New insights into fine equiaxed zone of laser-welded 2A97 Al-Li alloy

Abstract In this study, the concept of fine equiaxed band (FEQB) was proposed for the first time, and the distribution range of the fine equiaxed zone (FEQZ) was redefined. Characterisation techniques including scanning electron microscopy, electron backscattered diffraction, energy dispersive spectroscopy, and transmission electron microscopy were employed to analyse the microstructures, orientations, micro-segregations, and precipitates within the grain of the FEQZ. The results indicate the existence of tiny precipitates, mainly T1 and θ′ along with a small amount of δ′ within the randomly oriented fine equiaxed grain with spherical morphology, and no obvious dendrite structure was observed. The micro-segregation of Cu and Mg occurred at the grain boundaries, resulting in the generation of intermetallic phases at grain boundaries derived mainly by eutectic action. The dominant intermetallic phase enveloping that grain is T1, and a small amount of plate-like precipitate S′ is formed at the junction of three or more grains. The bands formed by these closely connected grains are called FEQB. Furthermore, the region covered by the FEQBs is called FEQZ.