The corrosion behavior of as-cast AZ91C magnesium alloy was studied by performing friction stir processing (FSP) and FSP followed by solution annealing and then aging. Phase analysis, microstructural characterization, potentiodynamic polarization test and immersion tests were carried out to relate the corrosion behavior to the samples microstructure. The microstructural observations revealed the breakage and dissolution of coarse dendritic microstructure as well as the coarse secondary [Formula: see text]-Mg[Formula: see text]Al[Formula: see text] phase which resulted in a homogenized and fine grained microstructure (15[Formula: see text][Formula: see text]m). T6 heat treatment resulted in an excessive growth and dispersion of the secondary phases in the microstructure of FSP zone. The potentiodynamic polarization and immersion tests proved a significant effect of both FSP and FSP followed by T6 on increasing the corrosion resistance of the cast AZ91C magnesium alloy. Improve in corrosion resistance after FSP was attributed to grain refinement and elimination of segregations and casting defects which makes more adhesive passive layer. Increase in volume fraction of precipitations after T6 heat treatment is determined to be the main factor which stabilizes the passive layer at different polarization values and is considered to be responsible for increasing the corrosion resistance.

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In this study, TIG welding was used to clad and repair the surface of cast AZ91C magnesium alloy. Then, friction stir processing and T6 heat treatment wrer applied on the welded region. Microhardness results showed an improvement in the mean hardness of welded zone and also FSPed zone. Increase in the mean microhardness of the welded zone after T6 heat treatment to the maximum value was also concluded. The results of wear test showed that the wear resistance of the welded area was improved. Further improvement in wear properties was obtained after friction stir processing and T6 heat treatment.

The 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.