Effect of First and Second Passes on Microstructure and Wear Properties of Titanium Dioxide-Reinforced Aluminum Surface Composite via Friction Stir Processing

Abstract

The dispersion of particles in polymer, ceramic and metal matrix composites via conventional routes was very difficult, due to agglomeration/clustering of particles, poor compatibility of properties of particle and matrix. So, an attempt has been made to uniformly disperse the titanium dioxide particles on the surface of aluminum matrix via two-pass friction stir processing. The effect of passes on particle distribution, microstructure, microhardness and wear properties was systematically investigated. Microstructural studies revealed a fine equiaxed grain structure in the stir zone due to the dynamic recrystallization. The first-pass surface composite sample results in agglomeration of particles toward the advancing side due to insufficient materials flow and strain. The second pass was carried out by changing advancing and retreating side of composite plate processed by the first pass. The results showed that marginal change in grain size was observed with homogeneous microstructure when compared to first-pass surface composite. Microhardness was carried out across the cross sections of the surface composites to obtain hardness profile. The tribological performance was assessed using a pin-on-disk tribometer. The result reveals that surface composites processed by the second pass show better hardness and wear resistance when compared to as-received aluminum. The wear mechanism shows a transition from adhesive wear in surface composites to the combination of abrasive and delamination wear in as-received aluminum.