Aluminum Brazing Sheet Precipitate Control
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Solution Overview
Problem
Heat exchangers in automotive applications face challenges with fin material durability due to high-temperature buckling and corrosion, particularly in thinner designs, where existing solutions fail to adequately prevent peeling-off and corrosion at brazed joints, leading to reduced service life and mechanical strength.
Innovation Solution
An aluminum alloy brazing sheet with specific compositions and processing methods, including controlled precipitate ratios and grain sizes, is used to enhance the mechanical strength and corrosion resistance of the fin material, preventing peeling-off and buckling during braze-heating, and maintaining performance in corrosive environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the fin material is made thinner to reduce weight, then weight reduction is achieved, but the mechanical strength is lowered and buckling of the fin occurs at the time of solder melting
Solution Approach 1:
The brazing sheet uses a composite structure with a core alloy (Al-Mn-Fe-Si-Zn) and skin alloys (Al-Si-Fe-Cu) on each surface. This composite material design allows the fin material to be thinner while maintaining mechanical strength through the synergistic effects of different alloy compositions and the precipitate reinforcement mechanism.
Solution Approach 2:
The invention controls the particle size of precipitates (Al-Mn-Fe-based or Al-Mn-Si-based metal compounds) to 0.1 μm or more but less than 3.0 μm, and maintains a specific number density ratio (A/B between 50-500) of coarse to fine precipitates. This precise parameter control of precipitate morphology and distribution enhances the fin material's resistance to high-temperature buckling while enabling thinner designs.
2Weight of moving object
If the fin material is made thinner, then weight reduction is achieved, but the resistance to high-temperature buckling is reduced
Solution Approach 1:
The composite structure of core alloy with skin alloys provides enhanced high-temperature stability. The specific composition ranges (Mn: 0.6-2.0%, Fe: 0.05-0.5%, Si: 0.4-0.9%, Zn: 0.02-4.0% in core alloy) are designed to maintain structural integrity at brazing temperatures while enabling thinner fin designs.
Solution Approach 2:
By controlling precipitate particle size (0.1-3.0 μm) and the number density ratio of coarse to fine precipitates (50-500), the invention optimizes the material's high-temperature buckling resistance. The precipitates act as reinforcement that prevents buckling during solder melting while allowing reduced material thickness.
3Reliability
If chromate-type chemical conversion treatment is used to prevent corrosion, then corrosion resistance is improved, but environmental regulations prohibit its use
Solution Approach 1:
The invention removes the harmful chromate-type chemical conversion treatment from the corrosion prevention system and replaces it with an intrinsic material-based solution. The core alloy composition (Al-Mn-Fe-Si-Zn) and skin alloy (Al-Si-Fe-Cu) are designed to provide corrosion resistance through controlled precipitate formation and electrochemical properties without requiring toxic chemical treatments.
Solution Approach 2:
The invention uses a sacrificial anode mechanism where the fin material (with higher Zn content in skin alloy) corrodes preferentially to protect the aluminum tubular body. This disposable-like sacrificial protection eliminates the need for chromate coatings while providing effective corrosion prevention in a environmentally friendly manner.
4Temperature
If the Si concentration in the core alloy increases during brazing, then the melting point of the core alloy is lowered, but solder erosion of the core alloy and fusion of the core alloy occur
Solution Approach 1:
The invention carefully controls the Si content in the core alloy (0.4-0.9%) and the particle size of Si-containing precipitates (0.1-3.0 μm) to balance melting point reduction with prevention of solder erosion. The controlled precipitate formation ensures that Si is distributed in a manner that lowers melting point sufficiently for brazing while preventing excessive Si concentration that would cause erosion and fusion during the brazing process.
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 effectively prevents preferential corrosion of fillets and peeling-off of fins, ensuring improved durability and extended service life of heat exchangers by enhancing the resistance to high-temperature buckling and corrosion resistance, even in thinner designs.
Implementation Method 1
the brazing sheet having... as a core alloy, an Al alloy containing Mn 0.6 to 2.0 mass%, Fe 0.05 to 0.5%, Si 0.4 to 0.9%, and Zn 0.02 to 4.0%... wherein a ratio A/B of a number density A (particles/mm 2) of coarse precipitates (having a particle size of 0.1 μm or more but less than 3.0 μm) to a number density B (particles/mm 2) of fine precipitates (having a particle size of 3.0 μm or more) of the Al-Mn-Fe-based or Al-Mn-Si-based metal compounds in a longitudinal cross-section of the core alloy before braze-heating satisfies 50 ≤ A/B ≤ 500
Implementation Method 2
At the time of solder melting and heating of a brazing sheet, silicon (Si) in the molten solder diffuses into a core alloy, and the Si concentration in the core alloy increases
Data Source
Figure 1(a)~2
Figure 3
AI summary
An aluminum alloy brazing sheet for heat exchangers, the brazing sheet having, as a core alloy, an Al alloy containing Mn 0.6 to 2.0 mass%, Fe 0.05 to 0.5 mass%, Si 0.4 to 0.9 mass%, and Zn 0.02 to 4.0 mass%, with the balance being Al and unavoidable impurities; and as a skin alloy disposed on each surface of the core alloy, an Al alloy containing Si 6.0 to 13.0 mass%, Fe 0.05 to 0.80 mass%, and Cu 0.05 to 0.45 mass%, with the balance being Al and unavoidable impurities, wherein a ratio A/B of a number density A (particles/mm2) of Al-Mn-Fe-based or Al-Mn-Si-based precipitates having a particle size of 0.1 µm or more but less than 3.0 µm, and a number density B (particles/mm2) of precipitates having a particle size of 3.0 µm or more in the core alloy, satisfies a relationship: 50 ≤ A/B ≤ 500, and wherein an average grain size of the core alloy in a longitudinal cross-section of a fin after braze-heating is 100 µm or more; and a method of producing the same.