Comprehensive tensile properties improved by deep cryogenic treatment prior to aging in friction‐stir‐welded 2198 Al–Li alloy

Abstract In order to improve the comprehensive mechanical properties, deep cryogenic treatment (DCT) prior to aging was carried out on friction‐stir‐welded (FSW) 2198 Al–Li alloy; afterward, the microstructure and tensile properties were characterized by means of optical microscopy (OM), transmission electron microscopy (TEM) and tensile testing. The results show that FSW 2198 alloy through DCT prior to aging (DAT) possesses superior tensile properties than conventional aging treatment (AT). The microstructural analysis reveals that DAT alloy exhibits a finer grain structure, since DCT might effectively alleviate the residual stress in FSW 2198 alloy and thus decrease the driving force for grain coarsening in subsequent aging process. Moreover, DCT generates dislocation multiplication, which provides more preferential nucleation sites for T1 (Al 2 CuLi) phase during subsequent aging treatment, resulting in high‐density fine T1 phases and thin precipitate‐free zone within DAT alloy. Such reasonable microstructure leads to DAT alloy possessing better strength‐ductility combination compared to AT alloy.