冷轧变形对Al-Cu-Li合金晶粒形态和耐损伤性能的影响

Effect of Cold Rolling Deformation on Grain Morphology and Damage Resistance of Al-Cu-Li Alloy

摘要:

采用金相显微镜（OM）、电子背散射衍射（EBSD）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、X射线衍射（XRD）和室温拉伸、撕裂和疲劳裂纹扩展试验方法，探究了中间退火后13%、23%、46%和68% 4种最终冷轧变形量对Al-3.9Cu-0.74Li-0.68Mg合金薄板晶粒形态与耐损伤性能的影响规律。结果表明，随中间退火后冷轧变形量增大，经固溶处理后薄板均发生了完全再结晶，对应的平均晶粒尺寸和长径比明显减小，晶粒更趋向于等轴状；时效态合金中的析出相主要为T₁（Al₂CuLi）相，4种变形量合金中T₁相尺寸、数量密度和体积分数差异不大，定量计算了不同强化机制对屈服强度的贡献，发现4种变形量合金的强化主要来自于T₁相的析出强化，其对屈服强度的贡献为335.79~366.54 MPa；随冷轧变形量增大，薄板的疲劳扩展速率增大，对应的疲劳性能恶化，而断裂韧性呈上升的趋势，细小的晶粒有利于断裂韧性的改善而不利于疲劳性能。

Abstract:

Metallographic microscope, electron backscatter diffractometer, transmission electron microscope, scanning electron microscope, X-ray diffractometer, and room-temperature tensile, tearing, and fatigue crack extension experiments were used to investigate the effect of the four final cold-rolling reductions (13%、23%、46%、68%) after intermediate annealing on the grain morphology and damage resistance of the Al-3.9Cu-0.74Li-0.68Mg alloy sheets. The results indicate that with increase in cold-rolling reduction after intermediate annealing, complete recrystallization occurs in the sheets after solid solution treatment, leading to a significant reduction in the average grain size and aspect ratio. The grains tend to become more equiaxed. The primary precipitates in the aged alloy are T₁ phase, and the size, number density, and volume fraction of T₁ phase show little variation among the four reduction levels. Quantitative calculations of the contributions of different strengthening mechanisms to the yield strength reveal that the strengthening of the alloys with the four reduction levels is mainly attributed to the precipitation strengthening of T₁ phase, contributing 335.79?366.54 MPa to the yield strength. With the increase in cold-rolling reduction, the fatigue crack growth rate of the sheets increases, resulting in deteriorated fatigue performance, while the fracture toughness shows an upward trend. Fine grains are beneficial for improving fracture toughness but detrimental to fatigue performance.