JP2001288580A - Surface treating method for magnesium alloy and magnesium alloy member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treating method for a magnesium alloy by which a dense and uniform chemical conversion film is deposited on the surface of a magnesium alloy in which a releasing agent, an oxide layer and a segregated layer of alloy components such as aluminum and zinc are present, and excellent corrosion resistance and adhesion for a coating film can be imparted thereto and to provide a magnesium alloy member subjected to surface treatment by the same surface treating method. SOLUTION: This surface treating method includes a degreasing process in which the surface of a magnesium alloy is degreased, a chemical etching process in which chemical etching treatment is performed and a chemical conversion treating process in which a chemical conversion film is deposited by a chemically treating solution. In the chemical etching stage, the surface of the magnesium alloy is brought into contact with a phosphoric compound-containing aqueous solution to deposit a film of magnesium phosphate by 10 to 2,000 mg/m2 as the coating weight of phosphorous, and the magnesium alloy member is obtained by being subjected to surface treatment by the same surface treating method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel surface treatment method used to impart excellent corrosion resistance and coating film adhesion to the surface of a magnesium alloy, and a magnesium alloy member surface-treated by the surface treatment method. .

[0002]

2. Description of the Related Art Many metal materials (aluminum alloys, steels, magnesium alloys, etc.) used for automobiles, motorcycles, home appliances, etc., are required to have corrosion resistance and aesthetic appearance, and thus have been subjected to various surface treatments. Later, it is painted and used. The purpose of the surface treatment is to remove contaminants such as cutting oil remaining on the material surface, form a dense chemical conversion film, and impart corrosion resistance and coating film adhesion.

In recent years, there has been a movement to actively apply a magnesium alloy, which is the lightest and most recyclable among practical metals, for the purpose of preserving the global environment. For example, in the field of automobiles, magnesium alloys have begun to be applied to members using steel or aluminum alloys in the past, due to vehicle weight reduction for the purpose of improving fuel efficiency. In the field of home appliances, there is a move from conventional plastics to magnesium alloys, which have excellent recyclability, mainly in the housings of laptop computers and mobile phones. Most of these magnesium alloy members are formed by a casting method called a die casting method or a thixomold method. These casting methods mold a magnesium alloy in a molten or semi-molten state by injecting it into a mold at high speed and high pressure, and are characterized by excellent dimensional accuracy and productivity. Some products are formed by a press forming method using a wrought magnesium alloy plate or a forging method.

Such a magnesium alloy member is coated after being subjected to a surface treatment, as in the case of steel and aluminum alloy. Since a magnesium alloy has the most active and easily corroded property among practical metals, it is important to form a dense and uniform chemical conversion film in the surface treatment step more than in the case of steel or an aluminum alloy. However, magnesium alloys are also extremely difficult materials to form a dense and uniform chemical conversion film. This is because the surface of the magnesium alloy is chemically non-uniform.

[0005] The chemical inhomogeneity of the surface of a magnesium alloy will be described in detail. In general, magnesium alloys used for automobiles, motorcycles, home appliances, etc. are added with a large amount of alloy components such as aluminum, zinc, and manganese in order to improve properties such as formability, mechanical strength, and ductility. ing. For example, in AZ91, the most common magnesium alloy for casting, aluminum is 9 as an alloying component.
% And zinc 1%. In the surface treatment step of forming a chemical conversion film using a chemical reaction, the behavior of these alloy components in the material often greatly affects the surface treatment property. In order to form a dense chemical conversion film, it is said that these alloy components are preferably densely and uniformly distributed in the material. However, in a magnesium alloy member formed by a die casting method or a thixomolding method, alloy components such as aluminum and zinc are often not segregated in the material but segregated.

Here, the segregation of the magnesium alloy will be described in more detail. Generally, segregation means a phenomenon in which the distribution of impurities and alloy components in a metal becomes non-uniform. Segregation most often occurs when the alloy solidifies. For example, in the case of molding by die casting or thixomolding, the part that first contacts the mold (near the overflow part)
Is solidified first, so that the purity is high. However, the concentration of impurities and alloying components is high in a portion solidified later (near the gate portion). Also, since the center of the thick part of the product solidifies last,
The alloy components may be segregated to an extremely high concentration,
In the die casting method and the thixomold method, the liquid phase in which the alloy component segregates at a high concentration passes through between the solid phases and presses out to the surface side by capillary action, because pressure is applied during solidification after injection. There is. These types of segregation are called macro segregation.

On the other hand, looking at the metal structure of a magnesium alloy, an α phase composed of high purity magnesium and a β phase of an intermetallic compound composed of an alloy component, for example, Mg17Al12
It is composed of In many cases, the β phase is not uniformly distributed in the material but segregates at the grain boundaries. This type of segregation is called micro-segregation.

[0008] As described above, macrosegregation and microsegregation both exhibit various behaviors depending on the cooling rate during casting, pressurizing conditions, and the like. For this reason, even if the alloys have the same composition, the degree of segregation and the metal structure vary depending on the shape and site of the member, casting conditions, and the like, whereby the surface becomes chemically non-uniform and a dense and uniform chemical conversion film is formed. It's getting harder.

As the surface treatment method of a magnesium alloy, the following three kinds of treatment steps are generally applied. (Treatment process 1) Degreasing → water washing → chemical conversion treatment → water washing → pure water washing →
Drying (processing step 2) Degreasing → water washing → chemical etching → water washing → chemical treatment → water washing → pure water washing → drying (processing step 3) degreasing → water washing → chemical etching → water washing → desmutting → water washing → chemical treatment → water washing → pure Washing → drying

[0010] Among these processing steps, the degreasing step aims at removing light organic dirt such as machine oil and cutting oil. The chemical etching step aims at dissolving and removing the surface layer such as the release agent, the alloy segregation layer and the hydroxide layer together with the mild organic soil such as machine oil and cutting oil. The desmutting process is intended to remove smut remaining on the surface in the chemical etching process, that is, residues such as corrosion products generated by etching and alloy components concentrated on the surface without being etched. In the chemical conversion treatment step, the purpose is to form a chemical conversion film such as chromate chromate or manganese phosphate on the surface to improve the corrosion resistance and the coating film adhesion.

These processing steps are properly used depending on the required performance for the surface treatment and the degree of contamination of the surface. For example, (Processing Step 2) or (Processing Step 3) is applied to a member to which a large amount of release agent is attached, and (Processing Step 1) is applied to a member to which a small amount of the release agent is attached.

Many inventions and findings relating to the surface treatment method have been reported so far. The chemical conversion treatment liquid is roughly classified into a treatment liquid containing hexavalent chromium (chromate) and a treatment liquid not containing hexavalent chromium (non-chromate). In the processing solution containing hexavalent chromium,
Processing solutions developed by Dow Chemical Company of the United States are widely known and have been put to practical use. For example, “Chromate treatment solution (Dow1 method)”, “bichromate treatment solution (Dow7 method)”
Method) "," Alkaline dichromate treatment solution (Dow9)
Method) ”,“ Manganese chromate treatment solution (Dow22 method) ”
And the like. These treatment liquids are relatively insensitive to surface variations and have excellent corrosion resistance and coating film adhesion.

[0013] However, the 6
Chromium (VI) is harmful to the human body, and a treatment solution containing no hexavalent chromium is desired. In addition, even when such a treatment liquid is used, a surface treatment method that is less susceptible to variations in the surface and that can provide a surface with more excellent corrosion resistance and coating film adhesion is desired.

Numerous inventions have been reported for chemical conversion treatment solutions containing no hexavalent chromium. For example, a method of applying a corrosion solution containing at least one selected from nitric acid, sulfuric acid, and phosphoric acid to a member to form a corrosion-resistant protective film is provided.
No. 3), at least one organometallic compound selected from metal alkoxides, metal acetylacetonates, and metal carboxylate, and an acid, alkali and salts thereof, or an organic compound having any one of a hydroxyl group, a carboxyl group, and an amino group. "A metal surface treatment method comprising at least one kind of film forming aid selected from compounds (Japanese Patent Application Laid-Open
No. 2,280,62)), by reacting the surface of a magnesium alloy member with an aqueous solution of an organic acid or a soluble salt of an organic acid to form a poorly soluble salt of magnesium and the organic acid on the magnesium surface. Surface treatment method and magnesium alloy part surface-treated by the method (JP-A-9-241861), zinc ion, manganese ion, phosphate ion, fluorine compound,
A method for forming a highly corrosion-resistant coating film of a magnesium alloy material by treating with an aqueous solution in which each concentration of a film forming aid, nickel ion, cobalt ion, and copper ion is specified (Japanese Patent Application Laid-Open No.
No. 24338) ", a method for treating a magnesium-based metal molded body with an aqueous solution containing at least one of permanganic acid or a water-soluble salt of manganic acid. 35073
Gazette)). However, all of these chemical conversion treatment solutions are susceptible to variations in materials, and have problems such as unstable performance.

Further, inventions relating to a degreasing agent used in the degreasing step and an etching agent used in the chemical etching step have been reported. For example, a "pickling bath for magnesium and magnesium alloys (JP-A-53-10223) in which at least one selected from sulfuric acid, hydrochloric acid, nitric acid and oxalic acid is added to an aqueous solution containing a predetermined amount of persulfate.
No. 1)), pickling the magnesium alloy and then desmutting the smut remaining on the surface with an alkaline aqueous solution containing a predetermined amount of ethylenediaminetetraacetic acid.
2202063) ").

An object of these inventions is to etch a surface of a magnesium alloy to remove a release agent, an oxide film and an alloy segregation layer. However, even when these methods are applied, it is difficult to form a dense and uniform chemical conversion treatment on the magnesium surface, and it is difficult to obtain excellent corrosion resistance and coating film adhesion.

[0017]

Accordingly, the present invention provides
It is intended to solve the above-mentioned problems of the prior art, and specifically, it is dense and uniform on the surface of a magnesium alloy in which a release agent, an oxide layer and a segregation layer of an alloy component such as aluminum or zinc are present. An object of the present invention is to provide a surface treatment method for a magnesium alloy capable of forming an excellent conversion coating and imparting excellent corrosion resistance and coating film adhesion, and a magnesium alloy member surface-treated by the surface treatment method. is there.

[0018]

Means for Solving the Problems The present inventors diligently studied means for solving the above-mentioned problems of the prior art. As a result, the surface of the magnesium alloy is brought into contact with an aqueous solution containing a phosphoric acid compound in a chemical etching step, and a release agent, an oxide layer and a segregated layer of alloy components are dissolved and removed, and a magnesium phosphate film is formed at the same time. Then, by performing a chemical conversion treatment, a dense and uniform chemical conversion film can be formed on the surface, and it has been newly found that the above-mentioned problems can be solved, thereby achieving the present invention.

That is, the surface treatment method for a magnesium alloy according to the present invention includes a degreasing step for degreasing the surface of the magnesium alloy, a chemical etching step for performing a chemical etching treatment, and a chemical conversion treatment for forming a chemical conversion film using a chemical conversion treatment solution. Wherein the chemical etching step comprises contacting the surface of the magnesium alloy with a phosphoric acid-based compound-containing aqueous solution to form a phosphorus deposition amount of 10 to 20.
This is a step of forming a 00 mg / m ² magnesium phosphate film.

A release agent applied to a mold at the time of casting adheres to the surface of a magnesium alloy member formed by a casting method called a die casting method, a thixomold method, a pressing method, a forging method, or the like. Chemically non-uniform surfaces such as alloy components such as aluminum, zinc, and manganese segregating, or reacting with oxygen in the air to grow thick oxide films General. For this reason, it is usually difficult to form a dense and uniform chemical conversion film. The surface treatment method of the present invention is particularly effective in forming a dense and uniform chemical conversion film on these surfaces and imparting excellent corrosion resistance and coating film adhesion.

The aqueous solution containing a phosphoric acid compound in the chemical etching step contains, as the phosphoric acid compound, at least one selected from the group consisting of orthophosphoric acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid and alkali metal salts thereof. And the concentration of the phosphoric acid compound is 1 to 2
It is preferable that the pH be in the range of 00 g / L and the pH be in the range of 1 to 12.

As the chemical conversion treatment solution in the chemical conversion treatment step, an acidic aqueous solution containing at least orthophosphoric acid and at least one metal ion selected from the group consisting of Zn, Mn and Ca at a pH of 2 to 6 or ,
At least one fluorine compound selected from the group consisting of hydrofluoric acid, hydrofluoric acid, zircon hydrofluoric acid and titanium hydrofluoric acid, and Mn, Mo, W, Ta,
An acidic aqueous solution having a pH of 2 to 6 and containing at least one metal oxyacid compound selected from the group consisting of Re, Nb, and V is preferable.

On the other hand, the magnesium alloy member of the present invention
The magnesium alloy is surface-treated by the surface treatment method of the present invention.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The surface treatment method of a magnesium alloy of the present invention (hereinafter, may be simply referred to as “surface treatment method”) will be described in detail below. The surface treatment method of the present invention is applied to a magnesium alloy member. The type of magnesium alloy is not particularly limited.
Magnesium alloys for casting such as Z91, AM60, ZK51 and ZK61 and magnesium alloys for spreading such as AZ31, AZ61 and ZK60. The method of forming the magnesium alloy member is not particularly limited, but examples thereof include a die casting method, a thixo molding method, a press molding method, and a forging method.

The method for treating the surface of a magnesium alloy of the present invention is based on the above (treatment step 1) "degreasing → washing with water → chemical etching → washing with water → chemical treatment → washing with water → washing with pure water → drying). The degreasing step, the chemical etching step, and the chemical conversion step are essential steps, and the other steps are appropriately set as necessary. When the surface of the magnesium alloy to be treated is excessively contaminated by the release agent or when the oxide film layer has grown extremely thick, the following (processing step 4) can be applied to the film. It is more preferable from the viewpoint of stabilizing the performance. (Treatment process 4) Degreasing → water washing → etching (acidic aqueous solution)
→ Rinsing → Desmutting → Rinsing → Chemical etching → Rinsing → Chemical conversion treatment → Rinsing → Pure water washing → Drying

The "etching (acidic aqueous solution)" in the above (processing step 4) is different from the "chemical etching" of the present invention, and is intended to simply perform etching using an acidic aqueous solution. Aqueous solution) ". Hereinafter, description will be made in the order of steps.

[Degreasing Step] Prior to the chemical etching step, the surface of the magnesium alloy is degreased. By degreasing,
In the chemical etching step described later, a dense and uniform magnesium phosphate film can be formed.

The degreasing treatment in the degreasing step is performed by bringing a magnesium alloy as an object to be treated into contact with a degreasing solution. Examples of the method of bringing the magnesium alloy to be treated into contact with the degreasing solution include a conventionally known immersion method, a spray method, and the like. In the present invention, any method can be applied (hereinafter, “ Similar in the concept of the term "contact.").

The composition of the degreasing solution that can be subjected to the degreasing step is not particularly limited as long as it can remove organic stains, but it is preferable to use an alkaline aqueous solution containing a surfactant. As the alkali builder of such a degreasing solution, hydroxides, phosphates, silicates, carbonates and the like of alkali metals can be applied. In addition, nonionic surfactants,
Both cationic and anionic types can be applied. Further, a chelating agent may be blended to increase the degreasing efficiency.

The temperature and time for contacting the degreasing solution with the magnesium alloy are not particularly limited, but the contact is preferably performed at 35 to 70 ° C. for 2 to 10 minutes depending on the degree of contamination of the magnesium alloy surface. The concentration of the degreasing solution is
It is set as appropriate depending on the degree of contamination of the magnesium alloy surface, the degreasing liquid component, and the like.

When the surface of the magnesium alloy to be treated is excessively contaminated by the release agent or when the oxide film layer has grown extremely thick, the above-mentioned (processing step 4) is used instead. Further, prior to degreasing, shot blasting may be applied to the surface of the magnesium alloy. By performing shot blast, contaminants remaining on the surface of the magnesium alloy can be physically removed.

When performing shot blasting, degreasing with the above degreasing solution can be omitted. However, when shot blasting is performed, the surface of the magnesium alloy usually contains abrasives by shot blasting and oil contained therein, so it is desirable to perform degreasing with the above degreasing liquid. In the present invention,
The process of applying the shot blast is also included in the concept of degreasing, and therefore, as the degreasing step which is an essential step of the present invention, a mode of the process of applying the shot blast alone, a mode of the degreasing alone using the degreasing solution, and And a mode of performing degreasing with the above-described degreasing solution after the process of applying the shot blast.

[Etching Step (Aqueous Aqueous Solution)] As described above, when the surface of the magnesium alloy to be processed is excessively contaminated by the release agent or when the oxide film layer grows extremely thick, It is desirable to provide an etching step (acidic aqueous solution) prior to a chemical etching step described later. By the etching step (acidic aqueous solution), contaminants remaining on the surface of the magnesium alloy can be chemically removed and the surface can be completely cleaned.

The etching treatment in the etching step (acidic aqueous solution) is carried out by bringing a magnesium alloy as an object to be treated into contact with the acidic aqueous solution. The acidic aqueous solution is not particularly limited as long as the contaminants on the magnesium alloy surface can be dissolved and removed, but sulfuric acid, nitric acid,
Preferably, hydrochloric acid, tartaric acid, oxalic acid or the like is applied. Conditions such as the concentration and temperature of the acidic aqueous solution and the contact time with the magnesium alloy surface are not particularly limited, and are appropriately adjusted depending on the degree of contamination of the magnesium alloy, components of the acidic aqueous solution to be used, and the like.

[Desmutting Step] When an etching process is performed in an etching step (acidic aqueous solution), a smut remains on the surface of the magnesium alloy. Therefore, it is desirable to provide a desmutting step.

The desmutting in the desmutting step is performed by bringing a magnesium alloy as an object to be treated into contact with the desmutting liquid. The desmutting liquid is not particularly limited as long as it can remove the smut remaining on the surface of the magnesium alloy. However, the desmutting liquid is a sodium hydroxide aqueous solution adjusted to pH 12 or more, or the smut removal from the surface of the magnesium alloy (Japanese Unexamined Patent Application Publication No. −2266
No. 3), a strong alkaline aqueous solution containing a chelate component.

The conditions such as the concentration of the desmutting liquid, the temperature, and the contact time with the magnesium alloy surface are not particularly limited, and the degree of smut adhesion on the magnesium alloy surface,
It is appropriately adjusted depending on the components of the desmutting liquid to be used and the like.

[Chemical Etching Step] The chemical etching step is a step of bringing a magnesium alloy as an object to be treated into contact with an aqueous solution containing a phosphoric acid-based compound to clean the magnesium alloy surface and simultaneously form a magnesium phosphate film. . Therefore, the treatment by the chemical etching step in the present invention is different from the treatment by an acidic aqueous solution generally called etching in that a film formation is also intended.

By the treatment in the chemical etching step,
Release agent and oxide layer remaining on the magnesium alloy surface
At the same time as dissolving and removing the segregated layer of
It becomes possible to form a magnesium oxide film. Ma
Magnesium phosphate skin formed on the surface of gnesium alloy
The film adhesion amount is 10 to 2000 mg / m as a phosphorus adhesion amount.
^TwoIs required, and more preferably 50 to 1000 mg /
m^TwoIt is.

When the amount of the magnesium phosphate film adhered is less than 10 mg / m ² as the amount of the phosphorus adhered, the substrate cannot be sufficiently covered with the magnesium phosphate film, and the corrosion resistance and the adhesion of the film may be reduced. . On the other hand, if the phosphorus adhesion amount exceeds 2000 mg / m ² , the film becomes coarse,
It causes corrosion resistance and coating film adhesion to decrease.

As described above, since the surface of the magnesium alloy is chemically non-uniform, the magnesium phosphate film is formed preferentially on chemically active sites on the surface of the magnesium alloy. That is, it is preferentially formed at a portion where aluminum or zinc as an alloy component is segregated at a high concentration or a portion where an oxide film is not formed thickly. As the phosphoric acid compound contained in the phosphoric acid compound-containing aqueous solution, it is preferable to use at least one selected from the group consisting of orthophosphoric acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, and alkali metal salts thereof. .

The concentration condition of the phosphoric acid compound-containing aqueous solution depends on the kind of the phosphoric acid compound, but the concentration of the phosphoric acid compound is preferably 1 to 200 g / L. If the concentration of the phosphoric acid compound is less than 1 g / L, it is difficult to obtain a predetermined amount of the attached phosphorus, and the concentration is 200 g / L.
If it exceeds L, the film may become coarse.

Further, p of the aqueous solution containing a phosphoric acid compound is p
The H condition is preferably an aqueous solution of 1 to 12. If the pH is less than 1, the etching may be excessive and the film may be rough. Further, when the pH is in a strongly alkaline region (p
In a region exceeding H12), etching is insufficient, a predetermined amount of phosphorus is not obtained, and good corrosion resistance and coating film adhesion cannot be obtained. In addition, in the chemical etching step, a magnesium phosphate film is formed on the surface of the magnesium alloy, and at the same time, the surface is also etched to dissolve and remove the release agent, the oxide layer, and the segregated layer of the alloy component. . For this reason, in the processing solution in the strong alkaline region,
Since the etching force on the magnesium alloy surface is weak, the release agent, the oxide layer, and the segregated layer of the alloy component are not sufficiently dissolved and removed, which may be a factor adversely affecting the corrosion resistance and the coating film adhesion.

The pH condition of the aqueous solution containing a phosphoric acid compound is preferably in the range of 1 to 10, more preferably in the range of 1 to 7. The adjustment of the pH of the phosphoric acid compound-containing aqueous solution is naturally determined by the selection and concentration of the phosphoric acid compound to be contained, but fine adjustment is made to sodium hydroxide, sodium carbonate, tertiary phosphoric acid toward the alkali side. An alkali component such as sodium and ammonia can be added to the acid side, and an acid component such as phosphoric acid, nitric acid, sulfuric acid, tartaric acid, and oxalic acid can be appropriately added to the acid side.

The temperature and time for contacting the magnesium alloy as the object to be treated with the aqueous solution containing the phosphoric acid compound vary depending on the type, concentration and pH of the aqueous solution containing the phosphoric acid compound, the type of the magnesium alloy as the object to be treated, and the like. In any case, it may be appropriately adjusted so as to achieve the above-mentioned phosphorus attachment amount.

[Chemical conversion treatment step] The surface of the magnesium alloy to be treated is cleaned and simultaneously formed with a magnesium phosphate film in a chemical etching step.
Usually, it is sufficiently washed with water and then subjected to a chemical conversion treatment step to perform a chemical conversion treatment. The chemical conversion treatment is performed by bringing a magnesium alloy as an object to be treated into contact with a chemical conversion treatment solution.

The chemical conversion treatment liquid is not particularly limited, and a conventionally known chemical conversion treatment liquid for magnesium or a magnesium alloy may be used, including a so-called chromate-based chemical conversion treatment liquid. However, the chromate-based chemical conversion solution contains hexavalent chromium harmful to the human body, and a chemical conversion solution containing no hexavalent chromium is preferable.

As the chemical conversion treatment liquid, the following (1)
It is desirable to select from the two types shown in (2) and (3). (1) An acidic aqueous solution having a pH of 2 to 6 containing at least orthophosphoric acid and at least one metal ion selected from the group consisting of Zn, Mn, and Ca.

In the chemical conversion treatment solution, the concentration of orthophosphoric acid is preferably in the range of 10 to 100 g / L, and more preferably in the range of 30 to 70 g / L. On the other hand, the concentration of metal ions is 1 to 10 g.
/ L, more preferably 3 to 7 g / L.

When the chemical conversion treatment is performed with the chemical conversion treatment liquid
The weight of the chemical conversion film depends on the type of metal ion.
However, as an adhesion weight of metal ions, 30 to 300 mg
/ M ^TwoIs preferably in the range of 50 to 200 mg
/ M^TwoMore preferably, it is within the range.

(2) at least one fluorine compound selected from the group consisting of hydrofluoric acid, hydrofluoric acid, zircon hydrofluoric acid and titanium hydrofluoric acid;
An acidic aqueous solution having a pH of 2 to 6 containing at least one metal oxyacid compound selected from the group consisting of n, Mo, W, Ta, Re, Nb, and V.

In the chemical conversion treatment liquid, the concentration of the fluorine compound is preferably in the range of 20 to 1000 mg / L, more preferably in the range of 50 to 500 mg / L. On the other hand, the concentration of the metal oxyacid compound is preferably in the range of 0.5 to 10 g / L, and more preferably in the range of 1 to 7 g / L.

When the chemical conversion treatment is performed with the chemical conversion treatment liquid
The weight of the chemical conversion film depends on the type of metal ion.
However, as an attached weight of metal ions, 10 to 300 mg
/ M ^TwoIs preferably in the range of 30 to 200 mg
/ M^TwoMore preferably, it is within the range.

Temperature of the chemical conversion treatment solution in the chemical conversion treatment step,
The contact time with the magnesium alloy to be treated may be appropriately set depending on the composition and concentration of the chemical conversion treatment solution, the surface condition of the magnesium alloy as the treatment object, the target weight of the chemical conversion film, and the like.

Since the magnesium phosphate film formed on the magnesium alloy surface in the chemical etching step has a low chemical activity, a chemical conversion film is hardly formed on the film by the chemical conversion treatment step. The chemical conversion film is formed at a portion where the magnesium phosphate film is not coated or a portion where the coating is not sufficiently coated.

As described above, since the magnesium phosphate film formed in the chemical etching step has low chemical activity, the film itself also functions as a chemical conversion film for improving corrosion resistance and coating film adhesion. For this reason, the part where the magnesium phosphate film could not be sufficiently covered in the chemical etching step is subjected to a chemical conversion treatment in the next chemical conversion treatment step, so that the surface of the chemically non-uniform magnesium alloy is dense and dense. A uniform chemical conversion film (that is, a composite film) can be formed, and excellent corrosion resistance and coating film adhesion can be imparted.

[Each rinsing step] Between the above steps,
Pretreatment liquid (degreasing liquid, acidic aqueous solution, desmutting liquid,
It is desirable to provide a water washing step in order to prevent problems (such as deterioration of the treatment liquid due to mixing of each treatment liquid) caused by taking out the aqueous solution containing the phosphoric acid compound or the chemical conversion treatment liquid to the next step. The water washing in the water washing step is performed by bringing a magnesium alloy as an object to be treated into contact with water. The degree of water washing (contact time, water purity / temperature, number of washing steps, dilution ratio, etc.) is not particularly limited, and may be appropriately determined in consideration of the concentration of each processing solution, the degree of influence when mixed into the next step, and the like. Just set it.

[Pure water washing step] Although the magnesium alloy that has undergone the chemical conversion treatment step has already been subjected to the surface treatment according to the present invention, the chemical conversion treatment liquid (including the one diluted by the water washing step) remaining on the surface is removed. Concentration during drying may corrode the surface of the magnesium alloy or the film formed on the surface. In addition, when a surface on which a trace amount of impurities (contamination) remains is coated later, coating defects such as bumps, cissing, and pinholes may occur on the coated surface. Further, when the coating is performed by dip coating, impurities may be mixed into the coating to be applied, thereby deteriorating the coating.

Therefore, it is desirable to carry out pure water washing in order to replace the chemical conversion treatment liquid remaining on the surface with pure water containing no impurities or containing a small amount of impurities. The pure water to be supplied to the pure water washing step does not have to be so-called pure water, and there is no problem as long as it is deionized water that is used as pure water in the coating industry.

[Drying Step] The magnesium alloy that has undergone the above-described steps (partly, if necessary) is desirably dried in order to evaporate water remaining on the surface. Of course, when coating with a water-based paint, drying is not essential because the coating itself is possible even if moisture remains on the surface. However, water gets into the paint,
Since the concentration of the paint may be affected in some cases, it is desirable to provide a drying step also in this case. The drying is not particularly limited. For example, air drying may be used, but oven drying using a hot air heater, an infrared heater, or the like is preferable.

As described above, the magnesium alloy member of the present invention is obtained by performing the surface treatment according to the surface treating method of the magnesium alloy of the present invention. The obtained magnesium alloy member of the present invention has excellent corrosion resistance as it is, but in order to further improve corrosion resistance, or in order to improve the aesthetics of the magnesium alloy member,
Painting is done as needed. The paint used for painting is
There is no particular limitation, and any of an aqueous system and a solvent system may be used. Further, the coating method is not particularly limited, and any conventionally known coating method such as spray coating, dip coating, and electrodeposition coating can be applied.

[0062]

EXAMPLES Several examples of the surface treatment method of the present invention are given below, and the effectiveness is shown in comparison with comparative examples. Of course, the present invention is not limited to the embodiments described below. The pH of each treatment solution in the chemical etching process was finely adjusted by appropriately adding sodium hydroxide to the alkali side and phosphoric acid to the acid side (except for Comparative Example 6).

[Test Materials] The following three types of magnesium alloy plates were used as test materials.・ AZ91D (ASTM standard product, die casting method, 10
0mm × 100mm × 1mm) ・ AM60B (ASTM standard product, die casting method, 10
0mm × 100mm × 1mm) ・ AZ31C (ASTM standard product, rolled plate, 100mm ×
100mm x 1mm)

[Measurement of Film Adhesion Amount] Magnesium Phosphate Film The amount of magnesium phosphate film formed in the chemical etching process was determined by measuring the amount of phosphorus in the film. Specifically, the measurement was performed using a commercially available fluorescent X-ray analyzer. In other words, a plurality of samples with different amounts of phosphorus adhering are known, and the intensity (cps) at this time is measured.
A calibration curve of the strength-adhesion amount is prepared in advance. Then, a sample to be measured is measured under the same conditions.
From this measured intensity, it was converted to the amount of adhesion based on the calibration curve.

The sample to be measured was obtained by subjecting each of the following Examples and Comparative Examples to a treatment by a chemical etching step, washing without any chemical treatment, drying, and cutting out for measurement. .

2. Chemical conversion film As described below, two types of manganese-based and zirconium-based were used as the chemical conversion treatment solution, and thus the amount of the film attached was determined by measuring the amount of manganese or zirconium attached to the film. Specifically, using a commercially available X-ray fluorescence spectrometer, the amount of adhesion was converted into the amount of adhesion based on a calibration curve prepared in advance from the measurement intensity, similarly to the measurement of the amount of phosphorus adhesion.

The samples to be measured were subjected to the chemical conversion treatment in the chemical conversion treatment steps in the following Examples and Comparative Examples, washed with water, dried, and cut out for measurement. However, the manganese adhesion amount is shown by subtracting the measured value before the chemical conversion treatment from the measured value after the chemical conversion treatment because manganese is also included as an alloy component in the test material (the measured value before the chemical conversion treatment is: It was also determined at the time of measuring the amount of phosphorus attached.)

<Example 1> A surface treatment was carried out using AZ91D as a test material under the following treatment steps, treatment liquid compositions and treatment conditions in each step. [Treatment process] Degreasing (alkali degreasing) → water washing → chemical etching → water washing → chemical formation → water washing → pure water washing → drying

[Treatment solution composition and treatment conditions in each step] Degreasing step (alkali degreasing); Fine Cleaner (registered trademark) MG101 (Nippon Parkerizing Co., Ltd.)
30 g / L, 60 ° C., 5 minutes, immersion treatment Chemical etching process: orthophosphoric acid, 30 g / L (p
H2.5), 25 ° C., 2 minutes, immersion treatment, phosphorus adhesion amount: 200 mg / m ² , chemical conversion treatment step; Magbond (registered trademark) P20 (manganese type, manufactured by Nippon Parkerizing Co., Ltd.), 200 g /
L, 43 ° C, 3 minutes, immersion treatment, manganese adhesion amount: 75m
g / m ²・ Washing between each process; tap water, 25 ° C., 30 seconds, immersion treatment ・ Pure water washing; deionized water (electrical conductivity 2 μS), pour over the entire surface ・ Drying: 120 ° C., hot air for 10 minutes Oven drying

Example 2 A surface treatment was performed in the same manner as in Example 1 except that the composition of the processing solution and the processing conditions in the chemical etching process were changed as described below.・ Chemical etching process; sodium orthophosphate, 30
g / L (adjusted to pH 9.5), 60 ° C., 5 minutes, immersion treatment, phosphorus adhesion amount: 130 mg / m ²

Example 3 A surface treatment was performed in the same manner as in Example 1 except that the composition of the processing solution and the processing conditions in the chemical etching process were changed as described below.・ Chemical etching process; orthophosphoric acid, 30 g / L (p
H2.5), 25 ° C, 6 minutes, immersion treatment, phosphorus adhesion amount: 500 mg / m ²

Example 4 A surface treatment was performed in the same manner as in Example 1 except that the composition of the processing solution and the processing conditions in the chemical etching process were changed as described below.・ Chemical etching process; orthophosphoric acid, 100g / L
(Adjusted to pH 2.5), 25 ° C, 6 minutes, immersion treatment, phosphorus adhesion amount: 1500 mg / m ²

Example 5 A surface treatment was performed in the same manner as in Example 1 except that the composition of the processing solution and the processing conditions in the chemical etching process were changed as described below.・ Chemical etching process; orthophosphoric acid, 30 g / L (p
H2.5), 25 ° C, 15 seconds, immersion treatment, phosphorus adhesion amount: 12 mg / m ²

Example 6 A surface treatment was performed in the same manner as in Example 1 except that the composition of the treatment solution and the processing conditions in the chemical conversion treatment step were changed as described below. Chemical conversion step: Magbond (registered trademark) M30 (zirconium-based, manufactured by Nippon Parkerizing Co., Ltd.), 50 g
/ L, 60 ° C, 1 minute, immersion treatment, zirconium adhesion amount:
50 mg / m ²

<Example 7> In Example 1, the test material was changed to AM60B, the amount of phosphorus adhering to the chemical etching step was set to 180 mg / m ² , and the amount of manganese adhering to the chemical conversion step was set to 70 mg / m ² . The surface treatment was performed in the same manner as in Example 1, except that the adjustments were made so as to correspond to the respective cases.

<Example 8> In Example 1, the test material was changed to AZ31C, and the amount of phosphorus adhering in the chemical etching step was 110 mg / m ² , and the amount of manganese adhering in the chemical conversion step was 30 mg / m ² , The surface treatment was performed in the same manner as in Example 1, except that the adjustments were made so as to correspond to the respective cases.

<Comparative Example 1> A surface treatment was performed in the same manner as in Example 1 except that the chemical etching step was omitted.

<Comparative Example 2> A surface treatment was performed in the same manner as in Example 7, except that the chemical etching step was omitted.

Comparative Example 3 A surface treatment was performed in the same manner as in Example 7 except that the chemical etching step was omitted in the processing steps in Example 8.

Comparative Example 4 A surface treatment was performed in the same manner as in Example 6, except that the chemical etching step was omitted in the processing steps of Example 6.

Comparative Example 5 A surface treatment was performed in the same manner as in Example 1 except that the composition of the processing solution and the processing conditions in the chemical etching process were changed as described below.・ Chemical etching process; orthophosphoric acid, 30 g / L (p
H2.5), 25 ° C, 10 seconds, immersion treatment, phosphorus adhesion amount: 5 mg / m ²

Comparative Example 6 Surface treatment was performed in the same manner as in Example 1 except that the chemical etching step was changed to an etching step (acidic aqueous solution) indicating the composition of the processing solution and the processing conditions described below. went.・ Etching process (acidic aqueous solution); sulfuric acid, 20g / L
(Adjusted to pH 2.5 with sodium hydroxide), 25 ° C, 3
0 seconds, immersion treatment (of course, phosphorus adhesion amount: 0 mg /
m ² )

[Evaluation Tests] The following evaluation tests were performed on the surface-treated magnesium alloy members of Examples and Comparative Examples obtained as described above. The results are summarized in Table 1 below. In each evaluation test,
The above was judged to be a practically acceptable level.

1. Corrosion resistance after surface treatment For each surface-treated magnesium alloy member (sample), a corrosion resistance evaluation test was performed as it was. A salt spray method according to JIS-Z2371 was applied to the evaluation test. The salt spray time was 72 hours, and the corrosion resistance of each sample after the completion of the salt spray was visually evaluated to evaluate the corrosion resistance after the surface treatment. The evaluation criteria are as follows. ◎: Corrosion area rate of less than 1% ○: Corrosion area rate of 1% or more and less than 3% △: Corrosion area rate of 3% or more and less than 5% ×: Corrosion area rate of 5% or more

2. Corrosion resistance after coating For each surface-treated magnesium alloy member, the surface is subjected to cationic electrodeposition coating (Electron-2000, manufactured by Kansai Paint Co., Ltd.) at 20 to 25 μm, and the temperature is adjusted to 180 ° C., 20 ° C.
The dried product was used as a sample for a corrosion resistance evaluation test after coating. A salt spray method according to JIS-Z2371 was applied to the evaluation test. In the sample, a cross-cut was previously applied to the coating film. The salt spray time is 720 hours,
The corrosion resistance after coating was evaluated by measuring the swelling width on one side from the cross cut of each sample after the completion of the salt spray.
The evaluation criteria are as follows. ◎: One-side swelling width from cross cut is less than 1 mm ；: One-side swelling width from cross cut is 1 mm or more and 3 mm
Less than △: One side swollen width from cross cut is 3 mm or more and 5 mm
Less than ×: One side swelling width from cross cut is 5 mm or more

3. Coating Film Adhesion Each of the surface-treated magnesium alloy members was subjected to the same coating as described in “2. Corrosion Resistance After Coating” above as a sample for the coating film adhesion evaluation test. The adhesion of the coating film is determined by the cross-cut tape method coating film adhesion test (JIS-K5400, 1m
m × 1 mm, 100) and evaluated by the number of remaining coating films. The evaluation was performed at the initial stage and after the water resistance test (40 ° C., 1000 hours). The evaluation criteria are as follows. ◎: No peeling of coating film (100/100 remaining coating film) ○: 98/100 or more and less than 100/100 remaining coating film △: 95/100 or more and less than 98/100 remaining coating film ×: 95 remaining coating film Less than / 100

[0087]

[Table 1]

As is clear from Table 1, in Examples 1 to 8 in which the surface of the magnesium alloy member was cleaned and the magnesium phosphate film was formed at the same time by the treatment in the chemical etching process, It can be seen that they are superior in corrosion resistance and coating film adhesion as compared with Comparative Examples 1 to 4, which are omitted. Further, in Comparative Example 5, when the amount of the applied film of manesium phosphate was smaller than a predetermined amount,
Sufficient performance was not obtained. Good performance was not obtained for Comparative Example 6 in which sulfuric acid was used in the chemical etching step.

[0089]

As described above, by treating the surface of a magnesium alloy with the surface treatment method of the present invention, a surface having excellent corrosion resistance and coating film adhesion can be formed.
In the surface treatment method of the present invention, since it is possible to form a dense and uniform chemical conversion film even on a chemically non-uniform surface, it is hardly affected by a product shape, a product part, casting conditions, and the like, and is stable. Performance can be demonstrated.

Further, the chemical etching solution used in the present invention does not contain hexavalent chromium which is harmful to the human body and the environment. Therefore, unless a so-called chromate agent is used as a chemical conversion treatment solution, the chemical etching solution is extremely useful industrially. Things.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23F 1/22 C23F 1/22 F-term (Reference) 4K026 AA01 BA01 BA03 BA12 BB06 BB08 CA13 CA16 CA18 CA24 CA25 CA28 CA29 CA31 EA08 EA12 4K057 WA01 WB01 WE04 WK05 WN07

Claims (5)

[Claims] 1. A surface treatment method comprising: a degreasing step of degreasing a surface of a magnesium alloy; a chemical etching step of performing a chemical etching treatment; and a chemical conversion treatment step of forming a chemical conversion film using a chemical conversion treatment solution. The magnesium alloy is characterized in that the etching step is a step of bringing the surface of the magnesium alloy into contact with an aqueous solution containing a phosphoric acid-based compound to form a magnesium phosphate film having a phosphorus deposition amount of 10 to 2000 mg / m ^2. Surface treatment method. 2. The phosphoric acid compound-containing aqueous solution in the chemical etching step contains at least one selected from the group consisting of orthophosphoric acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid and alkali metal salts thereof as the phosphoric acid compound. And the concentration of the phosphoric acid compound is 1 to 200 g.
The surface treatment method for a magnesium alloy according to claim 1, wherein the pH is within a range of 1 to 12 and the pH is within a range of 1 to 12. 3. The chemical conversion treatment solution in the chemical conversion treatment step is an acidic aqueous solution of pH 2 to 6 containing at least orthophosphoric acid and at least one metal ion selected from the group consisting of Zn, Mn and Ca. The surface treatment method for a magnesium alloy according to claim 1 or 2, wherein: 4. The chemical conversion treatment solution in the chemical conversion treatment step, wherein at least one fluorine compound selected from the group consisting of hydrofluoric acid, hydrofluoric acid, zircon hydrofluoric acid and titanium hydrofluoric acid, and Mn, Mo, W, Ta, R
at least one selected from the group consisting of e, Nb and V
The surface treatment method for a magnesium alloy according to claim 1 or 2, wherein the aqueous solution is an acidic aqueous solution having a pH of 2 to 6 and containing an oxygen acid compound of a kind metal. 5. A magnesium alloy member which has been surface-treated by the method for surface treating a magnesium alloy according to claim 1. Description: