Aluminum alloy thin-walled part casting metal mold coating and its preparation method and application

Abstract

The application belongs to the technical field of metal part coating, and particularly relates to an aluminum alloy thin-walled part casting metal mold coating, a preparation method thereof and application. The aluminum alloy thin-walled part casting metal mold coating comprises the following raw materials: 30-50% dispersion medium, 10-20% high-temperature binder, 5-10% high-temperature lubricant, 10-40% functional filler 1, 10-25% functional filler 2, 1-3% rheological additive and 0.5-2% process additive. The metal mold coating provided by the application has the ability to absorb and release latent heat. The application further provides a preparation method thereof. By controlling the feeding sequence and stirring conditions, it is ensured that the light hollow microbeads are not damaged, the nanoparticles are fully dispersed, the composite phase change material structure is complete, and finally the coating product with uniform and stable performance is obtained. The coating is used in the production of aluminum alloy thin-walled complex castings in casting and die casting processes.

Description

Technical Field

[0001] This invention belongs to the field of metal coating technology, specifically relating to metal mold coatings for casting thin-walled aluminum alloy parts, their preparation methods and applications. Background Technology

[0002] With the automotive, aerospace, and electronics and communications industries moving towards lightweighting, the application of thin-walled aluminum alloy components (such as automotive subframes, transfer case housings, and heat sink housings) is becoming increasingly widespread. These castings typically feature complex structures, thin walls (often 2-5 mm), large projected areas, and high dimensional accuracy requirements. When using metal molds for casting, the forming process faces a series of unique and interconnected core challenges.

[0003] Among the various challenges, filling difficulties are the primary issue. Since mold temperatures are typically much lower than molten aluminum temperatures, the window for optimal flowability is extremely short. For thin-walled, complex structures, the molten aluminum tends to solidify prematurely at the end of the runner or in thin-walled areas before completely filling the cavity, leading to defects such as cold shuts and incomplete filling, resulting in low yields. Simultaneously, solidification stress and deformation are significant problems. Differences in wall thickness across different parts of the casting cause severely uneven cooling rates. Thin-walled areas cool quickly and solidify and shrink first, while thick-walled areas or hot spots cool slowly and solidify and shrink later. This uncoordinated shrinkage process generates enormous thermal stress within the casting, easily causing warping, deformation, and even thermal cracking, severely impacting dimensional accuracy and structural integrity.

[0004] In addition, local hot spots formed in the wall thickness transition zone and the intersection of ribs, where the feeding channels are narrow or even blocked by the pre-solidified thin walls, make it difficult for the molten aluminum to be effectively fed, thus forming shrinkage porosity and shrinkage defects in these areas, which damage the airtightness and mechanical properties of the casting.

[0005] Besides internal quality defects, the interface between the casting and the mold is equally critical. When molten aluminum (approximately 700°C) comes into contact with the mold steel surface, a slight interfacial chemical reaction and welding tendency can easily occur. During casting demolding, this can cause the casting surface material to adhere to the mold, not only damaging the appearance quality of the casting and increasing cleaning costs, but also, in the long run, damaging the surface finish and dimensions of the mold cavity, thus reducing the mold's lifespan.

[0006] To address these challenges, applying a functional coating to the mold cavity surface is a crucial process in casting. An ideal coating should provide multiple functions, including heat insulation, regulating solidification sequence, assisting demolding, and protecting the mold. However, existing traditional mold coatings are mostly designed for general applications, exhibiting significant limitations in functionality and performance when dealing with high-performance thin-walled aluminum alloy parts.

[0007] While graphite-based coatings, which are currently widely used, have excellent thermal conductivity and self-lubrication properties, resulting in good demolding performance, their high thermal conductivity can drastically accelerate heat exchange between the mold and the molten aluminum, causing thin-walled areas to cool faster. This not only worsens the flowability of the casting but also exacerbates the temperature difference between different parts of the casting, leading to more prominent thermal stress and deformation problems.

[0008] Zinc oxide or talc-based coatings possess certain thermal insulation properties, but their insulation effect is unstable, and they have poor resistance to high-temperature molten aluminum erosion and repeated thermal cycling. The coating is prone to sintering, cracking, and peeling. After several uses, their thermal insulation performance deteriorates significantly, failing to guarantee the stability and consistency of casting quality.

[0009] While ordinary ceramic coatings offer better thermal insulation, they are typically thick and brittle in order to achieve sufficient strength and insulation. For thin-walled parts with extremely high dimensional accuracy requirements, excessively thick coatings can severely affect the dimensions of the casting, and the brittle coating is prone to cracking and peeling under thermal shock, with the flaking material potentially becoming part of the casting and forming inclusions. Furthermore, some ceramic materials may react adversely with molten aluminum. Summary of the Invention

[0010] The technical problem this invention aims to solve is to overcome the aforementioned deficiencies in existing technologies, providing a metal mold coating for casting thin-walled aluminum alloy parts. This coating possesses the ability to absorb and release latent heat. Furthermore, this invention provides a scientifically sound preparation method. By controlling the feeding sequence and stirring conditions, it ensures that the lightweight hollow microspheres are not damaged, the nanoparticles are fully dispersed, and the composite phase change material structure remains intact, ultimately yielding a coating product with uniform and stable performance. This coating can be applied to the production of complex thin-walled aluminum alloy castings in processes such as gravity casting, low-pressure casting, and die casting.

[0011] The metal mold coating for casting thin-walled aluminum alloy parts of the present invention comprises, by weight percentage, the following raw materials: 30%~50% dispersion medium, 10%~20% high-temperature binder, 5%~10% high-temperature lubricant, 10%~40% functional filler 1; 10%~25% functional filler 2, 1%~3% rheology modifier, and 0.5%~2% process aid;

[0012] Functional filler 1 is a mixture of inorganic hydrated salt, paraffin wax, silica aerogel, and activated alumina. This mixture is designed as a composite phase change heat storage material, with inorganic hydrated salt and paraffin wax serving as the core material, and silica aerogel and activated alumina serving as the porous wall material. The core material is encapsulated within the network pores of the wall material. This structure endows the coating with active "heat storage-release" capabilities, absorbing the impact heat from the molten metal during casting and releasing heat during the subsequent filling stage to delay the solidification of the molten metal, thereby stabilizing the temperature of the mold working surface. The inorganic hydrated salt is Na2SO4•10H2O.

[0013] Functional filler 2 is a mixture of hollow ceramic microspheres and nano-zirconia. It mainly provides excellent thermal insulation properties and enhances the thermal barrier and wear resistance of the coating.

[0014] The dispersion medium is deionized water; the high-temperature lubricant is flake graphite and / or boron nitride. When both flake graphite and boron nitride are included, their mass ratio is 70%–90%:10%–30%. Flake graphite provides excellent general lubricity, while boron nitride maintains stable lubrication at higher temperatures.

[0015] The high-temperature binder is a mixture of silica sol and aluminum dihydrogen phosphate, wherein the mass ratio of silica sol to aluminum dihydrogen phosphate is 3:1 to 1:1. Silica sol provides medium-temperature bond strength and coating density, while aluminum dihydrogen phosphate provides high-temperature ceramic bonding strength.

[0016] In the functional filler 1, the ratio of the total mass of inorganic hydrated salts and paraffin to the total mass of silica aerogel and activated alumina is 2:1. This ratio balances the heat storage capacity with the structural stability of the carrier.

[0017] In the functional filler 2, the mass ratio of hollow ceramic microspheres to nano-zirconia is 70%~85%:15%~30%. This ratio optimizes the synergy between thermal insulation effect and high-temperature strength of the coating.

[0018] The rheology modifiers are sodium carboxymethyl cellulose and bentonite, with a mass ratio of 60%~80%:20%~40%. Bentonite provides thixotropy and suspension properties, while sodium carboxymethyl cellulose provides viscosity and water retention.

[0019] The process aids are defoamers and wetting agents. The defoamers are organosilicon or mineral oil, preferably polydimethylsiloxane or modified polysiloxane. The wetting agents are nonionic surfactants, preferably acetylenic diols or fatty alcohol polyoxyethylene ethers.

[0020] The method for preparing the metal mold coating for casting thin-walled aluminum alloy parts includes the following steps:

[0021] (1) Preparation of base liquid: In a low-speed stirring tank, add dispersion medium, add rheology modifier while stirring, continue stirring to swell and hydrate, then add process aid, continue stirring to obtain base liquid;

[0022] (2) Premixing and adding of adhesive: Mix the high-temperature adhesive, and add the mixed adhesive to the base liquid in step (1) while stirring. Stir until fully mixed to obtain a mixed solution;

[0023] (3) Dispersion of functional filler 2: Under high-speed shear, hollow ceramic microspheres are first added to the mixed solution obtained in step (2) and fully dispersed. Then nano-zirconia and high-temperature lubricant are added and high-speed shear is maintained to obtain slurry.

[0024] (4) Protective addition of functional filler 1: Inorganic hydrated salt and paraffin are melted and mixed, and then mixed and impregnated with pre-activated silica aerogel and activated alumina porous carrier under vacuum conditions at 60~80℃. After cooling, the mixture is ground to obtain composite phase change thermal storage material. Then the composite phase change thermal storage material is added in batches to the slurry obtained in step (3) and mixed.

[0025] (5) Aging and viscosity adjustment: The slurry mixed in step (4) is sealed and aged for 6~8 hours to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

[0026] Step (1) Add rheology modifier under stirring at 300~400 rpm, continue stirring to swell and hydrate, then add process additive, increase the speed to 450~500 rpm and continue stirring; Step (2) Mix high temperature binder, add this mixed binder to the base liquid in step (1) under stirring speed of 350~450 rpm, increase the speed to 750~850 rpm and stir to fully blend.

[0027] In step (3), hollow ceramic microspheres are added to the mixed solution obtained in step (2) under high-speed shearing at 1200~1500 rpm.

[0028] Application of the coating for casting thin-walled aluminum alloy parts: The prepared coating is sprayed onto the metal mold that has been preheated to 180~220℃ using a spray gun, with a coating thickness of 0.03~0.3mm. Then, it is placed at 350~400℃ for sintering for 50~60 minutes and then removed.

[0029] This invention employs a coupling of "dynamic thermal management" and "structure / function integration." Functional filler 1 (composite phase change material) acts as a thermal buffer unit in the coating, absorbing or releasing a large amount of latent heat within a specific temperature range through the phase change process of inorganic hydrated salts and paraffin. Its porous wall material (silica aerogel and activated alumina) not only encapsulates the core material to prevent leakage but also contributes additional insulation and a high specific surface area, enhancing heat exchange efficiency. Functional filler 2 (insulation-enhancing filler) forms a static thermal resistance framework in the coating. Hollow ceramic microspheres provide extremely low heat conduction paths, while nano-zirconia fills the gaps and strengthens the high-temperature strength of the coating. The synergy of these two components transforms the coating from a simple passive insulation layer into an adaptive thermal regulation system: when high-temperature molten metal impacts, the phase change material rapidly absorbs heat, preventing a sudden rise in mold surface temperature; simultaneously, the insulation framework maximizes the barrier against heat transfer to the mold matrix; during the temperature drop phase, the phase change material releases heat to compensate for cavity heat loss, maintaining a more uniform and durable ideal temperature field. This organic combination of dynamic heat storage / release and static insulation fundamentally optimizes the thermal cycle in the casting process, making it particularly suitable for casting thin-walled aluminum alloy parts that are sensitive to temperature and have a fast solidification rate, thus achieving a technological leap from heat insulation to intelligent heat regulation.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) The metal mold coating for casting thin-walled aluminum alloy parts of the present invention combines composite phase change heat storage material (functional filler 1) with high-performance heat insulation material (functional filler 2) and composite lubrication system, so that the coating not only has excellent passive heat insulation and lubrication demolding performance, but also gives it active "heat storage-heat release" intelligent temperature regulation capability, which can effectively homogenize the temperature field of the working surface of the mold, and is particularly suitable for casting thin-walled aluminum alloy parts that are sensitive to thermal cycling, thereby reducing casting defects caused by sudden heat changes from the root.

[0032] (2) The preparation method of the metal mold coating for casting thin-walled aluminum alloy parts of the present invention adopts a stepwise dispersion and protective addition process. First, high-speed shearing ensures the uniform dispersion of nanofillers and hollow microspheres, constructing a stable slurry matrix. Subsequently, the pre-encapsulated composite phase change material is gently mixed in, maximizing the protection of the integrity of its micro-nano structure during processing and avoiding core material leakage or functional failure. This method ensures the reliability and consistency of the final performance of the coating.

[0033] (3) The coating of the present invention is sprayed onto a preheated metal mold. After medium-temperature sintering, the binder system can be fully ceramicized, so that the functional filler is firmly bonded in the dense coating network. This application process can stably achieve the thin, uniform and tough functional coating required by the design, and is easy to apply in actual production, ensuring that its intelligent temperature regulation and long-term protection effects are stably performed during the casting process. Attached Figure Description

[0034] Figure 1 The image shows an X-ray image of the aluminum alloy product produced from the mold after spraying in Example 1, which is a non-destructive test result.

[0035] Figure 2 This is an X-ray image of the aluminum alloy product produced from the mold after spraying in Example 2, showing the results of non-destructive testing.

[0036] Figure 3 This is an X-ray image of the aluminum alloy product produced from the mold after spraying in Example 3, showing the results of non-destructive testing.

[0037] Figure 4 This is an X-ray image of the aluminum alloy product produced from the mold after spraying in Example 4, showing the results of non-destructive testing.

[0038] Figure 5 X-ray image of aluminum alloy products produced from the mold after spraying, for comparison example 1.

[0039] Figure 6 X-ray images of aluminum alloy products produced from the mold after spraying, for comparison example 2, for non-destructive testing.

[0040] Figure 7 X-ray images of aluminum alloy products produced from the mold after spraying, for comparison example 3, for non-destructive testing.

[0041] Figure 8 X-ray images of aluminum alloy products produced from the mold after spraying, for comparison example 4, for non-destructive testing.

[0042] Figure 9 X-ray images of aluminum alloy products produced from the mold after spraying, for comparison example 5, for non-destructive testing. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments.

[0044] Unless otherwise specified, all raw materials and additives used in this invention are commercially available products.

[0045] Flake graphite: Commercially available from Qingdao Heilong graphite, with a carbon content of over 90% and a particle size of 325 mesh.

[0046] Hexagonal boron nitride: Commercially available from Zibo Qifeng Technology Co., Ltd., high-purity product with BN content of over 99.9%, white in color.

[0047] Hollow ceramic microspheres: Commercially available from Aluminum Corporation of China Limited, with a true density of 0.15~0.60 g / cm³, a strength of 60MPa~100MPa, and an average particle size (D50) of 100~150μm.

[0048] Bentonite is sodium-based bentonite.

[0049] Paraffin wax: Commercially available from China Petrochemical Corporation, melting point above 60℃: 0.5%-2.0% semi-refined wax.

[0050] Silica aerogel: The main commercial source is Zhejiang Nano Technology Co., Ltd., with a thermal conductivity of 0.015~0.025W / (m·K), a density of 180~250kg / m³ (including reinforcing fibers), a porosity of 80%~99.8%, and pores at the nanoscale (<100nm).

[0051] Specifically, the preparation method of the metal mold coating for casting thin-walled aluminum alloy parts includes the following steps:

[0052] (1) Preparation of base solution: In a low-speed stirring tank, add deionized water, and slowly add sodium carboxymethyl cellulose and bentonite in sequence while stirring at 300~400 rpm. After the addition is complete, increase the speed to 450~500 rpm and stir for 30 min to allow it to swell and hydrate, forming a uniform viscous liquid. Then add defoamer and wetting agent, and continue stirring for 10 min to obtain the base solution; the mass ratio of sodium carboxymethyl cellulose and bentonite is 60%~80%:20%~40%.

[0053] (2) Premixing and adding the binder: In another container, mix the silica sol and aluminum dihydrogen phosphate in a mass ratio of 3:1 to 1:1. Add this mixed binder to the base liquid in step (1) at a stirring speed of 350 to 450 rpm. After adding, increase the speed to 750 to 850 rpm and continue stirring for 20 minutes to fully integrate it and obtain a mixed solution.

[0054] (3) Dispersion of functional filler 2: Under high-speed shear at 1200~1500rpm, hollow ceramic microspheres were first added to the mixed solution obtained in step (2) and stirred for 15min to initially disperse them by utilizing their low density characteristics. Then, under continuous high-speed shear, nano-zirconia and high-temperature lubricant (flake graphite / boron nitride) were added and high-speed shear dispersion was maintained for 60min until the slurry was fine and uniform with no obvious particle feel, and the slurry was obtained; the mass ratio of hollow ceramic microspheres to nano-zirconia was 70%~85%:15%~30%;

[0055] (4) Protective addition of functional filler 1: Inorganic hydrated salt and paraffin are melted and mixed, and then mixed and impregnated with pre-activated silica aerogel and activated alumina porous carrier under vacuum conditions at 60-80℃. After cooling, the mixture is ground to obtain composite phase change thermal storage material. Then, the composite phase change thermal storage material is added in batches to the slurry obtained in step (3) and stirred at a stirring speed of 400~600rpm for 30min. The mass ratio of inorganic hydrated salt and paraffin to silica aerogel and activated alumina is 2:1.

[0056] (5) Aging and viscosity adjustment: The slurry after mixing in step (4) is transferred into a low-speed mixing tank at 200 rpm and aged in a sealed container for 6-8 hours to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

[0057] Example 1

[0058] The aforementioned metal mold coating for casting thin-walled aluminum alloy parts comprises, by mass percentage, the following raw materials: 35% deionized water, 15% a mixture of silica sol and aluminum dihydrogen phosphate (mass ratio 2:1), 5% flake graphite, 25% functional filler 1, 16% functional filler 2, 2% a mixture of sodium carboxymethyl cellulose and bentonite (mass ratio 70%:30%), 1% polydimethylsiloxane, and 1% fatty alcohol polyoxyethylene ether.

[0059] The method for preparing the metal mold coating for casting thin-walled aluminum alloy parts includes the following steps:

[0060] (1) Preparation of base solution: In a low-speed stirring tank, add deionized water, and slowly add sodium carboxymethyl cellulose and bentonite in sequence while stirring at 350 rpm. After the addition is complete, increase the speed to 480 rpm and stir for 30 min to allow it to swell and hydrate, forming a uniform viscous liquid. Then add polydimethylsiloxane and fatty alcohol polyoxyethylene ether, and continue stirring for 10 min to obtain the base solution.

[0061] (2) Premixing and adding the binder: In another container, the silica sol and aluminum dihydrogen phosphate are mixed evenly according to the mass ratio. The mixed binder is added to the base liquid in step (1) at a stirring speed of 400 rpm. After the addition is complete, the speed is increased to 800 rpm and the stirring is continued for 20 minutes to fully integrate it and obtain a mixed solution.

[0062] (3) Dispersion of functional filler 2: Under high-speed shear at 1300 rpm, hollow ceramic microspheres were first added to the mixed solution obtained in step (2), and stirred for 15 min. Then, under continuous high-speed shear, nano-zirconia and flake graphite were added, and high-speed shear dispersion was maintained for 60 min until the slurry was fine and uniform with no obvious particle feel. The functional filler 2 is a mixture of hollow ceramic microspheres and nano-zirconia with a mass ratio of 75%:25%.

[0063] (4) Protective addition of functional filler 1: Na2SO4•10H2O is melted and mixed with paraffin, and then mixed and impregnated with pre-activated silica aerogel and active alumina porous carrier at 70°C and vacuum for 40 min. After cooling, it is ground to obtain composite phase change thermal storage material. Then, this composite phase change thermal storage material is added to the slurry obtained in step (3) in 5 batches and stirred at 500 rpm for 30 min.

[0064] Functional filler 1 is a mixture of Na2SO4•10H2O, paraffin wax, silica aerogel, and activated alumina in a mass ratio of 2:2:1:1;

[0065] (5) Aging and viscosity adjustment: The slurry after mixing in step (4) is transferred into a low-speed mixing tank at 200 rpm and aged in a sealed container for 7 hours to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

[0066] Application: Apply the coating obtained above to a preheated metal mold (H13 low-pressure casting mold) using a spray gun. Then, sinter the mold at a set temperature of 380°C for 60 minutes and remove it after cooling.

[0067] Example 2

[0068] The aforementioned metal mold coating for casting thin-walled aluminum alloy parts comprises, by mass percentage, the following raw materials: 40% deionized water, 18% silica sol and aluminum dihydrogen phosphate mixture (mass ratio 1.5:1), 8% hexagonal boron nitride, 20% functional filler 1, 10% functional filler 2, 2% sodium carboxymethyl cellulose and bentonite mixture (mass ratio 60%:40%), 1% polydimethylsiloxane, and 1% fatty alcohol polyoxyethylene ether.

[0069] The method for preparing the metal mold coating for casting thin-walled aluminum alloy parts includes the following steps:

[0070] (1) Preparation of base solution: In a low-speed stirring tank, add deionized water, and slowly add sodium carboxymethyl cellulose and bentonite in sequence while stirring at 300 rpm. After the addition is complete, increase the speed to 500 rpm and stir for 30 min to allow it to swell and hydrate, forming a uniform viscous liquid. Then add polydimethylsiloxane and fatty alcohol polyoxyethylene ether, and continue stirring for 10 min to obtain the base solution.

[0071] (2) Premixing and adding the binder: In another container, the silica sol and aluminum dihydrogen phosphate are mixed evenly at a mass ratio of 1.5:1. The mixed binder is added to the base liquid in step (1) at a stirring speed of 450 rpm. After the addition is complete, the speed is increased to 850 rpm and the stirring is continued for 20 minutes to fully integrate it and obtain a mixed solution.

[0072] (3) Dispersion of functional filler 2: Under high-speed shear at 1400 rpm, hollow ceramic microspheres were first added to the mixed solution obtained in step (2), and stirred for 15 min. Then, under continuous high-speed shear, nano-zirconia and hexagonal boron nitride were added, and high-speed shear dispersion was maintained for 60 min until the slurry was fine and uniform with no obvious particle feel. The functional filler 2 is a mixture of hollow ceramic microspheres and nano-zirconia with a mass ratio of 70%:30%.

[0073] (4) Protective addition of functional filler 1: Na2SO4•10H2O is melted and mixed with paraffin, and then mixed and impregnated with pre-activated silica aerogel and activated alumina porous carrier at 75°C and vacuum for 40 min. After cooling, it is ground to obtain composite phase change thermal storage material. Then, this composite phase change thermal storage material is added to the slurry obtained in step (3) in 5 batches and stirred at 550 rpm for 30 min. Functional filler 1 is a mixture of Na2SO4•10H2O, paraffin, silica aerogel and activated alumina in a mass ratio of 2:2:1:1.

[0074] (5) Aging and viscosity adjustment: The slurry after mixing in step (4) is transferred into a low-speed mixing tank at 200 rpm and aged in a sealed container for 8 hours to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

[0075] Application: Apply the coating obtained above to a preheated metal mold (H13 low-pressure casting mold) using a spray gun. Then, sinter the mold at a set temperature of 380°C for 60 minutes and remove it after cooling.

[0076] Example 3

[0077] The aforementioned metal mold coating for casting thin-walled aluminum alloy parts comprises, by mass percentage, the following raw materials: 32% deionized water, 12% a mixture of silica sol and aluminum dihydrogen phosphate (mass ratio 3:1), 10% a mixture of flake graphite and hexagonal boron nitride (mass ratio 1:1), 31% functional filler 1, 10% functional filler 2, 3% a mixture of sodium carboxymethyl cellulose and bentonite (mass ratio 80%:20%), 1% polydimethylsiloxane, and 1% fatty alcohol polyoxyethylene ether.

[0078] The method for preparing the metal mold coating for casting thin-walled aluminum alloy parts includes the following steps:

[0079] (1) Preparation of base solution: In a low-speed stirring tank, add deionized water, and slowly add sodium carboxymethyl cellulose and bentonite in sequence while stirring at 380 rpm. After the addition is complete, increase the speed to 450 rpm and stir for 30 min to allow it to swell and hydrate, forming a uniform viscous liquid. Then add polydimethylsiloxane and fatty alcohol polyoxyethylene ether, and continue stirring for 10 min to obtain the base solution.

[0080] (2) Premixing and adding of binder: In another container, silica sol and aluminum dihydrogen phosphate are mixed evenly at a mass ratio of 3:1. At a stirring speed of 350 rpm, this mixed binder is added to the base liquid in step (1). After the addition is complete, the speed is increased to 750 rpm and the mixture is stirred for 20 minutes to fully integrate it and obtain a mixed solution.

[0081] (3) Dispersion of functional filler 2: Under high-speed shear at 1200 rpm, hollow ceramic microspheres were first added to the mixed solution obtained in step (2), and stirred for 15 min. Then, under continuous high-speed shear, nano-zirconia, flake graphite and hexagonal boron nitride were added and dispersed under high-speed shear for 60 min until the slurry was fine and uniform and had no obvious particle feel. The functional filler 2 was a mixture of hollow ceramic microspheres and nano-zirconia with a mass ratio of 85%:15%.

[0082] (4) Protective addition of functional filler 1: Na2SO4•10H2O is melted and mixed with paraffin, and then mixed and impregnated with pre-activated silica aerogel and activated alumina porous carrier at 65°C and vacuum for 40 min. After cooling, it is ground to obtain composite phase change thermal storage material. Then, this composite phase change thermal storage material is added to the slurry obtained in step (3) in 5 batches and stirred at 600 rpm for 30 min. Functional filler 1 is a mixture of Na2SO4•10H2O, paraffin, silica aerogel and activated alumina in a mass ratio of 2:2:1:1.

[0083] (5) Aging and viscosity adjustment: The slurry after mixing in step (4) is transferred into a low-speed mixing tank at 200 rpm and aged in a sealed container for 6 hours to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

[0084] Application: Apply the coating obtained above to a preheated metal mold (H13 low-pressure casting mold) using a spray gun. Then, sinter the mold at a set temperature of 380°C for 60 minutes and remove it after cooling.

[0085] Example 4

[0086] The aforementioned metal mold coating for casting thin-walled aluminum alloy parts comprises, by mass percentage, the following raw materials: 45% deionized water, 11% mixture of silica sol and aluminum dihydrogen phosphate (mass ratio 1:1), 6% hexagonal boron nitride, 10% functional filler 1, 25% functional filler 2, 1% mixture of sodium carboxymethyl cellulose and bentonite (mass ratio 70%:30%), 1% polydimethylsiloxane, and 1% fatty alcohol polyoxyethylene ether.

[0087] The method for preparing the metal mold coating for casting thin-walled aluminum alloy parts includes the following steps:

[0088] (1) Preparation of base solution: In a low-speed stirring tank, add deionized water, and slowly add sodium carboxymethyl cellulose and bentonite in sequence while stirring at 400 rpm. After the addition is complete, increase the speed to 470 rpm and stir for 30 min to allow it to swell and hydrate, forming a uniform viscous liquid. Then add polydimethylsiloxane and fatty alcohol polyoxyethylene ether, and continue stirring for 10 min to obtain the base solution.

[0089] (2) Premixing and adding of binder: In another container, silica sol and aluminum dihydrogen phosphate are mixed evenly at a mass ratio of 1:1. At a stirring speed of 420 rpm, this mixed binder is added to the base liquid in step (1). After the addition is complete, the speed is increased to 820 rpm and the stirring is continued for 20 minutes to fully integrate it and obtain a mixed solution.

[0090] (3) Dispersion of functional filler 2: Under high-speed shear at 1500 rpm, hollow ceramic microspheres were first added to the mixed solution obtained in step (2), and stirred for 15 min. Then, under continuous high-speed shear, surface-treated nano-zirconia and hexagonal boron nitride were added, and high-speed shear dispersion was maintained for 60 min until the slurry was fine and uniform with no obvious particle feel. The functional filler 2 was a mixture of hollow ceramic microspheres and nano-zirconia with a mass ratio of 75%:25%.

[0091] (4) Protective addition of functional filler 1: Na2SO4•10H2O is melted and mixed with paraffin, and then mixed and impregnated with pre-activated silica aerogel and activated alumina porous carrier at 80°C and vacuum for 40 min. After cooling, it is ground to obtain composite phase change heat storage material. Then, this composite phase change heat storage material is added to the slurry obtained in step (3) in 5 batches and stirred at 400 rpm for 30 min. Functional filler 1 is a mixture of Na2SO4•10H2O, paraffin, silica aerogel and activated alumina in a mass ratio of 2:2:1:1.

[0092] (5) Aging and viscosity adjustment: The slurry after mixing in step (4) is transferred into a low-speed mixing tank at 200 rpm and aged in a sealed container for 7.5 h to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

[0093] Application: Apply the coating obtained above to a preheated metal mold (H13 low-pressure casting mold) using a spray gun. Then, sinter the mold at a set temperature of 380°C for 60 minutes and remove it after cooling.

[0094] Comparative Example 1

[0095] Compared with Example 1, the formulation of functional filler 1 in this comparative example is changed. Functional filler 1 is replaced with "functional filler 1 is a mixture of Na2SO4•10H2O and paraffin wax in a mass ratio of 2:2", and silica aerogel and activated alumina are no longer added. That is, step (4) is replaced with: (4) Protective addition of functional filler 1: Na2SO4•10H2O and paraffin wax are melted and mixed to obtain a mixed material. Then, this mixed material is added to the slurry obtained in step (3) in 5 equal batches and stirred at 500 rpm for 30 min.

[0096] The same method as in Example 1 is used for application.

[0097] Comparative Example 2

[0098] Compared with Example 2, this comparative example removes functional filler 2. The metal mold coating for casting thin-walled aluminum alloy parts comprises the following raw materials by mass percentage: 40% deionized water, 18% silica sol and aluminum dihydrogen phosphate mixture (mass ratio 1.5:1), 8% hexagonal boron nitride, 30% functional filler 1, 2% sodium carboxymethyl cellulose and bentonite mixture (mass ratio 60%:40%), 1% polydimethylsiloxane, and 1% fatty alcohol polyoxyethylene ether.

[0099] Then the corresponding step (3) is removed, and step (4) directly uses the mixed solution from step (2).

[0100] The same method as in Example 2 is used for application.

[0101] Comparative Example 3

[0102] Compared with Example 1, this comparative example changes the type and proportion of high-temperature adhesive.

[0103] The metal mold coating for casting thin-walled aluminum alloy parts comprises, by weight percentage, the following raw materials: 35% deionized water, 15% single silica sol, 5% flake graphite, 25% functional filler 1 (same as Example 1), 16% functional filler 2 (same as Example 1), 2% mixture of sodium carboxymethyl cellulose and bentonite (mass ratio 70%:30%), 1% polydimethylsiloxane, and 1% fatty alcohol polyoxyethylene ether.

[0104] Preparation method: In step (2), silica sol is directly added as a binder, and the remaining steps are exactly the same as in Example 1.

[0105] Application: Same as in Example 1.

[0106] Comparative Example 4

[0107] Compared with Example 2, this comparative example changed the functional filler 2, using only hollow ceramic microspheres.

[0108] In the aforementioned metal mold coating for casting thin-walled aluminum alloy parts, the functional filler 2 is replaced with hollow ceramic microspheres (i.e., no nano-zirconia is added), and its total mass percentage remains 10%. The types and proportions of the remaining raw materials are exactly the same as in Example 2.

[0109] Preparation method: In step (3), only hollow ceramic microspheres are added for dispersion, and no nano-zirconia is added. The remaining steps are exactly the same as in Example 2.

[0110] Application: Same as in Example 2.

[0111] Comparative Example 5

[0112] Compared with Example 3, this comparative example changes the process of adding functional filler 1; the raw material ratio of the metal mold coating for casting thin-walled aluminum alloy parts is exactly the same as that in Example 3.

[0113] Preparation method: Only step (4) is changed. The composite phase change thermal storage material is added to the slurry obtained in step (3) all at once and stirred at 600 rpm for 30 min. The remaining steps are exactly the same as in Example 3.

[0114] Application: Same as in Example 3.

[0115] (1) The coatings prepared in the above examples and comparative examples were tested according to the standard, and the test results are shown in Table 1. Suspension stability: The coatings were left to stand for a specified time, and the volume ratio of the solid phase sedimentation between the upper and lower layers was measured.

[0116] Table 1 Test Results

[0117]

[0118] (2) The coatings prepared in the above examples and comparative examples were applied to metal molds after spraying, and their performance was tested. The results are shown in Table 2.

[0119] Table 2. Inspection results of metal molds after spraying.

[0120]

[0121] (3) Casting production tests were conducted on the molds after spraying in the above embodiments and comparative examples.

[0122] The molds used in the examples and comparative examples were preheated to 450°C after spraying. Then, molten aluminum (prepared according to A356) was poured in for low-pressure casting. The mold temperature and low-pressure casting machine parameters are shown in Tables 3 and 4. The cast aluminum alloy products underwent non-destructive testing. The X-ray magnification was 5x. Figure 1-9 As shown.

[0123] Table 3 Mold Temperature: °C

[0124]

[0125] Table 4 Low-pressure compressor parameters

[0126]

Claims

1. A metal mold coating for casting thin-walled aluminum alloy parts, characterized in that: By weight percentage, it includes the following raw materials: 30%~50% dispersion medium, 10%~20% high-temperature binder, 5%~10% high-temperature lubricant, 10%~40% functional filler 1; 10%~25% functional filler 2, 1%~3% rheology modifier, and 0.5%~2% process aid; Functional filler 1 is a mixture of inorganic hydrated salt, paraffin, silica aerogel and activated alumina, with the mass ratio of inorganic hydrated salt and paraffin to silica aerogel and activated alumina being 2:

1. Functional filler 2 is a mixture of hollow ceramic microspheres and nano-zirconia, with a mass ratio of hollow ceramic microspheres to nano-zirconia of 70%~85%:15%~30%; The high-temperature binder is a mixture of silica sol and aluminum dihydrogen phosphate, wherein the mass ratio of silica sol to aluminum dihydrogen phosphate is 3:1 to 1:

1.

2. The metal mold coating for casting thin-walled aluminum alloy parts according to claim 1, characterized in that: The dispersion medium is deionized water; the high-temperature lubricant is flake graphite and / or boron nitride.

3. The metal mold coating for casting thin-walled aluminum alloy parts according to claim 1, characterized in that: The rheology modifiers are sodium carboxymethyl cellulose and bentonite, with a mass ratio of 60%~80%:20%~40%.

4. The metal mold coating for casting thin-walled aluminum alloy parts according to claim 1, characterized in that: The process aids are defoamers and wetting agents. The defoamers are silicone-based or mineral oil-based, and the wetting agents are nonionic surfactants.

5. A method for preparing a metal mold coating for casting thin-walled aluminum alloy parts according to any one of claims 1-4, characterized in that: Includes the following steps: (1) Preparation of base liquid: In a low-speed stirring tank, add dispersion medium, add rheology modifier while stirring, continue stirring to swell and hydrate, then add process aid, continue stirring to obtain base liquid; (2) Premixing and adding of adhesive: Mix the high-temperature adhesive and add it to the base liquid in step (1) while stirring. Stir until fully mixed to obtain a mixed solution. (3) Dispersion of functional filler 2: Under high-speed shear, hollow ceramic microspheres are first added to the mixed solution obtained in step (2) and fully dispersed. Then nano-zirconia and high-temperature lubricant are added and high-speed shear is maintained to obtain slurry. (4) Protective addition of functional filler 1: Inorganic hydrated salt and paraffin are melted and mixed, and then mixed and impregnated with pre-activated silica aerogel and activated alumina porous carrier under vacuum conditions at 60~80℃. After cooling, the mixture is ground to obtain composite phase change thermal storage material. Then the composite phase change thermal storage material is added in batches to the slurry obtained in step (3) and mixed. (5) Aging and viscosity adjustment: The slurry mixed in step (4) is sealed and aged for 6~8 hours to obtain a metal mold coating for casting thin-walled aluminum alloy parts.

6. The method for preparing the metal mold coating for casting thin-walled aluminum alloy parts according to claim 5, characterized in that: Step (1) Add rheology modifier under stirring at 300~400 rpm, continue stirring to swell and hydrate, then add process aid, increase the speed to 450~500 rpm and continue stirring; Step (2) Mix high temperature binder, add this mixed binder to the base liquid in step (1) under stirring speed of 350~450 rpm, increase the speed to 750~850 rpm and stir to fully blend; Step (3) Under high speed shear at 1200~1500 rpm, first add hollow ceramic microspheres to the mixed solution obtained in step (2).

7. The application of a metal mold coating for casting thin-walled aluminum alloy parts according to any one of claims 1-4, characterized in that: The prepared coating is sprayed onto a metal mold that has been preheated to 180~220℃ using a spray gun, with a coating thickness of 0.03~0.3mm. Then it is sintered at 350~400℃ for 50~60 minutes and then removed.

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