Assessment of the powder extrusion of silicon-aluminium alloy

The silicon-aluminium alloys are, in general, brittle in behaviour and have comparably low strengths. However, Sumitomo Electric Industries claimed th at they had developed the so-called Sumi-Although alloys, which had tensile strengths ranging from 400 to 500 MPa. Such alloys were suitable to be use d for load bearing machine components. By performing the conventional proce sses of compaction, sintering and extrusion, this study assesses the import ant factors those affect the strength as well as other mechanical propertie s of the Al-Si powder forgings. The results showed that by mechanical compr ession it was difficult to obtain green compacts of considerable strength i f the particle sizes of the powder were small, e.g., less than the value of 45 mum. The tensile strengths of the sintered preforms as well as extruded products were mainly affected by the silicon grain sizes. Large silicon gr ains contained voids of various sizes, and the voids could not be dosed up in plastic deformation. In addition, many cracks could form in the silicon grains during a plastic deformation process. The cracks and the voids in th e silicon grains remarkably decreased the strengths of the alloys. Therefor e, by controlling the grain sizes of powder forgings of AI-Si alloys to be as small as possible, one can obtain higher tensile strengths of the alloys . (C) 2001 Elsevier Science B.V. All rights reserved.