Abstract This study investigates the interactive effects of terminal surface roughness and welding energy on the microstructure and mechanical properties of ultrasonic welded joints for EVR 25<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\it {mm^{2}}\)</EquationSource> </InlineEquation> copper wiring harnesses and T2 copper terminals used in electric vehicles. It aims to optimize the joint quality for electric vehicle applications by understanding how surface roughness and welding energy influence tensile strength, interfacial bonding, and electrical resistance. Ultrasonic welding technique was used to join copper wire harnesses at varying surface roughness (0.15 <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\it {\mu m}\)</EquationSource> </InlineEquation>, 0.36 <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\it {\mu m}\)</EquationSource> </InlineEquation>, 0.73 <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\it {\mu m}\)</EquationSource> </InlineEquation>, 1.18 <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\it {\mu m}\)</EquationSource> </InlineEquation>, 2.02 <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\it {\mu m}\)</EquationSource> </InlineEquation>) and welding energy levels (2000 J, 3000 J, and 4000 J). Results showed that increasing welding energy improves joint strength by promoting plastic deformation, enhancing interfacial temperature, and eliminating surface micro-protrusions. At 4000 J, tensile strength increases with decreasing surface roughness, while in the 2000–3000 J range, larger micro-protrusions on G60 joints lead to localized mechanical interlocking, slightly improving joint strength. The G2000–4000J joints exhibited the best mechanical and electrical performance, with a peak load of 3872.17N and a minimum resistance of 0.043 <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(m \Omega\)</EquationSource> </InlineEquation>, representing a 283.64% increase in peak load and a 36.76% reduction in resistance compared to the poorly performing G120–2000J joints. The combined effect of higher welding energy and reduced surface roughness results in a transition from mechanical interlocking to metallurgical bonding, significantly enhancing peak load. Hardness increases in the weld seam with higher energy but decreases in adjacent regions. Failure modes were influenced by surface roughness and energy; G60 and G2000 joints exhibited minor and extensive copper wire adhesion, respectively, while G320 joints showed a shift from interfacial pull-out to copper wire adhesion as welding energy increased. These findings provide valuable insights into optimizing ultrasonic welding parameters for improved joint reliability in electric vehicle applications. Graphic abstract

Interactive Effects of Welding Energy and Surface Roughness on Microstructural and Mechanical Characteristics of Ultrasonic-Welded Copper Wire–Terminal Joints

期刊论文
发表日期：

2026年4月22日

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Xingyi Wang,
Amr Monier,
Shengli Li,
Lyusha Cheng,
Xingang Ai,
Rui Guan,
Jianxiong Su,
Lan Zhang

摘要

Abstract

This study investigates the interactive effects of terminal surface roughness and welding energy on the microstructure and mechanical properties of ultrasonic welded joints for EVR 25 \(\it {mm^{2}}\) copper wiring harnesses and T2 copper terminals used in electric vehicles. It aims to optimize the joint quality for electric vehicle applications by understanding how surface roughness and welding energy influence tensile strength, interfacial bonding, and electrical resistance. Ultrasonic welding technique was used to join copper wire harnesses at varying surface roughness (0.15 \(\it {\mu m}\) , 0.36 \(\it {\mu m}\) , 0.73 \(\it {\mu m}\) , 1.18 \(\it {\mu m}\) , 2.02 \(\it {\mu m}\) ) and welding energy levels (2000 J, 3000 J, and 4000 J). Results showed that increasing welding energy improves joint strength by promoting plastic deformation, enhancing interfacial temperature, and eliminating surface micro-protrusions. At 4000 J, tensile strength increases with decreasing surface roughness, while in the 2000–3000 J range, larger micro-protrusions on G60 joints lead to localized mechanical interlocking, slightly improving joint strength. The G2000–4000J joints exhibited the best mechanical and electrical performance, with a peak load of 3872.17N and a minimum resistance of 0.043 \(m \Omega\) , representing a 283.64% increase in peak load and a 36.76% reduction in resistance compared to the poorly performing G120–2000J joints. The combined effect of higher welding energy and reduced surface roughness results in a transition from mechanical interlocking to metallurgical bonding, significantly enhancing peak load. Hardness increases in the weld seam with higher energy but decreases in adjacent regions. Failure modes were influenced by surface roughness and energy; G60 and G2000 joints exhibited minor and extensive copper wire adhesion, respectively, while G320 joints showed a shift from interfacial pull-out to copper wire adhesion as welding energy increased. These findings provide valuable insights into optimizing ultrasonic welding parameters for improved joint reliability in electric vehicle applications.

Graphic abstract