Creep of a thixoformed and heat treated AZ91 Mg-Al-Zn alloy

The creep response of a thixoformed and solution treated AZ91 Mg-Al-Zn alloy was investigated in the temperature range between 70 and 200 °C. Hardness measurements indicated that creep exposure resulted in the precipitation of a hardening phase, presumably the brittle β phase. Activation energy for creep was very close to the activation energy for Al in Mg. Since operating stress was relatively high, the stress dependence of minimum creep rate was described by the sinh equation, rather than by the conventional power law equation. The obtained stress exponent was close to 3, while the activation energy for creep as close to 140 kJ mol-1.