The effect of Zn addition on microstructure and mechanical properties of the Mg-2Er alloy was investigated by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The results show that the alloys with 1%and 2%Zn （mass fraction） are composed of the W-phase and theα-Mg matrix. Meanwhile, the addition of 4%-10%Zn results in the formation of the I-phase, the W-phase and theα-Mg matrix. When the addition of Zn reaches 12%, the W-phase disappears and the phase constituents of the alloys mainly include the I-phase and the Mg4Zn7 phase besides theα-Mg solid solution. The alloy containing 6%Zn has better mechanical properties, of which the ultimate tensile strength （UTS） and the yield tensile strength （YTS） are about 224 MPa and 134 MPa, respectively, companying an elongation of 10.4%.
The microstructure evolution of the Mg 5Zn 0.63Er（mass fraction,%） alloy containing quasicrystalline phase（I-phase） under the as-cast condition was investigated via different heat treatments.The results show that apart from the precipitation of the W-phase particles,the I-phase almost dissolves into the matrix after solid solution treatment at 480℃ for 10 h（T4 state）.The solution-treated alloy was aged at 175℃ for 6-100 h（T6 state）.The ultimate tensile strength of the peak-aged alloy is approximately 261 MPa companying with an elongation of 10.5%.The improvement of the tensile strength is mainly attributed to the presence of the rod-like MgZn 2 particles.
The microstructure and mechanical properties of the cast and extruded Mg-12Zn-1.5Er alloys were investigated. The I-phase observed in the cast Mg-12Zn-1.5Er alloy was broken during hot extrusion. The microstructure of the alloy was refined due to the dynamic recrystallization, and the equiaxed grains have size in the range of 2 5 μm. Moreover, a great deal of nano-scale particles precipitate in the recrystallized grains. Compared with the cast one, the extruded alloy shows a great improvement on the mechanical properties as the result of refined microstructure, the dispersed I-phase and the fine precipitates. The ultimate tensile strength and the yield tensile strength of this extruded alloy are 359 and 318 MPa, respectively.
The effects of ultrasonic treatment on the microstructure and mechanical properties of Mg-5Zn-2Er alloy at room temperature （RT） and high temperature （HT） were investigated. The microstructure and mechanical properties of the samples were studied by OM, SEM and MTS material tester. The results show that the microstructure and mechanical properties are improved after the ultrasonic vibration. The best effects of ultrasonic vibration on microstructure and mechanical properties were obtained with the ultrasonic vibration power of 600 W and time of 100 s. The cavitation and acoustic streaming caused by ultrasonic treatment play a major role in refining the microstructure and increasing mechanical properties of the alloy.
