Ultrasonic spot welding of Al-Cu sheets: A comprehensive study

Abstract

Electrification of vehicles presently grabs attention as an essential factor in most of the automotive manufacturing industries due to continuous upsurge in environmental pollution, unstable fuel prices, and stringent government policies against gasoline fuels. In order to tackle these challenges, a conservative and energy-efficient technique is required. The high power ultrasonic metal welding (USMW) process has been effectively used in the automotive industries for assembling lithium-ion (Li-ion) battery packs and its modules due to its solid-state principle. Aluminum (Al) and copper (Cu) are the two most crucial and commonly employed conductive metals. The joining of these materials by conventional methods is extremely difficult due to its higher thermal, chemical and physical properties. However, USMW yields better quality welds under the influence of optimal parametric conditions. In the current study, the effect of various weld parameters such as weld time, weld pressure, vibration amplitude, and different surface conditions are investigated to study the weld strength and failure behaviour by mechanical and microstructural analyses. The tensile shear and T-peel failure loads of the weld are maximum at the highest vibration amplitude with a moderate amount of weld pressure and weld time. Meanwhile, these weld strengths are decreased with an increase of surface roughness due to the disappearance of relative motion between the Al-Cu sheets. Micro-hardness study reveals the material softening and hardening phenomena during the welding process. The various types of weld qualities are also classified as ‘under weld,’ ‘good weld’ and ‘over weld’ based upon the nature of bond formation and spreading of microbonds across the weld interface at various weld parametric conditions. The future prospects of this USMW field is that 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.