Research On The Phase Equilibrium In Mg-rich Corner Of The Mg-Zn-Y System And Microstructure And Mechanical Properties Of As-extruded Mg-Zn-Y Alloy

As the lightest metallic structural materials, magnesium alloys have received increasing attention in the last decade because of their high potential in automotive, electronic and aerospace applications. However, the use of Mg-based alloys is currently limited due to the lack of effective strengthening phase. The Mg-Zn-Yalloys can provide more choices for the design of Mg-based alloys because of their variety structure and properties of ternary compounds. But there’s a substantial divergence of opinion within the ternary compounds and phase equilibrium of Mg-Zn-Y alloys. Meanwhile, the researches of mechanical properties of Mg-Zn-Y alloys are mainly focused on the high temperature, less on the high strain rate.In this work, the phase equilibrium relations of Mg-Zn-Y alloys at335℃,400℃have been investigated in details through the equilibrated alloy methods by scanning electron microscopic (SEM) with energy dispersive spectroscopy of X-ray (EDS), X-ray diffraction(XRD), differential scanning calorimetry(DSC) and transmission electron microscopy(TEM). Then three kinds of Mg-Zn-Y alloys were designed according to the previous research, the structure of compounds and the microstructure and the dynamic behavior at high strain rate conditions of as-extruded Mg-Zn-Y alloys have been investigated. The results obtained are as follows:(1) There are four three-phase regions in Mg-rich corner of the Mg-Zn-Y system at335℃:a-Mg+H+I、a-Mg+H+W、a-Mg+I+Z. Mg7Zn3+Z+Zn2Mg. The W-phase, H-phase, I-phase and Z-phase can equilibrium with a-Mg at335℃which can provide more choices for the design of Mg-based alloys.(2) There are three three-phase regions in Mg-rich corner of the Mg-Zn-Y system at400℃:a-Mg+H+I、a-Mg+I+Liq、Liq+Z+Zn2Mg. The Z-phase can not equilibrium with a-Mg at400℃. there will be no Liq in Mg-Zn-Y system at400℃if the Y/Zn>0.16. (3) The complete dynamic recrystallization occurs in the Mg98Zn1.2Y0.8alloy during extruding process at a temperature of300℃and a reduction ratio of16:1. The finer particles of compound H-phase dispersively distribute in the Mg-based solid solution with fine grain size, and the particles of Z-phase mainly distribute along the grain boundaries.(4) The incomplete dynamic recrystallization occurs in the Mg98Zno.8Y1.2and Mg98Zno.4Yi.6alloy during extruding process at a temperature of300℃and a reduction ratio of16:1. The particles of H-phase and X-phase mainly distribute along the grain boundaries in the Mg98Zn0.8Y1.2alloy. The particles of X-phase mainly distribute along the grain boundaries in the Mg98Zno.4Yi.6alloy.(5) At room temperature, the yield strength and the tensile strength of the as-extruded Mg-Zn-Yalloys rise with the increase of strain rates from100/s to667/s; The as-extruded Mg98Zn1.2Yo.8alloy has higher yield strength and tensile strength under the same conditions.The elongation of Mg98Znj.2Yo.8and Mg98Zn0.8Y12alloy also increases with the increase of strain rates while the elongation of Mg98Zn0.4Y1.6alloy reaches the lowest of11.5%.