Aluminum Heat Exchanger Core Composition for Brazed Joint Corrosion
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Solution Overview
Problem
Conventional heat exchanger cores experience early corrosion of brazed joints and fin materials when tubes with sprayed Zn coatings are combined with certain fin materials, leading to decreased corrosion resistance.
Innovation Solution
A heat exchanger core design with specific chemical compositions for fins and tubes, combined with a sacrificial anode layer formed on the outer surface of the tubes during brazing in a zinc vapor atmosphere, ensuring optimal natural electrode potentials to enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fin material with high Si content is used to improve brazing performance, then brazed joint strength is improved, but electrode potential difference increases causing early corrosion
Solution Approach 1:
The invention optimizes the Si content parameter within a specific range (2.0-3.0 mass%) rather than using high Si content. This balanced parameter selection achieves adequate brazing performance while controlling the electrode potential of the fin material to prevent excessive potential difference with Zn-coated tubes, thereby avoiding early corrosion.
Solution Approach 2:
The invention applies different compositional requirements to different elements within the fin material. Specifically, Si is controlled at 2.0-3.0 mass% for brazing performance, while Zn is controlled at 0.3-5.0 mass% to adjust electrode potential. This localized optimization of each element's content resolves the contradiction between joint strength and corrosion resistance.
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 design achieves a heat exchanger core with improved corrosion resistance by adjusting the natural electrode potentials of the fin, tube, and brazed joint regions, preventing early corrosion and maintaining structural integrity.
Implementation Method 1
a sacrificial anode layer, which has a natural electrode potential lower than that at an inner surface of the tube(s), is formed on an outer surface of the tube(s)
Implementation Method 2
by heating the assembly and performing brazing of the assembly in an atmosphere containing zinc vapor, the brazed joint(s) form(s) between the fin(s) and the tube(s)
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A heat exchanger core (1) has fins (2), tubes (3), and brazed joints (4) that join the fins (2) and the tubes (3). The fins (2) are composed of an aluminum alloy, which has a chemical composition comprising Si: 2.0 to 3.0 mass%, Fe: 0.05 to 1.2 mass%, Cu: 0.25 mass% or less, Mn: 0.3 to 1.8 mass%, and Zn: 0.3 to 5.0 mass%, the balance consisting of Al and unavoidable impurities. The tubes (3) are composed of an aluminum alloy extruded material containing Cu: more than 0.05 mass% and 0.6 mass% or less. A sacrificial anode layer (31) is formed on the outer surface of the tubes (3). The natural electrode potential of the sacrificial anode layer (31), the natural electrode potential of the inner surface of the tubes (3), the natural electrode potential of fillets in the brazed joints (4), and the natural electrode potential of the fins (2) satisfy specific conditions.