Modified chromium aluminum phosphate coating as well as application and application method thereof

Abstract

The invention discloses a modified chromium aluminum phosphate coating as well as application and an application method thereof. The modified chromium aluminum phosphate coating is prepared from the following components in parts by weight: 1 to 30 parts of Al3Cr (H2PO4) 12, 10 to 50 parts of Al (H2PO4) 3, 50 to 80 parts of H2O and 40 to 70 parts of Al2O3 powder. The preparation method comprises the following steps: dipping and lifting a cast aluminum alloy in the prepared modified chromium aluminum phosphate coating, and treating by adopting a steam-assisted curing device to obtain the ceramic coating. By using Al (H2PO4) 3 and Al3Cr (H2PO4) 12, low-temperature curing can be achieved, microcracks on the surface of the coating are improved, the coating which is more uniform and smoother and tightly combined with a base body is formed, and better corrosion resistance and durability are achieved; the method has the characteristics of simple operation steps, short preparation period and the like, and the prepared ceramic coating has better durability and corrosion resistance and has great practical value.

Description

Technical Field

[0001] The invention relates to a modified chromium aluminum phosphate coating and an application and an application method thereof, belonging to the technical field of coatings. Background Art

[0002] Aluminum alloy is the most widely used type of nonferrous metal structural material in industry, and is widely used in aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industries. Aluminum alloys can be divided into cast aluminum alloys and deformed aluminum alloys according to different processing methods. Cast aluminum silicon alloy uses Si (4% to 26%) as the main alloying component, has the advantages of high fluidity and low shrinkage, good casting performance, and wide application, and is the most used aluminum alloy.

[0003] Aluminum and aluminum alloys have active chemical properties. In the natural environment, a corrosion-resistant porous oxide film will form on the surface with a thickness of about 2 to 10 nm. It is very easy to be damaged and lose its protective effect on the alloy. In addition, this film will also lose its protective effect on the substrate in a humid or corrosive environment.

[0004] Improving the corrosion resistance of aluminum alloys can be achieved by improving the corrosion resistance of the alloy matrix and using surface corrosion protection treatment. Surface corrosion protection technology is an important method to improve the corrosion resistance of aluminum alloys. By isolating the matrix from the corrosive medium, it can not only improve the corrosion resistance of the alloy, but also improve other properties of the alloy, such as wear resistance, hydrophilicity, etc. At present, there are various technical means for surface modification of aluminum alloys, which are mainly divided into surface chemical treatment and surface electrochemical treatment. Surface chemical treatment is further divided into chemical pretreatment and chemical conversion treatment. The chemical pretreatment process includes chemical polishing, degreasing and alkali / acid washing of the matrix material. Chemical conversion treatment can be divided into chromate conversion film, phosphate conversion film, rare earth conversion film, etc. according to different treatment solutions. There are three main processes for surface electrochemical treatment, namely electroplating, anodizing and micro-arc oxidation. These surface treatment processes have been successfully applied in deformed aluminum alloys, but the alloying element content of cast aluminum alloys is high, and there are a large number of second phase particles in the organization, which will affect the continuity of the coating and the bonding performance of the matrix. Therefore, the process applied to the surface treatment of deformed aluminum alloys is not suitable for cast aluminum alloys.

[0005] There have been a lot of studies on the preparation of ceramic protective layers on the surface of aluminum alloy castings, such as thermal spraying, laser cladding, and micro-arc oxidation. The ceramic coatings prepared on the surface of aluminum alloy castings using these technologies have excellent corrosion resistance and wear resistance, and have achieved good results. However, thermal spraying, laser cladding, etc. are linear technologies, which have advantages in processing regular surfaces. However, cast Al-Si alloy castings usually have complex shapes and inner cavities, and these processes cannot adapt. In addition, the use of processes such as micro-arc oxidation, anodizing, and phosphate conversion film will produce waste liquid during the treatment process, involving problems such as waste liquid treatment. The ceramic coating prepared by the traditional thermochemical reaction method has good chemical and physical bonding properties with the substrate, as well as excellent high temperature resistance and corrosion resistance. However, the preparation temperature is high, and the heating temperature is generally above 300°C, while the aging temperature of the heat treatment of cast aluminum alloys usually does not exceed 160°C, and is not suitable for ordinary aluminum alloy die castings.

[0006] CN113174150A discloses an aluminum zinc phosphate coating and a method of use, and CN107058992A discloses a coating for preparing a composite coating on the surface of a cast aluminum alloy and a method of use. Both patents use a steam-assisted hardening process to successfully prepare a chemically bonded ceramic coating on the surface of an aluminum alloy casting, but the efficiency of steam heating is low, and the temperature of the ceramic layer cannot be adjusted. In view of the existing deficiencies, it is urgent to develop a production process that can improve the steam heating efficiency and adjust the temperature of the ceramic layer. Summary of the invention

[0007] Purpose of the invention: In view of the existing deficiencies, the first purpose of the present invention is to provide a modified chromium aluminum phosphate coating. The second purpose of the present invention is to provide an application of the modified chromium aluminum phosphate coating in the preparation of a composite coating on the surface of a cast aluminum alloy. The third purpose of the present invention is to provide a method for using the modified chromium aluminum phosphate coating to prepare a composite coating on the surface of a cast aluminum alloy.

[0008] Technical solution: The modified chromium aluminum phosphate coating of the present invention comprises the following components in parts by weight: 1 to 30 parts of Al3Cr(H2PO4) 12 , 10 to 50 parts of Al(H2PO4)3, 40 to 80 parts of H2O and 30 to 70 parts of Al2O3 powder.

[0009] Furthermore, the modified chromium aluminum phosphate coating comprises the following components in parts by weight: 1 to 20 parts of Al3Cr(H2PO4) 12 , 30-50 parts of Al(H2PO4)3, 50-75 parts of H2O and 50-65 parts of Al2O3 powder.

[0010] Furthermore, the particle size of Al2O3 powder is 600-1000 mesh. The particle size of Al2O3 powder will affect the reaction temperature and coating density. Fine Al2O3 powder is easy to react with Al3Cr(H2PO4). 12 It reacts with Al(H2PO4)3 to form a more stable substance, thereby improving the corrosion resistance of the coating.

[0011] The modified chromium aluminum phosphate coating of the present invention is used in preparing a composite coating on the surface of a cast aluminum alloy.

[0012] The method for preparing a composite coating on the surface of a cast aluminum alloy by using a modified chromium aluminum phosphate coating according to the present invention comprises the following steps:

[0013] (1) Al(H2PO4)3 and Al3Cr(H2PO4) 12 Dissolve in water, add Al2O3 powder, stir, and obtain modified chromium aluminum phosphate coating;

[0014] (2) The alkali-treated aluminum alloy casting is placed in a modified chromium aluminum phosphate coating and then taken out by immersion and lifting. After the coating on the alloy surface stops flowing obviously, the aluminum alloy is subjected to steam-assisted curing treatment to obtain an aluminum alloy casting with a ceramic coating on the surface.

[0015] Furthermore, in step (1), the added Al2O3 includes Al3Cr(H2PO4) 12 1.1 to 1.3 times the amount of Al2O3 powder required for the entire chemical reaction and 1.0 to 1.2 times the amount of Al2O3 powder required for the entire chemical reaction with Al(H2PO4)3.

[0016] Furthermore, in step (1), the stirring speed is 500±10 r / min and the stirring time is 30 min.

[0017] Furthermore, in step (2), the immersion time is more than 3 minutes.

[0018] Furthermore, in step (2), the temperature of the steam-assisted curing treatment is 105 to 135° C., and the time of the steam-assisted curing treatment is 60 to 90 minutes.

[0019] Furthermore, in step (2), the surface of the aluminum alloy casting coated with the modified chromium aluminum phosphate coating is placed in a steam environment, heated from the other side without the coating, and cured at 105-135° C. for 60-90 minutes.

[0020] Furthermore, in step (2), the alkali treatment refers to: placing the cast aluminum alloy in an alkaline solution for alkali washing, then ultrasonically washing with deionized water, and drying naturally. The purpose of the alkali treatment is to remove the oxide film on the surface of the cast aluminum alloy and activate the surface of the cast aluminum alloy. After the cast aluminum alloy is subjected to alkali treatment, the -OH generated on the surface of the cast aluminum alloy is conducive to reacting with the coating, and the surface roughness is increased, thereby improving the wettability of the coating to the cast aluminum alloy and further improving the bonding ability of the coating with the substrate.

[0021] Furthermore, the alkaline solution is a mixed solution of sodium hydroxide and sodium carbonate, wherein the concentration of sodium hydroxide in the mixed solution is 4-5wt%, the concentration of sodium carbonate is 3.5-4wt%, the mass ratio of sodium hydroxide to sodium carbonate is 5:4, the alkaline washing time is 2 minutes, and the deionized water ultrasonic cleaning time is 2 minutes.

[0022] In the above preparation method, the prepared modified chromium aluminum phosphate coating only needs to be coated once. Under the action of water vapor treatment, Al3Cr(H2PO4) in the system 12 The Al(H2PO4)3 reacts with the added Al2O3 powder to solidify. 12 It can improve the fluidity of the coating and promote uniform coating. The introduced Cr ions reduce the stress and strain generated by the phase change process by promoting the formation of amorphous structure, and increase the disorder of the system, thereby improving the stability of the system, reducing the crack sensitivity of the coating, and making it have better corrosion resistance and durability.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0024] (1) The present invention uses Al(H2PO4)3 and Al3Cr(H2PO4) 12 As a composite binder, it can react with Al2O3 powder at a relatively low temperature to solidify and prepare a continuous phosphate ceramic coating on the surface of the cast aluminum alloy substrate;

[0025] (2) The present invention uses Al3Cr(H2PO4) in the coating 12 It significantly improves the fluidity of the coating, reduces the crack sensitivity of the coating surface, forms a more uniform and smooth coating that is tightly bonded to the substrate, and has better corrosion resistance and durability;

[0026] (3) The steam-assisted curing device process used in the present invention separates heating and steam environment. The surface of the aluminum alloy casting coated with the modified chromium aluminum phosphate coating is placed in a steam environment, and the other side without the coating is heated. The casting heating and the coating steam environment are temperature-controlled separately, which significantly improves the processing efficiency. It has the characteristics of simple operation steps and short preparation cycle. At the same time, the prepared ceramic coating has better durability and corrosion resistance, and has great practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a steam-assisted curing treatment device used in the present invention;

[0028] Figure 2 The SEM images of the surface and cross section of the modified aluminum phosphate coating of Comparative Example 1, wherein (a) is a surface morphology image; (b) is a cross-sectional morphology image;

[0029] Figure 3 The SEM images of the surface and cross section of the modified aluminum magnesium phosphate coating of Comparative Example 2, wherein (a) is a surface morphology image; (b) is a cross-sectional morphology image;

[0030] Figure 4 The SEM images of the surface and cross section of the modified aluminum zinc phosphate coating of Comparative Example 3, wherein (a) is a surface morphology image; (b) is a cross-sectional morphology image;

[0031] Figure 5 The SEM images of the surface and cross-section of the modified chromium aluminum phosphate coating of Examples 1-4, wherein (a), (c), (e) and (g) are surface morphology images of Examples 1-4, respectively; (b), (d), (f) and (h) are cross-sectional morphology images of Examples 1-4, respectively;

[0032] Figure 6 The SEM images of the surface and cross section of the modified aluminum magnesium phosphate coating of Example 5, wherein (a) is a surface morphology image; (b) is a cross-sectional morphology image;

[0033] Figure 7 The SEM images of the surface and cross section of the modified aluminum magnesium phosphate coating of Example 6, wherein (a) is a surface morphology image; (b) is a cross-sectional morphology image;

[0034] Figure 8 The SEM images of the surface and cross section of the modified aluminum magnesium phosphate coating of Example 7, wherein (a) is a surface morphology image; (b) is a cross-sectional morphology image;

[0035] Fig. 9 This is a comparison chart of the polarization curve test results of the coating;

[0036] Fig.10is the charge transfer resistance (R) of the coating at different immersion times in 3.5 wt% NaCl solution ct ) comparison chart. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0038] The present invention can be better understood according to the following embodiments; and those skilled in the art will readily understand that the specific test results described in the embodiments are based on the cast aluminum-silicon alloy EN AC-43000 and are only used to illustrate the present invention. The surface treatment method is also suitable for other series of cast aluminum alloys, and should not and will not limit the present invention described in the claims.

[0039] Example 1

[0040] (1) 10 parts by weight of Al3Cr(H2PO4) 12 , 50 parts of Al(H2PO4)3, 60 parts of H2O are weighed as raw materials, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12 Calculated as 1.2 times the number required for the entire chemical reaction and 1.0 times the number required for the entire chemical reaction with Al(H2PO4)3, 62 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 1000 mesh, and stirred at a speed of 500r / min for 30min to obtain a modified chromium aluminum phosphate coating;

[0041] (2) The cast aluminum alloy EN AC-43000 sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0042] (3) Place the dried cast aluminum alloy sample in the coating and immerse it for 3 minutes. Use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle. Observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating does not flow significantly on the surface of the sample, place the cast aluminum alloy sample with the coating on a Figure 1 The sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the sample was placed in a water vapor environment, the heating temperature was 105°C, and the treatment lasted for 90 minutes to obtain a cast aluminum alloy sample with a modified chromium aluminum phosphate coating on the surface.

[0043] Example 2

[0044] The experimental process is the same as in Example 1, specifically as follows:

[0045] (1) 5 parts by weight of Al3Cr(H2PO4) 12 , 40 parts of Al(H2PO4)3, 50 parts of H2O are weighed, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12 Calculated as 1.3 times the number required for the entire chemical reaction and 1.2 times the number required for the entire chemical reaction with Al(H2PO4)3, 54.5 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 1000 mesh, and the mixture was stirred at a speed of 500r / min for 30 minutes to obtain a coating;

[0046] (2) The cast aluminum alloy sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0047] (3) Place the dried cast aluminum alloy sample in the coating and immerse it for 3 minutes. Use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle. Observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating does not flow noticeably on the surface of the sample, place the sample with the coating on a Figure 1 The sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the sample was placed in a water vapor environment, the heating temperature was 115°C, and the treatment was performed for 50 minutes to obtain a cast aluminum alloy sample with a modified chromium aluminum phosphate coating on the surface.

[0048] Example 3

[0049] The experimental process is the same as in Example 1, specifically as follows:

[0050] (1) 20 parts by weight of Al3Cr(H2PO4) 12 , 30 parts of Al(H2PO4)3, 50 parts of H2O are weighed, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12Calculated as 1.2 times the number required for the entire chemical reaction and 1.1 times the number required for the entire chemical reaction with Al(H2PO4)3, 57 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 1000 mesh, and the mixture was stirred at a speed of 500r / min for 30 minutes to obtain a coating;

[0051] (2) The cast aluminum alloy sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0052] (3) Place the dried cast aluminum alloy sample in the coating and immerse it for 3 minutes. Use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle. Observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating does not flow noticeably on the surface of the sample, place the sample with the coating on a Figure 1 The sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the sample was placed in a water vapor environment, the heating temperature was 135°C, and the treatment lasted for 60 minutes to obtain a cast aluminum alloy sample with a chromium aluminum phosphate ceramic coating on the surface.

[0053] Example 4

[0054] The experimental process is the same as in Example 1, specifically as follows:

[0055] (1) 20 parts by weight of Al3Cr(H2PO4) 12 , 40 parts of Al(H2PO4)3, 55 parts of H2O are weighed, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12 Calculated as 1.1 times the number required for the entire chemical reaction and 1.0 times the number required for the entire chemical reaction with Al(H2PO4)3, 62 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 1000 mesh, and stirred at a speed of 500r / min for 30min to obtain the coating;

[0056] (2) The cast aluminum alloy sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0057] (3) Place the dried cast aluminum alloy sample in the coating and immerse it for 3 minutes. Use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle. Observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating does not flow noticeably on the surface of the sample, place the sample with the coating on a Figure 1 The sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the sample was placed in a water vapor environment, the heating temperature was 120°C, and the treatment lasted for 80 minutes to obtain a cast aluminum alloy sample with a modified chromium aluminum phosphate coating on the surface.

[0058] Example 5

[0059] The experimental process is the same as in Example 1, specifically as follows:

[0060] (1) 40 parts by weight of Al3Cr(H2PO4) 12 , 20 parts of Al(H2PO4)3, 55 parts of H2O are weighed, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12 Calculated as 1.1 times the number required for the entire chemical reaction and 1.0 times the number required for the entire chemical reaction with Al(H2PO4)3, 64 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 1000 mesh, and the mixture was stirred at a speed of 500r / min for 30 minutes to obtain a coating;

[0061] (2) The cast aluminum alloy sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0062] (3) Place the dried cast aluminum alloy sample in the coating and immerse it for 3 minutes. Use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle. Observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating does not flow significantly on the surface of the sample, place the alloy sample with the coating on a Figure 1 The casting aluminum alloy sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the casting aluminum alloy sample was placed in a water vapor environment, the heating temperature was 125°C, and the treatment was carried out for 70 minutes to obtain a casting aluminum alloy sample with a modified chromium aluminum phosphate coating on the surface.

[0063] Example 6

[0064] The experimental process is the same as in Example 1, specifically as follows:

[0065] (1) 10 parts by weight of Al3Cr(H2PO4) 12 , 50 parts of Al(H2PO4)3, 60 parts of H2O are weighed as raw materials, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12 Calculated as 1.1 times the number required for the entire chemical reaction and 1.0 times the number required for the entire chemical reaction with Al(H2PO4)3, 61 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 1000 mesh, and the mixture was stirred at a speed of 500r / min for 30 minutes to obtain a coating;

[0066] (2) The cast aluminum alloy sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0067] (3) After the dried cast aluminum alloy sample is immersed in the coating for 3 minutes, use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle to observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating does not flow significantly on the surface of the sample, place the sample with the coating on a Figure 1 The sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the sample was placed in a water vapor environment, the heating temperature was 150° C., and the treatment lasted for 40 minutes to obtain a cast aluminum alloy sample with a chromium aluminum phosphate ceramic coating on the surface.

[0068] Example 7

[0069] The experimental process is the same as in Example 1, specifically as follows:

[0070] (1) 10 parts by weight of Al3Cr(H2PO4) 12 , 50 parts of Al(H2PO4)3, 60 parts of H2O are weighed as raw materials, and Al3Cr(H2PO4) 12 Add Al(H2PO4)3 to H2O and stir, then follow the same method as Al3Cr(H2PO4) 12 Calculated as 1.3 times the number required for the entire chemical reaction and 1.0 times the number required for the entire chemical reaction with Al(H2PO4)3, 63 parts of Al2O3 powder were added, the particle size of the Al2O3 powder was 200 mesh, and stirred at a speed of 500r / min for 30min to obtain a modified chromium aluminum phosphate coating;

[0071] (2) The cast aluminum alloy EN AC-43000 sample was placed in a mixed solution of NaOH and Na2CO3 for alkali washing for 2 minutes, then washed with pure water for 2 minutes, and dried naturally for later use, wherein the concentration of NaOH in the mixed solution was 5wt%, the concentration of Na2CO3 was 4wt%, and the mass ratio of NaOH to Na2CO3 was 5:4;

[0072] (3) After the dried cast aluminum alloy sample is immersed in the coating for 3 minutes, use tweezers to slowly pull the sample out of the liquid surface at a speed of 10 cm / min along a 30° angle to observe whether the coating is evenly spread on the surface of the sample. If not, repeat the above steps. When the coating surface does not flow significantly, place the sample with the coating on a Figure 1 The sample was treated in the steam-assisted curing treatment device shown in the figure, the coating on the surface of the sample was placed in a water vapor environment, the heating temperature was 105°C, and the treatment lasted for 90 minutes to obtain a cast aluminum alloy sample with a modified chromium aluminum phosphate coating on the surface.

[0073] Comparative Example 1

[0074] The specific process is the same as in Example 1, except that Al3Cr(H2PO4) is not added to the system. 12 , and the balance is made up with water to prepare an aluminum phosphate coating.

[0075] Comparative Example 2

[0076] The specific process is the same as in Example 1, except that Mg(H2PO4)2 is used instead of Al3Cr(H2PO4) in the system. 12 , a modified aluminum magnesium phosphate coating was prepared.

[0077] Comparative Example 3

[0078] The specific process is the same as in Example 1, except that Zn(H2PO4)2 is used instead of Al3Cr(H2PO4) in the system. 12 , a modified aluminum-zinc phosphate coating was prepared.

[0079] The surface structure characterization analysis of Examples 1-7 and Comparative Examples 1-3 was performed, and the results were as follows: Figure 2-8 See Figure 2 In Comparative Example 1, the aluminum phosphate coating has a rough surface, a large number of holes and penetrating microcracks, and the coating has a tendency to separate from the cast aluminum substrate; see Figure 3 In Comparative Example 2, the microcracks on the surface of the aluminum magnesium phosphate coating are significantly reduced, and the coating is well bonded to the cast aluminum substrate, indicating that the addition of Mg(H2PO4)2 can improve defects such as microcracks and pores on the coating surface, but defects such as microcracks and pores still exist; see Figure 4In Comparative Example 3, the microcracks on the surface of the aluminum zinc phosphate coating almost disappeared, but there were many holes, which were well bonded to the cast aluminum substrate, indicating that the addition of Zn(H2PO4)2 can reduce the microcracks on the coating surface; Figure 5 The modified chromium aluminum phosphate coating prepared in Examples 1-4 is composed of Figure 5 It can be seen that the surface of the modified chromium aluminum phosphate coating of Examples 1-4 is smooth and dense, the microcracks are basically gone, there are few holes, the coating is uniform and continuous, and it is tightly combined with the cast aluminum substrate, which shows that Al3Cr(H2PO4) 12 The addition of can reduce the sensitivity of cracks during the curing of the coating, and there are almost no microcracks on the coating surface, and only a small amount of pores; Figure 6 It can be seen that under the binder content of Example 5, the holes on the surface of the phosphate coating are relatively large, and there are even penetrating holes, and the coating defects are relatively large; Figure 7 It can be seen that at the temperature of Example 6, the phosphate coating has many fine holes on the surface, many through cracks, and poor corrosion resistance. Figure 8 It can be seen that Example 7 uses Al2O3 powder with a larger particle size, and the coating surface has more defects, the reaction is incomplete, and more Al2O3 is agglomerated together, and the particle size is larger, which is not conducive to forming a dense phosphate coating. As can be seen from the above, the amount of raw materials, the heating temperature and the particle size of the Al2O3 powder can affect the performance of the combined total coating. After experiments, it was finally concluded that 1 to 30 parts of Al3Cr(H2PO4) 12 , 10-50 parts Al(H2PO4)3, 50-80 parts H2O and 40-70 parts Al2O3 powder, the results are better, especially in 1-20 parts Al3Cr(H2PO4) 12 , 30-50 parts of Al(H2PO4)3, 50-75 parts of H2O and 50-65 parts of Al2O3 powder, and the particle size of Al2O3 powder is 600-1000 mesh, the heating temperature is 105-135 and the heat treatment is 60-90 minutes, the effect is better.

[0080] Polarization curve tests were performed on the coatings in Examples 1 to 7 and Comparative Examples 1, 2, and 3, and the polarization curves were fitted to electrochemical parameters, see Tables 1 and Fig. 9 .

[0081] Table 1 Electrochemical parameters of polarization curve fitting

[0082]

[0083]

[0084] from Fig. 9 As can be seen from Table 1, the self-corrosion potential of the substrate (cast aluminum alloy) is -0.741 V, and the self-corrosion current density is 3.379×10-4 A.cm -2 The self-corrosion potential of the coating of Comparative Example 1 shifted to -0.652 V, and the self-corrosion current density decreased to 4.154×10 -5 A.cm -2 , compared with the substrate, it dropped by one order of magnitude, and the corrosion inhibition efficiency η was 87.71%. The self-corrosion potential of the coating of comparative example 2 shifted positively to -0.642, and the self-corrosion current density decreased to 3.598×10 -5 A.cm -2 , compared with the substrate, it dropped by one order of magnitude, and the corrosion inhibition efficiency η was 89.35%. The self-corrosion potential of the coating of comparative example 3 shifted positively to -0.657, and the self-corrosion current density decreased to 4.897×10 -5 A.cm -2 , which is one order of magnitude lower than that of the substrate, and the corrosion inhibition efficiency η is 85.51%; the self-corrosion potential of the coating in Example 1 shifts positively to -0.610, and the self-corrosion current density decreases to 5.463×10 - 6 A.cm -2 , compared with comparative example 1, it decreased by 87%, compared with comparative example 2, it decreased by 84%, compared with comparative example 3, it decreased by 88%, and the corrosion inhibition efficiency η reached 98.38%; the self-corrosion potential of the coating of Example 2 shifted positively to -0.539, and the self-corrosion current density decreased to 6.748×10 -6 A.cm -2 Compared with comparative example 1, it decreased by 84%, compared with comparative example 2, it decreased by 81%, compared with comparative example 2, it decreased by 86%, and the corrosion inhibition efficiency η reached 98.00%. The corrosion resistance of Examples 3 and 4 was similar to that of Examples 1 and 2, and was significantly improved compared with the substrate and comparative examples 1 to 3. However, the phosphate coatings of Examples 5 to 7 had more defects, such as penetrating cracks or holes, and had poor corrosion resistance. Therefore, it was finally concluded that 1 to 30 parts of Al3Cr(H2PO4) 12 , 10-50 parts Al(H2PO4)3, 50-80 parts H2O and 40-70 parts Al2O3 powder, the results are better, especially in 1-20 parts Al3Cr(H2PO4) 12 The effect is better when 30-50 parts of Al(H2PO4)3, 50-75 parts of H2O and 50-65 parts of Al2O3 powder are added.

[0085] The coatings prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were immersed in a 3.5 wt % NaCl solution. Fig.10 As the immersion time increases, the charge transfer resistance (R ct ) gradually decreases, indicating that the corrosion resistance gradually decreases. At different immersion times, R ctThe R of the sample of Example 1 after immersion for 1 hour is much larger than that of the substrate and also larger than that of Comparative Examples 1 to 3, indicating that the modified chromium aluminum phosphate coating has better corrosion resistance. ct is 1.636×10 5 Ω·cm 2 , which is 32 times that of the cast aluminum matrix, significantly improving the corrosion resistance. ct Still 4.26×10 4 Ω·cm 2 , which is 8 times that of the cast aluminum substrate, indicating that it has a longer durability. The corrosion resistance of Examples 3 and 4 is similar to that of Examples 1 and 2. ct The phosphate coatings of Examples 5 to 7 have more defects, R ct Obviously lower than Examples 1 to 4. It can be concluded that 1 to 30 parts of Al3Cr(H2PO4) 12 , 10-50 parts Al(H2PO4)3, 50-80 parts H2O and 40-70 parts Al2O3 powder, the results are better, especially in 1-20 parts Al3Cr(H2PO4) 12 The effect is better when 30-50 parts of Al(H2PO4)3, 50-75 parts of H2O and 50-65 parts of Al2O3 powder are added.

Claims

1. A modified chromium aluminum phosphate coating, It is characterized in that The aluminum chromium phosphate coating comprises the following components in parts by weight: 1 to 30 parts of Al 3 Cr(H 2 PO 4 ) 12 、10~50 parts Al(H 2 PO 4 ) 3 , 50~80 parts H 2 O and 40-70 parts of Al 2 O 3 powder.

2. The modified chromium aluminum phosphate coating according to claim 1, It is characterized in that The chromium aluminum phosphate coating comprises the following components in parts by weight: 1 to 20 parts of Al 3 Cr(H 2 PO 4 ) 12 、30~50 parts Al(H 2 PO 4 ) 3 , 50~75 parts H 2 O and 50-65 parts of Al 2 O 3 powder.

3. The modified chromium aluminum phosphate coating according to claim 1, It is characterized in that Al 2 O 3 The particle size of the powder is 600-1000 mesh.

4. Use of the modified chromium aluminum phosphate coating according to any one of claims 1 to 3 in preparing a composite coating on the surface of a cast aluminum alloy.

5. A method for preparing a composite coating on the surface of a cast aluminum alloy by using the modified chromium aluminum phosphate coating according to any one of claims 1 to 3, It is characterized in that The following steps are involved: (1) Al(H 2 PO 4 ) 3 and Al 3 Cr(H 2 PO 4 ) 12 Dissolve in water and add Al 2 O 3 powder, and stirring to obtain a modified chromium aluminum phosphate coating; (2) The alkali-treated aluminum alloy casting is placed in a modified chromium aluminum phosphate coating and then taken out by immersion and lifting. After the coating on the alloy surface stops flowing obviously, the aluminum alloy is subjected to steam-assisted curing treatment to obtain an aluminum alloy casting with a ceramic coating on the surface.

6. The preparation method according to claim 5, It is characterized in that In step (1), the added Al 2 O 3 Including with Al 3 Cr(H 2 PO 4 ) 12 1.1 to 1.3 times the amount of Al required for all chemical reactions 2 O 3 Powder and Al(H 2 PO 4 ) 3 1.0 to 1.2 times the amount of Al required for all chemical reactions 2 O 3 powder.

7. The preparation method according to claim 5, It is characterized in that In step (1), the immersion time is 3 minutes. In step (2), the stirring speed is 500±10 r / min and the stirring time is 30 minutes.

8. The preparation method according to claim 5, It is characterized in that In step (2), the surface of the aluminum alloy casting coated with the modified chromium aluminum phosphate coating is placed in a steam environment, heated from the other side without the coating, and cured at 105-135° C. for 60-90 minutes.

9. The preparation method according to claim 5, It is characterized in that In step (2), the alkali treatment refers to: placing the cast aluminum alloy in an alkaline solution for alkali washing, then ultrasonically cleaning it with deionized water, and drying it naturally.

10. The preparation method according to claim 9, It is characterized in that The alkaline solution is a mixed solution of sodium hydroxide and sodium carbonate, wherein the concentration of sodium hydroxide in the mixed solution is 4-5wt%, the concentration of sodium carbonate is 3.5-4wt%, the mass ratio of sodium hydroxide to sodium carbonate is 5:4, the time of alkaline washing is 2-3 minutes, and the time of deionized water ultrasonic cleaning is 1-2 minutes.

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