Induction reheating of A356.2 aluminum alloy and thixocasting as automobile component

The development work for producing an automobile component by thixocasting using A356.2 alloy was introduced.As the first step,the alloy was electromagnetically stirred and solidified to produce a billet with non-dendritic microstructure.The microstructure depended on several process parameters such as stirring intensity,stirring frequency,cooling rate,and melt initial superheat.Through a series of computational studies and controlled experiments,a set of process parameters were identified to produce the best microstructures.Reheating of a billet with non-dendritic microstructure to a semisolid temperature was the next step for thixo-casting of the components.The reheating process was characterized for various reheating cycles using a vertical-type reheating machine.The induction heating cycle was optimized to obtain a near-uniform temperature distribution in radial as well as axial direction of the billet,and the heating was continued until the liquid fraction reached about 50%.These parameters were determined with the help of a computational fluid dynamics(CFD) model of die filling and solidification of the semisolid alloy.The heated billets were subsequently thixo-cast into automobile components using a real-time controlled die casting machine.The results show that the castings are near net shape,free from porosity,good surface finish and have superior mechanical properties compared to those produced by conventional die casting processes using the same alloy.

Optimization of Cu content for the development of high-performance T5-treated thixo-cast Al-7Si-0.5Mg-Cu(wt.%)alloy

Cu content has been successfully optimized in a thixo-cast and directly aged(T5-treatment)Al-7 Si-0.5 Mg(wt.%)alloy.Even after the 0.5%Cu addition,plate-like Al_(2)Cu(θ’)phases,which contribute to high strengths and large plasticity,are precipitated.The formation of a large fraction of Cu-containing brittle phases could be suppressed as well.Then,the Al-7Si-0.5Mg-0.5Cu alloy exhibits high ultimate tensile strength,0.2%proof stress,and elongation to failure of 296 MPa,209 MPa,and 8.8%,respectively.This results in a high quality index similar to that of solution-treated and subsequently aged(T6-treated)Al-7 Si-Mg alloys.A Cu addition over 1.0%further improves the strengths;however,this leads to poor ductility because of the high fraction of Cu-containing brittle phases.