Laser welding of ultrathin stainless steel 316L sheets

The technical challenge is raised when the aerospace industries require to join ultra thin stainless steel 316L sheets of thickness 50–100 μm. Distortion-free joining of such workpieces up to 5 feet long is achieved in this research by laser marginal lap welding using small clamp distance.; Ultra thin sheet metals has very sensitive response in weld geometry to heat input, and the weld geometry is importance for the weld strength. A three-dimensional heat conduction model was developed for a laser beam scanning on sheet metal of finite thickness but infinite length and width. The results show the weld depth is more difficult to control when it approaching the total thickness of the workpieces or when the total thickness of the work piece is smaller.; The clamp heat sink effect is more significant when the workpieces thickness is smaller. A conduction model accounting for heat loss into the clamps is developed to calculate the temperature profile during laser marginal lap welding of sheet metals. This model predicts the weld geometry fairly well. A strong clamp heat sink also produces a steep temperature distribution in the solid region around the weld pool resulting in lower thermal impact (temperature profile) to the heat-affected zone (HAZ).; Pitting corrosion resistance in the laser welded stainless steel 316L sheets is found to be severely degraded in the HAZ when using relatively weaker clamp heat sink. On the contrary, a strong heat sink can minimize the degradation of pitting resistance by reducing the susceptibility to pitting initiation. The HAZ microstructure for a weaker clamp heat sink consists of sub-granular δ-ferrite and partitioning of alloying elements between the δ-ferrite and austenite phases results in compositional heterogeneity. The compositional heterogeneity is the major cause for degradation of the pitting corrosion resistance. The temperature profile and mean diffusion distance in the HAZ, calculated with the conduction model developed in this research, predict the phase presence and phase size fair well. The conduction model can be used to select suitable clamp design to produce desired HAZ microstructure.