Microstructural and failure mechanism of laser welded 2A97 Al–Li alloys via synchrotron 3D tomography

Abstract

Good quality 1.2-mm-thick 2A97 Al–Li alloy butt joints were achieved by the fiber laser welding with the filler ER5356. Thorough investigations were then performed on the microstructure, porosity size and location, softening behavior, tensile strength and fatigue limit, together with failure mechanism via the third-generation synchrotron X-ray microtomography. Results show that the very narrow EQuiaxed Zone (EQZ) inside the weld composed of small-sized grains can be clearly observed when magnifying the fusion line. EQZ appears to be the weakest region across the weld, giving the lowest hardness. Generally, the grain size and distribution are less responsible for the softening. Furthermore, both sides of EQZ with acute microstructure and property gradient induce the stress concentration. EQZ appears to play a crucial role in degrading the mechanical strength and cracking resistance. Laser welded 2A97 Al–Li alloys with ER5356 demonstrate better mechanical properties in terms of tensile strength and fatigue limit compared to those with ER4047. Keywords: Aluminum–lithium alloys, Laser beam welding, Non-dendritic equiaxed zone, Fatigue crack initiation and growth, Synchrotron radiation X-ray microtomography