Heat Exchanger Brazing Sheet for Flux-Reduced CAB Soldering
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Solution Overview
Problem
Existing methods for producing aluminum heat exchangers face challenges in achieving continuous production without using wetting agents or fluxes, which can degrade fluid channels and cause performance issues, while flux-free processes are structurally complex and costly.
Innovation Solution
A semi-finished product for heat exchangers is designed with a core material containing 0.1% to 1.5% magnesium, a brazing layer with up to 0.2% magnesium, and a corrosion-reducing intermediate layer with 0.2% to 0.4% magnesium, allowing for a CAB brazing process that reduces or eliminates the need for fluxes by diffusing magnesium to break up oxide layers and create a protective gas atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluxes such as potassium aluminum fluoride are used in the CAB brazing process to improve wettability, then the soldering behavior is improved, but the fluid channels degrade and precipitation occurs causing performance issues
Solution Approach 1:
The invention extracts and eliminates the harmful flux (potassium aluminum fluoride) from the brazing process by using a flux-free CAB brazing method. Instead of applying external flux, the patent uses magnesium-containing core material that provides self-fluxing properties through magnesium oxide formation, thereby removing the source of fluid channel degradation and precipitation while maintaining soldering capability
Solution Approach 2:
The invention introduces magnesium-containing core material as an intermediary substance that mediates between the aluminum components and the brazing process. The magnesium diffuses to the surface and reacts with oxygen to form magnesium oxide, which acts as a self-fluxing agent that improves wettability without the harmful effects of traditional fluxes. This intermediary mechanism enables flux-free brazing with good soldering behavior
2Manufacturing precision
If a vacuum soldering process is used to achieve flux-free soldering, then the soldering behavior is improved, but the production process becomes batch-oriented and requires high design effort for continuous production
Solution Approach 1:
The invention changes the atmospheric parameter from vacuum to controlled atmosphere (CAB - controlled atmosphere brazing). By using a protective gas atmosphere with controlled oxygen content instead of vacuum, the process enables continuous production while maintaining flux-free conditions. The magnesium-containing core material provides sufficient protection against oxidation in this controlled atmosphere, allowing for continuous processing without the complexity of vacuum systems
Solution Approach 2:
The magnesium-containing core material provides self-service by automatically providing fluxing action through magnesium diffusion and oxide formation. This self-fluxing mechanism eliminates the need for external flux application and simplifies the process setup, enabling continuous production without complex vacuum or multiple chamber systems
3Manufacturing precision
If magnesium is added to the core material to break up oxide layers and enable flux-free soldering, then the soldering behavior is improved, but the corrosion resistance may be compromised
Solution Approach 1:
The invention applies local quality by creating a layered structure with different magnesium concentrations. The core material contains magnesium (0.1-1.5%) for fluxing action, while the corrosion-reducing intermediate layer has controlled magnesium content (0.2-0.4%) that provides corrosion protection. The brazing layer has low magnesium (max 0.2%) to ensure good soldering. This spatial distribution of magnesium allows flux-free brazing in the core while protecting against corrosion at the surface
Solution Approach 2:
The invention uses composite material structure with multiple layers having different compositions and functions. The core material, intermediate layer, and brazing layer form a composite structure where each layer is optimized for its specific function: fluxing, corrosion protection, and soldering. This composite approach allows the magnesium in the core to provide fluxing action while the intermediate layer protects against corrosion, resolving the contradiction between soldering behavior and corrosion resistance
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 approach enables continuous production of heat exchangers with improved corrosion resistance and reduced flux usage, minimizing fluid channel degradation and maintaining effective soldering without the need for costly oxygen reduction measures.
Implementation Method 1
the magnesium present in the core material, which diffuses into the solder layer during the brazing process, the oxide layer on the material surface can be broken up during the brazing process
Implementation Method 2
The magnesium escaping from the material reacts with the oxygen molecules near the surface, resulting in a partial depletion of oxygen in the residual vacuum, at least in the area of the material surfaces. This reduces or prevents reoxidation or increased oxidation of the material surface
Implementation Method 3
a CAB brazing process that reduces or eliminates the need for fluxes by diffusing magnesium to break up oxide layers and create a protective gas atmosphere
Data Source
Figure 1~2
Figure 3~5
AI summary
The invention relates to a semi-finished product (370) for semi-finished components (360) for producing a heat exchanger (100), in particular using a CAB soldering process (450), made from a core material (410) and having a solder layer (420) and a solder layer at least on one side between solder layer (420) and core material (410) arranged corrosion-reducing intermediate layer (440), wherein the core material (410) consists of an Al3000 alloy or an Al6000 alloy, which has 0.1% to 1.0% Mg, wherein the Solder layer (420) consists of an Al4000 alloy containing a maximum of 0.2% Mg, with the corrosion-reducing intermediate layer (440) consisting of an Al1000 alloy or an Al7000 alloy containing 0.1% to 1.0% Mg having. Due to the matched Mg concentrations in the individual areas (410, 420, 440), it is possible to carry out a CAB soldering process (450) at least for a plate-type (110) or shell-type (230) heat exchanger.