JPH10219496A - Surface treatment of magnesium-base metallic formed compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a highly corrosion-resistant coating film without generating a harmful product by forming the dense oxide film of crystalline magnesium oxide by the anodization using an electrolyte having a specified composition and then coating the oxide film with the baking metal corrosion inhibiting composition contg. a water-soluble chromate compd. and zinc powder. SOLUTION: A magnesium-base metallic formed is anodized by using the alkaline electrolyte contg. at least one kind of compd. selected from a group consisting of the oxide, hydroxide and salt of groups IIb and IVb amphoteric metals and an aluminate or the electrolyte contg. at least one kind of salt selected from a group consisting of alkali metal carbonate or alkaline-earth metal carbonate and an alkali metal halide to form a hard and dense oxide film. Subsequently, the oxide film is coated with the baking metal corrosion inhibiting composition contg. a water-soluble chromate compd. and zinc powder, and high corrosion resistance and high rust inhibiting property are imparted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating the surface of a magnesium-based metal compact, and
The present invention relates to a method for treating a surface of a magnesium-based metal molded body capable of forming a coating film having excellent corrosion resistance on the surface of the magnesium-based metal molded body.

[0002]

2. Description of the Related Art Conventionally, magnesium-based metals composed of magnesium and its alloys have been used for various applications. In particular, magnesium alloys have a density of about 2/3 that of aluminum alloys, are the lightest among practical metal materials, have good machinability, and have high strength / density ratios. Etc. can be adopted.

However, a magnesium-based metal compact which can be obtained by molding the magnesium-based metal is immediately oxidized in the atmosphere and oxidized on its surface, as suggested by the ionization tendency of magnesium. That a coating is easily formed, that the adhesion of the coating is reduced when, for example, a top coat is formed on the oxide film, that the corrosion resistance to seawater or an aqueous chloride solution is extremely low, and that hydrochloric acid, sulfuric acid, and the like are used. There is a problem that it is easily soluble in acids such as nitric acid and the like.

[0004] Conventional methods aimed at improving the corrosion resistance of the magnesium-based metal compact include:
For example, (a) a method in which a chemical conversion treatment is performed by immersing in a bath employing a chromate, a manganese salt, a fluoride or the like alone or a combination thereof; (b) a galvanic method employing steel, stainless steel, or the like And (c) anodizing treatment.

However, in the method (a), there are problems such as generation of harmful mist and troublesome treatment of harmful wastewater. Therefore, in addition to facilities such as a treatment bath for performing chemical conversion treatment, harmful mist is collected. Equipment, a treatment facility for harmful wastewater, and the like are necessary, and furthermore, a magnesium-based metal molded body that has been subjected to a chemical conversion treatment cannot achieve a long-term anticorrosion effect.

In the method (b), the film formed on the surface-treated magnesium-based metal compact is a chemically unstable lower oxide. Can not demonstrate
Further, even when the method (b) was used in combination with the coating after the surface treatment, a long-term anticorrosion effect could not be realized.

The method (c) is described in JP-A-61-3
No. 4,200, Japanese Patent Publication No. 5-8278 and the like disclose a method of forming a corrosion-resistant film on magnesium, aluminum, their alloys, and the like.
Its corrosion resistance could not be said to be sufficient.

Further, Japanese Patent Publication No. 60-50228 (hereinafter referred to as Document 1) discloses “boric acid or boron oxide, a water-soluble chromic acid compound, zinc or aluminum alone or a mixture thereof, or an alloy powder thereof. A metal anticorrosive coating composition comprising a glycol compound, water and / or an organic solvent "(see claim 1 of Document 1).

[0009] In the above-mentioned Document 1, for example, there is no harmful mist generated, there is no need for wastewater treatment, and there is no danger of pollution. However, the corrosion resistance of the magnesium-based metal is not sufficient. I couldn't say.

[0010]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the conventional surface treatment method for a magnesium-based metal molded article and improves the surface of the magnesium-based metal molded article to have good corrosion resistance. It is an object of the present invention to provide a method for treating the surface of a magnesium-based metal molded body without causing harmful products during the treatment.

An object of the present invention is to provide a two-layer structure comprising a hard and dense first film and a second film having a sacrificial protection function formed on the first film on the surface of the magnesium-based metal compact. It is an object of the present invention to provide a surface treatment method for a magnesium-based metal molded body, which can effectively form a coating film of the present invention.

Another object of the present invention is to provide a surface treatment method for a magnesium-based metal molded body capable of imparting excellent corrosion resistance to a magnesium-based metal molded body without generating harmful products. It is in.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to modify the surface of a magnesium-based metal molded body, and as a result, the surface of the magnesium-based metal molded body has been crystallized by a specific anodic oxidation treatment. Forming a dense anodic oxide film of magnesium oxide, and then applying a treatment to coat a baking type metal anticorrosion composition containing a water-soluble chromic acid compound and zinc powder, without generating harmful products It has been found that a highly corrosion-resistant coating film can be formed on the surface of a magnesium-based metal compact. The present invention has been completed based on such findings.

Means of the present invention for solving the above-mentioned problem is to provide a magnesium-based metal compact by:
(B) an alkaline electrolyte containing at least one compound selected from the group consisting of oxides, hydroxides and salts of amphoteric metals belonging to Group IIb and Group IVb, and an aluminate; Any one of the electrolytic solutions containing at least one salt selected from the group consisting of alkali metal carbonates and alkaline earth metal carbonates at a concentration of 2 N or more, and an alkali metal halide. A surface treatment method for a magnesium-based metal molded body, comprising performing anodizing treatment in an electrolytic solution, and then coating with a baking-type metal anticorrosive composition containing a water-soluble chromic acid compound and zinc powder.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the surface treatment method of the present invention, the magnesium-based metal compact is formed by (1) Group IIb and Group IVb of the periodic table.
Alkaline electrolyte containing an aluminate and at least one compound selected from the group consisting of oxides, hydroxides and salts of amphoteric metals belonging to the group (hereinafter referred to as a first electrolyte). And (2) an electrolysis comprising at least one salt selected from the group consisting of alkali metal carbonates and alkaline earth metal carbonates at a concentration of 2 N or more, and an alkali metal halide. Anodizing treatment in any one of the liquid solutions (hereinafter referred to as a second electrolyte solution), and then coating with a baking-type metal anticorrosion composition containing a water-soluble chromic acid compound and zinc powder. .

First, the anodic oxidation treatment will be described below. The magnesium-based metal compact can be obtained, for example, by molding a magnesium-based metal such as magnesium or an alloy thereof.

As the magnesium alloy, for example,
Mg-Al-based alloys, Mg-Zn-based alloys, Mg-Mn-based alloys, Mg-Ag-based alloys, Mg-rare earth element-based alloys, and the like can be given.

The first electrolyte will be described.

Examples of the oxides, hydroxides and salts of the amphoteric metals belonging to groups IIb and IVb of the periodic table include zinc and tin oxides, zinc and tin hydroxides,
Examples include amphoteric metal compounds such as sodium zincate, potassium zincate, sodium stannate, and potassium stannate. These compounds may be used alone or in combination of two or more. Further, in addition to the amphoteric metal compound, for example, a lead compound can be employed.

The aluminate may be NaAlO ₂
And KAlO ₂ . These various aluminates can be used alone or in combination. Since the aluminate is formed in a solution in which aluminum hydroxide is dissolved in an alkali hydroxide or the like, the aluminum hydroxide is dissolved in the alkali hydroxide or the like without directly using the aluminate. It is also possible to use aluminates which are formed in situ.

The content of the aluminate in the first electrolytic solution is preferably in the range of 5 to 50 g / l, and the content of the amphoteric metal compound is preferably in the range of 1 to 20 g / l. Weight ratio is 0.05 ~
It is preferably in the range of 0.3.

Further, in addition to the aluminate and the amphoteric metal compound, a fluoride, a phosphate and a carbonate of an alkali metal are added to the first electrolytic solution in order to improve conductivity. Alternatively, an acidic oxide such as potassium permanganate may be added to accelerate the oxidation reaction in the anodic oxidation treatment.

The first electrolytic solution can be prepared by mixing aluminate with oxides, hydroxides and salts of amphoteric metals belonging to groups IIb and IVb of the periodic table and water. More preferably, an appropriate amount of an aluminate such as NaAlO ₂ and KAlO ₂ is dissolved in water, and the pH is adjusted to 11.5 or more using sodium hydroxide or potassium hydroxide. It can be prepared by adding oxides, hydroxides and salts of amphoteric metals belonging to Group IIb and Group IVb, and contains alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. It can be prepared by dissolving aluminum hydroxide or simple aluminum in the above aqueous solution.

The anodic oxidation treatment is described in JP-A-61-3
The method described in "Surface treatment method for magnesium and its alloys" described in JP-A-4200 and the "Surface treatment method for magnesium, aluminum and their alloys" described in JP-B-5-8278 are employed. can do.

More specifically, in the anodic oxidation treatment using the first electrolytic solution, either DC or AC can be used as a power source. For example, when DC is used as the power source, the first electrolytic solution can be used. In an electrolytic bath filled with the above conditions, the magnesium-based metal compact was used as an anode, a stainless steel plate, a lead plate and the like was used as a cathode, and the electrolysis conditions were a bath temperature of -10 to 80 ° C and a current density of 0.1 to 20 A / dm. By performing electrolysis within the range of ² , anodizing treatment can be performed. When an alternating current is used as a power source, the anodizing treatment can be performed in the same manner as described above using the magnesium-based metal compact as a counter electrode. By such an anodizing treatment, a dense white film having a thickness of about 0.5 to 50 μm can be formed on the surface of the magnesium-based metal compact.

According to this anodic oxidation treatment, a dense anodic oxide film having, for example, a uniform white color and being hard and excellent in corrosion resistance can be formed on the surface of the magnesium-based metal molded body.

Next, the second electrolyte will be described.

The at least one salt selected from the group consisting of alkali metal carbonates and alkaline earth metal carbonates includes sodium carbonate, potassium carbonate and lithium carbonate in view of solubility in water. An alkali metal carbonate can be suitably used. These carbonates need to be used in the second electrolyte so as to have a concentration of 2N or more. If the concentration is lower than this, a good anodic oxide film having good crystallinity and higher hardness cannot be obtained.

The alkali metal halide includes:
For example, in order to form a dense anodic oxide film having no pores on the surface of a magnesium-based metal, an alkali metal halide added as a film formation promoter can be mentioned. Examples thereof include potassium, potassium iodide, sodium fluoride, and sodium iodide. By using such a film formation accelerator, a dense anodic oxide film that does not require sealing treatment as a post-treatment of anodic oxidation treatment can be formed on the surface of the magnesium-based metal molded body.

Further, an acidic oxide such as potassium permanganate can be added to the second electrolytic solution as needed in order to accelerate the oxidation reaction in the anodic oxidation treatment.

The concentration of the alkali metal halide in the second electrolytic solution is preferably 5 to 30 g / liter.

The second electrolyte comprises, for example, at least one salt selected from the group consisting of an alkali metal carbonate and an alkaline earth metal carbonate, and an alkali metal halide. It can be prepared by dissolving in water so as to have a concentration of 2N or more.

In the anodic oxidation treatment using the second electrolytic solution, either DC or AC can be used as a power source. For example, when DC is used as the power source, the electrolytic solution filled with the second electrolytic solution can be used. In the bath, the magnesium-based metal compact was used as an anode, a stainless steel plate,
A lead plate or the like is used as a cathode, and an electrolysis condition is a bath temperature of -10 to 80.
Anodization can be performed by electrolysis at a temperature of 0.1 ° C. and a current density of 0.1 to 20 A / dm ² . When an alternating current is used as a power source, the anodizing treatment can be performed in the same manner as described above using the magnesium-based metal compact as a counter electrode. By such an anodizing treatment, a dense white film having a thickness of about 0.5 to 50 μm can be formed on the surface of the magnesium-based metal compact.

According to the anodic oxidation treatment, the surface of the magnesium-based metal compact is made of crystalline magnesium oxide as a main component, does not require a sealing treatment, is hard, and has a dense anodic oxidation excellent in corrosion resistance. A coating can be formed.

In the method of the present invention, the anodized magnesium-based metal compact is coated with a baking-type metal anticorrosive composition containing a water-soluble chromic acid compound and zinc powder.

Next, the coating process will be described below.

The water-soluble chromic acid compound is not particularly limited, and a known compound can be used.
For example, chromic anhydride, chromic acid, water-soluble metal salts of chromate, bichromate and the like can be mentioned. Among these, chromic anhydride, calcium chromate, zinc dichromate, potassium dichromate, sodium dichromate, magnesium dichromate, calcium dichromate, and the like can also be suitably used.

The zinc powder may have any shape, but is preferably in the form of flakes (also referred to as scales), particularly having an average thickness of 0.01 to 1 μm, preferably 0 to 1 μm. .1 to 0.5 μm and the length of the longest part is 20 μm
It is preferably flakes of m or less, preferably 15 μm or less. The zinc powder can be used together with the aluminum powder.

As a method of coating the magnesium-based metal compact having the anodic oxide film formed thereon with a baking-type metal anticorrosive composition containing a water-soluble chromic acid compound and zinc powder, for example, Baking a baking type metal anticorrosion composition containing a compound and zinc powder,
A method of forming a coating film (hereinafter sometimes referred to as baking type chromic acid-metal powder processing) may be used.

The content ratio of the water-soluble chromic acid compound in the baking type metal anticorrosion composition is 1 to 12% by weight, preferably 2% by weight, based on the finally obtained baking type metal anticorrosion composition. ~ 8%.

The content ratio of the zinc powder in the baked metal anticorrosion composition is 10 to 40% by weight, preferably 15 to 30% by weight, based on the finally obtained baked metal anticorrosion composition. %.

In the baking type metal anticorrosion composition,
In addition to the water-soluble chromic acid compound and the zinc powder,
If necessary, boric acid and / or boron oxide, cobalt salt, nickel salt, oxohydroxy low molecular weight ether,
pH adjusters, wetting agents, water, organic solvents and the like can be blended.

As the boric acid, orthoboric acid which is generally commercially available is suitable. If necessary, metaboric acid, tetraboric acid and the like can be blended in place of or together with the above-mentioned orthoboric acid.

When the above-mentioned boric acid and / or boron oxide is blended, its content in the baking type metal anticorrosion composition is usually based on the total weight of boric acid and / or boron oxide and the water-soluble chromic acid compound. 10 to 75% by weight,
Preferably it is 15 to 50% by weight.

When the content of the boric acid and / or boron oxide is within the above range, a composition exhibiting an excellent anticorrosion action in both saline and fresh water environments can be obtained.

The above-mentioned cobalt salt and nickel salt can be contained in the stoving type metal anticorrosion composition, either of them, or both can be contained. Can be used in combination.

In any case, the compounding amount of the cobalt salt and / or the nickel salt is usually 0 to 12% by weight, preferably 1 to 10% by weight, based on the whole baked metal anticorrosive composition.

As the oxohydroxy low-molecular-weight ether, glycol and its low-molecular-weight ether-type polymer can be used. Specifically, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, triethylene glycol and triethylene glycol can be used. Examples thereof include propylene glycol, diacetone alcohol, and similar homologs, and mixtures thereof.

When these oxohydroxy low-molecular-weight ethers are contained, they act as reducing agents for water-soluble chromic acid compounds and can be converted into chromic acid compounds.
In addition, when the baking-type metal anticorrosive composition is heated after being applied to the surface of the magnesium-based metal molded body, it is volatilized gradually during the formation of the coating film, thereby preventing the solvent and the like from being volatilized. In addition, it is possible to easily form a uniform anticorrosion coating film.

The pH adjuster is effective when used when the water-soluble chromic acid compound is strongly acidic. This pH
The preparation adjusted the pH of the baking type metal anticorrosion composition to 3.0 to 3.0.
6.0, usually used to prepare lithium and metals such as lithium, strontium, calcium, barium, magnesium, zinc, cadmium and metals belonging to Group IIA or higher. Selected from oxides and hydroxides. This preparation is
The pH of the baked-type metal anticorrosion composition is adjusted to 3.0 to 6.0 to keep the storage stability of the baked-type metal anticorrosion composition in the best condition, and the zinc powder and the acid in the liquid rapidly increase. To prevent the adhesion of the coating layer from deteriorating or the appearance from being darkened.

The wetting agent is used in the stoving type metal anticorrosion composition to assist the suspension and dispersion of the zinc powder. Examples of the wetting agent include nonionic surfactants, particularly alkylphenol polyethoxy adducts, for example, "Nopco 15" manufactured by Diamond Shamrock, USA.
92 "(registered trademark).

The water is not particularly limited, and the organic solvent is not particularly limited. However, considering the danger of fire and the adverse effect on the body of the worker, it is preferable to use the water as the solvent.

The baking type metal anticorrosion composition can be prepared by mixing the above components by a known method, for example, using a high-speed stirrer.

As a preferred baking type metal anticorrosion composition,
JP-B-60-50228, JP-B5-51672
Patent Application Publication No. 2005/0110, A composition containing a metal such as chromic anhydride, zinc and aluminum, a pH adjuster such as an oxide and a hydroxide of a metal, an oxohydroxy low molecular weight ether such as a polyglycol, and a solvent (For example, it is commercially available and available as Dacrodip (registered trademark).).

In the baking type chromic acid-metal powder treatment method, the baking type metal anticorrosive composition containing a water-soluble chromic acid compound and zinc powder is baked to form the magnesium-based metal having the anodic oxide coating formed thereon. A coating film can be formed on the surface of the molded article.

The baking-type metal anticorrosion composition usually comprises a water-soluble chromic acid compound such as chromic anhydride and a first component containing water as the main components, a metal powder such as zinc powder and oxohydroxy low molecular weight ether. It is provided to the user as a combination with the second component contained and the thickener.

At the time of use, the user mixes the first component, the second component, and the thickener, applies a predetermined amount to the surface of the magnesium-based metal compact on which the coating film is to be provided, and bake. .

The coating amount of the baking type metal anticorrosion composition is as follows:
Usually, it is an amount necessary for finally forming a coating layer of several μm or more.

The coating may be, for example, brush coating, tampo coating, spray coating, hot spray coating, air spray coating, electrostatic coating, roller coating, curtain flow coating,
It can be performed by a known method such as flow coating, dip coating, electrodeposition coating, and spatula coating. When immersion coating is employed, after immersion, extra drops may be removed by centrifugal shaking or vibration.

In the baking, a magnesium-based metal compact coated with a baking-type metal anticorrosion composition is heated in a hot air circulating furnace (gas burning furnace or electric furnace), far infrared heating furnace, infrared heating furnace, high frequency induction heating furnace. Or a combination thereof. The heating is performed at a temperature of 180 ° C. or more for at least 0.2 seconds or more, preferably at a temperature of 200 ° C. or more for 0.5 seconds or more, and more preferably at a temperature of 260 ° C. or more for 0.5 seconds or more.

This coating treatment can be repeated if necessary.

In this coating treatment, it is usually preferable to form a coating film having a thickness of 1 μm or more, preferably 3 μm or more. When the thickness of the coating film is 3 μm or more, more stable corrosion resistance can be exhibited.

The coating amount of the coating film was 0.2 g /
m ^{2 to} 14 g / m ² , preferably ^{2 to} 10 g / m ^2
2 If the adhesion amount is less than 0.2 g / m ² , the rust prevention effect becomes insufficient in a corrosive environment. In addition, the adhesion amount is 14 g / m
^If it exceeds ² , cracks tend to occur in the coating film during bending, which adversely affects workability.

Suitable coating films are, for example, 10 to 40
Wt%, selected from the group consisting of flaky zinc powder, a mixture of flaky zinc powder and flaky aluminum powder, a flaky zinc alloy powder, and a mixture of flaky zinc alloy powder and flaky aluminum alloy powder At least one metal powder, 1-12% by weight of a water-soluble chromic acid compound, 0-9
Wt% boric acid compound, 0-4 wt% pH adjuster, 0 wt%
~ 12 wt% nickel and / or cobalt salts, 7 ~
A baking-type metal anticorrosion composition comprising 30% by weight of a polyglycol such as oxohydroxy low molecular weight ether, 0 to 4% by weight of a surfactant and the balance of water and / or a water-compatible organic solvent is a magnesium-based metal. It is formed by applying to the surface of a molded body and baking.

In the magnesium-based metal molded body subjected to the anodizing treatment and the baking-type chromic acid-metal powder treatment, various organic resin paints such as alkyd, acrylic, epoxy, urethane and polyester may be used, if necessary. Coating such as an inorganic paint using ethyl silicate, ethyl titanate, sodium silicate, lithium silicate, chromic acid or the like as a binder can be performed.

The above-mentioned various organic resin paints, inorganic paints and the like are applied as a top coat on the magnesium-based metal molded body which has been subjected to the anodizing treatment and the baking type chromic acid-metal powder treatment to form a coating film. Thereby, a synergistic effect between the anodized film formed by the anodizing treatment and the high corrosion resistant film having excellent corrosion resistance composed of the coating film formed by the baking type chromic acid-metal powder treatment, and the topcoat paint Thus, a coating having high corrosion resistance and capable of exhibiting a high rust prevention effect can be realized.

In the present invention, a hard and dense first film can be formed by the anodic oxidation treatment, and sacrificial protection is performed on the first film by the baking type chromic acid-metal powder treatment. An effective second coating can be effectively formed.

In the highly corrosion-resistant coating film having a two-layer structure composed of the first coating film and the second coating film, the second coating film is formed on the harder and denser first coating film. It has a coating, and the zinc powder in the second coating has a sacrificial protective action to improve the corrosion prevention of the magnesium-based metal compact, so that it has excellent corrosion resistance even under severe corrosion conditions. In particular, a high degree of corrosion resistance can be exhibited in a damaged portion of the coating reaching the substrate.

Now, the present invention will be described in further detail with reference to Examples. In addition, the corrosion resistance in each example was evaluated as follows.

(Evaluation of corrosion resistance) The depth of the test substrate by the cutter knife is the depth to reach the base of the test substrate, the length is 50 mm, and After making two wounds whose points cross each other, a salt spray test method using a 5% by weight aqueous solution of sodium chloride (JI
After performing the test according to SZ-2371), the state of occurrence of corrosion was visually observed.

(Example 1) J containing 9% by weight of aluminum, 1% by weight of zinc, and the remainder magnesium was used as a test substrate.
Die casting plate of magnesium base alloy AZ91D described in IS H2222 (70 × 150 × 3 mm)
Was prepared.

Using the test substrate as an anode, a stainless steel plate (SUS304) as a cathode, and a KOH concentration of 150 g
/ Liter, Al (OH) ₃ concentration 35 g / liter,
KF at a concentration of 35 g / liter and ZnO at a concentration of 5 g / liter
Anodizing treatment was performed in an alkaline bath filled with an electrolytic solution adjusted to 1 liter under electrolysis conditions of a bath temperature of 20 ° C. and a DC current density of 0.5 A / dm ² for 30 minutes. As a result, a dense white anodic oxide film having a thickness of 12 μm was formed on the surface of the test substrate. Thereafter, baking-type chromic acid-metal powder treatment was performed. As a metal anticorrosion composition for treatment, Dacrodip (registered trademark) having the following composition was used and prepared.

<Composition of dacrodip> 6% by weight of chromic anhydride 27% by weight of flaky zinc powder 3% by weight of pH adjuster 20% by weight of polyglycols 1% by weight of surfactant 43% by weight of water Formed on the surface, immerse the anodized test substrate in the dacro dip,
Centrifuged off. Next, the test substrate was placed in an electric heating hot air circulating furnace, and after the temperature of the test substrate reached 300 ° C. in the furnace, the test substrate was held at the same temperature for 5 minutes to perform baking. The coating thickness of the metal anticorrosion composition is 3 μm.
Met.

When the corrosion resistance of the magnesium-based alloy die-cast plate obtained in this manner was evaluated, the silvery white surface was slightly discolored in the scratched portion and the non-scratched portion with the cutter knife in 24 hours. However, no corrosion product of the magnesium alloy was observed.

(Example 2) Anodizing was performed in the same manner as in Example 1 except that a pure magnesium material M1 was used instead of the die-casting plate of the magnesium base alloy AZ91D. Baking type chromic acid-metal powder treatment. The thicknesses of the anodized film and the film formed by the baking type chromic acid-metal powder treatment were 12 μm and 3 μm, respectively. When the corrosion resistance of the magnesium-based alloy die-cast plate thus obtained was evaluated, almost the same results as in Example 1 were obtained.

(Example 3) In Example 1, a lead plate was used for the cathode, and KOH was used as an electrolyte at a concentration of 150%.
g / liter, K ₂ SnO ₃ at a concentration of 10 g / liter,
NaAlO ₂ at a concentration of 40 g / liter, KF at a concentration of 20
Anodizing treatment was performed in exactly the same manner as in Example 1 except that the electrolytic solution adjusted to g / liter was used, and then baking-type chromic acid-metal powder treatment was performed. The thicknesses of the anodized film and the film formed by the baking type chromic acid-metal powder treatment were 15 μm and 3 μm, respectively. When the corrosion resistance of the magnesium-based alloy die-cast plate thus obtained was evaluated, almost the same results as in Example 1 were obtained.

Example 4 In Example 1, except that the temperature of the test substrate reached 350 ° C. in the electric heating type hot air circulating furnace, and then the test substrate was kept at the same temperature for 5 minutes to perform baking. A baking type chromic acid-metal powder treatment was performed in exactly the same manner as in Example 1. The thicknesses of the anodized film and the film formed by the baking type chromic acid-metal powder treatment were 12 μm and 2 μm, respectively. When the corrosion resistance of the magnesium-based alloy die-cast plate thus obtained was evaluated, almost the same results as in Example 1 were obtained.

(Embodiment 5)
CO ₃ and KI were 200 g / l and 10 respectively.
Anodizing treatment was performed in exactly the same manner as in Example 1 except that a carbonate bath filled with an electrolytic solution containing a concentration of g / liter was used, followed by baking-type chromic acid-metal powder treatment. The thicknesses of the anodized film and the film formed by the baking type chromic acid-metal powder treatment were 3 μm and 3 μm, respectively. When the corrosion resistance of the magnesium-based alloy die-cast plate thus obtained was evaluated, almost the same results as in Example 1 were obtained.

(Example 6) Anodizing treatment was performed in the same manner as in Example 5 except that the bath temperature of the carbonic acid bath was changed to 50 ° C, followed by baking type chromic acid-metal powder. Processing was performed. The thicknesses of the anodized film and the film formed by the baking type chromic acid-metal powder treatment were 4 μm and 3 μm, respectively. When the corrosion resistance of the magnesium-based alloy die-cast plate thus obtained was evaluated, almost the same results as in Example 1 were obtained.

(Comparative Example 1) Anodizing treatment was performed in the same manner as in Example 1, except that only the anodic oxidation treatment was performed and the baking type chromic acid-metal powder treatment was not performed. . The magnesium-based alloy die-cast plate thus obtained was evaluated for corrosion resistance. As a result, in 1 hour, the scratched portion and the non-scratched portion were discolored by the corrosion of magnesium into white and dark black mottled patterns. Was.

(Comparative Example 2) Anodizing treatment was performed in the same manner as in Example 5 except that only the anodic oxidation treatment was performed and the baking type chromic acid-metal powder treatment was not performed. . The magnesium-based alloy die-cast plate thus obtained was evaluated for corrosion resistance. As a result, in 1 hour, the scratched portion and the non-scratched portion were discolored by the corrosion of magnesium into white and dark black mottled patterns. Was.

Comparative Example 3 A baking type chromic acid-metal was performed in exactly the same manner as in Example 1 except that only the baking type chromic acid-metal powder treatment was performed without performing the anodizing treatment. Powder treatment was applied. The magnesium-based alloy die-cast plate thus obtained was evaluated for corrosion resistance. As a result, in 1 hour, the scratched portion and the non-scratched portion were discolored by the corrosion of magnesium into white and dark black mottled patterns. Was.

[0084]

According to the present invention, the surface of a magnesium-based metal molded body is first subjected to anodizing treatment using a specific electrolytic solution to form a hard and dense anodic oxide film, and then to a water-soluble chromium. By applying a coating treatment with a baking type metal anticorrosion composition containing an acid compound and zinc powder, a high corrosion resistant coating film that provides good corrosion resistance and rust resistance can be effectively formed, and furthermore, during processing Without the generation of harmful products.

Furthermore, the coating film formed in the present invention can contain zinc and aluminum, which are often used as an additive metal of a magnesium alloy, so that the magnesium-based metal compact can be suitably recycled. It can be used as a solution to the recent garbage problem.

In the present invention, by combining the anodic oxidation treatment and the baking type chromic acid-metal powder treatment, a highly corrosion-resistant coating film having excellent corrosion resistance can be formed on the surface of the magnesium-based metal compact. .

The excellent corrosion resistance according to the present invention cannot be achieved by the anodic oxidation treatment alone, nor can it be achieved by the baking type chromic acid-metal powder treatment alone.

Claims (1)

[Claims] 1. A magnesium-based metal molded body, comprising:
An alkaline electrolyte containing at least one compound selected from the group consisting of oxides, hydroxides and salts of amphoteric metals belonging to Groups IIb and IVb of the periodic table, and an aluminate; (2) an electrolyte containing at least one salt selected from the group consisting of alkali metal carbonates and alkaline earth metal carbonates at a concentration of 2 N or more, and an alkali metal halide; Surface treatment of a magnesium-based metal molded body characterized in that it is subjected to anodizing treatment in any one of the above electrolyte solutions and then coated with a baking-type metal anticorrosion composition containing a water-soluble chromic acid compound and zinc powder. Method.