Al-Si Sandwich Material High-Temperature Strength
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Solution Overview
Problem
Existing sandwich materials for brazing lack sufficient yield and strength at high temperatures, leading to issues such as silicon penetration during brazing, poor corrosion resistance, and limited fatigue and creep resistance, which are critical for applications like heat exchangers in automobile engines.
Innovation Solution
A sandwich material comprising a core layer with a high manganese content and a barrier layer with a high silicon content, where the layers have similar deformation resistance, allowing for improved adhesion and recrystallization control during rolling, and subsequent heat treatment to form dispersoids that inhibit recrystallization and enhance strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the material is cold worked to increase strength, then the strength increases, but the material may lose the strength increase upon brazing due to recrystallization
Solution Approach 1:
The material is cold worked before brazing to increase strength, and the process is designed so that the material does not recrystallize during brazing, thereby retaining the strength increase. This preliminary strengthening action is maintained through controlled brazing parameters.
Solution Approach 2:
The brazing process parameters (temperature, time, atmosphere) are controlled to prevent recrystallization of the cold-worked material, thereby preserving the strength increase achieved through cold working while still achieving the brazing objective.
2Ease of manufacture
If the material is heated to brazing temperature, then the braze layer melts and forms joints, but silicon from the braze penetrates the material being brazed causing melting or poor seams
Solution Approach 1:
A barrier layer is introduced as an intermediary between the core material and the braze layer. This barrier layer prevents silicon penetration from the braze into the core material during brazing, while still allowing the braze to form proper joints. The barrier layer acts as a mediator that protects the core material from harmful silicon diffusion.
3Manufacturing precision
If a barrier layer is added to prevent silicon penetration, then seam quality improves, but the material structure becomes more complex
Solution Approach 1:
The material is segmented into distinct layers: a core layer and a barrier layer. This segmentation allows each layer to have optimized properties - the core layer provides structural integrity while the barrier layer prevents silicon penetration. The segmentation resolves the contradiction by separating the functions of structural support and silicon protection into different layers.
Solution Approach 2:
The material system becomes a composite structure with a core layer and a barrier layer. This composite approach allows combining materials with different properties - the core material provides mechanical strength while the barrier material provides silicon resistance. The composite structure achieves both good seam quality and controlled complexity through functional differentiation.
4Weight of moving object
If the fin thickness is reduced to save weight, then weight decreases, but the fin strength at high temperature decreases leading to collapse
Solution Approach 1:
The fin material uses a composite structure with a core layer and barrier layer, where the core layer is optimized for high-temperature strength. This allows thin fins to maintain sufficient strength at operating temperatures while achieving weight reduction. The composite structure enables thinner cross-sections without sacrificing load-bearing capacity.
Solution Approach 2:
The material composition parameters are optimized to achieve high strength-to-weight ratio. By controlling the alloying elements and layer thicknesses, the material achieves sufficient high-temperature strength in thinner sections, enabling weight reduction while maintaining structural integrity at operating temperatures.
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 results in a sandwich material with high yield and strength at both low and high temperatures, improved corrosion resistance, and reduced material thickness, leading to weight savings and increased efficiency in heat exchanger production.
Implementation Method 1
The penetration of the silicon occurs by diffusion, melting of the outer layer, or so-called 'liquid film migration'
Implementation Method 2
the material is prevented from recrystallising entirely during the heat treatment which brazing entails
Implementation Method 3
The high silicon content in the braze layer causes the braze layer to melt at lower temperature than the underlying core layer
Implementation Method 4
flow away due to capillary forces and surface tension differences
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a method for making a sandwich material for brazing, comprising the steps of: - providing a core layer of a first alloy that contains (by wt. %): 0.5-2.0% Mn, < 1.0% Mg, < 0.2% Si, < 0.3% Ti, < 0.3% Cr, < 0.3% Zr, < 0.2% Cu, < 3% Zn, < 0.2% In, < 0.1% Sn and < 0.7% (Fe+Ni), the rest Al and <0.05% of each of unavoidable contaminants; - providing a barrier layer of a second alloy that contains (by wt. %): < 0.2% Mn+Cr, < 1.0% Mg, 1. 6-5% Si, < 0.3% Ti, < 0.2% Zr, < 0.2% Cu, < 3 % Zn, < 0.2% In, < 0.1 % Sn and < 1.5% (Fe+Ni), the rest Al and < 0.05% of each of unavoidable contaminants; - rolling the layers together so that they adhere and form a sandwich material; - heat treating the sandwich material at a predetermined temperature and for a predetermined time so that the Si-content is equalised to 0.4-1% in both core layer and barrier layer; - rolling the sandwich material to a final thickness.