JPS581094A - Method for forming colored protective film on surface of magnesium material - Google Patents

Abstract

PURPOSE:To obtain an excellent colored protective film having various color tones, by constituting an electrolytic bath so that soluble salt such as copper, iron, etc. is contained in a solution of silicate, etc. in an Mg material surface protective film forming method by spark discharge. CONSTITUTION:A solution which contains more than 1 kind among soluble salt such as copper, iron, Ni, Co, silver, Cr, Mn, Al and Ca, in a solution containing silicate, or silicate and alkali metal hydroxide is used as an electrolytic bath. In this bath, Mg as the anode, and iron, Ni, etc. as the cathode are soaked respectively, DC voltage of an optional waveform is applied, and it is boosted until spark discharge is generated. This voltage is further boosted in order to obtain desired thickness and color tone of a film. In this way, a colored film having various color tones can be formed by metal kind to be added.

Description

Detailed Description of the Invention: It relates to a method of forming a colored protective film on the surface of a magnesium material (hereinafter referred to as a magnesium material), in particular, applying electricity to a magnesium material as an anode in an electrolytic bath, and achieving corrosion resistance, chemical resistance, and resistance through spark discharge. The present invention relates to a method of forming a long lasting inorganic colored protective film on the surface of a magnesium material.

From a chemical standpoint, magnesium material is a metal that is extremely susceptible to corrosion. However, magnesium materials have various advantageous properties including lightness. Therefore, in order to eliminate these chemical disadvantages and further expand the range of use as industrial materials, advanced anti-corrosion technology is required. Research on the law is being conducted.

Broadly speaking, anticorrosion treatment methods for magnesium materials include painting methods, chemical film formation methods, and electrolytic conversion film formation methods.

Corrosion prevention using painting methods is achieved by coating with an organic film such as paint or enamel, but as the formation of bottle holes is unavoidable, corrosion resistance decreases with thin films (less than 20 μm), and it is necessary to thicken the film by recoating. . Although such a film exhibits resistance to chemical attack, it deteriorates especially under high temperature conditions and its adhesion to the magnesium material becomes poor.

There are many methods for forming chemical films, including the chromic acid method, selenite method, stannate method, phosphate method, and fluoride method. Chromate treatment is used to form an anti-corrosion film by immersing the material in a solution containing the components and utilizing a chemical reaction. Although this method is excellent in terms of economy and workability, it is inferior in corrosion resistance, and in a high humidity atmosphere, decolorization occurs and corrosion progresses significantly. Therefore, if corrosion resistance is desired, the chemical coating is further coated and used as a base treatment for coating, and in this case, adhesion to the magnesium material is most important.

There are two types of electrochemical conversion film forming methods: an anodic oxide film forming method and a spark discharge method to which the present invention relates. Typical methods for forming anodic oxide films include H, A, and E in alkaline baths.
, method, DOW12 method, DOW17 method for acid bath.

There are methods such as the DOW9 method and Cr22 treatment, but the anodic oxidation film produced by such a method is a colored, dull and opaque film, and its corrosion resistance is comparable to that of the above-mentioned chromate film.

In contrast to these methods, prior art methods relating to the formation of an inorganic colored protective film by spark discharge to which the present invention relates include U.S. Pat.
There is a method disclosed in No. 99 and No. 4184926.

The method described in U.S. Pat. This is an electrolytic method that consists of immersing a metal in a metal, applying a voltage of at least 220V between the anode and cathode to produce a spark discharge, and then increasing the voltage to 350 to 1500V until a film is electrodeposited on the surface. The colored film is formed using vanadium, arsenic, boron, chromium, titanium, soot, and antimony in the electrolytic bath.

By adding large amounts of alkali metal salts of tungsten and molybdenum. However, as an example of a colored film disclosed in this document, there is only one example of a black film on aluminum material in a sodium vanadate additive bath, and the color tone of the film caused by other additives and the color tone on magnesium material are unknown. .

The method described in the above US Pat. No. 4Y3G34999 uses an alkali metal hydroxide and S i 03
-2 and at least one anion, e.g. BO, -, B
O3-3, B, Q, 2. Ash, -3, C'03-2
．． CrO2-2, Cr2O, -21Mo04-2.
This method uses a strong alkaline electrolytic bath containing PC% -3,'rho, -2°WO4-2, W70□, but this document does not disclose any examples of colored coatings. Furthermore, the various methods described in the US Patent No. 1 require a relatively long time (30 to 60 minutes) to form the desired corrosion-resistant coating.

The method described in the above-mentioned US Pat. No. 1,418,4926 is to form a corrosion-resistant film on the magnesium material by first treating the Mg/Rum material with a hydrofluoric acid water bath to form a fluoromadai-sium layer, and then applying the alkali metal. A silicate film is formed on the fluoromagnesium layer by immersing it in an electrolytic bath consisting of a silicate and alkali general hydroxide aqueous solution and applying a voltage between the Magne/Lum material anode and cathode until a visible spark is produced. By maintaining this voltage until formation. Formation of a colored film using this method requires a secondary treatment, which involves forming a milky white film in advance by the method described above, and then performing the same treatment using an electrolytic bath containing potassium silicate and potassium vanadate. .

Although the darkening method allows color shading from white to black to be obtained, it requires a secondary treatment to form a colored film, and it also has problems such as the use of toxic hydrofluoric acid as a preliminary surface preparation.

The protective film formed by the spark discharge method is glass-like and thicker than films formed by other methods, and has excellent corrosion resistance, chemical resistance, durability, etc.

It is therefore an object of the present invention to eliminate the drawbacks of the prior art and to provide thick, thick, and
The objective is to obtain an inorganic colored protective film with excellent corrosion resistance, chemical resistance, and durability. Furthermore, an object of the present invention is to form the above-mentioned colored protective film in a short period of time through subsequent treatment without any preliminary surface conditioning compared to conventional colored film forming methods. .

In order to achieve the above objective, the inventors investigated various coating methods and found that copper,
An electrolytic bath containing a small amount of soluble salts of iron, nickel, cobalt, silver, chromium, manganese, aluminum, and calcium is used as an electrolytic bath, and a magnesium material is used as an anode and current is applied to produce a spark discharge on the anode surface. It has been found that colored protective films of various tones can be obtained on the surface of magnesium materials by this process.

In more detail, the method of the present invention includes copper, iron, nickel, cobalt, silver, chromium, manganese, aluminum, etc. in an aqueous solution containing a silicate or a silicate and an alkali metal hydroxide. An aqueous solution containing one or two or more of soluble salts of calcium and calcium is used as an electrolytic bath, and a magnesium material is used as an anode and iron, stainless steel or nickel is used as a cathode and immersed in the electrolytic bath, and a DC voltage is applied. The voltage is increased until a spark discharge occurs. The voltage is further increased to obtain the desired film thickness and color tone. In this way, a colored protective film of the desired color tone is formed on the surface of the anode magnesium material.

When carrying out the method of the present invention, there is no need for preliminary surface preparation such as 7) treatment with an aqueous hydrohydric acid solution to form a fluoromagnesium layer. That is, the magnesium material can be used as it is without any pre-treatment for stationery. Of course, conventional degreasing, washing, pickling with ferric nitrate or the like, or the formation of a chemical film as described above can also be carried out as a pretreatment.

Such preliminary surface conditioning has little effect on the inherent corrosion resistance of the colored protective coating.

The silicates used in the uninvented method have the general formula M,
,0-n5iO,,(M represents an alkali metal, n is 0
Various water-bathable or water-dispersible materials represented by positive numbers from 5 to 20, such as sodium silicate, sodium metasilicate, potassium silicate, lithium silicate, colloidal silica, etc. can be mentioned. These silicates can be used alone or as a mixture of two or more. The silicate concentration varies depending on the color tone of the desired film, but it can be used up to a saturation concentration of 5V13 or higher.The preferred range is:
It is 10-300 f/J3.

If an aqueous bath solution containing no alkali metal hydroxides is used as the electrolytic bath, i.e. an aqueous solution containing only silicates and soluble salts of the above-mentioned metals, the silicates used are mixed in a molar ratio (
5i02/M20) is preferably 2.5 or less, and in this case, the silicate concentration is preferably relatively high (50 or more).

In electrolytic treatment using a silicate with a molar ratio of 25 or more, if no alkali metal hydroxide is contained, the initial current density must be extremely high in order to obtain an applied voltage that produces a spark discharge on the surface of the anode magnesium material. Therefore, in the current density range of 0, 1 to 10 A/dff+2 using the uninvented method described below, spark discharge does not substantially occur, and colloidal substances with poor adhesion may precipitate or may form on the surface of the magnesium material. Only an anodic oxide film is formed. Such a film does not have the corrosion resistance targeted by the present invention.

The electrolytic bath used in the method of the invention has a small concentration, the value of which is determined by the individual hydroxide concentration or the combination of hydroxides. The preferred alkali metal used in the process of the invention is sodium. , potassium and lithium, and preferably contain a small amount (5z or more) of alkali metal hydroxide.

The hydroxide can be used up to a saturation concentration, but the preferred range for the colored protective coating according to the method of the present invention is 10 to 10 f/, depending on the relative amount to the silicate concentration above.
It is J3.

The metal salt added to the silicate bath solution or the aqueous solution containing a silicate and an alkali metal hydroxide in order to obtain a colored film is copper.

Iron, nickel, cobalt, silver, chromium, manganese.

Salts of aluminum and calcium, which can be used alone or in combination of two or more. Metal salts include sulfates, nitrates, carbonates, phosphates, hydroxides, halides such as chlorides, organic acid salts such as acetates, cyanides, etc. can also be used. However, when the above metal salt types are added to an alkaline electrolytic bath containing the above-mentioned silicate,
Must be used as a soluble salt. That is, among the metal salts mentioned above, those insoluble in the alkali silicate solution should be added after first forming a complex such as an EDTA complex, an ammine complex, or a cyanide complex to form a soluble salt.

For example, when using copper sulfate as a copper salt, first dissolve it in the ratio of copper sulfate: EDTA・2Na = I°I ~ 1:2 (molar ratio) l, and use caustic alkali to reduce h to 10~11.
After adjusting it to the above-mentioned alkali silicate solution, it may be added to the above-mentioned alkali silicate solution to form an electrolytic bath. The concentration of the metal salt added varies depending on the type of metal salt and the desired color tone.

It can be used as a metal up to a saturation concentration of 0 to 11 or higher.

A colored film having a color tone approximately as described below is formed depending on the type of added metal, but the color tone and shade are not limited to these, as they vary depending on the electrolytic conditions, electrolytic bath concentration, etc. Naori ROMs include chromic acid, chromate monodichromate, and chromium nitrate.

Any trivalent chromium salt such as chromium sulfate can be used.

Copper ・・・・・・・・・・・・ Gray to black-gray, gray-green, reddish-brown iron ・・・・・・・・・・・・ Blue-green to
Black, ocher nickel ・・・・・・ Light brown to dark brown, ocher cobalt ・・・・・・ Green to blue,
Yellow to yellow-green silver ・・・・・・・・・・・・ Yellowish ROM ・・・・・・ Yellow to yellow-green to green Manganese ・・・・・・・・・ Light brown to brown to reddish-brown , ocher aluminum ・・・・・・ Grayish white to gray calcium
...... The color tone and density of the grayish-white to gray colored film are as described above (the relative amounts of alkali metal hydroxide, silicate, added metal salt, processing voltage, processing time, processing current density, etc.) However, in order to further obtain various color tones and shades, alkali metal carbonates, alkali metal phosphates, alkali metal boric acid fl/salts, etc. can be added to the electrolytic bath. p, +l+ is 8
A value of 5 or more is preferable, and a value of 85 or less may cause undesirable phenomena such as gelation. For this purpose, gelation and precipitation can be prevented by adding bald conditioners and stabilizers.

When forming a colored protective film, a DC voltage with various waveforms such as a rectangular waveform, a sawtooth waveform, a single-phase full-wave waveform, and a single-phase half-waveform can be applied.

At this time, it is advantageous to apply a DC voltage with a pulse waveform such as a rectangular waveform or a sawtooth waveform because colored films of various shades of color are likely to be formed and the spark discharge voltage can be significantly reduced.

In the electrolytic treatment, as described above, the magnesium material to be treated is used as an anode and iron, stainless steel or nickel is used as a cathode, and is immersed in the above electrolytic bath, a DC voltage is gradually applied until a spark discharge occurs, and then the spark discharge is maintained. The voltage may be increased to a predetermined voltage while maintaining the voltage until a colored protective film of desired thickness and color tone is formed. For example, in constant current electrolysis, the applied voltage is continuously changed to maintain a constant anode current density, producing intense spark discharge on the anode surface.
Thereafter, electricity is continued while maintaining the voltage until the film has a desired thickness of one color tone. If constant current electrolysis cannot be performed, first apply a voltage to achieve a certain anode current density, and as a film forms, a rapid decrease in current value will be observed, so at this time the initial current density will be reached. Apply more voltage.

By repeating this operation, intense spark discharge is generated on the anode surface, and the film has a desired thickness and color tone. The current density can be arbitrarily selected in the range of 01 to 10λ/drrF, and this current density has almost no relation to the spark discharge voltage, but if the current density is low, it may take a long time to apply up to a predetermined voltage. In the case of high current density, problems such as the smoothness of the colored protective film and an increase in the electrolytic bath temperature occur.
It is preferable to set it to 2A/drn2.

The thickness of the film formed is determined by the electrolytic bath concentration, electrolytic bath temperature, processing voltage, processing time, processing current density, etc. Among these, the electrolytic bath temperature is determined depending on the desired film, but it is usually The temperature is 5 to 80°C.

The invention will now be explained in more detail with reference to examples.

Example 1 Silica potassium 40 t/43, sodium hydroxide 40
A magnesium alloy plate AZ31C having a surface area of 50 crl and a thickness of 3 mm was used as an anode and an iron plate was used as a cathode.

Sawtooth waveform DC voltage with anode current density 08A/drI
? If the voltage is applied continuously while maintaining the voltage at 15V, a spark discharge will occur at approximately 15V. The voltage was increased to 30V and maintained for 5 minutes. This energization is accompanied by intense spark discharge. A smooth, ocher-colored, glass-like film was formed on the anode plate, and the thickness of the film was about 15 μm.

Example 2 A magnesium alloy plate AZ31C with a surface area of 50 crtt and a thickness of 311 ff was immersed as an anode and an iron plate as a cathode in an aqueous solution consisting of sodium silicate I OOf/J), 5 degrees of sodium hydroxide, and 1 portion of chromium nitrate. Then, the sawtooth waveform DC voltage is set to an anode current density of 05A/dr.
If the voltage is applied continuously while maintaining the voltage at I]2, a spark discharge will occur at about 15V. The voltage was increased to 30V and maintained for 10 minutes.

This energization is accompanied by intense spark discharge. A green, smooth, glass-like film was formed on the anode plate. The thickness of the film was approximately 30 μm.

Example 3 Potassium silicate 140 f/3, potassium hydroxide 5
0 VI3.

A surface area of 50 d in an aqueous solution consisting of 8 parts of nickel sulfate and 12 parts of disodium ethylenediaminetetraacetate.

A magnesium alloy casting plate AZ91C with a thickness of 2III is used as an anode and an iron plate is used as a cathode.
If a single-phase full-wave waveform DC voltage is gradually applied while maintaining the voltage at //dd, a spark discharge will occur at about tzov. voltage 20
The voltage was increased to 0.0 cm, and the treatment was carried out for 5 minutes while maintaining this voltage. This energization is accompanied by intense spark discharge.

A brown smooth glass-like film was formed on the anode plate, and the thickness of the film was about 20 μm.

Example 4 Sodium metasilicate nonahydrate (molar ratio 09-11) 2
00ff/J3 and silver cyanide 2! A magnesium alloy plate AZ31C as an anode and an iron plate as a cathode are immersed in an aqueous solution consisting of
If a sawtooth wave DC voltage is gradually applied while maintaining the voltage at -, a spark discharge will occur at about 15V. The voltage was increased to 30V, and the treatment was carried out for 3 minutes while maintaining this voltage.

This energization is accompanied by intense spark discharge. A smooth, aromatic, lath-like yellow film with a thickness of about 10 μm was formed on the anode plate. Q Example 5 Potassium silicate 80 is 1. Sodium hydroxide 30! ,
Cobalt sulfate 3? and 5 t/l of disodium ethylenediaminetetraacetate with a surface area of 50 ffl.
, by using a 3 mm thick magnesium alloy plate AZ31C that has been chromate treated as an anode and an iron plate as a cathode, and gradually applying a sawtooth wave DC voltage while maintaining the anode current density at 0.8 A/drn2. Approximately 20
A spark discharge occurs at V. The voltage was increased to 30V, and current was applied for 10 minutes while maintaining this voltage. A blue glass-like smooth film was formed on the anode plate, and the thickness of the film was about 30 μm.

The colored and protective films formed by the methods described in Examples 1 to 4 above are far more resistant to strong acids and strong alkalis than the magnesium material coated with p by the conventional method. It was a durable film with resistance. Furthermore, each film has good adhesion to paint and excellent abrasion resistance.

Claims (1)

[Claims] In the method of forming copper, iron, nickel,
An aqueous silicate solution containing at least one soluble salt of cobalt, silver, chromium, manganese, aluminum and calcium, or an aqueous solution containing at least one of the above soluble salts, a silicate, and an alkali metal hydroxide. A method characterized in that the applied voltage is a DC voltage with an arbitrary waveform.