Creep behaviour of deep cryogenic treated AZ91 magnesium alloy

Deep Cryogenic Treatment (DCT) is known to have beneficial effects on the mechanical behaviour of some alloys. It was also reported that it can improve the mechanical properties, and in particular the creep strength, of Mg alloys. The present study is aimed at checking the effect of DSC treatment on the high temperature behaviour of the Mg AZ91 alloy by means of comparative creep tests at 100 and 200 °C carried out on DCT or simply high pressure die-cast specimens. In addition, the role played by initial microstructure was investigated by comparative creep tests on annealed and solution treated specimens. These mechanical tests were joined to scanning electron and optical microscopy observations on the creep specimens prior and after their high temperature exposure and to Differential Scanning Calorimetry (DSC) analyses to investigate the thermal stability and microstructural evolution of the alloy. The experimental study demonstrated that the effect of initial microstructure is by far more important than that of the cryogenic treatment and that DSC analyses could add useful information for microstructure-based creep models.