Microstructure, mechanical properties and texture investigation of As-cast and extruded AZ91 Mg alloys

Abstract

In this work, calcium, strontium, and cerium were introduced as alloying elements to the AZ91 alloy, which served as the base material. It was discovered through microstructural research using an optical microscope (OM) and a field emission scanning electron microscope (FESEM) that the AZ91 base alloy has an interdendritic network of β -Mg17Al12 and a magnesium matrix. The dispersion of the interdendritic network was more evenly distributed in the corresponding squeeze cast AZ91 alloys as a result of the addition of individual calcium, strontium, and cerium. Ca, Sr, and Ce additions resulted in the refinement of the secondary phase (Mg17Al12) in the microstructure. Ce addition creates a new rod-like phase known as Al11Ce3, Ca addition creates a skeleton-like structure of β -Mg17Al12, and Al2Ca while Sr addition creates bright needle-like structures of Al4Sr intermetallics. The volume percentage of β -Mg17Al12 was significantly reduced with individual Ca, Sr, and Ce additions and combined additions of Ca and Sr due to the production of new Al2Ca, Al4Sr and Al11Ce3 intermetallics. The average grain size was found to be reduced with individual Ca, Sr, and Ce additions, as seen by the grain size calculated from Electron Backscatter Diffraction (EBSD) maps. There are certain differences in the tensile properties like yield strength , ultimate strength and elongation of the AZ91 alloy and it was discovered that adding these components improved its hardness.