Flux-Less Aluminum Brazing Sheet Composition for Heat Exchangers
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Solution Overview
Problem
Existing flux-less brazing methods for aluminum alloy heat exchangers face challenges in achieving sufficient brazing properties due to issues like MgO formation and inadequate Bi content in brazing filler materials, leading to reduced efficiency and effectiveness.
Innovation Solution
A method for brazing an aluminum alloy brazing sheet in an inert gas atmosphere at 560°C to 620°C without flux, where the sheet includes a core material with limited Mg content and a brazing filler material containing Si, Bi, and Mg, with specific compositional relationships to inhibit MgO formation and enhance flowability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vacuum brazing is used to achieve flux-less brazing, then brazing quality is improved and flux-related problems are eliminated, but equipment cost and operation complexity increase significantly
Solution Approach 1:
The patent replaces vacuum environment with inert gas atmosphere (nitrogen or argon) for flux-less brazing. The inert gas prevents oxidation of the brazing filler material while avoiding the complexity of vacuum equipment. This allows flux-less brazing to be performed using conventional atmospheric brazing equipment, significantly reducing equipment cost and operational complexity while maintaining brazing quality.
Solution Approach 2:
The patent uses inexpensive inert gas (nitrogen or argon) that can be easily introduced and discharged from the brazing environment, replacing expensive and complex vacuum systems. The inert gas serves its protective function during brazing and is then simply vented, making the process economically viable and operationally simple.
2Reliability
If Mg content in brazing filler material is increased to improve brazing properties, then brazing performance is enhanced, but MgO formation accelerates during heating, reducing brazing quality
Solution Approach 1:
The patent applies preliminary protective action by introducing inert gas atmosphere before and during the heating process. This prevents oxidation of Mg in the brazing filler material before it can form harmful MgO. By establishing the protective inert atmosphere in advance, the brazing filler material can contain higher Mg content for improved brazing performance without the risk of MgO formation during heating.
Solution Approach 2:
The inert gas atmosphere (nitrogen or argon) creates an oxygen-free environment that prevents Mg oxidation. This allows the brazing filler material to utilize Mg's beneficial effects on brazing performance (such as improving wetting and lowering melting point) without the counteracting harmful effect of MgO formation, which would occur in atmospheric oxygen during conventional brazing.
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 method achieves excellent brazing properties by preventing MgO formation and promoting Bi's getter function, leading to improved flowability and oxidation resistance of the brazing filler, resulting in enhanced brazing performance and corrosion resistance.
Implementation Method 1
promoting Bi's getter function
Implementation Method 2
Mg vaporization
Implementation Method 3
brazing an aluminum alloy brazing sheet in an inert gas atmosphere at a heating temperature in a range of from 560°C to 620°C
Implementation Method 4
enhanced brazing performance and corrosion resistance
Data Source
Figure 1~2A
Figure 2B
Figure 3
AI summary
Provided is a brazing method for an aluminum alloy brazing sheet provided with a core material and a brazing material in which the Si content of the brazing material is denoted by Csi, the Bi content of the brazing material is denoted by CBi, the Mg content of the brazing material is denoted by CMg-b, the Mg content of the core material is denoted by CMg-c, CMg = CMg-b + CMg-c / 2, and an aluminum alloy brazing sheet satisfying 3 ≤ CSi ≤ 13, 0.13CMg-0.3 ≤ CBi ≤ 0.58CMg0.45, CMg-b ≥ 0.1, and 0.2 ≤ CMg ≤ 1.1 is brazed in an inert gas atmosphere at a heating temperature of 560-620 °C without using flux.