An investigation of second phases in as-cast AZ31 magnesium alloys with different Sr contents

Second phases in the AZ31 as-cast magnesium alloys with different Sr contents (0, 0.1, 0.5, 1.0, 2.0, and 5.0 wt%) were investigated using scanning electron microscopy, energy dispersive spectrometry, differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. The results indicated that the Mg21(Zn, Al)17 phase with small amount was formed in the AZ31 as-cast alloy without Sr addition, in addition to the Mg17Al12 phase. At the same time, the alloy with the addition of 0.1 wt% Sr mainly consisted of the α-Mg, Mg17Al12, Mg21(Zn, Al)17, and Al4Sr phases. In addition, the α-Mg, Mg21(Zn, Al)17 and Al4Sr phases were found to be the main second phases for the alloy with the addition of 0.5 wt% Sr. However, only the α-Mg, Al4Sr and (Mg, Al)17Sr2 phases were mainly formed in the AZ31 alloy with the addition of 1.0 wt% Sr. As for the alloys with the additions of 2 and 5 wt% Sr, their as-cast microstructures were mainly composed of the α-Mg and (Mg, Al)17Sr2 phases.