MXPA01004311A - Composition and process for treating metal surfaces - Google Patents

Abstract

A composition for treating metal surfaces that contains, at a weight ratio from 1:5,000 to 5,000:1, at least one metal acetylacetonate selected from the group consisting of Al(C5H7O2)3, V(C5H7O2)3, VO(C5H7O2)2, Zn(C5H7O2)2, and Zr(C5H7O2)4, and at least one compound selected from water-soluble inorganic titaniumcompounds and water-soluble inorganic zirconium compounds provides a non-chromate-type composition for imparting an excellent corrosion resistance and paint adherence to the surfaces of metals, particularly aluminum and its alloys, magnesium and its alloys, and zinc and its alloys.

Description

COMPOSITION AND PROCESS FOR TREATING METALLIC SURFACES FIELD OF THE INVENTION This invention relates to a liquid, aqueous, novel composition which will henceforth be called a "bath" for brevity, without intending to say that it should be used only by immersion, and a process for treating a metal surface. The composition and process can provide the surfaces of different metals, especially aluminum, aluminum alloys, magnesium, magnesium alloys and galvanized steel sheet, excellent corrosion resistance and excellent paint adhesion. The baths used to treat surfaces of aluminum and aluminum alloys can be broadly classified into chromate type baths and non-chromate type baths. Chromic acid chromate conversion baths and chromate phosphoric acid conversion baths are common examples of chromate type treatment baths. Chromic acid chromate conversion baths reached their first practical application in about 1950, and even now they are widely used for the surface treatment of heat exchangers for automobiles, aluminum wheels, building materials and aerospace materials. The main components in chromic acid chromate conversion baths are chromic acid and an accelerator of the fluoride reaction. This type of bath produces a conversion coating containing moderate amounts of hexavalent chromium on the metal surface. The phosphoric acid chromate conversion baths originated with the invention described in U.S. Patent No. 2,438,877. The main components in chromate phosphoric acid conversion baths are chromic acid, phosphoric acid and hydrofluoric acid. A conversion coating whose main component is hydrated chromium phosphate is formed by this type of bath on the metal surface. In view of the fact that the resulting conversion coating does not contain hexavalent chromium, this type of bath is in wide use at present as a treatment under the paint layer for body materials and materials for beverage can covers. Although the conversion coatings that are generated by these chromate-type surface treatment baths exhibit excellent corrosion resistance and excellent adhesion to paint films, these treatment baths also contain toxic hexavalent chromium, and the associated environmental problems have caused The use of treatment baths that are completely free of hexavalent chromium is desirable.

The treatment bath described in Japanese Patent Application Laid-open (Kokai or unexamined) Number Sho 52-131937 (131.937 / 1977) is a common invention of chrome-free, chromate-free surface treatment baths. This surface treatment bath is an aqueous, acidic coating solution (pH = about 1.5 to 4.0) containing phosphate, fluoride and zirconium or titanium or a mixture thereof. The treatment of metal surfaces with this surface treatment bath causes the formation on the metal surface of a conversion coating whose main component is a zirconium or titanium oxide. This non-chromate type surface treatment bath offers the advantage of not containing hexavalent chromium and for this reason is widely used in the present to treat surfaces of stretched and iron coated aluminum cans, hereinafter commonly referred to as "DI". Unfortunately, the coating produced by this non-chromate type surface treatment bath is less resistant to corrosion than the chromate coatings. The method of treatment described in Japanese Patent Application Laid-Open (Kokai or unexamined) Number Sho 57/41376 (41.376 / 1982) consists of treating the surface of aluminum, magnesium or an alloy thereof with an aqueous solution which contains at least a selection of titanium salts and zirconium salts, at least one selection of imidazole derivatives, and an oxidant selected from nitric acid, hydrogen peroxide and potassium permanganate. Although the corrosion resistance of the coatings produced by this treatment bath had been considered acceptable 15 years ago, this level of corrosion resistance is, without a doubt, unsatisfactory in the present. Japanese Patent Application Laid Open (Kokai or unexamined) Number Sho 56-136978 (136,978 / 1981) teaches a conversion bath typically consisting of an aqueous solution containing a vanadium compound and at least one compound selected from the group consisting of group consisting of titanium salts, zirconium salts and zinc salts. However, the conversion coating formed by this treatment bath can not be expected to have a corrosion resistance better or even as good as that of a chromate film in the case of the challenge by long-term anticorrosion tests. Thus, as already described, the use of the prior art non-chromate surface treatment baths mentioned above is still associated with problems with corrosion resistance of the conversion coatings produced. It is for this reason that at present, non-chromate type surface treatment baths are little used on surface treatment lines where a particularly good corrosion resistance is required, for example, for heat exchangers of aluminum alloys and coils metallic aluminum and sheet metal. In summary, then, a bath still has to be established to treat surfaces of aluminum and aluminum alloys that do not contain hexavalent chromium, that have an excellent effluent treatment capacity and that have the ability to form highly corrosion resistant conversion coatings. and highly adherent to painting. To treat magnesium surfaces and magnesium alloy surfaces, chromate treatments such as those described by the JIS (Japanese Industrial Standard) H-8651 and MIL M3171 are in use to treat magnesium surfaces and alloys of magnesium. The conversion coatings that are generated by these chromate-type surface treatment baths exhibit excellent corrosion resistance and excellent adhesion to paint films, but these treatment baths also contain highly toxic hexavalent chromium. The associated environmental problems have made it desirable to use treatment baths that are completely free of hexavalent chromium. The process described in Japanese Patent Laid-open No. Hei 3-6994 (6,994 / 1991) is a common invention of the non-chromate-type surface treatment baths, without chromium for magnesium and its alloys. This treatment process consists of a phosphate treatment followed by a treatment with silica and then a silicone treatment after the silicate treatment. The coating of the phosphate treatment by itself provides a low level of corrosion resistance and adhesion to the paint when used as a treatment under the paint for magnesium surfaces and magnesium alloys. This treatment method also requires a multi-stage treatment process, uses high treatment temperatures and requires prolonged treatment times. The phosphate-based surface treatment methods known for magnesium and its alloys include methods employing treatment baths based on zinc phosphate, iron phosphate, calcium phosphate or zirconium phosphate. However, it is considered that these methods do not produce consistent corrosion resistance that is satisfactory on a practical level. A treatment with manganese phosphate is described in category 7 of JIS H-8651. This treatment bath is not acceptable from a practical point of view because it contains chromium, requires high treatment temperatures of 80 ° C to 90 ° C, and requires prolonged treatment times of 30 to 60 minutes. Another example of non-chromate type technology is found in Japanese Patent Application Laid-open (Kokai or unexamined) Hei Number 9-228062 (228,062 / 1997), which teaches a surface treatment process using an aqueous solution containing at least one organometallic compound selected from metal alkoxides, metal acetylacetonates and metal carboxylates and at least one film forming or auxiliary stabilizer from the formation of films selected from acids, bases and their salts and organic compounds containing the group hydroxyl, carboxyl group or amino group. This aqueous solution is applied to magnesium materials at a temperature of 0 to 50 ° C. However, again, the conversion coating formed by this treatment bath can not be expected to have corrosion resistance better than or even as good as that of a chromate film in the case of challenge by long-term anticorrosion testing. . Thus, as already described, the use of the prior art, non-chromate, surface treatment baths mentioned above for magnesium and its alloys remains associated with problems with the corrosion resistance of the conversion coatings produced and with inadequate treatment conditions from a practical point of view, that is, high treatment temperatures, long treatment times and high bath concentrations. It is for these reasons that at present the non-chromate type surface treatment baths have little use in surface treatment lines where a particularly good corrosion resistance and adhesion to paint is required, for example, for alloy materials of magnesium for automobiles, aerospace materials, materials for electronic devices and instruments and materials for communication devices and instruments. In summary, then, a bath still has to be established to treat magnesium and magnesium alloy surfaces that do not contain hexavalent chromium, that have excellent process characteristics and that have the ability to form highly adherent, highly corrosion resistant conversion coatings. To painting. Chromate treatments and phosphate treatments are the treatment processes that are generally applied to galvanized materials. Chromate treatments provide excellent coating performance, but the corresponding treatment baths contain toxic chromium and therefore increase the problems with respect to the working environment and effluent discharge. In some cases, zinc phosphate treatments can not provide acceptable corrosion resistance. The non-chromate type technologies for galvanized materials can be exemplified by the processes described in the following patent documents: Japanese Patent Application open to the public (Kokai or unexamined) Number Hei 1-104783 (104,783 / 1989) describes a process for producing sheet metal of steel with the treated surface. In this process, galvanized sheet steel with zinc, aluminum or a zinc-aluminum alloy is coated with an alcohol solution containing at least a selection of the alkoxides and acetylacetonates of Si, Ti, Zr, Al, W, Ce , Sn and Y. An oxide of the metal present in the solution is then formed on the surface of the steel plate by heating at 200-500 ° C after the application of the bath. This preparative method presents some problems with the work environment and energy costs, because it must use a flammable alcohol and requires very high temperatures for the formation of the coating. In this way, as in the case of aluminum materials and magnesium materials, a bath should still be established for the treatment of surfaces of galvanized materials that do not contain hexavalent chromium, that have excellent process characteristics and that have the capacity to form conversion coatings highly resistant to corrosion, highly adherent to the paint. The present invention is directed to solving the problems described above for the prior art. In more specific terms, a main objective of the present invention is to provide a non-contaminating composition and process for treating surfaces of at least one of the following: aluminum and its alloys, magnesium and its alloys and zinc-coated steel and its alloys which They can impart excellent corrosion resistance and excellent paint adhesion.

BRIEF COMPENDIUM OF THE INVENTION It has been found that conversion coatings highly resistant to corrosion, highly adherent to paint can be formed on metal surfaces by the use of a special surface treatment composition containing in convenient proportions at least one metal acetylacetonate. selected from the group consisting of Al (C5H702) 3r V (C5H702) 3, V0 (C5H702) 2, Zn (C5H702) 2 and Zr (C5H702) 4 and at least one compound selected from water-soluble inorganic titanium compounds and compounds of inorganic zirconium soluble in water.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED MODALITIES A composition according to the present invention for treating metal surfaces comprises, preferably consists mainly of, and most preferably consists of water and the following components: (A) a component of at least one acetylacetonate metal selected from the group consisting of A1 (C5H702) 3, V (C5H702) 3, V0 (C5H702) 2, Zn (C5H702) 2 and Zr (C5H702) 4, and (B) a component of at least one compound selected from water-soluble inorganic titanium compounds and water-soluble inorganic zirconium compounds, the components (A) and (B) being present in a weight ratio of (A) to (B) which is from 1: 5000 to 5000: 1. A bath according to the present invention for treating metal surfaces preferably, independently for each preference: - has a pH from 2.0 to 7.0; - contains from 0.01 to 50 grams of the component (A) as already described per liter of the bath, this concentration unit being freely applied in the future to any constituent of the bath and being commonly abbreviated as "g / 1"; and - it contains from 0.01 to 50 g / 1 of the component (B) as already described. A process according to the present invention for treating metal surfaces preferably forms on the metallic surface a conversion coating of the organic-inorganic compound at a coating weight of 5 to 2000 milligrams of the coating per square meter of the coated surface, this unit of coating weight being hereinafter commonly abbreviated as "mg / m2", by contacting the bath described above to treat metal surfaces with aluminum or an alloy thereof, magnesium or an alloy thereof or zinc or an alloy of East. An important feature of the present invention is the formation of an organic-inorganic composite coating. It is considered that the corrosion resistance of the resulting conversion coating in particular is improved by the formation of this organic-inorganic composite coating. The water-soluble inorganic titanium compound and / or the water-soluble inorganic zirconium compound, which is an essential component in the surface treatment composition of the present invention, can be one or more selections, for example from sulfates, oxysulfates, nitrates, phosphates, chlorides, ammonium salts and titanium and zirconium fluorides. As long as this component is an inorganic compound soluble in water, its specific type is not critical. However, at least for economy, at least one of the fluorotitanic and fluorozirconic acids and the salts of these acids are preferred. The composition (s) of titanium and / or inorganic zirconium (s) soluble in water is considered to precipitate on the surface of the metal workpiece such as, for example, the oxide, phosphate or fluoride of Ti or Zr and thus it forms a framework or skeleton element of the organic-inorganic composite coating that is produced with the metal acetylacetonate that precipitates at the same time. In addition, the presence of Ti and / or Zr also improves the barrier performance (interception capacity) of the coating with respect to corrosive environments and as a result enables the formation of a coating having a corrosion resistance and adhesion to the paint. superior to the use of only metallic acetylacetonate. The proportion of the concentration of metallic acetylacetonate: water-soluble inorganic compound is preferably at least, with increasing preference in the given order, 1.00: 100, 1.00: 50, 1.00: 10, 1.00: 7.0, 1.00: 5.0, 1.00: 3.0, 1.00: 2.0 or 1.00: 1.40 and independently of preference is no greater than, with increasing preference in the given order, 400: 1.00, 100: 1.00, 10: 1.00, 7.0: 1.00, 5.0: 1.00 or 2.5: 1.00. The organic-inorganic composite coating formed when this weight ratio is below 1: 5000 will have poor corrosion resistance, while the organic-inorganic composite coating production becomes difficult above 5000: 1. A bath according to the present invention for treating metal surfaces mainly employs water and the above-described surface treatment composition. This bath contains the metal acetylacetonate preferably from 0.01 to 50 g / 1 and, more preferably, from 0.1, or even more preferably, 1.0 to 20 g / 1. Although a conversion coating with a metal acetylacetonate content below 0.01 g / 1 will be formed, such coating will usually have poor corrosion resistance and paint adhesion. Good quality conversion coatings are still formed above 50 g / 1, but since no further increase in performance above 50 g / 1 is obtained, such concentrations are not economical due to the additional cost of the bath.

The content of the water-soluble inorganic titanium compound (s) and / or water-soluble inorganic zirconium compound (s) is preferably from 0.01 to 50 g / 1 and more preferably from 0.05 or even more preferred 0.5 to 10 g / 1. Although a conversion coating will be formed with a content below 0.01 g / 1, such coating will usually have poor corrosion resistance. Conversion coatings with good quality are still formed above 50 g / 1, but since no further improvement in performance above 50 g / 1 is obtained, such concentrations are not economical due to the additional cost of the bath. The pH of a surface treatment bath according to the present invention should be within the range of 2.0 to 7.0 and, preferably, is within the range of 3.0 to 6.0. A pH below 2.0 prevents the precipitation of metallic acetylacetonate on the metal surface and may cause irregularities or uneven appearance due to excessive etching of the metal surface. The formation of a highly corrosion resistant conversion coating deteriorates strongly at a pH above 7.0, and a pH above 7.0 can also cause problems with the stability of the bath due to a pronounced tendency of the metal ions present in the the bath to form a precipitate at such pH values. As necessary, the pH of the surface treatment bath of the present invention can be adjusted to the desired range by the use of an acid such as nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid or fluorosilicic acid, or a base such as sodium hydroxide. , sodium carbonate, potassium hydroxide or ammonium hydroxide. The stability of the treatment bath can be strongly deteriorated during the execution of the surface treatment of the present invention by elution in the bath of the metal ions, for example, aluminum, magnesium or zinc ions from the metal workpiece. In such cases, it is possible to add to the bath an organic acid or the alkali metal salt thereof as a sequestering agent to chelate the metal ions. The organic acids used for this purpose can be exemplified with gluconic acid, heptogluconic acid, oxalic acid, tartaric acid, organophosphonic acids and ethylenediaminetetraacetic acid. It is also possible to use an oxidizing agent to accelerate the formation of the conversion coating of the present invention. This oxidizing agent can be exemplified by hydrogen peroxide, tungstic acid and its salts, molybdic acid and its salts, permanganic acid and its salts, and water-soluble organoperoxides such as tert-butyl hydroperoxide ((CH3) 3C-0-0H) . The mass per unit area, commonly referred to as "coating weight", of the conversion coating of the organic-inorganic compound formed by the process described herein is preferably from 5 to 2000 mg / m2 and most preferably from 50 , or still more preferably 140 to 500 mg / m2. The corrosion resistance and paint adhesion may be inadequate with a coating weight below 5 mg / m2. Although excellent corrosion resistance is obtained with coating weights above 2000 mg / m2, no further increase in performance is obtained above 2000 mg / m2 and such coating weights are therefore non-economic due to the additional cost. Coating weights above 2000 mg / m2 are also undesirable because they cause conspicuous irregularities in the appearance of the relining and tend to damage the adhesion of the paint. With respect to the metallic components (Al, V, Zn, Zr, Ti) that can constitute the conversion coating, their chemical characteristics are not critical in the coating itself, for example, its state of union, oxidation state, degree of polymerization or increase in molecular weight, and the like. Highly resistant to corrosion conversion coatings highly adherent to paint can be formed by contacting the surface treatment bath of the invention with aluminum or an alloy thereof, magnesium or an alloy of this or zinc or an alloy of East. This process to treat the surface of different types of metals will be explained in more detail in the following. The surface treatment bath of the invention is used in a preferred embodiment as part of the following process operations: (1) Surface cleaning / degreasing (this can be neutral / alkaline or solvent-based cleaning / degreasing) (2) Rinse with water (3) Surface treatment using the surface treatment bath of the present invention (4) Rinse with water (5) Rinse with deionized water (6) Drying. The surface treatment bath of the present invention is preferably contacted with the metal surface for 1 to 600 seconds to 10, or more preferably 35 to 80 ° C. The reactivity between the treatment bath and the metal surface will usually be inadequate at contact temperatures below 10 ° C, and inadequate reactivity will prevent the formation of good quality conversion coatings. A conversion coating is still formed at contact temperatures above 80 ° C, but the correspondingly increasing energy costs create undesirable economics for these temperatures. The degree of reaction will usually be inadequate in a treatment time of less than one second, avoiding the formation of a conversion coating highly resistant to corrosion. At the other end of this range, no further improvement is observed in the corrosion resistance and adhesion to the paint of the conversion coatings in times in excess of 600 seconds. The contact with the surface treatment bath of the invention can be carried out by any means that obtains the required contact, being the dip or spray the most commonly used. A composition bath for surface treatment according to the invention can conveniently be applied to pure aluminum and aluminum alloys containing at least 50% by weight of aluminum. Applicable aluminum alloys comprise multicomponent alloys, for example, Al-Cu, Al-Mn, Al-Si, Al-Mg, Al-Mg-Si and Al-Zn-Mg, and metals in which electrodeposition has been performed Al or Al alloy, for example steel sheet electroplated with Al. The composition for the surface treatment and the bath according to the invention can also be conveniently applied to pure magnesium and magnesium alloys containing at least 50% in weight of magnesium. The applicable magnesium alloys comprise multicomponent alloys such as Mg-Al-Zn, Mg-Zn and Mg-Al-Zn-Mn, and the magnesium or alloys can be electrodeposited on other metals. The zinc and zinc alloys to which the invention can be conveniently applied include in particular metals in which the Zn electrodeposition has been performed, including the zinc-electroplated steel sheet, by hot dip, the electroplated steel sheet with hot dip zinc, galvanized, electroplated steel sheet with Al / Zn alloy (Galfan ™ and Galvalume ™), electrogalvanized steel sheets and electrogalvanized steel sheets with alloy. Such factors as the shape and dimensions of the metallic substrate to which the invention is applied are not crucial and, for example, the invention comprises the treatment of the sheet and the different types of castings. The surface of the workpiece can be in any condition as long as a metal is present as described at least on a portion of the surface. For example, the surface may be cold rolled or electrodeposited as such, or it may have been subjected to a treatment such as shot blasting, corrugation with acid or alkali, or activation. The effects of the composition, the bath and the process of the invention are more specifically illustrated in the following through the working and comparative examples.

EXAMPLES 1 TO 5 AND COMPARATIVE EXAMPLES 1 TO 4 The following sample substrate materials were used in these examples: Al-Mn alloy plates, according to the Japanese Industry Standard ("JIS") 3004, with dimensions of 150 millimeters ( hereinafter commonly abbreviated as "mm") x 70 mm x 0.2 mm thick; Die-cast sheets with dimensions of 150 mm x 100 mm x 1 mm thickness of AZ91D magnesium alloy as specified by JIS H2222; and steel sheets electrodeposited with zinc, hot dipped, annealed and galvanized with dimensions of 150 mm x 70 mm x 0.8 m thick.

CONDITIONS OF THE PROCESS Samples with treated surface were prepared by treatment according to the following operations in sequence (1) - (2) - (3) - (4) - (5) - (6). (1) Degreasing (43 ° C, 2 minutes, immersion), using a 2% aqueous solution FINE-CLEANER® L4460A and 1.2% FINECLEANER® L4460B (both chemicals from Nihon Parkerizing Co., Ltd.). (2) Rinse under running water (room temperature, 30 seconds, spray). (3) Surface treatment (immersion) as detailed in the following tables. (4) Rinse under running water (room temperature, 30 seconds, spray). (5) Rinse with deionized water (room temperature, 30 seconds, spray). (6) Drying (80 ° C for 3 minutes in a pressure and convection oven). ("Ambient temperature" means temperature as normally maintained in buildings for the comfort of the human, that is, approximately 18-23 ° C). The metal acetylacetonates which are used are mentioned below in Table 1, the water-soluble titanium compounds used are mentioned below in Table 2, the water-soluble zirconium compounds used are mentioned below in Table 3, and the reagents that are used to adjust the pH of the surface treatment baths are mentioned later in Table 4, in each case together with the identification symbols used for these in the last tables.

Table 1 Table 2 Table 3 Table 4 The surface treatment was carried out using the treatment conditions and the surface treatment bath compositions reported in Tables 5 and 6. The amounts of the reagents reported in the columns for the composition of the treatment bath in Tables 5 and 6 they are values calculated for the pure reagent. The surface treatment conditions used in Comparative Examples 5 to 9 are reported below. Comparative Example 1 used an acetylacetonate as the sole component of the treatment bath to provide a comparative example testing the formation of a metallic acetylacetonate coating alone. Comparative Example 2 used a water-soluble titanium compound as the sole component of the treatment bath to provide a comparative example for testing the formation of a coating of the inorganic titanium compound alone. Comparative Example 3 employed a treatment bath consisting of the water-soluble inorganic titanium compound and the water-soluble inorganic zirconium compound to provide a comparative example for testing the formation of a coating of the inorganic compound constituted of titanium and zirconium but which lacks metallic acetylacetonate. Comparative Example 4 was directed to the formation of coatings with very low coating weights. In Comparative Example 5, a 2% solution in water of a zirconium phosphate surface treatment agent (ALODINE® 4040 from Nihon Parkerizing Co., Ltd.) was used to carry out the surface treatment. This solution was applied to the Al alloy sheet previously described by spraying for 60 seconds at 50 ° C, after which the corrosion resistance and adhesion to the paint were evaluated. In Comparative Example 6, an aqueous solution of a commercial phosphoric acid surface treatment agent (mixed aqueous solution of 4% ALCHROM® K702SL and 0.3% ALCHROM® K702AC, both from Nihon Parkerizing Co., Ltd. was used. ) to carry out the surface treatment. This solution was applied to the Al alloy sheet previously described by spraying for 20 seconds at 50 ° C, after which the corrosion resistance and adhesion of the paint were evaluated.

The pH value for these baths was not reported.

In Comparative Example 7, a 7% solution in water of a commercial chromic acid surface treatment agent (ALCHROM® 713M from Nihon Parkerizing Co., Ltd.) was used to carry out the surface treatment. This solution was applied to the Al alloy sheet previously described, the Mg alloy sheet and the Zn electroplated steel sheet for 60 seconds at 40 ° C, after which the corrosion resistance and adhesion were evaluated. To painting. In Comparative Example 8, a treatment bath based on MIL-M3171C (TYPE III, with an average sodium bichromate component) was used for the surface treatment. This bath was applied to the Mg alloy sheet by immersion for 30 minutes at 95 ° C, after which the corrosion resistance and adhesion of the paint were evaluated. In Comparative Example 9, after greasing (1) and rinsing with water (2) the workpiece was immersed for 30 seconds at 25 ° C in a 0.1% aqueous solution of a commercial titanium-based surface conditioner (PREPALENE® 4040 from Nihon Parkerizing Co., Ltd.). This was followed by surface treatment with an aqueous solution of a commercial zinc phosphate-based surface treatment agent (mixed aqueous solution of 5% PALBOND® L3020, 0.5% additive 4813, 2% additive 4856 and 1% neutralizer 4055, all from Nihon Parkerizing Co., Ltd.). This bath was applied to the steel plate electrodeposited with Zn by immersion for 120 seconds at 43 ° C, after which the corrosion resistance and adhesion of the paint were evaluated.

METHODS OF EVALUATION (1) Weight of the coating: The weight of the coating of the entire composite organic-inorganic coating was measured using a fluorescence x-ray analyzer or removal of the electrodeposited metal layer by immersion for 5 minutes at 90 ° C in a 5% by weight aqueous solution of chromic acid. (2) Corrosion resistance: The corrosion resistance was evaluated using the salt spray test described in JIS Z-2371. The degree of corrosion developed in the sheet with the treated surface was evaluated visually after the salt spray test and reported on the following scale: ++ = corrosion area less than 10%; + = corrosion area at least 10%, but less than 30%; ? = corrosion area at least 30%, but less than 50%; x = corrosion area at least 50%. The salt spray times for each of the samples with the treated surface were: For the Al alloy sheet 480 hours For the 24 hour Mg alloy sheet For the steel sheet electrodeposited with Zn 120 hours. (3) Adhesion of the paint: The adhesion test of the paint was performed on samples of Al alloy sheet, Mg alloy sheet and Zn electroplated steel sheet after the surface treatment under the conditions of the Examples 1 to 5 and Comparative Examples 1 to 9. The surface of the sample was coated to a dry film thickness of 10 microns (hereinafter commonly abbreviated as "μ") with an epoxy resin paint from Kansai Paint Co ., Ltd., and the sample was then baked for 10 minutes at 200 ° C. A grid of 100 frames (width = 2 mm) was subsequently introduced into the center of the painted sheet using a cutter, after which the sample was immersed for 60 minutes in boiling deionised water. After this challenge in boiling water, the painted sheet was dried in air and then subjected to a flaking test with a cellophane tape. The adhesion of the paint was evaluated based on the number of grid squares that were not detached. In this test, a large number of remaining frames is indicative of better adherence. A record of 98 or better indicates a satisfactory performance at the level of the practical application. The results of the evaluations are reported in Tables 5 and 6. These results demonstrate that the conversion coatings formed by the surface treatment baths of the present invention have a paint corrosion and adhesion resistance equal to that of the traditional chromate coatings. further, the results in these tables show that an excellent resistance to corrosion can be obtained by the formation in suitable coating weights of the coatings of the organic-inorganic compounds containing metallic acetylacetonate and at least titanium or zirconium.

Claims (8)

1. A liquid, aqueous composition for treating a metal surface, the composition comprises water and the following components: (A) a component of at least one metal acetylacetonate selected from the group consisting of A1 (C5H702) 3, V (C5H702) 3, VO (C5H702) 2, Zn (C5H702) 2 and Zr (C5H702) 4; and (B) a component of at least one compound selected from water-soluble inorganic, inorganic titanium compounds and water-soluble inorganic zirconium compounds, components (A) and (B) being present in a weight ratio of (A) a (B) which is from 1: 5000 to 5000: 1.

2. The aqueous liquid composition according to claim 1, wherein: the composition has a pH value from 2.0 to 7.0; - there is a concentration of component (A) that is from 0.01 to 50 g / 1; - there is a concentration of component (B) which is from 0.01 to 50 g / 1; and - the weight ratio of (A) to (B) is from 1.00: 100 to 400: 1.00.

3. The aqueous liquid composition according to claim 2, wherein: the composition has a pH value from 3.0 to 6.0; - there is a concentration of component (A) that is from 0.1 to 20 g / 1; - there is a concentration of component (B) which is from 0.05 to 10 g / 1; and - the weight ratio of (A) to (B) is from 1.00: 10 to 10: 1.00.

4. The aqueous liquid composition according to claim 3, wherein: - there is a concentration of the component (A) which is from 1.0 to 20 g / 1; - there is a concentration of component (B) that is from 0.5 to 10 g / 1; and - the weight ratio of (A) to (B) is from 1.00: 5.00 to 5.00: 1.00. The aqueous liquid composition according to claim 4, wherein the component (B) is selected from the group consisting of fluorotitanic acid, fluorozirconic acid and salts of these acids. 6. A process for forming a coating that reduces corrosion on a surface selected from the group consisting of aluminum and alloys thereof, magnesium and alloys thereof and zinc and alloys thereof by contacting the surface with an aqueous liquid composition of according to one of claims 1 to 5 for forming a coating having a mass per unit area that is from 5 to 2000 mg / m2. The process according to claim 6, wherein during the contacting of the aqueous liquid composition the composition is maintained at a temperature of 10 to 80 ° C, and the contact is maintained for a time that is from 1 to 600 seconds. . The process according to claim 7, wherein during the contact the aqueous liquid composition is maintained at a temperature of at least 35 ° C.