Influence of Ca and Ce Additions on Microstructure and Microhardness of Squeeze-Cast AZ91 Mg Alloy

Abstract

In this study, AZ91 alloy was used as the base material and calcium and cerium were added as alloying elements. Microstructural analysis through optical microscope (OM) and field emission scanning electron microscope (FESEM) revealed that AZ91 base alloy contains α-Mg matrix and β-Mg17Al12 interdendritic network. The inclusion of individual calcium and cerium resulted in a more homogeneous distribution of the interdendritic network in the AZ91-1wt.% Ca and AZ91-1wt.% Ce alloy. The secondary phase (Mg17Al12) was refined in the microstructure as a result of Ca and Ce addition where Ce addition forms a new rod-like phase that is recognized as Al11Ce3 and Ca addition forms a skeleton like structure of Mg17Al12 and Al2Ca. Due to the formation of new Al2Ca and Al11Ce3 intermetallics, the volume fraction of β-Mg17Al12 was more suppressed with Ca and Ce alloy additions. The grain size determined from Electron Backscatter Diffraction (EBSD) maps indicate the reduction in average grain size with individual Ca and Ce additions. The addition of these elements was found to improve the hardness of AZ91 alloy. Overall, the results of this study demonstrate the potential for using Calcium and Cerium as alloying elements in AZ91 alloy to improve its mechanical properties by modifying its microstructure.