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 that 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 used for load bearing machine components. By performing the conventional processes of compaction, sintering and extrusion, this study assesses the important factors those affect the strength as well as other mechanical properties of the Al–Si powder forgings. The results showed that by mechanical compression, it was difficult to obtain green compacts of considerable strength if the particle sizes of the powder were small, e.g., less than the value of 45 μm. The tensile strengths of the sintered preforms as well as extruded products were mainly affected by the silicon grain sizes. Large silicon grains contained voids of various sizes, and the voids could not be closed 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 the silicon grains remarkably decreased the strengths of the alloys. Therefore, by controlling the grain sizes of powder forgings of Al–Si alloys to be as small as possible, one can obtain higher tensile strengths of the alloys.