Brazing Sheet Oxide Fragmentation for Stable Flux-Free Brazing
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Solution Overview
Problem
Flux-free brazing methods for aluminum materials face challenges in maintaining brazeability due to fluctuations in dew point and oxygen concentration, as the breakdown of the oxide film by metal elements like Mg is insufficient, leading to degraded joint quality and productivity issues.
Innovation Solution
A method of manufacturing a brazing sheet involving hot rolling of a cladding slab with a core material and a filler material containing an oxide-film breakdown element, followed by acid etching to remove the oxide film and subsequent cold rolling, which fragments the oxide film, improving its breakdown during brazing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If flux-free brazing is performed using metal elements like Mg to break down oxide film, then flux application is eliminated and productivity improves, but the oxide film breakdown becomes insufficient when dew point and oxygen concentration fluctuate, leading to degraded brazeability
Solution Approach 1:
The patent applies preliminary action by forming oxide film fragments on the brazing sheet surface before the brazing process through etching and rolling operations. This pre-fragmentation ensures that when brazing occurs, the oxide film is already in a state conducive to rapid breakdown, eliminating the need for flux and maintaining reliable brazeability even when atmospheric conditions fluctuate.
Solution Approach 2:
The patent applies segmentation by dividing the continuous oxide film into numerous small fragments through etching and mechanical rolling. These fragmented oxide particles have increased surface area and reduced stability, making them much easier to break down during brazing compared to a continuous oxide film, thus improving brazeability without requiring flux.
2Manufacturing precision
If etching is performed to remove oxide film from brazing sheet surface, then oxide film removal is achieved, but oxide film reforms on the surface during cleaning and drying processes
Solution Approach 1:
The patent performs etching and rolling operations during the manufacturing process to create oxide film fragments on the brazing sheet surface. By establishing this fragmented oxide structure in advance, the patent ensures that even when oxide reforms during subsequent cleaning and drying, the reformed oxide maintains the fragmented morphology that facilitates easy breakdown during brazing.
Solution Approach 2:
The patent changes the physical state and morphology of the oxide film from a continuous layer to fragmented particles through controlled etching and mechanical rolling. This parameter change in oxide film structure ensures that regardless of whether oxide is present or reforms during processing, the fragmented nature maintains good brazeability by providing numerous breakdown initiation sites.
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 method enhances brazeability by creating fragile oxide film fragments that facilitate rapid breakdown during brazing, improving the fluidity of the filler material and reducing the impact of dew point and oxygen concentration fluctuations.
Implementation Method 1
etching a surface of the clad sheet using a liquid etchant that contains an acid
Implementation Method 2
subsequently cold rolling the clad sheet to a desired thickness
Implementation Method 3
brazing is performed utilizing an effect that breaks down an oxide film, in which a metal element, such as Mg, Li, etc., that is more readily oxidized than Al is present at the surface of the brazing sheet
Data Source
AI summary
In a brazing sheet manufacturing method, a cladding slab is prepared by overlaying at least a core-material slab composed of an aluminum material and a filler-material slab composed of an Al—Si series alloy, in which a metal element that oxidizes more readily than Al is included in at least one of the slabs. A clad sheet is prepared by hot rolling this cladding slab, which then has at least a core material layer composed of the core-material slab and a filler material layer composed of the filler-material slab and disposed on at least one side of the core material. Then, a surface of the clad sheet is etched using a liquid etchant that contains an acid. Subsequently, the clad sheet is cold rolled to a desired thickness. In flux-free brazing, such a brazing sheet is capable of curtailing degradation in brazeability caused by fluctuations in dew point and oxygen concentration.