Reduced temperature (22–100 °C) ageing of an Mg–Zn alloy

Heat treatment at intermediate temperatures (70–100 °C) doubles the age hardening response of the binary Mg–2.8 at.% Zn alloy when compared to the conventional T6 heat treatment and ambient temperature ageing. The maximal hardening produced at 70 °C is associated with the highest number density of the homogeneously distributed precipitates. At least six different types of coherent and semicoherent precipitates were simultaneously present in the microstructure aged at 70 °C: [0 0 01]Mg rods and laths, Guinier Preston (GP) zones, GP1 zones {0 0 0 1}Mg plates and prismatic precipitates containing 19–26 at.% Zn. Artificially aged alloy is strengthened mainly by sparsely distributed β′1 and β′2 precipitates and occasional GP zones. Strengthening in the naturally aged condition is produced by the combination of GP1 zones, prismatic precipitates and clusters containing about 20 Zn atoms.