Effect of FSP Pass Number on the Tribological Behavior of AZ31 Magnesium Alloy

Friction stir processing (FSP) in different pass number, accordingly one and four, was performed to AZ31 magnesium alloy. Optical and scanning electron microscopy (SEM) were used to investigate the effect of FSP and its pass number on the microstructure of FSPed samples. The hardness of thesamples was measured using microhardness measurement. Furthermore, wear behaviors of the samples, including wear rate and friction coefficient, were investigated using a reciprocal wear machine. To deduce the wear mechanism, SEM observations of the worn surface were carried out. Optical microscopy of FSPed samples showed grain refinement in the stir zone. Increasing FSP passnumber had a considerable effect on grain refinement. The average grain size of the as-received AZ31 base metal reduced from 11µm to about 4µm after four passes. Microhardness evaluations showed a substantial improvement by increasing FSP pass number, about 70% improvement. Wear tests results revealed enhanced tribological in FSPed samples. SEM observations of the worn surfaces indicated that the abrasion was the dominant wear mechanism governed in the samples.