Characterization Investigations of 2 wt% LaB₆ Particulate-Reinforced Al-7 wt% Si Matrix Composites Fabricated by Powder Metallurgy Methods

Abstract: In this study, first of all, sub-micron LaB₆ reinforcing particles were synthesized in the size range of 100–500 nm via mechanochemical synthesis and leaching steps. Afterwards, Al-7 wt% Si matrix alloy and 2 wt% laboratory synthesized LaB₆ powders were mechanically alloyed (MA’d) at different durations to constitute Al-7 wt% Si/2 wt% LaB₆. Followed by compaction under a pressure of 450 MPa in a uniaxial cold press, samples were sintered at 570 °C for 2 h in flowing Ar gas atmosphere. Microstructural characterizations of the powders and sintered samples were performed using X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM) techniques. Effects of both MA (0, 1, 4 and 8 h) and LaB₆ reinforcement (0 and 2 wt%) on the mechanical properties of the composites were determined in terms of microhardness and dry sliding tests. Both MA process and LaB₆ reinforcement were found to make positive contribution to the hardness and wear resistance values. As-blended and sintered Al-7 wt% Si matrix alloy had a hardness value of 0.43 GPa. On the other hand, 8 h MA’d and sintered Al-7 wt% Si/2 wt% LaB₆ composite had the highest hardness (0.97 GPa) and the 4 h MA’d one had the lowest wear rate (3.25 × 10⁻⁶ mm³/N mm) among all the sintered samples. The hardness and wear resistance values were increased by approximately 2 times in the 4 h MA’d and sintered Al-7 wt% Si-2 wt% LaB₆ composite compared to its 1 h MA’d counterpart. Graphic Abstract: [Figure not available: see fulltext.].