Al-Mn Heat Exchanger Fin Material for Post-Braze Strength
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Solution Overview
Problem
Current methods for producing aluminum fin materials for heat exchangers fail to achieve high post-braze strength, sagging resistance, and low susceptibility to liquid core penetration while maintaining adequate formability, especially when downgauging to thinner materials, due to limitations in alloying elements and processing techniques.
Innovation Solution
A method involving precise control of the net driving force for recrystallization during brazing, using an alloy composition of 0.3-1.5% Si, ≤0.5% Fe, ≤0.3% Cu, 1.0-2.0% Mn, ≤0.5% Mg, ≤4.0% Zn, and dispersoid-forming elements, with preheating and multiple rolling stages to create a microstructure of fine particles, which enhances post-braze strength and brazing performance without compromising formability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the fin thickness is reduced to decrease weight, then weight is reduced, but post braze strength deteriorates
Solution Approach 1:
The patent changes the material parameters by optimizing alloy composition (Mn: 0.5-2.0%, Si: 0.3-1.5%, Mg: 0.1-0.5%, Zn: 0.1-4.0%, Fe: ≤0.5%, Cu: ≤0.3%) and processing parameters (preheating temperature: 400-550°C, hot rolling temperature: 300-500°C, cold rolling reduction: 60-95%, annealing temperature: 200-400°C) to achieve a unique microstructure with fine dispersoid particles that provides high strength at reduced thickness
Solution Approach 2:
The patent creates a composite microstructure within the Al-Mn alloy by incorporating multiple alloying elements that form dispersoid particles during controlled processing, resulting in a material that combines the light weight of aluminum with the strength characteristics of a composite material system
2Strength
If Mg content is increased to improve post braze strength, then post braze strength is improved, but sagging resistance during brazing deteriorates
Solution Approach 1:
The patent optimizes the Mg content to a specific range (0.1-0.5%) and combines it with controlled amounts of Mn (0.5-2.0%), Si (0.3-1.5%), and other elements, along with specific heat treatment parameters (preheating 400-550°C, annealing 200-400°C) to achieve the desired balance between strength and sagging resistance
Solution Approach 2:
The patent creates a multi-element alloy system where Mg works synergistically with Mn, Si, Zn, and Fe to form a complex microstructure with dispersoid particles that provides both high strength and good sagging resistance, rather than relying on Mg alone
3Ease of manufacture
If thin strip is delivered in half hard condition to improve formability, then formability is improved, but handling difficulty increases
Solution Approach 1:
The patent delivers the strip in H24 temper with specific mechanical properties (0.2% proof stress: 100-200 MPa, elongation: 3-8%) achieved through controlled cold rolling reduction (60-95%) followed by annealing at 200-400°C, creating an optimal balance between strength and formability for handling and forming operations
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 method achieves high post-braze strength, improved sagging resistance, and reduced liquid core penetration during brazing, along with enhanced formability, allowing for the use of thinner fins with adjustable corrosion potential, suitable for heat exchanger applications.
Implementation Method 1
precise control of the net driving force for recrystallization during brazing
Implementation Method 2
create a microstructure of fine particles
Data Source
Figure 1a~2b
AI summary
The present invention provides a method for producing AlMn strip or sheet for making components by brazing, as well as the products obtained by said method. In particular this method is related to fin materials used in heat exchangers. The fins can be delivered with or without a braze cladding depending on application. Rolling slabs are produced from a melt which contains 0.3-1.5% Si, ≤0.5% Fe, ≤0.3% Cu, 1.0-2.0% Mn, ≤0.5% Mg, ≤4.0% Zn, ≤0.3% each of elements from group IVb, Vb, or VIb elements, and unavoidable impurity elements, as well as aluminium as the remainder in which the rolling slabs prior to hot rolling are preheated at a preheating temperature of less than 550°C, preferably between 400 and 520°C, more preferably between 450 and 520°C to control the number and size of dispersoid particles, and the preheated rolling slab is hot rolled into a hot strip. The strip is thereafter cold rolled into a strip with a total reduction of at least 90%, and the cold rolled strip is heat treated to obtain a 0.2% proof stress value that is 50 - 90% of its proof stress value in the as cold rolled condition to a proof stress value in the range between 100 and 200 MPa. The strip may alternatively be produced by twin-roll strip casting. The composition of the melt tailors the microstructure development during the complete processing to give the desired post braze properties and performance during brazing in combination with adequate delivery properties of the strip. In particular the high post braze strength combined with a good sagging resistance and low susceptibility to liquid core penetration during brazing, as well as a relatively good formability in the delivery condition prior to fin forming.