An analysis of strain–time relationships for creep in an as-cast Mg–Al–Si alloy

Two models of strain–time creep curve description were applied to a set of experimental data obtained recently by testing a newly developed Mg–Al–Si–RE alloy (AS21X) produced by die-casting. Due to the absence of extensive tertiary creep, the simplified equations for constant-stress creep tests of the Li–Akulov and Bagley–Jones–Freed models were used to identify material parameters in the 70–180 °C range. In both models, secondary creep rate data fit well in the whole stress–temperature range considered. The description of primary creep was generally good, except for the high-stress range at 70 °C. In all cases, the predicted strain vs. time creep curves became more accurate as the contribution of secondary creep to strain increased. Above 0.002% strain, the models can reliably be applied in the stress–temperature range investigated. The extrapolation of predicted times at fixed strains were one or more orders of magnitude above the highest experimental times (6×106 s for 0.02 strain) and will require additional testing at lower stress.