KR20010040194A - Process for preparing aluminum and/or magnesium with improved corrosion resistance after deoxidizing without using chromium compounds - Google Patents

Abstract

PURPOSE: A method for forming a base metal of a chromate coated film on the surface of aluminum or magnesium by using a treating solution not containing hexavalent chromium or ferricyanide. CONSTITUTION: The surface of metal is brought into contact with a solution for desmutting/removing an oxide film and then rinsed with rinse containing at least one chelating agent. As the solution for desmutting/removing the oxide film, a strong acid solution containing, as indispensable components, nitric acid and Fe¬3+ ion and further containing one kind or more selected from anions including molybdic acid ion, persulfuric acid ion and fluorine, sulfuric acid and a surfactant is used. The chelating agent can be selected from gluconic acid, tartaric acid, ethylenediaminetetraacetic acid, EDTA and NTA.

Description

PROCESS FOR PREPARING ALUMINUM AND / OR MAGNESIUM WITH IMPROVED CORROSION RESISTANCE AFTER DEOXIDIZING WITHOUT USING CHROMIUM COMPOUNDS}

The present invention relates to a method of improving the corrosion resistance of aluminum and / or magnesium by washing with a washing liquid in which a chelating agent is added to water between the deoxidation film process and the chemical conversion process of the treatment process.

Aluminum and magnesium objects are to be understood as meaning any object having a surface of at least 51% by weight of aluminum or magnesium. In the aerospace industry, (a) aluminum or magnesium is contained in significant concentrations of hexavalent chromium, ferricane Deoxidation treatment by contact with an aqueous solution composition containing ions and / or hydrofluoric acid, (b) rinsing with water, and (c) coating after forming a chromate conversion coating on the washed surface. There is a need for corrosion resistance, which has traditionally been achieved by a process sequence in which an aluminum surface is coated with an organic binder by treatment or the like. The hexavalent chromium and ferricyanide components of the conventional deoxidation film treatment compositions have many environmental problems. Compositions for the treatment of deoxidized films containing sulfuric acid and / or nitric acid and ferric ions are also known and have no environmental problems, but so far, aluminum and magnesium substrates treated with these deoxidants are considered suitable for aerospace applications. Corrosion resistance is not achieved.

Hereinafter, the present invention will be described for the use of aluminum only, because the present invention can be applied mutatis mutandis to magnesium although aluminum is the main application. Accordingly, one object of the present invention is to provide a suitable aqueous solution to deoxidize the substrate without using a significant amount of chromium, to clean the deoxidized substrate, and to react the deoxidized and washed substrate instantaneously with it. Contacting the composition to form a chromium-containing conversion coating on the deoxidized and washed substrate to impart good corrosion resistance to the aluminum substrate.

Another task is to provide a treatment composition suitable for this method.

Other challenges will be apparent from the description below.

Except in the claims and the examples, or unless otherwise indicated, all quantities used to indicate the quantity or reaction conditions and uses of materials in the specification of the invention describe the broadest scope of the invention. It is to be understood that the term "about" is used in the description. However, implementation within the numerical limits described is generally preferred. Also, unless stated otherwise in the specification, the values of percentage, "part" and ratio are by weight or mass, and the term "polymer" is "oligomer", "copolymer", "terpolymer" And a group or a class of materials suitable or preferred for a given purpose in connection with the present invention means that a mixture of two or more of the elements in the group or class is equally suitable or preferred. In addition, the description of each component in the chemical terminology is described in the composition by the chemical reaction described in the specification between one or more newly added components and one or more components already present in the composition when the other components are added. It means each component as it occurs as it is or added to the combination specified in the description of the specification, and does not necessarily exclude unspecified chemical action between each component in the mixture once mixed. Ionic material means that there are enough counter ions present in the composition and sufficient to exhibit electrical neutrality with respect to the material added to the composition, the concentration of which is expressed as the concentration of ions in any particular composition It is to be understood that it contains a complete chemical equivalent of a particular ion contained in the material added to the composition, regardless of the substantial degree of ionization, aggregation, etc. present. Implicitly specified ions are preferably selected from among other components specified in ionic form, as far as possible. Or you may select these counterions arbitrarily except the case where the counterion which acts against the objective of this invention is avoided. The term "mole" means "gram mol", regardless of whether the chemical species is an ion, unstable, hypothetical, or actually a stable neutral substance with a fixed molecule. And all its grammatical variations can be used for any species defined by any kind and number of atoms present. And the terms "solution", "soluble", "homogeneous phase", etc. not only include a true equilibrium solution or a homogeneous solution, but also mechanically disrupt the material for at least 100 hours or preferably at least 1000 hours. It is to be understood that it also includes dispersions which do not exhibit any visually detectable phase separation tendency when observed and maintained at a concentration within the range of 18 to 25 ° C.

It has been found that the corrosion resistance of aluminum treated as described above can be significantly increased by using a wash solution containing a component of a chelating agent in addition to water between the in-process deoxidation treatment and the conversion coating forming step.

Any method can be used as long as the aluminum substrate treated by the present invention can be subjected to a deoxidation film treatment. However, the method should hardly use chromium in order to achieve the environmental problem of the present invention. Accordingly, the method according to the present invention comprises a deoxidation film treatment step taught from the following US patents, all of which are US patents, ie 5,393,447 except to the extent that they do not have to be consistent with those explicitly set forth herein. (28 February 1995), 5,227,016 (July 13, 1993), 5,052,421 (October 1, 1991), 4,886,616 (12.12 December 1989), and 3,728,188 (8 August 1973) 17 is incorporated herein by reference in the present invention.

Preferably, the deoxidation film treatment step in the method according to the present invention is achieved by contacting a liquid deoxidized film treatment composition containing the following with a substrate to be treated.

Water and;

(A ₁ ) nitric acid;

(B ₁ ) ferric ions; And optionally one or more of the following ingredients:

(C ₁ ) molybdate and / or condensed molybdate anion,

(D ₁ ) persulfate (ie S ₂ O ₈ ^-2 , so-called “peroxydisulfate”) anions,

(E ₁ ) fluorine-containing anions,

(F ₁ ) sulfuric acid and / or sulfate ions,

(G ₁ ) surfactant, and

(H ₁ ) Dyes or other colorants.

For various reasons, it is desirable that these deoxidation film treatment compositions be substantially free of many of the components used in the composition for similar purposes in the prior art. Specifically, independently of each of the preferably minimized components listed below, when directly contacted with a metal by the method of the present invention, these components are at least per component of each of the following components: hexavalent chromium, silica, silicon Silicates, ferricyanides, ferrocyanides, thioureas, pyrazole compounds, saccharides, gluconic acid and salts thereof, glycerin, α-glucoheptanoic acid and salts thereof, and myoinositol phosphate esters, containing no four fluorine atoms and Preferably, these salts contain 1.0, 0.35, 0.10, 0.08, 0.04, 0.02, 0.01, 0.001 or 0.0002 percent or less in increasing order. In addition, the content of ferrous ions is preferably 5% or less, more preferably 3% or less, still more preferably 1.1% or less relative to the content of ferric ion.

In the deoxidation film treatment composition used in the present invention, the nitric acid concentration is preferably 10, 9, 8, 7.4, 6.8, 6.4, 6.2, 6.1, 6.0, 5.9, 5.7, as moles per liter of the total composition in increasing order. No more than 5.5, 5.3, 5.1, 4.9, 4.7, 4.5, 4.3, 4.1 or 3.9 (hereinafter commonly referred to as "mole (s) / l", commonly referred to as "moles per liter"), independently increasing preferably At least 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.3, 3.5 or 3.7 mole (s) / l.

As for ferric ions, the deoxidation film treatment composition used in the present invention is preferably at least 0.009, 0.02, 0.035, 0.05, 0.06, 0.07, 0.08 or 0.09 mole / l in increasing order, and requires a high removal rate. More preferably at least 0.11, 0.13, 0.14, 0.15, 0.17 or 0.19 mole (s) / l in increasing order, and independently these concentrations are preferably 1.0, 0.70, 0.62, It is 0.58, 0.50, 0.45, 0.37 or 0.30 mole / l or less, and considering maximum economy, More preferably, it is 0.27, 0.25, 0.23, or 0.21 mole / l or less in increasing order. Independently, the ratio of the concentration of ferric ion [mole (s) / l] to the nitric acid concentration [mole (s) / l] in the deoxidation film treatment composition used in the method of the present invention is preferably increased. 0.05: 1.0, 0.010: 1.0, 0.015: 1.0, 0.020: 1.0, 0.025: 1.0, 0.030: 1.0, 0.035: 1.0, 0.040: 1.0, 0.045: 1.0, 0.048: 1.0, 0.050: 1.0 or 0.052: 1.0 Above, independently, preferably in increasing order: 0.40: 1.0, 0.30: 1.0, 0.20: 1.0, 0.10: 1.0, 0.090: 1.0, 0.070: 1.0, 0.060: 1.0, 0.055: 1.0, 0.053: 1.0, 0.055: 1.0 or 0.053: 1.0 or less.

Although the presence of molybdate ions is not required, they are generally preferred. Although only those molybdenum atoms present in the form of molybdates or condensed molybdenum anions are believed to be effective and may be considered part of this component, furthermore, even if other forms of molybdenum such as molybdenum cations are present in the composition Since the degree of aggregation of acid ions is usually uncertain and does not appear to affect the good action of molybdate ions in the deoxidation film treatment composition used in the method of the present invention, the concentration of these ions is determined as a molybdenum atom. Expressed in stoichiometric equivalents. In the deoxidation film treatment composition used in the method of the present invention, the concentration of these molybdenum atoms in the molybdate ion is preferably at least 0.00080, 0.0015, 0.0025, 0.0050, 0.0070, 0.0080, 0.0085, 0.0090 or 0.0094 mole in increasing order. / l, independently, preferably 0.58, 0.41, 0.28, 0.20, 0.16, 0.12, 0.10, or 0.094 mole / l or less, and more preferably 0.080, 0.060, 0.040, 0.030, 0.025, 0.020, 0.0180, 0.0160, 0.0140, 0.0120, 0.0100 or 0.0096 mole / l or less. Independently, the ratio of the concentration [mole (s) / l] of the molybdenum atom in the molybdate ion to the nitric acid concentration [mole (s) / l] in the deoxidized film treatment composition used in the method of the present invention is preferable. Preferably in an increasing order of at least 0.00020: 1.0, 0.00040: 1.0, 0.00080: 1.0, 0.0010: 1.0, 0.0013: 1.0, 0.0017: 1.0, 0.0020: 1.0, 0.0023: 1.0 or 0.0025: 1.0, independently increasing preferably 0.030: 1.0, 0.017: 1.0, 0.0130: 1.0, 0.0110: 1.0, 0.0090: 1.0, 0.0070: 1.0, 0.0050: 1.0, 0.0040: 1.0, 0.0035: 1.0, 0.0030: 1.0 or 0.0027: 1.0 or less.

The presence of persulfate ions, which is optional component (D ₁ ) as described above, is preferred only when the extremely thick layer of stains is removed with the composition of the present invention, and the surface treated with the composition of the present invention may be prepared by iron shot ( commonly used solutions containing sodium sulfide, triethanol amine and alkali, which can be shot peening by iron shot or other methods to bury small iron particles, and then convert the iron particles to iron sulfide, etc. It is also preferable when etching with the solution of. The oxidation of the persulfate for this application allows for much faster desmuting and / or deoxidation treatment than other similar compositions omitting the persulfate. The concentration of persulfate in the deoxidation film treatment composition used in the process of the invention for these particular applications is preferably at least 0.020, 0.042, 0.051 or 0.060 mole (s) / l in increasing order, independently for practical use. This concentration in the composition is preferably 0.19, 0.16, 0.10, 0.091 or 0.080 mole (s) / l or less. In addition, in an operation composition containing persulfate independently, the ratio of the concentration of the molybdate [mole (s) / l] to the concentration of the molybdate [mole (s) / l] is preferably at least in increasing order. 5: 1.0, 10: 1.0, 15: 1.0, 20: 1.0 or 24: 1.0 independently, preferably in increasing order of 200: 1.0, 150: 1.0, 100: 1.0, 80: 1.0, 60: 1.0, 55: 1.0, 50: 1.0, 45: 1.0, 40: 1.0, 35: 1.0, 30: 1.0 or 26: 1.0 or less.

On the other hand, if the surface to be treated is covered only with the stain and / or oxide of the average thickness to be removed, and the stain and / or oxide does not substantially contain iron and / or iron sulfide inclusions, the persulfate may be various other major components in the composition. Since it is much more expensive than the components, it is preferable to omit it from the composition of the present invention for economic reasons.

The fluorinated component (E ₁ ) is preferred in most of the deoxidation film treatment compositions of the present invention and is preferably provided as soluble fluorine ions or bifluor ions, more preferably in the latter case. This is regarded as stoichiometric equivalents as fluorine ions, such as hydrofluoric acid or fluorometallic acid complexes or ions thereof that will exist regardless of the actual degree of ionization or aggregation in the deoxidation film treatment composition. The concentration as fluoride in the deoxidation film treatment composition used in the process of the invention is preferably at least 0.01, 0.028, 0.045, 0.055, 0.060, 0.065, 0.070, 0.074 or 0.078 mole / l, in increasing order, with a maximum rate For destaining and / or deoxidation treatment of, the concentration is more preferably at least 0.080, 0.85, 0.090, 0.095, 0.100 or 0.103 mole / l in increasing order, and independently this concentration in the working composition is preferably increased. It is 1.0, 0.7, 0.4, 0.28, 0.24, 0.22, 0.20 or 0.19 mole / l or less in order to carry out, More preferably, it is 0.120, 0.110 or 0.105 mole / l in consideration of economy. While not being bound by theory, it is believed that the main function of fluorine ions is to slightly promote etching of the treated surface, so alloys such as aluminum alloys of the 2xxx and 7xxx series, which have relatively higher content of elements that are much more electrochemically inert than aluminum. The use of this fluorine ion is particularly preferred when treating. When treating these alloys, the etch rate in the depth range of 1.3 × 10 ⁻⁴ to 6.4 × 10 ⁻⁴ cm per hour from the exposed surface of the alloy in the destaining and / or deoxidation film treatment step in the process of the invention Is preferred. This etch rate may be achieved by the preferred amount of fluorine ions described above, but otherwise it is desirable to adjust the concentration of fluorine to achieve this desired rate. In the case of other alloys which were conventionally recognized as being more easily destained, the amount of fluorine ions may be reduced or omitted together as described with any of the optional components described above.

It is generally preferred that sulfate ion, which is an optional ingredient (F ₁ ), is present in the deoxidation film treatment composition used in the process of the invention. The concentration of sulfate ions, including stoichiometric equivalents of any sulfuric acid present in the deoxidation film treatment composition used in the process of the present invention, is preferably in increasing order of at least 0.06, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.41, 0.48, 0.53, 0.57 or 0.59 mole / l, independently, preferably in increasing order of 5, 2.5, 1.9, 1.6, 1.2, 0.92, 0.85, 0.78, 0.73, 0.68, 0.64 , 0.62 or 0.60 mole / l or less. In general, it is desirable to obtain the content of sulphate in the composition according to the invention only from ferric sulfate and / or sulfuric acid in order to avoid other substances which have an unnecessary effect on performance. In addition, the ratio of the molar concentration of sulfate ion to the molar concentration of nitric acid in the working composition according to the present invention is preferably at least 0.020: 1.0, 0.030: 1.0, 0.040: 1.0, 0.050: 1.0, 0.060: 1.0, 0.070: 1.0, 0.080: 1.0, 0.090: 1.0, 0.11: 1.0, 0.13: 1.0 or 0.15: 1.0, independently, preferably in increasing order of 1.2: 1.0, 1.0: 1.0, 0.8: 1.0, 0.60: 1.0, 0.50: 1.0, 0.40: 1.0, 0.30: 1.0, 0.25: 1.0, 0.20: 1.0, 0.18: 1.0 or 0.16: 1.0 or less.

For component (G), most surfactants effective in dissolving the organic incorporation present on the surface to be treated and lowering the surface tension can be used in principle, but many types of surfactants are unstable in highly oxidizing acidic compositions. Another valuable function of the preferred surfactants is the delay that can actually occur between the time when the treated metal surface is removed from contact with the destain / deoxidation film treatment composition of the present invention and the time when the surface is cleaned. This ensures that the treated surface does not dries dry over time. Although it is known in the art to quickly clean after destaining or deoxidizing film to minimize the chance of contaminating the treated surface, it is actually 2 minutes to destaining large objects such as aircraft wings. A delay of about 3 minutes is common, and when the destaining / deoxidation film treatment composition is dried on the surface, staining of the dried portion is almost inevitable.

It has been found to be much more stable than many other surfactants, suitable for reducing the surface tension of the composition without easily producing bubbles, and not forming dry parts during transfer times of up to at least 3 minutes between treatment and washing, Thus a particularly preferred surfactant when requiring a surfactant is an ethoxylated acetylenic diol. In use, these are in the grams per liter of composition (hereinafter, simply referred to as "g / L") in increasing order, preferably in the working composition, 0.01 to 10, 0.1 to 5, 0.25 to 4, 0.55 to 3.0, 0.75 to 0.7 It is preferably present at a concentration within the range of 2.5, 0.85 to 2.0, 0.85 to 1.5, 0.90 to 1.5, 0.85 to 1.2, or 0.90 to 1.10. Most preferably, the surfactant component when present is two ethoxy Silylated tetramethyl decinediol, ie, one containing an equal amount of each of the hydrophile-lipophile balance (HLB) in the range of 7 to 9, and the other in the HLB range of 11.5 to 14.5. If no persulfate is present in the composition, no surfactant is required at all.

Component (H) is not believed to serve a technical purpose in the composition, but it is valuable to alert workers to safety by indicating the presence of strong acids in a visible color such as red. The amount of dyes or other pigments that can be readily recognized by the workers and which does not adversely affect the intended function of the composition or does not burden the economic cost can be readily selected by those skilled in the art.

In addition to the other features described above, the destain / deoxidation film treatment composition used in the method of the present invention preferably has a "point" of total acid in increasing order of at least 2, 4, 6, 8, 10, 12, 14 or 15, where the term "point" refers to a composition as about 10 mL of deionized water containing excess potassium fluoride to prevent precipitation of heavy metal hydroxides during titration. After diluting the sample, 5.0 mL of the sample of the composition is titrated and defined as equal to the number of mL of 1.0 N strong alkali (in sodium hydroxide) required to reach the end point with the phenolphthalein indicator. For the highest rates of destain / deoxidation film treatment, the point of total acid of the above definition of the working destain / deoxidation film treatment composition is preferably at least 18, 20, 21, 22 or 22.5 in increasing order. The points of total acidity of such destained / deoxidized film treatment compositions used independently in the process of the present invention are preferably 60, 50, 45, 35, 32, or 31 or less in increasing order, or in view of economics. The point of is preferably 29, 27, 26, 25 or 24 or less. In addition, the oxidation-reduction (redox) potential in the persulfate-containing destain / deoxidation film treatment composition independently used in the method of the present invention (this is a standard saturated calomel in which the potential of the platinum electrode immersed in the composition is immersed in the same composition. Measured in comparison with the electrode] is 800 to 1100, 900 to 1050, 950 to 1035, 975 to 1029, 985 to 1020, 991 to 1011, or 996 to 1006 in the order of increasing the oxidizing property of the standard electrode or more, preferably in increasing order. It shows the oxidative property of mv.

The deoxidation film treatment composition used in the expanded process of the present invention can be applied to the metal to be treated in a convenient manner, some of which are apparent to those skilled in the art. Immersion is the simplest and most often used. However, spraying or roll coating may also be used.

After the treatment with the destaining / deoxidation film treatment composition, the treated surface is treated with a solution in which at least one chelating agent is added to water, followed by washing by the method of the present invention. In particular, if the persulfate is contained in the destained / deoxidized film treatment composition, it is desirable to complete the treatment as soon as possible after removal of the treated surface from contact with the destained / deoxidized film treatment composition and as practical as possible. After drying, the destain / deoxidation film treatment composition is dried as it is on any part of the surface, and the surface may be stained by other methods. In general, 60, 50, 40, 30, 20, 15, 10, 8, in the increasing order, preferably between the step of removing the substrate from contact with the destaining / deoxidation film treatment composition and the step of contacting with the cleaning liquid. It is desirable to leave the interval not to exceed 6, or 4 seconds. However, if necessary, in particular, in the case of desulfurization / deoxidation film-containing composition, which contains no persulfate and at least the most preferred amount of nitric acid, between destaining / deoxidation film treatment and washing with an aqueous solution of chelating agent. There is no loss of corrosion resistance even if the allowance is about 90 seconds. After cleaning the surface, dry the surface frequently.

The wash liquor in the characteristic process steps according to the invention comprises water, carboxyl, carboxylate, noncarboxyl hydroxyl, amino, thio, phosphonic acid, phosphonate, phosphinic acid, and phosphinate It consists of at least one chelating agent selected from the group consisting of molecules containing at least two nucleophilic groups selected from the group consisting of groups, in which at least two groups are bonded to the atoms in the molecule and the aforementioned parent in the molecule It is preferable to form a molecule at a position where a 5- or 6-membered ring can be formed by a multivalent metal atom covalently covalently bonded to a nucleophilic atom (oxygen, nitrogen, sulfur, or phosphine-based phosphorus) in each nuclear group. Do. More preferably, the chelating agent is composed of gluconic acid, tartaric acid, ethylenediamine tetraacetic acid (hereinafter simply referred to as "EDTA"), nitrilotriacetic acid (hereinafter referred to as simply "NTA"), and water-soluble salts of these acids. It is selected from the group, More preferably, it is selected from EDTA and NTA.

Regardless of the exact chemical nature of the chelating agent in the wash liquor, the total concentration of the chelating agent molecule is preferably at least 0.0003, 0.0006, 0.0009, 0.0012, 0.0016, 0.0020, 0.0025, 0.0030, 0.0035, 0.0040, 0.0045, in increasing order. Or 0.0050 mole / l, independently, preferably in an increasing order of 0.10, 0.050, 0.040, 0.030, 0.025, 0.020 or 0.015 mole / l. If the concentration of nitric acid in the destain / deoxidation film treatment composition used before washing is at least 3.0 mole / l, and the chelating agent is tartaric acid or NTA, the concentration of the chelating agent molecules in the washing liquid is preferably 0.013 in increasing order. , 0.010 or 0.0070 mole / l or less.

As in the destain / deoxidation film treatment composition, the temperature at the time of contact and the contact time between the cleaning liquid and the metal to be treated vary widely. As a general guideline the temperature is typically at least 5, 10, 15, 17, 19, 20, 21, 22, or 23 ° C., preferably in increasing order, independently, preferably in increasing order of 80, 60, 50, 40, 35, 34, 33, 32, 31, 30, 29, 28, 27 or 26 ° C. or less, and the contact time is usually 0.1, 0.5, 1.0 in increasing order. It is at least 1.5, 1.8 or 2.0 minutes and is independently 32, 20, 15, 10, 8, 7, 6, 5.5, or 5.0 minutes, preferably in increasing order. In addition, the wash liquor is contacted with the metal surface to be treated by a convenient method, some of which are known to those skilled in the art. Immersion is the simplest and most often used. However, spraying or roll coating may also be used.

It is preferable to perform the above-mentioned destaining / deoxidation film treatment and washing in accordance with the chromate conversion coating forming treatment. Such treatment, more particularly, treatment in accordance with any one of the United States patents listed below, is suitable, and all of the disclosures of these patents are referenced in the present invention except to the extent that they are inconsistent with those explicitly set forth herein. It is used as.

U.S. Pat.Nos. 5,769,967, 5,451,271, 5,399,209, 5,395,655, 5,268,042, 4,966,634, 4,749,418, 4,668,305, 4,644,029, 4,475,957,183,772,4,437,183 4,146,410, 4,131,489, 4,059,452, 3,989,550, 3,876,435, 3,681,207, 3,632,447, 3,535,168, 3,505,129, 3,505,352, 3,493,441,9,49,349,349 No. 3,404,046, 3,404,044, 3,404,043, 3,397,091, 3,397,090, 3,391,032, 3,301,031, 3,385,738, 3,380,858, 3,377,212, 307,383,307 3,214,302, 3,202,551, 3,165,596, 3,090,710, 3,032,447, 2,988,465, 2,979,935, 2,967,791, 2,928,763, 2,927,046, 2,902,285,2,852,385 2,825,697, 2,814,577, 2,798,830, 2,798,829, 2,796,370.

The preferred liquid chromate conversion coating forming (hereinafter simply referred to as "chromating") composition used in the method of or according to the method of the present invention preferably contains water and the following components:

(A ₂ ) a constant concentration of dissolved hexavalent chromium;

(B ₂ ) a constant concentration of dissolved fluorine containing anions; And optionally one or more of the following components:

(C ₂₎ the components from the immediately preceding (A ₂₎ and (B ₂₎ an alkali soluble agent that is not part of any one of;

(D ₂₎ of the immediately preceding element shown in (A ₂₎ to (C ₂₎ the dissolved neutral salts that are not part of any one of;

(E ₂₎ the components from the immediately preceding (A ₂₎ to (D ₂₎ of dissolved trivalent chromium are not part of any one of;

(F ₂ ) A lysate of a redox reaction product which produces trivalent chromium dissolved from hexavalent chromium originally present in a liquid composition, wherein the lysate is the components (A ₂ ) to ( Not part of any of E ₂ );

For convenience and economics, the most preferred source of dissolved hexavalent chromium in the chromizing liquid composition used in the present invention is also commonly referred to as "chromic acid", "chromic acid" because the overall acidic conditions in the chromizing liquid composition are also preferred. It is called the anhydride CrO _3, "or" chromium trioxide ". However, a source of hexavalent chromium such as chromate salt and dichromate salt may be used instead. Regardless of these sources, the concentrations of the hexavalent chromium atoms present in the working chromizing compositions used in or according to the method of the present invention are preferably at least 0.60, 1.0, 2.0, 3.0, 3.5, 4.0, 4.5, 5.0, or 5.4 g / l, independently, preferably up to 50, 40, 30, 20, 15, 10, 8 or 6 g / l in increasing order.

Although the necessary component (B ₂ ) is a simple fluoride, i.e., anions of hydrofluoric acid and its salts and their salts, it is preferred to contain absolutely large amounts or all of the fluoride complex, wherein the fluoride complex is represented by the general formula M _x ( OH) _y F _z [where charge is not explicitly specified but is measured by other selection methods; M is an element selected from the group consisting of boron, silicon, aluminum, iron, titanium, zirconium, hafnium, x is an integer of +, preferably 1, y is 0, 1 or 2, preferably 0, z is an integer of + having a value of at least (4-y), preferably an salt corresponding to (4-y) or (6-y)] or a salt containing an acid or anion. You have to understand.

More preferably component (B ₂ ) contains fluoroborate anion (BF ₄ ⁻ ) at a concentration stoichiometrically corresponding to the concentration of NaBF ₄ , ie preferably in increasing order of at least 1.0, 2.0, 3.0 , 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, or 7.0 g / l, independently, preferably in increasing order of 50, 40, 30, 20, 15, 13, 11, 10.0, 9.5, 9.0 , 8.5, 8.0 or 7.5 g / l or less. Furthermore, component (B ₂ ) is independently an ion selected from the group consisting of fluorosilicate, fluororotitanate, and fluororozirconate, most preferably ion of fluororozirconate Is contained in a concentration corresponding to stoichiometry (stoichiometry for the fluorine ion content of each ion) at a concentration of K ₂ ZrF ₆ , that is, at least 0,3, 0.5, 0.7, 0.9 in increasing order. , 1.1, 1.3, 1.5, 1.7, 1.9 or 2.1 g / l, independently, preferably in increasing order of 20, 15, 10, 8.0, 7.0, 6.0, 5.0, 4.5, 4.0, 3.5, 3.0, 2.6, Or 2.3 g / l or less. Irrespective of the exact concentration, the molarity of all of the fluororosilicates, fluorourotitanate, and fluorourozirconate anions preferably gives a ratio to the molar concentration of fluoroborate anions in the chromizing composition. Preferably at least 0.02: 1.0, 0.04: 1.0, 0.06: 1.0, 0.08: 1.0, 0.10: 1.0, or 0.12: 1.0 in increasing order, independently 1.0: 1.0 in increasing order , 0.70: 1.0, 0.50: 1.0, 0.40: 1.0, 0.30: 1.0, 0.25: 1.0, 0.20: 1.0, 0.18: 1.0, 0.16: 1.0, or 0.14: 1.0 or less.

If at least component (A ₂ ) is derived from chromic acid, any alkalizer component (C ₂ ) is contained in the liquid chromizing composition used in or after the method of the invention to lower the acidity of the composition. Excessive etching occurs during mating. More specifically, component (C ₂ ) is preferably selected from alkali metal hydroxides. If component (C ₂ ) consists of an alkali metal hydroxide, it is preferably stoichiometrically corresponding to the concentration of sodium hydroxide, ie preferably in increasing order of at least 0.090, 0.11, 0.20, 0.30, 0.40, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, or 0.88 g / l, independently, preferably in increasing order of 8, 6, 4.0, 3.5, 3.0, 2.5, 2.0, 1.8, 1.6, 1.2 or 1.0 g / l or less.

In addition, if at least preferred concentrations of chromic acid and alkalizer are present, the chromizing composition used in or after the method of the present invention preferably contains a neutral salt of optional component (D ₂ ). More specifically, this component preferably contains an amount of alkali metal nitrate in stoichiometric (stoichiometric to nitrate) corresponding to the concentration of sodium nitrate, ie preferably in order of increasing at least 0.2, 0.4 , 0.6, 0.8, 1.0, 1.20 or 1.35 g / l, independently, preferably up to 10, 8, 6, 5.0, 4.0, 3.0, 2.5, 2.0, or 1.5 g / l in increasing order. Furthermore, component (D ₂ ) independently preferably contains one or more chlorides in an amount corresponding to a stoichiometric (stoichiometric to chloride) correspondingly to the concentration of sodium chloride, ie preferably to increase At least 0.003, 0.006, 0.009, 0.010, 0.015, 0.020, 0.025 or 0.029 g / l in order, independently 0.20, 0.15, 0.10, 0.080, 0.070, 0.060, 0.050, 0.040, 0.035 or in increasing order independently 0.031 g / l or less.

As is known, some of the chromium initially added in the hexavalent state is preferably reduced by an organic reducing agent such as methanol, formaldehyde, sugar, starch, etc., which produces carbon dioxide as a primary oxidation product. It is reduced to trivalent state. This is a common source of components (E ₂ ) and (F ₂ ). None of these components is preferred in the chromizing composition used in or after the method of the present invention.

The present invention is particularly advantageous for the treatment of aluminum alloys 7150, 7075, 2024, 2324, and 6061, and also severely with severe shot peening or mechanically treated and / or alkaline compositions prior to treatment with the present invention. It is advantageously applied to chemically etched or chemically milled aluminum or magnesium alloy surfaces.

EXAMPLE

Although this invention is demonstrated by the following Example and comparative example, these do not limit this invention. A single liquid composition for destaining / deoxidation film treatment was prepared and used in each example, which contains each component shown in Table 1 below as the remaining components of the composition in addition to water.

TABLE 1

ingredient Concentration, mole (s) / L HNO ₃ 3.8 Fe ₂ (SO ₄ ) ₃ 0.10 Molybdenum, from (NH ₄ ) ₂ Mo ₂ O ₇ 0.0094 H ₂ SO ₄ 0.29 NH ₄ HF ₂ 0.052

Type 2024-T3 aluminum, a conventional test panel, was washed in a conventional manner and kept at 26 ° C. while immersed in the destain / deoxidation film treatment composition described above for 10 minutes. The deoxidized panel was then suspended in air for 90 seconds, dried and then immersed in a chelating agent-containing wash, or as quickly as possible within 3 seconds, while maintaining the wash at a temperature of 26 ° C., in which case It was maintained for 5 minutes at. After elapse of time in the washing solution, each panel was taken out, washed with water, and then immersed in an aqueous solution of chromizing composition containing each component shown in Table 2 in addition to water. The chromizing composition was kept at 26 ° C. for 3.0 minutes while immersed.

TABLE 2

ingredient Concentration, gram (s) / L CrO ₃ 5.5 NaBH ₄ 7.2 K ₂ ZrF ₆ 2.2 NaOH 0.89 NaNO ₃ 1.4 NaCl 0.031

After the above immersion time in the chromizing composition, each panel chromated was taken out, washed with water and dried, followed by a salt spray test according to ASTM (American Society for Testing and Materials Method) B117. Table 3 shows the composition of the wash solution, the conditions between destaining / deoxidation film treatment and washing, and the results of the salt spray test.

TABLE 3

Time between destaining / deoxidation and cleaning, seconds Chelating Agent in Washing Liquid Salt Spray Test Results type g (s) / L 168 hours 336 hours Contrast 1 <3 none Not applicable fail fail Contrast 2 90 none Not applicable fail fail Example 1 <3 NTA 1.0 pass pass Example 2 90 NTA 1.0 pass pass Example 3 <3 NTA 2.0 pass pass Example 4 90 NTA 2.0 fail fail Example 5 <3 EDTA 1.0 pass pass Example 6 90 EDTA 1.0 fail fail Example 7 <3 EDTA 2.0 pass pass Example 8 90 EDTA 2.0 fail fail Example 9 <3 Tartaric acid 1.0 pass pass Example 10 90 Tartaric acid 1.0 fail fail Example 11 <3 Tartaric acid 2.0 pass pass Example 12 90 Tartaric acid 2.0 Pass / Fail Pass / Fail Example 13 <3 Gluconic Acid 1.0 pass pass Example 14 90 Gluconic Acid 1.0 fail fail Example 15 <3 Gluconic Acid 2.0 pass pass Example 16 90 Gluconic Acid 2.0 fail fail

NOTE Two sets of five test panels were tested under each condition shown in the table. In each example except Example 12, the two sets of panels showed the same results in the salt spray test. In Example 12 the treatment was done as nearly as possible, but one set of panels was pass and one set was rejected.

The concentrations of each chelating agent shown in Table 3 were extremely effective in improving the corrosion resistance in each conventionally treated panel that was quickly shifted between destaining / deoxidation film treatment and washing operation in the method of the present invention. Even though there was a 90 second interval between them, lower NTA concentrations were effective.

As described above, the present invention contributes to the technical field by increasing the corrosion resistance of aluminum and / or magnesium by washing with a washing liquid in which a chelating agent is added to water between the deoxidation film process and the chemical conversion process of the treatment process. It is expected to be large.

Claims (1)

Before chromating aluminum and magnesium, (1) the object to be treated is brought into contact with a stain removing agent or a deoxidation film treatment agent over a predetermined time; (2) In the pretreatment method in which the processed material is taken out of the above-described processing agent, and then the processed object is brought into contact with the washing liquid within a predetermined time to be in contact over a predetermined time, the washing liquid containing at least one chelating agent added to water is Using the method.