Numerical study on the effect of residual stress on mechanical properties of laser welds of aluminum alloy 2024

Abstract

The fusion zone is the weak area of weld joint which will experience complex thermal mechanical process during laser welding aluminum alloy 2024-T4. The resulting residual stress in the weld joint may exceed the yield stress, which will significantly affect the hardness and tensile strength. The purpose of this study is to predict the residual stress, and analyze its relationship with hardness and yield stress of the aluminum alloy 2024-T4 weld joint. Herein, three sequential models are established: (i) a thermal finite element model using double cone combined heat source that allows the prediction of time-dependent temperature distribution during laser welding of aluminum alloy 2024; (ii) a mechanical model using sequential coupling method and loading temperature in each increment to predict strain and residual stress; (iii) a theoretical empirical model to link the residual stress, hardness and yield stress. The simulated temperature field from the thermal model is in good agreement with the experimental result. The predicted stress field shows that the average von Mises stress at the center of the Al 2024-T4 and Al 2024-O weld joints are 303.60 MPa and 62.85 MPa, respectively, which are close to their yield stress. Moreover, it is found that the hardness decreases by 6 HV0.1 under the influence of residual stress in Al 2024-T4 fusion zone. The results indicate that the yield stress of 2024-T4 weld joint decreases by 16.5 MPa as a result of the residual stress. Above results indicate that residual stress has non-negligible influences on the mechanical properties of laser weld joint.