Effect of double-aging on the fracture toughness of 2090 and 2091 aluminum alloys

Effect of double-aging on the short-transverse fracture toughness of Al-Li alloys 2090 and 2091 was investigated by using a CNSB (chevron notched short bar) specimen. The fracture toughness KQVM is reduced with a progress of the firststep aging, but is fairly improved by a double-aging treatment. The double-aged alloy 2091 exhibits a superior strength-toughness balance to that of the single-aging. The increase in KQVM by the double-aging is attributed to a relaxation of intense slip due to dissolution of shearable δ' phase and growth of δ'-PFZ width. For alloy 2090, coasening of grain boundary precipitates concurs with the δ' phase dissolution, which assumedly accelerates microvoid growth at grain boundaries, leading to a lower improved toughness.