Influence of the milling process on TiB2 particle reinforced Al-7 wt.-% Si matrix composites

Al-Si metal matrix composites have generally been manufactured using casting methods. Powder metallurgy has been used as an alternative manufacturing technique to obtain more homogeneous and segregationfree products. In this study, 2 wt.-% TiB2 particle reinforced Al-7 wt.-% Si composites were manufactured using high energy ball milling, cold pressing (at 450 MPa) and pressureless sintering (at 570 °C for 2 h under Ar flow) techniques. The effects of different milling processes, such as mechanical alloying at room temperature and/or cryomilling in an isolated polycarbonate cylinder soaked in liquid nitrogen or sequential milling, on the Al-7 wt.-% Si-2 wt.-% TiB2 powders and corresponding bulk products were investigated. The microstructural, physical and mechanical properties of the composites sintered from the mechanically alloyed, mechanically alloyed and cryomilled, and sequentially milled powders were significantly improved as compared with those of asblended ones. The highest density, the highest microhardness and the lowest wear rate were obtained in a composite sintered from mechanically alloyed and cryomilled powders at 92.38 %, 214.14 ± 41.17 HV and 3.8 × 10-3 mm3·N-1 × m-1, respectively.