Die-casting aluminum drawing agent and preparation method thereof

Abstract

The invention discloses a die-casting aluminum drawing agent and a preparation method thereof, and relates to the technical field of metal material surface treatment. The die-casting aluminum drawing agent comprises a surfactant, an organic acid complexing agent, a corrosion inhibitor, a pH regulator, a modified nano reinforcing agent and deionized water, wherein the modified nano reinforcing agent is prepared by modifying nano silicon dioxide and nano aluminum oxide through a surface modifier. The method eliminates chromium, fluorine and nitric acid pollution in a traditional process, has the advantages of being good in treatment effect, safe to operate, economical, environmentally friendly and the like, and can be widely applied to surface treatment of the die-casting aluminum alloy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material surface treatment, in particular to a die-casting aluminum etching agent and a preparation method thereof. BACKGROUND

[0002] Die-casting aluminum alloys, especially high-silicon aluminum alloys such as ADC12 and A380, have been widely used in the fields of automobile manufacturing, electronic communication, aerospace, household appliances, etc. due to their excellent casting performance, good machining performance and relatively low cost. During the forming process of die-casting aluminum parts, a complex contamination layer often exists on the surface due to the use of release agents, high-temperature oxidation, and silicon segregation, etc. including grease, oxide scale, and silicon-rich layer, etc. These surface defects seriously affect the quality of subsequent surface treatment such as electroplating, spraying, and anodic oxidation, etc.

[0003] The traditional die-casting aluminum surface treatment process mainly adopts a multi-step chemical treatment method, which usually includes 8 to 10 processes such as chemical degreasing → water washing → acid pickling to remove oxide scale → water washing → lightening → water washing → passivation → water washing → drying, etc. These traditional processes have many serious problems, such as serious environmental pollution, complex and lengthy process flow, high energy consumption and low efficiency, poor operation safety, unstable treatment effect, poor adaptability, etc. In the prior art, the chromate passivation process uses hexavalent chromium compounds (such as chromic anhydride and sodium dichromate, etc.), and chromium(VI) is an internationally recognized strong carcinogen with teratogenic, carcinogenic, and mutagenic effects. The treatment of wastewater containing chromium is difficult and costly; the fluoride-containing acid pickling process uses hydrofluoric acid or ammonium hydrogen fluoride for pickling and activation, and fluoride ions pollute water bodies, destroy the ecological environment, and harm animals and plants and the human skeletal system; the use of nitric acid-based treatment agents produces nitrogen oxides through the decomposition of nitric acid, forming "yellow smoke" and causing air pollution and acid rain problems, and causing serious harm to the respiratory systems of operators, serious equipment corrosion, and high maintenance costs; the phosphating process produces phosphorus-containing wastewater, leading to water eutrophication, promoting the overgrowth of algae, and disrupting the balance of the water ecosystem.

[0004] The die-casting aluminum etching agent prepared by the present application discards harmful substances such as fluorine and nitric acid, eliminates environmental pollution from the source, simplifies wastewater treatment, conforms to the current green and environmentally friendly development direction, integrates multiple steps into one step, greatly reduces equipment investment and land area, and improves production efficiency. Moreover, the etching agent prepared by the present application is safe to operate and easy to use, can effectively improve the working environment, protect the health of operators, and reduce the risk of occupational health. SUMMARY

[0005] The present application aims to provide a die-casting aluminum etching agent and a preparation method thereof to solve the problems in the prior art.

[0006] In order to solve the above technical problems, the present application provides the following technical solutions: A method for preparing a whitening agent for die-cast aluminum includes the following preparation steps: (1) Pretreatment: Heat deionized water to 40~50℃, slowly add pH adjuster, and stir until completely dissolved; (2) Add organic acid complexing agent and corrosion inhibitor in sequence, keep the temperature at 45~55℃, and stir for 35~45min; (3) Slowly add the surfactant, controlling the addition rate to 1~2 kg / min, and stir for 20~30 minutes to obtain a mixed solution; (4) The modified nano-reinforcing agent is pre-dispersed in a small amount of deionized water and ultrasonically dispersed for 10-15 minutes to obtain a modified nano-reinforcing agent dispersion; the modified nano-reinforcing agent dispersion is added to the mixed solution and stirred for 10-20 minutes to obtain a mixed solution; (5) Maturation treatment: Maturate the mixture at 25~35℃ for 24~48h, stirring for 10 minutes every 6h during the process; (6) Pass through a 200-mesh sieve to obtain a die-cast aluminum whitening agent.

[0007] The die-cast aluminum whitening agent is formulated as follows, by weight percentage: 8%~12% surfactant, 3%~5% organic acid complexing agent, 2%~4% corrosion inhibitor, 10%~14% pH adjuster, 2%~4% modified nano-reinforcing agent, and the balance being deionized water.

[0008] As an optimization, the pH adjuster in step (1) is a buffer system of sodium carbonate and sodium silicate with a mass ratio of 3:1.

[0009] As an optimization, the corrosion inhibitor in step (2) is a mixture of benzotriazole and sodium molybdate in a mass ratio of 1:2.

[0010] As an optimization, the organic acid complexing agent in step (2) is a mixture of citric acid, tartaric acid and gluconic acid in a mass ratio of 2:1:1.

[0011] As an optimization, the surfactant in step (3) is a compound system of alkyl glycoside and fatty alcohol polyoxyethylene ether, with a mass ratio of 1:1.5.

[0012] As an optimization, the preparation method of the modified nano-reinforcing agent in step (4) is as follows: mix nano-silica and nano-alumina, add anhydrous ethanol at a total mass of 10 to 20 times that of the surface modifier, nano-silica and nano-alumina, stir at 200 to 500 r / min for 2 to 4 hours at 60 to 70°C, centrifuge to separate the precipitate, wash the precipitate with deionized water and anhydrous ethanol 3 to 5 times respectively, vacuum dry at 80 to 100°C for 6 to 8 hours, grind and pass through a 400-mesh sieve to obtain the product.

[0013] As optimization, the mass ratio of the nanometer silicon dioxide and the nanometer aluminum oxide is 1: (0.8-1.2).

[0014] As optimization, the nanometer silicon dioxide is fumed silica with a purity of ≥99.8% and a primary particle size of 15-25 nm; and the nanometer aluminum oxide is α-aluminum oxide with a purity of ≥99.5% and a primary particle size of 20-30 nm.

[0015] As optimization, the surface modifier is one or more of a silane coupling agent, a titanate coupling agent or an aluminate coupling agent, and the amount used is 1%-3% of the total mass of the nanoparticles.

[0016] Compared with the prior art, the present application has the following beneficial effects: The surfactant prepared by the complex system of alkyl polyglycoside and fatty alcohol polyoxyethylene ether has good biodegradability and can improve wettability; the fatty alcohol polyoxyethylene ether has good emulsifying property and permeability; the complex of the two can effectively reduce the surface tension and bring more uniform surface treatment effect; among the three organic acid complexing agents, citric acid has strong complexing ability and can effectively complex aluminum ions; tartaric acid has moderate complexing ability and its buffering effect; and gluconic acid has weak complexing ability and can prevent excessive corrosion; the three are used in combination to effectively control the corrosion degree of the surface of the die-casting aluminum; benzotriazole can form a protective film on the metal surface through coordination of heterocyclic nitrogen atoms; and sodium molybdate can form a molybdate protective layer through an oxidation-reduction reaction; and the complex of the two can form a dense composite protective film.

[0017] The modified nanometer reinforcing agent is prepared by treating the nanometer silicon dioxide and the nanometer aluminum oxide with a surface treatment agent; the nanometer silicon dioxide can provide abundant reaction sites; the abundant hydroxyl groups on the surfaces of the two and the functional groups introduced by the surface modifier can form stable binding sites with the metal surface to improve the binding strength; the complex of the nanometer silicon dioxide and the nanometer aluminum oxide can further improve the salt mist resistance of the die-casting aluminum; the nanometer aluminum oxide can provide more effective support; and the complex use of the nanometer silicon dioxide and the nanometer aluminum oxide can effectively improve the Ra value of the die-casting aluminum and make the surface smoother.

[0018] The die-casting aluminum degreasing agent provided by the present application abandons the chemical composition system containing harmful substances such as fluorine and nitric acid, and eliminates fluoride pollution and environmental hazard factors such as nitrogen oxides generated by nitric acid decomposition from the source. Moreover, the treatment temperature range is wide, the energy consumption is reduced compared with the high temperature requirement of 60-80 DEG C of the traditional process, and the energy-saving and emission-reduction policy guidance of the country is met. The operation safety is fundamentally improved, the whole treatment process is free of acid mist volatilization and irritating odor generation, the air quality of the working environment is significantly improved, the professional health of the operators is effectively protected, and the safety production risk of the enterprise is reduced. In addition, the present application realizes multifunctional integrated integration, a single medicament simultaneously has multiple functions such as efficient oil removal, complete removal of oxide skin, surface activation, corrosion protection and the like, simplifies the traditional complex process flow of 7-8 steps into 2-3 steps, greatly improves the production efficiency, and reduces the equipment investment and land area.

[0019] In terms of treatment performance, the surface treatment effect of the present application is excellent, and the process performance is stable. After the die-casting aluminum alloy workpiece is treated by the degreasing agent, the surface oxide skin and silicon segregation layer are completely removed, and the surface roughness Ra value can be controlled in the ideal range of 0.8-1.2 μm, providing excellent substrate conditions for subsequent surface treatment processes such as coating and electroplating. The corrosion resistance is significantly improved, and no white rust is generated in the neutral salt spray test for 168 hours, far exceeding the standard requirement of 96 hours in the industry, and the market prospect is wide. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0021] In the following examples and comparative examples, the surfactant is a compound system of alkyl glycoside and fatty alcohol polyoxyethylene ether, and the mass ratio is 1:1.5; the organic acid complexing agent is a mixture of citric acid, tartaric acid and gluconic acid, and the mass ratio is 2:1:1; the corrosion inhibitor is a mixture of benzotriazole and sodium molybdate, and the mass ratio is 1:2; the pH regulator is a buffer system of sodium carbonate and sodium silicate, and the mass ratio is 3:1; the nano-silicon dioxide is fumed white carbon black with a purity of ≥99.8% and a primary particle size of 15-25 nm; the nano-alumina is α-alumina with a purity of ≥99.5% and a primary particle size of 20-30 nm; and the surface modifier is a mixture of silane coupling agent, titanate coupling agent or aluminate coupling agent, and the mass ratio is 1:0.8:1.2. Example 1

[0022] The formula for the die-cast aluminum whitening agent is as follows, by weight percentage: 8% surfactant, 3% organic acid complexing agent, 2% corrosion inhibitor, 10% pH adjuster, 2% modified nano-reinforcing agent, and the balance is deionized water.

[0023] Nano-silica and nano-alumina were mixed at a mass ratio of 1:0.8. 1% of a surface modifier (based on the total mass of nano-silica and nano-alumina) and 10 times the total mass of anhydrous ethanol (based on the total mass of nano-silica and nano-alumina) were added. The mixture was stirred at 200 r / min for 2 h at 60 °C. The precipitate was separated by centrifugation. The precipitate was washed three times with deionized water and three times with anhydrous ethanol. It was then vacuum dried at 80 °C for 6 h, ground, and passed through a 400-mesh sieve to obtain the modified nano-reinforcing agent.

[0024] The preparation steps for die-cast aluminum whitening agent are as follows: (1) Pretreatment: Heat deionized water to 40°C, slowly add pH adjuster, and stir until completely dissolved; (2) Add organic acid complexing agent and corrosion inhibitor in sequence, keep the temperature at 45℃ and stir for 35 minutes; (3) Slowly add the surfactant, controlling the addition rate to 1 kg / min, and stir for 20 minutes to obtain a mixed solution; (4) The modified nano-reinforcing agent was pre-dispersed in a small amount of deionized water and ultrasonically dispersed for 10 minutes to obtain a modified nano-reinforcing agent dispersion; the modified nano-reinforcing agent dispersion was added to the mixed solution and stirred for another 10 minutes to obtain a mixed solution; (5) Maturation treatment: Maturate the mixture at 25°C for 24 hours, stirring for 10 minutes every 6 hours during the process; (6) Pass through a 200-mesh sieve to obtain the product. Example 2:

[0025] The formula for the die-cast aluminum whitening agent is as follows, by weight percentage: 10% surfactant, 4% organic acid complexing agent, 3% corrosion inhibitor, 12% pH adjuster, 3% modified nano-reinforcing agent, and the balance is deionized water.

[0026] Nano-silica and nano-alumina were mixed at a mass ratio of 1:1. 2% of the total mass of nano-silica and nano-alumina as a surface modifier and 15 times the total mass of nano-silica and nano-alumina as anhydrous ethanol were added. The mixture was stirred at 350 r / min for 3 h at 65 °C. The precipitate was separated by centrifugation. The precipitate was washed four times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 90 °C for 7 h. After grinding, the precipitate was passed through a 400-mesh sieve to obtain the modified nano-reinforcing agent.

[0027] The preparation steps for die-cast aluminum whitening agent are as follows: (1) Pretreatment: Heat deionized water to 45°C, slowly add pH adjuster, and stir until completely dissolved; (2) sequentially add the organic acid complexing agent and the corrosion inhibitor, keep the temperature at 50°C, and stir for 40 min; (3) slowly add the surfactant, control the adding speed at 1.5 kg / min, and stir for 25 min to prepare a mixed solution; (4) disperse the modified nano-enhancing agent in a small amount of deionized water in advance, prepare a modified nano-enhancing agent dispersion liquid by ultrasonic dispersion for 12 min, add the modified nano-enhancing agent dispersion liquid into the mixed solution, and continue to stir for 15 min to prepare a mixed liquid; (5) aging treatment: age the mixed liquid at 30°C for 36 h, and stir for 10 min every 6 h; (6) pass through a 200-mesh screen to prepare. Example 3:

[0028] The formula of the die-casting aluminum drawing agent 1 is as follows: the surfactant is 12%, the organic acid complexing agent is 5%, the corrosion inhibitor is 4%, the pH regulator is 14%, the modified nano-enhancing agent is 4%, and the balance is deionized water.

[0029] Mix the nanosilica and nanoalumina at a mass ratio of 1:1.2, add 3% of the total mass of the nanosilica and nanoalumina as a surface modifier, and 20 times of the total mass of the nanosilica and nanoalumina as anhydrous ethanol, stir at 70°C and 500 r / min for 4 h, centrifugally separate the precipitate, wash the precipitate with deionized water and anhydrous ethanol for 5 times respectively, vacuum dry at 100°C for 8 h, grind, and pass through a 400-mesh screen to prepare the modified nano-enhancing agent.

[0030] The preparation steps of the die-casting aluminum drawing agent are as follows: (1) pretreatment: heat the deionized water to 50°C, slowly add the pH regulator, and stir until completely dissolved; (2) sequentially add the organic acid complexing agent and the corrosion inhibitor, keep the temperature at 55°C, and stir for 45 min; (3) slowly add the surfactant, control the adding speed at 2 kg / min, and stir for 30 min to prepare a mixed solution; (4) disperse the modified nano-enhancing agent in a small amount of deionized water in advance, prepare a modified nano-enhancing agent dispersion liquid by ultrasonic dispersion for 15 min, add the modified nano-enhancing agent dispersion liquid into the mixed solution, and continue to stir for 20 min to prepare a mixed liquid; (5) aging treatment: age the mixed liquid at 35°C for 48 h, and stir for 10 min every 6 h; (6) pass through a 200-mesh screen to prepare.

[0031] Comparative Example 1: A traditional drawing agent containing fluorine and nitric acid is prepared by mixing concentrated nitric acid and hydrofluoric acid at a mass ratio of 95:5.

[0032] Comparative Example 2: The die-casting aluminum drawing agent is formulated as follows, in terms of weight percentage, surfactant 10%, organic acid complexing agent 4%, corrosion inhibitor 3%, pH adjuster 12%, nano-enhancing agent 3%, and the balance being deionized water.

[0033] The nano-silica and nano-alumina are mixed in a mass ratio of 1:1, 2% of the total mass of the nano-silica and nano-alumina is added as a surface modifier, 15 times the total mass of the nano-silica and nano-alumina is added as anhydrous ethanol, stirring is carried out at 65°C and 350 r / min for 3h, centrifugal separation is carried out to precipitate, the precipitate is washed 4 times with deionized water and anhydrous ethanol respectively, vacuum drying is carried out at 90°C for 7h, grinding is carried out, and then the modified nano-enhancing agent is obtained by passing through a 400-mesh sieve.

[0034] The preparation steps of the die-casting aluminum drawing agent are as follows: (1) Pretreatment: the deionized water is heated to 45°C, the pH adjuster is slowly added, and stirring is carried out until complete dissolution; (2) The organic acid complexing agent and the corrosion inhibitor are sequentially added, the temperature is maintained at 50°C, and stirring is carried out for 40 min; (3) The surfactant is slowly added, the addition speed is controlled to be 1.5 kg / min, stirring is carried out for 25 min, and a mixed solution is prepared; (4) The nano-enhancing agent is dispersed in a small amount of deionized water in advance, an ultrasonic dispersion is carried out for 12 min to prepare a nano-enhancing agent dispersion liquid; the nano-enhancing agent dispersion liquid is added to the mixed solution, and stirring is continued for 15 min to prepare a mixed liquid; (5) Maturation treatment: the mixed liquid is matured at 30°C for 36h, stirring is carried out for 10 min every 6h during the maturation; (6) Passing through a 200-mesh sieve to obtain.

[0035] Comparative Example 3: The die-casting aluminum drawing agent is formulated as follows, in terms of weight percentage, surfactant 10%, organic acid complexing agent 4%, corrosion inhibitor 3%, pH adjuster 12%, and the balance being deionized water.

[0036] The preparation steps of the die-casting aluminum drawing agent are as follows: (1) Pretreatment: the deionized water is heated to 45°C, the pH adjuster is slowly added, and stirring is carried out until complete dissolution; (2) The organic acid complexing agent and the corrosion inhibitor are sequentially added, the temperature is maintained at 50°C, and stirring is carried out for 40 min; (3) The surfactant is slowly added, the addition speed is controlled to be 1.5 kg / min, stirring is carried out for 25 min, and a mixed solution is prepared; (4) Maturation treatment: the mixed liquid is matured at 30°C for 36h, stirring is carried out for 10 min every 6h during the maturation; (5) passed through a 200-mesh screen to obtain.

[0037] Comparative Example 4: The formula of the die-casting aluminum brightener is as follows: 10% of surfactant, 4% of organic acid complexing agent, 3% of corrosion inhibitor, 12% of pH regulator, 3% of modified nano-alumina, and the balance of deionized water.

[0038] The nano-alumina, nano-alumina surface modifier with a mass of 2% of the nano-alumina, and anhydrous ethanol with a mass of 15 times of the nano-alumina were uniformly mixed, stirred at 350 r / min at 65°C for 3 h, and centrifuged to separate the precipitate. The precipitate was washed with deionized water and anhydrous ethanol for 4 times respectively, vacuum dried at 90°C for 7 h, ground, and then passed through a 400-mesh screen to obtain modified nano-alumina.

[0039] The preparation steps of the die-casting aluminum brightener are as follows: (1) Pretreatment: The deionized water was heated to 45°C, and the pH regulator was slowly added and stirred until completely dissolved; (2) The organic acid complexing agent and the corrosion inhibitor were sequentially added, and the temperature was maintained at 50°C, and stirred for 40 min; (3) The surfactant was slowly added, the adding speed was controlled at 1.5 kg / min, and stirred for 25 min to obtain a mixed solution; (4) The modified nano-alumina was dispersed in a small amount of deionized water in advance, and a modified nano-alumina dispersion was prepared by ultrasonic dispersion for 12 min. The modified nano-alumina dispersion was added to the mixed solution, and stirred for 15 min to obtain a mixed solution; (5) Aging treatment: The mixed solution was aged at 30°C for 36 h, and stirred for 10 min every 6 h; (6) passed through a 200-mesh screen to obtain.

[0040] Comparative Example 5: The formula of the die-casting aluminum brightener is as follows: 10% of surfactant, 4% of organic acid complexing agent, 3% of corrosion inhibitor, 12% of pH regulator, 3% of modified nano-alumina, and the balance of deionized water.

[0041] The nano-alumina, nano-alumina surface modifier with a mass of 2% of the nano-alumina, and anhydrous ethanol with a mass of 15 times of the nano-alumina were uniformly mixed, stirred at 350 r / min at 65°C for 3 h, and centrifuged to separate the precipitate. The precipitate was washed with deionized water and anhydrous ethanol for 4 times respectively, vacuum dried at 90°C for 7 h, ground, and then passed through a 400-mesh screen to obtain modified nano-alumina.

[0042] The preparation steps of the die-casting aluminum brightener are as follows: (1) Pretreatment: The deionized water was heated to 45°C, and the pH regulator was slowly added and stirred until completely dissolved; (2) sequentially add the organic acid complexing agent and the corrosion inhibitor, and keep the temperature at 50℃, and stir for 40 min; (3) slowly add the surfactant, control the adding speed to be 1.5 kg / min, and stir for 25 min to prepare a mixed solution; (4) disperse the modified nano-aluminum oxide in a small amount of deionized water in advance, and prepare a modified nano-aluminum oxide dispersion liquid by ultrasonic dispersion for 12 min; add the modified nano-aluminum oxide dispersion liquid into the mixed solution, and continue to stir for 15 min to prepare a mixed liquid; (5) maturation treatment: keep the mixed liquid at 30℃ for 36 h, and stir for 10 min every 6 h; (6) sieve through a 200-mesh screen to prepare.

[0043] Test example: Preparation of the sample: immerse the ADC12 die-casting aluminum alloy test piece with the size of 100*50*2 mm in the draw compound prepared in each example and the comparative example for 5 min at 50℃, then clean the test piece with flowing deionized water, and dry by blowing air to prepare the sample.

[0044] Salt spray corrosion test: according to the standard of GB / T 10125-2012, carry out the salt spray test on each sample in a neutral salt spray chamber, the NaCl concentration is 5%, the pH is 6.5-7.2, and the temperature is 35±2℃. Observe the time when white rust appears. The results are shown in Table 1.

[0045] Surface roughness test: according to the standard of GB / T 3505-2009, measure the surface roughness Ra value of each sample by using a Taylor Hobson Talysurf i series profilometer. The measurement length is 4.0 mm, the evaluation length is 0.8 mm*5, the sampling length is 0.8 mm, the Gaussian filter is used, and the cutoff wavelength is 0.8 mm. The results are shown in Table 1.

[0046]

[0047] From the experimental data comparison of Examples 1-3 and Comparative Examples 1-5 in Table 1, it can be found that the die-casting aluminum draw compound prepared by the preparation method of the die-casting aluminum draw compound has good roughness and salt spray resistance.

[0048] The difference between Comparative Example 2 and Example 2 is that the nano-enhancing agent is modified by the surface modifier. The white rust appearance time of Comparative Example 2 is obviously earlier than that of Example 2, which indicates that the modified nano-enhancing agent modified by the surface modifier has good dispersibility in the solvent, so as to be uniformly combined on the surface of the die-casting aluminum to form a coating layer, thereby effectively improving the salt spray resistance of the die-casting aluminum.

[0049] The difference between Comparative Example 4 and Example 2 is that no nano-aluminum oxide is added, and the difference between Comparative Example 5 and Example 2 is that no nano-silicon dioxide is added. The white rust of Comparative Examples 4 and 5 appears earlier than that of Example 2, indicating that silicon dioxide can provide abundant reaction sites, and nano-aluminum oxide can provide more effective support. The abundant hydroxyl groups on the surface of the two and the functional groups introduced by the surface modifier can form stable binding sites with the metal surface, improve the binding strength, and the use of nano-silicon dioxide and nano-aluminum oxide further improves the salt spray resistance of the die-cast aluminum.

[0050] The Ra value of Comparative Examples 4 and 5 is less than that of Example 2, indicating that silicon dioxide can provide abundant reaction sites, and nano-aluminum oxide can provide more effective support. The use of both can effectively improve the Ra value of the die-cast aluminum, and the surface is smoother.

[0051] After the die-cast aluminum alloy workpiece is treated with the above-described stripping agent, the surface oxide scale and silicon segregation layer are completely removed, and the surface presents a uniform silver-white metal luster with good surface roughness, providing excellent base conditions for subsequent surface treatment processes such as coating and electroplating. The corrosion resistance is significantly improved, and no white rust is produced in the neutral salt spray test for 168 hours, far exceeding the industry standard requirement of 96 hours, and the market prospect is broad.

[0052] The above-described specific embodiments further illustrate the purpose, technical solutions, and beneficial effects of the present application. It should be understood that the above-described embodiments are merely specific embodiments of the present application and are not intended to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a whitening agent for die-cast aluminum, characterized in that, The preparation steps include the following: (1) Pretreatment: Heat deionized water to 40~50℃, slowly add pH adjuster, and stir until completely dissolved; (2) Add organic acid complexing agent and corrosion inhibitor in sequence, keep the temperature at 45~55℃, and stir for 35~45min; (3) Slowly add the surfactant, controlling the addition rate to 1~2 kg / min, and stir for 20~30 minutes to obtain a mixed solution; (4) The modified nano-reinforcing agent is pre-dispersed in a small amount of deionized water and ultrasonically dispersed for 10-15 minutes to obtain a modified nano-reinforcing agent dispersion; the modified nano-reinforcing agent dispersion is added to the mixed solution and stirred for 10-20 minutes to obtain a mixed solution; (5) Maturation treatment: Maturate the mixture at 25~35℃ for 24~48h, stirring for 10 minutes every 6h during the process; (6) Pass through a 200-mesh sieve to obtain a whitening agent for die-cast aluminum; The die-cast aluminum whitening agent is formulated as follows, by weight percentage: 8%~12% surfactant, 3%~5% organic acid complexing agent, 2%~4% corrosion inhibitor, 10%~14% pH adjuster, 2%~4% modified nano-reinforcing agent, and the balance being deionized water.

2. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The pH adjuster mentioned in step (1) is a buffer system of sodium carbonate and sodium silicate with a mass ratio of 3:

1.

3. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The corrosion inhibitor in step (2) is a mixture of benzotriazole and sodium molybdate in a mass ratio of 1:

2.

4. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The organic acid complexing agent in step (2) is a mixture of citric acid, tartaric acid and gluconic acid in a mass ratio of 2:1:

1.

5. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The surfactant in step (3) is a compound system of alkyl glycoside and fatty alcohol polyoxyethylene ether, with a mass ratio of 1:1.

5.

6. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The preparation method of the modified nano-reinforcing agent in step (4) is as follows: mix nano-silica and nano-alumina, add anhydrous ethanol at a total mass of 10 to 20 times that of the surface modifier, nano-silica and nano-alumina, stir at 200 to 500 r / min for 2 to 4 hours at 60 to 70°C, centrifuge to separate the precipitate, wash the precipitate with deionized water and anhydrous ethanol 3 to 5 times respectively, vacuum dry at 80 to 100°C for 6 to 8 hours, grind and pass through a 400-mesh sieve to obtain the product.

7. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The mass ratio of nano-silica to nano-alumina is 1:(0.8~1.2).

8. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The nano-silica is fumed silica with a purity ≥99.8% and a primary particle size of 15~25nm; the nano-alumina is α-alumina with a purity ≥99.5% and a primary particle size of 20~30nm.

9. The method for preparing a die-casting aluminum whitening agent according to claim 1, characterized in that, The surface modifier is one or more of silane coupling agents, titanate coupling agents, or aluminate coupling agents, and the amount used is 1% to 3% of the total mass of the nanoparticles.

10. A die-casting aluminum whitening agent prepared by the method for preparing die-casting aluminum whitening agent according to any one of claims 1 to 9.

Images