Mechanical properties and fracture behavior of an ultrafine-grained Al-20 Wt Pct Si alloy

The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pet Si alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder size <26 mum was 322 MPa, while for the coarser powder (45 to 106 mum), it was 230 MPa. The tensile strength of the extruded bar from the fine powder (<26 mum) was also higher than that of the Al-20 wt pct Si-3 wt pct Fe (powder size: 60 to 120 mum) alloys. With decreasing powder size from 45 to 106 mum to <26 Am, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 mum at 3.5 m/s) was larger on the worn surface in comparison to the bars from the fine powders (5 mum at 3.5 M/s), attributed to the lower strength of the bars with coarse powders.