Synergistic Enhancement of Hardness, Tribological, and Corrosion Properties in AZ91D Alloy via Short-Time Low-Temperature Annealing

As one of the most widely used commercial die-cast magnesium alloys, AZ91D has been entensively applied in automotive and aerospace applications owing to its low density. However, its relatively low hardness, poor wear resistance, and limited corrosion behavior restrict its broader applications. Conventional solution and aging treatments often require long durations, motivating the search for shorter and more efficient processes. Thus, in the present work, AZ91D alloy was subjected to quenching at 430°C for 10 h followed by short annealing at 50, 100, and 300°C for 3 h. Microstructural analysis revealed significant changes; the grain size increased from ~30 µm in the as-received state to ~134 µm after annealing at 100°C, accompanied by precipitation of β-Mg17Al12 along grain boundaries. This condition yielded the best properties, with hardness increasing from 63 to 94 HV (+49.2%), a friction wear rate decreasing by ~40% (from 1.60 × 10–3 to 0.96 × 10–3 mm3 N–1 m–1), and corrosion current density dropping from 75.36 to 2.47 µA cm–2 in a 0.9 wt % NaCl solution. These findings demonstrate that short low-temperature annealing offers an efficient strategy to enhance the mechanical and corrosion performance of AZ91D alloy.