Effect Of Thermal Deformation(Compression, ECAP)- Prerecovery On Microstructure Properties And Anisotropy Of Ultra-high Strength Aluminum Alloy Al-10.78Zn-2.78Mg-2.59Cu-0.22Zr-0.047Sr

As a kind of high strength aluminum alloy,7000 series aluminum alloy will occur with evolution of microstructure during thermal deformation, and it can produce the anisotropy in the process of machining. Besides, the fine grain structure can usually make the alloy obtain excellent mechanical properties. ECAP is a kind of SPD that can form dense, large, relatively uniform ultra-fine crystal material. In this paper, the super high strength aluminum alloy Al-10.78Zn-2.78Mg-2.59Cu-0.22Zr-0.047 Sr was designed and prepared. Microstructure and properties of alloy processed by thermal deformation(hot compression, ECAP)-prerecovery was studied. The specific tasks and the achievements are as follows:(1) Effect of 45% hot compression-solution-aging treatment on the microstructure and properties of ultra-high strength aluminum alloy was studied. The results show that,high strength aluminum alloy has high strength in this process,and the yield strength and tensile strength were 656.2Mpa and 710.7Mpa under the peak aging(120?×48h). Anisotropy exists in hardness and electrical conductivity of the alloy,and the L-T direction is better than L-S and T-S direction( longitudinal L,transverse T and short transverse S). Quantitative calculation by EBSD and XRD analysis has proved that the dislocation strengthening and grain boundary strengthening is 42.1MPa. The maximum depth of the intergranular corrosion of the alloys in T-S, L-S and L-T were respectively 186.31?m, 212.74?m and 111.79 ?m. The maximum depth of intergranular corrosion and the morphology of intergranular corrosion have obvious anisotropy in the three directions. The exfloliation corrosion grades of the three directions are PB, EA and EB respectively, also presenting the anisotropy.(2) Effect of 45% hot compression- prerecovery-solution-aging treatment on the microstructure and properties of ultra-high strength aluminum alloy was studied. The results show that, prerecovery treatment can slightly refine grain size,with the average size reducing from 19.32 ?m to 17.76 ?m. Besides, it increases the proportion of low angle grain boundary from 0.789 to 0.821.Compared to the hot compression-solution state, the strength of the alloy increased slightly. The yield strength and tensile strength were 667.5Mpa and 720.0Mpa under the peak aging. The anisotropy of the hardness and conductivity of the alloy are still L-T>L-S>T-S(from good to bad). Quantitative calculation by EBSD and XRD analysis has proved that the dislocation strengthening and grain boundary strengthening is 32.1MPa, and the prerecovery process consumes the dislocation strengthening of the materials. The intergranular corrosion grade of thealloys in T-S, L-S and L-T were still four, besides, the exfloliation corrosion grades of the three directions were PC, EB and EB respectively. Prerecovery did not improve the corrosion resistance and the anisotropy of the alloys.(3) Effect of 45% hot compression-ECAP- prerecovery-solution-aging treatment on the microstructure and properties of ultra-high strength aluminum alloy was studied.The results show that, the grains grow up in three directions of T-S, L-S and L-T.Some grains are almost equiaxed with many subgrains and coarse recrystallization grain. The average size and proportion of low angle grain boundary are 23.20?m and0.516.Strength of alloy decreases,the yield strength and tensile strength are 578.6MPa and 626.1MPa at 120?×48h aging system. But the material plasticity significantly improves, with the extension rate increasing from 7% to 12.8%. The micro hardness and conductivity test shows ECAP makes the alloy more uniform, effectively eliminating the texture. Besides,ECAP improves intergranular corrosion resistance of alloy, the maximum depth of the intergranular corrosion of the alloys in T-S, L-S and L-T were respectively 90.11?m, 82.66?m and 101.63?m at 120?×48h aging system, but ECAP does not improve the corrosion resistance of the alloy effectively, the exfloliation corrosion grades of the three directions are PC, EB and EB respectively.ECAP improves the anisotropy of the material effectively.(4) Effect of hot compression-ECAP-hot compression prerecovery-solution-aging treatment on the microstructure and properties of ultra-high strength aluminum alloy was studied.The results show that,subsequent hot compression makes the grain refinement. More subgrains can be seen in the internal alloy. EBSD analysis shows that the average grain size decreases and the proportion of low angle are 14.99 ?m and 0.486.The strength of the alloy increased slightly. The yield strength and tensile strength are585.4MPa and 631.0MPa at 120?×48h aging system.with the material plasticity 12.6%.Micro hardness and conductivity tests show that the subsequent compression does not make the anisotropy. The corrosion resistance of the alloy was slightly decreased. The maximum depth of the intergranular corrosion of the alloys in T-S, L-S and L-T were respectively 115.18?m?70.46?m and 102.66?m under the peak aging,the exfloliation corrosion grades of the three directions are EB, EA and EA, the corrosion resistance is poor in T-S direction. Subsequent hot compression does not improve the comprehensive properties of ECAP alloy.