An investigation of formation of second phases in microalloyed, AZ31 Mg alloys with Ca, Sr and Ce

The present work studied the formation of new phases by adding alloying additions (Ca, Sr, and Ce) in AZ31 alloy at micro-levels (approximately 0.2 wt.% per element). Quantitative electron probe micro-analysis (EPMA) was used to identify the compositions of these phases; a comparison in the morphology and distribution of an identical phase in different alloy systems was made; and the thermodynamic software of FactSageTM was utilized to calculate the possible intermetallic phases during solidification. The results of EPMA showed the existence of phases other than Mg17(Al, Zn)12 and Al8Mn5 in AZ31 alloy, namely: Al2Ca, Al2Sr, Al11Ce3, Al8CeMn4, and Al2(Ca Sr); and these new phases were thermally stable at 450 oC for 10 h. The morphology and distribution of second phases in different alloy systems were self-consistent. These phases were well predicted by FactSageTM with recent light alloy database.