| Modern industry is put forward higher requirements of balance of resources and environment and society sustainable development. Semi- solid processing is one of the new processing of magnesium alloy. It has many unique advantages such as near-net forming, products of high quality and high performance and energy-saving. Magnesium alloy is widely applied in many fields and how to further enhance the properties of rare earth magnesium alloy is of great significance. This research is focused on preparation of semi-solid slurry of two kind of rare earth magnesium and the mechanism of high-energy ultrasonic vibration. And what’s more, the properties of rheo-squeeze casting components and the mechanism of crystallization behavior under pressure are discussed.The process of the semi- solid slurry of Mg-6Zn-1.4Y-0.6Zr(mass/%) alloy prepared by high-energy ultrasonic vibration(HUV) was studied. The research mainly included the effect of HUV time and power on the morpholo gy of the semi- solid slurry and the distribution of intermetallic phases. The results indica te that after applying HUV for 60s-90 s began at 643℃, the semi-solid slurry got good results. And when setting HUV time at 90 s, the best HUV power was 1200 W. The average grain diameter decreased by 68.2% and the average shape coefficient increased by 165.2% compared with not applying HUV. In 1200 W, the tensile strength and elongation of the alloy obtained maximum value which increased by 26.2% and 44.9% respectively when compared without HUV. Mg-6Zn-1.4Y-0.6Zr alloy were mainly composed of α-Mg, α-Zr, Mg3Y2Zn3(W phase) and Mg3Zn6Y(I phase) distribution along the grain boundaries. The changes of HUV power can not influence the phase composition, but HUV treatment can refine matrix grain and disperse grain uniformly, at the same time, it can make the intermetallic phases distribution along the grain boundaries refined.The process of the semi- solid slurry of Mg-6Zn-3RE-1.4Y-0.6Zr(mass/%) alloy prepared by HUV was sutdied. The results indicate that after applying HUV for 60s-90 s began at 640℃, the semi-solid slurry got good results. And when setting HUV time at 60 s, the best HUV power was 900 W. The average grain diameter decreased by 83.1% and the average shape coefficient increased by 252.4% compared with not applying HUV. In 900 W, the tensile strength and elongation of the alloy obtained maximum value and increased by 33.0% and 106.5% respectively when compared without HUV. Mg-6Zn-3RE-1.4Y-0.6Zr alloy were mainly composed of α-Mg, α-Zr, Mg12 Ce and Mg12 La combined with Zn, Y to form the rich rare-earth compounds, and Mg3Y2Zn3(W phase), Mg3Zn6Y(I phase) distribution along the grain boundaries. Under the effect of HUV, the grain morphology evolved from dendrite to rosette or nearly spherical, that was mainly due to the ultrasonic cavitation effect to promote heterogeneous nucleation and inhibit the growth of grain and dendrite.The influence of extrusion pressure on the microstructure and performances of Mg-6Zn-3RE-1.4Y-0.6Zr alloy formed by rheo-squeeze casting was studied. The results show that there were two types of particles named α1-Mg formed in the semi-solid slurry and α2-Mg formed in rheo-squeeze casting stage. With the pressure increased from 0MPa to 200 MPa, α1-Mg particles were refined and α2-Mg particles evolved from dendrite to rosette or nearly spherical. In 200 MPa, the average shape coefficient was 0.611 and the average grain diameter was 39 mm. The tensile strength and elongation of the alloy obtained maximum value which were 181 MPa and 8.2% respectively and increased by 20.5% and 86.4% respectively when compared without extrusion pressure. The changes of pressure can not influence the phase composition. On the one hand, the mechanism of the increased pressure on solidification organization of the alloy was mainly about the improvement of alloy melting point, improvement of the coefficient of heat tra nsfer between mold and casting and improvement of atom activation energy. On the other hand, the mechanism of the increased pressure on the properties of alloy was mainly about grain refinement, the reduction of casting defects and the increase of crystal dislocation. |
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