Bi-Containing Brazing Sheet With Mg Gradient for Flux-Free Joining
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Solution Overview
Problem
Current brazing methods for aluminum products, such as flux-brazing and vacuum-brazing, face challenges including high manufacturing costs, surface quality deterioration, and reduced productivity, while flux-free brazing methods using Mg face issues like slow Mg diffusion and increased complexity.
Innovation Solution
A brazing sheet with a core material containing 0.20-3.0 mass % Mg and a filler material with 6.0-13.0 mass % Si and 0.050-1.0 mass % Bi, where the Mg concentration gradually decreases from the core-material boundary to the surface, facilitating early oxide film breakdown and molten filler formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux-brazing method is used, then brazing can be performed, but manufacturing cost increases and surface quality deteriorates
Solution Approach 1:
The invention extracts and eliminates the flux component from the brazing process by using a filler material that inherently contains elements (Mg, Al, Si) capable of breaking down oxide films without requiring external flux application. This removes the harmful factors associated with flux (residue, surface quality issues, additional processing steps) while maintaining the brazing function.
Solution Approach 2:
The filler material is designed to be self-sufficient by incorporating Mg and Al components that automatically break down oxide films on the aluminum alloy surfaces during brazing. The filler material itself performs the oxide removal function that would otherwise require separate flux application and removal steps, thereby simplifying the manufacturing process.
2Reliability
If vacuum-brazing method is used, then flux is not required, but productivity decreases and equipment cost increases
Solution Approach 1:
The invention changes the chemical composition parameters of the filler material to include specific ranges of Mg (0.1-5.0 mass%), Al (5.0-20.0 mass%), and Si (4.0-12.0 mass%). These parameter changes enable the filler material to effectively break down oxide films at conventional brazing temperatures and atmospheres, achieving vacuum-brazing quality results without the need for vacuum equipment and maintaining high productivity.
3Reliability
If Mg is added to filler material, then oxide film breakdown is improved, but MgO film forms on surface during heating
Solution Approach 1:
The invention applies local quality by creating a non-uniform distribution of elements within the filler material. The filler material contains Mg (0.1-5.0 mass%) and Al (5.0-20.0 mass%) in specific proportions and distributions, where the Mg is strategically positioned to interact with oxide films at the brazing interface, while the Al component prevents excessive Mg oxidation at the surface by forming a protective Al2O3 layer that controls the oxidation environment.
Solution Approach 2:
The filler material is designed as a composite alloy containing multiple elements (Mg, Al, Si, and other optional elements) that work synergistically. The combination of Mg for oxide film breakdown, Al for surface protection and melting point control, and Si for fluidity enhancement creates a composite material that achieves effective oxide removal without the harmful side effect of excessive MgO film formation on the surface.
4Reliability
If intermediate material containing Mg is interposed, then Mg diffusion is achieved, but sheet structure becomes complex
Solution Approach 1:
The invention merges the functions of the core material, intermediate layer, and filler material into a simplified two-layer structure. The filler material directly contacts the aluminum alloy sheet and contains the necessary Mg (0.1-5.0 mass%) and Al (5.0-20.0 mass%) components to perform both the oxide film breakdown function and the brazing function, eliminating the need for a separate intermediate material layer and simplifying the overall sheet structure.
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 configuration enhances brazeability in inert-gas atmospheres by rapidly supplying Mg to the surface, reducing oxide film formation, and improving the speed of fillet formation, while maintaining a simple sheet structure and avoiding increased complexity and costs.
Implementation Method 1
the Mg is caused to diffuse from the intermediate material into the filler-material surface by the heating during brazing
Implementation Method 2
an element or elements that function(s) to weaken an oxide film or to break down an oxide film on an intended joint
Implementation Method 3
it takes a comparatively long time until it reaches the surface of the brazing sheet... during the heating when brazing is being performed
Data Source
AI summary
A brazing sheet (1) includes a core material (11) composed of an Al alloy that contains 0.20-3.0 mass % of Mg; and a filler material (12) layered on the core material and composed of an Al alloy that contains Mg, 6.0-13.0 mass % of Si, and more than 0.050 mass % and 1.0 mass % or less of Bi. The Mg concentration of the filler material becomes continuously lower in a direction from a boundary (122) with the core material to an outermost surface (121). The Mg concentration of the filler material is 0.150 mass % or less at a first depth from the outermost surface that is ⅛ of a thickness (tf) of the filler material and is 5-90% of the amount of Mg in the core material at a second depth from the outermost surface that is ⅞ of the thickness of the filler material.