Effects of Pressure on Microstructure and Mechanical Properties of Mg-14Gd-1Zn-0.4Zr Alloy during Heat Treatment
In view of the contradiction between sufficient solid solution of alloying elements and grain growth,the effects of pressure on solid solution process of alloying elements were investigated.The microstructure and mechanical properties of Mg-14Gd-1Zn-0.4Zr alloy after vacuum and atmospheric solution treatment as well as the mechanical properties of alloys in peak-aging state were analyzed.The influence mechanism of pressure on atomic solution process was described.The results indicate that the microstructure of as-cast Mg-14Gd-1Zn-0.4Zr alloy is mainly composed of α-Mg,(Mg,Zn)3Gd,14H LPSO phases.After solution treatment at 480℃×20 h at normal pressure,LPSO phase disappears and a small amount of(Mg,Zn)3Gd remains.After solution treatment at 500℃×20 h at normal pressure and 480℃×20 h at vacuum conditions,LPSO phase disappears and absence of residual(Mg,Zn)3Gd phase can be observed,however the grain size is coarsened slightly under vacuum condition,and the strength and plasticity are increased.The peak aging time of both alloys at 225℃is 24 h,and the tensile strength and elongation of the latter are significantly improved,with the tensile strength of(360.5±1.2)MPa,yield strength of(234.6±0.8)MPa,and elon-gation of(5.2±0.3)%.When the pressure is reduced to vacuum,the diffusion coefficient of atoms is increased and the solution efficiency is improved.Solid solution of Gd and Zn atoms can be achieved at a lower solution temperature,and the grain growth is retarded,thus improving overall strength and toughness.
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