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Ultrasonic Spot Welding of Nickel Foam Sheet and Aluminum Solid Sheet 
 

Nickel foam sheet composed of three‐dimensional (3D) triangular struts and aluminum solid sheet are welded via ultrasonic spot welding. The foam underwent acceptable thickness reduction and deformation, whereas most of the porous structures remain intact. Energy dispersive spectroscopy (EDS) analysis shows that little interdiffusion is noticed across the welding interface, leading to the formation of only a small amount of solid solution, and intermetallic compounds. Infrared temperature measurements show that the joint‐temperature variation of the welding interface is substantially lower than the solid‐solution temperature of Al/Ni, and the welding process is in solid state. The resistance of the joints is measured, and the contact resistance is calculated. The specimen with excellent interface connection exhibits low contact resistance. As the welding energy increases, the failure mode transitions from interfacial fracture to pull‐out fracture, with the tensile load and fracture energy reaching 58 and 69%, respectively, of those corresponding to the nickel foam base metal. Fracture occurs exclusively on the nickel foam sheet, and the fracture mode is ductile fracture.