Tribological characterization of Al7075-graphite composites fabricated by mechanical alloying and hot extrusion

Aluminum matrix composites (AMCs) are candidate materials for aerospace and automotive industry owing to their large elastic modulus, improved strength and low wear rate. A simple method for fabrication of Al7075-graphite composites produced by mechanical alloying (MI) and hot extrusion is described in this paper. Effects of milling time (0-10 h) and graphite concentration (0-1.5 wt.%) on friction, hardness and wear resistance of the AMC were investigated. Wear resistance was determined by the pin-on-disk wear method using 20 and 40 N normal loads at a 0.367 m/s sliding velocity. The worn surfaces were examined by scanning electron microscopy (SEM) to identify distinct topographical features for elucidation of the prevailing wear mechanisms. Experimental results indicated considerable improvement in AMC hardness and wear resistance by adding 1.5% G (wt.) and 10 h of milling, showing homogenous distribution of the reinforcement particles in the Al-base metal-matrix composite. It was found that abrasion is the dominant wear mechanism in all extruded composites, whilst a combination of adhesion and delamination seems to be the governing mechanism for the 7075 aluminum alloy.