Microstructures and Phase Transition Points of As-Cast Mg-Zn-Y System Alloys

摘要

As-cast microstructures and their distribution of Mg-Zn-Y ternary alloy with high magnesium, low zinc and yttrium were examined using Nikon Epiphot optical microscopy（OM）, RigakuD/max-3C X-ray diffraction（XRD）, and JEOL JSM-6700F scanning electron microscopy （SEM） equipped with an energy-dispersive X-ray spectroscopy （EDS）. In the as-cast microstructures, Yttrium and zinc tend to segregate at grain boundaries, therefore meets the compositional condition to form Mg-Zn-Y compounds at grain boundaries even with relatively low content of Y. The principal ternary phase in Mg-Zn-Y alloys can be consisted of W-phase （Mg3Y2Zn3）, Z-phase （Mg3YZn6） and X-phase （Mg 12YZn）. Combining differential thermal analyzer （DTA） the phase transformation temperature of alloys were discussed. The eutectic melting temperature of W-phase at 520 ℃, the phase transformation temperature of Z-phase at 445 ℃ and the melting temperature of X-phase at 540 ℃ are shown.