Microstructural stability and softening resistance of cast AZ81 and AZ81+1RE magnesium alloys

The elevated-temperature mechanical properties and resistance to softening of a cast AZ81 Mg alloy and its variant with 1 wt% La-rich rare-earth elements (RE) were characterized using hot hardness and hot shear punch tests (SPT). The superiority of AZ81+1RE over the base alloy, manifested by higher thermal stability and high- temperature mechanical properties as well as higher transition temperatures and lower softening coefficients, was discussed based on the microstructural characteristics of the tested alloys. These include refinement of the microstructure, decline in the amount of the thermally unstable /3-Mg17Al12 phase, and the creation of thermally stable Al11RE3 intermetallic particles that stabilizes the microstructure at high temperatures. It was shown that the reliability of the hot shear data to calculate the above softening parameters was assured by comparing with the results of traditional hot hardness.