Multi-Layer Aluminium Brazing Sheet for Crack-Resistant Thin Gauges
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Solution Overview
Problem
Conventional brazing sheet products face issues with large primary Si particles, which can lead to cracking and 'burning through' during the brazing process, especially in thin gauge materials, necessitating a solution to control Si particle size and prevent material erosion.
Innovation Solution
A multi-layered brazing sheet material is developed, comprising an aluminium alloy core layer with a first Al-Si alloy brazing clad layer on one or both sides and a second Al-Si alloy brazing clad layer with higher Si content positioned between the core and the first clad layer, optimizing Si distribution and preventing crack formation by forming a filler metal that levels compositional differences and limits Si diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the thickness of the aluminium brazing clad layer is reduced to save material, then material cost is reduced, but the risk of cracking and burning through during brazing increases
Solution Approach 1:
The brazing clad layer is divided into multiple sub-layers with different Si contents. The first sub-layer has lower Si content (4-10 wt.%) and the second sub-layer has higher Si content (10-20 wt.%), creating a gradient structure that prevents cracking while maintaining thin overall thickness
Solution Approach 2:
Different regions of the brazing clad layer have different Si concentrations tailored to their specific functions. The lower Si region provides crack resistance during forming, while the higher Si region ensures proper brazing flow and prevents burning through at the brazing interface
2Reliability
If the Si content in the brazing clad layer is increased to prevent burning through, then brazing process reliability is improved, but the risk of cracking during forming increases
Solution Approach 1:
The brazing clad layer is segmented into sub-layers with different Si contents. The first sub-layer with lower Si content maintains ductility and prevents cracking during forming operations, while the second sub-layer with higher Si content prevents burning through during brazing
Solution Approach 2:
The Si content parameter is varied through the thickness of the brazing clad layer, creating a gradient from lower Si content at the outer surface to higher Si content at the interface with the core alloy, optimizing both forming and brazing performance
3Strength
If primary Si particles are kept small to prevent cracking, then clad layer integrity is maintained, but the complexity of controlling Si particle distribution increases
Solution Approach 1:
By segmenting the brazing clad layer into sub-layers with different Si contents, the patent simplifies particle control. Each sub-layer can be independently optimized for particle size distribution, making it easier to prevent large primary Si particles (>10 μm) that cause cracking
Solution Approach 2:
The first sub-layer with lower Si content is specifically designed to have controlled, small Si particle distribution to prevent cracking during forming, while the second sub-layer handles the brazing function, localizing the particle control requirements to where they are most critical
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 multi-layered structure significantly reduces the occurrence of large primary Si particles, enhancing material forming characteristics, preventing cracking, and ensuring a reliable brazing process without material erosion, while maintaining cost-effectiveness by avoiding the use of very pure source materials.
Implementation Method 1
limits Si diffusion into the core layer
Implementation Method 2
The melting point of the brazing material is lower than the melting point of the aluminium substrate or aluminium core sheet
Data Source
Figure 1A~1B
AI summary
The invention relates to a multi-layered brazing sheet material comprising of an aluminium core alloy layer provided with a first brazing clad layer material on one or both sides of said aluminium core layer and at least one second brazing clad layer material positioned between the aluminium core alloy layer and the first brazing clad layer material, wherein the second brazing clad layer material is an Al-Si alloy brazing material having 11% to 14% Si, up to 4.5% Zn and up to 0.25% Mg, and wherein the first brazing clad layer material is an Al-Si alloy brazing material having 6% to 9% Si, up to 1.5% Zn and up to 0.25% Mg.