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Analysis on Process Matching of Direct‑Current Diffusion‑Welding Machine for Aluminum‑Copper Composite Bus‑Bar Welding
Sep 05,2026
Aluminum‑copper composite bus‑bar is a key transition conductive component for new‑energy power‑storage equipment, realizing the transition connection between aluminum‑material and copper‑material conductors. Direct‑current diffusion‑welding machine completes atomic inter‑diffusion bonding of aluminum‑copper interface under combined action of temperature and pressure. Because of huge differences in physical properties between aluminum and copper, unreasonable process matching will easily bring defects such as interface delamination, high contact resistance and low tensile strength.
I Physical‑Property Differences between Aluminum and Copper Affecting Diffusion‑Welding
1.Thermal‑conductivity gap: aluminum conducts heat much faster than copper. Under same heating condition, aluminum side temperature rises rapidly while copper side heats slowly.
2.Coefficient‑of‑thermal‑expansion difference: aluminum has larger thermal‑expansion coefficient. Under heating‑and‑cooling cycle, inconsistent shrinkage degree easily generates internal interface stress.
3.Oxidation characteristic: aluminum easily generates compact and stubborn oxide film. If it cannot be fully destroyed in welding, atomic inter‑diffusion will be blocked.
II Common Defects and Process‑Mismatch Causes
1.Interface delamination / partial non‑fusion
Causes: insufficient welding temperature, insufficient holding time, pressure not reaching set value; or oxide‑film on aluminum surface not thoroughly removed before welding.
2.Excessively high contact resistance
Causes: incomplete atomic inter‑diffusion at interface; residual oxide barrier; insufficient pressure leads to poor interface fitting.
3.Low tensile‑breaking strength, fracture at aluminum‑copper interface
Causes: insufficient temperature‑holding duration leads to thin diffusion layer; or excessive temperature causes brittle inter‑metallic compound layer at aluminum‑copper interface.
4.Serious deformation on aluminum side
Causes: excessive pressure, over‑high temperature; aluminum material softens severely under high‑temperature pressure, generating serious squeezing‑deformation.
III Core Process‑Matching Key Points
1.Pre‑weld surface‑treatment difference
Aluminum surface: must thoroughly remove oxide film. Mechanical polishing or chemical de‑oxidation shall be adopted. Welding shall be finished quickly after treatment to prevent secondary oxidation.
Copper surface: remove oil stain and surface oxide scale. Requirement for oxide‑removal is lower than aluminum side.
2.Temperature‑matching logic
Since aluminum heats faster than copper, cannot simply adopt equal‑temperature setting for both sides. Need to consider heat‑conduction difference, properly increase total heat input, ensure that copper side can reach effective diffusion‑welding temperature, meanwhile prevent aluminum side from over‑heating and over‑softening.
3.Pressure‑matching logic
Pressure cannot be too large to avoid excessive squeezing‑deformation of aluminum. Pressure cannot be too small, otherwise interface fitting is insufficient and diffusion is poor. Need to select proper pressure value according to cross‑section size of bus‑bar. For thin‑specification aluminum‑copper bus‑bar, low‑to‑medium pressure shall be adopted. For thick‑specification products, appropriately increase pressure.
4.Heat‑holding‑time matching
Too‑short holding time: diffusion‑layer is too thin, low bonding strength.
Too‑long holding time: brittle inter‑metallic compound will be continuously generated at aluminum‑copper interface, leading to brittle fracture.
Shall select moderate heat‑holding time according to product cross‑section.
5.Cooling‑under‑pressure procedure
After welding completion, cannot release pressure immediately. Shall implement slow cooling under pressure, offset the stress difference caused by inconsistent thermal‑shrinkage of aluminum and copper, reduce interface micro‑crack risk.
IV Equipment‑Tooling Adaptation Requirements
1.Electrode mold shall adopt material with good heat‑balance performance. Reduce unilateral heat‑gathering caused by different heat‑conduction of aluminum and copper.
2.Guarantee mold flatness and parallelism. Avoid partial stress concentration leading to local insufficient diffusion or excessive deformation.
3.For large‑size bus‑bar products, adopt multi‑zone pressure‑equalizing tooling to realize uniform stress on whole welding interface.
Wuxi Haifei Intelligent Equipment Co., Ltd. https://www.haifeiwelder.com/
Wuxi Haifei Intelligent Equipment Co., Ltd. has been focusing on the R&D and production of spot‑welding machines for 17 years. The company has obtained ISO9001 Quality Management System Certification, China Compulsory Certification (3C) and CE Certification. It is a National High‑tech Enterprise, a Specialized, Refined, Differential and Innovative Enterprise of Jiangsu Province, a Specialized, Refined, Differential and Innovative Enterprise of Wuxi, and a Gazelle Enterprise in the Southern Jiangsu National Self‑Dependent Innovation Demonstration Zone.
Should you be interested in our spot‑welding machines, please contact us: 400‑0510‑750.
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Wuxi HAIFEI Intelligent Equipment Co., Ltd.
Wuxi HAIFEI Welding Equipment Co., Ltd.
Add: 28 Shuiyun Road, Yuecheng, Jiangyin, Jiangsu Province, China. (Postal Code: 214404)
Mobile: +86 18915302352
Email: wushijie@jshaifei.com