COMPARATIVE INVESTIGATIONS OF THE MECHANICALLY ALLOYED and PRESSURELESS SINTERED Al–7 wt.% Si COMPOSITES REINFORCED WITH VARIOUS BORIDE PARTICLES
This study reports the milling time optimization of the Al-7 wt.% Si alloys by using planetary ball mill, the incorporation of 2 wt.% LaB6, NbB2, VB and TiB2 particles into Al-7 wt.% Si matrix and the fabrication of composites using cold pressing and pressureless sintering. Mechanical alloying (MA) time carried out for 4, 8, 12, 16 and 20 h was optimized via crystallite size and phase determinations and microstructural investigations. 12 h was chosen as optimum MA time. Then, different particulate reinforcements were added to Al-7 wt.% Si matrix to constitute boride reinforced composites. All composite powder batches were also milled for 12 h, then compacted and
sintered at 570°C for 5 h. Microstructural, physical and mechanical (hardness and wear volume loss) properties of these composites were performed. Hardness values of 120.8 ± 11.37 and 121.77 ± 19.02 were obtained for the LaB6 and TiB2 reinforced composites, respectively.