Assessment of the Microstructure, Solidification Characteristics and Mechanical Properties of AZ61 + xSr Magnesium Alloys

The effect of Sr addition on the solidification parameters of AZ61 alloy, such as liquidus and solidus temperatures, the nucleation under cooling temperature and dendrite coherency point (DCP), was investigated via the cooling curve thermal analysis method. The results revealed that by increasing the Sr content from 0 to 0.75 pct, the nucleation temperature increased about 8.2 °C and nucleation under cooling decreased about 3.5 °C. Also, it was found that increasing the Sr content suspended the dendrite coherency point and increased the solid fraction at this point. Mechanical properties of AZ61 alloy were characterized at room temperature through a compressive test. The results indicated the positive influence of Sr on compressive strength of the alloy. When the Sr content increased from 0 to 0.75 pct, the ultimate compressive stress increased from 186 to 280 MPa. This could be the result of a grain refining effect of Sr on AZ61 alloy and the formation of Al₄Sr and Al₃Mg₁₃Sr intermetallic compounds.