Refinement role of electromagnetic stirring and strontium in AZ91 magnesium alloy

Effect of strontium (Sr) addition and electromagnetic stirring on the microstructure of AZ91 alloy and refinement mechanism were investigated. It was found that Sr addition ranging from 0.1 to 0.3 wt.% caused refinement of as-cast microstructure, but did not form any new phases. Combined strontium alloying and electromagnetic stirring significantly decreased the grain size, changed the morphologies of the β-Mg17Al12 phases and reduced their volume percentage. The smallest grain size of AZ91 alloy was obtained in the case of 0.2 wt.%Sr addition with exciting voltage of 100 V. The increase of Vickers hardness (HV) and Brinell hardness (HB) value of AZ91 alloy were as a result of increasing solid solubility of solute elements (Al, Zn) in the matrix and refining-grain strengthening effect. The microstructural refinement was mainly attributed to the increase of the degree of undercooling and nucleation temperature of primary α phase on the basis of DTA analysis results.