The effects of friction stir processing on the wear behavior of cast AZ91C magnesium alloy

Abstract

AbstractThe microstructure and wear properties of AZ91C alloy were studied by performing solution annealing and then aging heat treatment, friction stir processing, and friction stir processing followed by solution annealing and aging. The heat-treated microstructure included fine dendritic grains (50 ± 14.2 μm) with a considerable dissolution and dispersion of continuous network-like β-Mg17Al12 precipitates at grain boundaries. Friction stir processing significantly refined the microstructure and grains (9 ± 2.3 μm); followed by the breaking-up and dissolution of dendrites and continuous β-Mg17Al12 precipitates. Heat treatment of the friction stir processed area resulted in excessive grain growth (175 ± 71.4 μm) and dispersion of fine β precipitates. Under a range of applied stresses (0.78 MPa, 2.44 MPa and 3.66 MPa) for the wear tests, only friction stir processed samples showed improvement in wear behavior at low stress, while at the higher stresses, along with the effectiveness of other processes it was the most effective process on improving the wear resistance. Heat treatment had the most effect on improving the wear resistance at the intermediate stress; moreover, applying it to the friction stir processed area remarkably enhanced the wear resistance at all stresses. Heat treatment of the friction stir processed area also resulted in the lowest friction coefficient values during the wear test, indicating the convenience of this process for wear performance of cast AZ91C alloy. Abrasion was shown as the dominant wear mechanism.