Zhongyun Fan

• Professor
• Managing Director at Brunel Centre for Advanced Solidification Technology (BCAST)

Al-Ti-B based master alloys have been widely used for grain refining of Al-alloys in industry for many decades. However, the effectiveness of such grain refiners is severely compromised when a few hundred ppm of Zr is present in the Al melt, and this phenomenon is referred to as Zr poisoning in the literature. So far the exact mechanisms for Zr poi...

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Recently, we have proposed a new framework for early stages solidification, in which heterogeneous nucleation and grain initiation have been treated as separate processes. In this paper, we extend our atomic-level understanding of heterogeneous nucleation to spherical cap formation for grain initiation on a single substrate using molecular dynamics...

Aluminium rich Fe-bearing intermetallic compounds (Fe-IMCs) plays a critical role in determining the mechanical properties of recycled aluminium alloys due to inevitable Fe accumulation during recycling. The Fe-IMCs which have a needle-/plate-like morphology are particularly detrimental, impairing the ductility and overall performance of aluminium...

In the cold chamber high pressure die casting (CC-HPDC) process for light alloys, strong shear stress generated by the fast-flowing melt through narrow runners breaks externally solidified crystals (ESCs). This work applies two runner configurations in the CC-HPDC process of aluminum alloy to address this. A comprehensive finite element model is es...

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of overheated aluminum alloy melt into the shot sleeve would lead to evaporation and burn...

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of overheated melt into the shot sleeve would lead to evaporation and burning of the lubr...

In addition to impurities in recycled aluminum alloys, non-metallic inclusions are a significant factor that deteriorates the material’s castability and final mechanical properties. This, therefore, restricts the ability to transition from a primary to secondary aluminum alloy. In this study, the cleanliness of the recycled A357 alloy was evaluated...

Silicon carbide (SiC) has been widely added into light metals, e.g., Al, to enhance their mechanical performance and corrosion resistance. SiC particle-reinforced metal matrix composites (SiC-MMCs) exhibit low weight/volume ratios, high strength/hardness, high corrosion resistance, and thermal stability. They have potential applications in aerospac...

The mechanism of 'Si poisoning' of Al-Ti-B based grain-refiners in Al-Si alloys has been a topic of intensive study for over half a century. We here investigate prenucleation of Al at the Si segregated interfaces between liquid Al and TiB 2 {0001} substrates using ab initio techniques. Our study reveals that chemical affinity between Ti and Si atom...

Bands of interdendritic porosity and positive macrosegregation are commonly observed in pressure die castings, with previous studies demonstrating their close relation to dilatant shear bands in granular materials. Despite recent technological developments, the micromechanism governing dilatancy in the high-pressure die casting (HPDC) process for a...

Addition of the early 3d transition metals results in formation of primary Al 3 T (T = Sc, Ti and V) phases in Al alloys during casting. The newly formed Al 3 T particles not only improve the mechanical performance of the products but also act as grain-refiners in the solidification processes. Meanwhile, experiments found impacts of impurities, suc...

Interfacial segregation can modify a substrate's heterogeneous-nucleation potency. In Al alloys inoculated with TiB 2 , for instance, Zr segregation degrades TiB 2 's nucleation potency and causes the loss of grain refinement, a phenomenon termed the Zr-poisoning effect. Here we use grain-refining tests to demonstrate that the addition of Mg can re...

Refinement of intermetallic compounds (IMCs) through enhancing heterogeneous nucleation during casting process is an important approach to improve the properties of aluminium alloys, which greatly increases the economy value of recycled Al-alloys. However, heterogeneous nucleation of IMCs is inherently more difficult than that of a pure metal or a...

The sump profile during direct-chill (DC) casting provides critical information for understanding the solidification mechanism. In this work, the influence of the solid packing fraction (SPF) at the dendrite coherency point on the sump profile of DC and melt-conditioned direct-chill (MC-DC) casting is taken into account in the numerical model. It w...

Elemental segregation driven by the reduction of the total Gibbs energy of the system has been widely observed at the melt/substrate interfaces in various Al- and Mg alloys containing different inoculant particles. This study provides experimental observations, analyses, and identifications of the formation of Y-segregation 2DCs at the Mg/MgO inter...

We present the results of ab initio molecular dynamics investigations on the atomic ordering and chemical interactions at the interfaces between liquid Mg and SiC{0 0 0 1} interfaces. The simulations reveal distinct borders between the SiC substrates and liquid Mg. The liquid Mg atoms adjacent to the substrates are bonded to the outmost C/Si atoms...

Segregation of foreign atoms on a solid substrate in a liquid metal modifies the geometry and chemistry of the substrate surface and, correspondingly, its potency to nucleate a solid metal. We here investigate the effects of the segregation of alkaline earth (AE) atoms, Mg, Sr, and Ba, at the interfaces between liquid Al and γ-Al2O3{1 1 1} substrat...

In this paper, we investigate prenucleation and heterogeneous nucleation in the liquid Pb/solid Al system as an example of systems with large lattice misfit, using molecular dynamics simulation. Solid Pb and Al have a large positive lattice misfit ( f) of 18.2% along the densely packed [110] direction. This study reveals that prenucleation occurs a...

θ-Al13Fe4 particles form as a primary Fe intermetallic compound (Fe-IMC) during the casting of commercial Al metals and alloys that inevitably contain Fe and Si as impurities. Moreover, the excellent mechanical performances of the Al-Cu alloys demand knowledge about the structural chemistry of the Fe-IMCs, including the θ-phase in the quaternary Al...

A fine and equiaxed solidification process delivers multidimensional benefits to Mg-alloys, such as improved castability, reduced casting defects, enhanced mechanical properties, increased corrosion resistance and potential for increased recycled contents. Despite extensive research on grain refinement of Mg-alloys in the last few decades, currentl...

The search for more efficient methods for degassing aluminum alloy melts has always been of great interest for the metal industry because the presence of hydrogen and oxides in the melts’ prior casting was detrimental to the integrity and properties of the final products. In this work, we present an overview of the progress and key findings from th...

Al 13 Fe 4 is one of the common Fe-containing intermetallic compounds (FIMCs) that forms during solidi-fication in Al alloys. Silicon (Si) as impurity or solute in Al alloys is easily doped into θ-Al 13 Fe 4 , which not only causes compositional variation but also modifies the lattice parameters, and in some circumstances, modifies or changes the c...

Heterogeneous nucleation and grain initiation are two different processes in early-stage solidification (ESS), although both are deterministic. Heterogeneous nucleation refers to the formation of a 2-dimensional (2D) nucleus (a crystal plane of the solid) that can template further growth, while grain initiation is the formation of a hemispherical c...

Control of Fe in Al alloys is a severe challenge for the full metal circulation to produce the recycled alloys with mechanical and physical performance as high as the primary alloys. The high restriction of Fe content is mainly due to the deterioration caused by the large-scale Fe-containing intermetallic compounds (FIMCs) in Al alloys. In this pap...

During solidification of metallic materials, heterogeneous nucleation occurs on substrates, either endogenous or exogenous. The potency of the substrates for nucleation is mainly dependent upon the atomic arrangements on the substrate surface, which are affected by the lattice misfit between the substrate and the nucleated solid, the surface roughn...

Prenucleation refers to the phenomenon of atomic ordering in the liquid adjacent to a liquid/solid interface at temperatures above its nucleation temperature. It produces a precursor for heterogeneous nucleation in the liquid and thus has a strong influence on the nucleation process. Oxide particles, including magnesia, spinel, and alumina, are ine...

This article provides an overview of high-pressure die casting (HPDC)-related research undertaken at the EPSRC Future LiME Hub between 2015–2022. The project aimed to identify the cause of variability in the tensile ductility of die-cast structures, and to develop novel processing techniques to address this issue. Variability in tensile ductility w...

Our current understanding of heterogeneous nucleation has been largely confined to the classical nucleation theory (CNT) that was postulated over 100 years ago based on a thermodynamic approach. Further advances in heterogeneous nucleation research requires detailed knowledge of atomistic activities at the liquid/substrate interface. In this work,...

The main problem of recycling aluminium scrap is the gradual accumulation of impurities, especially iron, which tend to form undesired intermetallic compounds that affect the integrity and the mechanical performance of the castings. In this paper, we aim to provide an overview on the topic of iron removal from aluminium melts through primary interm...

γ-Al2O3 particles form inevitably in liquid Al- alloys during liquid-handling and casting processes. Such oxide particles may act as potential nucleation sites during solidification. Recent research revealed that native γ-Al2O3 particles exhibit different potency for nucleating solid Al, which may reduce the number of potential nucleation sites in...

Our current understanding of heterogeneous nucleation has been dominated by the classical nucleation theory (CNT) with little progress of significance being made in past 100 years. In recent years under the financial support from EPSRC for the LiME Research Hub, we have made substantial progress on understanding heterogeneous nucleation at atomic l...

In this study, we used molecular dynamics (MD) simulations to investigate the atomic ordering in the liquid aluminum (Al) adjacent to the amorphous substrate with smooth and rough surfaces. This study revealed that the liquid exhibited layering within about 5 atomic layers but no visible in-plane atomic ordering at the interface with the smooth amo...

When casting aluminum alloy billets, high shear melt conditioning (HSMC) technology refines the resulting grain size, reduces the number of defects, and improves mechanical properties without the need to add polluting and expensive chemical grain refiners. These resultant improvements spring from the high shear rates that develop in the rotor–stato...

Without the addition of any grain refiner, the inclusion particles in a melt will induce heterogeneous nucleation and grain initiation during the solidification of metallic materials. However, with grain refiner addition, the exogenous particles (from the grain refiner) and the native inclusions (e.g., oxide particles) will co-exist in the melt, an...

Grain refinement is of importance for metallic materials since it provides multiple benefits, such as improved castability, reduced casting defects and improved mechanical properties. From extensive research carried out in the past decades, it has been widely accepted that solute is one of the crucial factors for achieving grain refinement. However...

In the cold chamber high-pressure die casting (CC-HPDC) process, alloy solidification in the shot sleeve due to heat loss leads to the formation of externally solidified crystals (ESCs), which have been proven to be closely related to microstructure inhomogeneity and mechanical properties of cast components. In this paper, the solidification behavi...

In this study, the composition templating theory for heterogeneous nucleation was applied to achieve TiB2 particles with Mn segregation on the surface, which supplied the initial composition for the heterogeneous nucleation. The interfacial segregation of added alloy element Mn and the other common impurities, such as Fe and Si, was investigated wi...

AlN particles are formed in liquid Al metals/alloys during liquid-dealing and casting. They may act as potential nucleation sites during solidification. Along its [0 0 0 1] axis, AlN consists of Al ³⁺ N ³⁻ dipolar double-atom layers in the ionic model. Thus, the AlN{0 0 0 1} substrates are terminated by either an Al ³⁺ or a N ³⁻ layer, being polar....

Among the available molten aluminum degassing methods, the industry uses rotary degassing due to its simplicity and improved performance compared to other available methods. For this method, the degassing efficiency is dependent on the effective size reduction and distribution of the gas bubbles inside the molten metal. However, strategies for impr...

Solute accumulation/depletion in the liquid around a growing solid particle during the solidification of metallic melts creates a constitutionally supercooled (CS) zone that has a significant effect on the final solidified grain structure. In this paper, we introduce two mechanisms related to the CS zone that affect grain size: one is the grain ini...

In this work, we investigate Cu solution in θ-Al13Fe4 and related Al-rich ω-Al7Cu2Fe and Al2Cu phases in the Al-Cu-Fe system using the first-principles density functional theory (DFT) with on-site Coulomb interaction correction. The results show preference of Cu at Al7, forming a ternary θ-Al76Cu2Fe24 at ambient conditions, and both Al7 and Al9 sit...

The automotive industry is speeding towards an electric future, with car companies like BMW and Volvo Cars initiating plans to shift their vehicle line-up to low-to-zero emission models. The UK government believes that the manufacture and sale of electric vehicles (EVs) will achieve an ambitious 60% share of the market by 2030. However, the sector...

The microstructure evolution and mechanical properties of quaternary Al-Cu-Si-Mg eutectic alloy prepared via arc melting and suction casting were studied. This alloy exhibits a single endothermic DSC peak with a melting temperature of 509 °C upon heating, suggesting a eutectic reaction. The cast alloy microstructure consisted of four phases, α-Al,...

This article unmasks the probabilistic nature of high-pressure die casting; specifically, the cause of scatter in the tensile ductility of die-cast Al8Si0.4Mn0.3Mg (wt.%) alloy. Scatter in tensile ductility is related to the size of large pores and non-metallic inclusions. We propose that these non-metallic inclusions form during the pyrolysis of c...

The breakup of agglomerates and bodies suspended in turbulent flows are important phenomena that influence many aspects of modern solidification processing. It is often assumed that breakup operates in high-pressure die casting, wherein molten metal is transported at high speed through a narrow orifice system. To test this assumption, X-ray tomogra...

The effects of T5 and T6 heat treatment on the microstructural development and mechanical properties of newly developed die-cast Al-xCu-2.2%Si-1.1%Mg (x=5, 6.6 and 10.6, in wt%) alloys were investigated. After T5 heat treatment to peak hardness, the main precipitates changes from β’’ in Al5Cu to β’’ and θ’ in Al6.6Cu and then to θ’ and Q’’-type pre...

Aimed at the mechanical property improvement in the high pressure die casting (HPDC) process for the aluminium alloy, two sets of shot curves (the baseline and the optimized condition) are designed to study their influence on the distributions of the ultimate tensile strength (UTS) and the elongation (El) for the as-cast ASTM tensile samples. Diffe...

We investigated the relative stability and structural properties of Al-Cu intermetallic compounds using the density-functional theory (DFT) with different approximations. We reveal the importance of the on-site Coulomb repulsion of Cu 3d electrons on the energetics and structural properties of Al-Cu compounds of free-electron nature. The finite-tem...

Controlling the formation of noncompact second phase particles during direct chill (DC) casting of aluminium alloys with grain refiner addition remains challenging, as it results in energy intensive homogenisation and deformation problems. In this work, we employed a novel strategy in the DC casting of A6082 alloy to produce billets with a fine-sca...

β-AlFeSi has a layered structure composed of FeAlSi blocks and exhibits a rich variety of crystal chemistry. Plate-like/rod-like β-AlFeSi particles formed in Al-based alloys have nontrivial influences on the mechanical performance of the cast parts. Here, we investigate the stability, crystal chemistry and electronic structure of the β-phase using...

Grain refinement not only enhances the mechanical performance of as-cast metallic materials but also provides an effective mechanism for controlling cast defects, such as macro-segregation, porosity and coarse second phase particles. Therefore, understanding grain refinement of alloys with different solute additions is of both theoretical and pract...

The degassing of aluminium alloy melts is a crucial step in the production of high-quality casting products, as the presence of dissolved hydrogen and oxide bi-films is detrimental to the mechanical properties. Current rotary degassing techniques are effective, but they lack efficiency because of the high gas flow and long processing times required...

Heterogeneous nucleation is a widespread phenomenon in both nature and technology. However, our current understanding is largely confined to the classical nucleation theory (CNT) postulated over a century ago, in which heterogeneous nucleation occurs stochastically to form a spherical cap facilitated by a substrate. In this paper, we show that hete...

Alumina (α- and γ-Al2O3) particles are formed in liquid Al-Mg alloys during the liquid dealing and cast processes. These native oxide particles have non-trivial influences on the microstructures and properties of the solidified parts, and may act as potential heterogenous nucleation sites during solidification. At present there is still a lack of u...

Three new ultrafine hypoeutectic die-cast alloys based on quaternary Al-Cu-Si-Mg system were developed. The CALPHAD thermodynamic modelling of Al-Cu-Si-Mg system based on Scheil description was conducted to predict the volume fractions of the eutectic mixtures. The designed volume fraction of eutectic mixtures of Al-xCu-2.2Si-1.1Mg (x = 5, 6.6 and...

AA6111 aluminum automotive body-sheet alloy has been formulated from 100% Taint Tabor scrap aluminum. Direct chill casting with and without high shear melt conditioning (HSMC) was used to produce the AA6111 alloy billets. Both homogenized and non-homogenized billets were extruded into sheets. The optical micrographs of the melt conditioned direct c...

SiC particulate reinforced A356 alloy metal matrix composites (MMCs) are synthesized using intensive melt shearing. The effect of reinforcing particle distribution on the fluidity of cast A356/10 vol.% SiC p composites is studied. Spiral length representing the fluidity of the composite melt was measured and liquid flow and soli-dification behaviou...

Nucleation plays a critical role in many natural and technological processes, and nucleation control requires detailed understanding of nucleation process at atomic level. In this study, we investigate the atomistic mechanism of heterogeneous nucleation in generic systems of liquid/substrate with positive lattice misfit (the solid has larger atomic...

θ-Al13Fe4 forms as a primary Fe-intermetallic compound (Fe-IMC) in the casting processes of most Al alloys. Si is added to Al alloys to improve the mechanical performance of products. Fe-IMCs including (Si doped) θ-Al13Fe4 have nontrivial impacts on the mechanical performances of the solidified Al-based components. Here, we investigate systematical...

Refinement and uniform dispersion of the free machining elements within the matrix is always desirable for aluminium billets produced by direct chill (DC) casting. The conventional grain refiner addition cannot ensure uniformity of microstructure and homogeneous distribution of insoluble or intermetallic phases. Melt conditioned direct-chill (MC-DC...

The application of computer aided engineering (CAE) has become a trend in manufacture industry due to its great efficiency and reliability. In casting industries, numerical modelling of the casting process based on CAE has replaced traditional trial-and-error R&D procedures in many aspects. With advanced parallel computing techniques and numerous c...

21 MgAl2O4 spinel particles exist inevitably in Al-Mg alloy melts and may act as potential 22 substrates for heterogeneous nucleation of solid aluminum during solidification processing. 23 In this paper we investigated systematically the atomic ordering of liquid Al adjacent to 24 liquid-Al/MgAl2O4{1 1 1} interfaces using an ab initio molecular dyn...

Al-5Ti-1B is the most widely used grain refiner for Al alloys. However, it is not effective for grain refining Al alloys containing more than 3 wt pct Si. This adverse effect of Si is referred to as Si poisoning. In spite of extensive experimental and theoretical investigations in the past decades, the exact mechanism for Si poisoning is still not...

Al 13 Fe 4 forms as a primary Fe-intermetallic compound (Fe-IMC) in the casting processes of most Al alloys. Si is added to Al alloys to improve the mechanical performances of the products. Fe-IMCs including (Si doped) θ-Al 13 Fe 4 have nontrivial impacts on the mechanical performances of the solidified Al-based parts. Here, we investigate systemat...

High shear melt conditioning technology refines the as-cast structure of light alloy melts, thereby improving the mechanical properties of the casting and reducing the occurrence of defects, without requiring chemical grain refiners. To upscale the technology and apply it to processes involving larger melt volumes, a computational fluid dynamics st...

To reveal the influence of porosity on the variability in mechanical properties of HPDC Al alloys, micro computed tomography was employed to investigate the morphology and 3D distribution of porosity in the tensile samples. Experimental results show that the variability in mechanical properties of HPDC AlSi7MgMn alloy is related to the pore size an...

The impact of high shear melt conditioning on the morphology and distribution of Fe intermetallic compounds was investigated in the processing of recycled AA6111 alloy by the twin roll casting process. The optical and scanning electron microscope (SEM) micrograph studies were carried out on twin roll casting (TRC) and melt conditioning twin roll ca...

The melt conditioned direct chill (MC-DC) casting process has been used to produce billets and extruded planks of AA5754 alloy formulated from 100% recycled Taint Tabor scrap aluminum. The billets were homogenized and then extruded into flat planks. Optical metallography of the MC-DC cast billets showed equiaxed refined grains in comparison to conv...

Grain refinement has been a topic of extensive research due to its scientific and technological importance as a common industrial practice for over seven decades. The traditional approach to grain refinement has been to reduce nucleation undercooling by the addition of potent nucleant particles. Here we show both theoretically and experimentally th...

SiC particulate reinforced A356 alloy metal matrix composites (MMCs) are synthesized using intensive melt shearing. The effect of reinforcing particle distribution on the fluidity of cast A356/10 vol.% SiCp composites is studied. Spiral length representing the fluidity of the composite melt was measured and liquid flow and solidification behaviour...

A short T6 heat treatment for Al–Si–Mg–Mn die-cast alloys was developed with a solution treatment time of only 10 min at 540 °C. Excellent mechanical properties were achieved with a yield strength of 334-349 MPa and elongation of 2.6–4.6%, which is competitive with other die-cast alloys subjected to T6 heat treatment. The effects of solution time a...

Magnesia (MgO) particles inevitably exist in Al-Mg based alloys and can act as potential nucleation sites during solidification processing. In this paper we investigated the effect of MgO substrates on the atomic ordering in the liquid Al adjacent to the liquid Al/solid MgO interfaces using an ab initio molecular dynamics approach. We found that at...

Native MgO particles in Mg-alloy melts have been recently exploited as potential substrates for heterogeneous nucleation during solidification, leading to significant grain refinement of various Mg-alloys. However, our current knowledge of the nature of the native MgO particles is still limited. In this work, we study both the physical and chemical...

The microstructure of Al-5Mg-2Si-0.4Mn-0.7Fe alloy solidified at different conditions were examined. Different kinds of eutectic structures such as (Al15(Fe,Mn)3Si2 + α-Al), (Mg2Si + α-Al) and (FIMCs + Mg2Si + α-Al) were selected due to the different primary phases formation. The phase relationships between the phases within the eutectic structures...

This paper describes the application of X-ray tomography to predict the tensile fracture properties of aluminium alloy die-castings containing natural casting defects. A new estimator (Z-project) is presented that can predict the areal fraction of porosity involved during tensile failure to a higher degree of accuracy than conventional methods, whi...

Magnesia (MgO) particles inevitably exist in liquid Mg and may be used as potential sites for heterogeneous nucleation to achieve effective grain refinement. Understanding of the atomic configurations on MgO surfaces and in the liquid Mg adjacent to the liquid Mg/MgO interfaces is therefore of both scientific and practical interests. We investigate...

The microstructure evolution and mechanical properties of recently developed die-cast Al-Si-Mg-Mn alloys were investigated. CALPHAD modelling, based on the thermodynamic database, was carried out to design Al-Si-Mg-Mn alloys with different solid fractions of the eutectic mixture. Experimental results confirmed that the new Al-Si-Mg-Mn alloys have e...

Prenucleation refers to the atomic ordering in the liquid adjacent to a liquid/substrate interface above the nucle-ation temperature. It provides a precursor for heterogeneous nucleation in the liquid adjacent to the interface. As magnesia (MgO) and alumina (Al 2 O 3) widely exist in and can be potential nucleation sites for Al-Mg based alloys, we...

The melt conditioned direct chill (MC-DC) casting process has been used for the production of billets of AA-6111 alloy formulated from recycled aluminium derived from incinerator bottom ash (IBA). The billets were homogenised and then extruded into planks. Optical metallography of the MC-DC billets showed equiaxed refined grains in comparison to DC...