Porosity and liquation cracking of dissimilar Nd:YAG laser welding of SUS304 stainless steel to T2 copper

In this study, we present experimental laser welding SUS304 stainless steel to T2 copper. The forming mechanism of fusion zone polygonal porosity and heat affected zone (HAZ) liquation cracking were systemically investigated and possible solutions to the welding process were also proposed. We deemed that the generation of HAZ liquation cracking mainly underwent three stages: crack incubation, crack initiation and crack growth. Formation of HAZ liquation cracking was closely related to precipitation of Cu-Fe compounds at grain boundaries and grain boundary liquation. The occurrence of porosity was determined by the keyhole instability correlated with fluid flow, keyhole free surface evolutions and composition segregation in a welding process. The susceptibility to HAZ liquation cracking can be effectively lowered by controlling the heat input during laser welding. In addition, the porosity in the fusion zone can be eliminated by reasonably adjusting laser deflection angle in the experiments, which greatly improved the microstructure and mechanical properties of welded joints.