Effect of Sr on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy

In this study, the effect of different amounts of Sr (0, 0.05, 0.5, 1 wt.%) was investigated on microstructure and mechanical properties of the AZ91 magnesium alloy. The microstructure and mechanical properties were investigated using optical microscope, scanning electron microscope (SEM), X-ray diffractometer (XRD) and tensile test. The results shown that by adding Sr, the volume fraction of the Mg17Al12 phase decreased. It was also found that the grain size decreased significantly by addition of Sr, after homogenization. In this case, the grain size decreased from 131 μm in AZ91 to 43 μm in AZ91 with 1 wt.% Sr. Furthermore, the optimum amount of UTS and elongation were observed by the addition of 1 wt.% Sr to AZ91 magnesium alloy. UTS and elongation increased from 129 MPa and 1.1% to 177 MPa and 2%, respectively, when the 1 wt.% Sr was added to the AZ91 alloy. The fracture surface observations showed that fracture mode in these alloys were cleavage and the Sr addition does not change the fracture mode.