Research On Microstructure Evolution And Mechanical Properties Of 6061 Aluminum Alloy By Dynamic Severe Plastic Deformation

Aluminum alloys have a wide range of applications in aviation,aerospace,automotive,and other areas,because of its excellent formability,corrosion resistance and high specific strength,and one of the preferred lightweight materials in the future.Twin crystals as an important deformation mechanism have always been a hot issue in the study of the deformation mechanism of materials.High-density deformed twins can effectively improve the ability of metal coordination deformation and the material’s breaking strength.In this paper,dynamic severe plastic deformation method is used to study the twinning phenomenon in 6061 aluminum alloy and the mechanical properties of the loaded sample were tested.The conclusions are as follows:(1)The microstructure changes of 6061 aluminum alloy after loading in RD,TD and ND directions were studied.EBSD characterization results showed that micron-sized twins appeared after loading in the RD direction,but no twins were found in the other two directions.(2)The influence of anisotropy on the formation of twins was discussed.The arrangement of grains in the RD direction is almost equiaxed,and a large amount of dislocations generated in the extrusion process have enough space to nucleate,propagate,and grow at the grain boundaries.As a result,micrometers twins are found in the RD direction,the other two directions are not found.(3)The mechanical properties of 6061 aluminum alloy loaded with D-ECAP were tested.Tensile test results show that the tensile strength of the sample after loading in the direction of RD increases the most,followed by ND and TD.The hardness of the samples after initial material,1 pass,2 passes and 3 passes was tested.It was found that the hardness increased with the increase of extrusion passes.(4)There are three reasons to explain the improved mechanical properties of 6061 aluminum alloy after D-ECAP loading,twin strengthening,dislocation strengthening,and grain boundary strengthening.The different orientations of twin boundaries and twin sides impede the movement of dislocations,which greatly increases the resistance of dislocation movements,thereby increasing the strength of the material.The continuous increase in the number ofdislocations leads to an increase in the dislocation density,which further increases the interaction between dislocations.This increases the flow stress of the material and the macroscopic performance is work hardening.According to the “Hall-Petch” relationship established by traditional dislocation theory,the smaller the grain size,the greater the yield strength of the material.After D-ECAP loading,the grain size is refined,the smaller the grain size,the greater the percentage of grain boundaries,the higher the strength of the material.