Heat Exchanger Fin Alloy Composition for Brazing Strength
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Solution Overview
Problem
Existing aluminum alloy fin materials for heat exchangers face challenges in achieving both high strength after brazing and excellent brazability, with previous solutions either compromising on durability or melting point.
Innovation Solution
The development of an aluminum alloy fin material with controlled chemical composition and metal structure, utilizing a twin-roll type continuous casting rolling method, and specific annealing and cold rolling processes to optimize the distribution of second-phase grains and solute atoms, ensuring high perimeter density and melting point, thereby enhancing strength and brazability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of the fin material is reduced to achieve weight reduction, then the weight decreases, but the strength after brazing heating becomes insufficient
Solution Approach 1:
The invention changes the chemical composition parameters of the aluminum alloy by precisely controlling the content ranges of Si (0.01-5 mass%), Fe (0.01-3 mass%), Mn (0.1-5 mass%), Cu (0.01-5 mass%), and Zn (0.1-10 mass%). This composition optimization enables the material to achieve both high strength after brazing and good brazability, resolving the contradiction between weight reduction and strength maintenance
Solution Approach 2:
The invention creates a composite microstructure consisting of Al-Mn-based intermetallic compounds, Al-Mn-Fe-based intermetallic compounds, and solid solution strengthened aluminum matrix. This composite structure provides both the strength needed to compensate for thinning and the appropriate melting point for good brazability
2Strength
If the concentration of Si, Fe, Cu, and Mn is increased to improve strength after brazing, then the strength increases, but the melting point decreases making brazability difficult to secure
Solution Approach 1:
The invention optimizes the parameter ranges of alloying elements to balance strength and melting point. Specifically, it controls Si at 0.01-5 mass%, Fe at 0.01-3 mass%, Mn at 0.1-5 mass%, Cu at 0.01-5 mass%, and Zn at 0.1-10 mass%. This balanced composition achieves high strength while maintaining a melting point of 570°C or higher, ensuring good brazability
Solution Approach 2:
The invention creates local intermetallic compound phases (Al-Mn-based and Al-Mn-Fe-based) distributed in the aluminum matrix. These localized high-strength phases provide the needed strength after brazing without requiring overall increases in alloying element concentrations that would lower the melting point
3Strength
If the concentration of Si and Fe is optimized to achieve high strength after brazing (141 MPa), then the strength improves, but the durability of the heat exchanger becomes questionable
Solution Approach 1:
The invention creates a composite structure with Al-Mn-based intermetallic compounds, Al-Mn-Fe-based intermetallic compounds, and solid solution strengthened matrix. This composite provides both high strength (145 MPa or higher) and improved durability through the sacrificial anode effect of Mn and Zn, which protect the base metal from corrosion
Solution Approach 2:
The invention introduces Mn and Zn as intermediary elements that provide sacrificial anode protection. These elements preferentially corrode to protect the aluminum base metal, thereby improving the overall durability and corrosion resistance of the heat exchanger while maintaining high strength
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 aluminum alloy fin material exhibits improved strength after brazing heating and excellent brazability, suitable for use in automotive heat exchangers, allowing for reduced thickness and enhanced performance.
Implementation Method 1
formation of an Al—Mn based intermetallic compound, an Al—Mn—Fe based intermetallic compound, an Al—Mn—Si based intermetallic compound, an Al—Mn—Cu based intermetallic compound, an Al—Mn—Fe—Si based intermetallic compound, and an Al—Mn—Fe—Cu based intermetallic compound
Implementation Method 2
the solute atoms have large solid solution
Implementation Method 3
adopting a twin-roll type continuous casting rolling method as the casting method
Implementation Method 4
properly controlling the heating temperature in annealing before the cold rolling pass, between passes, and after the pass in the cold rolling process
Implementation Method 5
properly controlling the rolling shape ratio of cold rolling
Implementation Method 6
Brazing joint is performed by a process of heating a constituent element including a brazing material to approximately 600° C., supplying a molten brazing filler metal to the joint
Data Source
AI summary
An aluminum alloy fin material for a heat exchanger is made of an aluminum alloy including 0.05 mass % to 0.5 mass % of Si, 0.05 mass % to 0.7 mass % of Fe, 10 mass % to 2.0 mass % of Mn, 0.5 mass % to 1.5 mass % of Cu, and 3.0 mass % to 7.0 mass % of Zn, with the balance being Al and unavoidable impurities. In an L-ST plane thereof, second-phase grains having an equivalent circle diameter equal to or more than 0.030 μm and less than 0.50 μm have a perimeter density of 0.30 μm/μm2 or more, second-phase grains having an equivalent circle diameter equal to or more than 0.50 μm have a perimeter density of 0.030 μm/μm2 or more, and specific resistance thereof at 20° C. is 0.030 μΩm or more.