Aluminum Brazing Sheet With Mg Gradient for Flux-Free Brazeability
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Solution Overview
Problem
Current flux-free brazing methods using inert-gas atmospheres face challenges with brazeability due to slow Mg diffusion, leading to potential brazing defects, increased complexity, and higher costs, especially when using multi-layered brazing sheets with intermediate materials.
Innovation Solution
An aluminum-alloy brazing sheet with a core material containing 0.40-2.50% Mg and a filler material with 6.0-13.0% Si and 0.010-0.050% Bi, where Mg concentration decreases continuously from the core-material boundary to the surface, facilitating rapid Mg supply and lowering the solidus temperature, thus improving brazeability without the need for flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg is added to the filler material in conventional brazing sheets, then oxide film breakdown capability is improved, but Mg oxidizes readily during heating forming MgO film that deteriorates brazeability
Solution Approach 1:
The patent applies preliminary action by pre-forming an Mg-containing intermediate layer between the core material and filler material before brazing. This intermediate layer contains Mg that will diffuse to the surface during heating, but the Mg is protected from oxidation during storage and transport. The Mg is released in a controlled manner during the brazing process to break down oxide films without forming harmful MgO films on the surface.
Solution Approach 2:
The patent uses an intermediate layer as a mediator between the core material and filler material. This intermediate layer contains Mg that serves as a controlled source of magnesium for oxide film breakdown. The intermediate layer mediates the release of Mg during heating, allowing beneficial oxide film breakdown while preventing harmful surface oxidation that would occur if Mg were simply added to the filler material.
2Reliability
If an intermediate material containing Mg is interposed between core material and filler material, then Mg diffusion to surface is enabled, but the number of layers increases making the brazing sheet structure more complicated
Solution Approach 1:
The patent merges the intermediate layer containing Mg with the filler material layer. Instead of creating a separate intermediate layer, the Mg-containing alloy is used as the filler material itself, which is then clad onto the core material. This combining approach enables Mg diffusion to the surface during brazing while avoiding the complexity of a multi-layer structure with distinct intermediate and filler layers.
Solution Approach 2:
The filler material in the patent serves multiple functions: it provides the bonding function of a traditional filler material while simultaneously serving as the Mg-containing intermediate layer that enables oxide film breakdown. The filler material is designed with specific composition (Al-Si-Mg alloy) that allows it to perform both the structural bonding role and the chemical function of releasing Mg for oxide film breakdown during brazing.
3Quantity of substance
If Mg is distributed uniformly in the filler material, then sufficient Mg is available for oxide film breakdown, but Mg reaches the surface slowly due to solid-state diffusion limitations
Solution Approach 1:
The patent applies local quality by creating a non-uniform Mg distribution within the filler material. The Mg concentration is highest near the interface with the core material and decreases toward the outer surface. This gradient distribution ensures that Mg is readily available at the interface for rapid diffusion to the surface during heating, while still providing sufficient total Mg quantity for effective oxide film breakdown. The local concentration gradient drives faster diffusion kinetics compared to uniform distribution.
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 enhances brazeability by ensuring sufficient Mg reaches the surface quickly, reducing oxidation, and simplifying the brazing sheet structure, thereby improving productivity and reducing costs while maintaining high-quality joints.
Implementation Method 1
Mg is caused to diffuse from the intermediate material into the filler-material surface owing to the heating during brazing
Implementation Method 2
there is a risk that an MgO film will form on the surface of the filler material during the heating when brazing is being performed, which will lead to deterioration in brazeability
Data Source
AI summary
A brazing sheet (1) includes a core material (11) composed of an Al alloy containing 0.40-2.50 mass % Mg; and a filler material (12) composed of an Al alloy containing Mg, 6.0-13.0 mass % Si, and 0.010-0.050 mass % Bi. The filler material is layered on a side of the core material and is exposed at an outermost surface (121). The Mg concentration in the filler material continuously decreases in a direction from a boundary (122) with the core material toward the outermost surface. The Mg concentration (c1/8) is 0.080 mass % or less at a depth (position P1/8) from the outermost surface that is ⅛ of the thickness tf of the filler material (12). The Mg concentration (c7/8) is 15-45% of the amount of Mg in the core material at a depth (position P7/8) from the outermost surface that is ⅞ of the thickness tf of the filler material.