Impacts of artificial aging state on the creep resistance of a rolled Mg-3.5Nd alloy

Abstract

This study investigates the impacts of artificial aging state on the tensile creep resistance of a hot-rolled Mg-3.5 wt%Nd alloy. The alloy was heat treated under different conditions, including solution treatment at 490 °C, under-aging for 2, 5, and 10 h, and peak-aging for 20 h at 220 °C. The samples were abbreviated as AS, A2, A5, A10, and A20, respectively. After aging for 2 h, many precipitates appeared in the under-aged A2 sample, most of which were lenticularβ′-phase precipitates. With an increasing aging duration, β′ transitioned to β1 and substantial solute depletion was observed. The A2 sample had no precipitate-free zone (PFZ), but PFZs formed in A5, widened in A10, and evolved into the widest in the peak-aged A20 sample. During creep testing at 250 °C, β1 phases precipitated in the AS sample, and atomic diffusion induced the formation and widening of PFZs. Pyramidal dislocations and β1 dissolution induced grain boundary migration and rapid PFZ widening in the A20 sample, which was less obvious in the A10 and A5 samples. The slightest solute depletion in the grain boundaries during artificial aging and the unconspicuous β1 dissolution during creep testing avoided fast PFZ widening in the A2 sample. Consequently, although the A20 sample had the highest strength at room temperature, wide PFZs and grain boundary migration led to severe stress concentration and deteriorated its creep resistance. Narrow PFZs and dislocations cutting the β′ phases in the A2 sample led to the best creep resistance.