Net-shape formation of hypereutectic Al-Si alloys by thixocasting of gas-atomised powder preforms

Abstract

Hypereutectic aluminium-silicon (Al-Si) alloys are well known for their lightness and good wear resistance and thus are widely used in the automobile industry. Fine primary Si particulates distributed evenly in these alloys improve their strength and machinability. However, it is difficult to create the fine Si particulates using conventional ingot metallurgy (IM) routes. Meanwhile, although powder metallurgy (PM) can create the fine Si particulates, it is less effective for producing net-shapes involving complex components. This work develops a method of combining semi-solid and powder processes to achieve both net-shapes and fine Si sizes. This method involved shaping a hot-consolidated powder preform in a semi-solid state using a die-casting machine. The present study optimises the processing procedures and examines the properties of the thixocasting. For comparison, a conventional thixocasting using feedstock made by the ingot metallurgy (IM) route was also conducted. Experimental results demonstrate that the thixocast specimens produced using powder preforms have better strength and finer Si particulates than those produced using the IM feedstock, verifying that the proposed method is feasible. (C) 2004 W. S. Maney Son Ltd.