CHARACTERIZATION AND PARAMETER OPTIMIZATION OF FRICTION STIR PROCESSED AA7075 HYBRID SURFACE COMPOSITES

The aerospace grade AA7075-T6 alloy possesses deprived surface properties because of its behavior prone to fretting fatigue and adhesive wear under dry sliding conditions. The frictional heating and repetitive surface loading lead to over-aging and surface covered with coarsened precipitates within the soft matrix. The coarsened isomorphous precipitates can be weakened easily by hard debris particles and brittle oxide phases formed between the mating surfaces. The AA7075 surface cannot be hardened like steels because of martensitic phase absence and coatings do not sustain with thin ice effect. Thus surface wear behavior improvement with retaining microhardness of the alloy is required for increasing its wider applications. For that surface isomorphous precipitates and soft matrix need to be protected through dispersion of hard thermally stable ceramic SiC/TiC with solid-lubricant graphite particles.