Study On Extrusion Forming Of AZ80+0.4%Ce Magnesium Alloy Wheel Hub And Mechanical Anisotropy Mechanism Of Key Parts

Since the 21st century,amid an increasingly severe energy crisis and environmental problems,energy conservation and emission reduction through lightweight has become the most urgent need for industries such as transportation,weapons and equipment,and aerospace to improve technical indicators further and reduce energy consumption.For example,in transportation,every 10%reduction in vehicle weight can increase fuel efficiency by 6%-8%.As the lightest metal structural material,the density of magnesium alloy is only 1.74/cm³,which is 2/3 of aluminum alloy and 1/4 of steel.At the same time,magnesium alloy has a high specific strength,good vibration reduction performance,and good thermal conductivity,making it an ideal material for the next generation of automobile wheels.In vehicle driving,the wheel hub is the critical part of the car that bears the vehicle’s weight,which is vulnerable to the action of alternating load.This article takes AZ80+0.4%Ce magnesium alloy and hollow billet forward extrusion forming process as the research object,aims to enhance the equivalent strain of the wheel spoke,optimizes the forming process through FEM analysis,and conducts extrusion forming tests on magnesium alloy wheel hubs.The microstructure evolution characteristics and texture characteristics of the hub-forming process were systematically studied,and the texture evolution law of the hub-forming process was reasonably speculated.Finally,combined with the microstructure analysis and mechanical performance response,the experimental analysis and VPSC crystal plasticity simulation verification were carried out for the tensile performance difference between the spokes and rim samples of the extruded hub and the mechanism of mechanical anisotropy of the extruded wheel was clarified.The main conclusions are summarized as follows:（1）The optimization of the shape parameters of the hollow billet significantly improves the equivalent strain of the spoke,which can effectively remove the deformation dead zone in the middle of the spoke,but has little effect on the deformation dead zone at the outer edge of the spoke.When the height-thickness ratio k of the hollow billet is more significant than 1.5,the hollow billet is prone to folding during forward extrusion.It is concluded that the best hollow billet shape parameter is high thickness k=1.5,and the outer radius R is 235mm.Under this parameter,the equivalent strain distribution of the spoke and rim of the extruded hub is similar.（2）Physical experiments show that the magnesium alloy undergoes continuous upsetting and extrusion deformation during the wheel hub forming process.The grains have significant dynamic recrystallization refinement after forming.The average grain size of the optimized deformed wheel spoke and the rim was measured by EBSD analysis to be 32.95μm and33.84μm,respectively,which is close to the equivalent strain results of FEM analysis.In particular,it is found that the dynamic precipitation of granularβ-Mg₁₇Al₁₂ phase caused by Al solute dissolution occurs in the matrix during the extrusion process,and a large number of discontinuous precipitates are precipitated during the air-cooling process after forming.The precipitated phase of the spoke is 27.33%,and the precipitated phase of the rim is 26.41%,which is nearly the same.（3）The analysis shows that the spoke and rim parts show different crystallographic texture types after forming.The spoke exhibits a unique ED-TD bimodal cross basal component,while the rim exhibits a TD-biased toward ND fiber texture.It is further found that in the process of hollow billet extrusion,the spoke part is||<||<||,and the rim part is||<||<||.The two’s three-dimensional stress states are different,leading to the differential preferential selection of each slip system activation under different stress states.（4）The mechanical properties test shows that although the extruded wheel spoke and rim have the same grain size and second-phase precipitation rate,the rim sample is 13.8%higher than the spoke sample in yield strength（YS）and 15.4%higher in ultimate tensile strength（UTS）.The relationship between the activation mechanism of the slip system and crystallographic texture in uniaxial deformation at room temperature was studied by experiments and VPSC crystal plasticity simulation analysis.The VPSC model was used to effectively predict the degree of opening of the slip system during deformation.It was demonstrated that the formation of TD texture in the spoke during deformation first promoted the opening of low activation stress tensile twinning.In contrast,the fiber texture in the hub region always maintained high columnar slip activation,which led to different texture hardening effects.