Effect Of Multi-pass Reciprocating Upsetting-extrusion On Grain Refinement And Mechanical Properties Of Rare Earth Magnesium Alloy

As a lightweight structural material widely used in aerospace,national defense and military industries,rare earth magnesium alloy has great potential for development.In this paper,the rare earth magnesium alloys in different states are used as the research objects to study the Mg-8Gd-3Y-0.5Zr alloy without LPSO phaseand the Mg-9Gd-3Y-2Zn-0.5Zr alloy with LPSO phase.Microstructure evolution law and toughening behavior during the deformation process of DT-RUE and IT-RUE were used to Mg-9Gd-3Y-2Zn-0.5Zr alloy,and the effects of different deformation temperature on the microstructure and mechanical properties uniformity were compared and analyzed.And the following main conclusions are drawn:Multi-pass RUE deformation has a significant refining effect on rare earth magnesium alloys with and without LPSO phase.The grains of the Mg-8Gd-3Y-0.5Zr alloy without LPSO phase were refined from 38.83 μm in the initial state to 6.72 μm after four passes RUE deformation.The grains of Mg-9Gd-3Y-2Zn-0.5Zr alloy containing LPSO phase were also refined from 90.08 μm in the initial state to 5.89 μm after 4 passes RUE deformation.Rare earth magnesium alloys containing LPSO phase show finer grain size and higher refinement ratio after four passes RUE deformation.This is benefited from the induction of DRX by the LPSO phase during its deformation process,and the fragmented LPSO phase can accelerate the formation of DRX grains through the PSN mechanism during the deformation process.The two alloys have excellent strength and toughness after four passes RUE deformation.The UTS of the Mg-8Gd-3Y-0.5Zr alloy without LPSO phase is 320 MPa,TYS is 258 MPa,and EL is 11.7%;The UTS,TYS and EL of Mg-9Gd-3Y-2Zn-0.5Zr reach 331.2 MPa,263.6MPa and 7.1%,respectively.It is worth noting that the surface vickers hardness of Mg-9Gd-3Y-2Zn-0.5Zr alloy with LPSO phase can reach 112 HV after four passes deformation,which is higher than that of Mg-8Gd-3Y-0.5 without LPSO phase（83HV）.The Mg-9Gd-3Y-2Zn-0.5Zr alloy containing LPSO phase was further deformed by two RUE processes（IT-RUE and DT-RUE）.The research shows that both the IT-RUE and DT-RUE deformation methods can effectively refine the grains,but the IT-RUE process can obtain a more uniform microstructure from the center region to the edge region.After the Mg-9Gd-3Y-2Zn-0.5Zr alloy was deformed by IT-RUE,the grain size of the central region,1/2R region and edge region was not much different.However,the DT-RUE deformed to form a gradient structure in which the grain size gradually decreased from the central region to the edge region.The mechanical properties analysis results show that the mechanical properties of the Mg-9Gd-3Y-2Zn-0.5Zr alloys deformed by IT-RUE are not very different in different regions.The mechanical properties of all regions of the alloy treated by DT-RUE are higher than IT-RUE,but the mechanical properties of each region are quite different.