Aluminum Alloy Brazing Sheet for Fluxless Large-Clearance Brazing
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Solution Overview
Problem
Existing methods for fluxless brazing of aluminum alloys in inert gas atmospheres face challenges in achieving reliable brazability, especially in joints with large clearances, due to issues with oxide film breaking and fillet formation, leading to distorted or discontinuous fillets.
Innovation Solution
An aluminum alloy brazing sheet with a brazing material cladded onto a core material, where the brazing material contains Si, Mg, Li, and Ca, forming oxides with a volume change ratio of 0.990 or less, allowing for effective exposure of the molten brazing material's surface without flux, enhancing brazability even in joints with large clearances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux is used in nitrogen gas furnace to break oxide film, then oxide film breaking is effective, but cost increases and defective brazing may occur due to nonuniform application
Solution Approach 1:
The invention extracts and eliminates the flux component from the brazing process by incorporating reactive elements (Mg, Li, Ca, Al) directly into the brazing material composition. These elements chemically react with the oxide film during brazing to break it down, replacing the need for separate flux application and eliminating associated costs and defects.
Solution Approach 2:
The reactive elements (Mg, Li, Ca, Al) in the brazing material serve as intermediaries that mediate between the molten brazing material and the oxide film. These elements chemically interact with the oxide film to break it down, enabling effective oxide removal without requiring external flux application.
2Reliability
If vacuum heating furnace is used for fluxless brazing with Mg evaporation, then oxide film is broken effectively, but expensive vacuum facilities are required and high maintenance cost is incurred
Solution Approach 1:
The brazing material is formulated to be self-sufficient in breaking its own oxide film through the inclusion of reactive elements (Mg, Li, Ca, Al) that chemically react with the oxide during brazing. This eliminates the need for external vacuum facilities or flux application, allowing the process to occur in simple nitrogen gas furnaces.
Solution Approach 2:
The invention changes the chemical composition parameters of the brazing material by incorporating specific reactive elements (Mg: 0.03-3.00 mass%, Li: 0.03-3.00 mass%, Ca: 0.03-3.00 mass%, Al: 3.00-10.00 mass%) that enable oxide film breaking through chemical reaction, replacing the need for vacuum heating and Mg evaporation.
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 solution provides excellent brazability in inert gas atmospheres without using flux, ensuring sound fillet formation and joint integrity by effectively breaking the oxide film and promoting wetting of the brazing material, even in complex geometries like heat exchangers.
Implementation Method 1
Mg, Li, and Ca break a film-like oxide formed on a surface of a brazing material during brazing heating, and effectively expose a new surface of the molten brazing material
Implementation Method 2
expose and wet the molten brazing material with a base material or a similarly molten brazing material
Implementation Method 3
expose and wet the molten brazing material with a base material
Data Source
AI summary
An aluminum alloy brazing sheet used for brazing in an inert gas atmosphere without using a flux includes a brazing material cladded onto at least one side surface of a core material. An oxide is formed on a surface of the aluminum alloy brazing sheet by brazing heating, the oxide including any one or two or more of Mg, Li, and Ca and having a volume change ratio of 0.990 or less to a surface oxide film formed before brazing heating, and an atomic molar ratio of Mg, Li, and Ca to Al in the oxide formed on the surface of the aluminum alloy brazing sheet before brazing heating is 0.50 or less. The present invention provides an aluminum alloy brazing sheet having excellent brazability in brazing in an inert gas atmosphere without using a flux, and a method for manufacturing the same.