预应变及时效处理对7A55铝合金残余应力及组织性能的影响

研究了预应变和时效处理对7A55铝合金残余应力和组织演变的影响。利用透射电镜和EBSD观察了微观组织,XRD测试了残余应力,显微硬度计测试了维氏硬度。试验结果表明:固溶后的试样,表面为压应力,沿轧制方向为-75 MPa,横向-115 MPa。经不同的预应变后,表面残余应力逐渐降低,施加2%的预应变后基本消除。180 ℃的时效温度下,残余应力的消减速度显著高于100 ℃和140 ℃下。随预应变量的增大,显微硬度逐渐增大,经3%的预应变后增大为92 HV0.5,提高了27.8%。显微硬度随时效时间的增加先增高后降低,峰值出现在15 h,100、140和180 ℃下时效时分别达到135、143和162 HV0.5。100 ℃×15 h的峰值硬度下晶内主要析出亚稳η′相,与基体呈共格关系;140 ℃时晶内析出相尺寸变大,出现圆片状η′相,与基体呈半共格关系;180 ℃时出现了短棒状η′相,尺寸达到5~20 nm,位相差小于10°的小角度晶界占了80%以上。

Effect of pre-strain and aging treatment on residual stress,microstructure and properties of 7A55 aluminum alloy

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%.