Aluminum-to-Copper Conductor Joining with Solder and Diffusion Bonding
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Solution Overview
Problem
Connecting aluminum or aluminum alloy electrical conductors to copper or copper alloy terminals is challenging due to issues with mechanical stability, electrical conductivity, and corrosion, particularly because of the formation of brittle intermetallic phases and differences in melting temperatures, which lead to inadequate welds and increased transition resistance.
Innovation Solution
A method involving coating the tube's inner surface with hard solder, plastic deformation to break up oxide layers, applying pressing force and current for Joule heating to create a hard solder connection, and subsequent diffusion or partial melting to minimize transition resistance and prevent re-oxidation, using a diffusion barrier like nickel to prevent intermetallic phase formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If aluminum conductors are directly connected to copper terminals, then weight is reduced, but mechanical stability and electrical conductivity deteriorate due to oxide layer formation and intermetallic phase formation
Solution Approach 1:
A transition piece with aluminum and copper portions is introduced as an intermediary component between the aluminum conductor and copper terminal. The aluminum portion connects to the aluminum conductor, while the copper portion connects to the copper terminal, avoiding direct aluminum-copper contact and preventing intermetallic phase formation. This mediator resolves the contradiction by enabling weight reduction through aluminum conductors while maintaining connection reliability.
Solution Approach 2:
The transition piece is constructed as a composite structure with both aluminum and copper portions, combining the advantages of both materials. The aluminum portion provides weight reduction compatibility with aluminum conductors, while the copper portion ensures reliable connection to copper terminals. This composite approach resolves the contradiction by integrating multiple material properties in a single connection component.
2Reliability
If aluminum conductors are crimped and welded to terminal elements, then electrical conductivity is improved, but mechanical durability deteriorates due to contact corrosion when moisture enters the connection
Solution Approach 1:
The transition piece acts as a sealed intermediary that prevents moisture from reaching the aluminum-copper interface. By providing a corrosion-resistant barrier, it protects the electrical connection from contact corrosion while maintaining good electrical conductivity through proper material matching and connection geometry.
3Strength
If the oxide layer on aluminum is broken up and wires are pressed together, then mechanical strength is improved, but transition resistance increases due to exposed fresh aluminum surface oxidizing rapidly
Solution Approach 1:
The transition piece is designed with pre-applied protective coatings (such as zinc or tin) on its aluminum-contact surfaces before the connection process. This preliminary protective layer is applied in advance to prevent rapid oxidation of the freshly exposed aluminum surface after crimping, thereby maintaining low transition resistance while still achieving strong mechanical connection through oxide layer disruption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method establishes durable, stable connections with reduced transition resistance and prevents fluctuations in connection quality by eliminating gaps for oxygen penetration and minimizing the formation of brittle intermetallic phases, ensuring strong and reliable electrical connections.
Implementation Method 1
Applying a predeterminable pressing force and a predeterminable current for a predeterminable time via electrodes, depending on the geometry and material properties of the tube and the strand, for generating Joule heating of the aluminum strand bundle
Implementation Method 2
Applying a further predeterminable pressing force and a further predeterminable current for a further predeterminable time, also depending on the geometry and the material properties of the tube and the strand, softening the aluminum strand bundle such that a diffusion of the aluminum strand bundle and/or an at least partial melting of the aluminum strand bundle occurs
Implementation Method 3
softening the aluminum strand bundle such that a diffusion of the aluminum strand bundle and/or an at least partial melting of the aluminum strand bundle occurs
Data Source
AI summary
A method for connecting an aluminum electrical conductor to a copper terminal is to be improved such that electrical connections between the conductor and the terminal can be established quickly and cost-effectively, these connections being durably stable and fluctuations in quality of these connections being prevented as far as possible. For this purpose the conductor is hard-soldered to the terminal in a first step, and a diffusion bond and/or fused bond with the hard solder layer is brought about in a second step by softening the aluminum strand bundle.