Matrix grain characterisation by electron backscattering diffraction of powder metallurgy aluminum matrix composites reinforced with MoSi_2 intermetallic particles

Abstract

The mechanical properties of particle-reinforced aluminum matrix composites (AMCs) are largely dependent on the microstructure of the materials, which in turn is largely dependent on the processing history [1]. Powder metallurgy (PM) is a commonly used processing technique for producing AMCs since it can reduce reinforcement segregation, typical of casting metallurgy processes [2]. When there is a large size difference between reinforcing and aluminum particles, high energy ball milling (BM) is used to manufacture AMCs successfully [3,4]. In the BM process, the aluminum particles are fragmented and re-welded continuously, during which the brittle reinforcing particles are fragmented and become embedded in the softer aluminum matter. EBSD has been used extensively to characterise submicrometer microstructure in monolithic deformed alloys [5,6]. However, to the authors' knowledge, EBSD has scarcely been used to investigate AMCs and there is limited information on the matrix microstructure of milled AMCs after consolidation processes such as extrusion [7–9]. In the present work, electron back-scattered diffraction (EBSD) has been used to characterise matrix grain size and grain orientation in six powder metallurgy AA6061/MoSi2/15p composites and three unreinforced matrices processed with and without ball milling, followed by hot extrusion. The aim is to know the effect of milling on the matrix grain structure of extruded AMCs