Research On Microstructure And Mechanical Properties Of Heat-resistant Mg-Nd-Zn-Zr Alloy By Work Hardening Technique

The rapid development of the aerospace industry puts forward higher requirements for the lightweight of structural parts.Compared with traditional commercial magnesium alloys,Mg-RE alloys have higher strength at 250?,which broadens the engineering application of magnesium alloys.However,due to the poor plasticity of Mg-RE alloys,their research focuses on fine-grain strengthening,solid solution strengthening and aging strengthening.There are few studies on work hardening technique.In this paper,based on the previous research on the solid solution-extrusion process of Mg-Nd-Zn-Zr alloy,the effects of extrusion parameters on the extruded microstructure were systematically studied,and the effects of microstructure refinement and texture change on the alloy strengthen and plasticity were quantified.Subsequently,based on room temperature pre-tensile and aging test of the extruded alloy,the rotary swaging process was used to strengthen the asextruded bar.The influence of the initial grain size on the structure and properties of the deformation strengthened alloy was analyzed,and the pre-deformed strengthening-aging strengthening was studied.The mutual influence relationship of quantification of the strengthening effect of the residual deformed structure.Based on the above research,four kinds of plastic processing technologies for cup parts with forging and indirect extrusion were designed to meet the requirements of engineering application.The influences of different plastic deformation paths on the microstructure and properties of tubular parts were studied and analyzed to provide feasible theoretical guidance and data support for the later forming of large tubular parts of Mg-RE alloy.Significant dynamic recrystallization(DRX)and microstructure transformation of basal plane texture were observed at 500? to 150?.Microcrystalline structure with size less than 5?m was obtained at 300?.As-extrued bar has excellent room temperature strength/plasticity with extrusion direction,elongation of 25?40%and yield strength of 116?250MPa,respectively.The deformed grains in the alloy have a<10-10>fiber texture parallel to the extrusion direction,and the DRXed grains show a decline {0002} basal texture,and the final texture is the result of the combined effect of the two.The yield strength of the extruded alloy decreases with the weakening of the base surface texture,which is in line with the Hall-Petch relationship including the effect of texture.The residual deformed microstructure introduced by warm extrusion can strengthen the alloy effectively.Grain refinement improves the non-uniform elongation during tensile process.The uniform elongation can be estimated by the initial equivalent mbas when the texture of the base plane along the extrusion direction weakens or tilts to increase.Pre-deformed-aging treatment is an effective way to strengthen metals.The grain size of the extruded alloy is about 2.9?6.3?m by rotary forging.The texture of the alloy changes from the inclined {0001} basal plane texture to the elongated{0001}<10-10>parallel axis texture.The residual deformed microstructure is up to 65%after rotary forging at 530? as-extrued,and the tensile yield strength at room temperature is up to 346MPa,and the ultimate tensile strength at 250? is up to 258MPa.The the rotary swaging alloy show a Hall-Petch relationship with negative slope k.Considering the effect of texture,the work hardening technique increases?0,bas by 16?27MPa.The DRX ratio of the solution-extruded cup is 23%,and the grain size of the deformed grains is 79.8?m.The proportion of DRXed grains is 45%and the deformed grains is refined to 5.1?m after the compression cup.The texture of the alloy is parallel to the maximum stress at the observation position of the sample,and the texture is weakened by discontinuous dynamic recrystallization(DDRX).The yield stress of the alloy is inconsistent under the influence of the texture.After aging,the strength of the alloy is improved,and the corresponding uniform elongation is improved by refining the grain size of the deformed grains.