A new multi-stage creep aging process for improving creep age formability and maintaining performance of Al-Li alloy

In response to the weak creep age formability of Al-Li alloy, the traditional single-stage creep ageing process cannot guarantee a balance between formability and performance. This work proposes a novel multi-stage creep aging process (MSCA), which obtains a better microstructure firstly at low temperature, then increases the temperature to obtain better formability, and finally compensates for the loss of strength caused by high temperature through the secondary precipitation strengthening at low temperature, achieving a good match between formability and performance. The MSCA can effectively increase creep strain without reducing strength and plasticity. By observing the internal microstructure of the material through various microscopic characterization methods, it was found that the first stage of MSCA needs to obtain a large amount of diffuse precipitates, so that it can suppress coarsening while obtaining a large creep strain in the second stage (high temperature) of MSCA; The selection of the second stage temperature should take into account the degree of dislocation recovery and precipitate re-solution, so that the strength of the third stage of MSCA can be improved by secondary precipitation strengthening; The third stage temperature should be lowered to avoid coarsening of precipitates and to ensure that the MSCA is still comparable to single-stage creep aging with a higher creep strain. This work has important implications for the refinement and development of creep aging.