Effect Of Different Preaging Treatment On Deformation And Precipitation Strengthening Mechanism Of 7N01 Aluminum Alloy

Based on 7N01 aluminum alloy used for high-speed train,this paper designs different solute atoms segregation states through pre aging treatment,optimizes the subsequent thermomechanical treatment process,and studies the interaction between different solute atoms segregation States and dislocations and their effects on grain size,microstructure and strengthening mechanism of the alloy.The main conclusions are as follows(1)Compared with the metastable and stable phases preset by peak aging and over aging,the solute clusters and GP regions preset by natural aging and under aging can pin more dislocations in the subsequent rolling process,resulting in stronger work hardening effect.(2)The results show that the structure,composition,number density and volume fraction of solute clusters are different with different natural aging time,different segregation state of alloy,and the work hardening effect in the subsequent rolling process is also completely different.Among them,the work hardening effect of natural aging for 90days in the subsequent rolling process is the highest,the yield strength is as high as 508MPa,and the tensile strength is as high as 544 MPa.(3)No matter whether the pre aging state before rolling is natural aging or under aging,the thermodynamic behavior of the rolled alloy is basically the same.The grain structure of the rolled alloy presents discontinuous sheet morphology,and the size of the solute clusters near the dislocation line is slightly larger than that of the clusters without dislocation area.The dislocation density of the rolled alloy increases slightly after 90 days of pre natural aging,and the grain refinement effect is very good Obviously,the size of the clusters is about 2 nm,and the number density is as high as 6.83×10²³/m³;after the subsequent artificial aging treatment,the size of precipitates in the alloy increases obviously,and the number density of precipitates decreases,but the volume fraction decreases more obviously.This is because during the subsequent aging process,many solute clusters re dissolve into the matrix,and only part of them evolve into precipitates.During the subsequent aging process,the lattice distortion decreases,the recrystallization occurs,the dislocation density decreases slightly,and the grain size increases slightly.The nano precipitates in the recrystallization are mainly GP region or metastable?'phase or?P phase.