A microporous etching solution, an aluminum alloy workpiece, and an aluminum alloy pretreatment method

Abstract

The application provides a micropore etching solution, an aluminum alloy workpiece and an aluminum alloy pretreatment method. The micropore etching solution can be used for aluminum alloy pretreatment. The aluminum alloy treated by the micropore etching solution has high peeling strength with a sprayed coating, and has good high-temperature resistance and high-pressure resistance. In addition, the aluminum alloy pretreatment method forms a micropore layer on the surface of the aluminum alloy by performing micropore etching treatment on the aluminum alloy subjected to oil removal treatment and acid pickling treatment by using the micropore etching solution, so that the aluminum alloy has high peeling strength with the sprayed coating, and has good high-temperature resistance and high-pressure resistance. Moreover, the preparation process has high production efficiency, low cost and is environment-friendly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface treatment of aluminum alloy profiles, and particularly relates to a microporous etching solution, an aluminum alloy workpiece and an aluminum alloy pretreatment method. BACKGROUND

[0002] Aluminum alloy is widely used in many parts of new energy vehicles to further improve the lightweight degree of the vehicle. Due to the presence of different alloying elements in the aluminum alloy, the corrosion resistance is poor. In order to improve the corrosion resistance, the industry often sprays the aluminum alloy, and pretreatment is required before spraying the aluminum alloy to strengthen the bonding force between the aluminum alloy substrate and the sprayed coating, so as to ensure the corrosion resistance and decoration performance of the aluminum alloy.

[0003] However, the film layer prepared on the surface of the aluminum alloy by the current aluminum alloy pretreatment process before spraying has poor bonding force with the sprayed coating, and cannot effectively and durably play its anticorrosion role, and cannot meet the performance requirements of high temperature resistance and high pressure resistance. SUMMARY

[0004] Therefore, the present application provides a microporous etching solution, an aluminum alloy workpiece and an aluminum alloy pretreatment method. The microporous etching solution can be used for aluminum alloy pretreatment. The aluminum alloy treated by the microporous etching solution has high peeling strength with the sprayed coating and good high temperature resistance and high pressure resistance. In addition, the aluminum alloy pretreatment method uses the microporous etching solution to perform microporous etching treatment on the aluminum alloy after oil removal treatment and pickling treatment, forms a microporous layer on the surface of the aluminum alloy, so that the aluminum alloy has high peeling strength with the sprayed coating and good high temperature resistance and high pressure resistance. Moreover, the preparation process has high production efficiency, low cost and is environmentally friendly.

[0005] Specifically, in a first aspect, the present application provides a microporous etching solution for aluminum alloy pretreatment, which comprises one or more of polyethylene glycol or polyethylene glycol ether, and trivalent chromium salt, molybdate, acid, amide, fluorosilicate and dispersant.

[0006] The microporous etching solution provided by the present application contains trivalent chromium salt and molybdate. In some embodiments, the trivalent chromium salt comprises one or more of chromium chloride, chromium sulfate, chromium nitrate and bromide. In some embodiments, the molybdate comprises one or more of sodium molybdate, potassium molybdate and ammonium molybdate.

[0007] The trivalent chromium salt in the microporous etching solution provides chromium ions as a chromium source, and the molybdate salt provides molybdenum ions as a molybdenum source, which are deposited on the surface of the aluminum alloy to prevent corrosion of the surface of the aluminum alloy substrate by the acid. In addition, the amide is adsorbed on the surface of the aluminum alloy, and the fluorosilicate reacts with the surface of the aluminum alloy to form a non-uniform and non-dense nanofilm, both of which slow down or hinder the displacement reaction of the chromium ions and the molybdenum ions with the aluminum alloy, and at the same time control the corrosion rate of the acid, resulting in different corrosion rates of different parts of the surface of the aluminum alloy, and thus a large number of microporous pits are formed. In addition, the polyethylene glycol or polyethylene glycol ether is adsorbed on the surface of the aluminum alloy while playing a certain barrier role and can disperse metal ions. The purpose of adding the dispersant is to disperse the metal ions, so that the metal ions do not locally aggregate, thereby improving the uniformity of the microporous pits.

[0008] The acid can cause corrosion on the surface of the aluminum alloy substrate. In some embodiments, the acid includes one or more of acetic acid, succinic acid, sulfamic acid, and salicylic acid, but is not limited thereto.

[0009] In some embodiments, the amide includes one or more of dimethylformamide, dimethylacetamide, and dimethylbenzamide. The optional fluorosilicate includes one or more of ammonium fluorosilicate, potassium fluorosilicate, and sodium fluorosilicate.

[0010] In some embodiments, the dispersant includes an alkali metal phosphate. In further embodiments, the alkali metal phosphate includes one or more of sodium tripolyphosphate, sodium hexametaphosphate, and sodium pyrophosphate. Preferably, the dispersant is sodium tripolyphosphate.

[0011] In some embodiments, the trivalent chromium salt has a mass concentration of 0.1 g / L-0.5 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 0.1 g / L-0.3 g / L, 0.2 g / L-0.4 g / L of the trivalent chromium salt, for example 0.15 g / L, 0.25 g / L. In some embodiments, the molybdate salt has a mass concentration of 0.1 g / L-0.5 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 0.1 g / L-0.3 g / L, 0.2 g / L-0.4 g / L of the molybdate salt, for example 0.15 g / L, 0.25 g / L. In some embodiments, the acid has a mass concentration of 3 g / L-12 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 3 g / L-8 g / L, 5 g / L-10 g / L of the acid, for example 4 g / L, 6 g / L, 7 g / L, 9 g / L. In some embodiments, the amide has a mass concentration of 3 g / L-6 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 3 g / L-5 g / L of the amide, for example 3.5 g / L, 4 g / L, 4.5 g / L. In some embodiments, the fluosilicate salt has a mass concentration of 1 g / L-5 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 1 g / L-3 g / L, 2 g / L-4 g / L of the fluosilicate salt, for example 1.5 g / L, 2.5 g / L, 3.5 g / L. In some embodiments, the polyethylene glycol or polyethylene glycol ether has a mass concentration of 0.1 g / L-0.5 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 0.1 g / L-0.3 g / L, 0.2 g / L-0.4 g / L of the polyethylene glycol or polyethylene glycol ether, for example 0.15 g / L, 0.25 g / L. In some embodiments, the dispersant has a mass concentration of 0.1 g / L-0.5 g / L in the microporous etching solution. Preferably, the microporous etching solution can contain 1.5 g / L-2.5 g / L of the dispersant, for example 1.5 g / L, 1.8 g / L, 2 g / L.

[0012] In some embodiments, the polyethylene glycol or polyethylene glycol ether has an average molecular weight of 4000-6000.

[0013] Using the microporous etching solution for pre-treatment of aluminum alloy before spraying can form a microporous layer, so that the bonding force with the sprayed coating is strong, the peeling strength is high, reaching more than 150 N, and it is resistant to high temperature and high pressure. The aluminum alloy spraying process referred to herein includes but is not limited to powder spraying and paint spraying.

[0014] In a second aspect, the present application provides an aluminum alloy pre-treatment method, comprising the following steps:

[0015] oil removal treatment and acid pickling treatment of the aluminum alloy, and

[0016] immersing the aluminum alloy subjected to the degreasing treatment and the pickling treatment into a microporous etching solution to perform a microporous etching treatment, thereby forming a microporous layer on the surface of the aluminum alloy,

[0017] wherein the microporous etching solution comprises one or more of polyethylene glycol or polyethylene glycol ether, and a trivalent chromium salt, a molybdate, an acid, an amide, a fluorosilicate, and a dispersant.

[0018] In some embodiments, the microporous etching treatment comprises: immersing for 1-5 minutes at 10-30°C. Preferably, immersing at 15-25°C.

[0019] In some embodiments, the degreasing treatment comprises: immersing the aluminum alloy into a degreasing solution with a pH of 3-10 to remove grease on the surface of the aluminum alloy. In further embodiments, the degreasing solution used is an acidic degreasing solution. In other embodiments, the degreasing solution used is an alkaline degreasing solution. The acidic degreasing solution or the alkaline degreasing solution can be selected according to the actual situation of the aluminum alloy workpiece.

[0020] In some embodiments, the aluminum alloy is immersed into the degreasing solution for 2-3 minutes under the assistance of ultrasonic waves.

[0021] In some embodiments, the aluminum alloy is immersed into the degreasing solution for 5-10 minutes at room temperature.

[0022] In some embodiments, the degreasing solution contains the following components (a)-(d):

[0023] (a) sodium silicate, ammonium hydrogen fluoride, and sodium carbonate,

[0024] (b) ethylenediamine tetramethylene phosphonic acid or tetrahydroxypropyl ethylenediamine, and

[0025] (c) a complexing agent, the complexing agent comprising one or more of sodium citrate, potassium citrate, citric acid, and potassium sodium tartrate,

[0026] (d) a surfactant, the surfactant comprising one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, OP-10, and peregal.

[0027] The presence of the complexing agent in the degreasing solution not only can complex various heavy metals to improve the degreasing efficiency, but also can ensure the slow release during the degreasing process and the brightness and appearance brightness of the surface of the aluminum alloy.

[0028] In some embodiments, the pickling treatment comprises: immersing the aluminum alloy into a pickling solution with a pH of 2-3. Through the pickling treatment, the unqualified layer, oxide and other impurities on the surface of the aluminum alloy, as well as the defects such as pits and cracks can be removed, so that the aluminum alloy with a flat surface is obtained, which is beneficial to the subsequent process.

[0029] Preferably, the aluminum alloy is immersed into the pickling solution at 10-30°C for 1-3 minutes. Preferably, the immersion is at 15-25°C.

[0030] In some embodiments, the pickling solution contains hydrofluoric acid, citric acid, sodium nitrate, sodium m-nitrobenzenesulfonate and polyethylene glycol.

[0031] In the third aspect, the present application provides an aluminum alloy workpiece, wherein a microporous layer is formed on the surface of the aluminum alloy workpiece, and the microporous layer is formed by the method of the second aspect of the present application or by the microporous etching solution of the first aspect of the present application.

[0032] In some embodiments, the microporous layer has a porosity of 20-70% and a pore size of 0.1-3 microns. Preferably, the porosity is 30-65%, 45-60%.

[0033] In some embodiments, a spray coating layer is arranged on the microporous layer. The spray coating layer on the microporous layer of the aluminum alloy workpiece can be formed by processes such as powder spraying and paint spraying. The powder spraying or paint spraying of the aluminum alloy can adopt electrostatic spraying technology, including powder electrostatic spraying and liquid-phase electrostatic spraying.

[0034] The spray coating layer can be an insulating coating. In some embodiments, the spray coating layer contains one or more of thermosetting resin, thermoplastic resin and fluorocarbon resin. For example, polyurethane resin, epoxy resin, acrylic resin, hydroxyl polyester resin, polyvinylidene fluoride resin.

[0035] In some embodiments, the thickness of the spray coating layer is 50-350 microns. Preferably, the thickness of the spray coating layer is 100-150 microns, or 150-250 microns, or 250-300 microns. The aluminum alloy workpiece of the present application can be combined with a spray coating layer with various thicknesses, especially within the above thickness range.

[0036] The aluminum alloy workpiece provided by the third aspect of the present application has high peel strength with the spray coating layer, reaching 150N or more; and the aluminum alloy workpiece has good high-temperature resistance and high-pressure resistance, is not easy to peel and bubble after high-temperature baking, can withstand a direct current voltage of more than 4000V, and can meet the voltage resistance requirements of vehicle-mounted battery insulation. In addition, the aluminum alloy workpiece has high adaptability with other workpieces, and has low cost and short construction period. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1A scanning electron microscope (SEM) image of the microporous layer according to Example 1 is shown. DETAILED DESCRIPTION

[0038] The technical solutions of the embodiments of the present application are described in detail below through a plurality of examples and comparative examples.

[0039] Example 1

[0040] (1) Oil removal and pickling treatment process

[0041] The aluminum alloy was immersed in an oil removal liquid with a pH of 3 for 3 minutes under ultrasonic assistance, wherein the oil removal liquid contained the following components: sodium silicate: 0.4 g / L; citric acid: 3 g / L; ammonium hydrogen fluoride: 5 g / L; ethylenediamine tetramethylene phosphoric acid: 0.7 g / L; sodium carbonate: 0.4 g / L; and peregal: 1 g / L.

[0042] The aluminum alloy treated by the oil removal liquid was immersed in a pickling liquid with a pH of 2 for 2 minutes at 10°C, wherein the pickling liquid contained the following components: hydrofluoric acid: 3 g / L; citric acid: 5 g / L; sodium nitrate: 2 g / L; sodium m-nitrobenzenesulfonate: 1.5 g / L; and polyethylene glycol 1000: 0.3 g / L.

[0043] (2) Microporous etching liquid treatment process

[0044] The aluminum alloy treated by the pickling liquid was immersed in a microporous etching liquid for 3 minutes at 10°C, wherein the microporous etching liquid contained the following components: chromium chloride: 0.3 g / L; sodium molybdate: 0.2 g / L; dimethyl formamide: 4 g / L; polyethylene glycol 5000: 0.3 g / L; sodium tripolyphosphate: 2 g / L; acetic acid: 8 g / L; and ammonium fluorosilicate: 3 g / L.

[0045] An aluminum alloy workpiece S1 with a microporous layer formed on the surface was prepared through the above steps. Figure 1 The scanning electron microscope (SEM) image shown demonstrates that a microporous layer is formed on the surface of the aluminum alloy workpiece.

[0046] Examples 2-9

[0047] The aluminum alloy was pretreated according to the oil removal and pickling treatment process and the microporous etching liquid treatment process described in Example 1 to prepare aluminum alloy workpieces S2-S9 with a microporous layer formed on the surface, with the difference being that the components of the microporous etching liquid used were different. The components of the microporous etching liquid of Examples 1-9 are listed in Table 1 below.

[0048] Table 1 Components of the microporous etching liquid of Examples 1-9

[0049]

[0050] Comparative Example 1

[0051] The aluminum alloy was pretreated according to the oil removal and pickling treatment process described in Example 1, except that the microporous etching liquid treatment was not performed, to obtain a common aluminum alloy workpiece DS1.

[0052] Comparative Example 2

[0053] The aluminum alloy was pretreated according to the oil removal and pickling treatment process described in Example 1, the microporous etching liquid treatment process, except that the microporous etching liquid used did not contain chromium chloride and sodium molybdate, to obtain a common aluminum alloy workpiece DS2.

[0054] Comparative Example 3

[0055] The aluminum alloy was pretreated according to the oil removal and pickling treatment process described in Example 1, the microporous etching liquid treatment process, except that the microporous etching liquid used did not contain acetic acid, to obtain a common aluminum alloy workpiece DS3.

[0056] Comparative Example 4

[0057] The aluminum alloy was pretreated according to the oil removal and pickling treatment process described in Example 1, the microporous etching liquid treatment process, except that the microporous etching liquid used did not contain dimethylformamide, polyethylene glycol and sodium tripolyphosphate, to obtain a common aluminum alloy workpiece DS4.

[0058] Comparative Example 5

[0059] According to the process described in the CN202111218244.3 patent Figure 1 , a common aluminum alloy workpiece DS5 was prepared.

[0060] Comparative Example 6

[0061] According to the process described in Example 1 of the CN201710287447.5 patent, a common aluminum alloy workpiece DS6 was prepared.

[0062] Spraying process

[0063] The pretreated aluminum alloy workpieces S1-S9 and DS1-DS6 were subjected to powder spraying treatment according to the following operations.

[0064] The aluminum alloy workpiece was dried at 80°C for 15 minutes, and the insulating powder was sprayed onto the outer surface of the aluminum alloy workpiece by an electrostatic spray gun to complete the first spraying. After baking, the powder was sprayed onto the outer surface of the aluminum alloy workpiece by the electrostatic spray gun to complete the second spraying. Finally, the sprayed aluminum alloy workpiece was placed in a curing oven and baked at 190°C for 20 minutes for curing and drying, to obtain a coating with a thickness in the range of 250-300 μm.

[0065] Test Example

[0066] The porosity of the microporous layer was measured using an industrial CT. The aluminum alloy workpieces of Examples 1-9 and Comparative Examples 1-6 were respectively subjected to T-peel strength (25 degrees) test, grid test, high temperature resistance test, and pressure resistance test after powder spraying. The results are summarized in Table 1 below. Among them, the T-peel strength (25 degrees) test was performed according to ASTM D1876 adhesive peel strength test method. The high temperature resistance test was to place the prepared aluminum alloy workpiece in an oven and heat it at 300°C for 10 minutes to observe the morphology change. The pressure resistance test was to directly place the prepared aluminum alloy workpiece in a pressure resistance tester and pass a direct current for 60 seconds to observe the morphology change.

[0067] Table 2 summarizes the test results of each aluminum alloy workpiece

[0068]

[0069]

[0070] As can be seen from the results in Table 2, the T-peel strength of the aluminum alloy workpiece provided by the embodiments of the present application is above 150N, can withstand a direct current of above 4000V, and no large-scale peeling phenomenon occurs on the surface of the workpiece after 300°C high temperature test. It shows that the T-peel strength of the aluminum alloy workpiece provided by the present application is high, and has good high temperature resistance and high pressure resistance. The T-peel strength of the aluminum alloy workpieces DS1-DS6 of the comparative examples is lower, and the high temperature resistance and high pressure resistance are worse.

[0071] The above describes exemplary embodiments of the present application. It should be noted that for those skilled in the art, without departing from the principles of the present application, some improvements and refinements can be made, which are also considered within the protection scope of the present application.

Claims

1. A microporous etching solution for pretreatment of aluminum alloys, characterized by, The microporous etching solution comprises one or more of polyethylene glycol and polyethylene glycol ether, and a trivalent chromium salt, a molybdate, an acid, an amide, a fluorosilicate, and a dispersant; The mass concentration of the trivalent chromium salt in the microporous etching solution is 0.1-0.5 g / L, the mass concentration of the molybdate is 0.1-0.5 g / L, the mass concentration of the acid is 3-12 g / L, the mass concentration of the amide is 3-6 g / L, the mass concentration of the fluorosilicate is 1-5 g / L, the mass concentration of the polyethylene glycol or the polyethylene glycol ether is 0.1-0.5 g / L, and the mass concentration of the dispersant is 1-3 g / L.

2. The micropore etching solution according to claim 1, wherein The trivalent chromium salt comprises one or more of chromium chloride, chromium sulfate, chromium nitrate, and chromium bromide.

3. The micropore etching solution according to claim 1, wherein The molybdate comprises one or more of sodium molybdate, potassium molybdate, and ammonium molybdate.

4. The micropore etching solution according to claim 1, wherein The acid comprises one or more of acetic acid, succinic acid, sulfamic acid, and salicylic acid; and the amide comprises one or more of dimethylformamide, dimethylacetamide, and dimethylbenzamide.

5. The micropore etching solution according to claim 1, wherein The dispersant comprises an alkali metal phosphate, which comprises one or more of sodium tripolyphosphate, sodium hexametaphosphate, and sodium pyrophosphate.

6. An aluminum alloy pretreatment method characterized by, The method comprises the following steps: subjecting the aluminum alloy to a degreasing treatment and an acid pickling treatment, and immersing the aluminum alloy subjected to the degreasing treatment and the acid pickling treatment in the microporous etching solution of any one of claims 1-5 to perform a microporous etching treatment, thereby forming a microporous layer on the surface of the aluminum alloy.

7. The pre-treatment method according to claim 6, characterized in that, The microporous etching treatment comprises immersion for 1-5 minutes at 10-30°C.

8. An aluminum alloy workpiece, characterized by, The surface of the aluminum alloy workpiece is provided with a microporous layer formed by the pretreatment method of claim 6 or 7, or formed by the microporous etching solution of any one of claims 1-5.

9. The aluminum alloy workpiece of claim 8, The microporous layer has a porosity of 20-70% and a pore size of 0.1-3 microns.

10. The aluminum alloy workpiece of claim 8, The microporous layer is provided with a spray coating layer containing one or more of a thermosetting resin, a thermoplastic resin, and a fluorocarbon resin.

11. The aluminum alloy workpiece of claim 10, The thickness of the spray coating layer is 50-350 microns.

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