Ultrasonic spot welding of Al/Mg alloys: A state-of-the-art review

Abstract

Lightweight materials like aluminum (Al) and magnesium (Mg) alloys are extensively used in automotive industries. The welding between these dissimilar alloys is inevitably essential to produce high-quality and reliable joints. High power ultrasonic metal welding (USMW) technology, which mimics the properties of solid-state bonding, offers a potential solution in welding of these difficult-to-weld materials. The superior characteristics of this welding process, such as low heat input, less weld time, and high production efficiency, reduce the tendency to form brittle intermetallic compounds (IMCs) and enhance the joint strength of Al/Mg dissimilar joints. The current study is focused on obtaining favorable performance measures during the USMW of dissimilar Al/Mg alloys through controlling the dominant input factors. The tensile shear (TS) and T-peel (TP) failure load firstly increased up to a specific limit and decreased further with the rise in weld energy. The compared fatigue strength results of Al/Mg dissimilar joints with other bonding techniques provides an insight into the fatigue failure mechanism. The mechanism behind the weld formation is discussed based on the fracture surface and interface morphologies, microstructure evolution, and IMC formation along the weld interface. At higher weld energy, the elevated interfacial temperature promoted the formation of Mg17Al12, Al3Mg2 IMCs and accelerated the elemental diffusion at the weld interface. Mechanical interlocking and dynamic recrystallization at the periphery of the weld interface due to severe shear deformation results in refining the grain structure. However, this detrimental interfacial reaction can be reduced by introducing a coating on the Mg surface. Thus, the process engineers can now adopt this technique to get best combinations of input parameters in USMW problems, and there is no need to depend on the manufacturer’s handbook.