Authors: Zhen Nan Fu, Shou Mei Xiong
Abstract: A cellular automaton (CA) based model for two-dimensional simulation of the grain
morphology of high pressure die casting magnesium alloy was developed. The heterogeneous
nucleation, the solute redistribution both in liquid and solid, the interface curvature and the growth
anisotropy during solidification were also considered in the model. By fitting the curve of grain
density distribution, parameters of continuous nucleation equation based on Gaussian distribution
were calculated. The microstructure simulation of step-shape die castings of AM50 magnesium
alloy was studied. The metallographic microstructure of the castings at the surface and center of
three steps with different initial die temperature was investigated. The simulation results were
compared with the experimental results and they were in good agreement on average grain size.
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Authors: Zhi Hua Gao, Jun Xu, Zhi Feng Zhang, Meng Ou Tang
Abstract: Annular electromagnetic stirring (A-EMS) process, developed by General Research Institute for Non-Ferrous Metals, is an advanced processing technology for conditioning liquid metal prior to solidification processing. A-EMS can avoid skin effect effectively, impose a higher shear rate and a higher intensity of turbulence to the liquid metal, and increase the area of the melt heat dissipation by means of innovatively combining noncontact electromagnetic stirring and an annular chamber with specially designed profiles. The solidification structure, composition macro-segregation and property of 7075 alloy were investigated under the conditions of the conventional casting, the conventional electromagnetic stirring casting and A-EMS casting. The results indicated that A-EMS melt processing technology had significant effects on grain refinement, reduction of composition macro-segregation and improvement of mechanical properties.
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Authors: Andreas Storz, Thomas Schubert, Thomas Weissgärber, Christoph Seyboldt, Kim Rouven Riedmüller
Abstract: The paper describes a cost effective and innovative combination of direct pressure sintering and subsequent thixoforming to produce MMC-components in (near-) net shape quality and, thus, to make these interesting materials attractive to mass production.First results of some combinations of aluminium matrix alloys with different ceramic reinforcements, consolidated by fast pressure sintering show the efficiency of this technology.The further processing of the consolidated billets has been performed by thixoforging. It can be shown, that the homogeneous microstructure from the direct pressure sintering stage with uniformly distributed ceramic reinforcements can be maintained over the semi-solid state and a full densification can be achieved. Form filling was complete and surface quality was comparable to forgings from conventional alloys.This new process flow shows advantages regarding the material yield in each of the processing steps. The (near-) net shape quality of thixoforged components allows a reduced effort for machining, which is of special importance for composite materials with a high content of wear resistant hard phases like SiC-particles.
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Authors: Ildiko Peter, Christian Castella, Mario Rosso
Abstract: The present chapter reports a short history and a state-of-the art of semi-solid techniques, with particular emphasis to the role of the liquid-solid fraction, being the rheological behaviour of the semi-solid slurry crucial and fundamental. The general description, with the related theoretical fundaments, is based on the data available in the recent and the past literature and finally it is integrated with some experimental results of the research carried out by the authors.
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