Microstructure evolution and strengthening mechanism of Al-Li alloy during thermo-electromagnetic forming process

The manufacturing process of thermo-electromagnetic forming process (TEP), which includes solution treatment, electromagnetic forming (EMF) and aging, is proposed to settle the problem of poor formability and avoid quenching distortion for Al-Li alloy at room temperature, while obtaining considerable performance. The microstructure evolution and strengthening mechanism of Al-Li alloy during TEP were investigated by means of microscopic characterization and mechanical property test. The results show that the strengthening T1 phases uniformly precipitate in grain and decorate the sub-grain/grain boundary in a stacked form for each TEP and conventional thermo-mechanical process (TMP) treated specimen. However, compared with TMP, TEP can obtain higher density and aspect ratio of T1 phases. The dislocations formed by EMF are different from quasistatic tensile (QST) in both configuration and density, which further increases the nucleation site of T1 phase and improves the aging kinetics compared with QST. Moreover, EMF enhances the thermal stability of T1 and effectively inhibits the coarsening of thickness. Higher strain strengthening and precipitation strengthening with considerable plasticity and fracture toughness of Al-Li alloy can be obtained through TEP. The relationship between microstructure characteristics and strengthening mechanism is further discussed. This study provides a new insight into the EMF combined heat treatment of the third-generation Al-Li alloy.