Brazed Aluminum Strip Interlayer for Corrosion and Core Penetration
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Solution Overview
Problem
Current materials for brazed heat exchangers face challenges in achieving high post-braze strength combined with excellent corrosion resistance and resistance to liquid core penetration, especially when using thinner strips, which is crucial for weight reduction in automotive applications.
Innovation Solution
A corrosion-resistant strip is developed with a core and an interlayer composition that includes specific elements like Mn, Si, and Cu, where the interlayer has a controlled texture component and grain size, and is processed to minimize recrystallization during brazing, resulting in a strip that is highly resistant to liquid core penetration and maintains formability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If thinner strip materials are used to reduce weight, then weight is reduced, but post-braze strength and corrosion resistance deteriorate
Solution Approach 1:
The strip is segmented into multiple functional layers: a core material providing structural strength and an intermediate layer providing corrosion resistance and controlling liquid core penetration. This segmentation allows each layer to be optimized for its specific function, enabling thinner overall thickness while maintaining strength and corrosion resistance.
Solution Approach 2:
The invention uses a composite structure combining different aluminum alloys in the core and intermediate layer. The core uses an Al-Mn-Si alloy for strength, while the intermediate layer uses a different composition optimized for corrosion resistance and brazing performance. This composite approach allows the thin strip to achieve properties that neither material could provide alone.
2Weight of moving object
If thinner strip materials are used to reduce weight, then weight is reduced, but corrosion resistance deteriorates
Solution Approach 1:
The strip is segmented into multiple functional layers: a core material providing structural strength and an intermediate layer providing corrosion resistance and controlling liquid core penetration. This segmentation allows each layer to be optimized for its specific function, enabling thinner overall thickness while maintaining strength and corrosion resistance.
Solution Approach 2:
Different regions of the strip are given different compositions and properties: the core has properties optimized for strength, while the intermediate layer has properties optimized for corrosion resistance and brazing. This local differentiation of material properties allows the thin strip to achieve superior overall performance.
3Ease of manufacture
If conventional materials are used, then manufacturing is simple, but resistance to liquid core penetration deteriorates
Solution Approach 1:
The invention changes the compositional parameters of the intermediate layer, specifically controlling Si, Mn, Mg, and Fe content within precise ranges. These parameter changes create an intermediate layer that is resistant to liquid core penetration while maintaining ease of manufacture through conventional rolling and brazing processes.
Solution Approach 2:
The invention uses a composite structure combining different aluminum alloys in the core and intermediate layer. The core uses an Al-Mn-Si alloy for strength, while the intermediate layer uses a different composition optimized for corrosion resistance and brazing. This composite approach allows the thin strip to achieve properties that neither material could provide alone.
4Strength
If high post-braze strength is achieved through material alloying, then strength is improved, but corrosion resistance deteriorates
Solution Approach 1:
The strip is segmented into multiple functional layers: a core material providing structural strength and an intermediate layer providing corrosion resistance and controlling liquid core penetration. This segmentation allows each layer to be optimized for its specific function, enabling thinner overall thickness while maintaining strength and corrosion resistance.
Solution Approach 2:
The invention uses a composite structure combining different aluminum alloys in the core and intermediate layer. The core uses an Al-Mn-Si alloy for strength, while the intermediate layer uses a different composition optimized for corrosion resistance and brazing. This composite approach allows the thin strip to achieve properties that neither material could provide alone.
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 strip achieves superior post-braze corrosion properties, high strength, and excellent brazing performance with low susceptibility to liquid core penetration, enabling the use of thinner materials while maintaining product integrity.
Implementation Method 1
the interlayer is pre-heated to a temperature of 380-520°C prior to hot rolling so as to form dispersoid particles in the interlayer
Implementation Method 2
heat treating the cold rolled strip to the delivery temper with the purpose to soften the material by a tempering without any recrystallisation of the interlayer
Implementation Method 3
The lower corrosion potential on the surface is due to the existence of more manganese and copper in solid solution in the core centre than in the core surface. This is due to diffusion of especially silicon and copper between the core and the braze clad
Implementation Method 4
The joints form by capillary flow of the filler metal to the desired joint sites and solidify to form a solid metallic connection between individual components
Implementation Method 5
The joints form by capillary flow of the filler metal to the desired joint sites
Data Source
Figure 1a~2c
Figure 3a~4
Figure 5
AI summary
A corrosion resistant strip is disclosed. The strip comprises a core, and an interlayer adapted to be located between the core and an optional Al-Si based clad. The interlayer has a composition essentially consisting of (in percentages by weight): Si≤0.9%, Fe≤0.7%, Cu≤0.5%, Mn0.5-1.8%, Mg≤0.7%, Zn≤4.0%, Ni≤1.5%, elements selected from group IVb, Vb, and/or VIb of the periodic table ≤0.3% each and ≤0.5% in total ≤0.05 wt% each and ≤0.15 % in total, of unavoidable impurity elements, balance Al. The core is more noble than the interlayer after brazing. The interlayer exhibits a volume fraction of a texture component of at least 30%.