Aluminum Alloy Brazing Sheet for Flux-Free Brazing Shape Stability
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Solution Overview
Problem
The existing methods for brazing aluminum materials without using a flux, such as diffusing Mg into the brazing material, face limitations in adding sufficient Mg to break the oxide film and maintaining the shape of heat exchangers due to diffusion issues with Si, leading to poor brazability and productivity challenges.
Innovation Solution
An aluminum alloy brazing sheet is developed with a specific composition and structure, including a core material with controlled grain size and alloying elements like Mn, Mg, and Si, and a brazing material with high Si content, which allows for efficient Mg supply and reduced Si diffusion during brazing, enhancing brazability in inert gas or vacuum environments without flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Mg is diffused into the brazing material from the core material, then oxide film breakage is improved, but the core material may melt due to excessive Si diffusion into it
Solution Approach 1:
The patent optimizes the Mg content in the core material to a specific range (0.03-2.0 mass%) and controls the Si content (0.03-1.0 mass%) to balance oxide film breakage capability with prevention of core material melting. This parameter optimization resolves the contradiction by finding the optimal composition window where sufficient Mg is available for oxide film removal while Si diffusion remains controlled.
Solution Approach 2:
The patent creates a gradient composition structure where Mg is concentrated in the core material to provide oxide film breakage, while the brazing material contains Si (4.0-13.0 mass%) for proper brazing properties. The interface between these layers is designed to control diffusion rates, allowing local Mg supply to the brazing material while preventing excessive Si penetration into the core material.
2Reliability
If the Mg content in the core material is increased to improve oxide film breakage, then brazability is improved, but the solidus temperature of the core material decreases
Solution Approach 1:
The patent establishes an optimal Mg content range (0.03-2.0 mass%) in the core material that balances oxide film breakage capability with maintenance of solidus temperature above the brazing temperature. This parameter optimization ensures sufficient Mg is available for oxide film removal while preventing core material melting during the brazing process.
Solution Approach 2:
The patent creates a composite structure with a core material containing controlled Mg content and a brazing material layer with specific Si content. This composite design allows the core material to provide Mg for oxide film breakage while the overall system maintains appropriate melting characteristics for successful brazing.
3Strength
If the grain size of the core material is reduced to improve strength, then mechanical properties are improved, but Si diffusion into the core material increases causing shape loss
Solution Approach 1:
The patent optimizes the grain size of the core material to a specific range (20-300 μm) that balances mechanical strength with resistance to Si diffusion. This grain size control creates enough boundary resistance to Si diffusion while maintaining the strength requirements for heat exchanger applications.
4Reliability
If vacuum brazing is used to avoid flux, then product quality is improved, but equipment cost and maintenance cost increase
Solution Approach 1:
The patent enables the brazing material to self-clean its surface oxide film through Mg diffusion from the core material during the brazing process itself. This self-service oxide removal mechanism allows successful brazing in inert gas atmospheres without requiring vacuum equipment, thereby reducing equipment complexity and cost while maintaining brazing quality.
Solution Approach 2:
The patent enables brazing to proceed successfully in inert gas atmospheres (such as nitrogen or argon) by using Mg diffusion to break oxide films. This eliminates the need for expensive vacuum equipment while achieving brazing quality comparable to or better than vacuum brazing, as the inert atmosphere prevents oxide formation during the process.
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 solution achieves excellent brazability by promptly supplying Mg to break the oxide film and suppressing Si diffusion, thereby improving the bonding process and maintaining the shape of heat exchangers during brazing in inert gas or vacuum conditions.
Implementation Method 1
Mg added to the core material is diffused into the brazing material during brazing heating
Implementation Method 2
after melting of the brazing material is started
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 contains 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, with the balance being aluminum and inevitable impurities. The brazing material is formed of an aluminum alloy containing Si of 4.00 to 13.00 mass % with the balance being aluminum and inevitable impurities, and, in a drop-type fluidity test, a ratio α (α=Ka/Kb) of a fluid coefficient Ka is 0.50 or more.