Fluxless Brazing Sheet Composition for Oxide Film Control
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Solution Overview
Problem
Current brazing sheets used in fluxless brazing methods face issues such as degradation in brazeability due to oxidation of filler materials, particularly with high Mg content, leading to discontinuous fillets and increased materials costs, and challenges in forming satisfactory joints on complex shapes like hollow structures.
Innovation Solution
A brazing sheet with a core material containing Mg and a filler material comprising Si, Mg, Bi, and additional elements like Sb, Pb, Ba, Na, and Sr, where the Mg amount in the filler material is optimized to weaken the oxide film and enhance fluidity, allowing for rapid formation of continuous fillets without the need for intermediate layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the filler material contains a large amount of Mg to weaken oxide film, then the oxide film breaking capability is improved, but the filler material surface oxidizes readily during heating, leading to degradation in brazeability
Solution Approach 1:
The patent optimizes the Mg content parameter in the filler material to a specific range (0.03-1.0 mass%) rather than using a large amount. This parameter change balances the oxide film breaking capability with the prevention of excessive oxidation during heating, resolving the technical contradiction by finding the optimal value that satisfies both requirements.
Solution Approach 2:
The patent creates a composite filler material system containing Mg combined with other elements (such as Si, Al, and trace elements like Bi, Sb, Pb) in specific proportions. This composite composition allows the Mg to effectively break oxide films while the other elements suppress excessive oxidation during heating, resolving the contradiction through synergistic material design.
2Object-affected harmful factors
If Mg is included in the core material instead of filler material to avoid oxidation, then the oxidation problem is avoided, but the time for Mg to reach the filler material surface is extended, causing brazing defects
Solution Approach 1:
The patent takes preliminary action by directly including Mg in the filler material from the beginning, rather than relying on diffusion from the core material during the brazing process. This ensures Mg is immediately available at the filler material surface to break oxide films, eliminating the time delay associated with diffusion while preventing oxidation through controlled composition.
Solution Approach 2:
The patent uses the filler material itself as an intermediary that contains Mg, allowing Mg to be positioned exactly where it is needed (at the filler material surface) without requiring long-distance diffusion through the core material. This intermediary approach resolves the time delay issue by placing the active element directly in the functional location.
3Loss of time
If an intermediate material containing Mg is provided between core material and filler material to reduce time, then the Mg delivery time is shortened, but the number of layers increases leading to higher materials cost
Solution Approach 1:
The patent merges the functions of the core material and the intermediate Mg-containing layer by directly incorporating Mg into the filler material composition. This eliminates the need for a separate intermediate layer, reducing the number of layers and materials cost while maintaining rapid Mg availability through direct inclusion in the filler material.
Solution Approach 2:
The patent makes the filler material multi-functional by giving it both the primary function of joining and the secondary function of containing Mg for oxide film breaking. This eliminates the need for a separate intermediate layer that would only serve the Mg delivery function, reducing complexity while achieving the same technical effect.
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
The brazing sheet achieves improved brazeability by preventing oxidation and ensuring rapid wetting and filling of joints, even on complex surfaces, while reducing materials costs by eliminating the need for intermediate layers.
Implementation Method 1
due to a reaction between oxygen contained in the atmosphere in trace amounts and Mg in the filler material, a sturdy oxide film will be formed on the surface of the filler material
Implementation Method 2
Mg in the core material reaches the surface of the filler material, weakening of the oxide film due to Mg does not occur. Furthermore, because Mg diffuses within the core material, which is a solid body, and moves to the filler material
Data Source
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AI summary
A brazing sheet, in which brazeability when brazing in an inert gas atmosphere is satisfactory and an increase in materials cost can be constrained, and a manufacturing method thereof are provided. The brazing sheet includes: a core material having a chemical composition that contains Mg: 0.20 mass% or more and 1.3 mass% or less, the remainder being A1 and unavoidable impurities; and a filler material layered on the core material and having a chemical composition that contains Si: 6.0 mass% or more and 13.0 mass% or less, Bi: 0.0040 mass% or more and 0.070 mass% or less, and Mg: 0.050 mass% or more and less than 0.10 mass%, the remainder being A1 and unavoidable impurities. This brazing sheet is usable in brazing performed in an inert gas atmosphere or in a vacuum without using a flux.