An ionic liquid-based brightener for die cast aluminum surfaces and a method of making the same

Abstract

The present application relates to a kind of ion liquid-based whitening agent for die-casting aluminum surface and its preparation method.The whitening agent is made of the following components by weight parts: 1-butyl-3-methyl imidazolium tetrafluoroborate 2-8 parts, hydrogen peroxide 2-5 parts, phytic acid 0.05-1 part, succinic acid 0.05-1 part, acetylenic diol polyoxyethylene ether 0.01-0.5 part, imidazoline quaternary ammonium salt 0.01-1 part, stabilizer 0.01-0.1 part, deionized water 80-96 parts.The present application uses 1-butyl-3-methyl imidazolium tetrafluoroborate as film-forming accelerator, hydrogen peroxide as oxidant, phytic acid and succinic acid as low-concentration organic acid, through "oxidation-complexation-adsorption" synergistic mechanism, white conversion film is generated in situ on the surface of die-casting aluminum, and it is chromium-free, environmentally friendly and safe.

Description

Technical Field

[0001] This invention relates to the field of metal material surface treatment technology, and more particularly to an ionic liquid-based whitening agent for die-cast aluminum surfaces and its preparation method. Background Technology

[0002] Die-cast aluminum alloys are widely used in automotive parts, electronics and communications, and aerospace industries due to their excellent casting and machinability. However, the high levels of alloying elements such as silicon and copper in die-cast aluminum can easily result in a grayish-black or dark gray surface with uneven color, severely affecting the appearance quality of subsequent surface treatments such as coating and electroplating. Therefore, whitening the surface of die-cast aluminum to obtain a uniform and dense silvery-white appearance is a crucial step in its surface treatment process.

[0003] Existing aluminum whitening technologies for die casting mainly suffer from the following problems: Traditional processes often use chromium-containing passivation, but hexavalent chromium is carcinogenic and highly toxic, failing to meet environmental protection requirements. Electrochemical methods require external power supplies and complex auxiliary tooling, resulting in large equipment investments, numerous processing steps, and long processing times. Furthermore, they suffer from uneven current distribution for complex-shaped die castings, making it difficult to meet the needs of large-scale continuous production. In addition, some existing chromium-free chemical whitening agents often use high amounts of organic acids, leading to significant corrosion of the aluminum substrate during processing and poor bath stability.

[0004] In conclusion, developing a chromium-free, low-corrosion, uniformly film-forming, environmentally friendly, and highly efficient surface brightener for die-cast aluminum is a technical challenge that urgently needs to be solved in the current surface treatment field. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an ionic liquid-based whitening agent for die-cast aluminum surfaces and its preparation method. This whitening agent, through the synergistic effect of 1-butyl-3-methylimidazolium tetrafluoroborate, hydrogen peroxide, phytic acid, succinic acid, acetylacetonate polyoxyethylene ether, and imidazoline quaternary ammonium salt, achieves a white die-cast aluminum surface with excellent surface uniformity and salt spray resistance through a one-step chemical immersion method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] In a first aspect, an ionic liquid-based whitening agent for use on the surface of die-cast aluminum is provided, which is formulated from the following components in parts by weight:

[0008] 2-8 parts of 1-butyl-3-methylimidazolium tetrafluoroborate;

[0009] 2-5 parts hydrogen peroxide;

[0010] Phytic acid 0.05-1 part;

[0011] Succinic acid 0.05-1 part;

[0012] 0.01-0.5 parts of acetylacetonate diol polyoxyethylene ether;

[0013] 0.01-1 part of imidazoline quaternary ammonium salt;

[0014] Stabilizer 0.01-0.1 parts;

[0015] 80-96 parts of deionized water.

[0016] Furthermore, the stabilizer is selected from sodium pyrophosphate, sodium silicate, or sodium stannate.

[0017] Furthermore, the mass ratio of hydrogen peroxide to phytic acid is 5-40:1.

[0018] Furthermore, the hydrophilic-lipophilic balance value of the acetylacetonate diol polyoxyethylene ether is 8-13.

[0019] Furthermore, the pH value of the whitening agent is 3.5-4.0.

[0020] This invention utilizes hydrogen peroxide as a green oxidant to micro-etch and oxidize the surface of die-cast aluminum, removing residual mold release agent and oxide layer, exposing a clean aluminum substrate, and providing an active surface for subsequent film formation. Phytic acid, as a natural organic phosphonic acid, can rapidly complex with the aluminum ions dissolved from oxidation to form a network of organic-inorganic hybrid films with excellent corrosion resistance and a white appearance. 1-Butyl-3-methylimidazolium tetrafluoroborate, as a film-forming promoter, has cations that can selectively adsorb onto active sites on the aluminum surface, regulating the film growth rate and making the film crystallization more refined and uniform, thereby significantly improving the whiteness and gloss of the surface. Inorganic stabilizers are introduced to effectively inhibit the decomposition of hydrogen peroxide and the oxidative deterioration of ionic liquids by complexing trace metal impurity ions or adjusting the solution potential.

[0021] In a second aspect, a method for preparing the ionic liquid-based whitening agent for die-cast aluminum surfaces as described in the first aspect is provided, comprising the following steps:

[0022] (1) Mix 1-butyl-3-methylimidazolium tetrafluoroborate with deionized water and stir to dissolve at 20-40℃ to prepare a base solution;

[0023] (2) Add phytic acid, succinic acid and stabilizer to the base solution obtained in step (1) in sequence, and stir until completely dissolved;

[0024] (3) Adjust the temperature of the mixture obtained in step (2) to 25-30℃, slowly add hydrogen peroxide under stirring, and control the temperature not to exceed 35℃ during the addition process. After the addition is complete, continue stirring for 5-10 minutes.

[0025] (4) Add acetylacetonate diol polyoxyethylene ether and imidazoline quaternary ammonium salt to the mixture obtained in step (3) and stir to dissolve;

[0026] (5) Adjust the pH of the mixture obtained in step (4) to 3.5-4.0, and then pass it through a 200-400 mesh sieve to remove insoluble matter, thereby obtaining the ionic liquid-based whitening agent.

[0027] Furthermore, in step (1), the stirring speed is 100-300 rpm and the time is 15-30 minutes.

[0028] Furthermore, in step (2), the stirring speed is 150-250 rpm and the time is 10-20 minutes.

[0029] Furthermore, in step (3), the temperature during the addition of hydrogen peroxide does not exceed 35°C, and the stirring time is 5-10 minutes.

[0030] Furthermore, in step (4), the stirring speed is 100-200 rpm, the temperature is 20-30℃, and the time is 10-20 minutes.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) This invention innovatively introduces 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid as a film-forming promoter. The cations of this ionic liquid are positively charged and can preferentially adsorb onto the active sites on the surface of die-cast aluminum, achieving a dynamic balance between selective etching and film formation. The imidazoline quaternary ammonium salt corrosion inhibitor used in this invention has a similar structure to the cation of the ionic liquid. The two undergo synergistic co-adsorption on the aluminum surface, effectively filling the voids in the adsorption layer and forming a dense protective layer, significantly enhancing the corrosion inhibition effect. At the same time, the low concentration of ionic liquid ensures that the system has low viscosity and good fluidity, which is beneficial for industrial operation.

[0033] (2) This invention constructs a hydrogen peroxide-phytic acid dual film-forming system. Hydrogen peroxide acts as the main oxidant, oxidizing the aluminum surface in situ to form a white aluminum oxide / aluminum hydroxide film; phytic acid, utilizing its multidentate coordination ability, complexes with the aluminum ions generated by oxidation, depositing in situ to form a dense white conversion film of aluminum phytate. The composite superposition of the two white film layers significantly improves the whiteness and corrosion resistance of the die-cast aluminum surface. In addition, the pH value of the system is strictly controlled at 3.5-4.0, which, combined with the steric hindrance effect of ionic liquids, effectively inhibits the formation of free precipitates of aluminum phytate in the bulk solution, ensuring that the film-forming reaction only occurs on the aluminum surface and guaranteeing the stability of the bath solution.

[0034] (3) This invention utilizes the extremely low surface tension of acetylacetonate diol polyoxyethylene ether to enable the whitening agent to spread rapidly and penetrate into the micropores and complex structures of the die-cast aluminum surface. The presence of ionic liquid improves the adsorption state of surfactant at the interface, prolongs the effective wetting time, avoids surface spots caused by uneven wetting, and achieves overall uniform whitening. Detailed Implementation

[0035] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0036] The acetylenol polyoxyethylene ether used in the embodiments of the present invention is 2,4,7,9-tetramethyl-5-decyn-4,7-diol ethoxylate, which is a commercially available product (Evonik Surfynol 440, Surfynol 465).

[0037] The imidazoline quaternary ammonium salt used in the embodiments of the present invention is 1-(2-hydroxyethyl)-2-heptadecenylimidazoline quaternary ammonium salt. Example 1

[0038] Whitening agent formula (parts by weight):

[0039] 4 parts of 1-butyl-3-methylimidazolium tetrafluoroborate;

[0040] 3.5 parts hydrogen peroxide;

[0041] Phytic acid 0.5 parts;

[0042] 0.5 parts succinic acid;

[0043] 0.25 parts of acetylacetonate diol polyoxyethylene ether;

[0044] 0.5 parts of imidazoline quaternary ammonium salt;

[0045] Sodium pyrophosphate 0.05 parts;

[0046] 90 parts of deionized water.

[0047] Preparation method:

[0048] (1) Add 1-butyl-3-methylimidazolium tetrafluoroborate and deionized water to a reaction vessel and stir at 200 rpm for 23 minutes at 30°C until completely dissolved to prepare a base solution.

[0049] (2) Add phytic acid, succinic acid and sodium pyrophosphate to the base solution obtained in step (1) in sequence, and stir at 200 rpm for 15 minutes at 30°C.

[0050] (3) Adjust the temperature of the mixture obtained in step (2) to 28°C, and slowly add hydrogen peroxide under stirring. During the addition process, control the reaction temperature to not exceed 35°C. After the addition is complete, continue stirring for 8 minutes.

[0051] (4) Add acetylation glycol polyoxyethylene ether and imidazoline quaternary ammonium salt to the mixture obtained in step (3), and stir at 150 rpm for 15 minutes at 25°C until completely dissolved.

[0052] (5) Adjust the pH of the mixture obtained in step (4) to 3.7, and then pass it through a 300-mesh sieve to remove insoluble matter, thereby obtaining the ionic liquid-based whitening agent. Example 2

[0053] Whitening agent formula (parts by weight):

[0054] 2 parts of 1-butyl-3-methylimidazolium tetrafluoroborate;

[0055] Two parts hydrogen peroxide;

[0056] Phytic acid 0.05 parts;

[0057] 0.08 parts of succinic acid;

[0058] 0.03 parts of acetylacetonate diol polyoxyethylene ether;

[0059] 0.05 parts of imidazoline quaternary ammonium salt;

[0060] Sodium silicate 0.02 parts;

[0061] 95 parts of deionized water.

[0062] Preparation method:

[0063] (1) Add 1-butyl-3-methylimidazolium tetrafluoroborate and deionized water to a reaction vessel and stir at 100 rpm for 30 minutes at 20°C until completely dissolved to prepare a base solution.

[0064] (2) Add phytic acid, succinic acid and sodium silicate to the base solution obtained in step (1) in sequence, and stir at 150 rpm for 20 minutes at 20°C.

[0065] (3) Adjust the temperature of the mixture obtained in step (2) to 25°C, and slowly add 2 parts of hydrogen peroxide under stirring. During the addition process, control the reaction temperature to not exceed 35°C. After the addition is complete, continue stirring for 5 minutes.

[0066] (4) Add acetylacetonate polyoxyethylene ether and imidazoline quaternary ammonium salt to the mixture obtained in step (3), and stir at 100 rpm for 20 minutes at 20°C until completely dissolved.

[0067] (5) Adjust the pH of the mixture obtained in step (4) to 3.5, and then pass it through a 200-mesh sieve to remove insoluble matter, thereby obtaining the ionic liquid-based whitening agent. Example 3

[0068] Whitening agent formula (parts by weight):

[0069] 7 parts of 1-butyl-3-methylimidazolium tetrafluoroborate;

[0070] 5 parts hydrogen peroxide;

[0071] Phytic acid 1 part;

[0072] 1 part succinic acid;

[0073] 0.4 parts of acetylacetonate diol polyoxyethylene ether;

[0074] 1 part imidazoline quaternary ammonium salt;

[0075] Sodium pyrophosphate 0.1 parts;

[0076] 84 portions of deionized water.

[0077] Preparation method:

[0078] (1) Add 1-butyl-3-methylimidazolium tetrafluoroborate and deionized water to a reaction vessel and stir at 300 rpm for 15 minutes at 40°C until completely dissolved to prepare a base solution.

[0079] (2) Add phytic acid, succinic acid and sodium pyrophosphate to the base solution obtained in step (1) in sequence, and stir at 250 rpm for 10 minutes at 40°C.

[0080] (3) Adjust the temperature of the mixture obtained in step (2) to 30°C, and slowly add hydrogen peroxide under stirring. During the addition process, control the reaction temperature to not exceed 35°C. After the addition is complete, continue stirring for 10 minutes.

[0081] (4) Add acetylacetonate polyoxyethylene ether and imidazoline quaternary ammonium salt to the mixture obtained in step (3), and stir at 200 rpm for 10 minutes at 30°C until completely dissolved.

[0082] (5) Adjust the pH of the mixture obtained in step (4) to 4.0, and then pass it through a 400-mesh sieve to remove insoluble matter, thereby obtaining the ionic liquid-based whitening agent.

[0083] Comparative Example 1

[0084] Based on Example 1, hydrogen peroxide was not added, and all other conditions were the same as in Example 1.

[0085] Comparative Example 2

[0086] Based on Example 1, phytic acid was not added, and other conditions were the same as in Example 1.

[0087] Comparative Example 3

[0088] Based on Example 1, without adding hydrogen peroxide and phytic acid, all other conditions are the same as in Example 1.

[0089] Comparative Example 4

[0090] Based on Example 1, 1-butyl-3-methylimidazolium tetrafluoroborate was not added, and other conditions were the same as in Example 1.

[0091] Comparative Example 5

[0092] Based on Example 1, phytic acid and succinic acid were replaced with citric acid and tartaric acid, respectively, while other conditions remained the same as in Example 1.

[0093] Comparative Example 6

[0094] Based on Example 1, the acetylacetonate diol polyoxyethylene ether was replaced with an alkyl glycoside, and other conditions were the same as in Example 1.

[0095] Comparative Example 7

[0096] Based on Example 1, the imidazoline quaternary ammonium salt was replaced with benzotriazole, and other conditions were the same as in Example 1.

[0097] Comparative Example 8

[0098] Based on Example 1, without the addition of acetylation diol polyoxyethylene ether, all other conditions are the same as in Example 1.

[0099] Comparative Example 9

[0100] Based on Example 1, the pH value of the whitening agent was adjusted to 2.5, and other conditions were the same as in Example 1.

[0101] Comparative Example 10

[0102] Based on Example 1, the pH value of the whitening agent was adjusted to 5.5, and other conditions were the same as in Example 1.

[0103] Effect verification

[0104] Immerse the ADC12 die-cast aluminum test piece in the whitening agents prepared in the above examples and comparative examples, treat it at 40-70℃ for 5-15 minutes, remove it, rinse it with deionized water, and dry it to obtain a white surface. Test the surface whiteness, surface uniformity, coating adhesion and salt spray resistance.

[0105] Surface whiteness testing: A colorimeter (spectrophotometer) was used, employing the CIELab color space, D65 standard light source, and a 10° viewing angle. The instrument's measuring probe was placed vertically and firmly against the surface of the test piece. Five different locations (four corners and the center) were selected for measurement on each test piece, and the L value was recorded. The arithmetic mean was taken as the final result. The instrument was calibrated using a standard white board before testing. The testing was based on ASTM D2244 and ISO 7724.

[0106] Surface uniformity testing: Under a standard D65 light source, at a distance of approximately 300mm from the test piece, visually observe the uniformity of color on the surface, checking for defects such as obvious color differences, mottling, flow marks, and blackening. Surface uniformity is categorized into four levels: Excellent (completely uniform color, no color difference or mottling), Good (basically uniform color, with slight color differences or mottling), Medium (uneven color, with obvious color differences or mottling), and Poor (severely uneven color, with obvious blackened areas). The testing is based on GB / T15114.

[0107] Salt spray resistance testing: A neutral salt spray test was used. The test specimen was placed in a salt spray chamber, sprayed with a 5% sodium chloride aqueous solution, with the pH value controlled between 6.5 and 7.2, and the chamber temperature maintained at 35±2℃. The specimen was placed at an angle of 15 to 30° to the vertical. Continuous spraying was performed, and the specimen was removed and observed every 5 hours. The time when the first white rust appeared on the surface of the specimen was recorded. The test was conducted according to GB / T 10125-2012.

[0108] Table 1. Performance test results of each embodiment and comparative example.

[0109]

[0110] The results show that this invention achieves efficient whitening and corrosion protection of die-cast aluminum surfaces through the synergistic effect of its components. Compared with the examples, the whiteness and salt spray resistance of Comparative Examples 1 and 2 decreased significantly, while the performance of Comparative Example 3 was the lowest. This indicates that the oxidation film formation by hydrogen peroxide and the complexation film formation by phytic acid constitute a synergistic "oxidation-complexation" dual mechanism, both of which are indispensable and key to obtaining a high-whiteness, high-corrosion-resistant film. Comparative Example 4 shows that the ionic liquid, through selective adsorption on the aluminum surface, protects the aluminum matrix and disperses and stabilizes phytic acid, playing an important role in improving the whitening effect and bath stability. The decreased performance of Comparative Example 5 proves the superiority of the multidentate coordination structure of phytic acid in film density; the slight decrease in performance of Comparative Example 6 confirms that the ultra-low surface tension of acetylenic diol helps the solution penetrate into the micropores of die-cast aluminum and achieve uniform whitening; the decreased salt spray resistance of Comparative Example 7 verifies the "co-adsorption" effect formed by the structural similarity between imidazoline and ionic liquid, whose corrosion inhibition effect is superior to traditional corrosion inhibitors. Comparative Example 8 demonstrates that the ultra-low surface tension of acetylenic diol plays a crucial role in the penetration of the chemical solution into the micropores of die-cast aluminum and the achievement of overall uniform whitening. Comparative Example 9, due to excessive acidity leading to over-corrosion, showed a significant decrease in whiteness and salt spray resistance. In Comparative Example 10, the accelerated complexation reaction rate between phytic acid and aluminum ions easily resulted in the formation of free precipitates in the solution, leading to turbidity of the bath solution and uneven film formation.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An ionic liquid-based brightener for use on the surface of die-cast aluminum, characterized in that, It is formulated by weight of the following components: 2-8 parts of 1-butyl-3-methylimidazolium tetrafluoroborate; 2-5 parts hydrogen peroxide; Phytic acid 0.05-1 part; Succinic acid 0.05-1 part; 0.01-0.5 parts of acetylacetonate diol polyoxyethylene ether; 0.01-1 part of imidazoline quaternary ammonium salt; Stabilizer 0.01-0.1 parts; 80-96 parts deionized water; The pH value of the whitening agent is 3.5-4.

0.

2. The ionic liquid-based whitening agent for die-cast aluminum surfaces according to claim 1, characterized in that, The stabilizer is selected from sodium pyrophosphate, sodium silicate, or sodium stannate.

3. The ionic liquid-based brightener for die-cast aluminum surfaces according to claim 1, characterized in that, The mass ratio of hydrogen peroxide to phytic acid is 5-40:

1.

4. The ionic liquid-based brightener for die-cast aluminum surfaces according to claim 1, characterized in that, The hydrophilic-lipophilic balance value of the acetylacetonitrile polyoxyethylene ether is 8-13.

5. A method for preparing an ionic liquid-based whitening agent for die-cast aluminum surfaces as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Mix 1-butyl-3-methylimidazolium tetrafluoroborate with deionized water and stir to dissolve at 20-40℃ to prepare a base solution; (2) Add phytic acid, succinic acid and stabilizer to the base solution obtained in step (1) in sequence, and stir to dissolve; (3) Adjust the temperature of the mixture obtained in step (2) to 25-30℃, slowly add hydrogen peroxide under stirring, control the temperature during the addition process, and continue stirring after the addition is complete; (4) Add acetylacetonate diol polyoxyethylene ether and imidazoline quaternary ammonium salt to the mixture obtained in step (3) and stir to dissolve; (5) Adjust the pH of the mixture obtained in step (4) to 3.5-4.0, and then pass it through a 200-400 mesh sieve to remove insoluble matter, thereby obtaining the ionic liquid-based whitening agent.

6. The method for preparing an ionic liquid-based brightener for die-cast aluminum surfaces according to claim 5, characterized in that, In step (1), the stirring speed is 100-300 rpm and the time is 15-30 minutes.

7. The method for preparing an ionic liquid-based brightener for die-cast aluminum surfaces according to claim 5, characterized in that, In step (2), the stirring speed is 150-250 rpm and the time is 10-20 minutes.

8. The method for preparing an ionic liquid-based brightener for die-cast aluminum surfaces according to claim 5, characterized in that, In step (3), the temperature during the addition of hydrogen peroxide does not exceed 35°C, and the stirring time is 5-10 minutes.

9. The method for preparing an ionic liquid-based brightener for die-cast aluminum surfaces according to claim 5, characterized in that, In step (4), the stirring speed is 100-200 rpm, the temperature is 20-30℃, and the time is 10-20 minutes.

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