The development and application of magnesium alloys have been used more and more widely recent years, and great achievement has been already made in aerospace, automobile and 3C industry. Mg-Zn-Y-Zr alloys (ZW series alloys) are newly developed high strength heat-resistant magnesium alloys. Commercial DC casting results show that some ZW alloys are prone to hot tearing and it is nearly impossible to gain heavy gauge ingot. Since hot tearing is related to the microstructures, mechanical properties in the mushy zone. To understand the mechanism of hot tearing of ZW series alloys, and develop newly Mg-Zn-Y series alloys with good casting and mechanical properties, in this dissertation, investigation of relation among chemical composition, microstructure and phase, mechanical properties of mg-rich corner ZW alloys have been systematically studied. Relation among chemical composition, microstructure in mushy zone, characteristics of strength, hot tearing susceptibility is then characterized.
By microstructure observation and thermal analysis cooling curve research, it is found that microstructure, mechanical properties and solidification pathways depend not only on the chemical composition but Zn/Y ratio(Mass ratio) in Mg-Zn-Y-Zr alloys in mg-rich corner, Zn content between 2.00～6.36wt.%, Y content between 1.03～6.96wt. % and these alloys can be qualitatively divided into five phase areas. Alloys in different phase areas have different phase constitutes, solidification pathways except for α-Mg: No.1 phase area(Ⅰ), with low Zn and high Y content, 0.35
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