Microstructure Evolution And Mechanical Properties Of Light Weight Thin-walled Cabin Part Fabricated By Annular Channel Angular Extrusion

With the vigorous development of the aerospace industry,parts for the aerospace industry are advancing at a high speed in the direction of integration and weight reduction.Magnesium alloy,as the lightest metal structural material,has received extensive attention and favor in many fields such as aviation and aerospace.Thin-walled cabin/ shell-like parts are typical structural components that achieve integration and light weight.And as the main structural parts commonly seen in aerospace engineering,they are not only in high demand,but also as load-bearing components,thus requiring excellent mechanical properties.As a newly developed severe plastic deformation(SPD)process,the annular channel angular extrusion(ACAE)process can realize the one-time forming of cabin\shell members with single-pass extrusion,and it has high equivalent plastic strain.Thus,it is expected to be an ideal process for preparing high-performance magnesium alloy cabin\shell components in a short process.In this paper,using commercial AZ80 magnesium alloy as the research object,cabin\shell parts with different extrusion parameters were prepared.The deformation characteristics,microstructure characteristics and refinement mechanism of AZ80 alloy by ACAE process were discussed.The mechanical properties,fracture characteristics as well as strengthening mechanism were specific analyzed.This paper aims to provide data reference and basis for promoting the development of ACAE process in magnesium alloys.The main conclusions can be drawn:(1)The finite element analysis showed that the equivalent plastic strain of billet under ACAE would be significantly higher and more uniform than that of the traditional back extrusion process;the simulation of the deformation streamline distribution showed that the metal flow of the extrusion was mainly related to the shear deformation,and was affected by the additional friction force at the same time,which was consistent with the final experimental results.(2)The ACAE process has a strong ability of grain refinement for AZ80 alloy.The deformation temperature was the main factor of recrystallization.Under the given parameters,the grain size in the wall area of the extrusion could be refined to about 16.7-19.6μm compared with the initial size of about 350μm.The continuous dynamic recrystallization(CDRX)occurred during extrusion could be considered as the main grain refinement mechanism.(3)The evolution of precipitated phase appeared before and after extrusion.The static precipitates which appeared in the preheating of the billet at low temperature(300 ℃)hindered the dynamic recrystallization to some extent.With the increase of deformation temperature,the number of static precipitates decreased,and the dynamic precipitates at the fine grain boundary became the important factors for pinning boundary dislocations,promoting nucleation and limiting boundary migration.(4)The texture analysis shows that the texture evolution of the extruded part was mainly controlled by the shear stress and deformation temperature,which showed the competition between the two texture components,and was mainly related to the activation of <c+a> slip and the basal slip.Lower deformation temperature,finer grain structure and more dispersed precipitates could promote the weakening of texture intensity.(5)The mechanical properties of AZ80 alloy have been greatly improved after ACAE process.Compared with the initial state,the highest yield strength was increased about 1.9 times,the tensile strength was about 1.6 times,and the elongation was about 2.1 times.The significant improvement of mechanical properties was the result of the synergistic effect of fine grain strengthening and texture weakening.After grain refinement,the intergranular coordination was strengthened,the crack nucleation was restrained and the number of twins was meaningfully reduced,which improved the deformation uniformity.The weakening of texture could effectively promote the activation of basal slip during deformation at room temperature,which was an important factor for the reduction isotropy and the improvement of elongation to fracture of the material.