Multilayer Aluminum Brazing Sheet for Flux-Free Heat Exchangers
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Solution Overview
Problem
Conventional brazing processes require flux, which can lead to oxidation and edge cracking issues, and existing flux-free brazing methods are not compatible with all equipment, especially in heat exchanger applications.
Innovation Solution
An aluminium alloy multi-layered brazing sheet product with a 3xxx alloy core layer, a thin Mg-free covering clad layer with 2-6 wt.% Si, and an Al-Si brazing clad layer with 7-13 wt.% Si, where the Al-Si layer melts below the covering clad layer's liquidus temperature, preventing oxidation and allowing the Al-Si alloy to seep and form a brazed joint without flux in an inert gas atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional brazing processes are used with flux, then brazing can be performed on aluminium substrates, but oxidation and edge cracking issues occur
Solution Approach 1:
The invention extracts and eliminates the flux component from the brazing process by using a flux-free brazing sheet with specifically designed multi-layer composition. The Al-Si clad layer (7-13 wt% Si) serves as a self-fluxing brazing material that melts at lower temperature (540-620°C) than the aluminium core, providing liquidus temperature control without requiring external flux chemicals, thereby preventing oxidation and edge cracking.
Solution Approach 2:
The invention employs a composite multi-layer structure consisting of an aluminium core layer (3xxx series) combined with an Al-Si brazing clad layer (7-13 wt% Si) and a covering clad layer (2-6 wt% Si). This composite material design enables flux-free brazing by combining materials with different melting points and chemical compositions, where the Al-Si layer melts first to form the brazing joint while the covering layer remains solid to protect against oxidation.
2Object-affected harmful factors
If flux-free brazing methods are used, then oxidation protection is improved, but compatibility with existing equipment is limited
Solution Approach 1:
The invention changes the chemical composition parameters of the brazing sheet by incorporating an Al-Si clad layer with 7-13 wt% Si, which has a liquidus temperature of 540-620°C. This parameter change enables the brazing process to occur at temperatures below the solidus temperature of the aluminium core, allowing flux-free brazing to be performed on existing equipment without requiring specialized high-temperature or controlled-atmosphere furnaces.
3Ease of manufacture
If a multi-layered brazing sheet with Al-Si clad layer is used, then flux-free brazing is enabled, but the covering clad layer must maintain higher liquidus temperature
Solution Approach 1:
The invention applies local quality by creating distinct layers with different Si concentrations and properties: the Al-Si brazing clad layer (7-13 wt% Si) has high Si content for low melting point and self-fluxing capability, while the covering clad layer (2-6 wt% Si) has lower Si content to maintain higher liquidus temperature and structural integrity. This localized compositional differentiation enables flux-free brazing while preventing covering layer melting.
Solution Approach 2:
The invention adds a dimensional layering structure to the brazing sheet, creating a three-layer configuration (core-Al-Si clad-covering) with each layer serving a specific function. This dimensional organization allows the Al-Si layer to melt and flow for brazing while the covering layer remains solid, solving the temperature differential requirement through spatial separation of functions.
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 solution enables flux-free brazing with improved oxidation protection and compatibility with existing equipment, reducing production costs and edge cracking, while maintaining effective joint formation in heat exchanger applications.
Implementation Method 1
the Al-Si alloy brazing clad layer has a liquidus temperature in the range of 540-620°C and below the solidus temperature of the aluminium core alloy. Most brazing is done at temperatures between 560°C and 615°C.
Implementation Method 2
cause the Al-Si alloy brazing material to seep, due to volumetric expansion, through segregation portions of the covering clad layer onto a surface of the covering clad layer
Data Source
Figure 1A~1B
Figure 2
AI summary
The invention relates to an aluminium alloy multi-layered brazing sheet product for brazing in an inert-gas atmosphere without a flux, comprising a core layer made of a 3xxx alloy comprising <0.2 wt.% Mg, and provided with a covering clad layer comprising 2-6 wt.% Si on one or both sides of said 3xxx alloy core layer and a Al-Si brazing clad layer comprising 7-13 wt.% Si positioned between the 3xxx alloy core layer and the covering clad layer, wherein the covering clad layer has a thickness X1 and the Al-Si brazing clad layer has a thickness X2 and wherein X2 ≥ 2X1. The invention further relates to the use of an aluminium alloy multi-layered brazing sheet product in a flux-free controlled atmosphere brazing (CAB) operation to produce a heat exchanger apparatus.