Analysis of the creep behaviour of die-cast Mg-3Al-1Si alloy

The creep behaviour of die-cast Mg-3Al-1Si (AS31) alloy has been studied at 125 1C, 150 1C and 175 1C with stresses ranging 50-110 MPa. The alloy exhibits anomalously high stress exponents, i.e. 14.4 at 125 1C, 11.6 at 150 1C and 9.5 at 175 1C. Contrary to work reported previously, these high stress exponents cannot be rationalised using the threshold stress approach that is commonly adopted in analysing creep behaviour of dispersion strengthened alloys or metal matrix composites. It is shown that the observed high stress exponents are associated with the dominance of power-law breakdown creep in this study, and the stress dependence can be well described by the Garofalo sinh relationship with the natural exponent of 5. Transmission electron microscopy (TEM) observations reveal that cross-slip of 〈a〉 type dislocations is probably the controlling creep mechanism.