Investigation on Laser Welding of Al Ribbon to Cu Sheet: Weldability, Microstructure, and Mechanical and Electrical Properties

The pulsed laser welding of Al ribbon to Cu sheet was investigated for the electrical interconnections in power electronic modules. The various experimental conditions with the different laser powers, scan speeds, and heat inputs were employed for obtaining the defect-free Al/Cu joints. During the Al/Cu laser welding, the intermetallic compounds were formed in the welding zone. An electron probe microanalyzer and transmission electron microscopy confirmed the phases of intermetallic compounds, which were found to be Al4Cu9, Al2Cu, AlCu, etc. The computational fluid dynamics simulation revealed that the Marangoni effect induced the circulation of the molten pool, resulting in the mixture of Al and Cu and the formation of swirl-like structures at the Al/Cu joints. The tensile shear strengths and electrical resistances of the Al/Cu joints were measured, and they showed a strong correlation with the welding area. A decrease in mechanical strength and an increase in electrical resistance were measured with increasing the welding area of Al/Cu joints. Moreover, the process window for the defect-free Al/Cu joints was developed, and the experimental conditions for Al/Cu laser braze-welding were examined to minimize the intermetallic compounds formation at the Al/Cu joints.