CN113463141A - Method for improving acid-resistant salt spray corrosion resistance of zinc coating - Google Patents

Method for improving acid-resistant salt spray corrosion resistance of zinc coating Download PDF

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CN113463141A
CN113463141A CN202110715757.9A CN202110715757A CN113463141A CN 113463141 A CN113463141 A CN 113463141A CN 202110715757 A CN202110715757 A CN 202110715757A CN 113463141 A CN113463141 A CN 113463141A
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corrosion resistance
solution
acid
passivation
treatment
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CN113463141B (en
Inventor
吕玲
王力强
王利华
仲星屹
梁鑫
廖广其
詹中伟
张骐
孙志华
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Chengdu Aircraft Industrial Group Co Ltd
AECC Beijing Institute of Aeronautical Materials
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Chengdu Aircraft Industrial Group Co Ltd
AECC Beijing Institute of Aeronautical Materials
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/22—Electroplating: Baths therefor from solutions of zinc
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/53—Treatment of zinc or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/82—After-treatment
    • C23C22/83—Chemical after-treatment
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C25D5/52—After-treatment of electroplated surfaces by brightening or burnishing

Abstract

The invention discloses a method for improving the acid salt spray corrosion resistance of a zinc coating, which is characterized in that a part is subjected to pretreatment, alkaline zinc plating, bright dipping treatment, trivalent chromium passivation treatment, idle stop treatment, water-based silica sol sealing treatment and vacuum drying treatment in sequence, so that an excellent color passivation film with good bonding force, uniform color distribution and good acid salt spray corrosion resistance is prepared on the surface of the zinc coating of the part, and can pass a neutral salt spray test of more than 1440 hours and an acid salt spray test of 864 hours. The invention adopts the novel trivalent chromium passivation process and the water-based silica sol closed composite treatment to greatly improve the corrosion resistance of the zinc coating in the acid salt spray environment, and has the advantages of green and environment-friendly process, simple wastewater treatment and better practicability.

Description

Method for improving acid-resistant salt spray corrosion resistance of zinc coating
Technical Field
The invention belongs to the technical field of metal surface passivation treatment, and particularly relates to a method for improving the acid-resistant salt spray corrosion resistance of a zinc coating.
Background
Galvanization is the most cost effective method of protecting steel. However, the zinc layer is in a humid environment with CO in the air2、O2And a layer of white corrosion product is generated on the surface of the zinc layer, so that the appearance and the corrosion resistance of the zinc layer are influenced. Therefore, passivation treatment is often required after galvanization to improve the appearance and corrosion resistance.
Currently, passivation processes can be classified into hexavalent chromate passivation, trivalent chromium passivation, and chromium-free passivation according to the composition of the passivation solution. The traditional chromate passivation process is mature and has self-repairing capability, but hexavalent chromium which is a highly toxic and carcinogenic substance poses a great threat to the environment. Chromium-free passivation is not applied to mass production due to poor corrosion resistance. The toxicity of the trivalent chromium is only 1% of that of the hexavalent chromium, the passivation effect is similar, the corrosion resistance is very close to that of the hexavalent chromium, and the passivation technology is the most possible passivation technology for replacing the hexavalent chromium passivation; the reaction formula of the passivation film formation process of trivalent chromium passivation is as follows:
zn + oxidant → Zn2++ reduction products
Zn+2H+→Zn2++H2↑
2Cr3++6OH-→Cr2O3•3H2O
2Zn2++2Cr3++8OH-→2Zn（CrO2）•4H2O
The study shows that the passive film contains elements such as Zn, O, Cr and the like, and the composition of the passive solution does not contain any compound containing zinc ions, so that all zinc in the passive film comes from the dissolution of the zinc coating. The invention utilizes the Zn energy to dissolve into Zn in the passivation solution2+And can be mixed with Cr in solution3+At OH-The zinc layer is separated from the outside, so that the zinc layer is prevented from being dissolved again, the zinc layer is protected, and the corrosion resistance of the plating layer is enhanced.
At present, although trivalent chromium passivation applied to a zinc coating is reported, the corrosion resistance of the passivated zinc coating is greatly different, and the corrosion resistance is not good in an acid environment. However, galvanized components are increasingly used in marine environments at present and for some time in the future, and the hot and humid characteristics of the marine environment place higher demands on the resistance of the galvanized layer to acid salt spray corrosion, and effective improvement means are not available at present. Therefore, the invention provides the method for improving the corrosion resistance of the zinc coating in the acid salt spray environment by the composite treatment of the novel trivalent chromium passivation process and the aqueous silica sol sealing, and has obvious technical integration innovation advantages and higher application value.
Disclosure of Invention
The invention aims to provide a method for improving the acid-resistant salt spray corrosion resistance of a galvanized layer, and aims to solve the problems.
The invention firstly utilizes the Zn energy to dissolve into Zn in the passivation solution2+And can be mixed with Cr in solution3+At OH-The reaction is carried out under the action of the zinc oxide to generate an insoluble zinc-chromium compound, and a layer of passivation film is formed on the surface of the zinc layer; then, the water-based silica sol is adsorbed to the surface of the passive film or the inside of the micropores under the action of a surfactant carrier; both of themThe combined action of the zinc layer and the external environment separates the zinc layer, so that the zinc layer is prevented from being dissolved again, the zinc layer is protected, and the corrosion resistance, particularly the acid-resistant salt mist corrosion resistance of the coating is enhanced. The method can obtain a color passive film with good binding force, uniform color distribution, corrosion resistance, especially acid-resistant salt spray corrosion resistance and excellent performance on the surface of the zinc coating.
The invention is mainly realized by the following technical scheme: a method for improving the acid-resistant salt spray corrosion resistance of a zinc coating comprises the following steps:
step S100: preprocessing the part;
step S200: performing alkaline galvanizing on the pretreated part, firstly preparing an electrogalvanizing solution, then putting the part into the electrogalvanizing solution at 15-35 ℃ at a speed of 2.5A/dm2Electroplating for 30min at the current density;
step S300: carrying out light emitting treatment on the galvanized part;
step S400: preparing a trivalent chromium passivation concentrated solution, diluting the trivalent chromium passivation concentrated solution, and adjusting the pH value to 1.0-1.5 to obtain a trivalent chromium passivation solution; putting the part treated in the step S300 into a trivalent chromium passivation solution for passivation at the temperature of 50-60 ℃, and soaking for 50-70S;
step S500: stopping in the air, taking out the galvanized layer treated in the above steps, and staying in the air for 10-20s to ensure that a fresh passive film and O2Further carrying out oxidation reaction to fully oxidize the passivation film;
step S600: preparing an aqueous silica sol sealing solution, and immersing the galvanized layer passivated part treated in the step S500 into the aqueous silica sol sealing solution at the temperature of 60-65 ℃ for treatment for 50-60S; directly carrying out vacuum drying treatment after the air-out.
In order to better implement the present invention, further, in step S300, a light extraction treatment is performed in a light extraction liquid, where the light extraction liquid is 2wt% of dilute nitric acid.
In order to better implement the present invention, further, after the sealed galvanization passivation sample is taken out and stopped in the step S600, the galvanization passivation sample is directly placed into a vacuum drying oven for low temperature drying treatment without water washing, wherein the temperature is 80 ℃, and the time is 30 min.
In order to better realize the invention, the electrogalvanizing solution in the step S200 is prepared from 110-175 g/L of sodium hydroxide, 10-20 g/L of zinc oxide, 15 mL/L of nano-polymeric quaternary ammonium salt and 0.5 mL/L of trisodium nitrilotriacetate. The electrogalvanizing solution is prepared from sodium hydroxide, zinc oxide, nano-polymeric quaternary ammonium salt and nitrilotriacetic acid trisodium, and the dosage of the components is as follows: 110-175 g/L sodium hydroxide, 10-20 g/L zinc oxide, 15 mL/L nano polymeric quaternary ammonium salt, and 0.5 mL/L nitrilotriacetic acid trisodium salt.
In order to better implement the present invention, further, the trivalent chromium passivation concentrated solution in step S400 is prepared from 22g/L of chromium nitrate, 4mL/L of sulfuric acid, 1mL/L of wetting agent, 2.2mL/L of nitric acid, 1.1g/L of sodium salt, 4g/L of cobalt salt, and water, and in step S400, the trivalent chromium passivation concentrated solution is prepared according to the following ratio of 1:9 dilution is carried out. The trivalent chromium passivation concentrated solution is prepared from chromium nitrate, sulfuric acid, a wetting agent, nitric acid, sodium salt, cobalt salt and water, and the components are used in the following amounts: 22g/L of chromium nitrate, 4mL/L of sulfuric acid, 1mL/L of wetting agent, 2.2mL/L of nitric acid, 1.1g/L of sodium salt and 4g/L of cobalt salt.
In order to better implement the present invention, further, in step S400, the wetting agent is sodium dodecylbenzene sulfonate or polyethylene glycol 600.
In order to better implement the present invention, further, in step S600, the aqueous silica sol blocking solution is prepared from 10 g/L aqueous silica sol, 5g/L surfactant, and water. The aqueous silica sol confining liquid is prepared from aqueous silica sol, a surfactant and pure water, and comprises the following components in parts by weight: 10 g/L of aqueous silica sol and 5g/L of surfactant.
In order to better implement the present invention, further, the surfactant in step S600 is polyethylene glycol 600 or fatty alcohol-polyoxyethylene ether.
In order to better implement the present invention, further, the pretreatment in step S100 is to sequentially perform oil removal, activation, and neutralization treatment on the part.
In order to better implement the present invention, further, the oil removal in step S100 is: preparing chemical degreasing fluid, wherein the chemical degreasing fluid is prepared from 30g/L sodium hydroxide, 45g/L sodium carbonate and 25g/L sodium silicate; placing the parts into chemical degreasing liquid at 50-70 ℃ for treatment for 5-15 min; after the parts are deoiled, the parts are thoroughly cleaned by warm water, and the whole part surface is ensured to be hydrophilic. The chemical degreasing fluid is prepared from sodium hydroxide, sodium carbonate and sodium silicate, and the chemical degreasing fluid comprises the following components in parts by weight: 30g/L of sodium hydroxide, 45g/L of sodium carbonate and 25g/L of sodium silicate.
To better implement the present invention, further, the activation in step S100 is: preparing an activating solution, wherein the activating solution is prepared from 50-100 g/L hydrochloric acid and 40-50 g/L urotropine, and the part is placed in the activating solution and soaked for 1-2 min at room temperature; and cleaning the activated part by using deionized water. The activating solution is prepared from hydrochloric acid and urotropine, and the dosage of the components is as follows: 50-100 g/L hydrochloric acid and 40-50 g/L urotropine.
In order to better implement the present invention, further, the neutralization in step S100 is: and (3) putting the parts into a 30-50 g/L sodium carbonate solution and soaking for 1-2 min at room temperature.
The method comprises the following steps: chemical degreasing → warm water washing → activation → water washing → neutralization → water washing → alkaline zincate galvanizing → warm water washing → light extraction → water washing → trivalent chromium passivation → air stopping treatment → water washing → aqueous silica sol sealing → vacuum drying treatment.
The invention has the beneficial effects that:
after the treatment, a colorful passivation film layer with good binding force, uniform color and excellent corrosion resistance can be obtained on the surface of the zinc layer; the plating layer can pass neutral salt spray test of 1440h or more and acid salt spray test of 864 h. The invention adopts a novel trivalent chromium passivation process and water-based silica sol closed composite treatment to greatly improve the corrosion resistance of the zinc coating in an acid salt spray environment, and has the advantages of green and environment-friendly process and simple wastewater treatment.
Drawings
FIG. 1 is a picture of a zinc coating after trivalent chromium passivation and silica sol sealing composite treatment;
fig. 2 is a Tafel plot of differently treated alkaline zinc coatings in a 3.5% NaCl solution (pH = 3).
Detailed Description
Example 1:
a method for improving the acid-resistant salt spray corrosion resistance of a zinc coating comprises the following steps:
1) and (4) chemically removing oil. Preparing 30g/L sodium hydroxide, 45g/L sodium carbonate and 25g/L sodium silicate into a chemical oil removing solution; and (3) putting the Q235 steel sheet into chemical degreasing liquid at 50-70 ℃ for treatment for 5-15 min. After the parts are deoiled, the parts are thoroughly cleaned by warm water, the whole parts surface is ensured to be hydrophilic, and the deoiling is qualified if a continuous water film is used for more than 60 seconds.
2) And (4) activating. Activating the sample treated in the step 1), wherein the process parameters are as follows: 50-100 g/L hydrochloric acid and 40-50 g/L urotropine, and soaking for 1-2 min at room temperature. After activation, the sample was thoroughly washed with deionized water.
3) And (4) neutralizing. Activating the sample treated in the steps 1) and 2), wherein the process parameters are as follows: 30-50 g/L sodium carbonate, and soaking for 1-2 min at room temperature. Thoroughly washing the neutralized sample by deionized water
4) And (3) alkaline zinc plating. Preparing 150 g/L sodium hydroxide, 17 g/L zinc oxide, 15 mL/L nano polymeric quaternary ammonium salt and 0.5 mL/L nitrilotriacetic acid trisodium salt into an electrogalvanizing solution; putting the Q235 steel sheet treated by the steps 1), 2) and 3) into an electroplating solution at 15-35 ℃ to be 2.5A/dm2Electroplating for 30 min. And taking out the steel sheet, putting the steel sheet into deionized water at 45 ℃ for cleaning, then washing with flowing water, and finally washing with deionized water, wherein the plating layer is bright and has fine crystals, and the plating layer is qualified.
5) And (5) emitting light. Carrying out light extraction treatment on the sample treated in the steps 1), 2), 3) and 4), wherein the process parameters are as follows: and (5) soaking in dilute nitric acid (2%) for 1-3 s at room temperature. And after light emission, the sample is thoroughly washed by deionized water.
6) And (5) passivating trivalent chromium. Preparing trivalent chromium passivation concentrated solution by using 22g/L chromic nitrate, 4mL/L sulfuric acid, 1mL/L sodium dodecyl benzene sulfonate, 2.2mL/L nitric acid, 1.1g/L sodium salt, 4g/L cobalt sulfate and a solvent as pure water; and then diluting the prepared passivation concentrated solution according to the ratio of 1:9, and adjusting the pH value to 1.0-1.5 to obtain the trivalent chromium passivation solution. And (3) immersing the zinc coating sample obtained in the steps into a trivalent chromium passivation solution for passivation treatment at the temperature of 60 ℃ for 50 s.
7) And (5) performing idle stop processing. Taking out the galvanized layer treated in the steps, and staying in the air for 10-20s to ensure that a fresh passive film and O2Further oxidation reaction occurs to fully oxidize the passivation film. And then, thoroughly washing the sample by using deionized water, wherein the time is not more than 1 min.
8) And (5) sealing by using aqueous silica sol. 10 g/L of aqueous silica sol, 5g/L of polyethylene glycol 600 and pure water serving as a solvent are prepared into aqueous silica sol confining liquid. And (3) immersing the galvanized layer passivation sample treated in the steps into an aqueous silica sol sealing solution at 60 ℃ for sealing for 50 s.
9) And (5) vacuum drying treatment. Taking out the zinc coating closed sample treated in the steps, stopping the sample in the air, and directly placing the sample into a vacuum drying oven for low-temperature drying treatment without water washing; the temperature is 80 deg.C, and the time is 30 min.
The test method comprises the following steps:
neutral salt spray test: the neutral salt spray test was performed according to the standard ASTM B117-07. The test adopts a 5% neutral NaCl solution, the pH = 6.5-7.2, the temperature of a salt spray chamber is maintained at 35+1.1-1.7 ℃, and an uninterrupted spraying mode is adopted.
Acid salt spray test: the test selection standard GB 6459-86 acetic acid salt spray test. The tested salt spray solution is an NSS solution prepared by dissolving 5% of analytically pure NaCl in deionized water, and the PH value of the solution is adjusted to 3.3-3.5 by using analytically pure glacial acetic acid to obtain an ASS solution. The temperature of the salt spray chamber is maintained at 35+1.1-1.7 ℃, and an uninterrupted spraying mode is adopted.
As shown in fig. 1, after the zinc coating is subjected to trivalent chromium passivation and silica sol sealing composite treatment, the film layer presents a color with uniform color. As can be seen from FIG. 2, the corrosion resistance of the unpassivated zinc coating is poor, no obvious passivation region exists in the polarization curve, and the self-corrosion current density is high and is about 4.939 multiplied by 10-5A/cm2. After trivalent chromium passivation and silica sol sealing (60 ℃, 50 s), the self-corrosion potential of the zinc coating is obviously shifted forward, and the self-corrosion current density is reduced to 9.657 multiplied by 10-5A/cm2And the zinc layer shows obvious passivation tendency, and the corrosion resistance of the zinc coating is obviously improved. After 1440h of neutral salt spray test, no obvious red rust appears on the plating layer. The environment-friendly passivation film prepared on the surface of the zinc coating by the process has uniform color, good combination with the film and excellent corrosion resistance.
Example 2:
a method for improving the acid-resistant salt spray corrosion resistance of a zinc coating comprises the following steps:
1) and (4) chemically removing oil. Preparing 30g/L sodium hydroxide, 45g/L sodium carbonate and 25g/L sodium silicate into a chemical oil removing solution; and (3) putting the Q235 steel sheet into chemical degreasing liquid at 50-70 ℃ for treatment for 5-15 min. After the parts are deoiled, the parts are thoroughly cleaned by warm water, the whole parts surface is ensured to be hydrophilic, and the deoiling is qualified if a continuous water film is used for more than 60 seconds.
2) And (4) activating. Activating the sample treated in the step 1), wherein the process parameters are as follows: 50-100 g/L hydrochloric acid and 40-50 g/L urotropine, and soaking for 1-2 min at room temperature. After activation, the sample was thoroughly washed with deionized water.
3) And (4) neutralizing. Activating the sample treated in the steps 1) and 2), wherein the process parameters are as follows: 30-50 g/L sodium carbonate, and soaking for 1-2 min at room temperature. Thoroughly washing the neutralized sample by deionized water
4) And (3) alkaline zinc plating. Preparing 150 g/L sodium hydroxide, 17 g/L zinc oxide, 15 mL/L nano polymeric quaternary ammonium salt and 0.5 mL/L nitrilotriacetic acid trisodium salt into an electrogalvanizing solution; putting the Q235 steel sheet treated by the steps 1), 2) and 3) into an electroplating solution at 15-35 ℃ to be 2.5A/dm2Electroplating for 30 min. And taking out the steel sheet, putting the steel sheet into deionized water at 45 ℃ for cleaning, then washing with flowing water, and finally washing with deionized water, wherein the plating layer is bright and has fine crystals, and the plating layer is qualified.
5) And (5) emitting light. Carrying out light extraction treatment on the sample treated in the steps 1), 2), 3) and 4), wherein the process parameters are as follows: and (5) soaking in dilute nitric acid (2%) for 1-3 s at room temperature. And after light emission, the sample is thoroughly washed by deionized water.
6) And (5) passivating trivalent chromium. Preparing trivalent chromium passivation concentrated solution by using 22g/L chromic nitrate, 4mL/L sulfuric acid, 1mL/L sodium dodecyl benzene sulfonate, 2.2mL/L nitric acid, 1.1g/L sodium salt, 4g/L cobalt sulfate and a solvent as pure water; and then diluting the prepared passivation concentrated solution according to the ratio of 1:9, and adjusting the pH value to 1.0-1.5 to obtain the trivalent chromium passivation solution. And (3) immersing the zinc coating sample obtained in the steps into a trivalent chromium passivation solution for passivation treatment at the temperature of 60 ℃ for 50 s.
7) And (5) performing idle stop processing. Taking out the galvanized layer treated in the steps, and staying in the air for 10-20s to ensure that a fresh passive film and O2Further oxidation reaction occurs to fully oxidize the passivation film. And then, thoroughly washing the sample by using deionized water, wherein the time is not more than 1 min.
8) And (5) sealing by using aqueous silica sol. 10 g/L of aqueous silica sol, 5g/L of polyethylene glycol 600 and pure water serving as a solvent are prepared into aqueous silica sol confining liquid. And (3) immersing the galvanized layer passivation sample treated in the steps into 65 ℃ aqueous silica sol sealing liquid for sealing for 60 s.
9) And (5) vacuum drying treatment. Taking out the zinc coating closed sample treated in the steps, stopping the sample in the air, and directly placing the sample into a vacuum drying oven for low-temperature drying treatment without water washing; the temperature is 80 deg.C, and the time is 30 min.
The test method is as described in example 1 and is not described in detail. As can be seen from fig. 2, example 2 has a suitably increased sealing temperature and a prolonged sealing time as compared with example 1; at this time, the corrosion resistance of the zinc plating layer is better, and the self-corrosion current density of the zinc plating layer is only 8.317 multiplied by 10-6A/cm2The passivation interval was about 301 mV. After 1440h of neutral salt spray test, the plating layer has no obvious red rust and can pass 864h of acid salt spray test. The environment-friendly passivation film prepared on the surface of the zinc coating by the process has uniform color, good combination with the film and excellent corrosion resistance.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are included in the scope of the present invention.

Claims (10)

1. A method for improving the acid-resistant salt spray corrosion resistance of a zinc coating is characterized by comprising the following steps:
step S100: preprocessing the part;
step S200: performing alkaline galvanizing on the pretreated part, firstly preparing an electrogalvanizing solution, then putting the part into the electrogalvanizing solution at 15-35 ℃ at a speed of 2.5A/dm2Electroplating for 30min at the current density;
step S300: carrying out light emitting treatment on the galvanized part;
step S400: preparing a trivalent chromium passivation concentrated solution, diluting the trivalent chromium passivation concentrated solution, and adjusting the pH value to 1.0-1.5 to obtain a trivalent chromium passivation solution; putting the part treated in the step S300 into a trivalent chromium passivation solution for passivation at the temperature of 50-60 ℃, and soaking for 50-70S;
step S500: stopping in the air, taking out the galvanized layer treated in the above steps, and staying in the air for 10-20s to ensure that a fresh passive film and O2Further carrying out oxidation reaction to fully oxidize the passivation film;
step S600: preparing an aqueous silica sol sealing solution, and immersing the galvanized layer passivated part treated in the step S500 into the aqueous silica sol sealing solution at the temperature of 60-65 ℃ for treatment for 50-60S; directly carrying out vacuum drying treatment after the air-out.
2. The method as claimed in claim 1, wherein the electrogalvanizing solution in step S200 is prepared from 110-175 g/L NaOH, 10-20 g/L ZnO, 15 mL/L NAM quaternary ammonium salt, and 0.5 mL/L trisodium nitrilotriacetate.
3. The method for improving the acid salt spray corrosion resistance of the galvanized layer according to claim 1, wherein the trivalent chromium passivation concentrated solution in the step S400 is prepared from 22g/L of chromium nitrate, 4mL/L of sulfuric acid, 1mL/L of wetting agent, 2.2mL/L of nitric acid, 1.1g/L of sodium salt, 4g/L of cobalt salt and water, and the trivalent chromium passivation concentrated solution in the step S400 is prepared according to the weight ratio of 1:9 dilution is carried out.
4. The method for improving the acid-resistant salt-fog corrosion resistance of the galvanized layer as claimed in claim 3, wherein the wetting agent in the step S400 is sodium dodecyl benzene sulfonate or polyethylene glycol 600.
5. The method for improving the acid salt spray corrosion resistance of the galvanized layer according to claim 1, wherein the aqueous silica sol blocking solution in the step S600 is prepared from 10 g/L aqueous silica sol, 5g/L surfactant and water.
6. The method for improving the acid salt spray corrosion resistance of the galvanized layer as claimed in claim 5, wherein the surfactant in the step S600 is polyethylene glycol 600 or fatty alcohol-polyoxyethylene ether.
7. The method for improving the acid-salt-spray corrosion resistance of the galvanized layer according to claim 1, wherein the pretreatment in the step S100 is to sequentially remove oil, activate and neutralize the part.
8. The method for improving the acid salt fog corrosion resistance of the galvanized layer according to claim 7, wherein the degreasing in the step S100 is: preparing chemical degreasing fluid, wherein the chemical degreasing fluid is prepared from 30g/L sodium hydroxide, 45g/L sodium carbonate and 25g/L sodium silicate; placing the parts into chemical degreasing liquid at 50-70 ℃ for treatment for 5-15 min; after the parts are deoiled, the parts are thoroughly cleaned by warm water, and the whole part surface is ensured to be hydrophilic.
9. The method for improving the acid-resistant salt-fog corrosion resistance of the galvanized layer as claimed in claim 7, wherein the activation in the step S100 is: preparing an activating solution, wherein the activating solution is prepared from 50-100 g/L hydrochloric acid and 40-50 g/L urotropine, and the part is placed in the activating solution and soaked for 1-2 min at room temperature; and cleaning the activated part by using deionized water.
10. The method for improving the acid-resistant salt-fog corrosion resistance of the galvanized layer as claimed in claim 7, wherein the neutralization in the step S100 is: and (3) putting the parts into a 30-50 g/L sodium carbonate solution and soaking for 1-2 min at room temperature.
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