Effect of prolonged high-temperature exposure on the fatigue and fracture behavior of aluminum-lithium alloy 2090

Effects of prolonged exposures of 100–1000 h at 163°C on fatigue crack propagation and fracture toughness behavior have been studied in commercial aluminum-lithium alloy 2090-T8E41, and results compared with behavior in similarly over-aged 2124 alloy. Over-aging in 2090, which led to decreases in strength and toughness principally through the formation of plate-like copper-rich grain boundary precipitates and associated copper-depleted and δ′ precipitate-free zones, was found to result in increased fatigue crack growth rates above ∼ 10⁻⁹ m cycle⁻¹; near-threshold growth rates were less affected. Such behavior is related to a diminished role of crack-tip shielding during crack extension in over-aged microstructures, from less crack deflection and lower crack closure levels (from asperity wedging), arising from more linear crack paths. Despite this degradation in fatigue crack growth properties following high temperature exposure, crack growth rates in the over-aged 2090 remain comparable or superior to traditional high strength aluminum alloys, such as 2124-T351 and 7150-T651, due primarily to higher overall levels of crack-tip shielding.