Effects of Sb Content on Solidification Pathways and Grain Size of AZ91 Magnesium Alloy

Abstract

The phase constitution and solidification pathways of AZ91 + xSb (x = 0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91 + xSb (x = 0.1, 0.5, 1) is composed of α-Mg matrix, β-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after α-Mg nucleation, thus impossible acts as heterogeneous nucleus for α-Mg dendrite. Besides, the solid fraction at dendrite coherency point (f DCPs ) determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.