Multi-Layer Aluminum Brazing Sheet for Fluxless CAB Joints
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Solution Overview
Problem
Conventional brazing sheet products require flux for brazing, which can lead to oxidation and hinder the brazing process, and existing fluxless brazing technologies in inert gas atmospheres lack effective alternatives for achieving strong and reliable joints.
Innovation Solution
A multi-layered aluminium alloy brazing sheet with a 3xxx alloy core layer, a thin Si-rich covering clad layer, and an Al-Si brazing clad layer, where the covering clad layer has a solidus temperature higher than the Al-Si brazing clad layer's liquidus temperature, allowing the Al-Si alloy to melt and seep through the clad layer without oxidizing, facilitated by controlled Mg diffusion to prevent early Mg-oxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If flux is used for conventional brazing, then the brazing process can proceed, but oxidation occurs and the brazing process is hindered
Solution Approach 1:
The invention extracts and eliminates the flux component from the brazing process by using a fluxless brazing sheet with controlled Al-Si clad layers that provide inherent oxidation resistance and facilitate brazing without external flux materials
Solution Approach 2:
The invention creates an inert environment by using an aluminium alloy composition with specific Si content (6-13 wt.%) in the brazing clad layer that forms protective oxide barriers, effectively creating a chemically inert surface that prevents oxidation during brazing in inert gas atmosphere
2Strength
If Al-Si brazing clad layer melts and seeps through covering clad layer, then strong joints are formed, but oxidation may occur
Solution Approach 1:
The invention applies preliminary action by pre-forming a covering clad layer with 2-5 wt.% Si that acts as a protective barrier before brazing, which prevents oxidation of the underlying Al-Si brazing layer during the heating process while still allowing molten brazing material to penetrate through at brazing temperature
Solution Approach 2:
The invention utilizes parameter changes by controlling the Si content in different layers (2-5 wt.% in covering clad, 6-13 wt.% in brazing clad) and exploiting the temperature-dependent properties where the covering layer remains solid at brazing temperature to prevent oxidation while allowing molten brazing material to seep through and form strong joints
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
Enables fluxless brazing in an inert gas atmosphere with improved joint formation and reduced oxidation, ensuring strong and reliable brazed assemblies without the need for flux, suitable for applications like heat exchangers.
Implementation Method 1
the covering clad layer and the core layer are of aluminium alloys having a solidus temperature higher than the liquidus temperature of the Al-Si brazing clad layer
Implementation Method 2
facilitated by controlled Mg diffusion to prevent early Mg-oxide formation
Implementation Method 3
brazing in an inert gas atmosphere without a flux
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 0.20-0.75 wt.% Mg, and provided with a covering clad layer comprising 2-5 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 and the core layer are of aluminium alloys having a solidus temperature higher than the liquidus temperature of the Al-Si brazing 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 fluxfree controlled atmosphere brazing (CAB) operation to produce a heat exchanger apparatus