Aluminium Fin Alloy Composition for Brazed Heat Exchanger Strength
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Solution Overview
Problem
Current finstock materials for brazed heat exchangers face challenges in balancing high strength and conductivity after brazing with sufficient sag resistance and sacrificial protection, often compromising thermal performance due to rapid corrosion or reduced strength.
Innovation Solution
An aluminium finstock alloy composition of 0.8-1.25% Fe, 0.8-1.25% Si, 0.7-1.5% Mn, 0.05-0.5% Cu, with optional Zn, and controlled microstructure to maintain strength and conductivity, featuring fine intermetallic particles and a pancake grain structure for enhanced sag resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the finstock material uses traditional 3XXX series aluminium alloy with manganese, then the material provides good sacrificial protection and thermal conductivity, but the strength after brazing is insufficient and sag resistance is compromised
Solution Approach 1:
The patent changes the chemical composition parameters by adding Fe (0.5-1.5%), Si (0.5-1.5%), and Cu (0.1-0.5%) to the traditional Al-Mn alloy system. This parameter change transforms the alloy from a conventional 3XXX series to a modified composition that achieves both high strength after brazing (≥140MPa) and adequate sacrificial protection, resolving the contradiction between strength and reliability.
Solution Approach 2:
The patent creates a composite microstructure containing multiple intermetallic phases (Al-Fe-Si, Al-Cu, Al-Mn) within the aluminium matrix. This composite material approach allows the finstock to simultaneously achieve high strength through intermetallic reinforcement and maintain sacrificial protection through controlled corrosion behavior, addressing the contradiction between strength and reliability.
2Weight of moving object
If the finstock material is made thinner to reduce weight, then weight reduction is achieved, but strength and sag resistance deteriorate
Solution Approach 1:
The patent modifies the alloy composition parameters to include Fe, Si, and Cu additions that enable high strength at reduced thickness. The controlled microstructure with fine intermetallic particles provides reinforcement that allows thin-gauge finstock (0.5-1.5mm) to achieve ≥140MPa strength after brazing, resolving the contradiction between weight reduction and strength maintenance.
Solution Approach 2:
The patent creates a segmented microstructure with distributed intermetallic particles throughout the aluminium matrix. This segmentation at the microscale provides reinforcement throughout the material, enabling thin-gauge finstock to maintain high strength and sag resistance while reducing overall weight.
3Strength
If the finstock material uses higher alloy content to increase strength, then strength after brazing improves, but thermal conductivity and electrical conductivity decrease
Solution Approach 1:
The patent optimizes the alloy composition parameters by carefully controlling the amounts of Fe (0.5-1.5%), Si (0.5-1.5%), and Cu (0.1-0.5%). This controlled parameter change achieves high strength through intermetallic formation while limiting the total alloy content to minimize impact on thermal and electrical conductivity, resolving the contradiction between strength and energy loss.
Solution Approach 2:
The patent creates local quality differences by forming discrete intermetallic particles distributed throughout the aluminium matrix. The intermetallics provide strength locally at particle sites, while the aluminium matrix maintains good thermal and electrical conductivity in the bulk material, resolving the contradiction between strength enhancement and conductivity preservation.
4Strength
If the finstock material uses rapid cooling to refine grain structure for strength, then strength improves, but sag resistance during brazing deteriorates
Solution Approach 1:
The patent changes the cooling rate parameter from rapid cooling to controlled moderate cooling (1-10°C/s). This parameter change allows the formation of a pancake grain structure with appropriate size and morphology that provides both strength after brazing and sag resistance during the high-temperature brazing process, resolving the contradiction between strength and temperature resistance.
Solution Approach 2:
The patent creates equipotentiality in the grain structure by forming a uniform pancake grain morphology throughout the material. This equiaxed pancake grain structure provides consistent mechanical properties and sag resistance across the entire finstock, while the intermetallic particles provide uniform strength enhancement, resolving the contradiction between strength and temperature resistance.
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 achieves high post-brazing strength (≥140MPa) and electrical conductivity (≥46% IACS) while maintaining sacrificial protection and thermal efficiency, even at thin gauges, effectively addressing the balance of properties and weight reduction needs.
Implementation Method 1
It is common practice to make the fins electronegative relative to the tubes so that the fins act as sacrificial anodes
Implementation Method 2
Sag resistance is resistance to high temperature creep during the brazing cycle
Implementation Method 3
The fins and tubes are usually joined in a brazing operation
Data Source
Figure 1
AI summary
The present invention relates to an aluminium alloy product for use as a finstock material within brazed heat exchangers and, more particularly, to a finstock material having high strength and conductivity after brazing. The invention is an aluminium alloy finstock comprising the following composition in weight %: Fe 0.8-1.25; Si 0.8-1.25; Mn 0.70-1.50; Cu 0.05-0.50; Zn up to 2.5; other elements less than or equal to 0.05 each and less than or equal to 0.15 in total; and balance aluminium. The invention also relates to a method of making the finstock material.