Fracture and deformation potential of magnesium alloys at low temperatures

Abstract

Thermal dependency of uni-axial mechanical properties in ZK60 and fracture resistance of AZ31 magnesium alloys were determined at low temperatures regime. In ZK60, this mechanical behavior was characterized in terms of stress, strain, deformation and fracture modes, followed by Acoustic Emission (AE) tracking. In AZ31, fracture toughness was assessed in relation to crack orientations, accompanied by fracture modes classification and AE monitoring. As for the former alloy, a moderate decrease in ductility was found, followed by a considerable increase in stresses, while decreasing test temperature. In addition, regardless of low temperatures, slip is still a predominant deformation mode, which controls the early stages of plastic deformation. The transition to mechanical twinning propagation mode controls the linear strain hardening stage. This transition was found to be temperature-dependent, expressed by a moderate decrease in transition strain, whereas the transition stress remains almost constant. In AZ31 alloy, a significant decrease in fracture toughness was found in the L-T orientation at low temperatures. This transition was accompanied by a mixed fracture mode, a pop-in phenomenon in the load-cod curves and by changes in AE parameters. The unlike mechanical behavior at low temperature of ZK60 compared to AZ31 was attributed to the occurrence of additional slip deformation mechanisms, based on literature findings concerning the addition of elements to pure magnesium.