Heat exchanger and method for manufacturing a heat exchanger, thermal management system

Abstract

This application provides a heat exchanger and its manufacturing method, as well as a thermal management system. The heat exchanger includes a metal substrate, which comprises a manifold, heat exchange tubes, and fins. The heat exchange tubes are fixed to the manifold, and the inner cavity of the heat exchange tubes communicates with the inner cavity of the manifold. The fins are located between two adjacent heat exchange tubes. The heat exchanger also has a coating, which includes a chemical conversion film layer. The chemical conversion film layer is applied to at least a portion of the surface of the metal substrate. The chemical conversion film layer includes zirconium and vanadium elements, and further includes an auxiliary agent, which includes at least one of phosphate and organometallic chelates. The composite coating on the surface of the metal substrate of the heat exchanger of this application has excellent barrier effect and uniform film thickness, which can effectively improve the corrosion resistance and service life of the heat exchanger.

Description

Technical Field

[0001] This application relates to the fields of materials and heat exchanger technology, and in particular to a heat exchanger and its preparation method, and a thermal management system. Background Technology

[0002] Microchannel heat exchangers are highly efficient heat exchange devices developed in the 1990s and can be widely used in chemical, energy, and environmental fields. Because microchannel heat exchangers are located in the micrometer to sub-millimeter scale, they possess many characteristics that distinguish them from conventional heat exchangers, such as small size, light weight, high efficiency, and high strength.

[0003] Aluminum alloys possess advantages such as low density, excellent mechanical properties, good machinability, and strong electrical and thermal conductivity. As lightweight structural materials, they can effectively improve heat exchange efficiency and save costs when used in heat exchangers. However, aluminum has poor corrosion resistance; in the atmosphere, especially in humid environments, a thin oxide film easily forms on the surface of aluminum alloys. This film cannot meet industrial protection requirements and affects product quality stability. Therefore, developing new anti-corrosion coatings to enhance the corrosion resistance of all-aluminum microchannel heat exchangers has become an urgent problem to be solved in the industry. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a heat exchanger with excellent corrosion resistance, its preparation method, and a thermal management system thereof.

[0005] According to one aspect of this application, a heat exchanger is provided, the heat exchanger comprising a metal substrate, the metal substrate comprising a manifold, a heat exchange tube, and fins; the heat exchange tube is fixed to the manifold, the inner cavity of the heat exchange tube is in communication with the inner cavity of the manifold, and the fins are located between two adjacent heat exchange tubes; the heat exchanger further comprises a coating comprising a chemical conversion film layer, the chemical conversion film layer being coated on at least a portion of the surface of the metal substrate, the chemical conversion film layer comprising zirconium and vanadium, and the chemical conversion film layer further comprising an auxiliary agent, the auxiliary agent comprising at least one of a phosphate and an organometallic chelate.

[0006] In the above-mentioned solution, the heat exchanger surface provided in this application is coated with a chemical conversion film layer containing zirconium, vanadium, and auxiliary agents. The chemical conversion film layer containing zirconium and vanadium has a dense film structure and a strong bonding force with the heat exchanger metal substrate. When local pitting corrosion occurs in the heat exchanger, the chemical conversion film layer can inhibit the cathodic reduction reaction, thereby improving the corrosion resistance of the heat exchanger, extending the corrosion resistance time, and thus extending the service life of the heat exchanger. At the same time, the addition of auxiliary agents further enhances the density of the chemical conversion film layer, giving it better barrier and shielding properties, thereby making the heat exchanger have better corrosion resistance.

[0007] According to another aspect of this application, a method for preparing a heat exchanger as described above is also provided, the method comprising:

[0008] A metal substrate and a first coating are provided, wherein the metal substrate has at least one fluid channel for the flow of a heat exchange medium, and the raw materials for preparing the first coating include zirconium salt, vanadium salt and auxiliary agent precursor, wherein the auxiliary agent precursor includes at least one of phosphorus-containing compound and metal chelating agent.

[0009] The first coating is applied to at least a portion of the surface of the metal substrate, and a first curing treatment is performed.

[0010] The above-mentioned scheme can prepare heat exchangers with at least a portion of the surface having a chemical conversion film layer containing zirconium, vanadium, and at least one of phosphate and organometallic chelates, thereby improving the density of the coating on the surface of the heat exchanger and thus improving the corrosion resistance of the heat exchanger.

[0011] According to another aspect of this application, a thermal management system is also provided, the thermal management system including a compressor, a first heat exchanger, a throttling device, and a second heat exchanger, wherein the first heat exchanger and / or the second heat exchanger is a heat exchanger as described above or a heat exchanger prepared by the method described above; when there is refrigerant flowing in the thermal management system, the refrigerant flows into the first heat exchanger through the compressor, and after heat exchange occurs in the first heat exchanger, it flows into the throttling device, and then the refrigerant flows into the second heat exchanger, and after heat exchange occurs in the second heat exchanger, it flows back into the compressor.

[0012] In the above scheme, the first heat exchanger and / or the second heat exchanger used in the thermal management system are heat exchangers as described above or heat exchangers prepared by the preparation method of the heat exchangers described above. The chemical conversion film layer on at least part of the surface of the heat exchanger improves the corrosion resistance of the heat exchanger, thereby extending the service life of the thermal management system. Attached Figure Description

[0013] Figure 1The fabrication process flow diagram of the heat exchanger provided in this application;

[0014] Figure 2 The polarization curves of Comparative Example 1 and Example 1 of this application were tested in 3.5% NaCl solution;

[0015] Figure 3 The polarization curves of Example 1 and Comparative Example 2 of this application were tested in 3.5% NaCl solution;

[0016] Figure 4 The polarization curves of Examples 1 and 2 of this application were tested in 3.5% NaCl solution;

[0017] Figure 5 The surface corrosion of the coating sample of Example 1 of this application at 0d, 1d, 2d and 4d respectively;

[0018] Figure 6 The surface corrosion of the coating sample in Example 2 of this application at 0d, 1d and 2d respectively;

[0019] Figure 7 The surface corrosion of the coating sample of Comparative Example 1 at 0d, 1d and 2d are shown.

[0020] Figure 8 The surface corrosion of the coating sample of Comparative Example 2 at 0d, 30d, 55d, 70d and 90d is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Based on the technical solutions and embodiments provided in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the ranges, the endpoint values ​​of the ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges.

[0023] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "the," and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0024] In the description of this application, the list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. Furthermore, the terms "at least part of the surface," "at least a portion of the surface," "at least a portion of the surface," or other similar terms mean any part of the surface or the entire surface of the component. For example, at least a portion of the heat exchanger surface means a portion or several parts of the surface of the heat exchanger, or the entire surface of the heat exchanger.

[0025] In one specific embodiment, the present application will be further described in detail below through specific embodiments.

[0026] Among related technologies, microchannel heat exchangers are highly efficient heat exchange devices developed in the 1990s, and can be widely used in chemical, energy, and environmental fields. Microchannel heat exchangers possess many characteristics that differ from conventional scale equipment, such as small size, light weight, high efficiency, and high strength. Microchannel technology has also triggered technological innovations in fields such as thermal management systems for new energy vehicles, residential air conditioning, commercial air conditioning, and refrigeration equipment, aiming to improve efficiency and reduce emissions.

[0027] While the application of all-aluminum microchannel heat exchangers is gradually expanding, the pace of their adoption is relatively slow. One major technical bottleneck is the poor corrosion resistance of aluminum microchannel heat exchangers, which significantly reduces their service life. Therefore, improving the corrosion resistance of existing all-aluminum microchannel heat exchangers has become an urgent problem for the industry.

[0028] In existing technologies, chromate conversion films are typically used as a protective coating on the surface of all-aluminum microchannel heat exchangers. However, chromium is a heavy metal element that is harmful to the environment. In addition, current microchannel heat exchangers are connected using brazing technology, which requires flux treatment. Due to the presence of flux at the brazing sites, the chromate coating cannot react and cannot be applied to the brazing sites, which greatly reduces the corrosion resistance of the microchannel heat exchanger.

[0029] Further research has led to the development of zirconium-based conversion membranes. These membranes are green and non-toxic, possess good corrosion resistance and self-healing properties, making them a promising alternative to chromate conversion membranes. However, the coating thickness of zirconium-based conversion membranes on all-aluminum microchannel heat exchangers is relatively thin, and the coating is porous or defective, resulting in uneven film distribution and poor barrier effect. Furthermore, existing chemical conversion membranes only serve a barrier function to improve corrosion resistance, failing to enhance the corrosion resistance of the heat exchanger substrate in corrosive solutions and offering almost no protection. Therefore, improving zirconium-based conversion membranes to develop new anti-corrosion coatings to enhance the corrosion resistance of all-aluminum microchannel heat exchangers has become an urgent problem for the industry.

[0030] Therefore, based on the existing zirconium-based conversion coating process composition parameters, this application studies the effects of different components and contents on the composition, microstructure, and corrosion resistance of the chemical conversion film, and provides a heat exchanger, a method for preparing the heat exchanger, and a thermal management system. The heat exchanger has a dense anti-corrosion coating with adjustable thickness, which improves the density and barrier properties of the coating, further enhancing the corrosion resistance of the heat exchanger, thereby improving its heat exchange efficiency and service life. A detailed description of the technical solution is provided below.

[0031] Unless otherwise stated, percentages, proportions, or parts in this document are expressed by mass. A "part by mass" refers to the basic unit of measurement for the mass ratio of multiple components. One part can represent any unit mass, such as 1g, 1.68g, or 5g, etc.

[0032] This application provides a heat exchanger, which includes a metal substrate, a manifold, a heat exchange tube, and fins; the heat exchange tube is fixed to the manifold, the inner cavity of the heat exchange tube is connected to the inner cavity of the manifold, and the fins are located between two adjacent heat exchange tubes.

[0033] The heat exchanger also has a coating, which includes a chemical conversion film layer applied to at least a portion of the surface of the metal substrate, the chemical conversion film layer including zirconium and vanadium.

[0034] The heat exchanger provided in this application is coated with a chemical conversion film layer containing zirconium and vanadium. When local pitting corrosion occurs in the heat exchanger, the chemical conversion film layer can inhibit the cathodic reduction reaction, thereby improving the corrosion resistance of the heat exchanger and extending its corrosion resistance time.

[0035] In some embodiments, the chemical conversion coating further includes an auxiliary agent, which includes at least one of phosphates and organometallic chelates. Thus, the chemical conversion coating has a dense film structure and strong adhesion to the heat exchanger's metal substrate. The addition of the auxiliary agent can form one or more uniform and dense film layers distributed within the chemical conversion coating, blocking pores or defects in the chemical conversion coating and reducing the possibility of corrosive media penetrating and contacting the metal substrate. This results in better barrier and shielding effects, further improving the coating's corrosion resistance and service life. This application, by combining vanadium, zirconium, and the auxiliary agent, fully leverages the advantages of each component, resulting in a highly corrosion-resistant coating applied to the surface of the heat exchanger.

[0036] In the heat exchanger of this application, if the chemical conversion film layer is affected by external environmental factors and cracks occur, zirconium and vanadium elements can come into contact with the corrosive medium and transform into hydrates. Subsequently, the hydrates connect with zirconium elements or form an anti-corrosion barrier through hydrolysis, condensation and polymerization, thereby improving the density of the coating. At the same time, zirconium elements can also react with the metal substrate in contact with the chemical conversion film layer to form insoluble substances that are adsorbed or attached to the surface of the metal substrate, thereby enhancing the barrier effect of the metal substrate itself and improving the corrosion resistance of the metal substrate in corrosive solutions.

[0037] Since current microchannel heat exchangers use brazing technology for connection and require flux treatment, there are brazing areas on the surface of the heat exchanger. The zirconium and vanadium elements contained in the chemical conversion film layer of this application have good compatibility with the flux at the brazing areas, which can meet the bonding requirements of the heat exchanger surface coating and the brazing areas, and further improve the corrosion resistance of the heat exchanger.

[0038] In some embodiments, the coating also includes a silicon coating that is further away from the metal substrate than the chemical conversion film layer. That is, at least a portion of the outer surface of the heat exchanger metal substrate may be provided with the chemical conversion film layer and the silicon coating layer in sequence, with the silicon coating layer exposed to the environment.

[0039] In some embodiments, the silicon coating includes silicon dioxide. The presence of silicon dioxide enables the silicon coating to form a structure with relatively stable physical and chemical properties, making the silicon coating stable and dense, and improving the hydrophilicity, durability and corrosion resistance of the silicon coating.

[0040] In some embodiments, the silicon coating further includes organosilanes and titanium dioxide; that is, the silicon coating comprises organosilanes, silicon dioxide, and titanium dioxide, and has a three-dimensional network structure, with at least one of silicon dioxide and titanium dioxide filling the three-dimensional network structure. The three-dimensional network structure of the silicon coating exhibits good chemical stability and resistance to corrosive media, thereby increasing the durability and corrosion resistance of the silicon coating. Silica is stable and has a relatively high density (up to 2.65 g / cm³). 3 The presence of silica (silica) filling the three-dimensional network structure of the silicon coating increases its density and mechanical strength. Simultaneously, silica's high melting point enhances the thermal stability of the silicon coating. Titanium dioxide, a highly stable oxide with excellent acid resistance, reduces defects in the silicon coating, making it denser and thus strengthening its corrosion and acid resistance to some extent. The filling of silica and / or titanium dioxide into the three-dimensional network structure reduces the porosity of the silicon coating and provides flexibility to the network, making it less prone to cracking during drying. This application achieves a dense three-dimensional network structure through the silicon coating, which can impede the movement of ions in corrosive media, preventing corrosive substances from penetrating the coating to the metal substrate, thus achieving corrosion resistance, while also possessing good mechanical properties.

[0041] In this application, since the chemical conversion film layer is in contact with the surface of the silicon coating, there are some free zirconium ions in the chemical conversion film layer. The zirconium ions can diffuse into the silicon coating to catalyze the hydrolysis and condensation of the three-dimensional network structure, thereby further improving the density of the silicon coating. At the same time, it can also enhance the thickness of the coating on the surface of the metal substrate, improve the uniformity of the coating distribution, and further enhance the barrier performance of the silicon coating.

[0042] In some embodiments, the heat exchanger provided according to the embodiments of this application is provided with a chemical conversion film layer and a silicon coating layer. The chemical conversion film layer includes zirconium, vanadium, and auxiliary agents, while the silicon coating layer includes organosilane, silicon dioxide, and titanium dioxide. The chemical conversion film layer can be applied as a base coating layer to at least a portion of the surface of the metal substrate, and the silicon coating layer can be applied as a top coating layer to at least a portion of the surface of the chemical conversion film layer. Thus, the heat exchanger is first chemically converted to form a chemical conversion film layer, and then the surface of the heat exchanger is treated with a silicon coating. The silicon coating layer can bond with the surface of the heat exchanger after the chemical conversion film layer treatment through Si-O (silicon-oxygen) covalent bonds, exhibiting tight bonding and good durability. Furthermore, the dense film structure of both the chemical conversion film layer and the silicon coating layer enhances the barrier effect of the heat exchanger surface coating, improves the corrosion resistance of the heat exchanger surface, and extends the service life of the heat exchanger. Consequently, when the heat exchanger is used in air conditioning systems and heat pump systems, it is beneficial to extend its service life and improve its heat exchange efficiency.

[0043] In some embodiments, the thickness of the chemical conversion film is 10 nm to 1 μm, specifically 10 nm, 50 nm, 100 nm, 300 nm, 500 nm, 800 nm, and 1 μm, or other values ​​within the above range. The choice is made according to actual needs and is not limited here. Compared to traditional chemical conversion films (thickness generally less than or equal to 100 nm), the thickness of the chemical conversion film in this application has a wider adjustable range. It can be made into a thicker film structure according to requirements, improving the uniformity of film thickness and the barrier effect of the coating.

[0044] In some embodiments, at least a portion of the silica is hydrophilic modified silica with a particle size in the nanometer range, which is beneficial for forming a stable coating system.

[0045] In some embodiments, at least a portion of the titanium dioxide is hydrophilic titanium dioxide with a particle size in the nanometer range.

[0046] In some embodiments, the thickness of the silicon coating is 1 μm to 10 μm, and the specific thickness can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc. Of course, it can also be other values ​​within the above range. This application does not limit it here. Within the above-defined range, the silicon coating can form a film layer with uniform and dense film thickness.

[0047] In some embodiments, the cross-cut adhesion test assigns a grade of 0 to the coating's adhesion to the metal substrate. The cross-cut adhesion test typically involves, after the coating has adhered to the metal substrate, cutting a grid of 100 lines on the coating surface with a knife, attaching adhesive tape to the center of each grid, and then smoothly peeling it off. The degree of coating detachment is observed, and the condition of each grid is calculated to correspond to a standard. The coating in this application exhibits a low adhesion grade, meaning the cut edges are relatively smooth, with almost no peeling at the grid edges, indicating strong coating adhesion.

[0048] In some embodiments, the main structure of the metal substrate of the microchannel heat exchanger used in this application includes two manifolds, multiple heat exchange tubes, and at least one fin.

[0049] Multiple heat exchange tubes are arranged along the axial direction of the manifold and connected between two manifolds. Specifically, one end of the heat exchange tube along its length is connected to one of the two manifolds, and the other end along its length is connected to the other manifold. The inner cavity of the heat exchange tube is connected to the inner cavity of the manifold. The inner cavity of the heat exchange tube has multiple heat exchange microchannels extending along its length. Therefore, the heat exchange tube can be a microchannel flat tube or an elliptical tube, and when the heat exchange tube is a microchannel flat tube or an elliptical tube, the width of the heat exchange tube is greater than its thickness.

[0050] The fins are located between two adjacent heat exchange tubes. The fins are wavy along the length of the heat exchange tubes. The fins include several crests and several troughs. The crests and troughs of the fins are connected to the two adjacent heat exchange tubes respectively.

[0051] In some implementations, a window structure can be provided in a portion of the fins to form louvered fins, further enhancing heat transfer.

[0052] Understandably, the microchannels inside the heat exchange tubes connect the left and right manifolds to the microchannels, forming a sealed space. The fins are fixed between the heat exchange tubes, forming multiple heat dissipation units with the microchannels. The microchannels can then transfer the heat of the internal fluid to the air through the fins.

[0053] In some embodiments, the heat exchanger of this application has a coating, including a chemical conversion film and a silicon coating, which are applied to at least a portion of the surface of at least one of the manifold and / or heat exchange tube and / or fins. It is understood that the chemical conversion film and silicon coating may be applied to only a portion or all of the surface of one of the manifold, heat exchange tube, or fins; this arrangement can reduce the amount of coating used and lower the production cost of the heat exchanger. Alternatively, they may be applied to two or three portions or all of the surface of the manifold, heat exchange tube, or fins; this arrangement can more effectively protect the metal substrate and extend the service life of the heat exchanger. The method of coating the surface of the heat exchanger's metal substrate can be selected according to actual needs and is not limited herein.

[0054] In some embodiments, the microchannel heat exchanger is an all-aluminum microchannel heat exchanger. The structure of the microchannel heat exchanger and the connection relationships of its various components are conventional knowledge in the art and will not be described in detail here.

[0055] In practical applications, the above-mentioned heat exchanger can be used in a thermal management system. The thermal management system includes a compressor, a first heat exchanger, a throttling device, and a second heat exchanger. At least one of the first heat exchanger and the second heat exchanger is a heat exchanger containing the above-mentioned structure. When there is refrigerant flowing in the thermal management system, the refrigerant flows into the first heat exchanger through the compressor, and after heat exchange occurs in the first heat exchanger, it flows into the throttling device. Then, the refrigerant flows into the second heat exchanger, and after heat exchange occurs in the second heat exchanger, it flows back into the compressor.

[0056] In some embodiments, this application also provides a method for preparing the above-described heat exchanger, such as... Figure 1 The diagram shown is a flowchart of the fabrication process of the heat exchanger provided in this embodiment of the application, including the following steps:

[0057] A metal substrate and a first coating are provided, wherein the metal substrate has at least one fluid channel for the flow of a heat exchange medium, and the preparation of the first coating includes zirconium salt, vanadium salt and an auxiliary agent precursor, wherein the auxiliary agent precursor includes at least one of a phosphorus-containing compound and a metal chelating agent.

[0058] The first coating is applied to at least a portion of the surface of the metal substrate, and a first curing treatment is performed.

[0059] Furthermore, in the preparation process of the heat exchanger with coating provided in this application, the surface of the heat exchanger metal substrate is first pretreated, and then the first coating is applied to the pretreated metal substrate surface. After a first curing treatment, the heat exchanger is obtained.

[0060] It is understood that the heat exchanger of this application is a microchannel heat exchanger, and the aforementioned metal substrate includes at least one of a manifold, a heat exchange tube, and fins.

[0061] It is important to note that the first coating is not the same as the final coating. After the first coating is applied to at least a portion of the surface of at least one of the manifold, heat exchanger tube, or fins, the entire structure requires high-temperature curing to form a final coating. During this process, the functional groups in the first coating react chemically with the metal substrate of the heat exchanger and external corrosive media. Zirconium and vanadium elements can react with the corrosive media to form hydrates. Subsequently, these hydrates bond with the zirconium elements or polymerize through hydrolysis and condensation to form a corrosion barrier, achieving a self-healing effect. The preparation process of this heat exchanger is simple, easy to control, and highly feasible. The reaction is easy to carry out under mild conditions, resulting in minimal environmental pollution and making it suitable for industrial-scale production. The heat exchanger obtained through this preparation method exhibits excellent bonding, barrier, and corrosion resistance properties, extending its service life.

[0062] In some embodiments, the metal substrate is made of at least one of aluminum, magnesium, copper, and zinc. Preferably, the metal substrate is made of aluminum.

[0063] In some embodiments, the step of providing the metal substrate is followed by a step of pretreating the metal substrate, the pretreating step of the metal substrate including:

[0064] a. The surface of the metal substrate is sandblasted and polished, then cleaned with deionized water and / or anhydrous ethanol, and dried.

[0065] b. Perform alkaline washing on the surface of the metal substrate;

[0066] c. Pickling the surface of the metal substrate.

[0067] In the pretreatment process, in some embodiments, the sandblasting mesh size is 600-1000 mesh, and the minimum number of sandblasting passes is two. The surface is treated first with a smaller mesh size, followed by a larger mesh size. For example, the metal substrate surface is first polished with 600-grit SiC sandpaper, and then with 1000-grit SiC sandpaper. In some embodiments, the cleaning method may include water rinsing, ultrasonic cleaning with anhydrous ethanol, and finally water rinsing. Of course, the order of the above cleaning steps can be changed, or any one or two of the cleaning steps can be omitted. This application does not impose any particular limitation on the cleaning method. In some embodiments, the drying temperature is 35℃-50℃, and in further embodiments, it is 38℃-45℃, such as 40℃.

[0068] In the pretreatment process, the alkaline solution for alkaline washing comprises: 1 to 3 parts by weight of sodium hydroxide and 35 to 45 parts by weight of sodium carbonate dissolved in 1000 parts by weight of deionized water, stirred with a magnetic stirrer until the solution is clear, and then set aside. In some embodiments, the sodium hydroxide may be 1, 2, or 3 parts, the sodium carbonate may be 35, 38, 40, 43, or 45 parts, and the deionized water may be 50, 55, 60, 70, 75, or 80 parts. This application removes oil and oxides from the surface of a metal substrate by alkaline washing.

[0069] In the pretreatment process, the pickling acid solution includes: 3 to 8 parts by weight of glacial acetic acid and 80 to 100 parts by weight of nitric acid dissolved in 1000 parts by weight of deionized water, for later use. In some embodiments, the glacial acetic acid can be 3, 5, 7, or 8 parts, the nitric acid can be 80, 85, 90, 95, or 100 parts, and the deionized water can be 150, 155, 160, 165, or 170 parts. This application removes oxides or rust from the surface of the metal substrate by pickling.

[0070] In some embodiments, a step of preparing the first coating is included before the step of providing the first coating, the step of preparing the first coating including:

[0071] Based on a mass of 100 parts, 0.1 to 0.3 parts of potassium fluorozirconate, 0.1 to 0.3 parts of potassium metavanadate, 0.1 to 0.3 parts of sodium fluoride, 0.1 to 0.3 parts of oxidant, 2 to 4 parts of auxiliary agent precursor, and the balance water are mixed until the solution is clear to obtain a first coating. For example, the mass percentages of potassium fluorozirconate may be 0.1, 0.2, or 0.3 parts; the mass percentages of potassium metavanadate may be 0.1, 0.2, or 0.3 parts; the mass percentages of sodium fluoride may be 0.1, 0.2, or 0.3 parts; the mass percentages of oxidant may be 0.1, 0.2, or 0.3 parts; and the mass percentages of auxiliary agent precursor may be 2, 3, or 4 parts. The acidic salt containing zirconium and vanadium in the first coating, along with an oxidizing agent, enables the metal substrate, zirconium, and vanadium to chemically react with anions in the reaction system, generating stable compounds with relatively stable physical and chemical properties. Simultaneously, the addition of auxiliary precursors improves the density of the resulting film, further enhancing the corrosion resistance of the chemically converted film. Furthermore, zirconium and vanadium are non-toxic, reducing environmental pollution.

[0072] In some embodiments, the auxiliary precursor includes at least one selected from phosphate, tannic acid, chitosan, and polyvinyl alcohol. Phosphate, for example, is sodium dihydrogen phosphate or potassium dihydrogen phosphate. By adding the auxiliary precursor, this application can compensate for porosity or defects in the film layer, improve the film's density, and thus enhance its barrier effect. Sodium dihydrogen phosphate or potassium dihydrogen phosphate can react with the metal substrate to generate a denser compound, improving the film's density. Tannic acid, chitosan, and polyvinyl alcohol can be adsorbed onto the film surface through organic complexation, further improving the film's density. Simultaneously, the presence of organic substances such as tannic acid, chitosan, and polyvinyl alcohol can increase the thickness of the chemically converted film, strengthening the coating's barrier effect.

[0073] According to embodiments of the present invention, there are no restrictions on the source or specific type of raw materials for preparing the first coating. Those skilled in the art can flexibly select materials based on actual needs, as long as it does not limit the purpose of the present invention. For example, various raw materials well-known to those skilled in the art can be used, either commercially available products or prepared in-house. In some embodiments of this application, the oxidant includes tert-butyl hydrogen peroxide.

[0074] In some embodiments of this application, the method of applying the first coating to the pretreated heat exchanger surface includes, but is not limited to, at least one of dip coating, spray coating, brush coating, curtain coating, or roller coating. For ease of implementation, the first coating provided in the embodiments of this application can be applied to the pretreated metal substrate surface using spray or dip coating methods. For example, the pretreated metal substrate can be immersed in the first coating and kept at 40°C to 60°C for 20 to 40 minutes for a first curing treatment, so that the first coating forms a chemical conversion film layer on the surface of the metal substrate. Then, the heat exchanger with the chemical conversion film layer is removed and dried with cold air or air-dried naturally. Exemplarily, the temperature of the first curing treatment can be, for example, 40°C, 45°C, 50°C, 55°C, or 60°C; the time of the first curing treatment can be, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes.

[0075] In some specific embodiments, the preparation method of the first coating includes the following steps:

[0076] Based on a mass of 100 parts, 0.1 parts of potassium fluorozirconate, 0.1 parts of potassium metavanadate, 0.1 parts of sodium fluoride, 0.1 parts of tert-butyl hydroperoxide, 2 parts of sodium dihydrogen phosphate, and the balance water are mixed until the solution becomes clear to obtain the first coating. The equations involved in the oxidation reaction of the first coating on the surface of a metal substrate (taking aluminum as an example) are as follows:

[0077] (1) 2Al + 6H + →2Al 3+ +3H2

[0078] (2)Al 3+ +3Na + +6F - →Na3AlF6

[0079] (3) 2Al + 6H + +3ZrF6 3- +5H2O→2AlHOF·3ZrOF2+10HF+3H2

[0080] (4)Zr 4+ +3H₂O→ZrO₂·H₂O+4H +

[0081] (5)V 10 O 28 6- +6H + +2H₂O→5V₂O₅·H₂O↓

[0082] (6)HPO4 2- →H + +PO43-

[0083] (7)PO4 3- +Al 3+ →AlPO4

[0084] Therefore, it can be seen that mixing an acidic salt containing zirconium and vanadium with the oxidant tert-butyl hydroperoxide to form the first coating, under the action of the oxidant, aluminum, zirconium, and vanadium react with anions such as acid radicals and water in the acidic environment to generate a dense compound structure, reducing the chemical activity of the metal substrate and improving its thermodynamic stability. The chemical conversion film layer contains a mixture of zirconium oxide hydrate, vanadium oxide hydrate, aluminum phosphate, sodium hexafluoroaluminate, and 2AlHOF·3ZrOF2. Among them, the zirconium oxide hydrate is silver-gray, giving the surface of the chemical conversion film layer a silver-gray color. It is chemically stable, and its synergistic effect with vanadium oxide hydrate helps to improve the coating's resistance to pitting corrosion, thus improving the corrosion resistance of the heat exchanger. Sodium dihydrogen phosphate can react with aluminum under acidic conditions to generate dense aluminum phosphate, further improving the density of the coating.

[0085] In some embodiments, the preparation method of this application further includes: impregnating the heat exchanger with the chemical conversion film layer in a second coating and performing a second curing treatment to obtain a silicon coating.

[0086] In the above preparation steps, the second coating can form a dense barrier layer, which can further reduce the reactivity of the metal substrate surface, improve the corrosion resistance of the metal substrate, and block the direct contact between the environmental medium and the metal substrate. Finally, a stable compound film layer is formed on the surface of the heat exchanger metal substrate, which greatly improves the coating's adhesion and corrosion resistance.

[0087] In some embodiments, the step of preparing the second coating is included before providing the second coating. The second coating is prepared by the following steps: mixing a first precursor solution, a second precursor solution, and a third precursor solution.

[0088] The method for preparing the first precursor solution includes the following steps:

[0089] By weight, 4 to 7 parts of a first silane precursor, 3 to 5 parts of water, 6 to 8 parts of an organic solvent, and 4 to 7 parts of an acid are mixed and subjected to a first standing treatment for 4 to 8 hours to obtain a first precursor solution, which mainly comprises silica sol. For example, the weight percentages of the first silane precursor may be 4, 5, 6, or 7 parts; the weight percentages of water may be 3, 4, or 5 parts; the weight percentages of the organic solvent may be 6, 7, or 8 parts; the weight percentages of the acid may be 4, 5, 6, or 7 parts; and the first standing treatment time may be 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours.

[0090] Provided that the requirement of generating inorganic silica sol is met, the specific type of the first silane precursor can be varied. Specifically, in some embodiments, the first silane precursor includes at least one of tetraethyl orthosilicate and tetramethyl orthosilicate.

[0091] Provided that the requirement of generating inorganic silica sol is met, the specific types of organic solvents and acids can be diverse. Specifically, in some embodiments, the organic solvent includes alcohol solvents. Further, the alcohol solvent includes alcohol solvents with 1 to 10 carbon atoms, preferably alcohol solvents with 1 to 8 carbon atoms, and more preferably alcohol solvents with 1 to 4 carbon atoms. Further, in some embodiments, the solvent is any one or a mixture of any two or more of methanol, ethanol, ethylene glycol, and isopropanol in any proportion. Therefore, it is widely available, easily obtained, and inexpensive. In some embodiments, the acid includes at least one of glacial acetic acid and formic acid. These two acids are inexpensive, widely available, and have good performance. Further, the acid is glacial acetic acid.

[0092] In some specific embodiments, the preparation method of the first precursor solution includes the following steps:

[0093] By weight, 5.4 parts of tetraethyl orthosilicate, 4 parts of deionized water, 6.6 parts of anhydrous ethanol, and 5.4 parts of glacial acetic acid were mixed and allowed to stand for hydrolysis for 5 hours to obtain the first precursor solution. The equation or reaction mechanism involved in the first precursor solution can be described as follows:

[0094] (1) (C2H5O)4Si+4H2O→(OH)4Si +C2H5OH

[0095] (2)(OH)4Si→SiO2+2H2O

[0096] The first precursor solution of this application contains hydroxyl (-OH) hydrophilic groups, which makes the first precursor solution hydrophilic. At the same time, the inorganic silica prepared in the first precursor solution can improve the mechanical strength of the coating prepared subsequently.

[0097] In some embodiments, the preparation of the second precursor solution includes: mixing 9 to 13 parts by mass of a second silane precursor and 30 to 50 parts by mass of a solvent, followed by a second standing treatment for 3 to 8 hours. The second precursor solution mainly comprises an organosilane gel with a three-dimensional network structure. Exemplarily, the mass percentages of the second silane precursor may be 9, 10, 11, 12, or 13 parts; the mass percentages of the solvent may be 30, 35, 40, 45, or 50 parts; and the second standing treatment time may be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours.

[0098] Provided that the requirements for generating organosilane gels are met, the organosilane gels are mainly prepared from suitable and appropriate amounts of a second silane precursor and a solvent. The second silane precursor includes organosilanes and / or organosiloxanes. The organosilane can be γ-glycidoxypropyltrimethoxysilane (KH-560), or other types, such as hexamethyldisilazane (also known as hexamethyldisilazane, HMDS), i.e., (CH3)3Si-NH-Si(CH3)3, methyltriethoxysilane (MTES), dimethyldiethoxysilane (DDS), trimethylchlorosilane (TMCS), and dimethyldichlorosilane, or at least two of these. These will not be described in detail here. Other commercially available organosilanes or siloxanes can also be used, and this application does not impose any restrictions on them.

[0099] Provided that the requirement of generating organosilane gels is met, the specific type of solvent can be varied. Specifically, in some embodiments, the organic solvent includes alcohol solvents. Further, the alcohol solvent includes alcohol solvents with 1 to 10 carbon atoms, preferably alcohol solvents with 1 to 8 carbon atoms, and more preferably alcohol solvents with 1 to 4 carbon atoms. Further, in some embodiments, the solvent is any one or a mixture of any two or more of methanol, ethanol, ethylene glycol, and isopropanol in any proportion. Therefore, it is widely available, easily obtained, and low in cost. In some embodiments, the acid includes at least one of glacial acetic acid and formic acid. These two acids are low in cost, widely available, and have good performance. Further, the acid is glacial acetic acid.

[0100] In some specific embodiments, the preparation method of the above-mentioned second precursor solution includes the following steps:

[0101] By mass, 6.6 parts of KH560, 4 parts of methyltrimethoxysilane and 40 parts of anhydrous ethanol were mixed to obtain a solution, which was then allowed to stand for hydrolysis for 5 hours to obtain a second precursor solution.

[0102] The equations or reaction mechanisms involved in the above-mentioned second precursor solution can be summarized as follows:

[0103] (1)CH2CH(O)CH2O(CH2)3Si(OCH3)3+H2O→CH2CH(O)CH2O(CH2)3Si(OH)3+3CH3OH

[0104] (2)CH(O)CH2O(CH2)3Si(OH)3→nCH(O)CH2O(CH2)3SiO2+3H2O

[0105] (3)CH3Si(CH3O)3+3H2O→CH3Si(OH)3+3CH3OH

[0106] (4) CH3Si(OH)3→CH3SiO2+H2O

[0107] Therefore, this application obtains an organosilane gel through hydrolysis of a silane coupling agent and an organosiloxane. The organosilane gel contains linear Si-O-Si segments, which can covalently bond with the metal substrate to form Me-O-Si-O-. This enhances the adhesion of the coating on the heat exchanger surface and improves the corrosion resistance of the metal substrate in corrosive solutions, thus better fulfilling its barrier function. Here, Me represents a metal atom, specifically the metal atom in the metal substrate.

[0108] The preparation method of the above-mentioned third precursor solution includes the following steps:

[0109] By mass, 3 to 5 parts of titanium-containing compound, 6 to 8 parts of water, 12 to 15 parts of organic solvent, and 3 to 5 parts of acid are mixed and subjected to a third settling treatment to obtain a third precursor solution. For example, the mass parts of titanium-containing compound may be 3, 4, or 5 parts; the mass parts of water may be 6, 7, or 8 parts; the mass parts of organic solvent may be 12, 13, 14, or 15 parts; the mass parts of acid may be 3, 4, or 5 parts; and the time of the third settling treatment may be 2 hours, 3 hours, 4 hours, or 5 hours.

[0110] Provided that a stable organosilanes gel can be formed, the specific types of titanium-containing compounds and acids can be varied. Specifically, in some embodiments, the titanium-containing compound includes tetraethyl titanate. Of course, the titanium-containing compound can also be other titanium-containing compounds that can be hydrolyzed to form titanium dioxide, and this application does not impose any restrictions.

[0111] Provided that the requirement of generating organosilane gels is met, the specific types of organic solvents and acids can be diverse. Specifically, in some embodiments, the organic solvent includes alcohol solvents. Further, the alcohol solvent includes alcohol solvents with 1 to 10 carbon atoms, preferably alcohol solvents with 1 to 8 carbon atoms, and more preferably alcohol solvents with 1 to 4 carbon atoms. Further, in some embodiments, the solvent is any one or a mixture of any two or more of methanol, ethanol, ethylene glycol, and isopropanol in any proportion. This provides wide availability, easy access, and low cost. In some embodiments, the acid includes at least one of glacial acetic acid and formic acid. These two acids are low cost, widely available, and have good performance. Further, the acid is glacial acetic acid. Using alcohol solvents such as methanol, ethanol, and isopropanol helps to achieve uniform hydrolysis of organosilanes and / or siloxanes, and is widely available, easy to obtain, and low cost.

[0112] In some specific embodiments, the preparation method of the above-mentioned self-made third precursor solution includes the following steps:

[0113] By weight, 4 parts of tetrabutyl titanate, 6.6 parts of deionized water, 4 parts of glacial acetic acid, and 13.4 parts of anhydrous ethanol were mixed to obtain a solution. This solution was then allowed to stand for hydrolysis for 3 hours to obtain the third precursor solution. The equations or reaction mechanisms involved in the above third precursor solution are as follows:

[0114]

[0115] Therefore, in this step, tetraethyl titanate is used as a precursor, glacial acetic acid as a chelating agent for tetraethyl titanate, and anhydrous ethanol as a solvent. This allows tetraethyl titanate to hydrolyze uniformly in water and glacial acetic acid, reducing the aggregation of hydrolysis products and generating a stable titanium dioxide gel. The titanium dioxide gel contains -O-Ti-O segments and -Ti-O-Ti- segments. These segments can form covalent bonds with the metal substrate, improving the adhesion of the coating on the heat exchanger surface and the corrosion resistance of the metal substrate to corrosive media, thus better leveraging the barrier effect of the coating.

[0116] In the aforementioned first precursor solution, second precursor solution, and third precursor solution, the mass fraction of each component is calculated based on the total mass fraction of the first precursor solution, second precursor solution, and third precursor solution being 100.

[0117] In the preparation method of the heat exchanger of this application, a second coating is obtained by mixing a first precursor solution, a second precursor solution, and a third precursor solution. A metal substrate with a chemical conversion film layer is then impregnated with the second coating and subjected to a second curing treatment to obtain a silicon coating layer covering at least the surface of the chemical conversion film layer. During the mixing process of the first, second, and third precursor solutions, the hydrolysis products in the second and third precursor solutions undergo dehydration and condensation to form a three-dimensional network structure. Meanwhile, the silicon dioxide in the first and third precursor solutions adsorb or adhere to the three-dimensional network structure, forming a dense film structure with good compatibility. This results in a coating with both good mechanical properties and good corrosion resistance. Furthermore, the zirconium element in the first coating and the titanium element in the second coating can catalyze the hydrolysis, condensation, and organic polymerization reactions of the aforementioned three-dimensional network structure, forming an even denser coating and further enhancing the barrier properties of the prepared coating. Furthermore, during the mixing of the first precursor solution, the second precursor solution, and the third precursor solution, -Ti-O-Si-O- segments can be generated, which improves the tightness and durability of the coating.

[0118] In some embodiments, the second coating is applied to the heat exchanger by at least one of dip coating, spraying, brushing, spraying or roller coating. Considering that the organic and inorganic components in the second coating can be uniformly distributed on the surface of the chemical conversion film layer, dip coating (i.e., immersion treatment) is used to apply the second coating.

[0119] For example, the number of impregnation treatments is greater than or equal to 1, such as 1, 2, 3, 4, or 5 times. Within the above-mentioned limits, the complete impregnation of the heat exchanger, including the chemical conversion film layer, by the mixture can be guaranteed, so that the organic and inorganic components in the mixture can be evenly distributed on the surface of the chemical conversion film layer, and can fully penetrate the defects of the chemical conversion film layer and uniformly connect with the surface of the heat exchanger metal substrate, ensuring the uniformity of coating thickness and barrier effect.

[0120] In some embodiments, to ensure that the organic and inorganic components in the second coating are uniformly distributed on the surface of the chemical conversion film to form a stable coating, the temperature of the second curing treatment is 100°C to 150°C, and the time of the second curing treatment is 20 min to 40 min. Specifically, the temperature of the second curing treatment can be, for example, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C; and the time of the second curing treatment can be 20 min, 25 min, 30 min, 35 min, or 40 min.

[0121] To fully illustrate the corrosion-resistant performance of the heat exchanger provided in this application and to facilitate understanding of the invention, multiple sets of experiments were conducted for verification. The invention is further described below with reference to specific embodiments and comparative examples. Those skilled in the art will understand that the examples described in this application are only a portion of the examples, and any other suitable specific examples are within the scope of this application.

[0122] Example 1

[0123] 1. Preparation of coatings

[0124] (a) Preparation of the first coating:

[0125] Weigh out 1g of potassium fluorozirconate, 1g of potassium metavanadate, 2g of sodium fluoride, 1g of tert-butyl hydroperoxide and 30g of disodium hydrogen phosphate by mass and add them to 1L of deionized water. Stir with a magnetic stirrer until the solution is clear.

[0126] 2. Preparation of heat exchangers

[0127] (b) Pre-treatment of the heat exchanger tube surface includes: washing the heat exchanger tube with water, then performing 600-mesh and 1000-mesh sandblasting treatment on the surface of the heat exchanger tube in sequence, then ultrasonically cleaning the surface of the heat exchanger tube with anhydrous ethanol, then water system, and finally drying at 40°C.

[0128] (c) The first coating obtained in step (a) is sprayed onto the surface of the heat exchange tube in step (c), and cured at 50°C for 30 hours to obtain a heat exchanger with a chemical conversion film layer.

[0129] Example 2

[0130] 1. Preparation of coatings

[0131] (a) Preparation of the first coating:

[0132] Weigh 1g of potassium fluorozirconate, 1g of potassium metavanadate, 2g of sodium fluoride, 1g of tert-butyl hydroperoxide and 30g of disodium hydrogen phosphate and add them to 1L of deionized water. Stir with a magnetic stirrer until the solution is clear.

[0133] (b) Preparation of the second coating

[0134] Weigh out 5.4g of tetraethyl orthosilicate, 4g of deionized water, 6.6g of anhydrous ethanol and 5.4g of glacial acetic acid, mix them, and let stand for 5 hours to hydrolyze to obtain the first precursor solution.

[0135] Weigh out 6.6g of KH560, 4g of methyltrimethoxysilane and 40g of anhydrous ethanol, mix them to obtain a solution, let stand for 5 hours to hydrolyze, and obtain the second precursor solution.

[0136] Weigh out 4g of tetrabutyl titanate, 6.6g of deionized water, 4g of glacial acetic acid and 13.4g of anhydrous ethanol and mix them to obtain a solution. Let it stand for 3 hours to hydrolyze and obtain the third precursor solution.

[0137] The first precursor solution, the second precursor solution, and the third precursor solution are mixed to obtain a mixed solution for later use.

[0138] The equations or reaction mechanisms involved in the second coating can be as follows:

[0139]

[0140]

[0141] The hydrolysis products of tetraethyl orthosilicate, KH560, methyltrimethoxysilane and tetrabutyl titanate undergo mutual dehydration condensation to form a three-dimensional network structure.

[0142] 2. Preparation of heat exchangers

[0143] (c) Pre-treatment of the heat exchanger tube surface includes: washing the heat exchanger tube with water, then performing 600-mesh and 1000-mesh sandblasting treatment on the surface of the heat exchanger tube in sequence, then ultrasonically cleaning the surface of the heat exchanger tube with anhydrous ethanol, then water system, and finally drying at 40°C.

[0144] (d) The first coating obtained in step (a) is sprayed onto the surface of the heat exchange tube in step (c), and cured at 50°C for 30 hours to obtain a heat exchanger with a chemical conversion film layer.

[0145] (e) The heat exchanger obtained in step (d) above is immersed in the second coating obtained in step (b) above three times, and then dried and cured at 100°C for 30 minutes to obtain a heat exchanger with a chemical conversion film layer and an organic-inorganic hybrid silicon coating.

[0146] Example 3

[0147] The heat exchanger was prepared in the same manner as in Example 2, except that the preparation of the second coating included the following steps:

[0148] Weigh out 5.4g of tetraethyl orthosilicate, 4g of deionized water, 6.6g of anhydrous ethanol and 5.4g of glacial acetic acid by mass, mix them, and let stand for 5 hours to hydrolyze to obtain the first precursor solution.

[0149] Everything else is the same as in Example 2.

[0150] Examples 4-6

[0151] The heat exchanger was prepared in the same manner as in Example 2, except that the first coating was different.

[0152] In Example 4, the rare earth conversion coating was prepared by mixing 2g of potassium fluorozirconate, 1g of potassium metavanadate, 3g of sodium fluoride, 2g of oxidant, 25g of auxiliary precursor and 1L of water until the solution was clear, thus obtaining the first coating.

[0153] In Example 5, the rare earth conversion coating was prepared by mixing 3g of potassium fluorozirconate, 2g of potassium metavanadate, 2g of sodium fluoride, 3g of oxidant, 40g of auxiliary precursor and 1L of water until the solution was clear, thus obtaining the first coating.

[0154] In Example 6, the rare earth conversion coating was prepared by mixing 2g of potassium fluorozirconate, 3g of potassium metavanadate, 1g of sodium fluoride, 1g of oxidant, 30g of auxiliary precursor and 1L of water until the solution was clear, thus obtaining the first coating.

[0155] Everything else is the same as in Example 2.

[0156] Examples 7-9

[0157] The heat exchanger was prepared in the same manner as in Example 2, except that the first precursor solution was different.

[0158] In Example 7, 4g of the first silane precursor, 3g of water, 6g of anhydrous ethanol and 4g of acid were mixed and allowed to stand for hydrolysis for 6 hours to obtain the first precursor solution.

[0159] In Example 8, 5g of the first silane precursor, 4g of water, 7g of anhydrous ethanol and 6g of acid were mixed and allowed to stand for hydrolysis for 7 hours to obtain the first precursor solution.

[0160] In Example 9, 7g of the first silane precursor, 5g of water, 8g of anhydrous ethanol and 7g of acid were mixed and allowed to stand for hydrolysis for 8 hours to obtain the first precursor solution.

[0161] Everything else is the same as in Example 2.

[0162] Examples 10-12

[0163] The heat exchanger was prepared in the same manner as in Example 2, except that the second precursor solution was different.

[0164] In Example 10, 6g of KH560, 3g of methyltrimethoxysilane and 30g of anhydrous ethanol were weighed and mixed to obtain a solution. The solution was allowed to stand for hydrolysis for 3 hours to obtain a second precursor solution.

[0165] In Example 11, 7.5g of KH560, 3.5g of methyltrimethoxysilane and 40g of anhydrous ethanol were weighed and mixed to obtain a solution. The solution was allowed to stand for hydrolysis for 5 hours to obtain a second precursor solution.

[0166] In Example 12, 8g of KH560, 5g of methyltrimethoxysilane and 50g of anhydrous ethanol were weighed and mixed to obtain a solution. The solution was allowed to stand for hydrolysis for 8 hours to obtain a second precursor solution.

[0167] Everything else is the same as in Example 2.

[0168] Examples 13-15

[0169] The heat exchanger was prepared in the same manner as in Example 2, except that the third precursor solution was different.

[0170] In Example 13, 3g of tetrabutyl titanate, 6g of deionized water, 3g of glacial acetic acid and 12g of anhydrous ethanol were weighed and mixed to obtain a solution. The solution was allowed to stand for hydrolysis for 2 hours to obtain the third precursor solution.

[0171] In Example 14, 4g of tetrabutyl titanate, 7g of deionized water, 4g of glacial acetic acid and 14g of anhydrous ethanol were weighed and mixed to obtain a solution. The solution was allowed to stand for hydrolysis for 4 hours to obtain the third precursor solution.

[0172] In Example 15, 5g of tetrabutyl titanate, 8g of deionized water, 5g of glacial acetic acid and 15g of anhydrous ethanol were weighed and mixed to obtain a solution. The solution was allowed to stand for hydrolysis for 5 hours to obtain the third precursor solution.

[0173] Everything else is the same as in Example 2.

[0174] Comparative Example 1

[0175] The difference between Comparative Example 1 and Example 1 is that step (a) in Comparative Example 1 includes the following steps:

[0176] Weigh out 1g of potassium fluorozirconate, 2g of sodium fluoride, 1g of tert-butyl hydroperoxide and 30g of disodium hydrogen phosphate by weight and add them to 1L of deionized water. Stir with a magnetic stirrer until the solution is clear.

[0177] Comparative Example 2

[0178] The difference between Comparative Example 2 and Example 1 is that step (a) in Comparative Example 2 includes the following steps:

[0179] Weigh out 1g of potassium fluorozirconate, 1g of potassium metavanadate, 3g of sodium fluoride and 1g of tert-butyl hydroperoxide by mass and add them to 1L of deionized water. Stir with a magnetic stirrer until the solution is clear.

[0180] The coatings and heat exchangers of the above embodiments and comparative examples were subjected to performance tests respectively.

[0181] Polarization curve analysis:

[0182] Polarization curve testing used a conventional saturated calomel electrode as the reference electrode, a platinum electrode as the auxiliary electrode, and the sample as the working electrode. The sampling frequency was 2Hz, the measurement range was -600mV to 1200mV (relative to open circuit potential), and the scan rate was 0.5mV / s. Cview was used to fit the cathode segment of the polarization curve. Analyzing and studying polarization curves is one of the fundamental methods for explaining the basic laws of metal corrosion, revealing the mechanism of metal corrosion, and exploring corrosion control pathways. The curve obtained by plotting the electrode potential on the ordinate and the current flowing through the electrode on the abscissa is called a polarization curve. It characterizes the functional relationship between the driving potential of the corrosion galvanic cell reaction and the reaction rate current. The self-corrosion current density can be obtained by fitting the curve using software; generally, the lower the self-corrosion current density, the better the corrosion resistance of the material.

[0183] Polarization curve analysis results:

[0184] Figure 2 Table 1 shows the polarization curves of Comparative Example 1 and Example 1 tested in 3.5% NaCl solution. The fitting results of the polarization curve parameters for the two heat exchangers in Example 1 and Comparative Example 1 are also presented. The self-corrosion current density of the coating sample without vanadium in Comparative Example 1 and the coating sample containing zirconium, vanadium, and additives in Example 1 ranges from 3.01 × 10⁻⁶. -6 A / cm 2 It decreased to 1.03 × 10 -7 A / cm 2 The corrosion resistance of the coating samples containing zirconium, vanadium, and additives in this application has been significantly improved by an order of magnitude, indicating that the corrosion resistance of the coating samples has been significantly improved.

[0185] Table 1. Fitting results of polarization curve parameters for the two heat exchangers in Example 1 and Comparative Example 1

[0186] Sample <![CDATA[E corr (V)]]> <![CDATA[Icorr(A / cm 2 )]]> Comparative Example 1 -0.767 <![CDATA[3.01×10 -6 ]]> Example 1 -0.958 <![CDATA[1.03×10 -7 ]]>

[0187] Figure 3 Table 2 shows the polarization curves of Example 1 and Comparative Example 2 tested in 3.5% NaCl solution. The fitting results of the polarization curve parameters for the two heat exchangers in Example 1 and Comparative Example 2 are also shown. The self-corrosion current density of the coating sample without additives in Comparative Example 2 and the coating sample containing zirconium, vanadium, and additives in Example 1 ranges from 1.26 × 10⁻⁶. -6 A / cm 2 It decreased to 1.03 × 10 -7 A / cm 2 The corrosion resistance of the coating samples containing zirconium, vanadium, and additives in this application has been significantly improved by an order of magnitude, indicating that the corrosion resistance of the coating samples has been significantly improved.

[0188] Table 2. Fitting results of polarization curve parameters for the two heat exchangers in Example 1 and Comparative Example 2

[0189] Sample <![CDATA[E corr (V)]]> <![CDATA[Icorr(A / cm 2 )]]> Comparative Example 2 -0.642 <![CDATA[1.28×10 -6 <!-- 15 -->]]> Example 1 -0.958 <![CDATA[1.03×10 -7 ]]>

[0190] Figure 4 Table 3 shows the polarization curves of Examples 1 and 2 tested in 3.5% NaCl solution. Table 3 also shows the fitting results of the polarization curve parameters of the heat exchangers prepared in Examples 1-15. The self-corrosion current density of the chemical conversion film layer and silicon coating sample in Example 2, and the coating sample containing only the chemical conversion film layer in Example 1, ranges from 1.03 × 10⁻⁶. -7 A / cm 2 It decreased to 1.92×10 -9 A / cm 2 The corrosion resistance of the coating sample in Example 2 of this application decreased by two orders of magnitude, indicating that the corrosion resistance of the coating sample in Example 1 was significantly improved compared to that in Example 2.

[0191] Table 3. Fitting results of polarization curve parameters of heat exchangers prepared in Examples 1-15

[0192]

[0193]

[0194] Adhesion test:

[0195] The adhesion of a coating was determined using the cross-cut test according to GB / T9286-88. First, 11 parallel scratches, spaced 1 mm apart, were made on the coating surface of the aluminum alloy workpiece using a blade. Then, 11 more perpendicular scratches were made in the same manner, resulting in 100 small squares with a total area of ​​1 cm². 2 When marking the lines, ensure the pressure applied is sufficient to allow the blade to pierce the film layer and reach the substrate in one stroke. Then, gently brush away any remaining film layer along the diagonal of the grid with a soft brush. Cover all squares with 3M tape, pressing firmly with your fingers to ensure good contact between the tape and the film layer. Within 5 minutes of applying the tape, carefully peel it off. Determine the adhesion strength based on the proportion of the area where the film layer has peeled off to the total area of ​​the squares. Adhesion strength is divided into six levels from 0 to 5, with level 0 being the best and level 5 being the worst. The test results are shown in Table 4.

[0196] Table 4. Adhesion ratings of each embodiment and comparative example using the cross-cut adhesion test.

[0197]

[0198]

[0199] Acidic environment corrosion test:

[0200] The coating samples of Examples 1, 2, Comparative Examples 1 and 2 were immersed in an acidic environment of 3.5 t.% NaCl (pH=3). The immersion time for Example 1 was 0 days, 1 day, 2 days and 4 days, the immersion time for Comparative Examples 1 and 2 was 0 days, 1 day and 2 days, and the immersion time for Example 2 was 0 days, 30 days, 55 days, 70 days and 90 days. The surface corrosion of the coating samples of the examples and comparative examples was observed.

[0201] Results of corrosion test in acidic environment:

[0202] Figure 5 The surface corrosion of the coating sample of Example 1 of this application at 0d, 1d, 2d and 4d are shown. Figure 6 The surface corrosion of the coating sample in Example 2 of this application was observed at 0d, 1d, and 2d. Figure 7 The surface corrosion of the coating sample in Comparative Example 1 was observed at 0d, 1d, and 2d. Figure 8 To illustrate the surface corrosion of the coating samples in Comparative Example 2 at 0d, 30d, 55d, 70d, and 90d, the following tests were conducted. Figures 5-8 The comparison shows that the coating samples of Comparative Example 1 and Comparative Example 2 showed obvious corrosion on the second day of immersion, while the coating sample of Example 1 only showed corrosion on the fourth day of immersion, indicating that the coating sample of this application can significantly delay the onset of corrosion. The coating sample of Example 2 only showed relatively slight corrosion on the 70th day of immersion, indicating that the composite coating of this application can greatly increase the corrosion resistance of the heat exchanger.

[0203] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A heat exchanger, characterized in that, The heat exchanger includes a metal substrate, which includes a manifold, a heat exchange tube, and fins; the heat exchange tube is fixed to the manifold, the inner cavity of the heat exchange tube communicates with the inner cavity of the manifold, and the fins are located between two adjacent heat exchange tubes. The heat exchanger also has a coating comprising a chemical conversion film layer, the chemical conversion film layer being applied to at least a portion of the surface of the metal substrate, the chemical conversion film layer comprising zirconium and vanadium, and the chemical conversion film layer further comprising an auxiliary agent comprising at least one of phosphate and organometallic chelate. The coating further includes a silicon coating that is further away from the metal substrate than the chemical conversion film. The silicon coating comprises silicon dioxide, organosilane, and titanium dioxide. The silicon coating has a three-dimensional network structure, in which at least one of the silicon dioxide and the titanium dioxide is filled. The silicon coating is connected to the chemical conversion film through Si-O bonds.

2. The heat exchanger according to claim 1, characterized in that, The heat exchanger includes at least one of the following features (1) to (5): (1) The thickness of the chemical conversion film is 10 nm to 1 μm; (2) At least a portion of the silica is hydrophilic modified silica with a particle size in the nanometer range; (3) At least a portion of the titanium dioxide is hydrophilic titanium dioxide with a particle size in the nanometer range; (4) The thickness of the silicon coating is 1 μm to 10 μm; (5) The adhesion of the coating on the metal substrate was tested by cross-cut test and the result was grade 0.

3. A method for preparing a heat exchanger, characterized in that, Includes the following steps: A metal substrate and a first coating are provided, wherein the metal substrate has at least one fluid channel for the flow of a heat exchange medium, and the raw materials for preparing the first coating include zirconium salt, vanadium salt and auxiliary agent precursor, wherein the auxiliary agent precursor includes at least one of phosphorus-containing compound and metal chelating agent. The first coating is applied to at least a portion of the surface of the metal substrate, and a first curing treatment is performed. The metal substrate with a chemical conversion film obtained from the first curing treatment is impregnated in the second coating and then cured again. The preparation of the second coating includes the following steps: mixing a first precursor solution, a second precursor solution, and a third precursor solution to obtain the second coating; (1) The preparation of the first precursor solution includes the following steps: by mass, 4 to 7 parts of the first silane precursor, 3 to 5 parts of water, 6 to 8 parts of organic solvent and 4 to 7 parts of acid are mixed and then subjected to a first standing treatment. (2) The preparation of the second precursor solution includes the following steps: by mass, 9 to 13 parts of the second silane precursor and 30 to 50 parts of solvent are mixed and then subjected to a second standing treatment; (3) The preparation of the third precursor solution includes the following steps: by mass, 3 to 5 parts of titanium-containing compound, 6 to 8 parts of water, 12 to 15 parts of organic solvent and 3 to 5 parts of acid are mixed and then subjected to a third standing treatment.

4. The preparation method according to claim 3, characterized in that, The provision of the first coating includes the following steps: The preparation method comprises, by weight, 0.1 to 0.3 parts of potassium fluorozirconate, 0.1 to 0.3 parts of potassium metavanadate, 0.1 to 0.3 parts of sodium fluoride, 0.1 to 0.3 parts of oxidant, 2 to 4 parts of auxiliary precursor and the balance of water, and includes at least one of the following features (1) to (4): (1) The auxiliary agent precursor includes at least one of phosphate, tannic acid, chitosan and polyvinyl alcohol; (2) The oxidant includes tert-butyl hydrogen peroxide; (3) The temperature of the first curing treatment is 40℃~60℃; (4) The time for the first curing treatment is 20 min to 40 min.

5. The preparation method according to claim 3, characterized in that, The preparation method includes at least one of the following features (1) to (3): (1) The number of impregnation treatments is greater than or equal to 1; (2) The temperature of the second curing treatment is 100℃~150℃; (3) The time for the second curing process is 20 min to 40 min.

6. The preparation method according to claim 3, characterized in that, The preparation method includes at least one of the following features (1) to (3): (1) The first silane precursor includes at least one of tetraethyl orthosilicate and tetramethyl orthosilicate, the organic solvent includes at least one of anhydrous ethanol, ethylene glycol, methanol and isopropanol, the acid includes at least one of glacial acetic acid and formic acid, and the first standing treatment time is 4h to 8h. (2) The second silane precursor includes organosilane and / or organosiloxane, and the second silane precursor includes at least one of γ-glycidoxypropyltrimethoxysilane, hexamethyldisilazane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylchlorosilane and dimethyldichlorosilane, and the solvent includes at least one of anhydrous ethanol, ethylene glycol, methanol and isopropanol, and the second standing treatment time is 3h to 8h; (3) The titanium-containing compound includes at least one of tetraethyl titanate and titanium dioxide, the organic solvent includes at least one of anhydrous ethanol, ethylene glycol, methanol and isopropanol, the acid includes at least one of formic acid and glacial acetic acid, and the third standing treatment time is 2h to 5h.

7. A thermal management system, characterized in that, The thermal management system includes a compressor, a first heat exchanger, a throttling device, and a second heat exchanger. At least one of the first heat exchanger and the second heat exchanger is a heat exchanger as described in any one of claims 1 to 2 or a heat exchanger prepared by the method described in any one of claims 3 to 6. When there is refrigerant flowing in the thermal management system, the refrigerant flows into the first heat exchanger through the compressor, and after heat exchange occurs in the first heat exchanger, it flows into the throttling device. Then, the refrigerant flows into the second heat exchanger and undergoes heat exchange in the second heat exchanger.

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