Research On Microstructures And Properties Of Mg-Gd-Y-(Sr)-Zr Alloys

Mg-Gd-Y-Zr system magnesium alloys have excellent age hardening and good heat resistance. In the aerospace, defense industry, 3C, automobile and other fields, the system alloys have been received a great deal of attention. And nowadays they have become one of extremely favorable commercial application potential. In the paper, the microstructures and properties of Mg-Gd-Y-(Sr)-Zr system magnesium alloys are studied.In the paper, Mg-5Gd-3Y-0.5Zr is selection as the matrix alloy. By solid solution and aging treatment at different temperatures and times, the optimum heat treatment is chosen. On the basis, the effects of alkaline-earth element Sr on the microstructures and properties of the alloys are studied. By hardness test and tensile test, optical microscopy(OM), X-ray diffract meter(XRD), scanning electron microscopy(SEM) with energy disperse spectroscopy(EDS), the mechanical properties and microstructures of the alloys are tested and observed, respectively. The effects of the heat treatment on the microstructures and properties of the alloys are studied, and the function of Sr on the alloy is researched.Mg-5Gd-3Y-0.5Zr consists of α-Mg matrix and eutectic phases Mg5 Gd and Mg24Y5. After adding alkaline-earth element Sr, the new phase Mg17Sr2 separates out.By solid solution and aging treatment at different temperatures and times, Mg-5Gd-3Y-0.5Zr is heat-treated. The results show that: the optimum heat treatment of Mg-5Gd-3Y-0.5Zr alloy is 510℃×6h(solid solution) +225℃×12h(aging).Few amount addition of Sr can effectively refine the grain of Mg-5Gd-3Y-xSr-0.5Zr alloy, and modify the second phases in the alloy, making them become more fine and uniform distribution. However, adding more Sr although can continue to refine the grain size, but the second phases of the alloys increase and began to appear segregation phenomenon.With the increase of the content of Sr, the tensile strength and the yield strength and elongation of Mg-5Gd-3Y-xSr-0.5Zr alloy at room temperature all first increase and then decrease. When the content of Sr is 0.1%, the yield tensile strength, strength and elongation of the alloy at room temperature all reach the maximum value of 219.8MPa, 154.7MPa and 11.27% respectively.