Microstructure-property evolution of mechanically alloyed Al-20 wt% Si matrix powders and sintered composites reinforced withTiB₂ particulates

Microstructural, physical and mechanical properties of Al–20 wt% Si matrix alloy powders and those reinforced with TiB₂ and their sintered composites were investigated in relation to TiB₂ content and mechanical alloying (MA) durations. Al–20 wt% Si matrix alloy powders and those containing 5 and 10 wt% TiB₂ reinforcing particles were MA'd for 1, 2, 4, and 8 h followed by consolidation and sintering at 843 K. Si solubility in a-Al matrix increased with increasing MA duration. Increasing the TiB₂ content, on the other hand, resulted in a systematic drop in Si solubility over the same MA period. Scanning electron micrographs of the sintered samples revealed sub-micron-sized, rod-shaped Si and spherical Al₉Si phase particles. With increasing TiB₂ content and MA durations, the microhardness of the Al20Si/TiB₂ composites improved. The wear resistances of TiB2 reinforced composites better by 5 to 8 times than that of the as-blended and 1 h MA'd AlSi matrix alloy. Due to the presence of the Al₃Ti intermetallic phase, sintered composite samples containing 10 wt% TiB₂ particles MA'd for 8 h had the maximum hardness value and lower wear resistance values than those of the Al–20 wt% Si/5 wt% TiB₂ composites.