BRPI0519981B1 - process for coating metallic substrates, and compositions for use in a process for coating metallic substrates - Google Patents

Abstract

process for coating metallic substrates, and compositions for coating metallic substrates. The invention relates to an acidic aqueous solution for treating metallic substrates to improve the corrosion protection and adhesion bonding properties of the metal surface comprising effective amounts of water-soluble trivalent chromium compounds, fluorozirconates, effective amounts of at least one corrosion inhibitor such as benzotriazole, fluorometallic compounds, zinc compounds, thickeners, surfactants, and at least about 0.001 mol per liter of the acidic solution of a polyhydroxy and / or carboxylic compound as a stabilizing agent for the aqueous solution.

Description

4 'PROCESS FOR COATING METAL SUBSTRATES, AND, COMPOSITIONS FOR USE IN A PROCESS FOR COATING METAL SUBSTRATES ”ORIGIN OF THE INVENTION 10001] The present invention described herein was made by the United States Government employee (s) and may be manufactured is used by and for the Government for governmental purposes without paying any royalties.

REQUEST PE CONTINUED

This Order is a Continued-in-Part of Pending Order Serial No. NC-96343, filed April 21, 2005. CONTINUING GROUNDS FIELD OF THE INVENTION

The present invention relates to compositions and a process for using the compositions for preparing protective coatings on various metal substrates. The process comprises treating the metal substrates with effective amounts of an aqueous acidic solution containing at least one trivalent chromium compound, at least one fluorzirconate, at least one carboxylic compound and / or at least one polyhydroxy compound. corrosion inhibitor, and optionally effective amounts of fluorometallic compounds, such as fluortitanates, fluortan such acts, fl uorborates ,. fluorides, divalent zinc compounds, surfactants, wetting agents and / or thickening agents. More specifically, the present invention relates to stable acidic aqueous solutions and the process for treating various metal substrates including pre-coated metal substrates, such as anodized aluminum to improve metal substrate bonding and corrosion resistance properties. . The process comprises treating the metal substrates with a stable aqueous acid solution containing effective amounts of at least one water-soluble trivalent chromium salt, at least one water-soluble hexafluorzirconate, at least one water-soluble poly or mono-carboxylic compound water and / or a polyhydroxy compound, and at least one water soluble anti-wear or corrosion inhibiting agent. In addition, compounds that may be added to improve the color and stability of acidic solutions in small but effective amounts include at least one water-soluble hexa- or tetra-fluorometallic compound, divalent zinc salts, and effective amounts of water soluble thickeners and / or water soluble surfactants.

The present invention comprises a range of aqueous solutions or compositions of specific chemical compounds and processes for depositing coatings derived from these chemical compounds on a variety of metal substrates including pre-existing metal coated substrates. For example, the compositions or solutions are particularly useful for coating aluminum and aluminum alloy, i.e., conversion coatings to increase corrosion protection and paint adhesion; to seal anodic coatings to increase corrosion protection; for treatment of titanium or titanium alloys for improved paint adhesion; for treatment of magnesium alloys for improved paint adhesion and corrosion protection; to coat steel for improved paint adhesion and rust inhibition; and for post-treatment of phosphate, zinc, zinc-nickel, tin-zinc coatings and "sacrificial" cadmium coatings on iron alloys and other metal substrates, e.g., steel for improved paint adhesion and corrosion protection.

Many of today's pretreatment, aftertreatment, and sealant solutions are based on the use of hexavalent chromium chemistry. Hexavalent chromium is highly toxic and a known carcinogen. As a result, the solutions used to deposit these coatings and the coatings per se are toxic. Hexavalent chrome films or coatings, however, produce outstanding paint adhesion, good corrosion resistance, low electrical resistance and can be easily applied by dipping, spraying or scrubbing techniques. However, environmental laws, executive orders, and local occupation, safety and health (OSH) regulations are leading the military and commercial users to seek alternatives. In addition, the use of hexavalent chromium coatings is becoming more expensive as regulations become stricter and costs become prohibitive with future EEL and OSHA PEL restrictions. In addition, certain processes, such as spraying chromate solutions, are prohibited in some installations due to the risk of OSH, forcing less than optimal alternative solutions to be used. In short, hexavalent chromate coatings are technically outstanding, but from the cost, environmental and OSH perspective, alternatives are very desirable. As a result, research is to develop alternative metal finishing processes that are technically equivalent or superior to hexavalent chromate coatings without the health and environmental disadvantages.

Many of these alternatives, regardless of composition and application methods, have a tendency to precipitate solid material from solution especially after heavy use. This precipitation may, over time, weaken the effectiveness of the coating solution as the active compounds precipitate as insoluble solids. Additionally, solid precipitations have the potential to cap filters, lines and pumps for dip and spray applications. Therefore, better compositions are needed to stabilize acidic storage solutions and process applications that will not interfere with the deposition process or the subsequent performance of the deposited coating.

SUMMARY OF THE INVENTION

The present invention relates to compositions and processes for preparing corrosion resistant coatings on various metal substrates including precoated metal substrates, such as phosphate coatings or anodized coatings, comprising treating the metal substrates with a solution. acidic acid comprising chromium III equivalent compounds, fluorzirconates, corrosion or wear inhibitors, eg triazoles, and stabilizing compounds. Optionally, one or more fluorometallic compounds, surfactants, thickeners, and divalent zinc compounds may be added to the acid solutions. The present invention may be used to improve the adhesion of various other coatings, such as paints, to the metal surface and to prevent wear and corrosion of the metal surface, such as aluminum, steel surfaces. galvanized and the like. More specifically, the acidic solutions of the present invention also contain effective amounts of at least one water-soluble anti-wear or corrosion inhibiting compound together with stabilizing agents of polyhydroxy compounds and / or water-soluble carboxylic compounds containing one or more carboxylic functional groups having the general formula R-COO, wherein R is hydrogen or a lower molecular weight functional group or organic radical. Solution stabilizers, i.e., carboxylic compounds may be used in the form of acids or salts thereof. In some cases, salts of carboxylic stabilizers work better than acids of the same. For example, organic acids, such as formic, acetic, glycol, propionic, citric acid and other short or low molecular weight carboxylic acids, which naturally buffer in the slightly acidic pH range, may be used as stabilizers. of solution. The advantage of adding polyhydroxy or carboxylic stabilizers to the acidic solution is improved shelf life and shelf stability. work of solutions. The acidic solutions with the addition of the stabilizing agents had substantially no precipitation after more than twenty four months of life evaluation on. shelf and without any degradation of the performance of the coats. 10008] Figs 1-6 show the improved performance of an aluminum alloy coated with the triazole-containing solutions of the present invention compared to the same coatings without the corrosion inhibiting triazoles. Therefore, it is an object of the present invention to provide a stable acidic aqueous solution comprising trivalent chromium compounds, fluorzirconates, polyhydroxy compounds or carboxyl compounds and an effective amount of an inhibitor to coat metal substrates including pre-coated substrates for improving the adhesion and corrosion resistance properties of the metal.

It is another object of the present invention to provide a stable acidic aqueous solution having a pH ranging from about 1.0 to 5.5 comprising trivalent chromium compounds, fluorzirconates, anti-wear compounds and at least one polyhydroxy compound. and / or a carboxylic compound for treating metal substrates with or without a pre-existing metal coating.

It is another object of the present invention to provide a process for treating metal substrates to provide coatings of an identifiable color, good adhesion and improved corrosion resistance. 100012 It is another object of the present invention to provide a stable acidic aqueous solution. having a pH ranging from about 2.5 to 4.5, comprising trivalent chromium compounds, hexafluorzirconates, corrosion inhibitors and at least one carboxylic or polyhydroxy compound for treating metal substrates at ambient and higher temperatures, wherein said solutions Acidic acids do not contain substantially any hexavalent chromium.

These and another object of the present invention will become apparent by reference to the detailed description when taken in conjunction with the accompanying Figs. 1 to 6, (photos).

DESCRIPTION OF DRAWINGS

[00014] Fig. 1 (photo) shows the corrosion performance of the aluminum alloy panel (2024-T3) with a conversion coating derived from the composition of Example 1 without the triazoL inhibitor.

[00015] Fig. 2 (photo) shows the corrosion performance of the aluminum alloy panel (2024-T3) with a conversion coating derived from the composition of Example 1 with the benzotriazole inhibitor.

[00016] Fig. 3 (photo) shows the corrosion performance of aluminum alloy panel (2024-T3) with a conversion coating derived from the composition of Example 2, without the triazoL inhibitor.

Fig. 4 (photo) shows the corrosion performance of the aluminum alloy panel (2024-T3) with a conversion coating derived from the composition of Example 2 with the benzotriazole inhibitor.

[00018] Fig. 5 (photo) shows the corrosion performance of aluminum alloy panel (2024-T3) with a conversion coating derived from the composition of Example 3, with triazoL inhibitor.

Fig. 6 (photo) shows the corrosion performance of the aluminum alloy panel (2024-T3) with a conversion coating derived from the composition of Example 3 with the benzotriazole inhibitor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to stable acidic aqueous solutions and the process of using said aqueous solutions having a pH ranging from about 1.0 to 5.5, and preferably from about 2.5 to 4.5. or from 3.4 to 4.0 for the preparation of zirconium chrome coatings, eg, a conversion coating on metal substrates including, for example, pre-coated substrates such as aluminum or anodized phosphate coated substrates to enhance adhesion bonding and corrosion resistance properties. Phosphate coatings known in the art include, for example, zinc phosphate, iron phosphate, manganese phosphate coatings and mixed calcium and zinc phosphate coatings. The process comprises the use of the aqueous acid solution at temperatures ranging from about 48.9 ° C or higher, e.g. to about 93.3 ° C. The solutions comprise from about 0.01 to 100 grams and preferably from about 0.01 to 22 or from 5.0 to 7.0 grams per liter of the acidic solution of at least one water-soluble trivalent chromium compound, eg chromium sulfate, from about 0.01 to 24 grams and preferably from about 1.0 to 12 or from 1.0 to 6.0 grams per liter of the solution of at least one fluorzirconate, eg, a metal salt FbZrF6 alkaline, an effective amount sufficient to inhibit corrosion ranging, for example, from about 0.001 to 4.0 grams per liter and preferably from about 0.25 to 2.0 grams or from 0.25 to 1.0 grams. per liter of a water-soluble corrosion inhibitor and an anti-wear compound such as benzotriazole, and from about 0.001 to 2.0 grams, and preferably from 0.001 to 1.0 to 0.01 to 1, 0 moles per liter of the solution of at least one water soluble stabilizing agent or compound selected from the group consisting of carboxylic compounds, polyhydroxy compounds in mixtures of these stabilizing compounds in any relationship. If necessary, each of the compounds of the present invention may be used to its solubility limits in acidic aqueous solutions depending on the metal surface to be treated. The metal surfaces treated in accordance with the present invention may be any metal substrate which includes, for example, iron, zinc, magnesium, steel surfaces, including galvanized steel, aluminum and aluminum alloys. Any metal surface, including metal surfaces containing a protective or pre-existing metal coating, may be treated with the compositions of the present invention.

Coatings are applied after cleaning and deoxidation or pickling of the metal substrate, e.g. aluminum substrate by conventional mechanical or chemical techniques. The acidic solution of the present invention is applied at about room temperature to the metal substrate by dipping, spraying or scrubbing techniques similar to the process used for other metal treatments. The residence time in the solution ranges from about 1.0 to 60 minutes or more. With this solution, the residence time of 1.0 to 40 or 1.0 to 10 minutes produces an optimal film for color change, paint adhesion, and corrosion resistance. The residence time of 1.0 to 10 minutes produces an appreciable color change to the coating, depending mainly on the chemical composition of the aqueous solution. The remaining solution is subsequently rinsed from the metal substrate with deionized or tap water.

In some processes, depending on the physical characteristics of the metallic substrate, eg, the physical size of the steel or aluminum substrates, the addition of a thickener to the solution assists in optimum film formation during spraying and scrubbing applications by decreasing the thickness. evaporation of the solution. This mitigates the formation of dust deposits that degrade paint adhesion. The addition of thickeners also assists in film formation itself during large area applications and mitigates the diluting effect of rinse water that remains on the substrate during the processing of the previous steps. This process feature produces non-stripe films or coating and is an improvement in coloring and corrosion protection. Water soluble thickeners, such as cellulose compounds, may be present in the acidic aqueous solution in amounts ranging from about 0.0 to 20 grams per liter, and preferably from 0.5 to 10 grams, eg. from about 0.1 to 5.0 grams per liter of aqueous solution. Then, depending on the characteristics of the metal substrates, an effective but small amount of at least one water soluble surfactant or wetting agent may be added to the acid solution in amounts ranging from about 0.0 to 20 grams and preferably 0.5 to 10 grams, eg, 0.1 to 5.0 grams per liter of the acid solution. There are many water soluble surfactants known in the prior art and, therefore, for the purpose of the present invention, surfactants may be selected from the group consisting of nonionic, cationic and anionic surfactants.

Trivalent chromium is added to the solution as a water-soluble trivalent chromium compound, as a liquid or solid and preferably as a trivalent chromium salt. Specifically, in the formulation of the aqueous acidic solutions of the present invention, the chromium salt may conveniently be added to the solution in its water-soluble form, wherein the valence of chromium is +3. For example, some of the preferred chromium compounds are incorporated into the solution as Cr 2 (SO 4) 3, (NH 4) Cr (SO 4) 2, Cr (NO) 3-9H 2 O or KCr (SC> 4) 2, and any mixtures thereof. of these compounds. A preferred trivalent chromium salt concentration is within the range of about 5.0 to 7.0 grams per liter of aqueous solution. Particularly good results have been found to be obtained from these processes when the trivalent chromium compound is present in the solution in the preferred ranges.

Acid solutions may contain at least one divalent zinc compound to provide color and also improve corrosion protection of the metal as compared to other non-zinc treatment or compositions. The amount of zinc compounds may be varied to the extent of solubility to adjust the color of the coating, ranging from 0.0 to 100 grams to as little as about 0.001 gram per liter to 10 grams per liter, eg, from 0 to 100 grams. 0.5 to 2.0 grams of 2+ zinc cation. Divalent zinc may be provided by any chemical compound, e.g., salt that dissolves in water at the required concentration and is compatible with the other components in the acid solution. Divalent zinc compounds which are water soluble at the required concentrations preferably include, for example, zinc acetate, zinc telluride, zinc tetrafluorborate, zinc molybdate, zinc hexafluorsilicate, zinc sulfate, and the like, or any combination thereof. in any relationship. Treatment or coating of metal substrates may be performed at various temperatures including solution temperatures ranging from ambient to ambient, eg from about room temperature to about 48.9 ° C or higher to about 93.3 ° C. . Ambient temperature is preferred, however, as it eliminates the need for heating equipment. The coating may be air dried by any of the methods known in the art, including, for example, oven drying, forced air drying, exposure to infrared lamps, and the like.

The following Examples illustrate the stable acidic solutions of the present invention, and the method of use of the solutions in providing color recognition, enhanced adhesion bonding and corrosion resistant coatings for metal substrates including metal substrates having a pre-coated metal coating. existing. EXAMPLE 1 To one liter of deionized water, add 4.0 grams of potassium hexafluorzirconate, 3.0 grams of basic chromium III sulfate, 0.12 grams of potassium tetrafluorborate, and 0.25 grams of benzotriazole.

Stir the solution until all compounds are dissolved. Let stand at ambient conditions (21.1 - 26.7 ° C) until the pH reaches 3.70. EXAMPLE 2 To one liter of deionized water, add 4.0 grams of potassium hexafluorzirconate, 3.0 grams of basic chromium III sulfate, 2.3 grams of glycerol (0.025 moles), and 0.25 grams of benzotriazole. Stir the solution until all compounds are dissolved. Let stand at ambient conditions (21.1 - 26.7 ° C) until pH reaches 3.55. EXAMPLE 3 To one liter of deionized water, add 4.0 grams of potassium hexafluorzirconate and 3.0 grams of basic chromium III sulfate. Stir the solution until all compounds are dissolved. Maintain the pH between 3.25 and 3.50 for 14 days with dilute sulfuric acid and dilute potassium hydroxide and then adjust to a final pH of 3.90. Add 0.25 grams of benzotriazole. EXAMPLE 4 Prepare the solution as in Example 2, with the exception of replacing benzotriazole with 0.50 grams of 2-mercaptobenzimidazole. EXAMPLE 5 Prepare the solution as in Example 3, except that 0.25 grams of 2-mercaptobenzimidazole is added to benzotriazole. EXAMPLE 6 Prepare the solution as in Example 1, except that 0.25 grams of 2-mercaptobenzimidazole and 0.25 grams of 2-mercaptobenzazole are added to benzotriazole. EXAMPLE 7 The compositions of Examples 1, 2 and 3 were used to coat the aluminum alloy panels (2024-T3) as follows: The process comprises cleaning the 7.6 cm by 12 cm panels. 1.7 cm by 0.07 cm (2024-T3) in Turk 425 at 60 ° C for 15 minutes. Rinse in hot tap water using cascade double backflow. Immediately immerse the coupons in Turkish Smut Go for 5 minutes. Rinse with tap water at room temperature using cascade double backflow. Immediately immerse the panels in the compositions of Examples 1, 2 and 3 for 5 minutes at 21.1 - 26.7 ° C. Rinse in tap water at room temperature using double cascade backflow. Finally rinse with deionized water. Allow the panels to air dry and rest overnight. The coatings are ready for testing or subsequent coating with an organic finish coating e.g. epoxy base layer (MIL-PRF-23377). EXAMPLE 8 The test panels were cleaned and coated by the process shown in Example 7, then placed in a neutral salt mist (ASTM BI 17) at a 6 degree inclination from the vertical. After 3 weeks (21 days) in the salt mist, the coating performance is shown in Figure 1-6. Control coatings were made from the compositions of Examples 1, 2 and 3 without the addition of triazole wear inhibitors. It is evident from the comparison of Figures 1-6 (photos) that the addition of wear inhibitors resulted in a positive effect on the corrosion resistance of coatings made of the different compositions.

Corrosion inhibitors or anti-wear agents are water soluble compounds selected from the group consisting of triazoles, benzimidazoles, benzazoles, benzoxazoles and mixtures of these inhibitors in any relationship. Preferred corrosion inhibitors or anti-wear compounds include triazoles containing up to 12 carbon atoms, such as alkyls and preferably aryl triazoles. Aryl triazoles contain from 6 to 10 carbon atoms, including compounds such as benzotriazole and tolyltriazole, and alkyl triazoles containing up to six carbon atoms, such as methyl or ethyl triazole. Triazols, such as benzotriazole, are commercially available under the tradename COBRATEC. Anti-wear inhibitors are dissolved in the solutions in an effective amount sufficient to inhibit corrosion and preferably in amounts ranging from about 0.001 to 4.0 grams per liter, and more preferably in amounts of 0.25 to 2.0 grams. or about 0.25 to 1.0 gram per liter. Other useful triazoles include water soluble hydroxybenzotriazole, such as hydroxy-4-alkylbenzotriazoles, hydroxy-6-benzotriazole, hydroxy-5-chlorobenzotriazole, hydroxy-6-carboxybenzotriazole, hydroxy-5-alkylbenzotriazoles and the like.

Stabilizing carboxylic compounds added to aqueous acidic solutions include water-soluble acids and / or carboxylic acid salts, including water-soluble carboxylic acids and salts such as adipic, citric, acetic, citraconic, fumaric, glutaric, tartaric acids or the tetraacetic ethylenediamine acid provided in the hydrocarbon chain in the carboxylic group does not contain a significant number of carbon atoms which diminish the degree of solubility of the compounds. Combinations of two or more salts and / or acids may be used to obtain a specific pH. For example, lower molecular weight acids and / or salts, such as formate or potassium citrate, may be used at concentrations of at least 0.001 to 2.0 moles or from 0.001 to 1.0 mol per liter. These compounds are good stabilizers. Good results were obtained from acidic solutions prepared by the addition of about 0.01 mol per liter of potassium formate after 4 days of preparation of the initial solution. Good results are obtained if the stabilizing agents are hydroxy-containing carboxylic compounds and carboxylic groups including, for example, compounds such as citric acid, glycolic acid, lactic acid, gluconic acids, glutaric acid and salts thereof.

In addition to the carboxylic compounds as stabilizing agents for the solutions, a small but effective amount of polyhydroxy compounds may also be used as stabilizers in amounts ranging from about 0.001 to 2.0 and preferably from 0 ° C. .01 to 2.0 moles or 0.01 to 1.0 moles per liter. The compounds include trihydric compounds, e.g., glycerol and dihydric ether alcohols, e.g., glycol ethers including alkylene glycol ethers, such as triethylene glycol ether, propylene glycol ether, tripropylene glycol ether, or diethylene glycol ether. Other glycols include some of the lower molecular weight compounds such as ethylene glycol, propylene glycol, butylene glycol, cyclohexanol, and water soluble poly (oxyalkylene glycols), eg poly (oxyethylene) or poly (oxypropylene glycols) having Lower molecular weights ranging up to about 1000 may be employed to promote stability and dispersibility of solids in the coating bath or acid solutions. Other di- and trihydric aliphatic alcohols include water-soluble lower alkanols, such as di- or trihydric alkanols containing up to twelve carbon atoms. This class of di and trihydric lower alkanols may include glycols containing up to ten carbon atoms in the alkylene group, eg trimethylene glycol and polyglycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, dibutylene glycol, tributylene glycol, and other polyalkylene glycols, wherein the alkylene radical contains up to eight carbon atoms and preferably two to four carbon atoms. Combinations or mixtures of the carboxylic or polyhydroxy stabilizing compounds may be used in the acid solution in any relationship. In addition to the carboxylic or polyhydroxy stabilizing compounds, the aqueous acid solutions may contain small but effective amounts of 0.0 to 24 grams, eg 0.01 to 12 grams per liter of solution of at least one fluorometallic compound preferably. including stabilizing compounds such as hexafluortitanate, heptafluortantalate, tetrafluorborate and hexafluorsilicate.

In preparing the acidic solutions of the present invention, known water-soluble surfactants may be added to the trivalent chromium solutions in amounts ranging from about 0 to 20 grams per liter and preferably from about 5.0 to 10 grams. or from 1.0 to 5.0 grams per liter. Surfactants are added to the aqueous solution to provide better wetting properties by decreasing surface tension, thereby ensuring complete coverage and a more uniform film on metal substrates. Surfactants include at least one water soluble compound selected from the group consisting of nonionic, anionic and cationic surfactants. Some of the best known water-soluble surfactants include monocarboxyl imidoazoline, sodium alkyl sulfate salts (DUPONOL®), ethoxylated or propoxylated alkylphenol (IGEPAL®), alkylsulfonamides, alkaryl sulfonates, palmitic alkanol amides (CENTROL®), octylphenyl polyethoxy ethanol (TR ®), sorbitan monopalmitate (SPAN®), dodecylphenyl polyethylene glycol ether (TERGITROL®), alkyl pyrrolidones, polyalkoxylated fatty acid esters, alkylbenzene sulfonates and mixtures thereof. Other known water-soluble surfactants include, for example, nonylphenol ethoxylates, and fatty amine ethylene oxide adducts; see publication: "Surfactants and Detersive Systems" by John Wiley et al. in Kirk-Othmer's Encyclopedia of Chemical Technology, 3a. edition.

When large surfaces do not allow immersion or where vertical surfaces have to be sprayed, thickening agents may be added to retain the aqueous solution on the surface for sufficient contact time. The thickeners employed are known inorganic thickeners and preferably the organic water soluble thickeners added to the trivalent chromium solutions in effective amounts, eg, sufficient concentrations ranging from about 0 to 20 grams per liter and preferably from 0.5 to 10 grams or 1.0 to 5.0 grams per liter of acidic solution. Specific examples of some preferred thickeners include cellulose compounds, e.g., hydroxypropyl cellulose (Klucel), ethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, methyl cellulose and mixtures thereof. Other water soluble inorganic thickeners include colloidal silica, clays such as bentonite, starches, gum arabic, tragacanth, agar and various combinations.

After surface preparation of the metal substrate to be coated by conventional techniques, the solution may be applied by dipping, spraying or scrubbing techniques. The TCP solutions of the present invention may be used at elevated temperatures ranging up to 48.9 ° C or higher, e.g. up to 93.3 ° C and optionally applied by dipping to improve corrosion resistance of coatings. The residence time of the solution ranges from about 1 to 60 minutes, and preferably from 1.0 to 40 or from 1.0 to 10 minutes at about 23.9 ° C or more. After residence, the remaining solution is then completely rinsed off the substrate with tap water or deionized water. No further chemical manipulation of deposited films is required for excellent performance. Aqueous solutions may be sprayed from a spray tank apparatus designed to replace dip tanks.

Although the present invention has been described by a number of specific examples, it is obvious that there are other variations and modifications that may be made without departing from the spirit and scope of the present invention, as particularly shown in the appended claims.

Claims (29)

A process for coating metal substrates to improve the corrosion protection and adhesion bonding properties of metal comprising treating the metal substrates with an acidic aqueous solution having a pH ranging from 1.0 to 5.5. ; said aqueous acid solution comprising, per liter of solution, from 0.01 to 100 grams of soluble trivalent chromium compound (s), from 0.01 to 24 grams of fluorzirconate (s) of 0, 0 to 100 grams of divalent zinc compounds, from 0.0 to 20 grams of surfactants, from 0.0 to 20 grams of thickeners, characterized in that said acidic aqueous solution additionally comprises from 0.001 to 4 grams per liter of water soluble corrosion inhibitor (s) selected from the group consisting of triazoles, benzimidazoles, benzazoles and benzoxazoles, and 0.001 to 2 grams per liter of a stabilizing compound selected from the group consisting of polyhydroxy compounds, carboxylic compounds and mixtures of polyhydroxy and carboxylic compounds. Process according to Claim 1, characterized in that the metal substrates have a pre-existing metal coating thereon. Process according to Claim 2, characterized in that the pre-existing metal coated substrate is selected from an anodized aluminum and a phosphate coating. Process according to Claim 1, characterized in that the metal substrate is selected from an aluminum alloy and an iron alloy. Process according to Claim 1, characterized in that the stabilizing compound is selected from a hydroxy carboxylic compound, a formic acid, a propionic acid and water-soluble salts thereof. Process according to Claim 1, characterized in that the water-soluble corrosion inhibitor is benzotriazole. Process according to Claim 5, characterized in that the hydroxy carboxylic compound is selected from citric acid, glycolic acid and gluconic acid, glutaric acid and water-soluble salts thereof. Process according to Claim 1, characterized in that the aqueous acidic solution contains from 0.001 to 1.0 moles per liter of the carboxylic compound and the inhibitor is a triazole. Process according to Claim 1, characterized in that the aqueous acidic solution contains from 0.001 to 2.0 moles per liter of stabilizing compound and from 0.025 to 4.0 grams per liter of triazole. Process according to Claim 1, characterized in that the stabilizing compound is glycerol and the water-soluble corrosion inhibitor is a mixture of benzotriazole and tolyltriazole. Process according to Claim 1, characterized in that the stabilizing compound is a carboxylic compound having more than one functional carboxylic group per molecule. Compositions for use in a process for coating metal substrates to improve the corrosion protection and adhesion bonding properties of the metal as defined in claim 1 which comprise an aqueous acidic solution having a pH ranging from 1, 0 to 5.5 and, per liter of said solution, from 0.01 to 100 grams of trivalent chromium compound (s), from 0.01 to 24 grams of fluorzirconate (s), from 0.0 to 20 grams of Divalent zinc compounds, from 0.0 to 20 grams of surfactants, from 0.0 to 20 grams of thickeners, characterized in that said aqueous acid solution additionally comprises from 0.001 to 4 grams per liter of inhibitor (s). water soluble corrosion (s) selected from the group consisting of triazoles, benzimidazoles, benzazoles and benzoxazoles, and 0.001 to 2 grams per liter of a stabilizing compound selected from the group consisting of polyhydroxy compounds, carboxylic compounds and mixtures of compound are polyhydroxy and carboxylic. Compositions according to claim 12, characterized in that the stabilizing compound is a carboxylic compound having more than one functional carboxylic group per molecule. Compositions according to claim 13, characterized in that the carboxylic compound is a hydroxy carboxylic acid and the water-soluble salts thereof. Compositions according to claim 14, characterized in that the hydroxy carboxylic compound is selected from citric acid, glycolic acid, lactic acid, and water-soluble salts and combinations thereof. Compositions according to claim 12, characterized in that the carboxylic compound is at least one of formic acid, propionic acid and water-soluble salts thereof. Compositions according to claim 12, characterized in that the polyhydroxy compound is glycerol, the carboxylic compound is a lower molecular weight carboxylic acid or a water-soluble salt thereof and the water-soluble corrosion inhibitor is a triazole. Compositions according to claim 12, characterized in that the stabilizing compound is a mixture of a lower molecular weight carboxylic acid and a polyhydroxy compound. Compositions according to claim 17, characterized in that the stabilizing compound is a low molecular weight polyhydroxy compound, and the water-soluble corrosion inhibitor is mercaptobenzimidazole. Compositions according to claim 12, characterized in that the polyhydroxy compound is glycerol and the water-soluble corrosion inhibitor is at least one of benzotriazole and a mixture of triazoles. Compositions according to Claim 12, characterized in that the divalent zinc compound is a water-soluble zinc salt in the acidic aqueous solution in an amount ranging from 0.5 to 2.0 grams and the corrosion inhibitor. Water soluble is at least one of benzotriazole and mercaptobenzazole. Compositions according to claim 12, characterized in that the polyhydroxy compound is a polyalkylene glycol and the water-soluble corrosion inhibitor is benzimidazole. Compositions according to claim 12, characterized in that the pH ranges from 2.5 to 4.5, the trivalent chromium compound ranges from 0.01 to 22 grams, fluorzirconate is hexafluorzirconate ranging from 1.0 at 12 grams, the stabilizing compounds range from about 0.001 to 1.0 mol per liter, and the inhibitor is a triazole ranging from 0.001 to 4.0 grams per liter of solution. Compositions according to claim 23, characterized in that the stabilizing compound is a lower molecular weight carboxylic acid or a water-soluble salt thereof, and triazole is tolyltriazole. Compositions according to claim 12, characterized in that the stabilizing compound is a polyhydroxy compound and the water-soluble corrosion inhibitor is mercaptobenzazole. Compositions according to claim 12, characterized in that the divalent zinc compound ranges from 0.001 to 10 grams, and the water-soluble corrosion inhibitor is a benzazole. Compositions according to claim 12, characterized in that the thickeners and / or surfactants range from 1.0 to 5.0 grams, and the water-soluble corrosion inhibitor is mercaptobenzoxazole. Compositions according to Claim 12, characterized in that the aqueous acidic solution contains from 0.01 to 12 grams per liter of fluorometallic compound (s) selected from the group consisting of fluortitanates, fluorortantalates. , fluorborates, fluororsilicates and mixtures thereof, and the water soluble corrosion inhibitor is a mixture of said inhibitors. Compositions according to Claim 28, characterized in that the fluorometallic compound is selected from hexafluorsilicate and tetrafluorborate, the fluorzirconate is hexafluorzirconate, and the water-soluble corrosion inhibitor is selected from tolyltriazole and benzotriazole.