Effect of PA6 coating on the ultrasonic welding of CF/PA66 to 6061 aluminum alloy

Carbon fiber-reinforced thermoplastic composites (CFRTPs) are widely used in industrial manufacturing due to their excellent mechanical properties, and the joining of lightweight metal/CFRTP hybrid structure has gained more attention. Ultrasonic welding is a promising method for achieving metal/CFRTP dissimilar joining. In this study, 6061 aluminum alloy and carbon fiber-reinforced polyamide-66 (CF/PA66) were ultrasonically welded by preparing a PA6 coating on the surface of aluminum sheet as an interlayer. This paper investigates the effects of welding parameters on the joint mechanical property. Optimized process parameters (welding force 600 N, amplitude 60% and welding time 0.6 s) are determined by experiments. The effects of the thickness and crystallinity of the PA6 coating on the joint strength are investigated. The results show that there exists an optimal coating thickness that maximizes the joint strength. Low crystallinity of the coating contributes to high joint strength. Mixed failure mode (adhesive failure, substrate failure and cohesive failure) is observed based on the analysis on the fracture surface.