# Investigation of Intermetallics Formation and Joint Performance of Laser Welded Ni to Al
###### Abstract  
In this paper, laser welding Ni to Al using pulsed wave (PW) and continuous wave (CW) lasers was investigated. Weld quality and strength were evaluated in terms of cross-section examination, intermetallic compounds formation, microhardness, shear test and 90-degree peel test. The results show that deep penetration welding Ni to Al causes high melting pool temperature and severe material mixing, which could result in dominant AlNi\({}_{3}\) and AlNi intermetallics (IMCs) in the weld. These IMCs could significantly increase the hardness of the welding zone, but could also lead to the formation of defects, as well as reducing the ability to withstand the shear force and peel force applied to the weld. In comparison, using process optimization to maintain a shallow penetration or form a weld-braze joint, low melting pool temperature and minimum material mixing can be achieved. Hence, low-hardness Al\({}_{3}\)Ni IMCs are prevalent in the weld. This helps generate a defect-free dissimilar weld joint to withstand higher shear force and peel force. The findings show promising applications, such as the battery management system of electric vehicles, in which joining a Ni adaptor to an Al bus bar is required.  
laser welding; dissimilar material; intermetallics formation; joint strength +
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butt joints. [PERSON] et al. [17] investigated laser lap welding for producing similar and dissimilar material tab-to-busbar interconnects for Li-ion battery assembly. It was reported that it is feasible to weld dissimilar material tab-to-busbar interconnects using laser. They also studied laser welding Al to Ni by wobbling the laser beam. a circular weld seam with 5 mm diameter was formed. Based on their testing results, maximum shear-force of 930 N of the weld joint was obtained [17]. [PERSON] et al. [18] studied the characteristics of laser welding of a thin aluminum tab and steel battery case. The results verified that the laser power significantly affects the morphology of the weld, and formation of explosive holes significantly reduces the joint strength. [PERSON] et al. [19] reported laser welding of dissimilar copper and aluminum alloys in multilayer configuration for joining battery tabs. In their study, galvanometric scanner optics was used to obtain a spatial beam oscillation (circular wobbling) of the beam. The results confirmed that the presence of harder and brittle IMCs was reduced using the circular wobbling beam. All these studies tried to overcome the joint strength reduction resultant from the formation of IMCs for different types of dissimilar materials joining. However, there were few reports of laser welding of Ni to Al sheets for battery applications, in-depth study of the IMC formation mechanisms or examination of the relationship to with weld performance.  
In this paper, laser welding pure Ni to pure Al sheets was studied and compared using pulsed-wave (PW) and continuous-wave (CW) lasers. The novelty of this study is the proposed concept for regulating the laser welding process to achieve a weld-brazed joint. Micro-structure, hardness, phase formation and weld performance were investigated and tested. Mechanisms of defects formation and IMCs evolution were analyzed and discussed. This study is helpful for understanding the relationships among the laser welding process, weld quality and IMCs formation, as well as joint performance, to establish the welding strategy to achieve a sound Ni-Al joint.