Ultrasonic Spot Welding of Dissimilar Metals: Mechanical Behavior and Microstructural Analysis

Ultrasonic welding is considered to be one of the novel and innovative techniques used in semiconductor industries for several years. Recently, it has been a challenging task for the automobile industries to join soft and high thermal conductivity materials like aluminum to copper for lithium-ion battery assembly using conventional fusion welding process. The purpose of this study is to explore the effects of various process parameters like weld pressure, weld time, and vibration amplitude on the weld strength with microstructural analysis of Al-Cu ultrasonic welded joint. The results revealed that the tensile shear and T-peel strength increased with the increase in weld time and attained its maximum at 0.75 s. Afterward, these strengths were gradually decreased. Meantime, different types of microstructures with various properties and morphologies were also observed in the interface zone. The interfacial reaction between Al and Cu produces intermetallic compounds (IMCs) along with swirls and voids. From the energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) scans, it was noticed that at high weld time (0.9 s), a 1.5 lm thick IMC layer composed of Al2Cu and Al4Cu9 was formed. A three-dimensional finite element (FE) model was used to find out the compressive stress distribution beneath the sonotrode knurl and the contact stress on the bottom sheet during the delay time. The present work not only illustrates a better understanding of the welding mechanism and failure behavior but also it provides an insight of ultrasonic welding toward the improvement in the quality of weld.