Study On The Microstructure And Properties Of Mg-Y-Zn-Zr Magnesium Alloys

As the lightest metal structure material,magnesium alloys offer high specific strength,specific stiffness,superior damping capacity,excellent machinabilty and castability.Demands from automotive industry for increasingly lightweight components have resulted in an increased interest in magnesium alloy. However,most die-cast magnesium alloys have poor strength or bad creep resistant property ,which limit their application in automobile powertrain components. Considering that MEZ alloy(Mg-2RE-0.35Zn-0.3Zr) is an alloy with excellent creep property but low strength,cerium-rich mischmetal was substituted by yttrium and zirconium was added into the alloy in order to improve the tensile strength. The effects of yttrium on the microstructure and properties of gravity-casting Mg-Y-Zn-Zr alloy were studied, which was the basis of the research on the microstructure and properties of die-casting Mg-Y-Zn-Zr alloy.It indicated that with more yttrium added to gravity-casting Mg-Zn-Zr alloy,the grain was refined and the amount of the secondary phase on the grain boundary increased,therefor the thensile strength at ambient and elevated temperatures as well as creep property were improved. As result,when 3.5% Y was added,the tensile strength at room temperature and elevated temperature as well as the creep resistant property reached the peak.Then Mg-2.64%Y-0.96%Zn-0.35%Zr and Mg-4.51%Y-0.99%Zn-0.41%Zr alloys were used in the die-casting of automobile soleplate,which was proved to be a great success. The microstructure and property of the two die-casting Mg-Y-Zn-Zr alloy were studied. It was shown that the grain was refined and the secondary phase on the grain boundary manifolded in the die-casting Mg-Y-Zn-Zr alloy,which resulted the improvement of the thensile strength at ambient and elevated temperatures as well as creep property.For example,the ultimate tensile strength of Mg-2.64%Y-0.96%Zn- 0.35%Zr alloy increased to 221.6MPa and the creep strain of it at 200℃/70MPa for 100 hours approached to 0.093%,and the ultimate tensile strength of Mg-2.64%Y-0.96 %Zn-0.35%Zr amounted to 221.6MPa and the the creep strain of it at 200℃/70MPa for 100 hours equal to 0.083%.It can be concluded that die-casting Mg-2.64%Y- 0.96%Zn-0.35%Zr and Mg-4.51%Y-0.99%Zn-0.41%Zr alloy offer both high strength and excellent creep property.