Threshold creep behaviour of an MgZnCaCeLa alloy processed by rapid solidification

The creep behaviour of an Mg3ZnCa1.5Ce0.5La alloy processed by rapid solidification was investigated at temperatures ranging from 473 K to 523 K and applied stresses up to 82.6 MPa. It is shown that the minimum or steady-state creep strain rate is not attained up to a true creep strain of about 0.35. At least up to this creep strain, the true creep strain rate decreases in time essentially linearly for strains higher than 0.03. Thus primarily the true creep strain rate ε5 (the subscript 5 refers to a true creep strain of 0.05) is used to describe the creep behaviour of the alloy. ble logarithmic coordinates, the true creep strain rate ε5 depends on the applied stress in a way that strongly suggests a true threshold stress. The threshold stress σTH decreases with increasing temperature and the same holds for the true applied stress exponent n. The values of this stress exponent are low, decreasing from 3 at 473 K to 2 at 523 K. lied stresses ranging from about 10 MPa to about 85 MPa, the activation enthalpy (true activation energy) of creep ΔH is significantly higher than the activation enthalpy of diffusion in the alloy matrix lattice ΔHL. Analysis of the creep data suggests that the process (or dislocation mechanism) controlling the creep strain rate in the alloy is either dislocation slip in the basal planes dependent on cross slip to non-basal planes or, more probably, dislocation glide in non-basal slip planes dependent on the nucleation of kink motion.