Influence of Microstructure on Scratch-Induced Deformation Mechanisms in AZ80 Magnesium Alloy

Indentation scratch-induced wear in Mg-8 wt% Al-0.5 wt% Zn (AZ80) alloy is investigated in this study for solution-treated and peak-aged conditions. Aged alloy exhibited higher wear resistance, with 12–14 % reduction in wear volume. This is attributed to enhanced microstructural resistance to scratch wear due to precipitate phase. Ploughing was found to be the dominating material removal mechanism for both solution-treated and aged specimens. Microcutting was also active in solution-treated alloy, but not in aged alloy due to the presence of brittle Mg₁₇Al₁₂ intermetallic particles in the microstructure. The localized stresses induced by indenter tip were found to exceed theoretical shear strength for magnesium crystal, resulting in intergranular as well as transgranular fracture phenomena. Cracks were more prominent in aged alloy, which is ascribed to the suppression of twinning activity in aged alloy, resulting in non-fulfilment of von Mises criterion of plastic deformation. Scratch-induced plastic flow was more pronounced in solution-treated alloy, with twinning as the major plasticity mechanism.