Aluminum Brazing Sheet Fluxless Brazeability

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Solution Overview

Problem

Current fluxless brazing techniques face challenges in achieving satisfactory brazeability and corrosion resistance without using flux, particularly in atmospheric conditions with moderate oxygen concentrations and dew points, leading to issues like oxidation of Mg and formation of oxides, which affect the brazeability and external appearance of brazing sheets.

Innovation Solution

An aluminum-alloy brazing sheet with specific chemical compositions, where Mg is added to the core and Bi is added to the filler material, with strict upper and lower limits for Mg and Bi content, and restricted amounts of readily-oxidizable elements, allowing for fluxless brazing in an inert-gas atmosphere using conventional equipment without pretreatment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If Mg is added to the filler material to break up oxide films during fluxless brazing, then brazeability improves, but the Mg readily oxidizes during manufacture and heating, forming thick MgO layers that degrade brazeability and require pretreatment or strict atmosphere control

Engineering Contradiction:

ImprovebrazeabilityVSAvoidoxidation of Mg

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The brazing sheet is divided into two functional parts: a core containing Mg (0.35-0.8%) that provides oxidation protection, and a filler material containing Si (6-13%) and Bi (0.001-0.05%) with restricted Mg (<0.05%) that provides brazeability. This segmentation allows each part to perform its specific function without the drawbacks of the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The core acts as an intermediary that protects the filler material from oxidation. The Mg in the core sacrifices itself to prevent oxidation of the filler material during manufacture and heating, while the filler material maintains low Mg content to ensure good brazeability when needed.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If a thin film of metal with higher melting point is provided on the filler-material surface to prevent oxidation of Mg, then oxidation resistance improves, but it takes more time for the filler material to melt and flow, delaying joint formation and potentially causing brazing failures

Engineering Contradiction:

Improveoxidation resistanceVSAvoidtime to melt and flow

Core Design Contradiction:

Object-affected harmful factorsVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

3Reliability

If strict control of in-furnace environment (oxygen concentration ≤5 ppm, dew point ≤−60°C) is implemented to prevent oxidation, then brazeability improves, but new equipment and processes are required, becoming a major burden for manufacturers

Engineering Contradiction:

ImprovebrazeabilityVSAvoidequipment and process requirements

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The brazing sheet is designed to be self-protecting through its internal structure. The core with Mg content provides inherent oxidation protection to the filler material during manufacture and heating, eliminating the need for external protective measures such as vacuum equipment or strict atmosphere control systems.

Inventive Principle:

Principle #25Self-service

4Reliability

If acid washing or etching treatment is performed to remove surface oxides before brazing, then brazeability improves, but new equipment is required and manufacturing complexity increases

Engineering Contradiction:

ImprovebrazeabilityVSAvoidmanufacturing process simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The oxidation protection is built into the brazing sheet structure during manufacturing. The core with Mg content预先 (in advance) protects the filler material from oxidation during subsequent processing and storage, eliminating the need for preliminary etching or acid washing treatments before brazing.

Inventive Principle:

Principle #10Preliminary action

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 and corrosion resistance, enabling fluxless brazing in common production furnaces with improved brazeability and reduced equipment burdens, while maintaining the external appearance and preventing excessive oxidation.

Implementation Method 1

brazing is performed by making use of the break-up of oxide films by the evaporation of Mg (magnesium) in a material during heating when brazing is being performed

Methodology Applied

Scientific EffectEvaporation: Evaporation

Implementation Method 2

fine oxides are formed from the Mg within the filler material. These oxides function to fragment the dense oxide films present on the surfaces of the filler material, the materials to be joined, and the like

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

Bi has been traditionally used in vacuum-brazing methods... as an element that reduces the surface tension of molten-filler material and improves brazeability

Methodology Applied

Scientific EffectSurface tension reduction: Surfactant

Data Source

PatentUS10661395B2Aluminum-alloy brazing sheet

Publication Date: 2020.05.26 UACJ CORP

AI summary

A brazing sheet for brazing in an inert-gas atmosphere without using a flux has a core and a filler material clad to one side or both sides of the core. The core has a chemical composition that contains Mg: 0.35-0.8% (mass %; likewise hereinbelow), the remainder being composed of Al and unavoidable impurities. The filler material has a chemical composition that contains Si: 6-13% and Bi: 0.001-0.05% and Mg: limited less than 0.05%, the remainder being composed of Al and unavoidable impurities.