Conversion coating solutions and methods of use therefor

Abstract

A zirconium conversion coating solution may comprise an aqueous solution; non-fluoride containing zirconium compound; sulfuric acid; and an organic acid. A method of coating a substrate may comprise exposing the substrate to the zirconium conversion coating solution to form a coated substrate.

Description

CONVERSION COATING SOLUTIONS AND METHODS OF USE THEREFORCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application No. 63,672,842 (DBC 0257 MA / 69607.727) filed on July 18, 2024, which is hereby incorporated herein in its entirety.FIELD

[0002] Embodiments of the present disclosure generally relate to conversion coating solutions and methods of use therefor, and particularly to conversion coating solutions that do not include fluoride.BACKGROUND

[0003] In the art of treating metal surfaces, it is common practice to improve the corrosion resistance characteristics and adhesion / bonding qualities of a metal surface to subsequent materials by depositing a conversion coating or the like thereon. In conversion coating, the substrate is typically submerged in or otherwise exposed to a chemical solution (most commonly containing zirconium and / or phosphate) that reacts with the material of the substrate, thereby forming a coating layer on the surface of the substrate.SUMMARY

[0004] However, typical chemical solutions used for imparting zirconium conversion coatings often utilize fluoride and / or fluoridized zirconium compounds in the process. Particularly, fluoride-containing acids have traditionally be used to great effect in carrying the substance ultimately deposited on the substrate. However, fluoride-containing compounds are subject to increasingly stringent environmental restrictions in wastewater streams due to their negative toxicological and environmental effects. Accordingly, it may be desired to transition from fluoride-containing conversion coating solutions to non-fluoride-containing conversion coating solutions. Further, it would be advantageous if these non-fluoride solutions perform comparable to fluoride-containing solutions, such that motivation for use is not entirely regulation based.

[0005] Accordingly, provided herein are conversion coating solutions that do not incorporate fluoride, such that the environmental and toxicological concerns are mitigated. The coatings also exhibit high levels of reactivity with a metal substrate to form a conversion coating, corrosion resistance, and surface adhesion benefits comparable to fluoride-containing solutions.

[0006] In at least one embodiment, a zirconium conversion coating solution may comprise an aqueous solution; a non-fluoride containing zirconium compound; sulfuric acid; and an organic acid.

[0007] In another embodiment, a method of coating a substrate may comprise exposing the substrate to the zirconium conversion coating solution to form a coated substrate, wherein the zirconium conversion coating solution comprises an aqueous solution; a non-fluoride containing zirconium compound; sulfuric acid; and an organic acid.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0009] FIG. 1A illustrates a substrate exposed to a zirconium conversion coating solution having a pH of approximately 4.5 and including sulfuric acid, according to embodiments herein, the substrate showing signs of conversion coating deposition;

[0010] FIG. IB illustrates a substrate exposed to a zirconium conversion coating solution having a pH of approximately 4.5 and including methane sulfonic acid instead of sulfuric acid, according to embodiments herein, the substrate not showing signs of conversion coating deposition;

[0011] FIG. 1C illustrates a substrate exposed to a zirconium conversion coating solution having a pH of approximately 4.5 and including nitric acid instead of sulfuric acid, according to embodiments herein, the substrate not showing signs of conversion coating deposition;

[0012] FIG. 2 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to DI as shown in the depletion table test, according to embodiments herein;

[0013] FIG. 3 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to D2 as shown in the depletion table test, according to embodiments herein;

[0014] FIG. 4 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to D3 as shown in the depletion table test, according to embodiments herein;

[0015] FIG. 5 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to D4 as shown in the depletion table test, according to embodiments herein;

[0016] FIG. 6 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to D5 as shown in the depletion table test, according to embodiments herein;

[0017] FIG. 7 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to D6 as shown in the depletion table test, according to embodiments herein;

[0018] FIG. 8 illustrates four painted substrates subjected to a salt spray test under ASTM DI 654, the substrates pre-treated with a zirconium conversion coating solution corresponding to D7 as shown in the depletion table test, according to embodiments herein

[0019] FIG. 9A illustrates a painted substrate subjected to a salt spray test under ASTM DI 654, the substrate pre-treated with a fluoride-free zirconium conversion coating solution according to embodiments herein;

[0020] FIG. 9B illustrates a painted substrate subjected to a salt spray test under ASTM DI 654, the substrate pre-treated with a second fluoride-free zirconium conversion coating solution according to embodiments herein with a higher zirconium concentration than the pre-treatment solution used for the panels in FIG. 9A;

[0021] FIG. 9C illustrates a painted substrate subjected to a salt spray test under ASTM DI 654, the substrate pre-treated with a commercially available fluoride-containing zirconium conversion coating solution; and

[0022] FIG. 9D illustrates a painted substrate subjected to a salt spray test under ASTM DI 654, the substrate pre-treated with a commercially available phosphate-based conversion coating used for testing paint durability.DETAILED DESCRIPTION

[0023] As previously stated, embodiments herein are generally relate to conversion coating solutions and methods of use therefor, and particularly to zirconium conversion coating solutions that do not include fluoride and / or phosphate. Accordingly, at least some of the embodiments of the conversion coating solution herein may not comprise fluoride or phosphate.

[0024] In embodiments, the conversion coating solution may comprise an aqueous solution; a zirconium compound, sulfuric acid, and an organic acid. Accordingly, the conversion coating solution described herein may be regarded as a zirconium conversion coating solution. As described in detail herein, the zirconium conversion coating solution may also comprise an accelerator, a nonionic surfactant, or both.

[0025] Accordingly, as described herein, a method of coating a substrate may comprise exposing the substrate to the zirconium conversion coating solution, such as any zirconium conversion coating solution described herein, thereby forming a coated substrate. The method may further comprise exposing the coated substrate to one or more coatings of paint, thereby forming a painted substrate. The one or more coatings of paint may be multiple coatings of the same paint, coatings of a unique first paint followed by coatings of a unique second paint (such as colored paint followed by clear coat), or combinations thereof. As used herein, the substrate may comprise a metallic or non-metallic medium, such as, but not limited to steel, galvanized steel, aluminum, magnesium, or combinations thereof.

[0026] As previously stated, the zirconium conversion coating solution may comprise an aqueous solution. The aqueous solution may comprise fresh water, such as, but not limited to, potable water, mineral water, deionized water, tap water, distilled water, or combinations thereof. In one embodiment, the aqueous solution may be deionized water. The zirconium conversion coating solution may comprise a balance aqueous solution, in other words, the remaining weight percent (wt.%) of the zirconium conversion coating solution after including the zirconium compound, the sulfuric acid, the organic acid, the accelerator, the nonionic surfactant, any other component, or combinations thereof may be aqueous solution.

[0027] As previously stated, the zirconium conversion coating solution may also comprise a zirconium compound, as previously stated. The zirconium compound may not comprise fluoride, such that the zirconium compound may be regarded as a non-fluoride containing zirconium compound. The zirconium compound may comprise zirconium acetate. The zirconium compound may additionally or alternatively comprise ammonium zirconium (IV) carbonate, zirconium (IV) carbonate, zirconium (IV) dinitrate, zirconium (IV) nitrate, zirconium (IV) sulfate, zirconium carbonate, zirconium dinitrate, zirconium n-propoxide, zirconium oxide, or combinations thereof.

[0028] Additionally or alternatively, the zirconium compound may comprise a zirconium carboxylate, such as but not limited to zirconium acetate, zirconium formate, zirconium oxylate, zirconium methanetetracarboxlate, or any other zirconium carboxylate salt. In at least one embodiment, the zirconium compound may be zirconium acetate.

[0029] The zirconium conversion coating solution may comprise from 0.5 wt.% to 8 wt.% zirconium acetate, such as from 0.5 wt.% to 1 wt.%, from 1 wt.% to 2 wt.%, from 2 wt.% to 4 wt.%, from 4 wt.% to 6 wt.%, from 6 wt.% to 8 wt.%, or any combinations of the previous ranges or smaller range therein, such as from 2 wt.% to 6 wt.%. However, without being limited by theory, the zirconium conversion coating solution may also be diluted depending on customer / user preference.

[0030] Accordingly, the weight percent zirconium acetate in the zirconium conversion coating solution (as well as any other component of the zirconium conversion coating solution) may be diluted by a factor of 10, 100, 1,000, etc., such that the ranges above also contemplate, for example, 0.0005 wt.% to 0.0008 wt.%, from 0.005 wt.% to 0.008 wt.%, from 0.05 wt.% to 0.08 wt.%, from 0.0005 wt.% to 8 wt.%, and so on. As previously stated, this dilution factor, and the modified ranges therefrom, may apply to all of the components of the zirconium conversion coating solution, with the remaining balance being the aqueous solution.

[0031] As previously stated, the zirconium conversion coating solution may also comprise sulfuric acid. Without being limited by theory, sulfuric acid may be preferred over other acid species, such as but not limited to nitric acid, alkylsulfonic acid, hydrochloric acid or similar, due to sulfuric acid having a greater ratio of free acid to total acid than the other species. As described in further detail herein, when acid species without sufficiently great ratios of free acid to total acid are used, lower pHs (less than 4) of the zirconium conversion coating solution are required to begin depositing the conversion coating on the substrate. However, this lower pH increases the risk of the substrate flash rusting when exposed to the zirconium conversion coating solution. This rust may then reduce the adhesion corrosion resistance of the subsequently applied paint layer, thereby reducing the effectiveness of the conversion coating as a whole when non-sulfuric acids are utilized.

[0032] The zirconium conversion coating solution may comprise from 0.5 wt.% to 10 wt.% sulfuric acid, such as from 0.5 wt.% to 1 wt.%, from 1 wt.% to 2 wt.%, from 2 wt.% to 4 wt.%, from 4 wt.% to 6 wt.%, from 6 wt.% to 8 wt.%, from 8 wt.% to 10 wt.%, or any combinations of the previous ranges or smaller range therein, such as from 2 wt.% to 6 wt.%, as well as any dilution factors of the previous ranges, such as 10, 100, 1,000, etc.

[0033] As previously stated, the zirconium conversion coating solution may also comprise an organic acid, such as but not limited to a carboxylic acid, a hydrocarboxylic acid, or both. For example, and in embodiments, the hydrocarboxylic acid may comprise an alpha, beta, or omega hydroxylic acid, such as, but not limited to, acetic acid and / or lactic acid. The zirconiumconversion coating solution may comprise from 0.5 wt.% to 8 wt.% organic acid, such as from 0.5 wt.% to 1 wt.%, from 1 wt.% to 2 wt.%, from 2 wt.% to 4 wt.%, from 4 wt.% to 6 wt.%, from 6 wt.% to 8 wt.%, or any combinations of the previous ranges or smaller range therein, such as from 2 wt.% to 6 wt.%, as well as any dilution factors of the previous ranges, such as 10, 100, 1,000, etc.

[0034] Without being limited by theory, the organic acid may act as a stabilizing agent for the zirconium conversion coating solution, such that the zirconium may remain solubilized in the solution during adjustment to an end-use concentration and pH, i.e., prior to deposition onto the substrate. It is contemplated that the organic acid may allow the zirconium conversion coating solution to remain stable and useable over many iterations of coating a substrate.

[0035] As previously stated, the zirconium conversion coating solution may also comprise an accelerator, such as but not limited to a nitroaromatic sulfonate salt (such as sodium nitrobenzene sulfonate), hydroxylammonium sulfate, ammonium dimolybdate, hydroxylamine hydrochloride, or combinations thereof. In at least one embodiment, the accelerator may be sodium nitrobenzene sulfonate. The zirconium conversion coating solution may comprise from 0.5 wt.% to 5 wt.% accelerator, such as from 0.5 wt.% to 1 wt.%, from 1 wt.% to 2 wt.%, from 2 wt.% to 3 wt.%, from 3 wt.% to 4 wt.%, from 4 wt.% to 5 wt.%, or any combinations of the previous ranges or smaller range therein, such as from 3 wt.% to 4 wt.%, as well as any dilution factors of the previous ranges, such as 10, 100, 1,000, etc. Without being limited by theory, the accelerator may act to increase the rate of oxidation and / or reduction occurring on the substrate during the coating process.

[0036] As previously stated, the zirconium conversion coating solution may also comprise a nonionic surfactant, such as an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, an alcoxylated alchohol, an ethoxylated alcohol, or combinations thereof. For example, and in embodiments, the nonionic surfactant may include, but may not be limited to, alkyl phenyls, fatty amines, fatty alcohols, fatty acids, vegetable oils, block / random copolymers, or combinations thereof.

[0037] In at least one embodiment, the nonionic surfactant may be (INCI name) Meroxapol 174, CAS 9003-11-6. The zirconium conversion coating solution may comprise from 0.1 wt.% to 5 wt.% nonionic surfactant, such as from 0.1 wt.% to 1 wt.%, from 1 wt.% to 2 wt.%, from 2 wt.% to 3 wt.%, from 3 wt.% to 4 wt.%, from 4 wt.% to 5 wt.%, or any combinations of the previous ranges or smaller range therein, such as from 3 wt.% to 4 wt.%, as well as any dilution factors of the previous ranges, such as 10, 100, 1,000, etc. Without being limited by theory, the nonionicsurfactant may operate to decrease the surface tension of the substrate and / or zirconium conversion coating solution, thereby increasing a rate of transfer of the zirconium conversion coating solution onto the substrate. Further, the nonionic surfactant may also provide a dispersive effect, increasing stability of the concentrate by minimizing the precipitation of the accelerator ingredients from the solution.EXAMPLES

[0038] As previously stated, sulfuric acid may be preferred over other acid species due to the relatively greater ratio of free acid to total acid, which may increase the operable pEI of the conversion coating solution, reduce the risk of flash rusting, and thereby increase the adhesion of the subsequent paint layer as well as the effectiveness of the conversion coating solution as a whole. This may be shown with respect to Tables 1-2 below, as well as with reference to FIGS. 1A-1C.

[0039] Particularly, Table 1 shows the composition of various fluoride-free zirconium conversion coating solutions, wherein Samples A, B, C, and D include sulfuric acid, hydrochloric acid, methane sulfonic acid, and nitric acid respectively as the acid included.

[0040] Table 1 : Conversion Coating Compositions for Acid Testing

[0041] Table 2 shows the procedure for exposure of the conversion coating solution to the steel substrate.

[0042] Table 2: Procedure for Conversion Coating for Acid Testing

[0043] Table 3 shows the subsequent observed deposition, or lack thereof, of the conversion coating solution on a substrate for various pHs of the conversion coating solution. FIGS. 1A-1C show the visual results for 4.5 pH conversion coating solution for samples A, C, and D. As shown, samples C and D included no deposition, whereas sample A did show deposition.

[0044] Table 3: Conversion Coating Deposition Results for Acid Testing

[0045] As shown in Table 3, deposition occurred only for a pH of 3 for the conversion coatings not including sulfuric acid, whereas deposition occurred for all pHs for the sulfuric acid conversion coating, according to embodiments herein.

[0046] The zirconium conversion coating solutions described herein were also tested to determine their performance in at least four aspects, stability over time, ability to continually supplement with additional solution, paint adhesion, and corrosion resistance.

[0047] Initially, the zirconium conversion coating solutions were subjected to a depletion test where a bath of the zirconium conversion coating solution was alternatively exposed to steel substrates and supplemented with additional zirconium conversion coating solution. The substrates were first cleaned then rinsed before exposure to the bath, followed by another rinsing, ambient drying, then oven drying at 48.9 °C (120 °F). The aqueous solution used for the depletion test was tap water. The results for the depletion testing are shown below in Table 4, and indicate that the zirconium conversion coating solution can be supplemented as necessary to allow continued treatment of substrates.

[0048] Table 4: Depletion Test of Zirconium Conversion Coating Solution

[0049] To test the corrosion resistance of the zirconium conversion coating, select substrates from D1-D7 (Systems 1-7 corresponding to D1-D7) were painted and subjected to a salt spray under ASTM Bl 17-16, as well as a subsequent scribe measurement under ASTM DI 654, the results of which are shown below in Table 5.

[0050] Table 5: Salt Spray Corrosion Testing of Subsequently Painted Substrates

[0051] To test the adhesion properties of the zirconium conversion coating, select substrates from D1-D7 were again chosen and painted before being subjected to a paint adhesion tape test under ASTM D3359-17, the results of which are shown below in Table 6 and FIGS. 2-8. Again, systems 1-7 and FIGS. 2-8 correspond to D1-D7, respectively.

[0052] Table 6: Paint Adhesion Tape Test of Subsequently Painted Substrates

[0053] As shown in the above examples, the zirconium conversion coating solution exhibited significant stability, ability to supplement, adhesion benefits, and corrosion resistance. Further, as shown in Tables 5 and 6, the substrates exhibited adhesion benefits and corrosion resistance across the supplementation of the bath.

[0054] Finally, the fluoride-free zirconium conversion coating solution (A, B) was tested as compared to a commercially available fluid containing a zirconium conversion coating solution (C) and a commercially available iron phosphate coating solution (D) as shown below in Table 7. As shown in Table 7, the fluoride-free zirconium conversion coating solutions performed similar or better than those containing fluoride. This can also be shown with respect to FIGS. 9A-9D, illustrating Systems A, B, C, and D, respectively.

[0055] Table 7: Fluoride-free Zr Conversion Coating vs. Fluoride Containing Zr Alternatives

[0056] The present disclosure may include one or more aspects. A first aspect may comprise a zirconium conversion coating solution. The zirconium conversion coating solution may comprise an aqueous solution; a non-fluoride containing zirconium compound; sulfuric acid; and an organic acid.

[0057] A second aspect may include the first aspect, wherein the non-fluoride containing zirconium compound comprises a zirconium carboxylate.

[0058] A third aspect may include any previous aspect, wherein the non-fluoride containing zirconium compound comprises zirconium acetate.

[0059] A fourth aspect may include any previous aspect, wherein the organic acid comprises a carboxylic acid, a hydroxycarboxylic acid, or both.

[0060] A fifth aspect may include any previous aspect, and may further comprise an accelerator comprising a nitroaromatic sulfonate salt, hydroxylammonium sulfate, ammonium dimolybdate, hydroxylamine hydrochloride, or combinations thereof.

[0061] A sixth aspect may include any previous aspect, and may further comprise a nonionic surfactant.

[0062] A seventh aspect may include any previous aspect, wherein the nonionic surfactant comprises an ethoxylated surfactant, a propoxylated surfactant, or both.

[0063] An eighth aspect may include any previous aspect, and may further comprise an accelerator comprising sodium nitrobenzene sulfonate; a nonionic surfactant comprising an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, an alcoxylated alchohol, an ethoxylated alcohol, or combinations thereof, and wherein: the non-fluoride containing zirconium compound comprise zirconium acetate, and the organic acid comprises lactic acid.

[0064] A ninth aspect may include any previous aspect and may further comprise from 0.5 wt.% to 8 wt.% zirconium compound; from 0.5 wt.% to 10 wt.% sulfuric acid; from 0.5 wt.% to 8 wt.% organic acid; and the balance aqueous solution.

[0065] A tenth aspect may include any previous aspect, and may further comprise from 0.1 to 5 wt.% nonionic surfactant; and from 0.5 wt.% to 5 wt.% accelerator.

[0066] An eleventh aspect may include any previous aspect, and may additionally or alternatively comprise a method of coating a substrate, comprising exposing the substrate to a zirconium conversion coating solution to form a coated substrate, wherein the zirconium conversion coating solution comprises: an aqueous solution; a non-fluoride containing zirconium compound; sulfuric acid; and an organic acid.

[0067] A twelfth aspect may include the eleventh aspect, and may further comprise exposing the coated substrate to a paint, thereby forming a painted substrate.

[0068] A thirteenth aspect may include either the eleventh or twelfth aspects, wherein the substrate comprises steel, galvanized steel, aluminum, magnesium, or combinations thereof.

[0069] A fourteenth aspect may include any of the eleventh through thirteenth aspects, wherein the zirconium conversion coating solution further comprises: an accelerator; and a nonionic surfactant.

[0070] A fifteenth aspect may include any of the eleventh through fourteenth aspects, the accelerator comprises a nitroaromatic sulfonate salt, hydroxylammonium sulfate, ammonium dimolybdate, hydroxylamine hydrochloride, or combinations thereof.; and the nonionic surfactant comprises an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, an alcoxylated alchohol, an ethoxylated alcohol, or combinations thereof.

[0071] A sixteenth aspect may include any of the eleventh through fifteenth aspects, wherein the organic acid comprises a carboxylic acid, a hydroxycarboxylic acid, or both.

[0072] A seventeenth aspect may include any of the eleventh through sixteenth aspects, wherein the zirconium conversion coating solution further comprises: an accelerator comprisingsodium nitrobenzene sulfonate; a nonionic surfactant comprising an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, or both, and wherein: the non-fluoride containing zirconium compound comprises zirconium acetate, and the organic acid comprises lactic acid.

[0073] An eighteenth aspect may include any of the eleventh through seventeenth aspects, wherein the zirconium conversion coating solution comprises: from 0.5 wt.% to 8 wt.% non- fluoride containing zirconium compound; from 0.5 wt.% to 10 wt.% sulfuric acid; from 0.5 wt.% to 8 wt.% organic acid; from 0.1 to 5 wt.% nonionic surfactant; from 0.5 wt.% to 5 wt.% accelerator; and the balance aqueous solution.

[0074] A nineteenth aspect may include any of the eleventh through eighteenth aspects, wherein the non-fluoride containing zirconium compound comprises a zirconium carboxylate.

[0075] A twentieth aspect may include any of the eleventh through nineteenth aspects, wherein the non-fluoride containing zirconium compound comprises zirconium acetate.

[0076] Having described the subject matter herein in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope herein, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects herein are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[0077] ft is noted that one or more of the following claims utilize the term “wherein” as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term “comprising.” ft is noted that the use of the terms “having” or “including”, or grammatical variations thereof, in this disclosure should also be interpreted in like manner as the more commonly used open-ended preamble term “comprising”.

Claims

CLAIMS1. A zirconium conversion coating solution comprising: an aqueous solution; a non- fluoride containing zirconium compound; sulfuric acid; and an organic acid.

2. The zirconium conversion coating solution of claim 1 , wherein the non-fluoride containing zirconium compound comprises a zirconium carboxylate.

3. The zirconium conversion coating solution of claim 1 , wherein the non-fluoride containing zirconium compound comprises zirconium acetate.

4. The zirconium conversion coating solution of any of claims 1-3, wherein the organic acid comprises a carboxylic acid, a hydroxycarboxylic acid, or both.

5. The zirconium conversion coating solution of any previous claim, further comprising an accelerator comprising a nitroaromatic sulfonate salt, hydroxylammonium sulfate, ammonium dimolybdate, hydroxylamine hydrochloride, or combinations thereof.

6. The zirconium conversion coating solution of any previous claim, further comprising a nonionic surfactant.

7. The zirconium conversion coating solution of claim 6, wherein the nonionic surfactant comprises an ethoxylated surfactant, a propoxylated surfactant, or both.

8. The zirconium conversion coating solution of any previous claim, further comprising: an accelerator comprising sodium nitrobenzene sulfonate; a nonionic surfactant comprising an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, an alcoxylated alchohol, an ethoxylated alcohol, or combinations thereof, and wherein: the non-fluoride containing zirconium compound comprise zirconium acetate, and the organic acid comprises lactic acid.

9. The zirconium conversion coating solution of any previous claim, comprising: from 0.5 wt.% to 8 wt.% zirconium compound; from 0.5 wt.% to 10 wt.% sulfuric acid; from 0.5 wt.% to 8 wt.% organic acid; and the balance aqueous solution.

10. The zirconium conversion coating solution of claim 9, further comprising: from 0.1 to 5 wt.% nonionic surfactant; and from 0.5 wt.% to 5 wt.% accelerator.

11. A method of coating a substrate comprising exposing the substrate to a zirconium conversion coating solution to form a coated substrate, wherein the zirconium conversion coating solution comprises: an aqueous solution; a non- fluoride containing zirconium compound; sulfuric acid; and an organic acid.

12. The method of claim 11, further comprising exposing the coated substrate to a paint, thereby forming a painted substrate.

13. The method of either claim 11 or 12, wherein the substrate comprises steel, galvanized steel, aluminum, magnesium, or combinations thereof.

14. The method of any of claims 11-13, wherein the zirconium conversion coating solution further comprises: an accelerator; and a nonionic surfactant.

15. The method of claim 14, wherein: the accelerator comprises a nitroaromatic sulfonate salt, hydroxylammonium sulfate, ammonium dimolybdate, hydroxylamine hydrochloride, or combinations thereof.; andthe nonionic surfactant comprises an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, an alcoxylated alchohol, an ethoxylated alcohol, or combinations thereof.

16. The method of any of claims 11-15, wherein the organic acid comprises a carboxylic acid, a hydroxycarboxylic acid, or both.

17. The method of any of claims 11-16, wherein the zirconium conversion coating solution further comprises: an accelerator comprising sodium nitrobenzene sulfonate; a nonionic surfactant comprising an ethoxylated copolymer surfactant, a propoxylated copolymer surfactant, or both, and wherein: the non-fluoride containing zirconium compound comprises zirconium acetate, and the organic acid comprises lactic acid.

18. The method of claim 17, wherein the zirconium conversion coating solution comprises: from 0.5 wt.% to 8 wt.% non-fluoride containing zirconium compound; from 0.5 wt.% to 10 wt.% sulfuric acid; from 0.5 wt.% to 8 wt.% organic acid; from 0.1 to 5 wt.% nonionic surfactant; from 0.5 wt.% to 5 wt.% accelerator; and the balance aqueous solution.

19. The method of any of claims 11-18, wherein the non-fluoride containing zirconium compound comprises a zirconium carboxylate.

20. The method of any of claims 11-19, wherein the non-fluoride containing zirconium compound comprises zirconium acetate.

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