into low quality cast products, or exported.
This scrap could be transformed into a low cost, low carbon feedstock for wrought product and high quality castings by the adoption of High Shear Processing (HSP) technology. This innovative new technology is based on a novel physical melt conditioning process that can be applied both to batch and continuous metal processing.
It is based on leading edge research into the heterogeneous nucleation and growth in aluminium alloys, and its promotion by dispersed oxides. The project will bridge the gap to industrialization through the involvement of a research-capable SME who will design and manufacture a prototype small industrial-scale HSP unit and then make recommendations regarding improved equipment design and likely process costs. Other SME partners will assist with economic modelling, through a life cycle analysis, which will comprise the costs of the process and the energy savings together with the impact in the carbon footprint. RecyCAL could have a major impact on the EU wrought and cast aluminium industry, leading to the consolidation of the primary and secondary industry sectors. The project could transform the EU aluminium metals cycle from one that is currently resource intensive to one that is sustainable.
13. AMS Copper - anti-microbial, self-cleaning copper composite coatings applied in metallic objects against infections transmission H Nadendla
Infection prevention measures aim to ensure the protection of people who might be vulnerable to acquiring an infection both in the general community and while receiving care due to health problems. The basic principle of infection prevention and control is hygiene. Hygiene could be divided in personal hygiene (e.g. hand washing) and inanimate object disinfection (e.g. use of chemicals for cleaning and sanitizing). However, hygiene practices is not enough to fight against infections. Indeed, the estimated annual cost of medical care for treating infectious diseases in Europe is about €120 billion while HealthCare Acquired Infections are directly responsible for approximately 37,000 deaths annually and contribute to a further 110,000 across the EU. This is because, every person comes in contact several times per day with bacteria via touching inanimate objects such as handrails, shopping carts, door knobs etc and thus, the hazard of infections is more than evident. In order to overcome this important social problem, the SMEs participants propose a novel solution to be used against diseases transmission: The application of new copper based coatings in metallic objects with photo-catalytic imposed anti-microbial and self-cleaning activity. These new composite coatings will consist of a copper matrix and chemically modified TiO2 nano-particles as reinforcing mean, and will present enhanced photo-catalytic activity under visible light irradiation. They will be applied in various metallic objects such as handles, door knobs or rails, which can potentially be reservoirs of communicable viruses, and thus will lead to a decrease of the risk of getting infected by a factor of >50%.
1. Continuous development of the melt conditioned high pressure die casting (MC-HPDC) process for shape casting of Al- and Mg-alloys M. Xia, H. Zhang, Pete Lloyd, Z Fan The high pressure die casting (HPDC) process is characterised by high efficiency, high volume and low cost. However, the HPDC components contain a substantial amount of porosity and other cast defects, resulting in inadequate mechanical performance for demanding structural applications. The objective of this project is to develop a new shape casting technology, namely, the MC-HPDC process, which maintains the advantages of the HPDC process but provides components with improved mechanical properties. The MC-HPDC process combines the worldwide patented MCAST (melt conditioning by advanced shear technology) process for melt conditioning and the conventional cold chamber HPDC process for component shaping. In this project the MC-HPDC process is continually optimised and developed for process efficiency, versatility with alloy compositions, equipment robustness and component quality.
2. Industrial scale trial production of LM24 engine mounting brackets by the MC-HPDC process H. Zhang, M. Xia, J. B. Patel, G. M. Scamans, Z Fan Vehicle weight reduction and fuel savings is an important strategy for the automotive industry through the use of more lightweight components like aluminium alloy, which is one of the lightest available commercial metals with a density approximately one third that of steel or copper. Among Al casting alloys, especially for high efficient high pressure die casting (HPDC), LM24 is widely used because of its excellent castability and melt fluidity. However, a substantial amount of porosity and other cast defects contained in the HPDC components deteriorates the mechanical properties for demanding structural applications. Nucleation controlled solidification under highly intensive shearing in MCAST (Melt Conditioning by Advanced Shearing Technology) is adopted to condition the melt before the net shape casting by the conventional HPDC. These two steps form a new process named MC-HPDC (Melt Conditioned High Pressure Die Casting) which may reduce all kinds of cast defects and improve the mechanical properties. An industrial scale trial is carried out to produce real LM24 engine mounting brackets.
3. Industrial scale trial production of AM60 automotive seat frames by the MC-HPDC process M. Xia, H. Zhang, J. B. Patel, G. M. Scamans, Z Fan Magnesium alloys are receiving increased attention as structural materials in transport industry, owing to their high strength-to-weight ratio, ease of casting and superior machinability. Among the most widely used magnesium alloys, AM60 has the optimum combination of ductility and strength. However, the hot tearing, hot crack, and porosity defects always accompany this alloy. The Melt Conditioned High Pressure Die Casting (MC-HPDC) process, which combines the newly developed MCAST (Melt Conditioning by Advanced Shearing Technology) process and the conventional cold chamber HPDC process, is used in this project to reduce these critical defects in the AM60 automotive seat frame components, which are produced in a series of industrial scale trials and to improve the mechanical properties by achieving a fine and uniform microstructure through enhanced heterogeneous nucleation controlled solidification under intensive forced convection.
4. Microstructure and mechanical properties of LM24 Al-alloy processed by the MC-HPDC process H.T. Li, H. Kotadia, H. Zhang, M. Xia, N. Hari-Babu, Z Fan Microstructure formation in high-pressure die casting (HPDC) is still not completely understood, and as a consequence, the mechanical properties have not been optimised even though components have been successfully manufactured by the process for more than a century. The melt conditioning by advanced shear technology (MCAST) is a novel technology for processing liquid metal. This project aims to understand the microstructural development and resulting mechanical properties by introduction of melt conditioning (MC) prior to HPDC, i.e., MC-HPDC process. The in-depth understanding of the microstructural evolution will enable us to produce sound die-casting components with high integrity and high mechanical performance.
5. The evolution of Fe-containing intermetallics during the MC-HPDC process H.T. Li, Zhang, M. Xia, Z Fan Due to the very limited solid solubility of iron in Al, the occurrence of Fe-containing intermetallic phases in casting Al alloys is unavoidable. Therefore, elimination or decrease of the negative influence of Fe-containing intermetallics on casting integrity and mechanical properties in Al alloys have been a challenging issue for both academic researchers and industrial communities. The melt conditioning by advanced shear technology (MCAST) is a novel technology for processing liquid metal. The melt conditioned liquid metals are characterised by fine and uniformly dispersed oxides particles and uniform compositional and thermal fields. This project aims to tailor the microstructural development through the introduction of melt conditioning (MC) prior to HPDC, i.e., MC-HPDC process, with emphasis on the evolution of Fe-containing intermetallics during the MC-HPDC process. This understanding and knowledge will reinforce our basis to optimise the microstructural development and help to achieve high pressure diecastings with high performance.
6. Microstructure and mechanical properties of commercial cast Al-alloys processed by the MC-HPDC process H. Kotadia, H. Zhang, N. Hari-Babu, Z Fan Al-Si alloys are commonly used in automotive, aerospace and other engineering sectors. High pressure die cast (HPDC) process is commonly used to fabricate components based on these alloys. However, the HPDC components of these alloys contain defect bands, concentrated early solidified large crystals (large grains), eutectic phase segregation, porosity and other cast defects, resulting in inadequate mechanical performance. Since their mechanical properties can be greatly altered by the microstructure, in this project we aim to engineer the microstructure by conditioning the liquid metal via applying intensive shearing prior to feeding to the HPDC process. This process is referred to as Melt Conditioned Advanced Shearing Technology (MCAST). The MCAST process, developed by Professor Fan and co-workers at BCAST, has been a major advancement in solidification research in the recent years. This project uses this technology to engineer the microstructure so as to overcome some of the problems associated with conventional HPDC for hyper and hypo eutectic Al-Si systems.
7. Refinement of primary Si in hyper-eutectic Al-Si based Al-alloys by intensive melt shearing Z. F. Zhang, N. Barke, H. Kotadia, Z. Fan The objective of this project is to produce primary Sl phase with fine particle size, equiaxed morphology and uniform distribution in an Al-alloy matrix. Intensive melt shearing provided by the MCAST process has been used to condition the hyper-eutectic alloy melt before casting under different solidification conditions. The effects of shear rate, shearing temperature, cooling rate during solidification, alloying elements are systematically investigated. In addition the interaction between melt conditioning and addition of chemical grain refiners is also being studied.
8. Up-cycling of scrap cast Al-alloys by the MC-HPDC process H.T. Li, H. Zhang, M. Xia, G. M. Scamans, Z Fan The advantages of using Al alloys for automotive applications are well known, as provides up to 55 percent weight savings when compared to steel—which translates into improved fuel economy and reduced greenhouse gas and polluting emissions. On the other hand, the remelting of recycled Al alloys saves almost 95% of the energy needed to produce prime aluminium from ore. So the up-recycling of scrap cast Al alloys may significantly contribute to the building of a sustainable society. The MCAST developed in BCAST provides a versatile and robust means for conditioning liquid metal prior to solidification. The melt conditioned liquid metals are characterised by fine and uniformly dispersed oxides/inclusions particles and uniform compositional and thermal fields. For the recycling of scrap cast Al-alloys, detrimental influence resulting from inclusions, Fe phases and oxides can be considerably reduced or positively harnessed through the introduction of MC process. As a result, when combined with the conventional cold chamber HPDC process for component shaping, the novel MC-HPDC process will enable us to achieve up-cycling of scrap Al-alloys.
9. Microstructure and mechanical properties of scrap AM50/60 Mg-alloy processed by the MC-HPDC process S. Tzamtzis, H. Zhang, M. Xia, N. Hari-Babu, G. M. Scamans, Z Fan The rapid growth of Mg-alloys in automotive applications means a similar rapid increase in Mg-alloy scrap from both manufacturing (new scrap) and end-of-life vehicles (old scrap). Therefore, recycling Mg-alloy scrap is becoming an important technical challenge to the researchers. Scrap normally consists of increased oxide inclusion clusters when compared to primary alloy. In earlier work, it has been shown that by applying intensive shearing, the clusters of ceramic particulates embedded in liquid metal could be dispersed well. This project aims at applying the dispersive mixing nature of MCAST to produce high quality components of AM50/60 Mg alloys scrap from the manufacturing industries. Preliminary results show that no large oxide films or particle clusters are present in MCAST recycled AM50/60 Mg-alloy scrap. The research work is being focussed on the solidification behaviour of conditioned melt, microstructures and mechanical properties of MC-HPDC AM50/60 scrap processed under different conditions.
10. Processing of Mg-alloy based MMCs by intensive melt shearing S. Tzamtzis, H. Zhang, N. Hari-Babu, Z Fan Mg alloy based MMCs possess good specific strength when compared to Al alloys, composites and steel alloys. However, agglomeration of reinforced particles is a key processing problem that is to be addressed in processing high performance metal matrix composites (MMCs). Current processing methods exhibit extremely low ductility due to the presence of agglomerated reinforced particles in the ductile matrix. Recently we have shown that the clustering behaviour due to the cohesive nature of reinforced particles could be suppressed by applying a sufficient shear stress on these clusters that are embedded in liquid Aluminium metal. A specially designed twin-screw machine, developed at Brunel University and in which the liquid undergoes high shear stress and high intensity of turbulence, has been used to implement intensive shearing. We are aiming to produce MMCs based Mg alloy (AZ91D) matrix and SiC/MgO reinforcement, under high shear stress and turbulence conditions magnesium liquid. Optimising the processing conditions under which uniformly distributed reinforcement particles could be achieved is the primary objective of this project. The influence of micro and macro spatial variation of the reinforcement particulates on the mechanical properties, particularly the tensile strength and elongation, will be investigated by producing tensile bars using MC-HPDC process.
11. Microstructure and mechanical properties of Al-alloy based MMCs processed by the MC-HPDC process S. Tzamtzis, H. Zhang, N. Hari-Babu, Z Fan Metal Matrix Composites (MMCs) have attracted interest for application in numerous fields. The current processing methods often produce agglomerated particles in the ductile matrix and as a result they exhibit extremely low ductility. The key idea to solve the current problem is to adopt a novel process allowing the application of sufficient shear stress on particulate clusters embedded in liquid metal to overcome the average cohesive force or the tensile strength of the cluster. In this project, Al-Si cast alloy/SiCp composites have been produced using a conventional stir casting technique and a novel process. Evaluation of microstructure and mechanical properties suggests that the significant improvement in the distribution of the reinforcement in the matrix led to simultaneous improvement in ultimate tensile strength and tensile elongation. We believe that the results obtained in this project could contribute for further use of MMCs in engineering applications
12. Microstructural evolution of Al-Sn-Cu based immiscible alloys processed by the MC-HPDC process H. Kotadia, H. Zhang, N. Hari-Babu, Z Fan Immiscible alloys with a microstructure in which a soft phase dispersed homogeneously in a hard matrix have great potential applications in advanced bearing systems, especially for the automotive industry. Though the melt of an immiscible alloy is miscible at the temperature above the miscibility gap, it decomposes into two liquids when it passes through the liquid miscibility gap. Despite great efforts made worldwide, including extensive space experiments, no casting techniques so far can produce the desirable microstructure. Based on extensive experience in mixing the immiscible alloys, liquids offered by the rheomixing process for immiscible alloys have been successfully developed at BCAST (Brunel Casting Advanced Solidification Technology) using an MCAST (Melt Conditioning Advanced Shearing Technology) unit. Our experimental results have confirmed that intensive melt shearing is an effective way to achieve fine and uniform dispersion of the soft phase without macro-demixing, and that such a dispersed microstructure can be further refined in alloys with precipitation of the primary phase prior to the demixing reaction.
13. Effects of intensive melt shearing on the solidified microstructure of Mg-alloys M. Xia, Y. Zuo, Z Fan Owing to the unavoidable inclusions in liquid metal, the nucleation of an untreated liquid always starts from the larger inherent nucleation sites in the liquid. The high intensive shearing effect of patented melt condition by advanced solidification technology (MCAST) offers extremely dispersed inclusions and uniform temperature distribution which promised an enhanced nucleation process and a fine and uniform solidified microstructure. The objective of this project is to evaluate the shearing effect on Mg liquid alloys under different shearing or solidification conditions. The grain refinement effect is being evaluated in this project under different fixed cooling rate for different alloys and the nucleation mechanism of melt conditioned liquid was analyzed by pressurized filtration technology combining with SEM and TEM.
14. Effects of intensive melt shearing on the nature of oxide in liquid Mg-alloys Y. Wang, M. Xia, Z Fan The oxidation of Mg alloys is inevitable due to the strong affinity of magnesium with oxygen. MgO films are usually present in Mg-alloy melt through chemical reaction with oxygen during heating, melting and melt handling process even though the melt is usually under a protective atmosphere. The presence of the long and coarse oxide films in the alloy melts is the main type of casting defect, which in turn results in a detrimental effect on the mechanical performance of the solidified materials. In this project, intensive shearing is imposed on the alloy melt at a certain temperature above the alloy liquidus, realising the significant modification of the oxides. The oxide films are effectively broken up and those nano-sized individual MgO particles inside the oxide films can be considerably dispersed. Therefore, the dispersed distribution of the fine MgO particles has no longer the detrimental effects.
15. The potency of Al8Mn5 intermetallics as heterogeneous nucleation sites for solidification of Mg-alloys Y. Wang, Z Fan, X. Zhou, G. Thompson Manganese is one of the common elements added to commercial AZ and AM series of Mg-alloys. Its addition is essential for enhancing the corrosion resistance by removing the detrimental effect of iron by precipitation of Al-Mn-Fe compounds from liquid alloys. Manganese usually reacts with aluminium to form Al8Mn5 intermetallic particles. During the long time search for effective and practical grain refiners for Al-bearing Mg alloys, the ability for the Al8Mn5 particles to act as potent nucleation sites for the a-Mg grains during the solidification of the Mg-Al alloys has been the subject of debate. In this project, in order to facilitate the investigation of the intermetallics, the particles are collected by pressurised filtration of Mg-Al alloy melts. Advanced analytical electron microscopy, including high-resolution transmission electron microscopy (HRTEM), is conducted focusing on the interfaces between the Al8Mn5 intermetallic particles and the a-Mg grains. The extensive HRTEM examination indicates that there is no crystallographic orientation relationship (OR) between Al8Mn5 and a-Mg crystals, suggesting that Al8Mn5 particles are very unlikely to act as potent nucleation sites for the a-Mg during solidification of Mg-Al based alloys.
16. Enhanced nucleation in Mg-alloys by intensive melt shearing Y. Wang, M. Xia, Z Fan Refinement of as-cast microstructure of alloys is usually achieved through enhanced heterogeneous nucleation by the addition of grain refiners to the melt. Compared with Al-alloys, grain refinement for Mg-alloys is more important since (i) Mg-alloys have an HCP structure which is inherently more difficult to plastically deform compared with FCC Al-alloys, and (ii) Mg-alloys have a considerably larger Hall-Petch coefficient than Al-alloys, and grain refinement is a more efficient way to improve mechanical properties. Although zirconium has been identified as an efficient grain refiner for Al-free Mg-alloys, there is yet an effective grain refiners for the Al-bearing Mg-alloys, such as the AM and AZ series alloys. In this project, a significant grain refinement is observed for Mg-Al alloys via the melt shearing. The microstructural examination shows that the MgO films are effectively broken up and the nano-sized MgO particles are dispersed and distributed uniformly in the melt. Analytical electron microscopy revealed that the MgO particles, formed in-situ in the melt, have a specific orientation relationship (OR) and a small lattice misfit with the a-Mg matrix. It is these fine and dispersed MgO particles achieved by melt shearing that act as the potent sites to enhance the heterogeneous nucleation, resulting in the observed grain refinement for the Mg-Al based alloy.
17. The nature of oxides in intensively sheared liquid Al-alloys Y. Wang, H.-T. Li, M. Xia, Z Fan, X. Zhou, G. Thompson Surface oxidation occurs inevitably during heating, melting and solidification of aluminium alloys. It has been shown that the oxide films and inclusions are readily entrained into the castings by the turbulence of melt processing, and thus play a key role in determining the properties of aluminium alloys. These oxide films are associated frequently with the other casting defects, such as porosity and cracks with a strong influence on the amount of the defects, which therefore detriments the performance such as strength and ductility as well as corrosion resistance of the aluminium castings. Usually, specific technologies have to be applied to remove as many of the oxides as possible to ensure the alloy melt is clean enough prior to casting. In this work, based on the study of the oxides in the melt, a physical approach, intensive melt shearing, is utilised to modify the morphology of the oxide in the melt. The advanced electron microscopy revealed that there exist basically two types of oxide films, MgAl2O4 spinel films and Al2O3+MgAl2O4 films. By using intensive melt shearing, the MgAl2O4 spinel and Al2O3 particles are effectively dispersed and distributed uniformly in the melt. Both the MgAl2O4 and Al2O3 particles are observed to be associated with the iron-containing intermetallics and eutectic silicon, indicating the heterogeneous nucleation by the oxide particles.
18. Grain refinement of MCAST Mg-alloys after repeated melting Y. Zuo, M. Xia, Z. Fan Melt conditioning by advanced shear technology (MCAST) has been proposed in BCAST and it is demonstrated that the MCAST can refine the grain size of Mg-alloys. This project aims to obtain the effect of repeated melting on the grain refinement of Mg-alloys by MCAST and try to keep the grain refining effect after repeated melting. This project is very significant for the application of MCAST in industry. If the grain refinement can be kept after repeated melting, the metal melt can be treated and cast into ingots in a centralized place and then the MCAST cast ingots can be carried to anywhere for DC casting, twin roll casting, die casting, sand casting and so on, which not only provide a grain refining effect but also save the cost of the MCAST machine. In addition, by this centre batch processing, it is easy to apply MCAST in industry without any change in the existent process and machines. This project currently focuses on AZ91 Mg alloy and will extend to other Mg alloys.
19. Measurement of undercooling of intensively sheared liquid Al- and Mg-alloys B. Jiang, H. Men, M. Xia, Y. Zuo, Z Fan Undercooling, as the driving force for solidification, is the difference between liquid melting temperature and the lowest nucleation temperature. For intensively sheared liquid Al- and Mg-alloys, comparing their undercooling with the non-sheared alloys’, using the undercooling as an input into growth theories, and contrasting between different experimental results, a reasonable explanation for the formation of advantages of sheared alloys could be provided. The objective of this project is to develop a stable method for cooling curve measurement, which maintains the measurement of undercooling, to discover the main experimental influences, and to control and adjust these influences. Currently we have done several groups of experiments on AZ91 to rule out some significant influences and succeed in obtaining a rough quantity of this alloy. More precise experiment adjustments will be made in the following steps to acquire more precise data.
20. Development of the MC-DC casting process for continuous casting of wrought Al-alloy billets and slabs Y. Zuo, M. Xia, G. M. Scamans, Z Fan The semi-continuous direct-chill (DC) casting process holds a prominent position in commercial aluminum alloy processing, especially in the production of high strength alloy and large sized ingots. However, using the conventional DC casting process, it is difficult to avoid casting defects such as macrosegregation, casting crack, coarse structure and non-uniformity of structures. The objective of this project is to develop a new technology, melt conditioned direct chill casting, namely the MC-DC process, for continuous casting of wrought Al-alloy billets and slabs, which can refine grain size, improve uniformity of microstructure and composition, and reduce casting defects. The MC-DC process combines the worldwide patented MCAST for melt conditioning with the conventional direct chill (DC) casting process. In this project, the MC-DC process is continually optimized and developed for process efficiency, ingot quality and equipment robustness.
21. Microstructural evolution of Al-alloys during the MC-DC casting process Y. Zuo, M. Xia, Z Fan A new process melt conditioned direct chill (MC-DC) casting process has recently been proposed in BCAST at Brunel University to refine grain structures and reduce casting defects. It has been demonstrated that the microstructure of MC-DC cast billets or slabs is much finer and more uniform than that of conventional DC cast ones. To understand the grain refining mechanism of the MC-DC process, the microstructural evolution of Al-alloys during the MC-DC casting process will be investigated in this project. The objective of this project is to understand the solidification behaviour and microstructural evolution of Al-alloys during the MC-DC casting process. In this project, the relationship between the average grain size of the MC-DC ingots and the melt conditioning parameters will be created. The size and distribution of grains and second phase particles will be controlled by MC-DC casting process.
22. Grain refinement of Mg-alloys in MC-DC cast Mg-alloys Y. Zuo, M. Xia, Z Fan Grain refinement is favorable for reducing homogenization time, eliminating hot tearing during the casting process and improving the deformability of Mg alloys. Magnesium alloys have been developed so much in recent years and are widely used in the world now. Usually the semi-continuous direct-chill (DC) casting process has been used to produce magnesium alloy ingots. However, it is difficult to get high quality magnesium alloy ingots with fine, uniform structures and low macrosegregation by using the conventional DC casting process. The objective of this project is to continually develop the MC-DC casting process to make Mg-alloy ingots with fine and uniform microstructure and low content of casting defects and understand the mechanism of grain refinement in Mg-alloys by MC-DC casting process. It has been demonstrated that the MC-DC casting process can remarkably refine grain size of AZ31 and AZ91 Mg-alloys. Further investigation will focus on the grain refinement of other Mg-alloys by the MC-DC casting process and the mechanism of grain refinement.
23. Evolution of Fe-containing intermetallics in Al-alloys during the MC-DC casting process S. Arumuganathar, M. Xia, Z Fan The direct chill (DC) casting process is widely used for the production of Al-alloys ingots which are later worked to shape. Fe is an inevitable and detrimental impurity element present in Al-alloys. The presence of Fe and Si, and variation of the cooling rate from the ingot surface to the centre lead to produce ingots with variations of size and morphology of Fe intermetallics across the cross section of DC Al ingots. The MC-DC casting process combines patented MCAST (Melt conditioning by advanced shear technology) for melt conditioning and conventional DC caster for the production of high quality billets and slabs. However, it is crucial to understand and quantify the formation of Fe intermetallics in the MC-DC ingots since the presence of brittle needle shape Fe compounds will have a pivotal role in controlling the properties and subsequent processing of Al ingots. In this project, a systematic study will be carried out to assess the formation of Fe-intermetallics across the cross section of the Al-alloys ingots during MC-DC casting process.
24. Industrial scale trial production of wrought Al-alloy billets by the MC-DC process Y. Zuo, M. Xia, J. B. Patel, G. M. Scamans, Z Fan Billets with a fine and uniform microstructure are favorable for deformation and improving mechanical properties. High quality Al-alloy billet has been produced in the laboratory and it has been demonstrated that the MC-DC process has obvious grain refining effect on Al-alloy billet. However, the MC-DC process has not been used on an industrial scale at the moment. This project focusses on industrial scale trial production of wrought Al-alloy billets by the MC-DC process. The objective of this project is to continually improve the MC-DC process by doing industrial scale trials to make it suitable for application in industry.
25. Development of the twin roll casting (TRC) process for production of Mg-alloy strips I. Bayandorian, M. Xia, R. Kyete, G. M. Scamans, Z Fan Magnesium sheet products offer a high strength-to-weight ratio that makes them attractive for structural applications in the automotive, aerospace, electronics, healthcare and general engineering industries. However, conventional Magnesium processing technologies are not effective for the commercially viable manufacture of sheet and extruded sections. Increased penetration of wrought magnesium alloys into industrial applications is dependant upon developing improved process technologies that simplify the production, route and enhance mechanical properties. Conventionally, magnesium alloy sheet products are produced by hot and/or cold rolling of large rolling blocks (30 1000 2000mm3), which require repeated cycles of cold rolling and annealing. The rolling blocks are a coarse-grained material and repeated annealing and rolling is expensive and time consuming with a low metal yield and as a result the carbon footprint is very high. Recently, twin roll casting (TRC), which produces magnesium alloy strip (i.e. 3 mm-6 mm in thickness) directly from a liquid melt, has been developed to reduce the cost of strip production and the complications related to solid state deformation processing of Magnesium alloys from large billets. Twin roll casting (TRC) offers a more promising route for the economical production of Magnesium sheet. The objectives of this project are:
- To develop a step-change technology for the production of high quality magnesium alloy strip;
- To understand the scientific principles underpinning the development of the TRC technology.
26. Development of the melt-conditioned twin roll casting (MC-TRC) process for production of high quality Mg-alloy strips I. Bayandorian, M. Xia, R. Kyete, G. M. Scamans, Z Fan Twin roll casting (TRC) offers a more promising route for the economical production of magnesium sheet but unfortunately, it produces strip with coarse and non-uniform microstructure, severe defects, and centre line segregation and poor surface quality. There is a commercial need and a scientific challenge to overcome these problems. The objectives of this project are:
- To develop a step-change technology for the production of high quality magnesium alloy strip;
- To understand the scientific principles underpinning the development of the MC-TRC technology.
MC-TRC (Melt Conditioned Twin Roll Casting) is a new process developed to overcome the disadvantages of the conventional TRC process, by conditioning liquid metal prior to solidification processing. This technology produces high quality strip by focusing on the control of solidification. Solidification control is achieved by an MCAST (Melt Conditioning by Advanced Shear Technology) unit which feeds a twin roll caster. Better mechanical properties at room and elevated temperature, higher quality of strips in terms of lower amounts of defects, lower required energy, rolling and annealing steps of the MC-TRC rolled sheet compare to TRC sheet are some of the results which are achieved so far.
27. Development of the melt-conditioned twin roll casting (MC-TRC) process for production of high quality Al-alloy strips M. Xia, Ritwik, G. M. Scamans, Z Fan Twin roll casting (TRC) offers a promising route for the economical production of Al sheets combining casting and hot working into one step process, but unfortunately it normally produces strips with coarse and non-uniform microstructures and severe central line segregation for high alloying element containing alloys. In order to eliminate chemical composition segregation and structural non-uniform of conventional TRC strips, intensive solidification control offered by patented melt conditioning technology was introduced into the conventional TRC process. In this project, various alloys with high alloying element contents are processed by melt conditioned TRC (MC-TRC) to reach limited segregation, optimized grain size and uniform microstructure. The subsequent hot working is applied to evaluated hot workability of MC-TRC strips.
28. Optimisation of the hot rolling conditions for MC-TRC Mg-alloy strip I. Bayandorian, R. Kyete, G. M. Scamans, Z Fan MC-TRC (Melt Conditioned Twin Roll Casting) is a new process developed to overcome the disadvantages of the conventional TRC process, by conditioning liquid metal prior to solidification processing. The objectives of this project are:
- To optimise the conditions for homogenisation and hot rolling stages of MC-TRC Mg-alloy strip;
- To understand the microstructural evolution and mechanical behaviour of rolled strip with fine and uniform grain size produced by the MC-TRC process compared with coarse and non-uniform grain size produced by the TRC process during and after the hot-deformation process.
Results show that the the Recrystallization rate for the MC-TRC strip is more than 6 times faster than the TRC strip from the as-cast state. The Recrystallized grain size is extremely fine for the MC-TRC strip (11μm), compared to the TRC strip (350 μm). The elongation both at ambient and elevated temperatures of the MC-TRC strip is approximately 3 times that of the TRC strip. The advantage of having higher elongation is that the sheet can be formed into more complex components. These improved properties are because of the uniform and fine final microstructure with fewer defects such as voids and cracks formation without centre line segregation during the strip production stage.
29. Microstructural evolution of Mg-alloys during the MC-TRC process I. Bayandorian, M. Xia, R. Kyete, G. M. Scamans, Z Fan MC-TRC (Melt Conditioned Twin Roll Casting) is a new process developed to overcome the disadvantages of the conventional TRC process, by conditioning liquid metal prior to solidification processing. This technology produces high quality strip by focusing on the control of solidification. Solidification control is achieved by an MCAST (Melt Conditioning by Advanced Shear Technology) unit which feeds a twin roll caster. Better mechanical properties at room and elevated temperature, higher quality of strips in terms of lower amounts of defects, lower required energy, rolling and annealing steps of the MC-TRC rolled sheet compare to TRC sheet are some of the results which are achieved so far. The objectives of this project are:
- To understand the scientific principles underpinning the development of the MC-TRC technology
- To assess the microstructural evolution during the casting stage of the MC-TRC process
Results show that the fine and well-dispersed nucleated agents for solidification (MgO particles) can enhance significantly the nucleation rate and result in very fine, well-distributed final solid grains and much fewer defects in middle of the final strip, e.g. central line segregation and surface cracks.
30. Al-alloy slabs produced from scrap alloys by the MC-DC process for automotive body applications S. Kumar, N. Hari-Babu, G. M. Scamans, Z Fan Direct Chill (DC) casting is a conventional casting process for producing Al and Mg wrought alloy billets. This process often results in non-uniform columnar grains throughout the ingots in addition to cast defects such as macro and micro segregations, voids and cracks. In addition, the presence of inclusions and impurities in the scrap metal limits this conventional DC casting process to produce high quality Al ingot directly from scrap metal. The key objective of this project is to develop the casting process and technology which can directly recycle the scrap metal into high quality ingot for automotive body applications. This can be achieved by combining the “Melt Conditioned Advanced Shearing Technology” (MCAST) with the DC casting process and is referred to as the “MC-DC” process. In this project, the MC-DC process will be further developed to obtain high quality slabs from scrap alloys containing various amounts of impurities and inclusions. Finally, the recycled ingots will be used to produce components for automotive applications.
31. Al-alloy strip produced from Al-alloy scrap by the MC-TRC process S. Kumar, N. Hari-Babu, G. M. Scamans, Z Fan Twin Roll Casting (TRC) is a continuous near net shape casting process to produce sheets directly from liquid metal. The main limitation of this process is that it results in non-uniform grains distributed along the cross section of the strips and severe casting defects such as centre line segregation, surface bleed and edge cracks. The main objective of this project is to develop an advanced sheet producing technology, called Melt Conditioned Twin Roll Casting (MC-TRC), which can produce the sheets with minimised defects. In the MC-TRC process, the conditioned liquid metal is cast into high quality strips using conventional twin roll caster. MC-TRC processed strips show fine uniform grain distribution along the cross section without centre line segregation and other casting defects. Work is in progress to produce high quality sheets from the Al-alloy scraps using this advanced near net shaped MC-TRC process.
32. Effects of impurity and inclusions in scrap Al-alloy on the microstructure and mechanical properties of MC-TRC Al-alloy scrap S. Kumar, N. Hari-Babu, G. M. Scamans, Z Fan There is a significant need to use more scrap metal rather than primary Al in response to the demands for Al alloys from the automobile industry and for reducing CO2 emissions from the Al processing industry. Most of the cast processes fail to accommodate the scrap material because of the presence of impurities and inclusions. The impurities present in the liquid metal react with other alloying elements and form brittle intermetallic phases. The presence of inclusions and intermetallics makes casting difficult and also degrades the final mechanical properties. The main objectives of this project are to understand the influence of impurities and inclusions on the microstructural evolution and mechanical properties of strip cast by the advanced near net shape MC-TRC process and to increase the tolerance levels of the impurities and inclusions in MC-TRC processed sheets, without much loss in the final properties. A preliminary study shows that the MC-TRC process offers fine, uniform grain distribution, less segregation regime and most importantly uniformly distributed fine intermetallics associated with impurities when compared to TRC. The work is in progress to understand the effect of impurities on the formation of various intermetallics, the mechanical properties and impurity tolerance levels of the MC-TRC strips.
33. Development of the rheoextrusion process for the production of extruded profiles directly from liquid alloys M. Xia, S. Liang, Z Fan Extrusion process has been a widely used hot or cold working process for high application performance and accurate forming process. However, the extrusion process has been unpractical due to its time-consuming nature and cost implication because the original structure of conventional billets normally has non-uniform microstructure and severe chemical composition segregations, accumulated porosity and other casting defects. Rheoextrusion process is a newly developed technology which combines the casting and extrusion processes into one step. It offers a fine and uniform microstructure, eliminates porosity and uniform chemical composition distribution, resulting in a higher quality than the casting process and more cost-effective than the conventional extrusion route. The objective of this project is to produce extruded profiles directly from liquid or melt conditioned semisolid alloys by a proper designed counter-rotating rheoextruder. Various alloys are extruded under different optimization conditions in this project. The microstructure and deformation mechanism under high solid fraction semisolid state are analyzed by various analysis technologies.
34. Microstructural evolution of Sn-Pb based model alloys during the rheoextrusion process S. Liang, M. Xia, Z Fan Conventional hot extrusion reductions are achieved through large plastic deformations requiring a number of processing steps and large loads; this is time consuming and expensive. Due to processing conditions, the final microstructures are often non-uniform and prone to defects. A rheoextrusion process has been developed in BCAST. During the rheoextrusion process, liquid alloy is sequentially fed into the slurry maker whereby it is transformed into high quality semisolid slurry with a designated solid fraction. The objective of this project is to investigate the microstructure evolution of Sn-Pb based model alloys during the rheoextrusion process.
35. Optimisation of the rheoextrusion conditions for direct production of Mg-alloy bars from liquid Mg-alloys S. Liang, M. Xia, Z Fan Rheoextrusion process, which combines the casting and extrusion into one step, has many advantages over many other processes. It can obtain higher quality components than casting routes and be more cost-effective than conventional extrusion route. This project aims to optimize the rheoextrusion conditions for obtaining Mg-alloy bars directly from liquid Mg-alloys. In this project, magnesium alloy bar with a fine and uniform microstructure throughout the bar can be obtained after rheo-extruded at high solid fraction. Further optimisation is being carried out for process efficiency, versatility with alloy compositions and component quality.
36. Microstructure of rheoextruded Zn-based alloy bars J. B. Patel, S. Liang, M. Xia, Z Fan The Rheo-extrusion (RE) process innovatively adapts the well-established high shear dispersive mixing action of the twin-screw extruder to the task of in situ creation of a slurry with fine and spherical solid particles followed by direct extrusion into desirable rods, tube or any complex extruded profiles. Compared with conventional extrusion, the RE process produces fine and uniform microstructures and in turn reduces the processing steps to a minimum. In this project, the rheo-extrusion process is experimented with Zn-based alloys in terms of microstructure refinement and processing feasibility, in direct comparison with a conventionally extruded Zinc based product.
37. Non-Newtonian behaviour of liquid metals under high shear rate V. Varsani, H. Men, Ritwik, Z Fan It is widely believed that liquid metals and alloys are Newtonian liquids; namely, the viscosity of metallic liquids is independent of shear rates. However, the data of viscosity for the liquid metals and alloys are largely absent, and sometimes differ to a great extent from data obtained usually at low shear rates. The object of this project is to investigate the effect of shear rates on viscosity of liquid metals and clarify their rheological behaviour, especially at high shear rate. Two concentric cylinder viscometers, which are specially designed for working with metallic liquids at high temperature and high shear rate, have been developed. Systematic experiments have been conducted to investigate the rheological behaviour of various liquid metals. We have confirmed experimentally that metallic liquids are not Newtonian liquids, but Non-Newtonian liquids. The viscosity of liquid metals increases linearly with the increase of shear rate, showing a clear shear-thickening behaviour.
38. Rheological behaviour of binary alloys as a function of alloy composition V. Varsani, H. Men, Ritwik, Z Fan The rheological behaviour of liquid metals exhibits Non-Newtonian characteristics. The viscosity is a structural-sensitive property, and therefore one expects that the shear rate dependence of viscosity could be related to the density, atomic size and atomic packing density. The object of this project is to investigate the effect of compositions in binary systems on the shear rate dependence of viscosity. The measurements on the viscosity of pure metals, eutectic and compound compositions in Sn-Pb and Mg-Pb binary systems have been conducted, which indicates a clear shear thickening behaviour. The extrapolated value at 0 shear rate exhibits qualitative agreement with the data from the literature and a maximum at compositions corresponding to the eutectic and compound compositions, demonstrating that this project provides an accessible approach to obtain the viscosity of metals and alloys.
39. Atomic packing liquid alloy systems exhibiting compound forming, eutectic forming and immiscible behaviour V. Varsani, H. Men, Ritwik, Z Fan Our previous work revealed that the viscosity h of liquid metals exhibits a linear increase with the shear rate γ, and the increase in h with γ varied with different liquid metals and alloys. Thus, one expects that the relationship between h and γ, revealed in our work, could reflect the internal structures of the materials, such as the atomic packing density( f( n)). The object of this project is to investigate the effect of f( n) on the γ dependence of viscosity, namely the slope d h/d γ, for various liquid alloys, including the monotectic, eutectic and compound forming liquids. The monotectic alloys (repelling between A and B atoms) have a low f( n) and the compound forming liquids (attractive between A and B atoms) have a high f( n), while the simple alloys including the eutectic systems (random atomic packing) have a f( n) in between those of the monotectic and compound alloys. We demonstrated that the slope f( n) in plot of d h/d γ- r r2 can be used as an indicator of the atomic density in the liquids. Thus we further confirmed the non-Newtonian behaviour of the liquid metals and alloys, and also offer an approach to compare relatively the atomic packing densities of different metallic liquids using a rheological method.
40. Modelling the non-Newtonian behaviour of liquid metal sand alloys V. Varsani, H. Men, Ritwik, Z Fan The viscosity of liquid metals and alloys can be described by several theoretical models, such as Born-Green, Percus-Yevick and hypernetted-chain equations, using the pair potential and radial distribution functions. However, the effect of shear rates on the viscosity was not represented in these approximate equations. The object of this project is to model the non-Newtonian behaviours of liquid metals and alloys in a wide range of shear rates. Our work has revealed that the liquid metals and alloys exhibit a clear shear-thickening behaviour, especially at high rates, and this behaviour cannot be described by the previous models, and was possibly overlooked experimentally and theoretically under the conditions of low shear rates. In this project, the viscosity of varied liquid metals and alloys was measured, and the non-Newtonian behaviours were analyzed. This project could establish the relationship between the viscosity of liquid metals and alloys and their internal structures.
41. Development of a new technique for x-ray diffraction of liquid metals and alloy under intensive melt shearing H. Men, Z Fan The thermophysical properties of liquid metals, such as conductivity, diffusivity and viscosity, are all structure-sensitive and there also exists a direct connection between the local order and nucleation barrier; therefore the change of local order in liquids could influence the physical properties and nucleation process. However, so far the direct observation of this local order within flows has been experimentally inaccessible. The object of this project is to investigate the local structures of liquid metals in fluid flows using the diffraction method. We developed a method to perform in-situ observation on the local structure of liquid metals under intensive melt shearing provided by a twin-screw machine. The well pronounced curves of structure factor and pair distribution function for liquid metals, including Sn, Ga and In, were obtained. This project provided an accessible approach to the study of atom arrangement in liquid metals and alloys under dynamic conditions. Further work needs to be conducted to investigate the structures of liquid alloys under dynamic conditions, and to obtain information about partial pair distribution function of liquid alloys.
42. Medium rang order (MRO) in liquid Sn under dynamic conditions H. Men, Z Fan It is generally believed that short-range-order (SRO) exists within the overall disorder in liquid metals and alloys. Structure factor of liquid Sn exhibits a well-defined shoulder in high Q side of main peak, and covalent clusters may form in bulk liquid at static state. The object of this project is to investigate the local structure of liquid Sn under dynamic conditions. The diffraction measurements of liquid Sn were conducted at static state and dynamic conditions. At high shear rates, liquid Sn displays a distinct prepeak on the curves of the structure factor, which is directly related to the occurrence of medium-range-order. The occurrence of MRO possibly corresponds to the formation of complete tetrahedral clusters in liquid Sn, which is incomplete at the static state. The mechanism of the MRO formation in liquid Sn under dynamic condition is not clear yet. Further work needs to be conducted to clarify the mechanism.
43. Structural changes in liquid metals induced by intensive melt shearing H. Men, Z Fan Rheological behaviours of metallic liquids indirectly indicate that local structures of liquid metals may be changed in fluid flows, and nonequilibrium molecular dynamics simulation also reveals that simple fluids can undergo two-dimensional ordering in the plane perpendicular to the flow, signalling onset of a phase transition. The object of this project is to investigate the structural transitions of metallic liquids induced by intensive melt shearing using the diffraction method. The in-situ diffraction measurements of liquid Sn at static state and under dynamic conditions were conducted. The enhanced covalent character of Sn pairs in liquid Sn with an increase of shear rates was observed. The mechanism of this structural change under dynamic conditions is also not clear yet, and one possible reason is that the solid surface-induced atomic ordering may give rise to the enhanced atomic ordering in bulk liquids under dynamic conditions, due to the enormous amount of ever-renewing liquid/solid interface created by the twin-screw unit. Further work needs to be conducted in order to fully understand the mechanism.
44. Molecular Dynamic (MD) modelling of atomic ordering at solid/liquid interface J. Bhatt, Z Fan Solid-liquid interfaces play a prominent role in a wide range of technological and phenomenological applications in which heterogeneous atomistic interactions are involved. Technologically, the properties of the macroscopic end-product are governed by the microscopic structure created at the interface. Atomistic details of the interface cannot, however, be obtained through experiments beyond a certain precision. One effective way of overcoming this problem is to study the evolution of the system at the atomic scale through molecular dynamics simulation. We are using this method to investigate how the structure of a solid substrate suspended into a liquid affects the ordering in the surrounding liquid at the interface. It is believed that an understanding of the nature of this ordering will help improve the quality of metals solidifying from inoculated melts.
45. Molecular Dynamic (MD) simulation heterogeneous nucleation on potent substrates J. Bhatt, Z Fan Any first order phase transformation passes through an initial stage of nucleation, whereby the system must overcome a free energy barrier that acts as an impediment to the transformation. Heterogeneous nucleation, wherein foreign particles of the condensed phase are already present in the non-condensed phase, is usually much more efficient than homogeneous nucleation, wherein there are no foreign particles present. This is because in heterogeneous nucleation the presence of the foreign particle lowers the free energy barrier. In solidification of metals, experiments show that adding certain inoculant particles in the melt improves the solidification process. Nevertheless, from a theoretical point of view there continues to be a poor understanding of heterogeneous nucleation in liquids aided by microscopic solid substrates (often called ‘nucleant’ particles). A theoretical understanding of this phenomenon would enable us to better choose the nucleant particles that would maximise the efficiency of solidification and the quality of the metals. We are studying this problem through molecular dynamics modelling that allows us to obtain the energy profile of a chosen sample of metal as a function of its state variables.
46. Analytical modelling of the columnar/equiaxed transition (CET) during solidification of intensively sheared alloy melt H. Men, B. Jiang, Z Fan Oxide particles have been playing an important role in solidification behaviour of alloys by influencing the process of both nucleation and growth. Some researchers have formulated certain theories about what the influence could be when the particles are well dispersed and been supported by their experimental results. However, since no conclusive theory has been worked out and the influence is always a notable issue, the urgency of understanding this solidification behaviour is greater than before. The objective of this project is to develop a numerical model for guiding future experiments, predicting solidification behaviours, and, at the same time, inspecting and verifying experimental results. The project has just been carried out, and some certain work has been achieved, yet the main objective that we have been working on has not been achieved.
47. Numerical modelling of the solidification behaviour of alloy melt with well dispersed oxide particles H. Men, B. Jiang, Z Fan Columnar-to-equiaxed transition (CET) is the phase transformation process which occurs during columnar growth when new grains grow ahead of the columnar front in the undercooled liquid. Under certain conditions, these grains can stop the columnar growth and then the solidification microstructure becomes equiaxed. The objective of this project is to work out an analytical model of CET during solidification of intensively sheared alloy melt, which could provide a theoretical explanation of the differences between sheared and non-sheared alloy melt, and show the influence of the shearing process in solidification; also it might provide us the supreme influencing factors during the process of solidification which might better guide future experiments. This project will be based on existing theories in the field of CET and experimental results carried out by other researchers in BCAST, but will focus on understanding the physical process and working out an analytical model.
48. DSC investigation of precipitation of Fe-containing intermetallic particles from alloy melt with intensive melt shearing H. Men, Z Fan Formation of fine, equiaxed grains and a uniform microstructure with reduced chemical segregation is desirable for as-cast microstructure of metals and alloys, which could be obtained primarily through controlling the nucleation process or initiation of growth. However, the mechanism to trigger the nucleation or initiation of growth for the primary phase often remains as an open question. The object of this project is to investigate the precipitation of Fe-containing intermetallic particles with the DSC method, and to clarify the mechanism about nucleation of the Fe-containing intermetallic particles. The DSC measurement was conducted for the samples with and without intensive melt shearing on our Netzsch 409 DSC. The analysis of the solidification behaviour of Fe-containing intermetallic particles could reveal the mechanism of its nucleation and its effect on subsequent microstructures. This project is underway.
49. Development of the MCAST process to higher temperature alloys M. Xia, S. Cook, Z. Cassinath, J. B. Patel, Z Fan High temperature alloys can offer excellent mechanical or physical performance at different application environments whereas non-uniform microstructure and chemical composition segregation of as-cast structures may cause severe porosity, hot tearing, hot cracking and other casting defects, resulting in non-constancy and non-uniform properties. Newly developed Melt Conditioning by Advanced Solidification Technology (MCAST) has proven effective for uniformizing microstructure and chemical composition segregation for most low melting point alloys so far. It offers a fine and uniform microstructure with low porosity under high intensive shearing effect of MCAST. Owing to the proper microstructure, MCAST components normally present constant high application performance. The objective of this project is to combine MCAST with the conventional downstream forming process to achieve a uniform microstructure and constant properties of high temperature alloys. The MCASTer is modified for high temperature application and various high temperature alloys will be processed under a suitable forming process. The property constancy will be properly analysed.
50. Design Optimisation of the MCAST equipment Z. Cassinath, S. Histead, J. B. Patel, Z Fan Melt Conditioning advanced solidification technology (MCAST) is a novel way of processing alloys for the metallurgical industry. Presently, we have equipment capable of delivering melt conditioning to liquid alloy. This MCAST machine is currently being industrially tested. The objective of the project is to address any issues and invent a design that will avoid any foreseeable problems and rectify ones that our industrial partners have identified while testing the machine. This will be done by optimising the design of the machine so that it can eventually be manufactured and sold as a product. Currently the project is in the inception phase (understanding of the restraints and engineering problems) and I am working on a series of experiments relating to the thermal accounting well as addressing mechanical and design issues. An inception report will be produced and submitted.
51. High efficiency Al-Ti-B based grain refiners produced by the MCAST process M. Xia, Y. Zuo, H.-T. Li, Z. Fan Al-Ti-B has successfully acted as a grain refiner for Al alloys for decades in industry, but its nucleation efficiency has been disappointing, which is less than 5 wt % in conventional utilization, owing to non-uniform naturally distributed particle size. The objective of this project is to achieve a narrow grain size distribution of Al-Ti-B alloys using the high intensive shearing effect of patented Melt Condition by Advanced Solidification Technology (MCAST) and hence to enhance the nucleation ability of Al-Ti-B alloys. In this project, MCAST is combined with the conventional forming process for presenting a fine and uniform microstructure with required narrow size distribution. The processing will be continually optimized and developed for process efficiency and nucleation efficiency.
52. Physical grain refining vs chemical grain refining Y. Wang, M. Xia, Y. Zuo, Z. Fan A fine grain size usually results in an increase in mechanical properties, such as ambient temperature strength, toughness and ductility. Currently, an effective method to achieve a fine grain structure is by controlled solidification using a grain refiner to promote heterogeneous nucleation. In spite of the large volume of work carried out on grain refinement over the past half century, significant challenges remain, such as (i) the very low refinement efficiency, (ii) agglomeration of the added refiner particles, (iii) restricted applicability due to the so-call poisoning effects, and (iv) the detrimental effect of non-nucleating refiner particles on the subsequent thermo-mechanical processing. In this project, significant grain refinement for both Mg- and Al-alloys is achieved by using intensive melt shearing. Unlike the chemical grain refining, this is a physical approach that does not involve addition of any grain refiners. Instead, the potent nucleation sites are the in-situ oxide particles which are formed in-situ in large numbers and wetted completely by the melt. The shearing is to achieve the suitable size and size distribution required for the heterogeneous nucleation. The advantages of the physical grain refining approach are: 1) it is applicable to both cast and wrought alloys without any limitation to alloy composition and without any poisoning effect by alloying elements; 2) it turns the harmful oxide inclusions into useful nucleation sites for grain refinement; 3) it has no detrimental effect on down stream processing; 4) it increases the tolerance to the impurity elements (e.g., iron), so more scrap metal can be directly recycled in-house without going through chemical purification. 5) it does not contaminate the alloy and therefore does not cause any concern for further recycling.
53. Solidification behaviour of eutectic alloys under intensive melt shearing Y. Wang, G. Liu, S. Ji, Z. Fan The eutectic solidification can constitute as high as 40% of the microstructure in commercial cast alloys. Being brittle, totally eutectic alloys do not have much commercial use despite their low melting point. As coupled period lamellar (or fibrous) growth morphology is only kinetically favourable due to diffusion coupling of rejected solutes at the interface, intensive convection is expected to alter the evolution of the eutectic structure. However, experiments have so far been inconclusive with regard to any such effect presumably because of the inability of the imposed convection to alter the extremely fine diffusion layer ahead of the eutectic interface. In this project, intensive melt shearing with strong turbulence is explored noting that the scale of turbulence may match the characteristic diffusion length for eutectic growth. In contrast to past observation of negligible effects of convection on eutectic morphology, the intensive melt shearing considerably alters the evolution of eutectic microstructure. The effects on eutectic solidification range from increased undercooling and metastable solidification to decoupling of growth cooperation, compact spherical duplex microstructure and degenerated and divorced microstructure. This opens up a potential use of physical field to alter and control eutectic solidification to improve mechanical properties of cast alloys or new alloy development based on eutectic compositions. Such physical approach is applicable to alloy systems as opposite to the chemical approaches used in specific alloys to modify eutectic structure.
54. The interaction between chemical grain refining and physical grain refining Y. Zuo, M. Xia, Y. Wang, Z. Fan As known, grain refinement is favorable for reducing homogenization time, eliminating hot tearing during casting process, improving the deformability and improving mechanical properties. It is therefore very significant to obtain a fine and uniform microstructure. There are two approaches for grain refining. One is chemical grain refining achieved by addition of grain refiners, such as Zr, Ca for magnesium alloys and Al-Ti-B master alloy for aluminum alloys. The other one is physical grain refining. The MC-DC casting process can provide physical grain refining without any deliberate chemical grain refiner addition. The physical grain refinement provided by the MC-DC casting process has many advantages over the conventional chemical grain refining approach. It can refine microstructure without contamination of the alloy and does not cause any recycling concerns, which is very significant for saving resources and energy. The objective of this project is to improve the efficiency of grain refiners and entirely or partially replace chemical grain refining with physical grain refining. The project investigates the grain refining effect of melt conditioning and the effect of melt conditioning on the efficiency of grain refiners.
55. Analytical modelling of heterogeneous nucleation with potent substrates Z Fan Classical theory for heterogeneous nucleation predicts that the potency of a substrate depends on the contact angle defined by the Young’s equation. However, for potent substrates where the interface between the solid crystal and the substrate becomes coherent or semi-coherent, the interfacial energy between the liquid and the substrate will be larger than the sum of the other two interfacial energy terms, and hence the Young’s equation breaks down, and so does the classical nucleation theory. An epitaxial model for heterogeneous nucleation on potent substrates is being developed. In this model, nucleation takes place by ordering the liquid atoms on the substrate layer by layer, forming a coherent interface and a solid phase with a crystal structure resembling that of the substrate (the pseudomorphous phase). The elastic strain in the pseudomorphous phase increases with the layer thickness, and at a critical thickness misfit dislocation will be introduced to release the elastic energy and transform the pseudomorphous phase into the equilibrium phase and the coherent interface into a semi-coherent one, which completes the nucleation process. It is found that the epitaxial nucleation model can explain a number of nucleation related phenomena, such as hyper-nucleation, solute effects and edge-to-edge matching.
56. Sand casting of A201 alloy with intensive melt shearing M. Xia, H. Zhang, H.-T. Li, Z Fan A201 has been widely used in aircraft and automotive industries for its high strength, especially, high-temperature strength, and good ductility. But it normally demonstrates poor castability owing to less fluidity of the second phase at the late stages of solidification. Developed dendrites would suppress the filling and feeding process in the casting process. The objective of this project is to provide a new solution for A201 sand casting by enhancing the castability of A201 alloy in order to offer a high quality sand cast component by combining Melt Conditioning with sand casting. Patented Melt Conditioning by Advanced Solidification Technology (MCAST) can extremely suppress the formation of dendrites and chemical composition segregation, refine and uniformize microstructure, and reduce the possible porosity, hot tearing and other casting defects during the solidification, which is offered by enhanced heterogeneous nucleation owing to high intensive shearing effect of MCAST. In this project, the fluidity of conditioned melt, hot tearing, porosity and primary and intermetallic phases of the cast after melt conditioning are evaluated. The process efficiency and component quality are continually optimized.
57. Microstructure and mechanical properties of melt-conditioned sand cast (MC-SC) LM25 alloy H.-T. Li, M. Xia, H. Zhang, Z Fan The oxides are readily generated during melting, transferring and pouring of Al alloys in an open atmosphere with a bi-film morphology feature. In turn, these oxides can cause directly or indirectly occurred casting defects such as shrinkage, gas porosity and hot tearing. As a result, mechanical properties such as strength, ductility, fatigue and fracture toughness are reduced. LM25 alloy is a critical alloy for aerospace applications where a combination of high strength and toughness is required. The melt conditioning by advanced shear technology (MCAST) is a novel technology for processing liquid metal prior to solidification. The melt conditioned liquid metals are characterised by fine and uniformly dispersed oxides particles and uniform compositional and thermal fields. This project aims to achieve optimised microstructure and mechanical properties in sand cast LM25 alloy through the combination of melt conditioning and sand casting process.
58. Processing of Mg-alloy based MMCs for potential biomaterial applications Hari Babu Nadendla Metals are more suitable for load-bearing applications compared with ceramics due to their combination of high mechanical strength and fracture toughness. Mg is a lightweight metal and its fracture toughness is greater than ceramic biomaterials such as hydroxyapatite (HA), while the elastic modulus and compressive yield strength of magnesium are closer to those of natural bone than is the case for other commonly used metallic (Titanium, Stainless steel, Co-Cr alloy) implants. Bone powder (hydroxyapatite) is known to reduce the Mg corrosion and a composite based on Mg/HA has been proposed to be the future of biomaterial implants. In this project, a stir cast method that was developed originally for the fabrication of MMC has been adapted to produce a high strength Mg composite in which nano-scale HA inclusions have been dispersed uniformly in Mg matrix. Preliminary results suggest that the presence of HA particulates in Mg matrix has improved its hardness significantly. The future work is to include fabricating components that are suitable for testing their tensile properties and investigating their corrosion resistance against physiological environment; most importantly there is a need to develop a more practical experimental setup for their fabrication.
59. Processing of MgB2 superconductor through infiltration and growth method Hari Babu Nadendla MgB2 superconductor has been commonly processed by the Mg vapour diffusion process through Boron fibres. However, fabrication of high dense bulk MgB2 superconductors routinely has not been very successful, due to the highly volatile nature of Mg liquid at elevated temperatures. It is important to note that hot isostatic press has been successfully used to produce high dense (.95%) cylindrical bulk pellets with strongly connected bulk MgB2, and this process has a limited use for producing complex shapes. Other conventional processing routes led to the formation of large porous media and low density values ranging from 50% to 70%, due to evaporation of Mg during processing. At BCAST we have developed a novel processing route called Infiltration and Growth process, processing high dense MgB2 with complex shapes. It involves infiltrating Mg liquid into pre-defined Boron precursor complex pellets. This process resulted in high density (>95%) with high critical current densities (106 A/cm2 at 20 K). This work has significant potential in developing high performance superconducting wire, bulk components and most importantly in joining of MgB2 wire.
60. Development of novel grain refiner for Al alloys Hari Babu Nadendla, M. Nowak We are investigating the influence of chemical additions to Al alloys on their grain size. This investigation resulted in development of effective grain refiner for Al alloys.
61. Development of a degassing system for aluminium casting processing based on ultrasound (Ultragassing) Noe Alba-Baena, Dmitry Eskin Ultragassing project targets the development and application of ultrasonic degassing treatment to light alloys, thus enhancing significantly the value fo the components produced by the EU foundries in terms of safety and quality of their cast parts. The main innovations tackled within the project are the following:
- Elimination of harmful and environmentally unfriendly gases,
- Elimination of rotational, porous and fragile contaminant components
- Optimized scheme that allows short treatment time with maximum benefit
- Applicability to both continuous and batch processes
- Applicability to a wide range fo castin processes and liquid metals
The project is funded by the European Union's Seventh Framework Programme managed by REA-Research Executive Agency http://ec.europa.eu/research/rea
(FP7/2007-2013) under grant agreement no 286344