Effect Of Dy On The Microstructure And Properties Of ZMT613 Alloy

Wrought magnesium alloy is a promising magnesium alloy.Continuous research and development of new high-performance wrought magnesium alloys is still the focus of magnesium alloy research,to meet the performance requirements of wrought magnesium alloys in the domestic and international market.This paper takes the development of a new Mg-Zn-Mn series wrought magnesium alloy as the research background,and takes the ZMT613 wrought magnesium alloy developed by the research group as the research object.The rare earth element Dy was added in ZMT613magnesium alloy by alloying modification method.The effect of rare earth element Dy on the as-cast and extruded ZMT613 alloy microstructure and room temperature are systematically studied by optical microscope,scanning electron microscope,differential thermal analysis,energy spectrum analysis,X-ray diffraction,hardness test and tensile mechanical property test.Based on the above research,the effects of different heat treatment processes on the microstructure and room temperature mechanical properties of extruded ZMT613-x Dy(x=0,0.2,0.5,0.8,1.2)alloys are studied,the main results are as follows:The phase of as-cast ZMT613 alloy is mainly composed of?-Mg,Mg₇Zn₃,Mg Zn₂,?-Mn and Mg₂Sn phases.After adding Dy element,MgSnDy ternary phase is formed in the alloy.With the increase of Dy content,the coarse?-Mg dendrite is gradually refined,and the number and size of MgSnDy phase are gradually increased.After extrusion,the dynamic recrystallization of the alloy is sufficient,the recrystallized grains are evenly distributed and the size is small.After adding Dy element,the average grain size of the extruded ZMT613 alloy is refined from 10?m to3?4?m.Meanwhile,the mechanical properties are improved,when the addition of Dy is 0.2wt.%,the mechanical properties of the alloy are the best,and the yield strength,tensile strength and elongation are 242MPa,344MPa and 10.97%,respectively.The amount of the second phase in the alloy decreases obviously after after solution treatment at 420°C for 2h,and the undissolved second phase particles are mainly?-Mn and MgSnDy phases.Overall,the solution effect of the alloy is ideal.In order to determine the best T6 two-stage aging treatment process,the ZMT613-0.2Dy alloy with the best mechanical properties in the extruded state is selected for the two-stage aging study.After pre-aging,the hardness was 62.3HB.During the period of last-aging,the hardness increased sharply,and reached the highest at 12h,at this time,the hardness reached 91.6HB.After that,the alloy was overaged,and the hardness gradually decreased to stability.Therefore,the optimum technology of T6 two-stage aging is 420?×2h+90?×24h+180^oC×12h.Dy content and aging treatment process have important influence on the mechanical properties of the alloy.The results show that the mechanical properties of ZMT613 alloy are improved after T5 treatment,but the mechanical properties of ZMT613 alloy decrease after Dy addition.T6 treatment improves the mechanical properties of the alloy more obviously,after T6 treatment,a large amount of Mg Zn₂phase precipitates in the alloy.After T6 two-stage treatment,the number of precipitated Mg Zn₂ phases is large and the size is small,which has the best strengthening effect on the alloy,its mainly because of the pre-aging treatment.The yield strength,tensile strength and elongation of T6 single and T6 two-stage aging ZMT613 alloy are 302MPa,351MPa and 7.8%and 327MPa,385MPa and 5.1%,respectively.Compared with that of extruded ZMT613 alloy,the yield strength and tensile strength are increased by36.7%,9.7%and 48.0%,19.4%,respectively.The results show that the mechanical properties of T6 aged alloy are further improved with the addition of Dy,and the best mechanical properties are ZMT613-0.2Dy alloy.The yield strength,tensile strength and elongation of T6 single and T6 two-stage aging are 336MPa,399MPa and 4.4%and354MPa,416MPa and 3.47%respectively.The yield strength and tensile strength of T6single and T6 two-stage aging are increased by 11.3%,13.7%and 8.3%,8.1%respectively.However,with the increase of Dy content,the mechanical properties of the alloy decrease.The reason is that the higher the content of Dy,the greater the number of coarse MgSnDy phases and the stronger the fracture effect on the matrix.