Al-Mn Heat Exchanger Fin Material for Sagging-Resistant Brazing
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Solution Overview
Problem
Current methods for producing aluminum strips for heat exchangers face challenges in achieving high post-braze strength, sagging resistance, and formability while minimizing corrosion potential, especially when using thin clad fins and slow braze heating cycles, which often result in insufficient properties and susceptibility to liquid core penetration.
Innovation Solution
The production of an aluminum strip with a specific composition and processing method involving controlled cold rolling and heat treatment to achieve a proof stress value of 100-200 MPa, combined with the addition of dispersoid particles and controlled zinc content, to enhance sagging resistance and formability, and adjust corrosion potential for brazing applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strip is delivered in half hard condition with restricted formability to maintain strength, then post braze strength is improved, but formability when forming fins deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the proof stress within a specific range (50-90% of as-cold-rolled strength, corresponding to 100-200 MPa) through controlled cold rolling reduction (90-98%) and specific heat treatment parameters (temperature 300-500°C, time 10-60 minutes). This optimized parameter range simultaneously achieves adequate post-braze strength and sufficient formability for fin forming operations.
2Weight of moving object
If thinner strip is used to reduce weight, then weight reduction is achieved, but sagging resistance and resistance to liquid core penetration deteriorate
Solution Approach 1:
The patent creates a composite microstructure within the aluminum alloy by controlling the formation of dispersoid particles (Al3Mn, Al6Mn) through specific Mn content (1.0-2.0%) and heat treatment. These dispersoid particles act as reinforcement phases that significantly enhance sagging resistance and liquid core penetration resistance, enabling thinner strip usage without compromising reliability.
Solution Approach 2:
The patent optimizes multiple parameters including Mn content (1.0-2.0%), Si content (0.1-0.5%), cold rolling reduction (90-98%), and heat treatment parameters (temperature 300-500°C, time 10-60 minutes) to achieve a proof stress of 100-200 MPa. This parameter optimization enables thinner strip (50-200 μm) to maintain adequate sagging resistance and braze integrity.
3Reliability
If Zn is added to reduce corrosion potential for sacrificial protection, then corrosion resistance is improved, but formability and sagging resistance deteriorate
Solution Approach 1:
The patent optimizes Zn content within a specific range (0.1-1.0%) rather than using high Zn concentrations. This controlled parameter approach, combined with Mn (1.0-2.0%) and Si (0.1-0.5%), achieves adequate corrosion potential for sacrificial protection while maintaining formability and sagging resistance that would be compromised by higher Zn additions.
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 resulting strip exhibits high strength, excellent sagging resistance, low susceptibility to liquid core penetration, and good formability, enabling the use of thinner fins with improved weight reduction in heat exchangers while maintaining brazing performance and corrosion resistance.
Implementation Method 1
cold rolling and heat treatment to achieve a proof stress value of 100-200 MPa
Implementation Method 2
heat treatment to the delivery temper with the purpose to soften the material by a tempering
Implementation Method 3
addition of dispersoid particles and controlled zinc content, to enhance sagging resistance and formability
Implementation Method 4
controlled zinc content, to enhance sagging resistance and formability, and adjust corrosion potential for brazing applications
Data Source
Figure 1~2
Figure 3a~3b
Figure 3b
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 of thin gauge used in heat exchangers. Rolling slabs are produced from a melt which contains <0.3% Si, ≤0.5% Fe, ≤0.3% Cu, 1.0- 2.0% Mn, ≤0.5% Mg, ≤4.0% Zn, ≤ 0.5% Ni,≤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 550o 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, also for thin strip and slow brazing cycles, as well as a relatively good formability in the delivery condition prior to fin forming.