Aluminum Alloy Cladding for Heat Exchanger Corrosion Control
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Solution Overview
Problem
Conventional aluminum alloy clad materials for heat exchangers face challenges in preventing preferential corrosion at joint portions while providing sacrificial protection and supplying brazing filler metal during brazing heating.
Innovation Solution
A clad material composition comprising a core aluminum alloy, an intermediate layer with specific alloy composition and structure, and a first or second brazing filler metal, along with a sacrificial anode material, where the intermediate layer contains Al-Mn based intermetallic compounds to enhance corrosion resistance and brazability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sacrificial anode material made of Al-Zn based alloy is cladded to prevent pitting corrosion, then corrosion resistance is improved, but Zn becomes concentrated in the brazing filler metal at joint portions causing preferential corrosion
Solution Approach 1:
The cladding structure is divided into multiple functional layers: a core material layer, an intermediate layer with controlled Zn content, and a brazing filler metal layer. This segmentation prevents Zn concentration at joint portions by restricting Zn primarily to the intermediate layer, while the brazing filler metal layer contains minimal Zn to avoid preferential corrosion.
Solution Approach 2:
Different layers are assigned different Zn concentrations based on their specific functions. The intermediate layer has higher Zn content (0.1-10 mass%) for sacrificial protection, while the brazing filler metal layer has controlled Zn content (0-5 mass%) to prevent preferential corrosion at joints, creating local quality variations throughout the cladding structure.
2Reliability
If an Al-Zn based intermediate layer is disposed between brazing filler metal and core material to provide sacrificial protection, then both brazability and sacrificial protection are achieved, but the problem of preferential corrosion in joint portion is not prevented
Solution Approach 1:
The Zn content in the brazing filler metal layer is precisely controlled within 0-5 mass%, which is lower than conventional Al-Zn based brazing filler metals. This parameter change maintains brazability while preventing excessive Zn concentration that would cause preferential corrosion at joint portions.
Solution Approach 2:
The cladding combines multiple materials with different compositions: a core material (Al-Mn based), an intermediate layer (Al-Zn-Si based with 0.1-10 mass% Zn), and a brazing filler metal layer (Al-Si based with controlled Zn). This composite structure achieves both sacrificial protection and resistance to preferential corrosion.
3Adaptability or versatility
If conventional clad materials are used for stacked-plate type water-cooling heat exchangers, then design flexibility is improved, but pitting corrosion destroys the aluminum oxide film causing corrosion perforation
Solution Approach 1:
The cladding provides different properties at different locations: the intermediate layer with higher Zn content provides sacrificial protection for the passage surface exposed to cooling water, while the brazing filler metal layer with controlled Zn content provides corrosion resistance at joint portions where brazing occurs and prevents preferential corrosion.
Solution Approach 2:
The multi-layer composite cladding combines Al-Mn core material, Al-Zn-Si intermediate layer, and Al-Si brazing filler metal layer to simultaneously achieve design flexibility for stacked-plate heat exchangers and resistance to both pitting corrosion and preferential corrosion.
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
The solution effectively prevents preferential corrosion in joint portions, ensures sacrificial protection, and maintains excellent brazability and corrosion resistance, making it suitable for automotive heat exchanger applications.
Implementation Method 1
clad a sacrificial anode material made of an Al-Zn based alloy to give the sacrificial protection feature, so as to prevent the corrosion perforation caused by pitting corrosion
Implementation Method 2
such clad material and a corrugated fin material are combined and brazed at a temperature as high as about 600°C to be joined together
Data Source
Figure 1
AI summary
Provided is an aluminum alloy clad material including an aluminum alloy core material, an intermediate layer material that is clad on one surface of the core material, and a first brazing filler metal that is clad on a surface of the intermediate layer material, the surface not being on the core material side, wherein the core material, the intermediate layer material, and the first brazing filler metal each include an aluminum alloy having a predetermined composition, the existence density of Al-Mn based intermetallic compounds having a circle-equivalent diameter between 0.1 and 1.0 µm inclusive in the intermediate layer material before brazing heating is at least 1.0 × 105 pieces/mm2, and the existence density of Al-Mn based intermetallic compounds having a circle-equivalent diameter between 0.1 and 1.0 µm inclusive in the intermediate layer material after brazing heating is at least 1.0 × 104 pieces/mm2. Further provided is a method for producing the aluminum alloy clad material.