Multi-Layer Aluminum Brazing Sheet for Flux-Free CAB Joints
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Solution Overview
Problem
Conventional brazing processes for aluminum alloys often require flux, which can lead to oxidation and hinder the brazing performance, especially in inert gas atmospheres, due to the formation of unwanted oxide layers and the need for precise temperature control to manage the liquidus and solidus temperatures of the brazing materials.
Innovation Solution
A multi-layered aluminum alloy brazing sheet with a 3xxx-series core layer and Al-Si brazing clad layers, where the covering clad layer has a higher liquidus temperature than the Al-Si brazing clad layer, preventing oxidation and allowing the Al-Si alloy to melt and spread without forming excessive Mg-oxide, facilitated by controlled Mg diffusion from the core layer to the brazing clad layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux is used in conventional brazing processes for aluminum alloys, then the brazing can proceed at controlled temperatures, but oxidation occurs and forms unwanted oxide layers that hinder brazing performance
Solution Approach 1:
The patent removes flux from the brazing process entirely by using a multi-layered brazing sheet with a core layer and covering clad layers. The covering clad layer is designed to prevent oxidation without requiring external flux, thereby extracting the harmful flux-related oxidation problem from the system while maintaining reliable brazing performance.
Solution Approach 2:
The patent employs a composite multi-layered brazing sheet structure consisting of a core layer and covering clad layers with different compositions. This composite material design allows the covering clad layer to provide oxidation protection while the internal structure enables proper brazing, resolving the contradiction between preventing oxidation and achieving reliable brazing without flux.
2Ease of manufacture
If precise temperature control is implemented to manage liquidus and solidus temperatures of brazing materials, then brazing can be controlled, but the process complexity increases
Solution Approach 1:
The patent modifies the compositional parameters of the brazing sheet by creating a multi-layered structure with specific alloying elements in each layer. This changes the thermal parameters (liquidus and solidus temperatures) of the material itself, allowing the material to self-regulate the brazing process without requiring complex external temperature control systems.
Solution Approach 2:
The multi-layered brazing sheet is designed to self-regulate the brazing process through its inherent thermal properties. The covering clad layer and core layer work together to control heat distribution and phase changes, enabling the material to perform temperature management functions autonomously without complex external control mechanisms.
3Reliability
If the covering clad layer has a higher liquidus temperature than the Al-Si brazing clad layer, then oxidation is prevented and Al-Si alloy melts and spreads properly, but the material structure becomes more complex
Solution Approach 1:
The patent divides the brazing sheet into multiple functional layers: a core layer and covering clad layers with distinct compositions and properties. This segmentation allows each layer to perform its specific function - the covering clad layer prevents oxidation while the Al-Si brazing clad layer provides proper material flow - resolving the contradiction between achieving reliable performance and maintaining simple 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
Enables efficient flux-free brazing in an inert gas atmosphere by preventing oxidation and ensuring proper flow of the molten material, resulting in improved joint formation and reduced operational complexity.
Implementation Method 1
controlled Mg diffusion from the core layer to the brazing clad layer
Implementation Method 2
allowing the Al-Si alloy to melt and spread
Implementation Method 3
preventing oxidation and allowing the Al-Si alloy to melt and spread without forming excessive Mg-oxide
Data Source
Figure 1A~1B
Figure 2
AI summary
Described herein is an aluminium alloy multi-layered brazing sheet product for brazing in an inert-gas atmosphere without a flux, comprising a core layer made of a 3xxx alloy comprising 0.20-0.75 wt. % Mg, and provided with a covering clad layer comprising 2-5 wt. % Si on one or both sides of said 3xxx alloy core layer and a Al-Si brazing clad layer comprising 7-13 wt. % Si positioned between the 3xxx alloy core layer and the covering clad layer, wherein the covering clad layer has a thickness X1 and the Al-Si brazing clad layer has a thickness X2 and wherein X2 ≥ 2X1. The invention further relates to the use of an aluminium alloy multi-layered brazing sheet product in a fluxfree controlled atmosphere brazing (CAB) operation to produce a heat exchanger apparatus.