Interpretation of constant-load and constant-stress creep behavior of a magnesium alloy produced by rapid solidification

The creep behaviour of an Mg–Zn–Ca–Ce–La alloy produced by rapid solidification was investigated by means of constant-load creep tests carried out at 498, 523 and 548 K. The analysis of strain rate as a function of applied stress suggests that in the ranges of stress and temperature studied, the creep mechanism is glide on basal plane controlled by cross-slip on non-basal planes or dislocation glide limited by the nucleation of kinks. This behaviour contrasts with previous results obtained in pure Mg where cross-slip on non-basal planes was the rate-controlling mechanism only at higher temperatures. The different behaviour of this alloy is attributed to the very fine grain size typical of rapidly solidified material. The enhancement in strain rate observed in the present alloy can be attributed to grain-boundary sliding accommodating the strain produced by dislocation creep mechanisms (glide on non-basal plane controlled by cross-slip or dislocation glide limited by the nucleation of kinks) that operate in the subgrain interior.