ES2238058T3 - USE OF MOLIBDATE IN A COLMATATE PROCEDURE OF AN OXIDE LAYER OBTAINED BY ALUMINUM ANODIZATION. - Google Patents

Abstract

The consolidation by hydration of the oxide layer obtained by anodization of aluminium or aluminium alloy is carried out in bath under the following conditions: (a) base of the bath: dematerialized water containing 1 to 5 g/l of an anti-corrosion agent with a molybdenum oxide (MoO3) base; (b) bath temperature: 90 - 100[deg]C; (c) duration of immersion: 20 - 60 minutes; (d) pH of the bath: 6 +- 1; (e) the time and the temperature being in inverse relation; (f) the method allowing a rate of hydration of between 10 and 30%, preferably between 15 and 25%. An independent claim is also included for the preparation of anodized and consolidated aluminium or aluminium alloy components in which the consolidation is carried out by the inventive method.

Description

Use of molybdate in a procedure of clogged with an oxide layer obtained by anodizing aluminum.

The present invention relates to a filling process by hydration of the oxide layer obtained by anodizing aluminum or an aluminum alloy, devoid of hexavalent chromium.

Aluminum alloys are, despite the development of the compounds, the most used materials in Aircraft and helicopter cells. Therefore, they continue the main concerns being protection against corrosion and gluing assembly of these materials.

Currently, to answer these needs, wet surface treatments such as For example, anodization are the most widespread. To improve the corrosion resistance of anodized aluminum alloys, It is necessary to incorporate a stage called "colmatado". This operation involves transforming alumina cells anhydrous in monohydrated alumina of formula Al 2 O 3, nH 2 O by simple immersion in pure water at 100 ° C. Alumina hydrated then has a volume 33% higher than alumina anhydrates what causes the "clogging" of the pores.

The addition of chromates to clogged water It allows to reinforce the corrosion resistance of the film. In effect, chromate ion is one of the most corrosion inhibitors effective for aluminum. Inhibition is due to formation in the metal surface of a protective film formed by the Chromate ion reduction.

But it is already known that the chromate ion could be both toxic and carcinogenic. Taking into account these possible risks to the environment and health, a series of restrictions have to be applied regarding the use of such
Market Stall.

Due to these risks, the inventors have Aiming to find a non-harmful chromium substitute hexavalent, maintaining the properties of resistance to corrosion of the material and its adhesion capacities with respect to Paint systems

Numerous studies have been carried out to date to try to replace hexavalent chromium. Thus, it has been mentioned, the use of rare earth salts (Shih H. et al. , ASTM Spec. Tech. Publ. (1992), 1134 , 180-195), as well as the use of diluted vanadate solutions or the formation of a zirconium oxide on the surface of the material (Hinton BRW, Metal Finishing (1991), 9 , 55-61).

Many of these different compounds are used in the presence of a polymer to surface form a resin capable of having good protective properties (Hinton BRW, Metal Finishing (1991), 10 , 15-20).

The patent JP-A-02 025592 describes a process of filling an aluminum oxide layer obtained by anodization. The bath of colmatado is an aqueous solution of molybdate containing a benzotriazole or a tolitriazole and the Molybdate used can be Na2 MoO4 or K2 MoO4 at a concentration preferably between 500 and 5,000 ppm, ie 0.5 and 5 g / l. No pH values have been specified, duration of immersion or hydration rates.

Now the inventors have discovered, surprisingly, that molybdenum oxide could be used as a replacement product for hexavalent chromium in the procedure of colmatado.

Also, the invention aims at a filling process by hydration of the oxide layer obtained by anodizing aluminum or an aluminum alloy, being the bath of colmatado realized in the following terms:

-

base Bath: demineralized water containing an anti-corrosion agent based on molybdenum oxide (MoO3) at a rate of 1 to 5 g / l of molybdenum oxide,

-

bath temperature: 90-100 ° C,

-

immersion duration: 20-60 minutes, and

-

pH of bathroom: 6 +/- 1,

time and temperature are inversely related and the aforementioned procedure allows a proportion of hydration between 10 and 30%, preferably between 15% and 25%

In the sense of the present invention, the hydration ratio mass represents the amount of water fixed during clogging with respect to the total mass of the coating (alumina + water).

In a preferred embodiment of the invention, molybdenum oxide is present in salt form, preferably in the form of sodium molybdate, potassium or ammonium, or in the form of a complex, preferably in the form of a complex of amine and molybdic acid.

In an even more advantageous embodiment of the invention, molybdenum oxide is present in the form of ammonium molybdate Ammonium molybdate can be used or either directly in the form of a salt that contains 85% MoO_ {3} or in the form of pure molybdenum oxide by adding ammonia according to the following equation:

\hskip0.5cm

+

\hskip0.5cm

6 NH_{4}OH

\hskip0.5cm

\rightarrow

\hskip0.5cm

(NH_{4})_{6}Mo_{7}O_{24}

\hskip0.5cm

+

\hskip0.5cm

3 H_{2}O7 MoO_ {3}

 \ hskip0.5cm 

+

 \ hskip0.5cm 

6 NH4OH

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\ rightarrow

 \ hskip0.5cm 

(NH 4) 6 Mo 7 O 24

 \ hskip0.5cm 

+

 \ hskip0.5cm 

3 H2O

Particularly advantageously, the clogging procedure is performed in the following terms:

-

base Bath: demineralized water containing an anti-corrosion agent based on molybdenum oxide (MoO3) at a rate of 3.6 g / l of oxide of molybdenum, 0.75 g / l of ammonia and 3 g / l of acetate ammonium,

-

bath temperature: 97 ° C,

-

immersion duration: 40 minutes

The pH of the baths used in the procedure according to the invention is stabilized at 6 +/- 1 by addition of a buffer salt such as, for example, acetate ammonium.

The filling process according to the invention It can be used on pure aluminum or alloys of Aluminum type 2024 T3, 5086 or 7075 T73 previously anodized according to a conventional anodizing method, such as sulfuric, chromic, alkaline or anodizing methods sulfoboric

The invention also aims at a Manufacturing process of aluminum or alloy parts anodized and clogged aluminum characterized in that the bath of colmatado is performed under the following conditions:

-

base Bath: demineralized water containing an anti-corrosion agent based on molybdenum oxide (MoO3) at a rate of 1 to 5 g / l of molybdenum oxide,

-

bath temperature: 90-100 ° C,

-

immersion duration: 20-60 minutes, and

-

 pH of the bathroom: 6 +/- 1,

Time and temperature are inversely related and said procedure allows a proportion of hydration between 10 and 30%, preferably between 15 and 25%

The pieces obtained after clogging according to The present invention has a very good resistance to corrosion, between 500 and 750 hours and the proportions of hydration correspond to those observed with a clogged classic in the presence of hexavalent chromium. On the other hand, the paint system offers perfect adhesion as well as a excellent behavior against salt spray corresponding which is obtained with chromic oxidation followed by a clogged with hexavalent chromium.

The following examples illustrate the invention.

1. Measured characteristics 1.1. Corrosion resistance

It is measured by the salt spray test according to ISO 9227-NSS

1.2. Hydration ratio

The hydration rate measurement is performed by a gravimetric measurement of the hydration of the coating.

1.3. Non-destructive tests on anodization chrome

The thickness of the layer is measured by a test according to ISO 2360; colmatado is measured by the method of absorption of dyes referenced NF A 91408, and continuity The layer is measured by the ISO 2085 reference test.

1.4. Adhesion of a polyurethane paint system flexible

The adhesion of the paint has been measured according to the technique described by the PRC-De Soto company that includes the successive applications of a primary hooking layer P99, to phenolic butyral base, followed by the application of a primary anticorrosion PAC 33, followed by a layer of PU 66 based finish of polyurethane; the aforementioned denominations are Trademarks of the company PRC-De Soto.

The first layer has a thickness of 4 to 11 um, the total of the first two layers have a thickness of 14 to 29 µm, and the total of the three layers a thickness of 39 to 64 \ mum.

A "Q + S" adhesion test according to the ISO 2409-1976 is valued after 14 days of immersion in water

1.5. Corrosion resistance of the oxidation system chromic anodic (OAC) + paint

A cross-shaped scratch is carried out on the protection and the exposed part is left for 3,000 hours.

2. Essays

First test

A pilot line with 250 vats is used l volume; The alloy used is the 2024 T3 shaped alloy of a specimen of dimensions 120 x 60 x 08 mm, raw rolling. After degreasing and rinsing, the specimens are anodized for about 40 minutes to an hour in a bath that contains 35 to 60 g / l chromic acid under a strain between 5 and 90 volts and a current density electric 0.5 to 50 amps / cm2. The anodized piece is rinsed for about 2 minutes and immersed in a bath clogged containing either 85% ammonium molybdate MoO 3 added directly to the bath, or ammonium molybdate prepared by adding ammonia in MoO3 according to the equation:

\hskip0.5cm

+

\hskip0.5cm

6 NH_{4}OH

\hskip0.5cm

\rightarrow

\hskip0.5cm

(NH_{4})_{6}Mo_{7}O_{24}

\hskip0.5cm

+

\hskip0.5cm

3 H_{2}O7 MoO_ {3}

 \ hskip0.5cm 

+

 \ hskip0.5cm 

6 NH4OH

 \ hskip0.5cm 

\ rightarrow

 \ hskip0.5cm 

(NH 4) 6 Mo 7 O 24

 \ hskip0.5cm 

+

 \ hskip0.5cm 

3 H2O

The duration of the immersion in the bathroom Colmatado is 20 minutes and the temperature of the bath is 97ºC.

The results are presented in Table 1 next.

TABLE 1

one

There is a good behavior against the corrosion between 550 and 650 hours with the two types of derivatives of Molybdenum oxide and hydration of approximately 30%. The test Dye absorption shows that the clogging is complete.

Second test

The conditions are the same as in the first assay, but the pH is buffered to 6 with ammonium acetate. This test has been performed as in the first trial using MoO 3 + NH 4 OH with a MoO 3 concentration of 1 g / l or 3.6 g / l, the bath temperature being 85 or 97 ° C. The Results are presented in Table 2 below.

TABLE 2

2

There is a very good behavior against salt spray between 500 and 700 hours and about hydration ratios greater than 20% corresponding to the that are observed with the classic clogged.

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Third test

The clogged bath comprises 3.6 g / l of MoO 3 to which ammonia NH 4 OH and acetate have been added ammonium. The bath temperature is 97ºC and the immersion time It is 40 minutes. The specimens used are 2024 T3 specimens and 7075 T7.

A paint system has been applied on two test tube series:

P99 + PAC 33 \ times 2 + PU 66 (ref. 5440/2047)

A series of test pieces is used to measure the paint adhesion and the other is used to evaluate the resistance to corrosion

The results are grouped in the two tables 3 and 4 following:

TABLE 3

3

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TABLE 4

4

There is a good behavior against the salt spray with 2024 T3 alloy and performance satisfactory with the 7075 T7 alloy which is by nature very corrosion sensitive.

The proportion of hydration, the thickness of the layer, the continuity of the layer and the absorption tests of Coloring are compliant.

The paint system offers adhesion perfect before and after water immersion, as well as a Excellent behavior against salt spray.

The aforementioned results show that the Molybdenum can be used as a chrome replacement element hexavalent in some baths of colmatado.

The parts treated by the procedure of the invention has a thickness, a continuity of layer, a absorption of dyes identical to those obtained after chromic anodization and clogging with hexavalent chromium.

The corrosion resistance measured by the behavior against salt spray is completely satisfactory and much more than 500 hours of exposure.

On the other hand, the paint system offers a perfect adhesion as well as excellent behavior against the salt spray also corresponding to that obtained after chromic oxyanodization and hexavalent chromium filling.

Claims (5)

1. Colmatado procedure by hydration of the oxide layer obtained by anodizing aluminum or an aluminum alloy, characterized in that the bath of colmatado is carried out under the following conditions:

-

base Bath: demineralized water containing an anti-corrosion agent based on molybdenum oxide (MoO3) at a rate of 1 to 5 g / l of molybdenum oxide,

-

bath temperature: 90-100 ° C,

-

immersion duration: 20-60 minutes,

-

pH of bathroom: 6 +/- 1,

time and temperature being in relation inverse and allowing said system a proportion of hydration between 10 and 30%, preferably between 15 and 25%. 2. The filling process according to claim 1, characterized in that the molybdenum oxide is present in the form of a salt, preferably in the form of sodium, potassium or ammonium molybdate or in the form of a complex, preferably in the form of a complex of Amine and molybdic acid. 3. The filling process according to claim 1, characterized in that the molybdenum oxide is present in the form of ammonium molybdate. 4. Colmatado method according to claim 1, characterized in that the colmatado bath is carried out under the following conditions:

-

base Bath: demineralized water containing an anti-corrosion agent based on molybdenum oxide (MoO3) at a rate of 3.6 g / l of oxide of molybdenum, 0.75 g / l of ammonia and 3 g / l of acetate ammonium,

-

bath temperature: 97 ° C, and

-

immersion duration: 40 minutes

5. Procedure for preparing anodized and clogged aluminum or aluminum alloy parts, characterized in that the clogging is carried out according to any one of claims 1 to 4.