Effect Of Intermediate Thermo-mechanical Treatment On Microorganization And Mechanical Properties Of Mg-Gd-Y-Zn-Zr Alloy

Rare-earth magnesium alloys have attracted their attention because of their advantages of low density,high specific strength and specific stiffness,and easy recovery.However,the magnesium alloy is a dense row hexagonal structure,which leads to its poor plasticity at room temperature,which severely limits its widespread use in practical applications.By introducing the second phase particles as nucleation points before the deformation,the pre-aging treatment can promote the grain refinement during the deformation process and improve the comprehensive mechanical properties,which makes it possible to prepare the high strength and toughness rare earth magnesium alloy by combining the pre-aging treatment with forward extrusion process and promote its wide application in industrial production.In this paper,mg-9Gd-4Y-2Zn-0.5Zr（wt.%）alloy was taken as the research object,and the effect of pre-aging treatment and multistage forward extrusion process on the microstructure evolution and mechanical properties was analyzed by changing the sequence.The main research contents and conclusions are as follows:（1）the multi-stage extrusion between alloy after the preliminary results indicate that after aging treatment,intersecondary heat treatment precipitate a large number of second phases that can provide a nucleation for the formation of dynamic recrystallization grains during deformation to promote the dynamic recrystallization of the alloy,,at the same time can pinning grain boundaries hinder recrystallization grain growth,improve the comprehensive mechanical properties of alloy.The yield strength,tensile strength and elongation at break of the alloy after secondary heat treatment are 335 MPa,415MPa and 10.1%,respectively.（2）After pre-aging treatment before extrusion,the tensile strength of the alloy is increased to 409 MPa,increased by 10 MPa,and the elongation at break reaches 9.9%,67.8% higher than that of the conventional primary extrusion.The microstructure analysis shows that fine grain strengthening and precipitation strengthening play a dominant role,which can compensate for the decrease of texture strengthening effect caused by the random orientation of dynamic recrystallized grains.（3）The combination of pre-peak aging and inter-pass pre-aging can make the alloy after multistage forward extrusion obtain uniform and fine microstructure,and significantly improve the yield strength and tensile strength of the alloy,which are increased from 315 MPa and 401 MPa to 364 MPa and 449 MPa,respectively.However,the elongation of the alloy decreases from 7.8% to 5.2% after conventional multistage forward extrusion.