Multilayer Aluminum Brazing Sheet for Fluxless Heat Exchanger Joining
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Solution Overview
Problem
Current brazing technologies for heat exchangers in the heat exchanger industry face challenges such as the need for flux application, which leads to residue issues, corrosion, and increased costs, particularly when using Mg-containing alloys, as they form compounds that hinder wetting and joint formation, limiting the use to non-heat treatable alloys and those with low Mg content.
Innovation Solution
A multilayer aluminium brazing sheet configuration with a Mg-rich interlayer and an Al-Si braze alloy, where the interlayer has a higher melting temperature than the braze alloy, allowing Mg to diffuse and break the oxide layer for fluxless brazing, enhancing joint formation and corrosion protection without the use of external flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux is applied to break up oxide layer and facilitate wetting, then brazing joint formation is improved, but flux residues cause corrosion, clogging, and environmental harm
Solution Approach 1:
The invention extracts and eliminates the flux from the brazing process by using a multilayer aluminium brazing sheet with an Al-Si-Mg interlayer that provides oxide-breaking functionality internally. The Mg diffuses to the surface during heating to break up the oxide layer, allowing wetting and joint formation without external flux application, thereby removing the source of harmful residues.
Solution Approach 2:
The Al-Si-Mg interlayer acts as an intermediary that provides the oxide-breaking function traditionally performed by flux. The Mg in the interlayer diffuses to the surface and reacts with the oxide layer, facilitating wetting and joint formation without requiring external flux chemicals, thus eliminating residue problems.
2Strength
If Mg is added to aluminium alloy to increase strength, then mechanical strength is improved, but Mg reacts with flux to form high melting temperature compounds that prevent wetting and joint formation
Solution Approach 1:
The invention segments the Mg content across different layers: the core aluminium alloy contains Mg for strength (0.2-2.5%), while the Al-Si interlayer contains additional Mg (0.05-0.5%). This segmentation allows the core to provide strength while the interlayer provides oxide-breaking functionality during brazing, resolving the conflict between strength and brazability.
Solution Approach 2:
The Mg is pre-positioned in the Al-Si interlayer before brazing. During the brazing heating process, the Mg diffuses to the surface in advance to break up the oxide layer, ensuring that wetting and joint formation can proceed successfully. This preliminary positioning of Mg eliminates the need for flux and prevents the formation of high melting temperature compounds that would hinder brazing.
3Reliability
If CAB process is used with flux to achieve reliable brazing, then joint formation is improved, but costs, energy consumption, and environmental impact increase
Solution Approach 1:
The invention extracts and eliminates the flux application step and associated CAB process complexity by incorporating oxide-breaking functionality directly into the multilayer brazing sheet structure. The Al-Si-Mg interlayer provides the necessary oxide disruption internally, simplifying the brazing process to fluxless heating in controlled atmosphere.
Solution Approach 2:
The multilayer brazing sheet is self-sufficient in providing oxide-breaking functionality through its Al-Si-Mg interlayer. The Mg in the interlayer automatically diffuses to the surface during heating to break up the oxide layer, eliminating the need for external flux application and complex CAB process control, thereby reducing process complexity and costs.
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 configuration enables effective fluxless brazing with improved joint quality and corrosion resistance, reducing residue issues, costs, and environmental impact, while allowing for the use of higher Mg content alloys, thus enhancing the production of heat exchangers.
Implementation Method 1
the interlayer is sacrificial to the core... Mg to diffuse and break the oxide layer
Implementation Method 2
the need to apply a flux to break up, dissolve or dislodge the superficial oxide layer
Implementation Method 3
the outer material is a thin covering layer covering an Al-Si based alloy... During the temperature ramp up stage of a braze cycle the intermediate Al-Si layer will first start to melt
Implementation Method 4
The flux breaks up, dislodges or dissolves the superficial oxide layer of the filler metal to facilitate wetting between a molten filler and the surfaces of individual heat exchanger components
Data Source
AI summary
An aluminium brazing sheet comprising an aluminium alloy core material covered by an interlayer and an Al-Si braze alloy is disclosed. The interlayer consists of an aluminium alloy comprising ≤1.0% Si and 0.1-2.5 % Mg. The Al-Si braze alloy comprises 5-14% Si and 0.01-1.0% Bi. The core material and the interlayer has a higher melting temperature than the braze alloy.