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

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.