Papers by Author: Zhong Yun Fan

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Authors: Douglas Watson, Shou Xun Ji, Zhong Yun Fan
Abstract: Super-ductile diecast aluminium alloys are critical to future lightweighting of automotive body structures. This paper introduces a diecast aluminium alloy that can satisfy the requirements of these applications. After a review of currently available alloys, the requirement of a diecast aluminium alloy for automotive body structural parts is proposed and an Al-Mg-Si system is suggested. The effect of the alloying elements, in the composition, has been investigated on the microstructure and mechanical properties, in particular the yield strength, the ultimate tensile strength and elongation.
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Authors: Guo Sheng Peng, Yun Wang, Ming Xu Xia, Zhong Yun Fan
Abstract: The interaction between Zr addition and intensive melt shearing on grain refinement of commercial purity Mg has been investigated experimentally. It was found that, without intensive melt shearing, the grain structure of Mg is changed from columnar grains to equiaxed grains with the increase in Zr concentration. However, with intensive melt shearing, the grain structure of Mg undergoes a complex change as a function of Zr concentration; for instance, the grain structure showed equiaxed grains at 0.1wt. % Zr concentration, while it was changed to columnar grains at 1wt. % Zr concentration. It was noted that, particularly, under the intensive melt shearing condition, the grain size of Mg with minor addition of Zr (0.1%) was further decreased to 134 ± 4 μm compared with that of Mg without Zr addition (217 ± 15 μm).
167
Authors: Zhong Yun Fan, Patrick S. Grant, Brian Cantor
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Authors: Reza Haghayeghi, Yuan Liu, Zhong Yun Fan
Abstract: Melt Conditioned Direct Chill (MC-DC) casting is a new development for producing high-quality billets and slabs. In the MC-DC process, liquid metal is continuously fed into a MCAST (melt conditioning by advanced shear technology) machine, where the liquid metal is subjected to high shear rate and high degree of turbulence provided by a twin screw mechanism at temperatures either above or below the alloy liquidus, and the conditioned liquid metal is then fed continuously into a Direct Chill (DC) caster to produce billets or slabs. The MC-DC process is applicable to both Al- and Mg-alloys. In this paper we present our experimental investigations of the effects of processing parameters on the microstructural and compositional uniformity of 5xxx and 7xxx series Al-alloys. It has been confirmed by our experiments that the MC-DC process can produce billets and slabs with fine and uniform microstructure, uniform chemical compositions and much reduced cast defects, such as porosity and cracks.
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Authors: Zhong Yun Fan, Hai Jun Niu, Alfred Peter Miodownik, T. Saito, Brian Cantor
423
Authors: Yan Huang, Zhong Yun Fan
Abstract: The novel melt conditioned twin roll casting (MCTRC) process, in which the melt is conditioned by intensive shearing prior to twin roll casting, has allowed magnesium sheets to be produced with a fine and uniform microstructure and substantially reduced segregations across the sheet thickness. It is thus possible to eliminate the extensive downstream processing via repetitive hot rolling, which is required after conventional twin roll casting, and to produce sheets to the required thickness for forming. The present work was conducted to study the feasibility of producing magnesium sheets ready for stamping by the MCTRC process, focusing on the development of microstructures and textures. An AZ31 magnesium alloy was used in the investigation and MCTRC experiments were carried out to produce sheets of 6 mm and 2.5 mm in thickness respectively. After MCTRC, the 6 mm sheet was processed following the conventional procedures via homogenization, hot rolling and annealing, whereas the 2.5 sheet was only homogenized. Experimental results showed that: 1) the as-cast microstructures for both sheets were similalr in terms of grain size and distribution and their texture intensity and components were also similar, being dominated by basal components with a small fraction of primatic components; 2) downstream processing by hot rolling substantially intensified the basal textures for the 6 mm sheet; 3) the 2.5 mm sheet subjected only to homogenization after casting showed a grain structure similar to that obtained after repetitive hot rolling and annealing with substantially weakened textures. Mechanisms of texture formation and development during MCTRC and downstream processing are discussed in the paper.
87
Authors: H.R. Kotadia, J.B. Patel, Zhong Yun Fan, Evelyn Doernberg, Rainer Schmid-Fetzer
Abstract: The growing importance of Al-Sn based alloys for producing self lubricating bearing materials in automotive industries necessitates the development of new alloys for improved performance. The recent thermodynamic work by Schmid-Fetzer at Clausthal University of Technology predicted that the addition of Cu to the binary Al-Sn system makes the miscibility gap stable. With the guidance of the calculated phase diagram, experimental investigations were conducted on the ternary Al-Sn-Cu system to understand the solidification behaviour of this immiscible system under intensive forced convection. The experimental focus was to investigate the effects of shear rate, shearing temperature and cooling rate on the solidified microstructure.
529
Authors: Kawther Al-Helal, Ian Stone, Zhong Yun Fan
Abstract: P-doped γ-Al2O3 was found to be a potent substrate to nucleate primary silicon whilst good modification of the eutectic matrix is retained during solidification of hypereutectic Al-Si alloys. On using P-doped γ-Al2O3 could be a perfect and clean source of P without additional impurities. The optical micrographs show that the morphologies of primary silicon crystals in solidification of Al-18Si alloy are changed from irregular coarse morphologies to fine regular particles. The average particle size of primary Si decreased from 52 μm to 25 μm and 22 μm in adding P-doped α-Al2O3 and P-doped γ-Al2O3 respectively. It was clear that P-doped γ-Al2O3 led to good refinement of primary Si and the modification effect on eutectic Si was retained in solidification of commercial purity Al-18Si alloy. Adding P-doped γ-Al2O3 give a good primary Si refinement to Al-18Si alloy if compared with the addition of P and using finer P doped γ-Al2O3 powder give narrower particle size range similar to that of adding P.
550
Authors: Michael Hitchcock, Zhong Yun Fan
Abstract: Solidification behaviour of 357 Al-alloy under intensive forced convection in the rheo-die-casting (RDC) process, was investigated experimentally to understand the effects of the intensity of forced convection and shearing time on the nucleation and growth behaviour. It was found that under intensive forced convection, heterogeneous nucleation occurred continuously throughout the entire volume of the solidifying melt. All the nuclei could survive due to the uniform temperature and composition fields created by the forced convection. This has been named as ‘effective and continuous nucleation’. It is also found that the nuclei grow spherically with an extremely fast growth rate. This makes the primary solidification essentially a slow coarsening process, in which Ostwald ripening takes place by dissolution of the smaller particles. In addition, it was found that intensive forced convection suppresses partially the formation of the primary phase, promote nucleation of the primary particles, and hinders the particle growth.
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