Low-cost gas-phase aluminizing process capable of controlling quality of aluminized layer
By integrating in-situ hydrogen reduction and aluminizing, the problems of oxide contamination and high equipment modification costs in vapor phase aluminizing technology have been solved. This has enabled controllable aluminized layer quality and reduced costs, enhanced adaptability, and suitability for parts with no margin and applications where dry sandblasting is prohibited.
Patent Information
- Application Number
- CN202511244703.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-02
- Publication Date
- 2025-12-02
AI Technical Summary
Existing vapor phase aluminizing technology suffers from problems such as oxide contamination, insufficient process flexibility, and high equipment modification costs, resulting in uneven aluminized layer quality and excessively high processing costs.
The process of in-situ hydrogen reduction and aluminizing is adopted. By preparing an aluminizing agent containing aluminum iron powder, activator, atmosphere conditioner and hydrogen generator, and combining it with staged temperature control, the in-situ reduction of oxides on the surface of parts and the precise control of the aluminizing process are achieved.
This process achieves oxide-free infiltration layer with a clear interface, improves the thermal shock resistance of the infiltration layer, reduces processing costs, and broadens the application range of the process to meet the processing needs of different parts.
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Figure CN121046775A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metal material coating, and in particular relates to a low-cost vapor phase aluminizing process with controllable diffusion layer quality. Background Technology
[0002] With the continuous increase in the operating temperature of hot-end components of aero-engines, higher requirements are placed on the high-temperature oxidation resistance and resistance to combustion gas thermal corrosion of materials. Surface aluminizing technology, as a key protective measure, relies on introducing aluminum elements into the surface of parts to form a dense alumina layer that protects the substrate from corrosion. Currently, the mainstream aluminizing processes include chemical vapor deposition, solid aluminizing, and slurry aluminizing, but all three have significant drawbacks: chemical vapor deposition is complex, has high processing costs, and key equipment and technologies are controlled by developed countries, posing supply chain risks; solid aluminizing and slurry aluminizing methods easily clog pores and internal cavities, making it difficult to clean the aluminizing agent after sintering, and the uniformity of the aluminized layer is poor at sharp corners and small holes.
[0003] Although the vapor phase aluminizing technology developed in recent years has made progress in terms of uniformity of the aluminized layer, production efficiency and environmental protection, the following problems still exist: (1) Oxide contamination of the mold shell: ceramic mold shell contamination may exist on the surface of the casting, resulting in weak points in the aluminized layer; (2) Insufficient process flexibility: for parts with no allowance or in situations where dry sand blowing is prohibited, traditional pretreatment methods are prone to damage the surface and affect the quality of the aluminized layer.
[0004] To address these two issues, one proposed solution is to place the parts in a hydrogen atmosphere for aluminizing. However, this process requires a long-term, large-volume supply of hydrogen, which must be highly pure. Furthermore, it cannot avoid gas vortices caused by tooling design or part structure, resulting in poor reduction in some areas of the part. In addition, most traditional vapor phase aluminizing furnaces are not equipped with a hydrogen supply system, and the cost and time required for hardware and control software modifications are high. Multiple process tests are needed to ensure the processing effect of new parts and tooling. Summary of the Invention
[0005] This invention addresses three major pain points in existing vapor-phase aluminizing technologies: difficulty in removing oxide impurities, reliance on modifications to the hydrogen supply system, and limited process adaptability. It proposes a low-cost vapor-phase aluminizing method that requires no equipment modification and offers controllable aluminized layer quality. The core of this low-cost vapor-phase aluminizing process with controllable aluminized layer quality lies in the integrated design of in-situ hydrogen reduction and aluminizing. The specific technical solution is as follows: (1) Preparation of aluminizing agent: The aluminizing agent includes a main aluminizing agent, an atmosphere conditioner, and a hydrogen generator; the main aluminizing agent includes aluminum iron powder and an activator, the activator including ammonium chloride, ammonium bifluoride, or a mixture thereof; the atmosphere conditioner is aluminum chloride; the hydrogen generator includes calcium hydride, lithium aluminum hydride, and magnesium hydride. The mass of Al in the aluminum-iron powder used in the main permeation agent should be >40%, and the mass of the added activator should be 0.8%-2% of the mass of the aluminum-iron powder; the amount of aluminum chloride atmosphere conditioner should be less than 2% of the mass of the aluminum-iron powder.
[0006] The amount of hydrogen generator used is 0.005%-0.05% of the mass of aluminum-iron powder (calculated based on the mass ratio of releasable hydrogen) or the amount of hydrogen released by the hydrogen generator is 1-10 times the container volume (calculated based on the volume ratio of releasable hydrogen under the decomposition temperature and atmospheric pressure of the hydrogen generator). During the decomposition and reduction stage (800℃-900℃), hydrogen is used to reduce the oxides on the surface of the parts in situ and to act as an electron donor to accelerate the aluminizing process. Some hydrogen generators (such as lithium aluminum hydride) can increase the concentration of active aluminum atoms in the atmosphere during decomposition, which can improve the aluminizing rate.
[0007] (2) Staged temperature-controlled aluminizing: Atmosphere replacement stage: Argon or other inert gases are used to replace the air in the furnace.
[0008] Activation stage of the aluminizing agent: Depending on the selected activator and ratio, the aluminizing agent can be kept at 200℃-450℃ for 1-2 hours to fully activate it. Decomposition and reduction stage: Heat to the decomposition temperature of the selected hydrogen generator, 800℃-900℃, and hold for 2 hours to allow the hydrogen generator to release hydrogen gas and complete the reduction of oxides on the surface of the parts. Vapor phase aluminizing stage: Continue heating to 900℃-1100℃ and hold for 1h-6h to obtain an aluminized layer on the surface of the part.
[0009] By adjusting the temperature and time, the thickness of the aluminized layer can be precisely controlled to be 18μm-65μm, and the aluminum content in the aluminized layer is 23%-32%.
[0010] For parts with no margin, wet sandblasting, ultrasonic cleaning, scouring pad scrubbing, or a combination of several cleaning methods can be used instead of dry sandblasting to clean the surface of the parts before vapor phase aluminizing, thus avoiding changes in the size of the parts.
[0011] Through the above-mentioned technical means, the present invention achieves the following significant advantages: 1. Improved aluminizing layer quality: The aluminized layer is free of oxide contamination, and the interface is clear (e.g., ...). Figure 1-3As shown in the figure, after an oxidation test at 1100℃ / 24h and 1100℃ / 60 cycles of water-cooled thermal shock, there was no peeling or cracking (in Comparative Example 1, cracks appeared after 47 cycles of water-cooled thermal shock). This eliminates contamination of the infiltrated layer by the shell oxide, reduces weak points in the infiltrated layer, and improves the thermal shock resistance of the infiltrated layer. 2. Reduced process cost: This avoids the dependence on specialized equipment in traditional hydrogen reduction processes, saves on equipment hydrogen system modification costs, and the cost of the hydrogen generator is only 1 / 5-1 / 3 of that of traditional hydrogen, further reducing costs. 3. Enhanced adaptability: The thickness of the infiltrated layer can be linearly controlled by temperature-time parameters (18μm-65μm) to meet different processing requirements; it is suitable for parts with no margin and for conditions where dry sandblasting is prohibited, broadening the scope of application of the process. Attached Figure Description
[0012] Figure 1 This is a cross-sectional view of the aluminized layer after vapor-phase aluminizing in Example 1.
[0013] Figure 2 This is a cross-sectional view of the aluminized layer after vapor-phase aluminizing in Example 2.
[0014] Figure 3 This is a cross-sectional view of the aluminized layer after vapor-phase aluminizing in Example 3.
[0015] Figure 4 This is a cross-sectional view of the aluminized layer after vapor-phase aluminizing in Comparative Example 1. Detailed Implementation
[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. It should be noted that the embodiments described in this invention are only for further explanation and illustration, and not for limiting their application scope. Based on this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention.
[0017] The oxidation experiment in the example is as follows: a portion of the aluminized parts is cut as a test piece, and the test piece is placed in an air furnace at 1100℃±10℃ for 23h-27h. After being taken out and air-cooled to room temperature, the surface condition of the test piece is visually inspected and recorded at a distance of 200mm-400mm from the test piece under an ambient illuminance of >750lux.
[0018] The thermal shock test is performed as follows: a specimen of about 40mm×20mm is cut from the aluminized part, the specimen is heated to 1100℃, and after the temperature is balanced, the specimen is taken out and cooled to room temperature with water, which is one thermal shock cycle; after several thermal shock cycles, the surface condition of the specimen is visually inspected and recorded.
[0019] Example 1 K417G high-temperature alloy blades were selected as the base material, and the surface was subjected to wet sandblasting treatment. After cleaning the parts with acetone, they were ultrasonically cleaned in 70℃ hot water for 60 minutes. Aluminizing was then carried out in a 71.6L furnace.
[0020] (1) Preparation of aluminizing agent: The content of each component in the aluminizing agent is as follows: 20 kg of aluminum-iron alloy powder (Al content 47 wt.%), 1.3% of the mass of aluminum-iron powder by activator ammonium chloride, 1% of the mass of aluminum-iron powder by atmosphere conditioner aluminum chloride, and 20 g of calcium hydride hydrogen generator (corresponding to twice the volume of hydrogen gas in the container); the above aluminizing agent is loaded into the aluminizing furnace.
[0021] (2) Staged temperature-controlled aluminizing: The blades were placed in an aluminizing furnace and heated to 450°C in an argon atmosphere for 2 hours for activation. The temperature was then increased to 850°C and held for 2 hours to decompose and reduce the oxides on the surface of the parts. The temperature was then increased to 1000°C and held for 5 hours for vapor-phase aluminizing. The furnace was then cooled to 500°C and then rapidly cooled to room temperature.
[0022] The resulting aluminized layer had a thickness of 50μm-57μm and an aluminum content of 27wt.%. After an oxidation test at 1100℃ for 24 hours and a water-cooled thermal shock test at 1100℃ for 60 cycles, the aluminized layer showed no peeling or cracking. The cross-section of the aluminized layer is shown below. Figure 1 As shown.
[0023] Example 2 K417G high-temperature alloy blades were selected as the base material, and the surface was subjected to dry sandblasting treatment; then ultrasonically cleaned in 70℃ hot water for 15 minutes. Aluminizing was then carried out in a 71.6L furnace.
[0024] (1) Preparation of aluminizing agent: The content of each component in the aluminizing agent is as follows: 20 kg of aluminum-iron alloy powder (Al content 47 wt.%), the mass of the activator ammonium bifluoride is 0.8% of the mass of the aluminum-iron powder, the mass of the atmosphere conditioner aluminum chloride is 1.9% of the mass of the aluminum-iron powder, and the hydrogen generator lithium aluminum hydride 10 g (corresponding to 0.005 wt.% hydrogen content); the above aluminizing agent is loaded into the aluminizing furnace.
[0025] (2) Staged temperature-controlled aluminizing: The substrate was placed in an aluminizing furnace and activated at 250°C for 2 hours in an argon atmosphere; then heated to 800°C and held for 2 hours; then heated to 1000°C and held for 2.5 hours for vapor-phase aluminizing; and then cooled to 500°C in the furnace and then rapidly cooled to room temperature.
[0026] The resulting aluminized layer had a thickness of 28μm-34μm and an aluminum content of 23wt.%. After an oxidation test at 1100℃ for 24 hours and a water-cooled thermal shock test at 1100℃ for 60 cycles, the aluminized layer showed no peeling or cracking. The cross-section of the aluminized layer is shown below. Figure 2 As shown.
[0027] Example 3 K417G high-temperature alloy blades were selected as the base material, and sandblasting was prohibited. After cleaning the parts with acetone and wiping them manually, they were ultrasonically cleaned in 70°C hot water for 60 minutes. Aluminizing was then carried out in a 71.6L furnace.
[0028] (1) Preparation of aluminizing agent: The contents of each component in the aluminizing agent are as follows: 20 kg of aluminum-iron alloy powder (Al content 48 wt.%), 1.7% of the mass of aluminum-iron powder by the activator ammonium chloride, 0.2% of the mass of aluminum-iron powder by the atmosphere conditioner aluminum chloride, and 50 g of magnesium hydride hydrogen generator (corresponding to 8 times the volume of hydrogen gas in the container); the above aluminizing agent is loaded into the aluminizing furnace.
[0029] (2) Staged temperature-controlled aluminizing: The matrix was placed in an aluminizing furnace and activated at 450°C for 2 hours in an argon atmosphere; then heated to 900°C and held for 2 hours; then heated to 1000°C and held for 2 hours for vapor-phase aluminizing; and then cooled to 500°C in the furnace and then rapidly cooled to room temperature.
[0030] The resulting aluminized layer had a thickness of 21μm-27μm and an aluminum content of 24wt.%. After an oxidation test at 1100℃ for 24 hours and a water-cooled thermal shock test at 1100℃ for 60 cycles, the aluminized layer showed no peeling or cracking. The cross-section of the aluminized layer is shown below. Figure 3 As shown.
[0031] Comparative Example 1 The difference between this comparative example and Example 1 is that no atmosphere conditioner and hydrogen generator are added, and alumina is added to ensure that the quality of the aluminizing agent remains unchanged. Other preparation methods are the same as in Example 1.
[0032] The same K417G high-temperature alloy blades as in Example 1 were used as the substrate; the surface was subjected to wet sandblasting treatment; after cleaning the parts with acetone, they were ultrasonically cleaned in 70°C hot water for 60 minutes. Aluminizing was then carried out in a 71.6L furnace.
[0033] (1) Preparation of aluminizing agent: The content of each component in the aluminizing agent is as follows: 20 kg of aluminum-iron alloy powder (Al content 47 wt.%), 1.3% of the mass of aluminum-iron powder by the activator ammonium chloride, and 1.1% of the mass of aluminum-iron powder by alumina (without added aluminum chloride and calcium hydride); the above aluminizing agent is loaded into the aluminizing furnace.
[0034] (2) Staged temperature-controlled aluminizing: The blades were placed in an aluminizing furnace and activated at 450°C for 2 hours in an argon atmosphere. Then, the temperature was raised to 850°C and held for 2 hours to decompose and reduce the oxides on the blade surface. The temperature was then raised to 1000°C and held for 5 hours for vapor-phase aluminizing. The furnace was then cooled to 500°C and then rapidly cooled to room temperature.
[0035] The resulting aluminized layer has a thickness of 25μm-34μm, an aluminum content of 23wt.%, and exhibits significant oxide contamination, such as... Figure 4 As indicated by the arrow in the image; after an oxidation test at 1100℃ for 24 hours, there was no peeling or cracking. However, after 47 cycles of water-cooled thermal shock at 1100℃, cracks appeared on the surface of the infiltrated layer.
Claims
1. A low-cost vapor-phase aluminizing process with controllable aluminizing layer quality, characterized in that, Includes the following: (1) Preparation of aluminizing agent: The aluminizing agent includes a main aluminizing agent, an atmosphere conditioner, and a hydrogen generator; the main aluminizing agent includes aluminum iron powder and an activator, the activator including ammonium chloride, ammonium bifluoride, or a mixture thereof; the atmosphere conditioner is aluminum chloride; the hydrogen generator includes calcium hydride, lithium aluminum hydride, and magnesium hydride. (2) Staged temperature-controlled aluminizing: Atmosphere replacement stage: Inert gas is used to replace the air in the furnace; Activation stage of the aluminizing agent: First, keep it at 200℃-450℃ for 1-2 hours to fully activate the aluminizing agent; Decomposition and reduction stage: Heat to 800℃-900℃ and hold for 2 hours to allow the hydrogen generator to release hydrogen gas and complete the reduction of oxides on the surface of the parts; Vapor phase aluminizing stage: continue heating to 900℃-1100℃ and hold for 1h-6h; an aluminized layer is obtained on the surface of the part.
2. The low-cost vapor-phase aluminizing process with controllable aluminizing layer quality according to claim 1, characterized in that, The mass of Al in the aluminum-iron powder is >40%.
3. The low-cost vapor-phase aluminizing process with controllable aluminizing layer quality according to claim 1, characterized in that, The activator has a mass of 0.8%-2% of the aluminum-iron powder mass.
4. The low-cost vapor-phase aluminizing process with controllable aluminizing layer quality according to claim 1, characterized in that, The mass of the atmosphere conditioner is less than 2% of the mass of the aluminum-iron powder.
5. The low-cost vapor-phase aluminizing process with controllable aluminizing layer quality according to claim 1, characterized in that, The amount of hydrogen generator used is 0.005%-0.05% of the mass of aluminum-iron powder, or the amount of hydrogen gas released by the hydrogen generator when heated is 1-10 times the container volume.
6. The low-cost vapor-phase aluminizing process with controllable aluminizing layer quality according to claim 1, characterized in that, The thickness of the aluminized layer is 18μm-65μm, and the aluminum content in the aluminized layer is 23%-32%.
7. The low-cost vapor-phase aluminizing process with controllable aluminizing layer quality according to claim 1, characterized in that, For parts with no allowance, wet sandblasting, ultrasonic cleaning, scouring pad scrubbing, or a combination of these cleaning methods can be used to clean the surface of the parts before aluminum infiltration to avoid changes in the size of the parts.