Microstructure-based finite element analysis of mesoscale strain localization and macroscopic mechanical properties of aluminum alloy 2024 laser weld joint

Abstract

The microstructure and residual stress can be modified by laser welding, which significantly affect the strength and ductility of materials. In this work, a microstructure-based finite element model is established to investigate the mesoscale strain localization and the macroscopic mechanical properties of the 2024 aluminum alloy laser weld joint. The residual stress in different welding processes is predicted, and its effect on the elastic-plastic constitutive model of constituent phases is evaluated. The stress-strain curves of α-Al phase and eutectic phase are calculated using instrumented indentation method. Actual microstructure graphs of the joints are used as the representative volume elements in the model. The mesoscale strain distribution, macroscopic deformation response and the damage initiation are predicted quantitatively during uniaxial tensile deformation. The model is validated by comparing with experimental results, i.e., fusion profile, distortion, strain localization bands, tensile test curves, and good agreements are achieved. It is found that the strain and stress in the constituent phases of the fusion zone are extremely inhomogeneous. There are significant strain localization bands in the α-Al phase and high stress concentration zones in the eutectic phase. The dendritic arm spacing and eutectic phase size decrease, and the percent of eutectic increases during high power matching with high welding speed within certain limits. In this case, the bearing capacity of eutectic phase increases, and the strain inhomogeneity decreases. As a result, the strength (358.8 MPa) and ductility (6.21%) of the joint can be increased by the optimized laser power (5 kW) and welding speed (140 mm/s).