Composite Coating for Molten Al-Si Corrosion Resistance
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Solution Overview
Problem
Current corrosion-resistant coatings for molten Al-Si alloy heat exchange tubes in solar thermal power generation systems face issues with porosity, poor bonding, and high internal stress, leading to corrosion and mechanical instability due to the formation of brittle phases and inadequate thermal expansion coefficient matching.
Innovation Solution
A composite coating comprising an aluminized layer, a TiO2 thin film layer, and an Al2O3 thin film layer, applied through a sequence of surface treatment, aluminizing, sand-blasting, and atom layer vapor deposition, to enhance bonding and reduce internal stress, with the TiO2 layer preventing metal penetration and the Al2O3 layer improving thermal expansion coefficient matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer aluminized coating is applied to protect against molten Al-Si alloy corrosion, then corrosion resistance is improved, but bonding strength decreases and porosity increases leading to coating failure
Solution Approach 1:
The patent applies a composite coating structure consisting of an aluminized layer and a ceramic layer (SiO2, TiO2, or ZrO2). The aluminized layer provides corrosion resistance through Al2O3 formation, while the ceramic layer provides a dense, low-porosity barrier that prevents metal penetration and improves bonding. This composite structure resolves the contradiction by combining materials with complementary properties rather than relying on a single-layer coating.
Solution Approach 2:
The ceramic layer acts as an intermediary between the aluminized layer and the molten Al-Si alloy environment. It prevents direct contact between the molten metal and the substrate, blocks penetration paths, and reduces porosity effects. The ceramic layer mediates the interaction between the corrosive environment and the underlying structures, protecting them while maintaining coating integrity.
2Reliability
If ceramic powder (SiO2, TiO2, ZrO2) is doped onto the coating surface to improve corrosion resistance, then corrosion protection is enhanced, but porosity increases allowing Al atoms to penetrate and generate brittle phases
Solution Approach 1:
The patent uses a composite coating where the ceramic layer (SiO2, TiO2, or ZrO2) forms a dense, low-porosity barrier that prevents Al atom penetration. Unlike doped ceramic powder that creates porous structures, the ceramic layer in this composite coating provides continuous coverage that blocks diffusion paths, preventing the formation of brittle intermetallic compounds while maintaining corrosion protection.
Solution Approach 2:
The ceramic layer provides localized dense protection at the coating surface where corrosion attack occurs. This local quality enhancement creates a barrier precisely where needed - at the interface with the molten Al-Si alloy - preventing metal element dissolution without requiring the entire coating structure to be porous or thick.
3Stability of the object's composition
If TiB2 ceramic powder is used in the coating to improve high temperature resistance, then thermal stability is improved, but brittle phases form at temperatures over 400°C causing mechanical property degradation
Solution Approach 1:
The patent changes the ceramic material parameter from TiB2 to alternative ceramics (SiO2, TiO2, or ZrO2) that do not form brittle phases at operating temperatures. This parameter change in material selection resolves the contradiction by selecting ceramics that maintain both thermal stability and mechanical properties at temperatures above 400°C, avoiding the formation of detrimental intermetallic compounds.
Solution Approach 2:
The patent replaces TiB2, which has limited high-temperature stability due to brittle phase formation, with alternative ceramic materials that provide sufficient thermal protection without the degradation issue. This substitution uses materials that are effective for the required service life without the long-term stability problems of TiB2 at elevated temperatures.
4Ease of manufacture
If the coating structure does not match thermal expansion coefficients, then coating application is simplified, but internal stress increases causing coating cracking and peeling
Solution Approach 1:
The composite coating structure with the ceramic layer provides a gradient in thermal expansion properties. The ceramic layer (SiO2, TiO2, or ZrO2) has thermal expansion characteristics that bridge the mismatch between the aluminized layer and the substrate, reducing internal stress accumulation. This layered composite approach simplifies manufacturing while preventing stress-induced failure.
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 composite coating achieves strong bonding, reduced internal stress, and improved corrosion resistance by preventing metal diffusion and enhancing structural stability, resulting in a 73.1% to 82.3% decrease in corrosion rate compared to single-layer coatings.
Implementation Method 1
After aluminum enters an alloy surface, an intermetallic compound (IMC) is formed, and a reaction diffusion area is formed on the surface
Implementation Method 2
when oxidizing, an aluminide surface is provided with an Al2O3 thin film to prevent the continuous reaction between the substrate and the environment
Implementation Method 3
a TiO2 thin film layer and an Al2O3 thin film layer from a surface of a substrate to an outside in sequence by an atom layer vapor deposition
Data Source
AI summary
The invention provides a molten Al—Si alloy corrosion resistant composite coating and a preparation method and application thereof. The composite coating layer comprises an aluminized layer and a TiO2 film layer from a surface of a substrate to the outside in sequence. The preparation method of the coating layer comprises the following steps: (step S1) making a surface treatment to an Fe-based alloy, and then aluminizing with a solid powder penetrant; (step S2) sand-blasting the aluminized Fe-based alloy; (step S3) washing and drying the Fe-based alloy which has been sand-blasted; and (step S4) depositing the TiO2 film layer on a surface of the dried aluminized Fe-based alloy by using an atom layer vapor deposition. The application of the molten Al—Si alloy corrosion resistant composite coating is used for a solar thermal power generation heat exchange tube.