Blue laser welding of copper-to-tinned steel and its pre-and-post processing for battery joining application

Abstract

Electrification has increased the need for high-quality copper welding, which is challenging due to high infrared laser wavelength reflectivity and post-processing requirements for welding copper. This preliminary study investigates a three-step approach, whereby: (1) green laser cleaning of copper, (2) blue laser welding of copper-to-tinned steel using a 1.5 kW CW laser emitting 445 nm, and (3) laser (shock) peening with a green (532nm) laser source using a compact/portable shock processing system for the first-time. Experiments on 0.9 mm copper over a 0.3 mm tinned steel were conducted following an assessment of the microstructure, hardness, shear strength,and residual stresses. Green laser cleaning improved surface roughness and impurity removal, while blue laser welding increased hardness, but introduced porosity and cracks. Triangular spot geometry yielded the best shear strength, especially when preceded by cleaning. Laser peening enhanced grain structure and the hardness, but had limited effect on shear strength. Residual stress analysis showed tensile stresses from cleaning/welding. Laser peening mitigated weld induced tensile residual stresses, though complete reversal to compressive stress was not achieved with the applied laser intentisties. The treatment demonstrates potential for improving residual stress states in dissimilar metal welds, with effectiveness dependent on process intensity and depth of influence as focused in future work. Future work will also optimize all three processes to improve copper weldability and structural integrity