B4C particulate-reinforced Al-8.5 wt% Si-3.5 wt% Cu matrix composites: Powder metallurgical fabrication, age hardening, and characterization

Abstract

The present work investigates microstructural and mechanical properties of B4C particulate-reinforced Al-8.5 wt% Si-3.5 wt% Cu matrix composites prepared by a successive process of mechanical alloying (MA), cold pressing, and pressureless sintering. The effects of B4C amount, milling duration, and heat treatment were investigated. The MA (for 0, 3, 5, and 7 h) in a high-energy vibratory ball mill was applied to elemental powder blends, in which 0, 5, 7.5, and 10 wt % B4C was incorporated as reinforcing particles. Mechanically alloyed (MAed) powders were uniaxially pressed and sintered for 2 h at 550 °C then subjected to an aging heat treatment to improve the mechanical properties. Based on XRD, SEM, and TEM microstructural investigations, compared to the as-blended case, the MAed powders possessed a semi-equiaxed morphology and homogenous structure, with higher lattice strain and smaller crystallite size. In addition, the Al-8.5 wt% Si-3.5 wt% Cu-xB4C (x = 0, 5, 7.5, and 10 wt%) composites consolidated from the MAed powders exhibited improved mechanical properties, including microhardness, wear resistance, and compressive strength. The hardness of the 5 h-MAed Al-8.5 wt% Si-3.5 wt% Cu–10B4C composite was 167 H V, and yield and compressive strength were 362 MPa and 454 MPa, respectively. This sample also exhibited one of the lowest wear rates, 5.82 × 10−5 mm3/m.N, roughly 17 and 10 times lower than that of the 5 h-MAed Al-8.5 wt% Si-3.5 wt% Cu sample and its as-blended counterpart, respectively. Furthermore, the hardness and compressive strength of 5 h-MAed Al-8.5 wt% Si-3.5 wt% Cu–10B4C composite increased to 231 H V and 475 MPa, respectively, after the age-hardening treatment.