A passivation agent for die-cast aluminum and aluminum alloy conversion film and a preparation method thereof

Abstract

The application belongs to the technical field of metal surface treatment, and particularly relates to a passivation agent for a conversion film of die-cast aluminum and aluminum alloy and a preparation method thereof, which comprises gamma-aminopropyl triethoxysilane, cyclopentadienyl dibutoxy titanium chloride, fatty alcohol polyoxyethylene ether sodium carboxylate, zirconium isooctoate, aluminum coupling agent AL-M and water. The passivation agent for the conversion film of the die-cast aluminum provided by the application does not contain strong acid, strong base and phosphorus components, is friendly to the environment, is safe to operate in production and use, has a simple operation process, does not have obvious corrosion or discoloration on a metal substrate, and can reach 120 hours in neutral salt spray.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a passivating agent for conversion coating of die-cast aluminum and aluminum alloys and its preparation method. Background Technology

[0002] Die-cast aluminum and aluminum alloys possess advantages such as lightweight, high strength, and good thermal conductivity, making them widely used in the automotive, aerospace, electronics, construction, sporting goods, and outdoor products industries. Their superior performance makes them an ideal alternative to traditional materials, and with advancements in technology and materials science, their application areas will continue to expand. Because aluminum is relatively reactive, aluminum products are easily oxidized if exposed directly to air; therefore, surface treatment is crucial. Applying a chemical passivation coating (aluminum passivator) to the surface of die-cast aluminum and aluminum alloys provides a solid foundation for corrosion protection and aesthetics.

[0003] Currently, the passivation process for die-cast aluminum and aluminum alloys is still mainly chromate passivation. Chromate passivation films have excellent self-healing properties and corrosion resistance, making them suitable for almost all die-cast aluminum and aluminum alloy passivation materials. However, in traditional chromate passivation processes, the chromate content in the passivation bath is usually high, such as 20-50 g / L, the operating temperature is often high, such as 80-90℃, and the passivation time is long, such as 10-20 minutes. Furthermore, chromium is a toxic heavy metal that poses potential hazards to human health and the environment. Chromium compounds easily release harmful substances such as hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) during preparation and use, which pose risks of carcinogenicity, mutagenicity, and sensitization. According to relevant environmental regulations, the use and emission of chromium-containing passivating agents are strictly limited, making the development of environmentally friendly, chromium-free passivating agents an inevitable trend.

[0004] Chinese patent CN 103320780 A discloses a high-efficiency room-temperature aluminum alloy passivation solution and its preparation process. Based on 100 parts by weight, it contains the following substances: 0.136–0.707 parts potassium dichromate, 0.043–0.50 parts ammonium fluoride, 0.043–0.44 parts ferric chloride, 0.48–0.98 parts citric acid, 0.48–0.98 parts rare earth metals, 0.48–0.98 parts boric acid, and 95.41–98.34 parts pure water. This passivation solution can operate stably at 20–35°C, with a passivation time of 15–50 seconds and a drying temperature of 60–80°C. However, this passivation solution contains chromium salts, which are extremely harmful to the environment, and at a relatively high concentration. Furthermore, the passivation speed is too fast, resulting in a passivation film with high porosity and insufficient adhesion, making it unsuitable for large-scale use.

[0005] Chinese patent CN 106119825 A discloses an aluminum passivating agent, which, by weight, consists of the following components: 1-2 parts calcium chloride, 8.5 parts malonic acid, 6.5 parts organophosphonic acid, 1.8 parts 2-phospho-1,2,4-tricarboxylate butane, 2.3 parts hydroxypropyl cellulose, 2.1 parts castor oil polyoxyethylene ether, 0.7 parts β-naphthylamine, 1.5 parts isomeric decaol polyoxyethylene ether, 1.1 parts titanium acetylacetonate, and 40 parts deionized water. While this aluminum passivating agent can form a good passivation film on the aluminum alloy surface, the film alters the original color. Furthermore, its neutral salt spray performance is poor, resulting in poor effectiveness for die-cast aluminum workpieces and making it difficult to achieve ideal results.

[0006] Therefore, for existing die-cast aluminum and aluminum alloy conversion film passivating agents used for metal passivation treatment, forming a passivation conversion film on the metal surface, the corrosion resistance, rust prevention, wear resistance, heat resistance, cold resistance, weather resistance, surface finish of the conversion film, and the requirement that the system retains the original color of the workpiece and is free of phosphorus and environmental pollutants are technical problems that urgently need to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a passivating agent for conversion coating of die-cast aluminum and aluminum alloys and its preparation method. This agent does not contain strong acids or alkalis, nor harmful components such as chromium and phosphorus. It is environmentally friendly, does not cause significant corrosion or discoloration to the substrate, and its conversion coating exhibits strong corrosion resistance, rust prevention, abrasion resistance, heat resistance, cold resistance, weather resistance, and surface smoothness. It can retain the original color of the substrate and enhance its brightness, and can withstand neutral salt spray for up to 120 hours.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A passivating agent for conversion coating of die-cast aluminum and aluminum alloys includes γ-aminopropyltriethoxysilane, cyclopentadienyldibutoxytitanium chloride, sodium fatty alcohol polyoxyethylene ether carboxylate, zirconium isooctanoate, aluminum coupling agent AL-M, and deionized water.

[0010] This invention synergistically combines γ-aminopropyltriethoxysilane, cyclopentadienyl dibutoxytitanium chloride, sodium fatty alcohol polyoxyethylene ether carboxylate, zirconium isooctanoate, and aluminum coupling agent AL-M. γ-aminopropyltriethoxysilane, as an organosilicon compound, reacts with the aluminum surface to form a film-forming framework of organosilica-alumina compound, providing adhesion sites for subsequent film formation. Cyclopentadienyl dibutoxytitanium chloride exhibits excellent chelating properties, while zirconium isooctanoate serves not only as a catalyst but also as a crucial component of the passivation film. Sodium fatty alcohol polyoxyethylene ether carboxylate is a surfactant with good dispersibility and emulsifying properties, enabling uniform dispersion of the passivating agent components in the solution and improving the passivation effect. During the passivation process, a film-forming framework containing aluminum oxide (A₂O₃) is first formed on the surface of the die-cast aluminum and aluminum alloy substrates. With the continuous reaction of γ-aminopropyltriethoxysilane, zirconium isooctanoate, and cyclopentadienyldibutoxytitanium chloride, Ti and Zr oxides are gradually introduced into this framework, and the conversion film framework gradually takes shape. However, the adhesion of the framework at this stage is poor. The introduction of the aluminum coupling agent AL-M can form chemical bonds with the aluminum surface, enhancing the adhesion of the passivation layer and improving the passivation effect. To further demonstrate the rationality of this formulation, the passivated die-cast aluminum and aluminum alloys were tested using scanning electron microscopy and energy dispersive spectroscopy. The results show that the passivation film consists of two layers: an aluminum oxide layer near the metal surface and a compound layer containing Zr and O near the surface. When polymers and their derivatives are added to the passivation solution, an organic film is formed on the surface of the passivation film. The study shows that this film is very thin. Both Zr and Ti elements are present in the passivation film, and the Ti and Zr elements are uniformly distributed on the substrate surface and around the active sites.

[0011] This invention provides a passivating agent for conversion coating of die-cast aluminum and aluminum alloys. It does not contain strong acids or alkalis, nor harmful components such as chromium and phosphorus, and is environmentally friendly. Its conversion coating has strong corrosion resistance, rust prevention, abrasion resistance, heat resistance, cold resistance, weather resistance, and surface smoothness. It can retain the original color of the substrate and enhance its brightness. It can withstand neutral salt spray for up to 120 hours.

[0012] The effects of introducing the above-mentioned raw materials are as follows:

[0013] γ-aminopropyltriethoxysilane: The main film-forming framework. As an organosilicon compound, it reacts with oxides on the aluminum surface to form a protective organosilicon layer. This protective layer improves passivation and enhances the corrosion resistance and wear resistance of aluminum materials.

[0014] Cyclopentadienyl dibutoxytitanium chloride: As a titanium compound, it possesses excellent chelating properties. It can react with oxides on the aluminum surface to form a protective layer of titanium compound. This protective layer enhances the passivation effect and improves the corrosion resistance and wear resistance of aluminum materials.

[0015] Sodium fatty alcohol polyoxyethylene ether carboxylate: As a surfactant, it has good dispersibility and emulsifying properties. It can uniformly disperse the various components of the passivating agent in the solution, ensuring the uniformity of the passivating agent and improving the passivation effect.

[0016] Zirconium isooctanoate: As a catalyst and passivating agent, it can react with oxides on the aluminum surface to form a protective layer of organic acid salts. This protective layer can enhance the passivation effect and improve the corrosion resistance and wear resistance of aluminum materials.

[0017] Aluminum coupling agent AL-M: As a special compound, it can form chemical bonds with the aluminum surface. These chemical bonds enhance the adhesion between the passivation layer and the aluminum surface, improve the passivation effect, and ensure the stability of the passivation layer.

[0018] Preferably, the components include the following parts by weight:

[0019] The γ-aminopropyltriethoxysilane: 10-15 parts;

[0020] The cyclopentadienyl dibutoxy titanium chloride: 0.5–2 parts;

[0021] The sodium fatty alcohol polyoxyethylene ether carboxylate: 0.5-2 parts;

[0022] Zirconium isooctanoate: 0.5–2 parts;

[0023] The aluminum coupling agent AL-M: 1 to 5 parts;

[0024] Deionized water: 74–87.5 parts.

[0025] Preferably, the components include the following parts by weight:

[0026] The γ-aminopropyltriethoxysilane: 13 parts;

[0027] The cyclopentadienyl dibutoxy titanium chloride: 1.5 parts;

[0028] Sodium carboxylate of fatty alcohol polyoxyethylene ether: 1.5 parts;

[0029] Zirconium isooctanoate: 1.5 parts;

[0030] The aluminum coupling agent AL-M: 3 parts;

[0031] Deionized water: 79.5 parts.

[0032] A method for preparing the above-mentioned passivating agent for conversion coating of die-cast aluminum and aluminum alloys includes the following steps:

[0033] (1) Add some deionized water to the container, heat it while stirring, add the γ-aminopropyltriethoxysilane and the cyclopentadienyldibutoxytitanium chloride, and keep it warm and stir until completely dissolved;

[0034] (2) Add the sodium fatty alcohol polyoxyethylene ether carboxylate and the aluminum coupling agent AL-M, and stir until completely dissolved;

[0035] (3) Lower the temperature, add the zirconium isooctanoate, and stir until completely dissolved;

[0036] (4) Add the remaining ionized water to the total volume of the solution, stir well, and obtain the passivating agent for die-cast aluminum and aluminum alloy conversion film.

[0037] Preferably, the volume ratio of deionized water added in step (1) and step (4) is 3:4; in step (1), the temperature is raised to 65°C; in step (3), the temperature is lowered to room temperature.

[0038] An application of the above-mentioned passivating agent for conversion coating of die-cast aluminum and aluminum alloys, used for passivation of die-cast aluminum and aluminum alloy workpieces.

[0039] Preferably, it includes the following steps:

[0040] A. Perform surface cleaning on the die-cast aluminum and aluminum alloy workpieces; perform appropriate surface cleaning such as degreasing and dewaxing on the die-cast aluminum and aluminum alloy workpieces;

[0041] B. Acidification is performed on the die-cast aluminum and aluminum alloy workpieces to remove surface impurities and further remove surface metal ash.

[0042] C. Dilute the passivating agent for conversion coating of die-cast aluminum and aluminum alloy with deionized water to obtain a passivation industrial liquid. Stir evenly and passivate the die-cast aluminum and aluminum alloy workpieces to obtain passivated die-cast aluminum and aluminum alloy workpieces.

[0043] D. The passivated die-cast aluminum and aluminum alloy workpieces are cured.

[0044] Preferably, in step A, the surface cleaning includes one or more of degreasing and dewaxing; step C includes: diluting the passivating agent for die-cast aluminum and aluminum alloy conversion coating with deionized water to 30-100 times its volume to obtain the passivation industrial liquid, stirring evenly, controlling the temperature at 20-35°C, and passivating the die-cast aluminum and aluminum alloy workpieces for 1-3 minutes; step D includes: curing the passivated die-cast aluminum and aluminum alloy workpieces in an oven at 100°C.

[0045] A passivated workpiece obtained by the above application.

[0046] Compared with the prior art, implementing the present invention has the following beneficial effects:

[0047] 1. It abandons the traditional strong acid, strong alkali and high chromium heavy metal system. All materials used are low toxicity, phosphorus-free, and use easily biodegradable surfactants, which greatly reduces the COD of the system and meets the requirements of chemical production.

[0048] 2. The passivation operation is carried out at a normal temperature of 20-35℃, which saves energy. The passivation working solution is relatively stable, which can avoid the problem of thin film or loose and porous film due to excessively high or low temperature, which will reduce the corrosion resistance of the film. The passivation film has good quality and is easy to control.

[0049] 3. The film formation speed is moderate, the passivation film does not change the original color of the workpiece, the passivation time is moderate, and it is easy to implement;

[0050] 4. The resulting passivation film has good corrosion resistance, and can withstand salt spray tests for more than 120 hours (with no white rust or white spots on the workpiece surface). It has low porosity and does not require the use of a sealant.

[0051] 5. The resulting passivation film adheres firmly and can greatly improve the adhesion between the workpiece and the paint or powder coating. Attached Figure Description

[0052] Figure 1 The image shows the scanning electron microscope and energy dispersive spectroscopy (EDS) results of the aluminum substrate before passivation.

[0053] Figure 2 The image shows the results of scanning electron microscopy and energy dispersive spectroscopy tests on the passivated aluminum substrate.

[0054] Figure 3 The image shows the 3D fluorescence electron microscope test results of the aluminum substrate before passivation.

[0055] Figure 4 This is a 3D fluorescence electron microscope image of the passivated aluminum substrate. Detailed Implementation

[0056] To make the technical solution of the present invention easier to understand, the present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. Modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and substance of the present invention are all within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0057] Example of effect 1

[0058] Examples 1-7 and Comparative Examples 1-8 respectively show the composition ratios of the passivating agents for die-cast aluminum and aluminum alloy conversion films of the present invention, as detailed in Table 1. The ingredient values ​​are by mass, with the remainder being water. Furthermore, to highlight the superiority of cyclopentadienyldibutoxytitanium chloride, Comparative Example 9 replaced the organic cyclopentadienyldibutoxytitanium chloride in the formulation with inorganic titanium chloride, while keeping all other conditions unchanged, and a control experiment was conducted.

[0059] Table 1. Formulation composition of Examples 1-7 and Comparative Examples 1-9

[0060]

[0061]

[0062] The preparation methods of the passivating agent for die-cast aluminum and aluminum alloy conversion coating in Examples 1-7 and Comparative Examples 1-9 are as follows: Add 600 ml of deionized water to a 2000 ml beaker, heat to 65°C with stirring, add γ-aminopropyltriethoxysilane and cyclopentadienyldibutoxytitanium chloride, and keep warm and stir until completely dissolved; add sodium fatty alcohol polyoxyethylene ether carboxylate and aluminum coupling agent AL-M, and stir until completely dissolved; lower the temperature to room temperature, add zirconium isooctanoate, and stir until completely dissolved; add the remaining required deionized water to the total volume of the solution, stir well, and the passivating agent for die-cast aluminum and aluminum alloy conversion coating of the present invention can be obtained.

[0063] Performance testing

[0064] In this embodiment of the invention, the neutral salt spray corrosion test (NSS) method for workpieces treated with die-cast aluminum and aluminum alloy conversion film passivating agent is as follows: referring to ISO3768 standard, the selected workpieces after treatment are placed in a salt spray corrosion test chamber. The salt water contains 5% (wt) sodium chloride, pH value is 6.5-7.2, temperature is (35±2)℃, mist drop is 1-2 mL / (h·cm2), and the time is 120 hours. After that, observe whether there is rust. If there is rust, measure the rust area and calculate the percentage of the rust area to the surface area of ​​the workpiece.

[0065] Porosity of the conversion film: Take a distilled aqueous solution containing 14% sodium chloride, 0.35% aluminum reagent, and 1.0% white gelatin, stored in a brown bottle. Cut filter paper into pieces 10 cm long and 10 cm wide. Use plastic tweezers to immerse the paper pieces in the solution, remove them, drain off any excess solution, and cover the passivation film surface of the workpiece (the conversion film should be longer and wider than 10 cm). After 5 minutes, remove the paper and observe the film surface. Red spots indicate porous areas. Take three parallel samples for each test and calculate the average number of orange-red spots per square centimeter.

[0066] Adhesion of conversion film and powder coating: The test was conducted according to the method described in the national standard GB / T 9286-1998 "Paints and Varnishes Cross-cut Test". One horizontal and one vertical cross-cut tester was used to make 100 1mm cross-cuts on the surface of the sample. 2 The grid is divided into squares, requiring the substrate to be exposed at the scratches. After marking the grid, special 3M tape is applied to the entire marked area, and then the tape is quickly peeled off. This is repeated 5 times. The paint film in the marked area is observed with a magnifying glass to see if there is any peeling. The paint peeling is rated according to its degree.

[0067] The specific test results are shown in Table 2:

[0068] Table 2

[0069]

[0070]

[0071] This invention provides a passivating agent for conversion coatings on die-cast aluminum and aluminum alloys. During the passivation process, a film-forming framework containing aluminum silicate is first formed on the surface of the die-cast aluminum or aluminum alloy substrate. With the continuous reaction of γ-aminopropyltriethoxysilane, zirconium isooctanoate, and cyclopentadienyldibutoxytitanium chloride, Ti and Zr oxides are gradually introduced into this framework, and the conversion coating framework is gradually formed. However, the adhesion of the framework is poor at this stage. The introduction of the aluminum coupling agent AL-M can form chemical bonds with the aluminum surface, enhancing the adhesion of the passivation layer and improving the passivation effect. The synergistic effect of these four components improves the passivation efficiency.

[0072] As shown in Tables 1 and 2, insufficient addition of γ-aminopropyltriethoxysilane prevents the formation of a film-forming framework during passivation, resulting in poor corrosion resistance. Excessive γ-aminopropyltriethoxysilane causes whitening or uneven coloring on the workpiece surface, affecting subsequent salt spray performance. Insufficient or absent addition of zirconium isooctanoate and cyclopentadienyldibutoxytitanium chloride leads to large areas of white spots on the workpiece after film formation, while excessive addition results in a few spots, affecting subsequent salt spray performance. Insufficient or absent introduction of the aluminum coupling agent AL-M leads to poor adhesion of the coating on the workpiece. Since the conversion film formed during passivation involves a two-way reaction of dissolution and film formation, the orderly introduction of components in specific proportions can greatly improve the film formation effect and passivation efficiency.

[0073] Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and 3D fluorescence electron microscopy (3DFEM) were performed on the aluminum substrates before and after passivation. The results are as follows: Figures 1-4 As shown. From the appendix Figures 1-4 This further demonstrates that Example 6 is the best among the optimal proportions. Figure 1 and Figure 3It is a raw, untreated workpiece with a relatively rough surface and an Al composition. Figure 2 and Figure 4 The finished product after optimal treatment has a relatively dense passivation film on its surface, and the film is composed of Al, Ti and Zr oxide film. Corresponding to the theory, it is this passivation film that blocks the corrosion of environmental acids and alkalis, thereby improving salt spray performance.

[0074] Furthermore, experiments conducted in Comparative Example 9, where the organic compound cyclopentadienyldibutoxytitanium chloride was replaced with the inorganic compound titanium chloride, showed that the surface salt spray performance was significantly worse after the replacement, comparable to Comparative Example 4, and the passivation film failed to form. The following are possible reasons for this result: 1. Difference in reactivity between the two compounds in the system: Cyclopentadienyldibutoxytitanium chloride possesses a cyclopentadienyl structure and exhibits high reactivity. Titanium chloride, on the other hand, does not contain a cyclopentadienyl structure and has lower reactivity. Therefore, replacing cyclopentadienyldibutoxytitanium chloride with titanium chloride may lead to a decrease in the reaction rate or prevent the reaction from proceeding. 2. Impurity introduction: Cyclopentadienyldibutoxytitanium chloride is an organic compound, while titanium chloride is an inorganic compound. Replacing cyclopentadienyldibutoxytitanium chloride may introduce impurities, affecting the purity and performance of the passivating agent. 3. Deterioration in passivation film quality: Cyclopentadienyldibutoxytitanium chloride exhibits good performance in aluminum passivation films, providing excellent protection. Replacing cyclopentadienyldibutoxytitanium chloride with titanium chloride may lead to a decrease in the quality of the passivation film, affecting the protective effect on the aluminum surface. Therefore, replacing the organic cyclopentadienyldibutoxytitanium chloride with inorganic titanium chloride in this formulation system will bring adverse consequences such as differences in reactivity, impurity generation, and a decrease in the quality of the passivation film, ultimately resulting in a result similar to Comparative Example 4.

[0075] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a reference structure" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A passivating agent for conversion coating of die-cast aluminum and aluminum alloys, characterized in that, The components include the following parts by weight: γ-aminopropyltriethoxysilane: 10-15 parts; Cyclopentadienyl dibutoxytitanium chloride: 0.5~2 parts; Sodium fatty alcohol polyoxyethylene ether carboxylate: 0.5~2 parts; Zirconium isooctanoate: 0.5~2 parts; Aluminum coupling agent AL-M: 1~5 parts; Deionized water: 74~87.5 parts.

2. The passivating agent for conversion coating of die-cast aluminum and aluminum alloys as described in claim 1, characterized in that, The components include the following parts by weight: The γ-aminopropyltriethoxysilane: 13 parts; The cyclopentadienyl dibutoxy titanium chloride: 1.5 parts; Sodium carboxylate of fatty alcohol polyoxyethylene ether: 1.5 parts; Zirconium isooctanoate: 1.5 parts; The aluminum coupling agent AL-M: 3 parts; Deionized water: 79.5 parts.

3. A method for preparing a passivating agent for conversion coating of die-cast aluminum and aluminum alloys as described in claim 1, characterized in that, Includes the following steps: (1) Add some deionized water to the container, heat it while stirring, add the γ-aminopropyltriethoxysilane and the cyclopentadienyldibutoxytitanium chloride, and keep it warm and stir until completely dissolved; (2) Add the sodium fatty alcohol polyoxyethylene ether carboxylate and the aluminum coupling agent AL-M, and stir until completely dissolved; (3) Lower the temperature, add the zirconium isooctanoate, and stir until completely dissolved; (4) Add the remaining deionized water to the total volume of the solution, stir well, and obtain the passivating agent for die-cast aluminum and aluminum alloy conversion film.

4. The preparation method according to claim 3, characterized in that, The volume ratio of deionized water added in step (1) to step (4) is 3:4; in step (1), the temperature is raised to 65°C; in step (3), the temperature is lowered to room temperature.

5. The application of the passivating agent for conversion coating of die-cast aluminum and aluminum alloys as described in claim 1, characterized in that, Used for passivation of die-cast aluminum and aluminum alloy workpieces.

6. The application as described in claim 5, characterized in that, Includes the following steps: A. Clean the surface of the die-cast aluminum and aluminum alloy workpieces; B. Acidification of the die-cast aluminum and aluminum alloy workpieces; C. Dilute the passivating agent for conversion coating of die-cast aluminum and aluminum alloy with deionized water to obtain a passivation industrial liquid. Stir evenly and passivate the die-cast aluminum and aluminum alloy workpieces to obtain passivated die-cast aluminum and aluminum alloy workpieces. D. The passivated die-cast aluminum and aluminum alloy workpieces are cured.

7. The application as described in claim 6, characterized in that, In step A, the surface cleaning includes one or more of degreasing and dewaxing; the operation in step C includes: diluting the passivating agent for conversion coating of die-cast aluminum and aluminum alloy with deionized water to 30 to 100 times the volume to obtain the passivation industrial liquid, stirring evenly, controlling the temperature at 20 to 35°C, and passivating the die-cast aluminum and aluminum alloy workpieces for 1 to 3 minutes; the operation in step D includes: curing the passivated die-cast aluminum and aluminum alloy workpieces in an oven at 100°C.

8. A passivated workpiece obtained by the application as described in claim 5.

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