Three-Layer Brazing Sheet for Flux-Free Fillet Formation
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Solution Overview
Problem
Existing brazing sheets face issues with brazeability in inert-gas atmospheres due to oxidation of filler material surfaces, leading to defects such as discontinuous fillets and reduced quality, especially when using high oxygen concentrations and rapid temperature-rise rates, and struggle with hollow structures where filler is drawn into the interior, causing brazing defects.
Innovation Solution
A brazing sheet with a core material containing up to 1.3% Mg, an intermediate material with 0.4-6.0% Mg, and a filler material with 6.0-13.0% Si, 0.004-0.070% Bi, and 0.050-0.10% Mg, which reduces oxidation and enhances fluidity to ensure continuous fillet formation even on hollow structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large amount of Mg is contained in the filler material to weaken the oxide film, then the oxide film weakening effect is improved, but the filler material surface oxidizes readily in inert-gas atmosphere, forming a sturdy oxide film that degrades brazeability
Solution Approach 1:
The patent applies local quality by creating a layered structure where Mg is concentrated in the intermediate material layer adjacent to the filler material, rather than distributing it throughout the filler material. This localized placement allows Mg to migrate to the filler surface and weaken oxide films during brazing, while the filler material itself remains low-Mg and resistant to oxidation in the inert-gas atmosphere.
Solution Approach 2:
The intermediate material acts as an intermediary between the core material and filler material. It contains the Mg that will eventually migrate to weaken oxide films, but protects the filler material from direct oxidation. The intermediate layer serves as a reservoir and delivery mechanism for Mg, releasing it at the appropriate time and location during the brazing process.
2Object-affected harmful factors
If Mg is not included in the filler material to avoid oxidation, then filler material oxidation is prevented, but the oxide film weakening effect does not occur timely, leading to brazing defects
Solution Approach 1:
The patent applies preliminary action by pre-positioning Mg in the intermediate material layer before brazing begins. During the brazing heating process, Mg naturally migrates from the intermediate material to the filler material surface, ensuring oxide film weakening occurs at the right time without requiring Mg to be present in the filler material from the start. This preliminary placement of Mg resolves the timing issue for oxide film weakening.
Solution Approach 2:
The intermediate material containing Mg serves the dual purpose of protecting the filler material while simultaneously providing the oxide film weakening function. The Mg in the intermediate material self-regulates by migrating to the filler surface when needed, eliminating the need for external flux or additional processing steps.
3Productivity
If high temperature-rise rate is used to improve productivity, then brazing speed is improved, but filler is drawn into hollow structures, causing brazing defects
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the filler material (specific Si and Bi content ratios) and the intermediate material (Mg content). These compositional changes alter the physical properties of the filler, particularly its fluidity and surface tension, allowing it to maintain proper flow characteristics even during rapid temperature-rise brazing processes, thereby preventing filler intrusion into hollow structures.
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 weakening the oxide film and increasing fluidity, allowing for rapid and sufficient filler deposition at intended joints, even under high temperature-rise conditions and in hollow structures, while maintaining cost-effectiveness.
Implementation Method 1
Mg in the intermediate material can break down the oxide film on the surface of the filler material
Implementation Method 2
because Mg diffuses within the core material, which is a solid body, and moves to the filler material
Implementation Method 3
an intermediate material with 0.4-6.0% Mg, and a filler material with 6.0-13.0% Si, 0.004-0.070% Bi, and 0.050-0.10% Mg, which reduces oxidation and enhances fluidity
Data Source
AI summary
A brazing sheet brazing suitable for brazing performed in an inert gas atmosphere or in a vacuum without using a flux has a three-layer composition. An aluminum alloy core material contains Mg: 1.3 mass % or less. An aluminum alloy intermediate material is layered on the core material and contains Mg: 0.40-6.0 mass %. An aluminum alloy filler material is layered on the intermediate material and contains Si: 6.0-13.0 mass %, Bi: 0.0040-0.070 mass %, and Mg: 0.050-0.10 mass %.