Effect Of Ni And Bi Alloying On Mircostructure And Properties Of Mg_96.5Y_1.5Zn₁Mn₁ Alloy With Long Period Stacking Ordered Sructure Phase

Magnesium and its alloys are highly sought after by aerospace,automotive and electronic industries due to their advantages of low density,easy recovery and abundant reserves.In particular,Mg-Y-Zn alloys containing Long Period Stacking Order?LPSO?structure with excellent comprehensive mechanical properties have attracted great interest of researchers.However,the high price of Y limits the promotion of Mg-Y-Zn alloys in the industrial field.Therefore,it is of great significance to study how to obtain high performance Mg-Y-Zn alloys under low Y consumption.In this study,the method of Ni and Bi alloying is used to prepare high performance Mg-Y-Zn alloys with low content of Y by traditional casting.Mg_96.5Y_1.5Zn₁Mn₁ alloy is selected as the master alloy.Firstly,the effect of Ni alloying on the precipitation of quasicrystal phase?I phase?in as-cast Mg_96.5Y_1.5Zn₁Mn₁ alloy is investigated.The cast Mg alloy with LPSO phase and I phase composite strengthening is obtained for the first time,Ni element participates in and promotes the precipitation of the I phase with the composition of Mg₃?Zn,Ni?₆Y.Moreover,the ultimate tensile strength of as-cast Mg₉₆Y_1.5Zn₁Mn₁Ni_0.5 alloy is 210 MPa and the elongation is 9.5%.Secondly,the effect of Bi alloying on the precipitation of LPSO phase and the growth mode between LPSO phase and W phase in Mg_96.5Y_1.5Zn₁Mn₁ alloy are studied.It is shown for the first time that Bi element can change the growth mode of LPSO phase and W phase to be divergent growth.Besides,The addition of appropriate amount of Bi element can promote the precipitation of the LPSO phase.The promotion effect of Ni and Bi composite addition on the precipitation of the LPSO phase is greater than that of single element alloying.The ultimate tensile strength of Mg_95.9Y_1.5Zn₁Mn₁Ni_0.5Bi_0.1 alloy in as-cast condition is 235MPa and the elongation is 11.9%.Thirdly,the effects of Ni and Bi alloying on the precipitation of 14H-LPSO phase and W phase spheroidization in solid solution?furnace cooled?Mg_96.5Y_1.5Zn₁Mn₁ alloy are investigated.It is concluded that Ni and Bi composite alloying can promote the precipitation of the 14H-LPSO phase,and the addition of Bi element can promote W phase spheroidization and short W spheroidization time;Finally,the effect of Ni and Bi alloying on the dynamic recrystallization behavior of Mg_96.5Y_1.5Zn₁Mn₁ alloy are investigated by extrusion treatment with different extrusion temperatures and speeds.The results show that Ni alloying accelerates the precipitation of dynamic recrystallization,while Bi alloying delays dynamic crystallization precipitation.The Mg_95.9Zn₁Y_1.5Mn₁Ni_0.5Bi_0.1.1 alloy obtained ultimate tensile strength of 384 MPa,yield strength of 380 MPa and elongation of 13.4%under the extrusion process of 340??10 mm/min.The increase of the yield strength is owing to the combination of Bi element promotes the precipitation of the twins,the decrease of dynamic recrystallized grain size?1.07?m?and the formation of the 14H-LPSO phase kink bands under compressive stress.In this paper,the effect of Ni and Bi alloying on the as-cast,solid solution and as-extruded microstructure evolution and mechanical properties of Mg_96.5Y_1.5Zn₁Mn₁ alloy are studied.The influence of two elements on the precipitation of I phase and LPSO phase,the growth mode of LPSO phase and W phase,the precipitation of 14H-LPSO phase,the spheroidization of W phase and the dynamic recrystallization behavior are systematically analyzed.The research results provide an effective idea for applying of Ni and Bi alloying in Mg-Y-Zn alloys and obtaining the high-performance Mg alloys at low Y consumption.