Cooling Velocity And Heat-treatment Parameters Effect On The Microstructure And Mechanical Properties Of Mg-Y-Gd-Zn Alloys

Based on the experience of the heat-resistant developing, several high strength heat-resistant Magnesium alloys were prepared by adding Zn into (Mg₉₆Y₃Gd₁)_99.85Zr_0.15 alloys.Study of the cooling velocity and heat-treatment parameters effect on the microstructure and tensile properties of Mg-Y-Gd-Zn alloys were carried out; effect of the Zn addition on the microstructure of matrix and precipitates, the distribution and the crystallography characters of the precipitates were studied using OM,XRD and SEM; the formation,trasition and contribution of the LPSO structure and its effect on the mechanical properties of the alloys were studied.Mg-Y-Gd-Zn alloys present high properties at elevated temperature. As the addition of Zn, high-temperature stable phases Mg₁₂Y₁Zn₁ with 18R long period stacking order(LPSO) are formed in the boundaries. It also improves the properties of Mg-Y-Gd-Zn alloys at elevated temperature. And other LPSO structures are also discovered in matrix of the (Mg₉₅Y₃Gd₁Zn₁)_99.85Zr_0.15 alloy According to the optimizing of heat-treatment parameters , UTS of (Mg₉₆Y₃Gd₁)_99.85Zr_0.15 and (Mg₉₅Y₃Gd₁Zn₁)_99.85Zr_0.15 alloys reaches 322MPa and 290MPa, along with the TYS reaches 233MPa and 185MPa respectively at room temperature. Thanks to the starting of several slip systems , the improvement of the plasticity, and the high-temperature stable phases Mg12Y1Zn1 in the boundaries, Mg-Y-Gd-Zn alloys exhibit a higher properties at elevated temperature than at room temperature.Through comparing the microstructure of the casting (Mg₉₅Y₃Gd₁Zn₁)_99.85Zr_0.15 alloy of three cooling velocity and controlling the heat-treatment parameters, the evolving of the LPSO structure is discussed, and the processing parameters of controlling the LPSO structure are found. In the end, influence of the LPSO structure to the Mg-Y-Gd-Zn alloys is discussed.