Abstract: Effect of pre-strain and aging treatment on the residual stress, microstructure evolution and mechanical properties of 7A55 aluminum alloy were investigated by using TEM, EBSD, XRD and micro-hardness tester. The results indicate that the surface stress of the solution treated specimens is compressive, being -75 MPa and -115 MPa along rolling and transversal directions respectively. The residual stress decreases with the increase of pre-strain and almost being eliminated after 2% pre-strain. The subduction rate of residual stress for aging at 180 ℃ is obviously quicker than that at 100 ℃ and 140 ℃. The hardness increases with the increase of pre-strain, and after 3% pre-strain it increases to 92 HV0.5, i.e. by 27.8%. The hardness increases first and then decreases with the increases of aging time, and reaches 135, 143 and 162 HV0.5 respectively when aging at 100, 140 and 180 ℃ for 15 h. When aging at 100 ℃ for 15 h where the peak hardness is obtained, the metastable η′ phase is mainly precipitated inside grains and has a coherent relation with the matrix. When aging at 140 ℃, the size of the intragranular precipitated phase increases, and semi-coherent disk-like η′ phase appears. While aging at 180 ℃, short rod-like η′ phase with a size of 5-20 nm appears, and the grain boundary with small angles (<10°) accounts for more than 80%.

Key words: 7A55 aluminum alloy, residual stress, pre-strain, aging