The influence of laser pulse shape and separation distance on dissimilar welding of Al and Cu films

Pulsed Nd:YAG laser welding of Aluminum-Copper (Al-Cu) electrical connections has been investigated, focusing attention on the definition of optimal process parameters to achieve low thickness joints by varying the laser pulse shape and separation distance. Heterogeneous joints comprising Al and Cu are often required in electrical applications due to the inherent characteristics of these materials. Nevertheless, welding of dissimilar metals such as Al and Cu involves many challenges due to the high reflectivity and poor weldability between the materials, which produce brittle microstructural compounds that lead to a reduction in mechanical and electrical properties. Metallurgical, mechanical, electrical and thermal analyses have been performed on Al-Cu lap joints to evaluate the effect of different pulse separation distances and shapes on the resulting weld seam. Process optimization achieved welded joints with a low penetrating depth and maximum tensile loads of over 110 kgf. Preliminary experiments were carried out to establish a process parameter feasibility window. A first set investigated variations in pulse energy and distance for square pulses, while a second set saw variation of the pulse energy, pulse distance and pulse shape. It was found that an optimal pulse distance for a specific parameter set exists, while a pulse shape that includes material preheating produces better results in terms of mechanical strength and electrical resistance than a pulse with high initial peak power.