Effect of Pulsed Current Melt Treatment on Solidification Microstructure and Mechanical Properties of Mg-3Al-1Sn-0.5Ca Alloy

The effect of pulsed current melt treatment on the solidification microstructure and mechanical properties of Mg-3Al-1Sn-0.5Ca alloy cast in graphite moulds was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and an electronic universal testing machine. The results show that pulsed current melt treatment can refine the primary grains and second phases of Mg-3Al-1Sn-0.5Ca alloy remarkably, and simultaneously improves its tensile and compressive properties. Under the optimal parameters, compared with the untreated alloy, the pulsed-current-treated alloy exhibits a 69.5% reduction in grain size and a 68.9% decrease in the average length of striated secondary phase. Meanwhile, its tensile strength rises by 14% and the elongation improves by 100%. Within the pulse voltage range of 0~400 V and pulse frequency range of 0~10 Hz, both grain size and the average length of striated secondary phases decrease steadily as these two parameters increase. When the melt treatment temperature ranges from 660 ℃ to 750 ℃ and the treatment time from 0 to 60 s, the grain size and the average length of striated secondary phase of the pulsed-current-treated alloy first decrease and then increase as the two parameters rise. The transition occurs at 690 ℃ and 30 s. The compressive properties of the Mg-3Al-1Sn-0.5Ca alloy show a consistent variation trend with grain size and the average length of striated secondary phases.