Multi-Layer Brazing Sheet Composition for Sacrificial Corrosion Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing aluminum brazing sheets for heat exchanger applications lack sufficient long-life corrosion resistance, particularly in contact with cooling fluids, due to inadequate electrochemical potential profiles between the core and innerliner alloys.
Innovation Solution
A multi-layered brazing sheet with carefully balanced alloying elements such as Zn, Cu, Si, Mn, and Mg, where the core has a higher corrosion potential than the interliner, and the braze cladding contributes to sacrificial protection through diffusion layers, ensuring a minimum 20mV difference in corrosion potential post-brazing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zn containing innerliner is used to improve corrosion resistance, then the sacrificial protection is enhanced, but the corrosion potential difference between interliner and core may be insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ranges of alloying elements (Zn: 0.5-5.0%, Cu: 0.05-2.0%, Si: 0.05-1.0%, Mn: 0.05-1.0%, Mg: 0.05-0.5%) in the interliner and core to achieve the required corrosion potential difference of at least 20mV. This compositional optimization ensures adequate sacrificial protection while maintaining brazability and mechanical properties.
Solution Approach 2:
The patent employs composite materials by creating a multi-layered structure with an interliner containing specific alloying elements combined with a core and braze cladding. This composite approach allows the interliner to provide sacrificial protection through controlled electrochemical potential, while the core provides structural integrity and the braze cladding enables joining.
2Reliability
If Cu is added to the core to increase corrosion potential, then the electrochemical profile is improved, but the solidus temperature approaches the brazing temperature
Solution Approach 1:
The patent applies parameter changes by limiting the Cu content in the core to a specific range (0.05-2.0%) and optimizing the balance with other alloying elements. This controlled composition increase the corrosion potential through Cu's electrochemical contribution while keeping the solidus temperature sufficiently below the brazing temperature to ensure proper brazing processability.
3Reliability
If the interliner composition is optimized for sacrificial protection, then the corrosion resistance is improved, but the brazing capability may be affected
Solution Approach 1:
The patent applies parameter changes by optimizing the interliner composition within specific ranges (Zn: 0.5-5.0%, Cu: 0.05-2.0%, Si: 0.05-1.0%, Mn: 0.05-1.0%, Mg: 0.05-0.5%) that simultaneously achieve adequate sacrificial protection (≥20mV corrosion potential difference) and maintain brazability. These controlled compositional parameters ensure both corrosion resistance and manufacturing feasibility.
Solution Approach 2:
The patent applies local quality by differentiating the composition of the interliner from the core and braze cladding. The interliner is specifically designed with alloying elements optimized for electrochemical protection, while the core provides structural properties and the braze cladding is optimized for joining, allowing each layer to fulfill its specific function.
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 significantly enhances the sacrificial protection of the core, providing improved long-life corrosion resistance and maintaining the formability and brazing capabilities of the alloy.
Implementation Method 1
The Zn containing innerliners act as sacrificial anode, forcing the corrosion to attack the inner surface of the heat exchanger in a lateral way instead of penetrating the layer by localized pitting or intergranular corrosion.
Implementation Method 2
with the core having the highest corrosion potential. According to tests a difference in corrosion potential between interliner and core after brazing should be at least 20mV and preferably 30mV.
Implementation Method 3
However, during the processing of the material, and the heat up phase of the brazing cycle, a diffusion layer between braze liner and inter liner will have been formed. The additional difference in corrosion potential, caused by the presence of this diffusion layer on top of the inter liner is used to enhance the sacrificial protection.
Implementation Method 4
After brazing, the braze liner will be almost disappeared because it flows away. However, during the processing of the material, and the heat up phase of the brazing cycle, a diffusion layer between braze liner and inter liner will have been formed.
Data Source
Figure 1~2
Figure 3
AI summary
The invention pertains to a multi-layered brazing sheet with improved long life corrosion resistance which is achieved by balancing the Zn, Cu, Mn, Si and Mg content of the core and interliner alloy. To this end the brazing sheet comprises a core of a 3xxx alloy, an inner braze cladding of a 4xxx alloy , and between core and inner braze cladding an interliner of a 3xxx alloy, wherein the 3xxx alloy of the core comprises 0.55 - 1.0 wt% Cu, 0.7 - 1.8 wt% Mn, < 0.3 wt% Mg, < 0.4 wt% Zn and the 3xxx alloy of the interliner < 0.25 wt% Cu, 0.5 - 1.5 wt% Mn, < 0.3 wt% Mg, 0.1- 5.0 wt% Zn . Instead of a 3xxx alloy also a lxxx or 7xxx alloy could be used for the interliner.