Study On Microstructure And Mechanical Properties Of WE71 Magnesium Alloy Cylindrical Parts

Cylindrical parts are commonly used structural parts in aerospace and military industries.With the rapid development of modern industry,higher and higher requirements are put forward for their lightweight,service temperature,and mechanical properties.Aiming at the improvement of mechanical properties and the uniformity of microstructure and properties of magnesium alloy cylindrical parts,this paper takes WE71 magnesium alloy(Mg-7Y-1Nd-0.5Zr(wt.%))as the research object,and systematically studies back extrusion and multi-layer The microstructure evolution and performance characteristics of the cylindrical parts prepared by the two forming processes of backward extrusion(BE)and multi-directional forging(MDF)+BE during the deformation process were explored.Performance rare earth magnesium alloy cylindrical parts and super large cylindrical parts provide the necessary theoretical support and experimental basis.The WE71 magnesium alloy extruded bar was selected as the initial alloy,the flow stress curve of the alloy was obtained through the hot compression test,the constitutive equation was established,the hot working diagram was drawn,and the suitable processing range was given that the temperature was about 460? and the strain rate was near 0.01 s-1.Then the BE and MDF+BE process of WE71 magnesium alloy were numerically simulated by DEFORM software.The results show that the MDF+BE process can significantly increase the maximum equivalent strain of cylindrical parts and increase the equivalent strain of each area.In the initial WE71 magnesium alloy,the second phases were mainly composed of square Y-rich phase,circular Zr particle and irregular eutectic Mg-RE phase.The average grain size and dynamic recrystallization rate of the initial alloy at the Center and Outer were 68.3 ?m,81.4%and 27.3 ?m,98.8%,respectively.The second phases in back-extruded WE71 magnesium alloy cylindrical parts were mainly square Y-rich phase,elemental Zr particles and Mg5RE phase.The changing trend of average grain size and dynamic recrystallization rate from the inner wall to the outer wall was consistent:in the compression area and shear area,the average grain size from inner wall to the outer wall increases gradually,while the dynamic recrystallization rate decreases gradually.In the stable forming area,the average grain size from the inner wall to the outer wall increases at first and then decreases,and the dynamic recrystallization rate decreases gradually,which was consistent with the changing trend of numerical simulation.The introduction of a multi-directional forging process before back extrusion can not only reduce the size and increase the number of Mg5RE phases in the alloy,but also refine the average grain size of the cylindrical part,significantly increase the fine grain content,and form a bimodal grain structure in the area with small strain.Comparing the mechanical properties of the two at room temperature,the ultimate tensile strength(UTS),yield strength(YS)and elongation of the MDF+BE cylindrical part were higher than those of BE cylindrical parts.Ordered solute clusters formed by single or multiple RE-rich atomic columns appeared in WE71 magnesium alloy after aging for 2 hours,and the solute clusters began to evolve into zigzag or RE-hexagons precipitates with aging time.During peak aging,a large number of ?' phases were formed and uniformly distributed in the Mg matrix,in which the ultimate tensile strength,yield strength and elongation of the compression area c and stable forming area h under the peak aging state of the MDF+BE cylindrical part were 358 MPa,23 1 MPa,3%and 381 MPa,272 MPa,4%,respectively;when the aging time was further extended to 500 h,the coarsening ?' phase was still stably distributed in the Mg matrix,?' phase has good high temperature thermal stability.