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.