GB2146042A

GB2146042A - Treating anodized aluminium

Info

Publication number: GB2146042A
Application number: GB08425023A
Authority: GB
Inventors: Hiroshi Watanabe; Isao Shimamura; Masao Abe; Masashi Mizusawa
Original assignee: Pilot Pen Co Ltd; Pilot Man Nen Hitsu KK
Current assignee: Pilot Corp
Priority date: 1983-07-15
Filing date: 1984-10-04
Publication date: 1985-04-11
Also published as: JPS6021397A; GB8425024D0; GB2146042B; GB8425023D0; GB2146043B; GB2146043A

Abstract

A method for surface treatment of aluminium or aluminium alloys comprises treating aluminium or an aluminium alloy having an anodically oxidized film according to the steps of: (1) dipping in a first solution containing at least one salt selected from calcium salts, magnesium salts, barium salts, strontium salts, zinc salts, lead salts, titanium salts and aluminium salts; and (2) subsequently electrolyzing with a second solution containing one or more substances which react with the product from said salt in the micropores of the anodically oxidized film to be converted into a white or grayish white compound. o

Description

SPECIFICATION Surface treatment of aluminium or aluminium alloys The present invention relates to a surface treatment method, which comprises forming a white or grayish white substance in micropores of the anodically oxidized film of aluminium or aluminium alloy.

In the prior art, aluminium and aluminium alloys have been widely used as, for example, construction materials, name-plates, vehicles, decorative materials, etc., with colouration according to various materials. The colour tones have been, for example, metallic colour tones in construction materials, giving cold impressions, such as amber colour, gold colour, and silver colour. Therefore, aluminium and aluminium alloys in the field of construction materials which are of warm pastel colour tone on a base of opaque white colour or grayish white colour have been desired.

In order to realize a pastel colour tone, it is necessary to obtain a base colour of opaque white colour or grayish white colour, and for this purpose several methods of surface treatment for opaque whitening have been proposed.

That is, examples of methods for forming opaque white anodically oxidized films are as follows: (1) The method in which an aluminium material is subjected to whitening on its surface by alternating current electrolysis, direct-current electrolysis, or dipping (as disclosed in Japanese Patent Publications No. 28921/1965 and No. 1523/1966); (2) The method in which an opaque white anodically oxidized film is obtained according to a primary electrolytic method (e.g., the Ematal method as disclosed in Japanese Patent Publications No. 28147/1979 and No. 28148/1979); (3) The method, in which, after application of an anodically oxidized film, secondary electrolysis is carried out to obtain an opaque white anodically oxidized film (as disclosed in Japanese Patent Publications No. 14519/1960 and No. 11248/1979, and Japanese Laid-open Patent Application No. 37631/1975).

However, these methods involve the following problems. The chemical reagent employed is expensive or is a toxic substance, or its solution is unstable or requires a high bath voltage. Also, the extent of opaque whitening obtained is insufficient in practical application. Thus, under the present circumstances, coating methods are actually employed in place of these methods.

We have carried out research on the method for colouration of aluminium or aluminium alloys to a tone based on opaque white or grayish white and have found that forming a white or grayish white substance in the pores of an anodically oxidized film according to the method described below, is very effective as a method for obtaining a basic opaque white or grayish white colour.

It has been found that a white or grayish white substance can be formed in a high concentration not found in the prior art in the pores of an anodically oxidised film of aluminium or an aluminium alloy by dipping, as a first step, aluminium or an aluminium alloy having an anodically oxidized film in a solution containing a specific salt such as for example a calcium salt or electrolyzing with said solution, thereby causing the product from this salt to enter into the micropores of the anodically oxidized film, and then, in a subsequent, second step, dipping the product from the first step in a solution containing a substance which reacts with the product from the salt to be converted into a white or grayish white compound carrying out electrolysis with the solution.The term "product from the salt" as used herein refers to a compound containing the metal of the salt, the metal per se or the salt per se and is used in this meaning in the present specification and claims.

Thus, the present invention provides a method for surface treatment of aluminium or aluminium alloys, which comprises treating an aluminium or an aluminium alloy article having an anodically oxidized film according to the following two steps (1) and (2): (1) a step of dipping the article in a first solution containing one or more salts selected from calcium salts, magnesium salts, barium salts, strontium salts, zinc salts, lead salts, titanium salts and aluminium salts or electrolyzing with the first solution; and (2) a subsequent step of dipping the article in a second solution containing one or more substances which react with the product from the above-mentioned salt in the micropores of the anodically oxidized film to be converted into a white or grayish white compound or electrolyzing with the second solution.

By dipping, in the first step, aluminium or an aluminium alloy applied with an anodically oxidized film in a first solution containing one or more salts selected from calcium salts, magnesium salts, barium salts, strontium salts, zinc salts, lead salts, titanium salts and aluminium salts or electrolyzing with the first solution, the product from the salt is caused to enter into the micropores of the anodically oxidized film. The electrolysis may be carried out according to direct-current electrolysis, alternating-current electrolysis or electrolysis by a current with a waveform having the same effect as a direct-current or alternating-cu rrent.

A waveform having the same effect as a direct current or alternating current as herein mentioned is inclusive of, for example, AC-DC superimposing waves, DC or AC intermittent waves, PR waves, pulse waves, incomplete rectified waves, etc., including also waveforms which are combinations of these. Further included is a waveform of the so-called current restoration method, in which the voltage is changed in carrying out electrolysis with the above waveforms.

In the subsequent second step, the treated product from the first step is dipped in a second solution containing one or more substances which react with the product from the salt to be converted into a white or grayish white compound, or electrolysis is carried out with the second solution. The substance which reacts with the product from the salt to be converted to a white or grayish white compound has, for example, as its principal ingredient, a substance as set forth below.

First, examples of inorganic substances are: inorganic acids such as sulphuric acid, phosphoric acid, nitric acid, hydrochloric acid, hydrofluoric acid, and sulphamic acid; alkali salts and ammonium salts of the above inorganic acids such as sodium phosphate, sodium fluoride, and ammonium fluoride; alkali hydroxides such as sodium hydroxide and potassium hydroxide; alkali carbonates such as sodium carbonate and potassium carbonate; alkalis having an acid group such as sodium metasilicate, sodium orthosilicate, trisodium phosphate, sodium stagnate, potassium stagnate, sodium metaborate, and sodium pyrolate; and ammonia water.

Examples of organic substances are: aliphatic acids such as oxalic acid and acetic acid; salts of such aliphatic acids such as ammonium oxalate; amines such as monoethanol amine, diethanol amine, and triethanol amine; aliphatic sulphonic acids such as ethylsulphonic acid; aromatic acids such as benzoic acid; aromatic sulphonic acids such as cresol sulphonic acid, phenol sulphuric acid, tuluene sulphonic acid, and sulphosalicylic acid. In the case of organic substances, some of the derivatives and substituted compounds of substances as enumerated above may have similar actions.

By dipping the product in a second solution containing one or more of these substances or carrying out electrolysis with this solution, these substances are caused to react with the product from the salt introducted into the micropores by the electrolysis in the first step to form a white or grayish compound in the micropores. If necessary, this step is followed by a post-treatment such as conventional pore sealing or drying. The waveform in the electrolysis to be applied in this case can be the same as in the first step.

Examples of the calcium salt to be used in the electrolysis in the first step are calcium nitrate, calcium chloride, calcium acetate, calcium bromide, and calcium iodide. Examples of barium salts are barium nitrate, barium chloride, barium acetate, barium bromide, and barium iodide. Magnesium salts may be, for example, magnesium nitrates, magnesium chloride, magnesium acetate, magnesium bromide, magnesium iodide, and magnesium sulphate. Strontium salts may include, for example, strontium nitrate, strontium chloride, strontium acetate, strontium bromide, and strontium iodide. As zinc salts, there are for example, zinc sulphate, zinc nitrate, zinc chloride, zinc acetate, zinc bromide, and zinc iodide. Typical examples of lead salts, are lead nitrates, lead chloride, and lead acetate.Suitable aluminium salts are, for example, aluminium sulphate, sodium aluminate, aluminium phosphate, aluminium chloride, and aluminium oxalate. Examples of titanium salts are titanium sulphate and titanium potassium oxalate.

In the first step, the aforesaid salt is contained in a concentration of about 1 g/litre to saturation, preferably about 10 to 50 g/litre. The conditions of dipping in this solution are 20 to 80"C, preferably 40 to 650C, for the liquid temperature, and about 1 to 50 minutes, preferably about 10 to 30 minutes, for the dipping time.

The electrolysis conditions in this first solution, in the case of direct-current electrolysis, with the use of aluminium or an aluminium alloy as the cathode, are about 5 to 50 V, preferably about 10 to 25 V, for the voltage, about 10 to 500C, preferably about 15 to 30"C, for the liquid temperature, and about 30 seconds to 30 minutes, preferably about 3 to 10 minutes, for the time. In the case of alternating-current electrolysis, the voltage, the liquid temperature and the time are the same as in direct-current electrolysis.

On the other hand, the second solution containing the aforesaid substance used in the second step contains the substance in a concentration of about 0.5 g/litre to 200 g/litre, preferably about 1 to 50 g/ litre. The dipping conditions in this solution are 10 to 80"C, preferably 30 to 600C, for the liquid temperature, and about 30 seconds to 50 minutes, preferably about 10 to 30 minutes, for the dipping time.

The electrolysis conditions in this second solution, in case of direct-current electrolysis, with the use of aluminium or an aluminium alloy as the cathode, are about 5 to 40 V, preferably about 10 to 30 V, for the voltage, about 10 to 40"C, preferably about 20 to 30"C, for the liquid temperature, and about 30 seconds to 20 minutes, preferably about 3 to 10 minutes, for the time. In the case of alternating-current electrolysis, the voltage, the liquid temperature and the time are the same as indirect-current electrolysis.

Thus, according to the present invention, a white or grayish white product can be obtained in the pores of the film, and the density of the product is shown as the white colour density of the anodically oxidized film finally obtained in Table 1, as compared with those of the prior art.

TABLE 1 Sample White Colour Density White film of invention Very good White coating, white porcelain Very good White film of the prior art Slightly inferior Silver-finished anodically oxidized film (silver aluminium sash), aluminium coin of 1 yen Not white (metallic colour Further, as another advantage of the present invention, the liquid conditons (liquid composition, pH, temperature, etc.) and the electrolytic conditions (current, voltage, waveform, etc.) in the first step can be chosen from wide ranges because the form of the aforesaid substance in the micropores is note restricted to a narrow range, and the substance is only required to be introduced more deeply and in greater quantity into the micropores.Also, the liquid conditions the treatment conditions (electrolytic conditions, dipping conditions) in the second step can be chosen from very wide ranges because it is only basically required that the chemical, electrochemical reaction between the aforesaid substance in the micropores and the liquid component can be carried out sufficiently to form a white or grayish white insoluble compound. Of course, there are suitable combinations of the first step and the second step, which are so many in number for the wide ranges of choice and cannot be enumerated here but can be determined easily by those skilled in the art by routine experimentation.

Furthermore, it is also possible to add to each solution in the first step and the second step various additives such as a pH buffering agent, surfactant, reaction accelerator, and reaction inhibitor, whereby the efficiency of formation of the white colour or grayish white substance as well as various properties such as the stability of the solution can be improved.

Still another salient feature to be noted in the present invention is that a pastel tone colouration with a base tone of opaque white or grayish white can be obtained by combination with various aluminium colouration methods already known in the art. Examples of the combinations of the step for colouration in the present invention and the aluminium colouration methods which can be adopted are listed in Table 2.

A: Aluminium alloy self-colouring method (Japanese Patent Publication No. 16341/1974 and others) B: Electrolytic self-colouring method (Kalcolor method and others) C: Electrolytic colouring method, Multi-step electrolytic colouring method (Japanese Patent Publication Nos. 1715/1963 and 67043/1974, and others) D: Inorganic or organic dip colouring, inorganic alternate dip colouring method E:Coating method (electrodeposition method) TABLE 2 Steps for Colouration Adoptable Colouration Methods Simultaneous with the anodic oxidation treatment A, B Between the anodic oxidation treatment and the electrolytic treatment in the first step C, D Between the electrolytic treatment in the first step and the treatment in the second step C, D simultaneous with the treatment in the second step C, D After the treatment in the second step C, D, E As shown in Table 2, the present invention can be combined with many colouration methods, whereby the provision of coloured materials of aluminium or an aluminium alloy adapted for the requirements in the market, coloured in pastel colour tone with warm tinctures based on opaque white or grayish white colour, such as cream colour, beige colour, ivory colour, and cherry colour can be realized.Realization of a colour tone with tincture of pastel tone according to such combinations of various colouration methods of aluminium or an aluminium alloy with the present invention can be made possible practically with ease according to the present invention. Accordingly, it can be stated here that the present invention is basically applicable or utilizable for all of these combination methods, irrespective of the difference in the steps or stages of such combinations.

The present invention is further illustrated by the following Examples. In all of these Examples, preparations of opaque coloured films by application of the present invention are illustrated, but the descriptions are made primarily of the portion concerning the present invention, and description of conventional pre-treatments or post-treatments are omitted.

The aluminium plate of JIS (Japanese Industrial Standard) A 1100P, the extruded aluminium material of JIS A 6063 and the aluminium plate of JIS A 5052 used in these Examples have compositions or purities as shown below.

JIS A 1100P Al 99 % or more Si + Fe 0.1 % or less Zn 0.1 % Cu 0.05 - 0.2 % Mn 0.05 % or less JIS A 6063 JIS A 5052 Mg 0.45 - 0.9 % Cu 0.1 % Fe 0.35 % or less Si 0.45 % Cu 0.1 % or less Fe 0.45 % Si 0.2 - 0.6 % Mn 0.1 % Mn 0.1 % or less Mg 2.2 - 2.8 % Zn 0.1 % or less Zn 0.1 % Cr 0.1 % or less Cr 0.15 - 0.35 % Al remainder Al remainder Example 1 An aluminium plate of JIS A 1100P was subjected to the pre-treatments of defatting, etching and smut removal, and then coated with an anodically oxidized film by direct-current electrolysis in an aqueous 15% sulphuric acid solution with a current density of 1.5 A/dm2 for 30 minutes, which was followed by electrolysis in an aqueous 30 gllitre solution of calcium acetate (30 "C) with an alternating-current voltage of 20 V for 10 minutes. After washing the plate with water, electrolysis was carried out in an aqueous 30 g/litre solution of phosphoric acid (30 "C) with an alternating-current voltage of 20V for 10 minutes to obtain an opaque white film on the surface of the aluminium plate.

Example 2 The same treatment as in Example 1 was applied to the extruded aluminium material of JIS A 6063, and then electrolysis was carried out with an aqueous 10 litre solution of barium acetate (30 "C) with a direct-current voltage of 15 V for 2 minutes. After washing the material with water, electrolysis was carried out with an aqueous 10 litre solution of sulphuric acid (30 "C) with an alternating-current voltage of 20 V for 20 minutes to obtain an opaque white film on the surface of the extruded aluminium material.

Example 3 The same treatment as in Example 1 was applied to the aluminium plate of JIS A 1100P, and then electrolysis was carried out with an aqueous 10 g/litre solution of zinc sulphate (25 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing the plate with water, electrolysis was carried out with an aqueous 20 g/litre solution of oxalic acid (30 5C) with a direct-current voltage of 15 V for 20 minutes to obtain an opaque grayish white film on the surface of the aluminium plate.

Example 4 The same treatment as in Example 1 was applied to the aluminium plate of JIS A 1100P, and then electrolysis was carried out with an aqueous 10 g/litre solution of lead acetate (25 "C) with a direct-current voltage of 15 V for 2 minutes. After washing the plate with water, the treated product was dipped in an aqueous 10 g/litre solution of ammonium fluoride (40 "C) for 20 minutes to obtain an opaque grayish white film on the surface of the aluminium plate.

Example 5 The same treatment as in Example 1 was applied to the aluminium plate of JIS A 1100P, and then electrolysis was carried out with an aqueous 10 g/litre solution of barium chloride (30 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing the plate with water, electrolysis was carried out with an aqueous 30 g/litre solution of ammonium oxalate (25 "C) with a direct-current voltage of 15 V for 15 minutes to obtain an opaque white film on the surface of the aluminium plate.

Example 6 The same treatment as in Example 1 was applied to the aluminium plate of JIS A 1100P, then electrolysis was carried out with an aqueous 10 g/litre solution of strontium iodide (25 "C) with a direct-current voltage of 15 V for 2 minutes. After washing the plate with water,the treated product was dipped in an aqueous 30 g/litre solution of trisodium phosphate at 40 C for 20 minutes to obtain an opaque white film on the surface of the aluminium plate.

Example 7 The same treatment as in Example 1 was applied to the aluminium plate of JIS A 1100P, and then electrolysis was carried out with an aqueous 30 g/litre solution of magnesium nitrate (30 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing the plate with water, the treated product was dipped in an aqueous 30 g/litre solution of sodium carbonate (40 "C) for 20 minutes to obtain an opaque white film on the surface of the aluminium plate.

Example 8 An anodically oxidized film was formed on an aluminium plate of JIS A 1100P in the same manner as in Example 1, and electrolysis was carried out with a coloured liquid containing 4 g/litre of stannous sulphate and 15 g/litre of sulphuric acid (25 "C) with an alternating-current voltage of 15 V for 3 minutes to impart an olive colour to the plate. After washing the plate with water, electrolysis was carried out with an aqueous 10 g/litre solution of calcium acetate (30 "C) with alternating-current voltage of 20 V for 5 minutes. After washing the plate with water, the treated product was dipped in an aqueous 10 g/litre solution of trisodium phosphate (40 "C) for 20 minutes to obtain an opaque beige film on the surface of the aluminium plate.

Example 9 An anodically oxidized film was formed on an aluminium plate of JIS A 1100P in the same manner as in Example 1, and electrolysis was carried out with an aqueous solution of 5 g/litre of sodium selenite and 15 g/litre of sulphuric acid (25 C} with an alternating-current voltage of 15 V for 3 minutes to impart a gold colour to the plate. After washing the plate with water, electrolysis was carried out with an aqueous 10 g/litre solution of magnesium sulphate (30 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing the plate with water, the treated product was dipped in an aqueous 10 g/litre solution of phosphoric acid (40 "C) for 20 minutes to obtain an opaque cream film on the surface of the aluminium plate.

Example 10 An anodically oxidized film was formed on an aluminium plate of JIS A 1100P in the same manner as in Example land the plate was dipped in a dye bath containing 2.5 g/litre of Almalite Gold 108 (dye produced by Kaname Shokai, Japan) (50 "C) for 5 minutes to impart a gold colour to the plate. After washing the plate with water, electrolysis was carried out with an aqueous 10 g/litre solution of aluminium sulphate (30 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing the plate with water, the treated product was dipped in an aqueous 30 g/litre solution of sodium carbonate (40 "C) for 20 minutes to obtain an opaque cream film on the surface of the aluminium plate.

Example ii An aluminium plate of JIS A 1100P was subjected to the pre-treatments of defatting, etching and smut removal, and then an anodically oxidized film self-coloured with a pale bronze colour was formed by direct-current electrolysis in an aqueous solution of 100 g/litre of sulphosalycilic acid and 0.5 g/litre of sulphuric acid (20 "C) with a current density of 3 A/dm2 for 30 minutes, which was followed by electrolysis in an aqueous 10 g/litre solution of titanium sulphate (30 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing with water, the product was dipped in an aqueous 20 g/litre solution of phosphoric acid (40 "C) to obtain an opaque beige film on the surface of the aluminium plate.

Example 72 The opaque white film obtained in Example 7 was subjected to pore sealing with an aqueous solution containing 3 g/litre or more of nickel acetate at 95 "C or higher temperature to obtain a film coloured in opaque, pale green colour.

Example 13 An aluminium plate of JIS A 5052 was coated with a yellow anodically oxidized film similarly as in Example 1 and thereafter electrolysis was carried out with an aqueous 10 g/litre solution of calcium acetate (30 "C) with an alternating-current voltage of 20 V for 5 minutes. After washing with water,the treated plate was dipped in an aqueous 30g/litre solution of sodium carbonate (40 "C) for 20 minutes to obtain an opaque cream film on the surface of the aluminium plate.

Example 14 The opaque white film obtained in Example 1 was washed with water and with hot water, and then subjected to electrophoretic coating treatment with an electrodeposition paint "Honeylite" containing acryl-melamine as the main component produced by Honey Kasei Co., Japan, at a liquid temperature of 22 "C with a direct-current voltage of 170 V for 3 minutes, which was followed by baking treatment, to obtain an opaque white composite film.

Example 15 The opaque white film obtained in Example 1 was washed with water, and electrolysis was carried out with a solution containing 15 gilitre of sulphuric acid and 5 g/litre of sodium selenite (25 "C) with an alternating-current voltage of 15 V for one minute, to obtain an opaque cream film on the surface of the aluminium plate.

Example 16 An anodically oxidized film was formed on an aluminium plate of JIS A 1100P in the same manner as in Example 1, and electrolysis was carried out with an aqueous 20 g/litre solution of calcium sulphate (30 "C) with an alternating- current voltage of 20 V for 5 minutes. After washing with water, electrolysis was carried out with an aqueous solution containing 15 g/litre of sulphuric acid and 5 g/litre of sodium selenite (25 "C) with an alternating-current voltage of 15 V for 1 minute. After washing with water, the treated product was dipped in an aqueous 20 g/litre solution of phosphoric acid (40 "C) for 15 minutes to obtain an opaque, white film on the surface of the aluminium plate.

Example 17 An anodically oxidized film was formed on an aluminium plate of JIS A 1100P in the same manner as in Example 1, and electrolysis was carried out with an aqueous 10 g/litre solution of calcium acetate (25 "C) with a direct-current voltage 15 V for 1 minute. After washing with water, the product was dipped in an aqueous 10 g/litre of ferric ammonium oxalate (50 "C) for 10 minutes. After washing with water, the treated product was dipped in an aqueous 30 g/litre solution of sodium carbonate (40 "C) for 15 minutes to obtain an opaque pale yellow film on the surface of the aluminium plate.

Example 18 An anodically oxidized film was formed on an aluminium plate of JIS A 1100P in the same manner as in Example 1, and electrolysis was carried out with an aqueous 20 g/litre solution of calcium acetate (30 "C) with a direct-current voltage 15 V for 1 minute. After washing with water, electrolysis was carried out with an aqueous solution of 5 litre of sodium selenite and 15 g/litre of sulphuric acid (30 "C) with an alternating-current voltage of 18 V for 20 minutes to obtain an opaque pale cream film on the surface of the aluminium plate.

Example 19 An aluminium plate of JIS A 1100P was subjected to the pre-treatments of defatting, etching and smut removal, and then coated with an anodically oxidized film by direct-current electrolysis in an aqueous 15% sulphuric acid solution was a current density of 1.5 A/dm2 for 30 minutes, which was followed by dipping in an aqueous 50 g/litre solution of aluminium sulphate (60 "C) for 20 minutes. After washing with water, the treated product was dipped in an aqueous 20 g/litre solution of phosphoric acid (40 "C) for 20 minutes to obtain an opaque white film on the surface of the aluminium plate.

Example 20 The same treatment as in Example 1 was applied to an extruded aluminium material of JIS A 6063, and then the plate was dipped in an aqueous 20 g/litre solution of calcium acetate (60 "C). After washing with water, electrolysis was carried out with an aqueous 30 g/litre solution of sulphuric acid (35 "C) with an alternating-current voltage of 20 V for 20 minutes to obtain an opaque white film on the surface of the extruded aluminium material.

Example 21 The same treatment as in Example 1 was applied to an aluminium plate of JIS A 1100P, and then electrolysis was carried out with an aqueous solution containing 5 g!litre of sodium selenite and 15 gllitre of sulphuric acid (30 "C) with an alternating-current voltage of 15 V for 1 minute to colour the plate with a gold colour. After washing with water, the coloured plate was dipped in an aqueous 30 g/litre solution of magnesium sulphate (60 "C) for 20 minutes. After washing with water, electrolysis was carried out with an aqueous 30 g/litre solution of phosphoric acid (30 "C) with an alternating-current voltage of 20 V for 20 minutes to obtain an opaque cream film on the surface of the aluminium plate.

Example 22 After an extruded aluminium material of JIS A 6063 was subjected to the pre-treatments of defatting, etching and smut removal, direct-current electrolysis was conducted with an aqueous solution containing 100 g/litre of sulphosalicylic acid and 0.5 g/litre of sulphuric acid (20 "C) with a current density of 3 A/dm2 for 30 minutes to form an anodically oxidized film self-coloured with a pale bronze colour, which was followed by dipping in an aqueous 10 g/litre solution of barium acetate (50 "C) for 20 minutes. After washing with water, the treated product was subjected to electrolysis with an aqueous 30 g/litre solution of ammonium oxalate with a direct-current voltage of 15 V for 5 minutes to obtain an opaque beige film on the surface of the extruded aluminium material.

Example 23 The opaque white film obtained in Example 20 was dipped in a dye bath containing 2.5 g/litre of Almalite Gold 108 (a dye produced by Kaname Shokai) (50 "C) for 5 minutes, to obtain an opaque cream film on the surface of the extruded aluminium material.

As described above, the coloured film of the present invention obtained in each example can be improved in durability by a pore sealing treatment or any of various clear coatings by electrodeposition, electrostatic coating, dipping, spraying, etc. Conventionally practiced.

Claims

1. A method for surface treatment of aluminium or aluminium alloys, which comprises treating aluminium or an aluminium alloy having an anodically oxidized film according to the steps of: (1) dipping in a first solution containing at least one salt selected from calcium salts, magnesium salts, barium salts, strontium salts, zinc salts, lead salts, titanium salts and aluminium salts; and (2) subsequently electrolyzing with second solution containing one or more substances which react with the product from said salt in the micropores of the anodically oxidized film to be converted into a white or grayish white compound.

2. A method according to claim 1, wherein said electrolysis is carried out according to any one of direct-current electrolysis, alternating-current electrolysis and electrolysis with a current of a waveform having an effect equal to direct current or alternating current.

3. A method according to claim 1 or 2, wherein the substance which reacts with the product from said salt to be converted into a white or grayish white compound is at least one member selected from the group consisting of inorganic acids, alkali or ammonium salts of inorganic acids, alkali hydroxides, alkali carbonates, aliphatic acids, salts of aliphatic acids, aromatic acids, salts of aromatic acids, aromatic sulphoric acids and derivatives, and substituted products thereof.

4. A method according to any preceding claim wherein at least one colouration treatment selected from alloy self-colouring, electrolysis self-colouring, electrolysis colouring, dip colouring and coating is conducted at any desired stage of said method.

5. A method for surface treatment of aluminium or aluminium alloys substantially as herein described with reference to the Examples.