Refinement role of electromagnetic stirring and calcium in AZ91 magnesium alloy

Effects of calcium addition and electromagnetic stirring on the microstructure of AZ91 magnesium alloy and refinement mechanism were investigated. The results show that calcium addition ranging from 0.1wt% to 0.3 wt% does not lead to formation of any new phases but cause the refinement of as-cast microstructure. However, combined calcium alloying and electromagnetic stirring significantly decrease the grain size, change the morphologies of the beta-Mg17Al12 phases,and reduce their volume percentage. The minimum grain size of AZ91 alloy is obtained in the case of the addition of 0.2 wt%Ca with exciting voltage of 100 V The microstructural refinement is attributed to the increase of the degree of undercooling and nucleation temperature of primary alpha-Mg phases on the basis of DTA analysis results.