CN113122833B

CN113122833B - Aluminum alloy passivation method

Info

Publication number: CN113122833B
Application number: CN202110385855.0A
Authority: CN
Inventors: 常龙
Original assignee: Ningbo Fenda New Energy Technology Co ltd
Current assignee: Ningbo Fenda New Energy Technology Co ltd
Priority date: 2021-04-11
Filing date: 2021-04-11
Publication date: 2022-07-15
Anticipated expiration: 2041-04-11
Also published as: CN113122833A

Abstract

The invention provides an aluminum alloy passivation method, which comprises the following processing steps: (1) sequentially carrying out heat treatment, mechanical polishing, oil removal and activation on the aluminum alloy; (2) and (3) passivating liquid treatment: the passivation solution consists of fluotitanic acid, fluozirconic acid, manganese sulfate, tartaric acid, sodium fluoride and sodium alkyl benzene sulfonate, and the treatment mode is soaking; (3) ultrasonic cleaning (4) ultra-high temperature water vapor treatment; the water vapor consists of 3-5wt.% of ethyl orthosilicate and distilled water, and the ultrahigh water vapor temperature is 110-^oC, injecting in a pulse mode; the method can effectively improve the dense plating of the passivation film, and the obtained passivation film has uniform thickness, is a yellow passivation film with the thickness of 4-5 mu m, and has strong corrosion resistance.

Description

Aluminum alloy passivation method

Technical Field

The invention relates to the technical field of aluminum or aluminum alloy surface treatment, in particular to an aluminum alloy passivation method.

Technical Field

Although aluminum is a highly active metal, a dense oxide film is formed on the surface under natural conditions because the oxide film has very low conductivity, and thus can prevent oxygen and other reactions and prevent corrosion of aluminum, aluminum has good corrosion resistance in the atmosphere, but is greatly affected by the atmospheric humidity, salt content and other impurity species, and is good in corrosion resistance in neutral aqueous solutions such as carbonate, chromate, acetate and sulfide, but is deteriorated in aqueous solutions of chloride, and is accelerated in acidic aqueous solutions as the hydrogen ion concentration increases, and is poor in corrosion resistance in sulfuric acid, dilute nitric acid and phosphoric acid, and is more rapidly corroded particularly in hydrochloric acid, and is hardly corroded in concentrated nitric acid (80% or more) because a dense and strong oxide film is formed, and is generally good in corrosion resistance in organic acids such as acetic acid, and is good in alkaline aqueous solutions, the oxide film is corroded by the destruction, but is not corroded by the regeneration of the oxide film in ammonia water.

The principle of the method is to change the metal surface from an activated state to a passivated state so as to slow the metal dissolution, and the actual passivation treatment process depends on the electrochemical reaction process of the metal surface, wherein the actual passivation treatment process comprises an anode dissolution step, in which the metal surface is oxidized, and certain ions in passivation solution are reduced along with a cathode process, and the generated low-valent ions and corrosion products of the metal form a passivation film on the surface.

The passivation solution system of the existing passivation film mainly comprises a molybdate system, a permanganate system, a rare earth system and a titanium zirconium system: the titanium zirconium system is a chromium-free treatment process for the surface of aluminum alloy which is mostly put into industrial production at present, and the research of the titanium zirconium system begins in the 80 th century. In the research and development of the thirty years, the titanium zirconium system covers the aspects of transportation, electronic communication, architectural section and the like from the initial surface passivation treatment of the pop can to the present day, and the titanium zirconium system has the potential capability of completely replacing a chromate system.

For example, CN 101967633A discloses a treatment fluid and a method for preparing a yellow passivation film containing Ti/Zr on the surface of an aluminum alloy. The components and concentrations of the treatment fluid are as follows: 0.5 g/L-2.0 g/L of fluotitanic acid, 0.4 g/L-2.0 g/L of fluozirconic acid, 2.0 g/L-5.0 g/L of manganese salt and 0.5 g/L-2.0 g/L of organic acid; the pH value of the treatment liquid is 2.0-3.0; the treatment solution does not contain chromium and other toxic substances, the conversion treatment does not need heating, the treatment time is 5-30 min, and a yellow chemical conversion coating containing Ti/Zr can be prepared on the surface of the aluminum alloy. The chemical conversion coating prepared by the method has excellent corrosion resistance, high bonding strength with a matrix, room temperature treatment and simple process, and does not contain hexavalent or trivalent chromium harmful to the environment and human body. Also visible in FIG. 3 are small pores due to the tendency of aluminum to react with hydrogen ions under acidic conditions (Al)³⁺+H⁺→Al³⁺+H₂×) resulting in the generation of pores, i.e., for those skilled in the art, since hydrogen evolution reaction of aluminum and hydrogen ions inevitably occurs during passivation, pores are formed during passivation, and the presence of the effect reduces the densification of the passivation film to some extent, resulting in the reduction of the passivation effect of the aluminum material. However, the prior art mainly focuses on the improvement of the passivation solution in the application to obtain a compact passivation film, and after passivation, the aluminum material is usually subjected to simple drying treatment, that is, channels generated in the passivation process are not subjected to additional treatment.

Disclosure of Invention

The invention aims to provide an aluminum alloy passivation method aiming at the problems of poor corrosion resistance, nonuniform passivation film, thin thickness, low compactness and the like of a passivation solution passivation film in the prior art.

The aluminum alloy passivation method comprises the following processing steps:

(1) the aluminum alloy is sequentially subjected to heat treatment, mechanical polishing, oil removal and activation.

The main purpose of the heat treatment, mechanical polishing, degreasing and activation treatment of the aluminum alloy is to improve the surface property of the metal substrate, so as to improve the binding force between the subsequent passivation film and the substrate and avoid the property of the passivation film from being weakened due to other substrate factors.

Wherein the heat treatment is 1vol.% O₂/N₂Under the mixed gas, at 250-300-^oC, constant temperature treatment for 15-20min, and heat treatment is carried out on the base material in advance to remove the thermal stress of the metal, pure inert gas protection is not required in the process, and natural alumina protection on the surface of the aluminum material is carried out, so that the content of O is 1vol.%₂/N₂The oxidation of (2) occurs slowly, the thickness of the oxide film on the surface of the aluminum material is still lower than micron level, and 1vol.% of O can be used in consideration of the cost performance of the protective atmosphere₂/N₂But it is more preferable to use a pure inert gas blanket.

Wherein, the mechanical polishing is to sequentially polish with 400#, 800#, 1200#, 2000#, 3000# sandpaper to the surface brightness.

This step is mainly aimed at removing the native oxide film and providing a flat substrate that facilitates the formation of a uniform passive film.

Wherein, the oil removal is that acetone, ethanol and deionized water are sequentially used for ultrasonic cleaning for 1-2 min.

In the above mechanical polishing process, no matter manual or mechanical polishing, or polishing paste is used, a part of grease is formed on the surface of the substrate, and the presence of the grease can obviously obstruct the formation of a micro-positive area and a micro-negative area, so that no passivation film is formed in the grease existing area.

Wherein the activation is soaking in nitric acid with pH =2.3 for 3-5s, and purging with nitrogen gas for drying.

The main purpose of the activation is to etch to form the relief areas, which favour the micro-positive and micro-negative areas, accelerating the subsequent formation of the passivation film.

The pretreatment process should be performed in sequence, if the heat treatment is performed later, an oxide film is formed again, if the activation is performed first, concave-convex defects are processed due to mechanical polishing, and the steps cannot be exchanged randomly.

(2) And (3) passivating liquid treatment: the passivation solution consists of fluotitanic acid, fluozirconic acid, manganese sulfate, tartaric acid, sodium fluoride and sodium alkyl benzene sulfonate, and the treatment mode is soaking.

Wherein the proportion of each component is as follows: 1-2g/L fluotitanic acid, 0.4-0.5g/L fluozirconic acid, 1.5-2g/L manganese sulfate, 1-2g/L tartaric acid, 1.7-1.9g/L sodium fluoride and 0.05-0.1g/L sodium alkyl benzene sulfonate.

The passivation solution is adjusted by ammonia water or sodium hydroxide to have pH =3.5 +/-0.2 and temperature of 27-30^oC, the time is 150-200 s.

Through the activation treatment, concave-convex defects are formed on the surface of the aluminum alloy, so that when the aluminum alloy is placed in the passivation solution, a large number of micro-negative areas and micro-positive areas are formed on the surface of the aluminum alloy.

Al → Al occurs in the region of the microclimate³⁺+3e^-(ii) a Generation of O in the micro-shadow region₂+2H₂O+4e^-→4OH^-，2H⁺+2e→H₂The progress of the cathodic reaction causes a local increase in pH, resulting in Zr in fluorotitanic acid and fluorozirconic acid⁴⁺+4OH^-→ZrO₂↓+2H₂O；Ti⁴⁺+4OH^-→ZrO₂↓+2H₂O, while Al is generated³⁺+3OH^-→Al(OH)₃Al (OH) known to the person skilled in the art₃Has a solubility product of 4.57X 10^-33； Ti(OH)₄Has a solubility product of 1.0X 10^-40；Zr(OH)₄Has a solubility product of 6.3X 10^-49(ii) a I.e. mainly Ti (OH)₄And Zr (OH)₄The subsequent dehydration and drying will form the corresponding metal oxide, which will inevitably generate hydrogen in the micro-shadow region during the reaction process, i.e. the obtained metal oxide is porous structure, such as (ZrTi) O₄The density of the coating can be improved by the aid of manganese in the porous oxide, sodium fluoride is used as an accelerator, tartaric acid is used as a complexing agent, sodium alkyl benzene sulfonate is used as a surfactant, and the components are used for obtaining a compact and low-pore passivation film.

(3) Cleaning: cleaning for 5-10s by using ultrasonic; the ultrasonic cleaning solution in the step (3) is 1-2wt.% citric acid deionized water solution.

The purpose of cleaning is (1) ultrasonic removal or acid corrosion removal of free oxide particles on the surface of the passive film; (2) hydrogen ions are introduced into the pore channels on the surface of the passivation film, and the hydrogen ions can catalyze the subsequent hydrolysis reaction of the ethyl orthosilicate.

(4) And (5) drying by cold air.

Removing the excessive acid liquid and water in the pore canal.

(5) Ultra-high temperature water vapor treatment; the water vapor consists of 3-5wt.% of ethyl orthosilicate and distilled water, and the ultrahigh water vapor temperature is 110-^oAnd C, injecting in a pulse mode.

The injection pressure of the ultrahigh-temperature water vapor treatment is 0.9-0.95 MPa.

The treatment time is 3-5s, the interval time is 10-15s, and the spraying times are 2-7.

As known to those skilled in the art, the hydrolysis of ethyl silicate proceeds very slowly in the presence of water only, and once catalyzed by an acid (H +) or a base (OH-), the hydrolysis rate is greatly increased, and the hydrolysis reaction is essentially the replacement of the ethoxy group (C2H5O-) in ethyl silicate by the hydroxyl group (-OH) in water, resulting in the conversion of ethyl silicate Si- (OC2H5)4 to silanol Si- (OH)4, which is highly active under ultra-high temperature and acid-catalyzed conditions and readily adsorbs to porous (ZrTi) O₄Surface of water vaporAnd under certain impact pressure state, the silicon oxide attached in the passivation film pore canal is beneficial to improving the coating compactness and further improving the corrosion resistance of the silicon oxide, and the silicon oxide attached in the non-pore canal does not substantially contribute to the corrosion resistance of the passivation layer.

(6) And (3) drying: at 40-50 deg.C^oAnd C, drying for 1-2h by hot air, naturally cooling, and drying and preserving for 24-48 h.

Advantageous effects

According to the invention, through passivation treatment on the aluminum alloy and superheated steam hole filling after passivation, dense plating of the passivation film is effectively improved, the obtained passivation film is uniform in thickness and is a yellow passivation film of 4-5 mu m, the corrosion resistance of the passivation film is strong, and the bonding force between the passivation film and the base material is high.

The passivating solution of fluotitanic acid, fluozirconic acid, manganese sulfate, tartaric acid, sodium fluoride and sodium alkyl benzene sulfonate prepared by the invention is stable and can be stable for 96 hours without precipitation in an open environment.

The preparation process and the treatment process of the invention are simple and convenient to operate, safe and pollution-free.

Drawings

FIG. 1 is an SEM image of an aluminum alloy passivation film obtained after passivation treatment;

FIG. 2 is an SEM image of an aluminum alloy passivation film obtained after passivation treatment and high-temperature steam treatment;

FIG. 3 is a corrosion topography for an untreated aluminum alloy of the present invention, example 2, and comparative examples 1-2.

Detailed Description

The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.

Example 1

A passivation method for aluminum alloy comprises the following processing steps:

Wherein the heat treatment is 1vol.% O₂/N₂Under mixed gas, at 250^oAnd C, performing constant temperature treatment for 15 min.

Wherein, the mechanical polishing is to gradually polish the surface to be bright by using sand paper of 400#, 800#, 1200#, 2000#, 3000 #.

Wherein, the oil removal is ultrasonic cleaning by using acetone, ethanol and deionized water in turn for 1min respectively.

Wherein the activation is a 3s soak in nitric acid at pH =2.3, and nitrogen purge drying.

(2) And (3) passivating liquid treatment: the passivation solution is composed of fluotitanic acid, fluozirconic acid, manganese sulfate, tartaric acid, sodium fluoride and sodium alkyl benzene sulfonate, and the treatment mode is soaking.

Wherein the proportion of each component is as follows: 1g/L fluotitanic acid, 0.4g/L fluozirconic acid, 1.5g/L manganese sulfate, 1g/L tartaric acid, 1.7g/L sodium fluoride and 0.05g/L sodium alkyl benzene sulfonate.

The passivation solution is adjusted by ammonia water or sodium hydroxide to have pH =3.5 +/-0.2 and temperature of 27-30^oC, the time is 150 s.

(3) Cleaning: cleaning for 5s by using ultrasonic; the ultrasonic cleaning solution in the step (3) is a deionized water solution of citric acid of 1 wt.%.

(4) And (5) drying by cold air.

(5) Ultra-high temperature water vapor treatment; the water vapor consists of 3wt.% of ethyl orthosilicate and distilled water, and the temperature of the ultrahigh water vapor is 110 DEG^oAnd C, injecting in a pulse mode.

And the injection pressure of the ultrahigh-temperature water vapor treatment is 0.9 MPa.

The treatment time is 3s, the interval time is 10s, and the spraying times are 2.

(6) And (3) drying: at 40^oC, drying for 1 hour by hot air, naturally cooling,and (5) drying and preserving for 24 h.

Example 2

Wherein the heat treatment is 1vol.% O₂/N₂Under mixed gas at 275 deg.C^oAnd (5) carrying out constant temperature treatment for 17.5min under the condition of C.

Wherein, the oil removal is ultrasonic cleaning by using acetone, ethanol and deionized water in sequence for 1.5min respectively.

Wherein the activation is a 4s soak in nitric acid at pH =2.3, and nitrogen purge drying.

Wherein the proportion of each component is as follows: 1.5g/L fluotitanic acid, 0.45g/L fluozirconic acid, 1.75g/L manganese sulfate, 1.5g/L tartaric acid, 1.8g/L sodium fluoride and 0.075g/L sodium alkyl benzene sulfonate.

The passivation solution is adjusted to have pH =3.5 +/-0.2 by ammonia water or sodium hydroxide and has the temperature of 28 DEG^oC, time 175 s.

(3) Cleaning: ultrasonic cleaning is used for 7.5 s; the ultrasonic cleaning solution in step (3) is a deionized citric acid solution of 1.5 wt.%.

(4) And (5) drying by cold air.

(5) Ultra-high temperature water vapor treatment; the water vapor consists of 4wt.% of ethyl orthosilicate and distilled water, and the ultrahigh water vapor temperature is 115 DEG^oAnd C, injecting in a pulse mode.

The injection pressure of the ultrahigh-temperature water vapor treatment is 0.925 MPa.

The treatment time is 4s, the interval time is 12.5s, and the spraying times are 4.

(6) And (3) drying: at 45^oDrying with hot air for 1.5hAnd naturally cooling, drying and preserving for 36 h.

Example 3

Wherein the heat treatment is 1vol.% O₂/N₂Mixed gas at 300 deg.C^oAnd C, performing constant temperature treatment for 20 min.

Wherein, the oil removal is ultrasonic cleaning by using acetone, ethanol and deionized water in sequence for 2min respectively.

Wherein the activation is a 5s soak in nitric acid at pH =2.3, and nitrogen purge drying.

Wherein the proportion of each component is as follows: 2g/L fluotitanic acid, 0.5g/L fluozirconic acid, 2g/L manganese sulfate, 2g/L tartaric acid, 1.9g/L sodium fluoride and 0.1g/L sodium alkyl benzene sulfonate.

The passivation solution is adjusted to have pH =3.5 +/-0.2 by ammonia water or sodium hydroxide and has the temperature of 30 DEG^oC, the time is 200 s.

(3) Cleaning: cleaning for 10s by using ultrasonic; the ultrasonic cleaning solution in the step (3) is 2wt.% citric acid deionized water solution.

(4) And (5) drying by cold air.

(5) Ultra-high temperature water vapor treatment; the water vapor consists of 5wt.% of ethyl orthosilicate and distilled water, and the ultrahigh water vapor temperature is 120 DEG^oAnd C, the injection mode is pulse injection.

And the injection pressure of the ultrahigh-temperature water vapor treatment is 0.95 MPa.

The treatment time is 5s, the interval time is 15s, and the spraying times are 7.

(6) And (3) drying: at 50^oC, drying the mixture for 2 hours by hot air,and naturally cooling, drying and preserving for 48 h.

Comparative example 1

The aluminum alloy passivation method comprises the following processing steps:

The passivation solution is adjusted to have pH =3.5 +/-0.2 by using ammonia water or sodium hydroxide and the temperature is 28 DEG^oC, time 175 s.

(3) And (3) drying: at 45^oAnd C, drying for 1.5 hours by hot air, naturally cooling, drying and preserving for 36 hours.

Comparative example 2

The aluminum alloy passivation method comprises the following processing steps:

Wherein, the oil removal is that acetone, ethanol and deionized water are used for ultrasonic cleaning in sequence, and the time is 1.5min respectively.

Wherein the activation is soaking in nitric acid at pH =2.3 for 4s, and drying with nitrogen purge.

(3) And (5) drying by cold air.

(4) Ultra-high temperature water vapor treatment; the water vapor consists of 4wt.% of ethyl orthosilicate and distilled water, and the ultrahigh water vapor temperature is 115 DEG^oAnd C, spraying continuously for 16 seconds.

(5) And (3) drying: at 45^oAnd C, drying for 1.5h by hot air, naturally cooling, drying and preserving for 36 h.

TABLE 1

And testing the passivated aluminum alloy by adopting a three-electrode system, wherein a reference electrode is a Saturated Calomel Electrode (SCE), and a counter electrode is a Pt electrode. Electrochemical tests were conducted in 3.5wt.% NaCl solution, as shown in the above table, for the untreated aluminum material, corrosion was very likely to occur due to the absence of passivation film or protection of natural oxide film Icorr =9.132 μ a/cm2, the corrosion current density was reduced to 1.263 μ a/cm2 without post-treatment, as in comparative example 1, and then post-treatment was conducted thereon, in which acid catalysis was omitted and continuous spraying was used, the main purpose of the present invention using acid catalysis and pulse spraying was to increase the filling amount of channels, but the corrosion current density was reduced to 0.314 μ a/cm2 without acid catalysis and pulse spraying, as in comparative example 2, the corrosion current density was increased to 0.165 μ a/cm2 as in acid catalysis-accelerated hydrolysis and pulse spraying, the density of the passivation film is further improved, and the corrosion resistance of the passivation film is effectively improved, as shown in figure 3, through a salt spray test, the passivation film prepared by the invention cannot generate an obvious corrosion phenomenon within 200h, in comparison with comparative examples 1-2, the passivation film has corrosion of different degrees, and the corrosion performance in table 1 is consistent with the corrosion morphology performance in figure 3.

In addition, as shown in fig. 1, an SEM image of the aluminum alloy passivation film obtained after passivation treatment of the present invention shows holes inevitably generated during passivation, as shown by black circles, and as shown in fig. 2, after steam post-treatment, the holes are effectively filled, and the density of the passivation film is further improved.

Although the present invention has been described above by way of examples of preferred embodiments, the present invention is not limited to the specific embodiments, and can be modified as appropriate within the scope of the present invention.

Claims

1. The passivation method of the aluminum alloy is characterized by comprising the following processing steps:

(1) sequentially carrying out heat treatment, mechanical polishing, oil removal and activation on the aluminum alloy;

(2) and (3) passivating liquid treatment: the passivation solution consists of fluotitanic acid, fluozirconic acid, manganese sulfate, tartaric acid, sodium fluoride and sodium alkyl benzene sulfonate, and the treatment mode is soaking;

the passivation solution comprises the following components: 1-2g/L fluotitanic acid, 0.4-0.5g/L fluozirconic acid, 1.5-2g/L manganese sulfate, 1-2g/L tartaric acid, 1.7-1.9g/L sodium fluoride and 0.05-0.1g/L sodium alkyl benzene sulfonate;

adjusting the pH of the passivation solution to be =3.5 +/-0.2 by using ammonia water or sodium hydroxide, wherein the temperature is 27-30 ℃ and the time is 150-200 s;

(3) cleaning: ultrasonic cleaning for 5-10s, wherein the ultrasonic cleaning solution is 1-2wt.% citric acid deionized water solution;

(4) ultra-high temperature water vapor treatment; the water vapor is water vapor which consists of 3-5wt.% of ethyl orthosilicate and distilled water, the temperature of the ultrahigh-temperature water vapor is 110-120 ℃, and the injection mode is pulse injection;

the pulse injection pressure is 0.9-0.95 MPa;

the pulse spraying treatment time is 3-5s, the interval time is 10-15s, and the spraying times are 2-7;

(5) and (3) drying: drying with hot air at 40-50 deg.C for 1-2 hr, naturally cooling, drying and preserving for 24-48 hr.

2. The method of passivating an aluminum alloy of claim 1, wherein said heat treating is 1vol.% O₂/N₂Under the mixed gas, the mixture is processed for 15 to 20min at the constant temperature of 250-300 ℃;

the mechanical polishing is to sequentially polish the surfaces of the two parts by using sand paper of 400#, 800#, 1200#, 2000# and 3000 #;

the oil removal is that acetone, ethanol and deionized water are sequentially used for ultrasonic cleaning, and the time is 1-2min respectively;

the activation is performed by soaking in nitric acid with pH =2.3 for 3-5s and blowing and drying by nitrogen.

3. A method for passivating an aluminum alloy as claimed in claim 1, wherein a cold air blow drying step is provided between step (3) and step (4).