Layered Aluminum Brazing Sheet for Flux-Free Vacuum Brazing Stability
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Solution Overview
Problem
Existing methods for brazing aluminum materials in inert gas atmospheres or vacuum without flux face challenges such as limited Mg quantity for oxide film breakage, grain size issues affecting heat exchanger shape, and decreased brazability due to oxide film formation and Si diffusion.
Innovation Solution
An aluminum alloy brazing sheet is developed with a two- or three-layer structure, where the core material and brazing material are specifically alloyed with elements like Mn, Mg, Si, and Fe to control grain size and composition, and the brazing material includes additional elements like Bi, Na, and Sr to enhance fluidity and brazability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg is added to the core material to break oxide film during brazing, then oxide film breakage is improved, but the solidus temperature of core material decreases and Mg diffusion into brazing material increases
Solution Approach 1:
The patent applies local quality by adding Mg specifically to the core material at controlled concentrations (0.03-2.0 mass%) rather than uniformly throughout the entire brazing sheet. This localized addition allows Mg to diffuse to the brazing material interface where it breaks oxide films, while limiting overall Mg content to maintain core material solidus temperature above brazing temperature
Solution Approach 2:
The patent changes the parameter of Mg concentration in the core material to an optimized range (0.03-2.0 mass%) and controls Si content (0.03-2.0 mass%) to balance oxide film breakage capability with solidus temperature maintenance. This parameter optimization ensures sufficient Mg diffusion for oxide removal while preventing excessive temperature reduction
2Ease of operation
If Si content in brazing material is increased to improve fluidity, then brazing fluidity is improved, but Si diffusion into core material increases causing grain boundary embrittlement
Solution Approach 1:
The patent optimizes Si content in the brazing material within a specific range (3-15 mass%) to achieve adequate fluidity for brazing operation. Simultaneously, it controls Si content in the core material to 0.03-2.0 mass% and limits Fe content to 0.03-2.0 mass% to minimize harmful Si diffusion and intermetallic compound formation at grain boundaries, thereby maintaining grain boundary strength
3Shape
If grain size of core material is reduced to improve heat exchanger shape, then shape maintenance is improved, but brazability decreases due to increased Si diffusion
Solution Approach 1:
The patent controls the grain size of the core material within a specific range (5-200 μm) to maintain heat exchanger shape while limiting excessive Si diffusion. Simultaneously, it optimizes Mg content (0.03-2.0 mass%) and Si content (0.03-2.0 mass%) in the core material to ensure sufficient Mg diffusion for oxide film breakage during brazing, thereby maintaining good brazability despite fine grain structure
4Reliability
If flux is used to break oxide film, then oxide film breakage is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies self-service by incorporating Mg into the core material composition, which automatically diffuses to the brazing material surface during brazing heating to break oxide films. This eliminates the need for external flux application, reducing manufacturing steps and costs while maintaining reliable oxide film breakage
Solution Approach 2:
The patent applies preliminary action by pre-adding Mg to the core material during brazing sheet manufacturing. This Mg is positioned in advance to diffuse to the brazing material interface during subsequent brazing heating, breaking oxide films before the brazing process begins, thereby eliminating the need for flux application
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 excellent brazability by suppressing Mg diffusion, ensuring efficient oxide film breakage, and minimizing Si diffusion into the core material, thereby maintaining the shape of heat exchangers and improving brazing stability.
Implementation Method 1
diffusion of Mg added to the core material into the brazing material
Implementation Method 2
Mg effectively acts on breakage of an oxide film on the surface of the brazing material
Data Source
AI summary
An aluminum alloy brazing sheet used for brazing of an aluminum material in an inert gas atmosphere or in vacuum is formed of a two-layer material in which a brazing material and a core material are stacked in this order. The core material is formed of an aluminum alloy and has a grain size of 20 to 300 μm, and the aluminum alloy includes Mn of 0.50 to 2.00 mass %, Mg of 0.40 to 2.00 mass %, Si of 1.50 mass % or less, and Fe of 1.00 mass % or less. The brazing material is formed of an aluminum alloy including Si of 4.00 to 13.00 mass % and one or two or more of Mn of 2.00 mass or less, Ti of 0.30 mass % or less, Zr of 0.30 mass % or less, and Cr of 0.30 mass % or less.