| As the lightest metal structure material,magnesium alloys with low density,high specific strength,good conductive thermal conductivity and other excellent properties,has a very broad application prospect and research value in the aerospace and other fields,but the lack of effective strengthening phase is the outstanding problem for the design of Mg alloys.Mix rare earth elements into the Mg-Zn binary alloy we will get abundant ternary compounds,those ternary compounds can effectively improve the performances of the magnesium alloy.So people pay their attention to the research of the Mg-Zn-RE alloy,and Mg-Zn-Y alloy get the most attention.But there are many controversials in the ternary compounds of Mg-Zn-Y alloy.The thermal stability of the ternary compounds and its related study phase equilibria in the Mg-Zn-Y alloy are researched in this paper by SEM,EDS,EPMA,XRD,DSC and TEM,determining low Y part at 400 ℃,437 ℃,450 ℃ isothermal section diagram,so that it can provide more possibilities for the design of Mg alloy.Get the conclusions as follows:There are four kinds of ternary compounds coexisting in the balance with a-Mg solid solution in the low Y part of Mg-Zn-Y alloy,including Z phase,I phase,H phase and W phase.the composition of Z phase with hexagonal structure is about Mg27.3Zn66.4Y6.3(at.%),the composition of icosahedron quasicrystal phase is Mg32-36Zn58-53Y10-11,the composition of H phase with hexagonal structure is about Mg25.1Zn58.3Y16.6,W phase with face-centered cubic structure has the composition about Mg26.5Zn49.4Y24.1.The temperature of the steady coexistence of a-Mg solid solution and Z phase which formming in the solidification process is not higher than 334 ℃,and Z phase translates into I phase with higher temperature.The reaction has a very small heat effect,and it’s accompanied by a small amount of atomic diffusion;Quasicrystal phase can also form in the normal solidification process,and coexists with a-Mg solid solution in balance up to 448 ℃,and translates into W phase with the temperature increasing,I phase which is translated by Z phase also changes into W phase with the temperature further rising;W phase can exist from room temperature up to 485.4 ℃,and when the temperature is higher than 485.4 ℃,the W phase began to melt;H phase can be stable in temperature not higher than 444 ℃.There are three three-phase areas in the low Y part of Mg-Zn-Y alloy at 400 ℃ and 437℃ isothermal section,respectively including:I phase + liquid + a-Mg;Z + Zn2Mg phase +liquid;H phase + W phase + α-Mg;There are two two-phase regions,respectively including:α-Mg + I phase;liquid + Z phase.At 400 ℃,the Z phase had already can’t coexist with a-Mg solid solution.There are one three-phase areas of W phase + liquid + α-Mg and one two-phase equilibrium of a-Mg + W phase in the low Y part of Mg-Zn-Y alloys at 450 ℃ isothermal section.At 450 ℃,H phase and quasicrystal phase no longer coexist with α-Mg solid solution in equilibrium.Comparing to 400 ℃ isothermal section,the liquid phase area at 450 ℃enlarges.500 ℃ liquid phase area further expands,all experimental alloys in α-Mg + liquid two phase equilibrium. |
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