Effect of Squeeze Casting and Combined Addition of Calcium and Strontium on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy.

In the present work, the effect of squeezing at 100 MPa during AZ91 Mg alloy casting has been studied, where the microstructure, texture, and mechanical properties of gravity die-cast (GC) and squeeze cast (SC) AZ91 alloy samples have been compared. Also, the effect of the combined addition of calcium (Ca) and strontium (Sr) on microstructure and mechanical properties of AZ91 alloy fabricated by SC has been investigated. The SC AZ91 alloy samples exhibited weaker texture than that of GC AZ91 alloy with a reduction in maximum texture intensity. The squeeze casting resulted in the refinement of the secondary phase (β-Mg17Al12) in the microstructure by reducing its segregation at the grain boundaries. The volume fraction of β-Mg17Al12 was more suppressed with Ca and Sr alloy addition due to the formation of new Al2Ca and Al4Sr intermetallics. The tensile properties of SC AZ91 samples were found to be better than that of GC AZ91 samples. Further improvements in mechanical properties were obtained after alloying with Ca and Sr, and the best combination of all tensile properties was obtained at (1% Ca + 0.9% Sr) addition. Higher Sr addition than 0.9% Sr degraded the strength as it induced brittleness in the material. [ABSTRACT FROM AUTHOR]