The microstructure, mechanical and wear properties of AZ91-x%B4C metal matrix composites in as-cast and extruded conditions

Abstract

In the present work, the AZ91 Mg alloy reinforced with different weight percentages of B4C (1 wt%, 3 wt%, 5 wt%, 10 wt% and 15 wt%) was investigated with the aim of improving its mechanical and wear resistance in the as-cast and extruded conditions. A simple and cost-effective method, stir casting process, was employed to fabricate light-weight AZ91-x%B4C composites. Microstructural characterization of the as-cast specimens revealed the reasonably uniform distribution of B4C particles, well-bonded B4C particles to the matrix and the presence of minimal porosity. It was revealed that B4C addition has a slight influence on the microstructure in as-cast state, whereas extrusion process had intense grain refinement and fracturing and dispersion of the Mg17Al12 phase resulted in the significant enhancement of compressive strength, hardness and wear properties. After the incorporation of B4C, a significant reduction in weight loss was observed, although the friction coefficient was increased. Scanning electron microscopic observation of the worn surfaces was conducted and the dominant wear mechanism was recognized as oxidation assisted abrasive for AZ91-xB4C composites. These results designate that the AZ91-xB4C composite can be considered as an outstanding material where high compressive strength and wear-resistant components are of great importance, primarily in the aerospace and automotive engineering parts.