| With the development of science and technology,the automotive industry,rail transit,electronic communications,aerospace and other fields have higher and higher requirements for high performance and green environmental protection.Magnesium is considered an ideal metal structural material.Adding rare earth elements such as Gd and Y to the magnesium alloy can make the magnesium matrix form a stable second phase structure under the effect of aging,and at the same time precipitate a precipitation phase containing rare earth elements,which can improve the overall performance of the alloy.Rare earth magnesium alloys have a large amount of waste in industrial production.The solid-phase recovery process can recover waste materials and improve economic benefits.Rotary extrusion is a new process that mixes pressure and shear,which can significantly improve the overall performance of the blank formed parts.,To make up for the performance defects of as-cast alloy and solid phase recovery alloy.In this paper,the as-cast,hot-press sintered,and spark plasma sintered Mg-7Gd-4Y-2Zn-0.4Zr alloys are used as experimental materials.Rotary extrusion experiments with different parameters are designed to study the mechanical behavior and microstructure at room temperature and high temperature.Evolve,analyze the law of its influence.This paper firstly characterizes and analyzes the oxide and bonding interface in the solid-phase regenerated rare earth magnesium alloy.There are four main stages in the generation of bonding interface:rearrangement stage,elastoplastic deformation stage,fracture and fragmentation stage,and interface bonding stage.The bonding interface is mainly composed of the rare-earth element-rich oxidation phase produced in the sintering stage,and the rare-earth element mainly comes from the transfer of elements in the matrix and the LPSO phase.The oxidized phase is an amorphous structure composed of nano-scale crystal grains.The bonding interface produced by spark plasma sintering is narrower.Subsequently,three kinds of rare earth magnesium alloy blanks were subjected to rotating extrusion process experiments with different parameters,and the effect of different parameters on the room temperature performance and structure of the rotating extrusion parts was studied.The overall mechanical properties of the bottom of the rotating extrusion are better than those of the side walls.The homogenized rare earth magnesium alloy has better performance under the condition of 475?1.2rad/s.Compared with the tensile strength before forming,the tensile strength is 216MPa and the elongation is 7.8%.After forming,the tensile strength of the sidewall reaches320.5MPa and the elongation at break reaches 9.1%.,The tensile strength of the bottom reaches 317.9MPa,and the elongation at break reaches 14.4%.At 425°C,the performance changes from brittleness to toughness.Hot-pressed sintered rare earth magnesium alloy has better mechanical properties at 450?2.4rad/s.Compared with the tensile strength before forming,the tensile strength is 195.6MPa and the elongation is 3.1%.After forming,the tensile strength of the sidewall reaches 295.8MPa and the elongation at break.It reaches 12.4%,the tensile strength of the bottom reaches 305.5MPa,and the elongation at break reaches 11.0%.Spark plasma sintering rare earth magnesium alloy has better mechanical properties at 450?2.4rad/s.Compared with the tensile strength before forming,the tensile strength is 199.0MPa and the elongation rate is 4.7%.After forming,the tensile strength of the sidewall reaches 292.2MPa and the elongation at break.Reach11.9%,the tensile strength of the bottom reaches 308.5MPa,and the elongation at break reaches 12.0%.Excessively high speed and temperature during the forming of solid-phase secondary magnesium alloy will cause the bonding interface to fracture,which will affect the mechanical properties.The tensile fracture at room temperature is generally ductile or quasi-cleavage fracture.Finally,the high-temperature mechanical properties and microstructure of three kinds of rare earth magnesium alloy rotary extrusion forming parts are analyzed.The tensile flow stress at high temperature is lower than that at room temperature,and the elongation at break is significantly higher than that at room temperature.At a strain rate of 0.001s-1,the tensile strength of the homogenized rare earth magnesium alloy can reach180.6 MPa,and the solid phase regenerated rare earth magnesium The maximum tensile strength of the alloy can reach 149.3MPa.At a strain rate of 0.1s-1,the tensile strength of the homogenized rare-earth magnesium alloy can reach 218.2MPa,and the tensile strength of the solid-phase regenerated rare-earth magnesium alloy can reach 190.1MPa,and the overall strain The higher the rate,the greater the tensile strength and the lower the elongation.High-temperature tensile fractures are all tough or quasi-cleavage fracture forms.The LPSO phase in the high-temperature fracture structure is bent along the tensile deformation direction,the LPSO at the grain boundary will be broken,and the high-temperature deformed structure will produce micro-holes,micro-cracks,etc.defect.The homogenized rare earth magnesium alloy basically does not produce dynamic recrystallization.The solid-phase regenerated rare earth magnesium alloy produces dynamic recrystallization.The low rate is beneficial to its development.Under the high rate of deformation,dynamic recrystallization is too late to occur,and it will cause microcracks in the matrix to affect high temperature performance. |
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