Effects of pulse shape on predicted thermomechanical strains in Nd:YAG laser welded aluminum

Abstract

Solidification cracking in pulsed laser welded alloys, including many commercial aluminum alloys, is a result of complex interactions between the laser welding process conditions, the solidification process, and the thermomechanical strains that are generated during welding. While temporal pulse shaping of the laser beam pulse has been shown to be capable of reducing or eliminating solidification cracking, a fundamental understanding of the influence of the pulse shape on cracking has yet to be established.In this study, the effects of temporal pulse shaping on weld pool development and on thermomechanical strains in laser spot welds created in pure aluminum were examined using a numerical model of the process. An axisymmetric thermoelastic-plastic stress analysis of transient conduction-mode welds was performed using the ABAQUS finite element program. Temperature-dependent thermophysical and mechanical properties of pure aluminum were included in the analysis. The spatial distribution of power density of the laser beam was entered into the model as a non-uniform heat flux using data obtained from a rotating-wire type laser beam analyzer (LBA). Three different pulse shapes were considered; rectangular, ramp-up and ramp-down. The predicted weld pool profiles compared favourably with experimental measurements. The results showed that the evolution of the weld pool and the thermal conditions during solidification were greatly affected by pulse shaping. Also, the mechanical strains varied temporally, but the spatial distribution and magnitude of the mechanical strains were similar for all three pulse shapes. These results suggest that pulse shaping may reduce solidification cracking in laser spot welds by changing the solidification conditions and subsequent solidification morphology, but has little effect on the thermomechanical strains in the weld metal.Solidification cracking in pulsed laser welded alloys, including many commercial aluminum alloys, is a result of complex interactions between the laser welding process conditions, the solidification process, and the thermomechanical strains that are generated during welding. While temporal pulse shaping of the laser beam pulse has been shown to be capable of reducing or eliminating solidification cracking, a fundamental understanding of the influence of the pulse shape on cracking has yet to be established.In this study, the effects of temporal pulse shaping on weld pool development and on thermomechanical strains in laser spot welds created in pure aluminum were examined using a numerical model of the process. An axisymmetric thermoelastic-plastic stress analysis of transient conduction-mode welds was performed using the ABAQUS finite element program. Temperature-dependent thermophysical and mechanical properties of pure aluminum were included in the analysis. The spatial distribution of power density of...