Aluminum Brazing Sheet Bi-Mg Intermediate Layer
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Solution Overview
Problem
Brazing aluminum without using a flux in an inert gas atmosphere or vacuum poses challenges due to insufficient oxide film destruction and deterioration of brazing properties, particularly with the use of Bi, which forms Bi-based oxides that degrade brazing performance.
Innovation Solution
An aluminum alloy brazing sheet is designed with a brazing material containing 6-13% Si and an intermediate material with 0.01-1.5% Bi and 1.5-13% Si, where Bi and Mg are eluted into the molten brazing material during heating, effectively embrittling the oxide film, thereby improving brazing properties without the need for flux or low-oxygen atmospheres.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Bi is added to the brazing material to promote oxide film destruction, then brazing properties are improved, but Bi-based oxide forms on the surface during manufacturing, causing discoloration and deterioration of brazing properties
Solution Approach 1:
The patent introduces an intermediate layer between the Al-Si brazing material and the Al-Mg core material. This intermediate layer contains Bi (0.01-1.5 mass%) and Si (1.5-13 mass%), which acts as a mediator to control the behavior of Bi during processing. The intermediate layer prevents Bi from forming harmful oxides on the surface during manufacturing while still enabling Bi to effectively destroy oxide films during brazing, thus resolving the contradiction between improving brazing properties and preventing harmful oxide formation.
Solution Approach 2:
The patent applies local quality by creating a layered structure with different compositions in different regions. The brazing material layer has high Si content (6-13 mass%) for proper brazing performance, while the intermediate layer has controlled Bi (0.01-1.5 mass%) and Si (1.5-13 mass%) content to prevent oxide formation. This spatial distribution of different material properties allows the system to simultaneously achieve good brazing properties and prevent Bi-based oxide formation on the surface.
2Object-generated harmful factors
If Bi content is reduced to suppress Bi-based oxide formation, then surface quality is improved, but the effect of Bi in breaking oxide film is insufficient
Solution Approach 1:
The intermediate layer serves as a reservoir for Bi, containing it in a controlled manner (0.01-1.5 mass%). During brazing, this intermediate layer releases Bi to the brazing material, providing sufficient Bi for oxide film destruction without having excessive Bi that would form harmful surface oxides during manufacturing. The intermediate layer thus mediates between the need for Bi in oxide film destruction and the need to limit Bi to prevent harmful oxide formation.
Solution Approach 2:
The intermediate layer is prepared in advance with controlled Bi and Si content during the cladding process. This preliminary preparation ensures that Bi is available in the correct quantity and location before brazing occurs. The Si in the intermediate layer (1.5-13 mass%) creates a composition that prevents premature oxide formation while enabling controlled Bi release during brazing, thus preliminarily setting up the conditions for successful oxide film destruction without harmful oxide formation.
3Object-generated harmful factors
If pretreatment is performed to remove Bi-based oxide, then surface quality is improved, but reoxidation occurs during preheating in inert gas atmosphere, losing the effect of pretreatment
Solution Approach 1:
The intermediate layer with controlled Bi (0.01-1.5 mass%) and Si (1.5-13 mass%) composition acts as a protective barrier that prevents reoxidation of Bi during preheating in inert gas atmosphere. This intermediate composition creates a surface that is resistant to oxidation, thereby maintaining the quality improvements from pretreatment and preventing reoxidation that would otherwise occur during the brazing process.
Solution Approach 2:
The patent changes the compositional parameters of the intermediate layer, specifically controlling Bi content at 0.01-1.5 mass% and Si content at 1.5-13 mass%. This parameter optimization creates a composition that is inherently resistant to oxidation during preheating, thus preventing reoxidation of Bi. The specific Si content range creates a protective effect that maintains surface quality through the preheating stage without requiring aggressive pretreatment that would be undone by reoxidation.
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 solution enables excellent brazing properties by promptly supplying Bi and Mg, effectively breaking the oxide film and enhancing joint formation without pretreatment or low-oxygen atmospheres, thus improving productivity and stability.
Implementation Method 1
promptly supplying Bi and Mg into the brazing material during brazing heating, causing these elements to be eluted in the molten brazing material after start of melting the brazing material
Implementation Method 2
effectively embrittling the oxide film on the surface of the brazing material
Data Source
AI summary
An aluminum alloy brazing sheet used for brazing aluminum, without using a flux, in an inert gas atmosphere or vacuum is formed by arranging a brazing material on one side or both sides of a core material made of pure aluminum or aluminum alloy, the brazing material including 6% to 13% by mass of Si and the balance being Al and inevitable impurities, and performing cladding with an intermediate material interposed between the core material and the brazing material, the intermediate material including 0.01% to 1.5% by mass of Bi, 1.5% to 13% by mass of Si, and the balance being Al and inevitable impurities, the intermediate material having a thickness of 2% to 35% of a thickness of the brazing material, wherein one or both of the intermediate material and the core material includes 0.4% to 6% by mass of Mg.