Aluminum Brazing Sheet Composition for MgO-Controlled Fluxless Brazing
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Solution Overview
Problem
In flux-free brazing of aluminum heat exchangers, the joining process is impaired by the formation of stable MgO films, which are difficult to decompose, leading to unstable joining properties, especially in tube and fin joining portions.
Innovation Solution
An aluminum brazing sheet with a multilayer structure containing an Al—Si—Mg—X brazing material, where the brazing material layer includes 0.05 to 2.0% Mg, 2.0 to 14.0% Si, and 0.01 to 0.3% of Bi, Ga, Sn, In, or Pb, with a total of these elements being 0.5% or less, and an oxide film with an MgO area ratio of 2% or less and crystallinity area ratio of 4% or less, is used to control the quality of the MgO film and improve brazability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux-free brazing is used to avoid fluoride flux reactions with Mg, then environmental safety and material compatibility are improved, but stable MgO film formation impairs joining quality
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Mg content (0.03-2.0 mass%) and Si content (2.0-14.0 mass%) in the brazing material, as well as the area ratio of MgO in the oxide film (2.0% or less). By adjusting these compositional parameters, the brazing material achieves optimal performance for flux-free brazing while minimizing harmful MgO film formation.
Solution Approach 2:
The patent employs composite materials by creating a multilayer structure consisting of a core material layer and a brazing material layer with specific composition (Al-Si-Mg system). The brazing material layer contains Al, Si, and controlled amounts of Mg, forming a composite structure that combines the benefits of different elements: Al provides base material properties, Si controls oxide film formation, and Mg enables flux-free brazing while minimizing MgO formation through precise compositional design.
2Reliability
If Mg content is increased to enhance brazing activity, then oxide film decomposition ability is improved, but MgO film formation increases and stabilizes
Solution Approach 1:
The patent resolves this contradiction through parameter changes by establishing an optimal Mg content range of 0.03-2.0 mass%, which is sufficient to provide brazing activity for oxide film decomposition but limited enough to prevent excessive MgO film formation. The Si content (2.0-14.0 mass%) is also controlled to modify oxide film characteristics and reduce MgO stability.
Solution Approach 2:
The patent applies local quality by creating a brazing material layer with localized and controlled Mg content distribution. The Mg is concentrated in the brazing material layer where it is needed for oxide film decomposition, while the overall Mg content remains limited to prevent excessive MgO formation. The oxide film itself exhibits local quality variations with MgO area ratio controlled to 2.0% or less.
3Reliability
If Bi or other elements are added to suppress oxide film formation, then brazability is improved, but material composition complexity increases
Solution Approach 1:
The patent applies parameter changes by adding small controlled amounts of specific elements (Bi: 0.003-0.3 mass%, or alternatively Ga: 0.003-0.3 mass%, Sn: 0.003-0.3 mass%, In: 0.003-0.3 mass%, or Pb: 0.003-0.3 mass%) to the Al-Si-Mg base composition. These minor additions significantly improve brazability by suppressing oxide film formation and modifying oxide film characteristics, while keeping the overall composition relatively simple and manageable.
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 stabilizes the joining process by controlling the quality of the MgO film, allowing for improved brazability and achieving favorable joining properties in flux-free brazing, comparable to traditional fluoride flux methods.
Implementation Method 1
Mg in the brazing material that has been melted and activated reduces and decomposes an Al oxide film on the surface of a joining portion
Implementation Method 2
the joining portions are likely to be affected by the atmosphere during brazing, and a MgO film is likely to grow on the surface of a Mg-added brazing material
Data Source
AI summary
An aluminum brazing sheet for flux-free brazing having a multilayer structure of two or more layers including at least one core material layer and one brazing material layer, wherein the brazing material layer is positioned on one or both sides of the core material layer and on an outermost surface of the brazing sheet. The brazing material layer is made of an Al—Si—Mg—X brazing material containing: in mass%, 0.05 to 2.0% of Mg, and 2.0 to 14.0% of Si, and further containing one or more of 0.01 to 0.3% of Bi, Ga, Sn, In and Pb, a total amount of Bi, Ga, Sn, In and Pb being 0.5% or less. X indicates one or more of Bi, Ga, Sn, In and Pb.