Al-Mn Brazing Sheet Composition for Corrosion-Resistant Heat Exchangers
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Solution Overview
Problem
Conventional aluminium brazing sheets used in heat exchangers face challenges in achieving a balance between post-braze strength, formability, and corrosion resistance, with limitations in preventing detrimental galvanic coupling and maintaining mechanical integrity.
Innovation Solution
An Al-Mn alloy sheet material with specific composition and manufacturing processes, including direct chill casting and continuous casting techniques, is developed to enhance post-braze yield strength and corrosion resistance, featuring a core alloy with controlled Mn, Si, Fe, Cu, Mg, Cr, Zr, and Zn content, and a brazing layer for improved thermal communication and corrosion protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional aluminium brazing sheets with 4xxx-series brazing clad layers are used, then brazing performance is achieved, but post-braze strength is insufficient and galvanic coupling occurs
Solution Approach 1:
The patent changes the chemical composition parameters of the core alloy by specifying precise ranges for Mn (1.50-1.80%), Si (0.10-0.45%), Fe (0.10-0.40%), Cu (≤0.07%), Mg (0.01-0.25%), Zn (≤0.25%), Ti (≤0.20%), and Cr+Zr (0.08-0.25%). This compositional optimization resolves the contradiction by achieving both high post-braze strength (>40 MPa yield strength) and corrosion resistance through controlled alloying elements that prevent galvanic coupling while maintaining mechanical integrity.
Solution Approach 2:
The patent creates a composite structure with a specifically formulated Al-Mn-Si-Fe-Cu-Mg-Zn-Ti-Cr-Zr core alloy combined with a 4xxx-series aluminium brazing clad layer. This composite material design allows the core alloy to provide structural strength and corrosion resistance while the clad layer provides brazing functionality, resolving the contradiction between strength and corrosion resistance by optimizing the interaction between layers.
2Strength
If higher strength alloys are used to improve post-braze strength, then mechanical integrity is enhanced, but formability deteriorates
Solution Approach 1:
The patent optimizes the alloy composition parameters to achieve a balance between strength and formability. By controlling Mn content at 1.50-1.80% (not excessively high) and adding specific amounts of Mg (0.01-0.25%) and Zn (≤0.25%), the material achieves post-braze yield strength >40 MPa while maintaining good formability for heat exchanger manufacturing processes such as rolling and forming.
Solution Approach 2:
The patent applies local quality by creating a layered structure where the core alloy provides the necessary strength and formability balance, while the brazing clad layer provides surface-level brazing functionality. This allows different regions of the material to have optimized properties for their specific functions, resolving the contradiction between overall strength and local formability.
3Ease of manufacture
If aluminium brazing clad layers with liquidus temperature of 540°C to 615°C are used, then brazing process is enabled, but galvanic coupling and corrosion resistance are compromised
Solution Approach 1:
The patent changes the electrochemical parameters of the core alloy by optimizing the composition with Mn (1.50-1.80%), Si (0.10-0.45%), and Cr+Zr (0.08-0.25%), which adjusts the corrosion potential to be compatible with the 4xxx-series brazing clad layer. This prevents detrimental galvanic coupling while maintaining the brazing capability enabled by the clad layer's liquidus temperature range of 540°C to 615°C.
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 Al-Mn alloy sheet material achieves high post-braze yield strength (>40 MPa) and tensile strength (>115 MPa) while maintaining good formability and corrosion resistance, effectively preventing galvanic coupling and ensuring reliable performance in heat exchanger components.
Implementation Method 1
a plurality of corrugated aluminium alloy fins being in thermal communication with said plurality of fluid-carrying tubes and structured to transfer heat away therefrom
Data Source
Figure 1
AI summary
Described herein is a brazed heat exchanger comprising at least one header, manifold and/or tube structured to hold a coolant or refrigerant; said header, manifold, and/or tube component including a plurality of apertures; a plurality of substantially parallel fluid-carrying tubes each extending substantially perpendicular from one of said plurality of apertures in said header plate, manifold, and/or tube component and structured to receive said coolant or refrigerant therethrough; and a plurality of corrugated aluminium alloy fins being in thermal communication with said plurality of fluid-carrying tubes and structured to transfer heat away therefrom. The header, manifold, and/or tube component is made from an aluminium alloy sheet material comprising, in wt.%: Mn 1.4%-1.8%; Si up to 0.7%; Fe up to 0.7%; Mg up to 0.30%; Cu up to 0.10%; Cr up to 0.25%; Zr up to 0.25%; Zn up to 0.50%; Ti up to 0.2%; balance aluminium and inevitable impurities.