KR100305009B1 - Method for forming a non-chromate oxide coating for an aluminum substrate - Google Patents

Abstract

(A) The present invention is a method of forming a cobalt conversion coating on a metal substrate to impart corrosion resistance and paint adhesion properties. The present invention has been developed instead of the chromic acid method of the prior art. The process of the present invention comprises: (a) a cobalt conversion solution consisting of an aqueous solution comprising soluble cobalt (III) 6 complex salt having a concentration from about 0.01 moles per liter of solution to the saturation limit of cobalt (III) ; (b) contacting the solution to a metal substrate for a sufficient time to form a cobalt conversion coating. The substrate may be aluminum, Cd, Zn, Zn-Ni and steel-plated aluminum alloy. Cobalt (III) 6 complex salt is present as [Co (NH ₃ ) ₆ ] X ₃ where X is Cl, Br, NO ₃ , CN, SCN, PO ₄ , SO ₄ , C ₂ H ₃ O _2, or CO ₃ . (B) The present invention provides a chemical conversion coating solution for producing a cobalt conversion coating on a metal substrate. This solution contains an aqueous solution containing soluble cobalt (III) 6 complex salt having a concentration from about 0.01 mole per liter of solution to the saturation limit of cobalt (III) 6 complex salt. The cobalt conversion solution may be prepared by a bed assembly sequence comprising (a) dissolving a cobalt (II) salt, (b) subsequently dissolving the metal nitrate, and (c) adding ammonium acetate. (C) The present invention provides coating products exhibiting corrosion resistance and paint adhesion properties. The product comprises a cobalt conversion coating comprising (a) a metal substrate and (b) a maximum volume percent aluminum oxide Al ₂ O ₃ and cobalt oxides CoO, Co ₃ O ₄ and Co ₂ O ₃ on the substrate.

Description

Method for forming a non-chromate oxide coating for an aluminum substrate

FIG. 1 is an x10,000 magnified micrograph of a test panel showing a cobalt conversion coating 310 of the present invention.

FIG. 2 is an x50,000 magnified micrograph of the first degree panel.

FIG. 3 is an x10,000 magnified micrograph of another test panel showing the side view of the cut section of the inventive cobalt conversion coating 320 at different angles.

FIG. 4 is an x50,000 magnified micrograph of a test panel of FIG. 3 showing a side view of the cut section of the inventive cobalt conversion coating 320 at different angles.

5 is an x10,000 magnified micrograph of another test panel showing another cobalt conversion coating 330 of the present invention.

6 is an x50,000 magnified micrograph of the test panel of FIG. 5;

FIG. 7 is an x10,000 magnified micrograph of another test panel showing the side view of the cut section of the inventive cobalt conversion coating 330 at different angles; FIG.

FIG. 8 is an x50,000 magnified photomicrograph of a test panel of FIG. 7 showing a side view of a cut-away portion of a cobalt conversion coating 330 of the present invention at different angles; FIG.

BACKGROUND OF THE INVENTION [

1) Field of the Invention

The invention relates to the field of chemical conversion coatings formed on metal substrates, for example aluminum substrates. More specifically, the present invention relates to a novel type of oxide coating (hereinafter referred to as " cobalt conversion coating ") that is chemically formed on a metal substrate. The present invention contributes to air and water quality preservation and greatly improves human environment.

2) Background Art

In general, the chemical conversion coating is chemically formed by " converting " the surface of the metal into a rigid adhesive coating so that all or a portion of the surface is composed of the oxidized form of the metal. Chemical conversion coatings can provide high corrosion resistance and strong bond affinity for paints. Industrial applications of paints (organic finishes) on metals generally require the use of chemical conversion coatings (especially when performance requirements are high).

Although aluminum has its own protection against corrosion by the formation of natural oxide coatings, this protection is not perfect. In the presence of moisture and electrolytes, aluminum alloys, especially high-copper 2000-series aluminum alloys such as alloy 2024-T3, corrode much faster than pure aluminum.

Generally, there are two ways to treat aluminum to form a beneficial conversion coating. One is anodizing (anodizing) which immerses aluminum components in chemical baths such as chromic acid or sulfuric acid baths and passes current through aluminum components and chemical baths. The resulting conversion coating on the surface of the aluminum component provides a bonding surface for corrosion resistant and organic finishes.

The second method is by chemically producing a conversion coating, usually referred to as a chemical conversion coating, which treats the aluminum component with a chemical solution such as a chromic acid solution without the use of electrical current. This chemical solution can be applied by immersion, manual and injection methods. The resulting conversion coating on the surface of the aluminum component imparts corrosion resistance and surface bonding to the organic finish. The present invention relates to this second method for producing a chemical conversion coating. This chemical solution may be applied by immersion, various types of hand or spray methods.

Chromic acid processes that are widely used to form chemical conversion coatings on aluminum substrates are described in US Pat. No. 2,796,370 to Ostrander et al., US Pat. No. 2,796,371, Military Process Specification MIL-C-5541 and Boeing Process Specification BAC 5719 disclose various implementations. These chromic acid chemical conversion baths include hexavalent chromium, fluoride, and cyanide, which have health and safety concerns as well as serious environmental problems. Typical chromate conversion baths, such as ALODIN 1200, have the following constituents: CrO ₃ - chromic acid (hexavalent chromium); NaF-fluorinated sodium room; KBF ₄ - potassium tetrafluoroborate; Potassium K ₃ Zr (CN) ₆ -hexafluorozirconate; K ₃ Fe (CN) ₆ - potassium ferricyanide; And HNO ₃ - nitric acid (for pH adjustment).

Over the aircraft and aerospace industries, many aluminum structural components and steel components, as well as Cd-plated, Zn-plated, Zn-Ni plated, are being processed using this chromic acid process technology. The chromate conversion film formed on the aluminum substrate meets the corrosion resistance criteria of 168 hours, but these are mainly for the paint adhesion of the surface substrate. Due to their relatively thin and low coating weight (40-150 mg / ft ² ), chromate conversion coatings have not been able to reduce fatigue life in aluminum structures.

However, environmental regulations in the US, particularly in California and elsewhere, have drastically lowered the acceptance criteria for hexavalent chromium compounds that escape and discharge from metal finishing processes. Therefore, chemical conversion processes employing hexavalent chromium compounds must be substituted.

The present invention, which does not employ hexavalent chromium compounds, is intended to replace the chromanic acid process used previously to form conversion coatings on aluminum substrates.

[Summary of the Invention]

(A) In one aspect, the present invention is directed to forming a cobalt conversion coating on a metal substrate to impart corrosion resistance and paint adhesion. The present invention has been developed to replace the chromic acid process of the prior art. (A) an aqueous solution containing soluble cobalt (III) 6 complex salt having a saturation concentration of cobalt (III) 6 complex salt at about 0.01 mole per liter of solution, and an aqueous solution of CH ₃ COOH Providing a cobalt conversion solution comprising; (b) contacting the substrate with the solution for a sufficient time to form a cobalt conversion coating, the substrate being aluminum, Cd, Zn, Zn-Ni, and aluminum plated with a steel. Cobalt (III) 6 complex salt is present in the form of [Co (NH ₃ ) ₆ ] X ₃ where X is Cl, Br, NO ₃ , CN, SCN, PO ₄ , SO ₄ , C ₂ H ₃ O ₂ , Or CO ₃ .

(B) In another aspect, the present invention relates to a chemical conversion coating solution for producing a cobalt conversion coating on a metal substrate, said solution having a saturation concentration of cobalt (III) 6 complex at about 0.01 mole per liter of solution Soluble cobalt (III) 6 comprises an aqueous solution containing a complex salt and acetic acid CH ₃ COOH. This cobalt conversion solution can be prepared by a bass configuration sequence comprising the following steps: (a) dissolving the cobalt (II) salt, (b) then adding Mg (NO ₃ ) ₂ .6H ₂ O , Ca (NO ₃ ) ₂ .6H ₂ O, NaNO ₃ , KNO ₃ , or LiNO ₃ , and then (c) adding ammonium acetate.

(C) In another aspect, the present invention relates to a coated product exhibiting corrosion resistance and paint adhesion, comprising: (a) a metal substrate, (b) aluminum oxide Al ₂ O ₃ And a cobalt conversion coating formed on the substrate comprising cobalt oxides CoO, Co ₃ O _4, and Co ₂ O ₃ .

[Description of Preferred Embodiments]

The drawings of the present invention are micrographs of a coating on an aluminum alloy test panel produced by a scanning electron microscope. Figures 1 to 8 are photomicrographs (operating at 30 KV) of an alloy 2024-T3 test panel with a cobalt conversion coating made by the present invention. Figures 1 and 2 show the cobalt conversion coating 310 formed by soaking in a typical cobalt coating solution at 140 ° F for 25 minutes. Figures 3 and 4 show a cobalt conversion coating 320 formed by soaking in a typical cobalt coating solution at 140 ° F for 15 minutes. FIGS. 5-8 illustrate a cobalt conversion coating 330 formed by soaking in a typical cobalt coating solution at 140 ° F for 20 minutes. No significant differences are visible between the coatings 310, 320, 330.

FIG. 1 is an x10,000 magnified micrograph of a test panel showing a cobalt conversion coating 310 of the present invention. This micrograph is a plan view of the top surface of the oxide coating 310 from an elevated angle. The top of the oxide coating 310 is porous and looks like a layer of chowmein noodles. This test panel was immersed in a cobalt conversion coating solution for 25 minutes. The white bar is 1 micron in length. The rounded portion, denoted by reference numeral 312, is an undefined impurity on the surface of the oxide coating.

FIG. 2 is an x50,000 magnified micrograph of the test panel of FIG. This micrograph is a top view of the top surface of the oxide coating 310 from an elevated angle. FIG. 2 is a close-up of a narrow area of the test panel. The white bar is 1 micron in length.

FIG. 3 shows a side view of the cut section of the inventive cobalt conversion coating 320 from an elevated angle as an x10,000 magnified micrograph of another test panel. The cut-away portion of the aluminum substrate of the test panel is denoted by 322. This test panel was immersed in the coating bath for 15 minutes. To make a micrograph, the test panel was bent and crushed to expose the transverse portion of the oxide coating 320. White bars are 1 micron in length.

FIG. 4 is an x50,000 magnified micrograph of the test panel of FIG. 3, showing a side view of the cut portion of the inventive cobalt conversion coating 320 from an elevated angle. FIG. 4 is a close-up of a narrow area of the test panel. The aluminum substrate of the test panel is denoted by 322. White bars are 1 micron in length.

FIG. 5 is an x10,000 magnified micrograph of a test panel showing another cobalt conversion coating 330 of the present invention. This micrograph is a top view of the top surface of the oxide coating 330 from an elevated angle. The upper portion of the oxide coating 330 is porous and has the same shape as that of the superficial layer. This test panel was immersed in a cobalt conversion coating solution for 20 minutes. The white bar is 1 micron in length. The rounded portion 332 is an unidentified impurity on the surface of the oxide coating.

6 is an x50,000 magnified micrograph of the test panel of FIG. 5; This picture is a top view of the top surface of the oxide coating 330 from an elevated angle. FIG. 6 is a close-up view of a narrow area of the test panel with a higher magnification. The white bar is 1 micron in length.

7 shows an x10,000 magnified micrograph of another test panel showing a side view of a fractured cross section of a cobalt conversion coating 330 from an elevated angle of the present invention. The aluminum substrate of the test panel is indicated by reference numeral 332. This test panel was immersed in a coating bath for 20 minutes. To take a micrograph, the test panel was bent and crushed to expose the cross-section of the oxide coating 330. White bars are 1 micron in length.

FIG. 8 is an x50,000 magnified micrograph of the test panel of FIG. 7, showing a side view of the fractured cross section of the cobalt conversion coating 330 from the elevated angle of the present invention. FIG. Figure 8 is a close-up of a narrow area of the test panel at a higher magnification. The aluminum substrate of the test panel is indicated by reference numeral 332. White bars are 1 micron in length.

The present inventors have invented two classes of cobalt conversion coatings. The first class is a cobalt conversion coating consisting of an oxide structure under unsealed conditions and is suitable for use in installations where paint adhesion is particularly important. The second class is a cobalt conversion coating consisting of an oxide structure under sealed conditions and is suitable for use in installations where corrosion resistance of exposed metal is required.

A significant amount of experimental research has been conducted to reach the present invention. Several kinds of polyvalent compounds were irradiated and alkali, acid or fluoride were used respectively or in combination. Among these compounds, there are vanadates, molybdates, lead platelets, iron salts and various borates. Film deposition of compounds containing these components on an aluminum alloy substrate was not detectable to a degree of corrosion protection and paint adsorption could not be achieved.

However, when the aluminum substrate was immersed in a cobalt (II) (CO ^{2 +} ) salt aqueous solution heated to a temperature of 82.2 ° C (180 ° F), a significant increase in corrosion protection was observed. This fact has led to the reaction of various cobalt (II) and cobalt (III) (Co ³⁺ ) reactions, especially those described in U.S. Patent Application No. 07 / 525,800, filed May 17, 1990 Respectively.

(II) salts such as CoX ₂ (where X = Cl, Br, NO ₃ , CN, SCN, PO ₄ , SO ₄ , C ₂ H ₃ O ₂ , CO ₃ ) and ammonium salts NH ₄ X In the presence of ammonium hydroxide (ammonia) for several hours to form a cobalt (III) hexaamine coordination complex salt.

The above reaction scheme (1) is described in U.S. Patent Application No. 07 / 525,800, filed on May 17, 1990. The use of ammonium hydroxide (ammonia) is to generate trivalent amine complex salts. After the application, further studies have shown that cobalt (III) hexamine complexation is produced with significant process advantages when ammonium hydroxide is replaced by ammonium acetate, CH3COONH4.

In the above, X is _{C1, Br, NO 3, CN} , SCN, PO 4, SO 4, C 2 H 3 O 2, CO 3.

This acetic acid buffer system does not require frequent pH composition required by the addition of NH ₄ OH to the ammonium hydroxide system because of the high evaporation rate of ammonia. Moreover, the acetic acid buffered cobalt amine complex salt solution works optimally in the pH range of 6.0 to 7.0. The resulting oxide coating is further improved in corrosion resistance by water compared to ammonium hydroxide systems. The weight of the oxide coating can easily be obtained from 20 to 240 mg / ft ² . A complete lack of ammonia odor has a clear advantage in terms of production compatibility. All of the X-reactants listed in Scheme (2) above have been successfully run to produce conversion coatings on aluminum substrates. However, nitrate showed the best results in terms of coating performance and appearance. From an environmental point of view, cyanide and thiocyanate are undesirable.

One important aspect of cobalt chemistry is the fact that cobalt (II) complexes tend to be oxidized by cobalt (III) complexes. For example,

It has been found that when an aluminum alloy substrate (such as alloy 2024-T3) is immersed in an aqueous solution containing the above cobalt (III) complex salt, a coating of bright pearlescent light is formed on the aluminum alloy giving excellent corrosion- . These coatings are comparable to conventional chromic acid conversion coatings at chromaticity.

The cobalt complex salt is not new. Cobalt (III) complexes have been created for use as oxidizing agents in the photographic industry to increase the sharpness of color photographs. For example, U.S. Pat. No. 4,088,486 to Bissonet discloses the cognitive use of cobalt (III) amine complexes.

It is surprising, however, that such cobalt (III) hexamine complexes can form oxide structures on aluminum substrates. The reaction mechanism of oxide formation is not exactly known at this point; While not wishing to be bound by any particular theory, it is believed that the formation of oxides is a chemical equilibrium action of the above reaction scheme (3). The oxidation ability of this cobalt (III) hexaamine complex salt is believed to be due to the formation of an oxide film (hereinafter referred to as " cobalt conversion coating ") observed on an aluminum substrate. Formation of the oxide structure was confirmed by instrumental analysis of the coating (Auger analysis and electron microscopy). A micrograph of the appearance of the cobalt conversion coating of the present invention is illustrated in FIGS.

In the above reaction formula (2), NH ₄ X which is an ammonium salt is reacted with a metal nitrate such as Mg (NO ₃ ) ₂ .6H ₂ O, Ca (NO ₃ ) ₂ .6H ₂ O, NaNO ₃ , KNO ₃ or LiNO ₃ , There was an additional improvement associated with the color density of the oxide coating:

In the above, X is _{C1, Br, NO 3, CN} , SCN, PO 4, SO 4, C 2 H 3 O 2, CO 3.

However, the preferred reaction can be found in the inclusion of cobalt nitrate as follows:

The importance of many parameters in terms of uniform boss chemistry and the uniform formation of oxide coatings becomes evident when experimenting with this initial formulation. These parameters are chemical reactant selection, chemical reactant concentration, bath composition sequence, pH adjustment, temperature and immersion time.

[Chemical Reactant Selection]

With respect to reactant selection, different types of cobalt salts may work for cobalt complexation. Cobalt (II) salts that can be dissolved in water include cobalt nitrate, Co (NO ₃ ) .6H ₂ O; Cobalt chloride, CoCl ₂ .6H ₂ O; Cobalt sulfate, CoSO _4; Cobalt acetate, Co (CH ₃ COO) ₂ .4H ₂ O; Basic carbonic acid cobalt, and 2CoCO ₃ .Co (OH) ₂ .H ₂ O. Each of the above cobalt (II) salts may be reacted with a metal nitrate such as ammonium acetate and Mg (NO ₃ ) ₂ .6H ₂ O, Ca (NO ₃ ) ₂ .6H ₂ O, NaNO ₃ , KNO ₃ or LiNO ₃ have.

Since cobalt amine complex salt formed with nitrate produces optimal coating performance results, the reactants for the aluminum and aluminum alloys are Co (NO ₃ ) 6 H ₂ O, Mg (NO ₃ ) ₂ .6H ₂ O and CH ₃ COONH ₄ .

Moreover, other cobalt (II) salts may be used if they have minimal solubility in water. The minimum required solubility is about 0.01 mole of cobalt (II) salt per liter of water at 20 < 0 > C.

Preferred chemical additives are oxidants, in particular hydrogen peroxide, H ₂ O ₂ being preferred. The function of the oxidant is to oxidize cobalt (II) ions to cobalt (III) ions in solution. The presence of hydrogen peroxide is not essential for feasibility, since the air stream flowing into the tank acts as an oxidant. Hydrogen peroxide increases the rate of oxidation of cobalt (II) ions to cobalt (III) ions in a solution, so that the solution can be operated at any time in a short time, making the commercial implementation of the present invention useful.

Thus, preferred chemical reactants and additives are:

Cobalt nitrate Co (NO ₃ ) 6H ₂ O

CH ₃ COONH ₄ such as ammonium acetate NH ₄ C ₂ H ₃ O ₂

Magnesium nitrate Mg (NO ₃ ) ₂ .6H ₂ O

Hydrogen peroxide (oxidizing agent) H ₂ O ₂

[Chemical concentration, pH adjustment, temperature and immersion time]

With respect to the chemical concentration, the dissolved concentration of the used cobalt (II) is from about 0.01 mole per liter of final solution to the saturation concentration of the employed cobalt (II) salt. Preferably, the dissolved concentration of the used cobalt (II) salt is from about 0.04 moles per liter of final solution to about 0.15 moles per liter of final solution. The concentration of the cobalt (III) hexaamine coordination complex is from about 0.01 mole per liter of final solution to the saturation concentration of the employed cobalt (III) hexaamine complex salt. Preferably, the concentration of the cobalt (III) hexaamine coordination complex is from about 0.04 moles per liter of final solution to about 0.15 moles per liter of final solution.

The concentration of the dissolved metal nitrate may be about 0.03 to 2.5 moles per liter of final solution. Preferably, the concentration of dissolved metal nitrate is from about 0.05 moles per liter of final solution to about 0.2 moles per liter of final solution.

The concentration of ammonium acetate may be about 0.06 to 6.0 moles per liter of final solution. Preferably, the concentration of dissolved ammonium acetate is from about 0.15 moles per liter of final solution to about 0.7 moles per liter of final solution; A stoichiometric excess of ammonium acetate is not harmful. The resulting acetic acid concentration can be about 0.05 to 5.0 mol per liter of final solution. Preferably, the resulting acetic acid concentration is from about 0.125 moles per liter of final solution to 0.6 moles per liter of final solution.

The pH of the bath may be 5.0 to 9.0, preferably 6.0 to 7.0, and most preferably 6.5. The temperature of the bath may be about 20-72 [deg.] C (68-160 [deg.] F). Above 72 ° C (160 ° F), gradual decomposition of cobalt (III) hexamine complex occurs. The appropriate temperature is 60 ± 2.8 ° C (140 ± 5 ° F). The immersion time may be about 3 to 60 minutes, and the appropriate immersion time may be 20 ± 5 minutes.

[Preferred Bass Manufacturing Procedure]

1. Fill a stainless steel tank equipped with an air agitation pump and heating coil at a temperature of 20-32.2 ° C (68-90 ° F) with 3/4 deionized water. Air agitation starts with a soft air bubble. (This tank may be equipped with a filtration device to remove solid impurities (dust, aluminum salts, etc.) during the process.

2. Add a large amount of cobalt (II) salt [Co (NO ₃ ) ₂ .6H ₂ O is preferred], and dissolve completely. When dissolved, a stainless steel basket can be used to hold cobalt salt particles suspended in water. The most preferred molar ratio of cobalt salt to ammonium acetate is about 1 to 6 (see equation (4) for the stoichiometric balance). The most preferred concentration of cobalt salt is about 0.077 moles per liter of final solution. The amount used is based on the molar ratio of cobalt salt to ammonium acetate over which an oxide coating with excellent paint adhesion properties can be produced.

3. A large amount of metal nitrate [Mg (NO ₃ ) ₂ .6H ₂ O is preferred] is now added. The concentration of this additive may not be added or it may be added up to 2.5 moles per liter of final solution. However, the most preferred amount for maximizing the pearl light of the conversion coating is about 0.10 moles per liter of final solution.

4. Ammonium acetate is now added and dissolved. When about 0.077 moles per liter of final solution is employed, which is the most preferred concentration of cobalt salt, the most preferred ammonium acetate concentration is 35.6 grams (0.46 moles) per liter of final solution. This concentration of ammonium acetate makes it possible to achieve about one to six, the most preferred molar ratio of cobalt salt to ammonium acetate. Proper air agitation is maintained.

5. Fill the tank with the final volume of demineralized water. Air agitation of this solution is maintained at room temperature for 2 to 3 hours. Then, a large amount of hydrogen peroxide, H ₂ O ₂ (preferably 30% by volume) is added. The preferred amount of the final solution was 1 liter of H ₂ O ₂ of about 0.03 to 0.1 moles [H ₂ O ₂ (30% by volume) of from about 3 to 10ml].

6. This solution is further maintained for at least 2 hours, preferably at 20-32.3 ° C (68-90 ° F) to allow cobalt (III) complexation with minimal amount of cobalt complexation [reaction (4) I make it. It becomes brown / red in solution like French wine. Preferably, the solution is maintained at a temperature of 20 to 32.2 DEG C (68-90 DEG F.) for a further 8 hours to produce a large amount of cobalt (III) complex salt to facilitate the efficient implementation of the cobalt conversion coating process. The solution is heated to the most preferred operating temperature of 60 ± 2.8 ° C. (140 ± 5 ° F). During the cobalt conversion coating process, the solution is subjected to adequate air agitation.

7. Optionally, prepare a second stainless steel tank (to be used for the oxide sealing step) equipped with an air agitation pump and a heating coil, and fill 3/4 of the demineralized water. This post-cobalt conversion coating step serves as a corrosion resistance promoter. This tank does not heat the required chemicals during addition.

8. Add a large amount of nickel sulfate, NiSO ₄ .6H ₂ O, magnesium nitrate, and Mg (NO ₃ ) ₂ .6H ₂ O to the sealing tank and dissolve. A preferred amount of nickel sulfate is 20 grams (0.076 moles) per liter of final solution. The preferred amount of magnesium nitrate is 20 grams (0.078 moles) per liter of final solution. And may be stirred to dissolve it if necessary.

9. Then fill the sealed tank with the final volume with demineralized water and heat at 200 ± 5 ° F. Further air agitation is not necessary.

[Preferred Overall Process Sequence]

The preferred overall process sequence can be summarized as follows.

[Process flow chart for maximizing paint adhesion]

(1) Pre-cleaning if necessary

(2) Mask and Rack as required,

(3) Alkali cleaning and rinsing

(4) Deoxidation and rinsing

(5) Oxide coating formation: 15 - 20 minutes at < RTI ID = 0.0 >

(6) Immersion rinsing: 68-140 ° F

(7) Drying - up to 140 ° F

[Process Flowchart for Maximizing Corrosion Resistance]

(1) Pre-cleaning if necessary

(2) Mask and Rack as required,

(3) Alkali cleaning and rinsing

(4) Deoxidation and rinsing

(5) Oxide coating formation: 15 - 20 minutes at < RTI ID = 0.0 >

(6) Immersion rinsing: 68-140 ° F

(7) Sealing according to requirements

(8) Rinse - room temperature, minimum 3 minutes

(9) Drying - up to 140 ° F

[General matters related to the process flow charts]

The cobalt conversion coating must be applied after completing the trimming and fabrication. The areas where the solution can be confined should not be subjected to immersion alkali cleaning or immersion deoxidation; Before application of the cobalt conversion treatment, a manual rinsing and deoxidation procedure should be used so that the water does not have a surface. A waterless surface is a surface that is sprayed with cleansing water at a temperature of 100 ° F or less, or where a continuous water film is maintained for at least 30 seconds after immersion and rinsing.

Rinsing and draining are required in the process, since each solution must be completely removed in order to avoid interference with subsequent successive runs of the solution. The parts should proceed from one stage to the next without delay and without the need for gaps to dry. If you need to handle wet areas, wear clean latex rubber gloves. After the conversion coating, only the dried part is treated as a clean fiber glove. For a process system that requires partial clamping fixation, the number and size of contact areas should be kept to a minimum, although adequate mechanical.

[Preliminary cleaning]

If the parts are oiled or painted, steam degreasing may be performed according to Boeing Process Design BAC 5408, emulsion cleaning may be carried out according to Boeing Process Design BAC 5763, or solvent cleaning according to Boeing Process Design BAC 5750 . Opened joints or spot-weld joints where the solution can be confined should be immersed in cold water (or hot and cold water) for 2 minutes after pre-cleaning.

[Masking and Racking]

Areas where a cobalt conversion coating is not required should be masked with a masking material. Injecting dissimilar metals (such as chromium, nickel or cobalt alloys or plating, sprayed with RES or titanium) and non-aluminum coated plasma sprays must remove the mask.

[Alkali cleaning]

Alkali rinsing and rinsing may be carried out in accordance with Boeing Process Design BAC 5749, with the exception of parts having open joints or point-welded joints. In this case, the rinse should be done for several minutes (at least 4 hours) with agitation for at least 10 minutes and then spray rinse by hand to prevent the solution from being trapped.

[Deoxidation]

Deoxidation and rinsing can be carried out in accordance with Boeing Process Design BAC 5765, except where the solution can be confined. The portion is rinsed using the method described in the " alkali cleaning " above. The castings can be deoxidized by any of the methods described below.

a. Deoxidation according to Boeing Process Design BAC 5765, Solution 37, 38 or 38.

b. Boing Process Design BAC 5748, Type II, Class 1 and Dry Polishing Casting by Rinse.

Specific solution compositions within the scope of the present invention are as follows:

In this composition, hydrogen peroxide, H ₂ O ₂ , can be seen to have been employed to convert the divalent cobalt salt to the trivalent cobalt hexaamine complex salt. The bubbling of the solution will be sufficient to convert cobalt (II) to cobalt (III) complexes, but the process will take time and it will take several days to get a complete conversion.

As noted above, a sealing step for the cobalt conversion coating is needed to produce a cobalt conversion coating with maximum internal corrosion performance (168 hours salt corrosion resistance when tested according to ASTM B117). To this end, we have found several useful sealants. These are described in U.S. Patent Application No. 07 / 621,132, filed on November 30, 1990. Then the simplification of the bath as well as the safety of the solution was further improved as follows.

[pH adjustment, temperature and immersion time]

The three parameters, pH control, temperature and immersion time, are important to the performance of the cobalt conversion coating.

Even though the coating is produced between pH 5.0 and 9.0, the preferred pH adjustment is to maintain between 6.0 and 7.0. The preferred pH range is maintained by the addition of a small amount of NH ₄ C ₂ H ₃ O ₂ periodically. At pH 5.0 or lower, the coating tends to lose its pearly hue and become almost colorless in appearance. At a pH of 6.5, the coating will have acceptable paint adhesion performance as well as good corrosion resistance.

The continuous operating temperature of 140 ± 5 ° F provides optimum results in terms of appearance and performance of the coating.

Immersion time tends to be influenced by temperature and pH control rather than by solution concentration. At 120-130 [deg.] F, an immersion time of 30 minutes or more is required for satisfactory conversion coating formation. At temperatures of 130 to 140 [deg.] F, a consistent and good functioning conversion coating is produced within 15 to 20 minutes. When the pH is increased (above 7.0), the immersion time can be reduced to 5 to 10 minutes, but a suitable coating is formed at around pH 6.5.

[Oxide coating analysis]

To illustrate the properties of the cobalt conversion coatings of the present invention, an agar oxide profile was performed using the same apparatus (in a different mode of operation) as the ESCA surface analysis using the Perkin-Elma Model 550 surface analyzer [ESCA = Spectroscopy: also known as XPS or X-ray photoelectron spectroscopy). This analysis showed that the cobalt conversion coating was composed of oxides, ie, aluminum oxide, a mixture of Al ₂ O ₃ and cobalt oxide, CoO, Co ₃ O ₄ and Co ₂ O ₃ in volume%. As used herein, the term " as volumetric by volume " means that the volume of this oxide is greater than the volume of any other oxide present. But. The expression " a large amount by volume% " does not mean that the volume of this oxide is 50% by volume or more.

In addition, this data showed that Al ₂ O ₃ was much in volume percentage in the lower part of the oxide coating (the part following the aluminum substrate). The central portion of the oxide coating was a mixture of CoO, Co ₃ O ₄ , Co ₂ O _3, and Al ₂ O ₃ . And, at the upper part of the oxide coating, it was shown that a large amount by volume% is a mixture of Co ₃ O ₄ and Co ₂ O ₃ .

Additional features of the cobalt conversion coating of the present invention can be found from the description of Figures 1 to 8 and Figures 1 to 8. Figures 1 and 2 show that the cobalt conversion coating 310 is formed by immersion in a typical cobalt conversion coating solution for 25 minutes. Figures 3 and 4 show that the cobalt conversion coating 320 is formed by immersion for 15 minutes in a typical cobalt conversion coating solution. Figures 5 through 8 show that the cobalt conversion coating 330 was formed by immersion in a typical cobalt conversion coating solution for 20 minutes. Comparing Figures 1 to 8, no significant structural differences can be found between the coating 310, the coating 320 and the coating 330. As can be seen in FIGS. 1, 2, 5 and 6, the upper surface of the cobalt conversion coating is shaped like a chow mein noodles, Thereby providing porosity for the gender. Beneath the top surface is a more dense and firm (non-porous) coating.

[Other Application]

The above composition illustrates the production of a cobalt conversion coating by immersion. This same principle applies to the production of conversion coatings by hand and spray application.

The above-mentioned patents, specifications and other public notice are incorporated herein by reference.

As will be apparent to those skilled in the art, the present invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. It is to be understood that the particular embodiments of the invention described above and the specific description of the process described above are intended to be illustrative in all aspects and not restrictive. The scope of the invention is set forth in the appended claims rather than limiting to the embodiments in the foregoing description. I believe that some and all equivalents are included in the claims.

Claims (24)

A method for forming an oxide film cobalt conversion coating that exhibits corrosion resistance and paint adhesion on a metal substrate, said method comprising the steps of: (a) providing an oxide film comprising a reaction aqueous solution comprising soluble cobalt (III) hexaamine complex salt and acetic acid (III) so that the concentration of the cobalt (III) hexaamine complex salt is from about 0.01 mole per liter of solution to the saturation concentration of the cobalt (III) hexaamine complex salt, wherein the cobalt (III) is [Co (NH _{3) 6]} in the form of X _3, wherein X is _{Cl, Br, NO 3, CN} , SCN, 1 / 3PO 4, 1 / 2SO 4, C 2 H 3 O 2 , and 1 / 2CO ₃ and the cobalt (III) hexamine complex salt is at least one selected from the group consisting of (1) a cobalt (II) salt in the presence of an oxidizing agent for oxidizing a cobalt (II) , (2) metal nitrate and (3) ammonium acetate. It has been manufactured by the response Sikkim; And (b) contacting the substrate with the solution to form the oxide film cobalt conversion coating to impart corrosion resistance and paint adhesion to the substrate. The method of claim 1, wherein the substrate is aluminum or an aluminum alloy to form an oxide film cobalt conversion coating that exhibits corrosion resistance and paint adhesion on the substrate according to claim 1, the method comprising: (a) (II) salt, a metal nitrate salt, and ammonium acetate in the presence of a cobalt (II) salt, wherein the concentration of the cobalt From about 0.01 mole to a saturating concentration of the cobalt (II) salt, the concentration of the metal nitrate is from 0.03 to 2.5 moles per liter of final solution, and the concentration of ammonium acetate is from about 0.06 to 6.0 moles per liter of final solution; And (b) contacting the substrate with the solution to form the oxide film cobalt conversion coating to impart corrosion resistance and paint adhesion to the substrate. 3. The process according to claim 1 or 2, wherein the concentration of the cobalt (III) hexaamine complex salt is from 0.04 to 0.15 liters per liter of solution. 3. The process according to claim 1 or 2, wherein the cobalt conversion solution has a pH of 5.0 to 9.0. The process according to any one of claims 1 to 5, wherein the cobalt conversion solution has a temperature of from 20 to 72 ° C (68 to 160 ° F). 3. The method of claim 1 or 2, wherein the substrate is contacted with the cobalt conversion solution for a time of from about 3 minutes to about 60 minutes. 3. The method of claim 1 or 2, wherein the concentration of the cobalt (II) salt is about 0.04 to 0.15 moles per liter of final solution, the concentration of metal nitrate is 0.03 to 0.2 moles per liter of final solution, RTI ID = 0.0 > 0.15 < / RTI > to 0.7 moles per liter of solution. 8. The process of claim 7, wherein the cobalt (II) salt is a cobalt (II) salt having a minimum solubility of 0.01 mole of cobalt (II) salt per liter of water at 68 ° F (20 ° C). The method of claim 7, wherein the cobalt (II) salt is CoX ₂ , wherein X is selected from the group consisting of Cl, Br, NO ₃ , CN, SCN, 1/3 PO ₄ , 1/2 SO ₄ , C ₂ H ₃ O _2, 2CO < _{3 &} gt ;. The method according to claim 7, wherein the metal nitrate is selected from the group consisting of Mg (NO ₃ ) ₂ .6H ₂ O, Ca (NO ₃ ) ₂ .6H ₂ O, NaNO ₃ , KNO ₃ or LiNO ₃ Lt; / RTI > 8. The method according to claim 7, wherein the cobalt conversion solution is made of a bath having the following order: (a) dissolving the cobalt (II) salt; (b) then dissolving said metal nitrate; And (c) ammonium acetate is then added. 8. The method of claim 7, wherein an oxidizing agent is added to the cobalt conversion solution to oxidize the cobalt (II) ions in the solution to cobalt (III) ions. The method of claim 12, wherein the oxidizing agent is characterized in that hydrogen, the H ₂ O ₂ peroxide. The method according to claim 1 or 2, further comprising the step of bringing the coated substrate into contact with a water-soluble sealing solution composed of nickel sulfate, NiSO ₄ .6H ₂ O, magnesium nitrate and Mg (NO ₃ ) ₂ .6H ₂ O, ≪ / RTI > The method of claim 1, wherein the metal substrate is aluminum or an aluminum alloy. An aqueous chemical bath for producing an oxide film cobalt conversion coating on a metal substrate, said chemical bath essentially comprising: (a) in the presence of an oxidizing agent for oxidizing cobalt (II) ions to cobalt (III) ions; (b) cobalt (II) salts; (c) a metal nitrate; Wherein the cobalt (II) salt is CoX ₂ , wherein X is selected from the group consisting of Cl, Br, NO ₃ , CN, SCN, _{1 / 3PO 4, 1 / 2SO} 4, is at least one selected from the group consisting of C ₂ H ₃ O _2, or 1 / 2CO _3. 17. The bass of claim 16, wherein the cobalt (II) salt is a cobalt (II) salt having a minimum solubility of 0.01 mole of cobalt (II) chloride per liter of water at 68 ° F (20 ° C). 18. The method of claim 16 or 17, wherein the metal nitrate is selected from the group consisting of Mg (NO ₃ ) ₂ .6H ₂ O, Ca (NO ₃ ) ₂ .6H ₂ O, NaNO ₃ , KNO ₃ , or LiNO ₃ ≪ / RTI > 18. A bath according to claim 16 or 17, characterized in that the cobalt conversion solution is prepared by a bath composed in the following order: (a) dissolving the cobalt (II) salt; (b) then dissolving said metal nitrate; And (c) ammonium acetate is then added. 18. A bass according to claim 16 or 17, wherein the solution has a pH of 5.0 to 9.0. 18. A bass according to claim 16 or claim 17, wherein the solution has a temperature of 20-72 [deg.] C (68-160 [deg.] F). 18. The bast of claim 16 or 17, wherein an oxidizing agent is added to the solution to oxidize the cobalt (II) ions to cobalt (III) ions. The bass of claim 22, wherein the oxidizing agent is hydrogen peroxide, H ₂ O ₂ . A method of using a chemical bath according to any one of claims 16 to 23 for producing a cobalt conversion coating on an aluminum or aluminum alloy substrate.