Al-Mn-Zn Fin Material for Corrosion-Resistant Heat Exchangers
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Solution Overview
Problem
Heat exchangers used in automobiles face challenges with corrosion, particularly pitting corrosion and grain boundary corrosion, which affect the durability and strength of fin joints and fins, especially under non-uniform Zn flame-spraying coverage and environmental stressors like acid rain.
Innovation Solution
A heat exchanger design featuring a triple-layer clad fin material with an aluminum alloy core containing Mn and Zn, and an Al-Si alloy brazing filler with controlled Si and Cu content, where the core material's grain structure is recrystallized to reduce grain boundary corrosion, and the brazing process ensures strong fillet formation and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Zn flame-spraying coverage is increased to protect tubes from pitting corrosion, then corrosion resistance of tubes is improved, but grain boundary corrosion of fins is accelerated and fin strength is reduced
Solution Approach 1:
The invention changes the chemical composition parameters of the fin material by adding specific amounts of Zn (0.5-3.0 wt%) and Mn (0.5-1.8 wt%) to the aluminum alloy core, and controls the grain size after brazing (average length 100-1000 μm, 4 or less in thickness direction). These parameter changes enable the fin material to resist grain boundary corrosion even when exposed to high Zn coverage from flame-sprayed tubes, thus resolving the contradiction between tube protection and fin strength maintenance.
2Weight of moving object
If fins are made thin-wall to reduce weight, then weight of heat exchanger is reduced, but durability of fin joints and fin strength is compromised
Solution Approach 1:
The invention uses a composite material structure consisting of an aluminum alloy core material with controlled grain structure and a brazing filler material layer. The core material contains specific Zn and Mn additions that provide corrosion resistance, while the controlled grain structure (few large grains) maintains mechanical strength. This composite approach allows thin-wall fins to achieve both weight reduction and sufficient durability through the synergistic effects of material composition and microstructure control.
3Reliability
If chromate type chemical surface treatment is used to achieve high corrosion-proofing, then corrosion resistance is improved, but environmental restrictions require removal of this treatment
Solution Approach 1:
The invention replaces the chromate-based chemical surface treatment with a sacrificial zinc-rich alloy system. The Zn-containing fin material and Zn flame-sprayed tube surface create a galvanic protection system where zinc acts as a sacrificial anode, corroding preferentially to protect the aluminum alloy structure. This approach eliminates harmful chromate chemicals while providing effective corrosion protection through the sacrificial zinc mechanism, which is environmentally acceptable.
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 enhances the durability and strength of fin joints and fins, maintaining performance even under high Zn flame-spraying coverage and corrosive conditions, improving the heat exchanger's resistance to corrosion and maintaining structural integrity.
Implementation Method 1
the both being joined by brazing
Implementation Method 2
a Zn concentrated layer is formed on the surface of a tube by flame spraying or the like to make this Zn concentrated layer play as a role of a sacrifice material
Implementation Method 3
a Zn concentrated layer is formed on the surface of a tube by flame spraying
Data Source
AI summary
A heat exchanger which has i) a fin material comprising a triple-layer clad material constituted of a core material composed of an aluminum alloy containing from 0.5 to 1.8% by weight of Mn and from 0.5 to 3.0% by weight of Zn and, provided on both sides of the core material, a brazing filler material composed of an Al—Si alloy containing from 6.5 to 13.0% by weight of Si and from 0.15 to 0.60% by weight of Cu and ii) an aluminum alloy tube having a Zn concentrated surface; the both having been brazed with each other; wherein, after brazing, recrystallized grains of the core material have an average length of from 100 to 1,000 μm in the lengthwise section of a fin and the recrystallized grains of the core material are 4 or less in average number in the thickness direction of that lengthwise section. This heat exchanger is improved in the durability of fin joints and fins themselves and their strength after corrosion.