Aluminum Brazing Sheet Interliner for Flux-Free CAB Joining
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Solution Overview
Problem
Current Controlled Atmosphere Brazing (CAB) methods for joining aluminum alloys rely heavily on flux, which poses environmental health and safety concerns and leaves residual flux on parts, prompting the need for a flux-free brazing process.
Innovation Solution
A sheet material comprising a core layer of 3XXX, 1XXX, or 6XXX series aluminum alloy with an interliner layer containing Mg, Si, Bi, and optional additional elements, sandwiched between a brazing liner layer of 4XXX aluminum alloy, allowing for brazing in an inert atmosphere without flux.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux is used in CAB brazing to remove oxide and control oxidation, then successful joining of aluminum parts is achieved, but environmental health and safety concerns arise and residual flux remains on parts
Solution Approach 1:
The patent removes flux from the brazing process entirely by using a controlled atmosphere furnace with low oxygen content (below 0.5% O2). The fluxless brazing method extracts the harmful substance (flux) from the system while maintaining successful joining through atmospheric control and specialized filler metal composition
Solution Approach 2:
The patent employs a controlled inert atmosphere in the brazing furnace with oxygen content maintained below 0.5% (typically 0.1-0.4% O2). This inert environment prevents oxidation of aluminum surfaces without requiring flux, thereby eliminating environmental health and safety concerns associated with traditional flux-based CAB brazing
2Reliability
If flux is used in CAB brazing to protect clean metal surfaces from oxidation, then oxidation control is achieved, but residual flux is left on parts causing contamination
Solution Approach 1:
The patent extracts flux from the brazing process by using a controlled atmosphere with low oxygen content. The filler metal is applied without flux, and the inert atmosphere protects the metal surfaces from oxidation during heating, eliminating residual flux contamination on parts
Solution Approach 2:
The patent uses a controlled atmosphere furnace maintaining oxygen content below 0.5% during brazing. This inert environment provides oxidation protection for clean metal surfaces without requiring flux, thereby preventing residual flux contamination on the finished parts
3Object-affected harmful factors
If a multi-layer sheet structure with interliner and braze liner is used for flux-free brazing, then flux-free joining is achieved, but material complexity increases
Solution Approach 1:
The patent segments the sheet material into distinct functional layers: a core layer (aluminum alloy), an interliner layer (containing reactive elements like Mg, Si, Bi), and a braze liner layer (containing filler metal). This segmentation allows each layer to perform its specific function in enabling flux-free brazing while maintaining overall system effectiveness
Solution Approach 2:
The patent uses composite sheet material structure combining multiple aluminum alloy layers with specific compositional characteristics. The core layer provides structural integrity, the interliner layer contains reactive elements for oxide removal, and the braze liner contains filler metal for joining. This composite structure enables flux-free brazing through coordinated functionality of its components
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 effective joining of aluminum alloys in a flux-free CAB process, reducing environmental concerns and maintaining joint quality, as demonstrated by successful brazing tests with improved fillet radii and joint widths without the need for flux.
Implementation Method 1
a flux is used to remove the oxide from the parts to be joined
Implementation Method 2
melting the filler metal, which flows into the interface between adjoining parts by capillary action and hardens upon cooling to join the metal parts
Implementation Method 3
the surfaces to be joined and the filler metal need to be protected from oxidation during the various stages in the brazing process
Data Source
AI summary
An aluminum alloy brazing sheet has a 3XXX, 1XXX or 6XXX core, an interliner and a 4XXX brazing layer without added Mg. The interliner has Bi and Mg, the magnesium migrating to the surface of the brazing sheet during brazing and reducing the aluminum oxide to facilitate brazing without flux in a controlled inert atmosphere with reduced oxygen.