Zhuojin Pipe Fitting Co., LtdTIG Arc Preheating Assisted Ultrasonic Seam Welding of Aluminum-Copper Dissimilar Joints
Literature Overview
This paper by Yu Jiang and colleagues from Harbin Institute of Technology (Weihai) investigates a novel hybrid welding approach for aluminum-copper dissimilar metal joints: TIG arc preheating assisted ultrasonic seam welding. The study addresses a longstanding challenge in joining dissimilar metals with vastly different thermal conductivities, melting points, and metallurgical compatibility. The research is particularly relevant for electrical busbar connections, heat exchangers, and power electronics packaging where aluminum-copper joints are common.
Hybrid Process Mechanism
The TIG arc preheating softens the base materials before ultrasonic welding is applied, facilitating the transfer of high-frequency vibrational energy to the interface. This preheating step is critical because the large thermal conductivity difference between aluminum and copper creates significant challenges for conventional ultrasonic welding.
Process Parameters and Interface Temperature
| TIG Current (A) | Interface Temperature (°C) | Interface Morphology | Joint Strength |
|---|---|---|---|
| Low (< 30 A) | Insufficient | Smooth, undulating | Fracture at Al-Cu interface |
| 30 A | Up to 446°C | Interlocking, continuous protrusions | Fracture in copper base metal, 2.58 kN |
The maximum interface temperature of 446°C achieved at 30 A TIG current is well below the melting point of either aluminum (660°C) or copper (1085°C), confirming that the process operates in a solid-state joining regime. This is critical because it prevents the formation of brittle intermetallic compounds.
Interface Microstructure and Metallurgical Analysis
EDS analysis confirms that no intermetallic compounds form at the aluminum-copper interface under the optimized process conditions. The interface exhibits characteristic features of solid-state bonding, including mechanical interlocking and continuous protrusions. The pure aluminum interlayer plays a dual role: it provides a compatible bonding surface and acts as a diffusion barrier to prevent direct contact between aluminum and copper, which would otherwise promote intermetallic compound formation.
Failure Mode Analysis
- Low TIG current: Insufficient preheating results in poor plastic flow at the interface, leading to incomplete bonding and fracture at the Al-Cu interface
- Optimized TIG current (30 A): Sufficient preheating combined with ultrasonic energy produces plastic flow and mechanical interlocking, resulting in fracture in the copper base metal with maximum tensile shear force of 2.58 kN
Engineering Practice Implications
This hybrid approach offers a practical solution for aluminum-copper joint fabrication in applications where both electrical conductivity and mechanical strength are required. The process avoids the formation of brittle intermetallic compounds that plague fusion welding of aluminum-copper joints. The use of a pure aluminum interlayer is a key process feature that should be incorporated into production procedures.
Key Questions and Reflections
The maximum tensile shear force of 2.58 kN for a 1 mm thick joint needs to be evaluated against the strength of the base metals to determine the joint efficiency. Additionally, the long-term stability of the joint under thermal cycling conditions is critical for applications in power electronics and electrical busbars. The formation of intermetallic compounds during service exposure to elevated temperatures could gradually degrade the joint strength, and this needs to be assessed through accelerated aging tests.
Study Insights
This research demonstrates a promising approach for joining aluminum and copper through a hybrid process that combines thermal preheating with solid-state welding. The key innovation is the use of TIG arc preheating to soften the materials and facilitate ultrasonic bonding, while the pure aluminum interlayer prevents intermetallic compound formation. The process parameters are relatively simple to control, making this approach potentially scalable for production applications. However, further work on joint durability under thermal cycling and elevated temperature conditions is needed to validate the approach for demanding applications.