High frequency cycling behaviour of three AZ magnesium alloys – microstructural characterisation

Abstract

Abstract Three Mg–Al–Zn alloys, namely AZ31, AZ63 and AZ91, were subjected to high frequency cyclic loading with the aim of revealing their fatigue behaviour. AZ63 and AZ91 alloys contained discontinuous and continuous precipitates and also the intermetallic compound Mg17Al12. Samples were loaded step by step at increasing stress amplitudes at room temperature. Three characteristics of the cycled samples were investigated: the sample surface, the fatigue fracture surface and the fracture surface after the static fracture of samples. Details of the fatigue and fracture behaviour were examined using scanning electron microscopy. The significant roles of twinning and dislocation movement during the high frequency cycling are discussed. The limited plasticity of alloys estimated during the high frequency cycling is due to a decrease in the moving dislocation density entering into the thermally activated process.