Abstract: This work concerns the distinguished roles of static aging and strain aging in the creep resistance of a hot-rolled Mg-4Y-3.5Nd alloy. The solution-treated sample is named AS while the peak-aged sample obtained from static aging at 220 °C is named AA. The strain aging (creep loading) was performed for both AS and AA samples at 220, 250 and 280 °C, respectively. The results showed that the creep resistance of both samples was closely related to the width of precipitate-free zones (PFZs). Under low stress, the dislocation cross-slip was effectively delayed by the precipitates and the existing PFZs widened slowly in the AA sample, leading to its stronger creep resistance compared to the AS sample. Inversely, under high stress, pyramidal 〈c+a〉 slip was more frequently activated, which could not be delayed by the coarsened precipitates. Consequently, the widening rate of PFZs became fast and the creep resistance became weaker in the AA sample. From the above-mentioned results, this work provides a novel guide for using Mg alloys with rare-earth addition. At the temperature range of 220-280 °C, static aging is positive for creep resistance under low stress, while directly performing strain aging without static aging is recommended for creep resistance under high stress.

Key words: Magnesium, Microstructure, Creep, Precipitation, Dislocation slip