A novel method for net-shape forming of hypereutectic Al-Si alloys by thixocasting with powder preforms

This work presents a novel and feasible method for net-shape forming of hypereutectic Al-Si alloy parts. This method, briefly termed as powder thixocasting in this paper, combines the techniques of thixocasting and conventional powder metallurgy. Consolidated preforms made of gas-atomized and pre-alloyed Al-25Si-2.5Cu-1Mg-0.5Mn powder were used as the feedstock for thixocasting. The alloy powder was preheated under protection of argon atmosphere and then was compacted to form powder preforms. The powder preforms were quickly heated into semi-solid state by induction coils and were immediately thixocast using a die-casting machine. A die with a center gate, a long runner and plate-shaped cavities was designed to examine the feasibility of this process. Results demonstrated that the powder preforms exhibits very good formability by this unique process. The powder thixocast products have satisfied strength and substantial structure with uniform distribution of fine Si particles, while the processing temperature is suitably controlled. This novel process was also successfully used to fabricate compressor scrolls for demonstration.