Effect of pre-aging on creep aging properties and microstructure evolution of 2195 Al-Li alloy

Creep aging forming (CAF) is a potential process to manufacture large integral components of Al-Li alloys, which exhibits poor formability and susceptibility to damage and cracking via traditional plastic forming processes. Al-Li alloys also have disadvantages, such as low creep and comprehensive properties. To address this problem, this study adopted pre-aging as a treatment process before creep aging (CA). The effects of pre-aging at different temperatures (65 °C, 90 °C, and 115 °C) on the CA of Al-Li alloys were evaluated at 155 °C for 18 h. Creep strain, the evolution of mechanical properties, and the microstructural characteristics were investigated as well. The results showed that pre-aging could effectively influence the subsequent CA behavior. As the pre-aging temperature increased, creep strain accumulation during CA decreased. Meanwhile, pre-aging significantly increased the elongation (EL) of the specimens after CA; Notably, the increase in EL did not compromise strength. Changes in the microstructure of the specimens after pre-aging and CA tests were observed by transmission electron microscopy. The effect of pre-aging on the subsequent CA properties mainly revealed that the strength was not lower than that of the specimen without pre-aging after the same CA test through adjusting the percentage and size of the T1 and θ′ phases. In addition, pre-aging could promote the transformation of the fracture mechanism from intergranular fracture to mixed fracture in the specimen after CA.