The effect of different rare earth elements content on microstructure, mechanical and wear behavior of Mg-Al-Zn alloy

The effect of Rare earths addition to AZ91 magnesium alloy and its influence on the microstructure and mechanical properties was investigated in this study. Addition of cerium rich misch metal to AZ91 alloy resulted in formation of needle shape particles, which had a very high thermal stability, providing superior mechanical properties compared to AZ91 magnesium alloy. As a result, the grain boundaries were less susceptible for grain boundary sliding at high temperatures. The steady state creep rates were specified and for the AZ91 alloy and the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the RE added samples, sliding of grain boundaries was greatly suppressed and the dislocation climb controlled creep was the dominant deformation mechanism. Dry sliding wear tests were also performed to investigate the effect of Rare Earth additives on wear response of AZ91 magnesium alloy. Weight loss values were determined and wear mechanisms of the alloys with different amount of REs were investigated. Abrasion, delamination and gross plastic deformation were identified as prevailing wear mechanisms. Abrasive wear that activated at lower loads and sliding speeds increased wear rates for less ductile specimens of Rare Earth enriched. However AZ91 alloy containing Rare Earth contents show superior resistance to gross plastic deformation which operated at more severe wear conditions. This is due to existence of Al11RE3 phase that posses attractive mechanical properties at elevated temperatures.