Modeling of transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 alloy. Part II-simulation results and experimental validation

As the mathematical model has been developed in part I, the simulation results of the transport phenomena and solidification cracking in laser spot bead-on-plate welding of AA6063-T6 aluminum alloy and the experimental validation are presented in this paper. Modeling results showed that the solute concentration in the solidified region continuously increases during the solidification process. As the temperature is lower than the coherent temperature (i.e., the temperature at which the coherent mushy zone is just formed), the strains accumulated in the coherent mushy zone increase with the increasing solid fraction. The amount of strain in the mushy zone is primarily determined by the life (i.e., time span) of the coherent mushy zone, which is determined by the solidification range and solidification time. The increased solidification range and consequently solidification time extend the life of the coherent mushy zone, which increases the amount of strain and thus increases the likelihood of solidification cracking. The modeling results are in agreement with the experimental results. Both the experimental and modeling results exhibited that solidification cracking is prone to occurring near the top surface and middle part of the weld bead and an increase of laser power leads to the higher cracking susceptibility.