ABSTRACT
Ultrasonic spot welding (USW) is gaining popularity in the fields of aviation, nuclear, and automobile manufacturing segments due to its operational flexibility, superior formability, low cost, and recyclability. The solid-state nature of this technique has substantially differentiated it from the fusion welding methods. The bonding of dissimilar metals like nickel (Ni) with aluminum (Al) alloys plays a dynamic role in electrical appliances and the aerospace and automotive industries. The objective of the present work is to understand the weld formation and interfacial characteristics between ultrasonic spot welded Al and Ni joints at several weld conditions. The ideal range of welding conditions with the weld energy, and weld pressure parameters, is uncovered by employing full factorial methodology. The tensile lap shear strength of the welded specimen gradually increases with the rise of these parameters followed by decrement due to the formation of fatigue cracks around the weld spot. An asymmetrical type of hardness profile is also observed at the weld cross-sectional area. At the weld interface, the Al sheet is softened by the weld energy, whereas the hardness value of the pure Ni sheet does not change noticeably. The microstructural observations also reveal several types of weld mechanisms like wavy pattern, mechanical interlocking, and necklace-like ultrafine structures at the weld cross section.
