Improvement of Fracture Toughness of Aluminum-Lithium Alloy 8090 Plate by Double Aging.

The short-transverse fracture toughness behavior of aluminum-lithium alloy 8090 plate was investigated by using a CNSB (chevron notched short bar) specimen. The fracture toughness KQVM was reduced with a progress of the first-step aging. The double-aged (DA) alloy, which was subjected to the initial underaging (UA2) at 433K followed by the second-step aging at a higher temperature for a short time, exhibited a fairly improved KQVM and a superior strength-toughness balance in comparison with the single-aged alloy, good enough to satisfy the toughness requirement in aircraft design, KQVM/σys≥2.5√mm, where σys is yield strength. The increase in toughness by DA treatment is attributed to the relaxation of intense slips due to dissolution of shearable δ' phase and growth of δ'-PFZ width, leading to the inhibition of intergranular fracture.