Creep behaviour of the ZM21 wrought magnesium alloy

Magnesium cast products have achieved a break-through into industrial lightweight applications, but the development is focusing on alloys belonging to the Mg–Al family, and only few alternative alloys, like the ZM21 alloy (2%Zn, 1%Mn) have been considered. Even though preliminary studies on ZM21 extrudability and high-temperature workability have been recently published, no information is available to date on its creep response. This study aimed at covering this gap, by carrying out creep tests between 100 and 150 °C, i.e. in the same temperature range considered in previous studies that analysed the creep behaviour of conventional (AZ91, AS21, AM60) and innovative (AE and similar) cast alloys. Minimum creep-rate dependence on applied stress has been described by means of the conventional Norton equation, obtaining a stress exponent n close to 20 at 100 °C. This value of the stress exponent is intermediate between that observed in AM50 (n close to 14) and the AE44 (n close to 30). On this basis, the creep response of the ZM21 has been compared with that of other wrought and cast Mg alloys.