Mechanical properties and failure behavior of AZ61 magnesium alloy at high temperatures

To investigate the mechanical behavior of AZ61 alloy in a mushy state, uniaxial tensile tests of as-extruded AZ61 alloy have been implemented at temperatures of 475–575 °C at a strain rate of 3 s⁻¹. Experimental results show that zero strength and zero ductility emerged at 575 and 525 °C, respectively. Abnormal coarse grains with sugar-like morphology and molten Mg₁₇Al₁₂ phases were observed in the brittle temperature range. The grain boundaries and surface were gradually covered partially or completely by a liquefied microstructure as temperatures increased. Small micropores developed into short cracks at temperatures above 525 °C and then to large cracks throughout the grain boundaries at 575 °C. It is therefore suggested that crack propagation was controlled by the quantity and distribution of molten phase in the mushy zone. Three types of interfacial wedge cracks are applied to explicate the fracture behavior of the alloy at elevated temperatures.