Rapidly solidified microstructure and failure analysis of powder metallurgy Al-Si alloys

The microstructure of the extruded bars showed a homogeneous distribution of eutectic Si and primary Si particles embedded in the Al matrix. The grain size of alpha-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si in the extruded bars was about 100-200 nm. The room temperature tensile strength of the alloy with a powder size < 26 mu m was 322 MPa, while for the coarser powder (45-106 mu m) it was 230 MPa. With decreasing powder size from 45-106 pm to < 26 mu m, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultra-fine grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 mu m at 3.5 m/s) was larger on the worn surface in comparison to the bars from the fine powders (5 mu m at 3.5 m/s) due to the lower strength of the bars with coarse powders. The fracture mechanism of failure in tension testing and wear testing was also studied.