KR100999313B1 - Magnesium or magnesium alloy article having electroconductive anodic oxidation coating on the surface thereof and method for production thereof - Google Patents

Abstract

The present invention relates to a product made of magnesium or a magnesium alloy having on its surface a conductive anodized film having a resistance value of 100? Or less measured between two terminals 10 mm apart from each other. The product is prepared by immersing magnesium or magnesium alloy in an electrolyte solution containing 0.1 to 1 mol / L of phosphoric acid groups, 0.2 to 5 mol / L of ammonia or ammonium ions, pH 8 to 14, and anodizing the surface thereof. Can be. Thereby, the product which consists of magnesium or a magnesium alloy which has an anodized film on the surface which is electrically conductive and has excellent corrosion resistance is provided.

Conductive anodized, magnesium or magnesium alloy products, electrical conductivity, corrosion resistance

Description

Magnesium or magnesium alloy article having electroconductive anodic oxidation coating on the surface thereof and method for production             

TECHNICAL FIELD This invention relates to the product which consists of magnesium or magnesium alloy which has an anodized film excellent in electrical conductivity on the surface. The present invention also relates to a method for producing such a product.

Since magnesium and magnesium alloys are the lightest among the practical metals, they have high specific strength, good heat dissipation, and excellent recycling properties compared to resins, and have recently been widely used for electric devices or automotive parts. Especially, it is used suitably as an electrical equipment case with the high performance of small size and light weight, and high designability and a high recyclability. However, since magnesium and magnesium alloys are susceptible to corrosion, surface treatment or coating having corrosion resistance is required.

By performing anodizing treatment on magnesium or magnesium alloy, excellent corrosion resistance can be imparted. Typically, anodization treatment, which is a treatment method called the Dow17 method or the HAE method, is generally carried out, whereby an anodized film having practically sufficient corrosion resistance can be formed. In addition, Japanese Laid-Open Patent Publication No. 11-502567 (WO96 / 28591) describes a method of anodizing magnesium or magnesium alloy by immersion in an electrolyte solution containing ammonia and a phosphate compound.

In addition, it is described in the following publication that a degree of corrosion resistance can be imparted by forming a magnesium or magnesium alloy, and a film having conductivity can be formed. Japanese Laid-Open Patent Publication No. 2000-96255 discloses a chemical conversion coating containing a certain amount of calcium, manganese and phosphorus and having an electrical resistivity of 0.1 Ω · cm or less. In addition, Japanese Laid-Open Patent Publication No. 2000-328261 discloses that an magnesium alloy surface is etched with an acidic aqueous solution having a pH of 1 to 5, and then contacted with an alkaline aqueous solution having a pH of 7 to 14 containing an organophosphorus compound. A method of treating a magnesium alloy surface in contact with a chemical conversion treatment liquid is described, and it is described that a product having a small surface resistance can be obtained.

It is desirable to be able to efficiently shield electromagnetic waves generated therefrom in various displays such as plasma displays or cellular phones. Since magnesium and magnesium alloys have good electrical conductivity, an electrical device case using them can have good electromagnetic shielding properties. In addition, in order to prevent malfunction in most electric devices, especially digital electronic devices, it is important to ground (earth) to remove the electronic noise, but if the case is magnesium or magnesium alloy, it is also possible to ground there.

By the way, as mentioned above, magnesium and magnesium alloy require surface treatment or coating which has corrosion resistance. In anodic oxidation treatment for imparting corrosion resistance to magnesium or magnesium alloy, the insulating oxide film is coated on the magnesium or magnesium alloy, so that electromagnetic shielding property is lost and it is impossible to ground it. For this reason, for example, a method of masking a part for grounding, anodizing, or anodizing the entire surface, and then scraping off part of the anodic oxide is employed. However, this method was cumbersome to raise production costs.

On the other hand, the film formed by the chemical conversion treatment has recently been reported to have electrical conductivity, such as the film described in JP-A-2000-96255 or JP-A-2000-328261. However, compared with the anodic oxidation treatment in which a strong oxide film is formed by energizing magnesium or magnesium alloy, the film formed by chemical conversion treatment merely immersed in the treatment liquid does not have sufficient corrosion resistance. This problem is particularly important in recent mobile device cases because corrosion resistance under various environments is required. For this reason, in the case where a film is formed by chemical conversion treatment, a plurality of layers of coating are further applied thereon to secure corrosion resistance somehow. However, it is not always easy to apply uniform coating to a complicated case of electrical equipment, and it is expensive to carry out a plurality of coating steps.

On the other hand, in the Dow17 method which is currently widely practiced as anodizing, the anodized film obtained contains chromium, and in the HAE method, manganese is contained. In addition, most of the products obtained by chemical conversion treatment contain heavy metal elements. Thus, it is unpreferable that heavy metal element is mixed in magnesium or a magnesium alloy at the time of recycling and using heavy metal element. In particular, since magnesium and magnesium alloys are characterized by superior recyclability compared to plastics, the amount of heavy metal elements that accumulate as the number of recycling is repeated cannot be ignored. In addition, it is not preferable that the treatment liquid contains a heavy metal element from the viewpoint of waste liquid treatment or the preservation of the surrounding environment.

This invention is made | formed in order to solve the said subject, Comprising: It aims at providing the product which consists of magnesium or a magnesium alloy which has an anodized film which has electrical conductivity and excellent corrosion resistance on the surface. Moreover, it aims at providing the method of manufacturing the product which consists of such magnesium or magnesium alloy. The anodic oxide film obtained in the present invention can solve the above problems even if it does not contain heavy metal elements, and thus is excellent in terms of recyclability or environmental conservation. In addition, even if the electrolyte solution used does not contain heavy metal elements, the anodized film can be formed, thereby contributing to environmental preservation around the plant and reducing waste liquid treatment costs.

The above object is achieved by providing a product made of magnesium or a magnesium alloy having a conductive anodized film on the surface of which the resistance of the film surface measured between two terminals 10 mm apart from each other is 100 Ω or less.

Conventionally, the film obtained by anodizing magnesium or magnesium alloy was an insulator as a film containing oxide as a main component. Rather, since it is an insulator, it was thought that a corrosion current does not flow in a magnesium or magnesium alloy main body, and oxidation oxidation deterioration of a main body can be prevented. By the way, as a result of earnestly examining by the present inventors, the film which is anodizing film and has sufficient electrical conductivity was found. Moreover, it became clear that the outstanding corrosion resistance which the anodic oxide film had conventionally has remained. Thereby, the product which consists of magnesium or magnesium alloy which has the outstanding corrosion resistance and favorable electrical conductivity was able to be provided. In particular, it is possible to provide an electrical device case having excellent electromagnetic shielding properties and grounding characteristics. At this time, it is preferable that the film thickness of the anodizing film is 0.01 to 10 µm in view of the balance between corrosion resistance and electrical conductivity.

In this invention, it is preferable that the said anodizing film contains 35 to 65 weight% of magnesium elements and 25 to 45 weight% of oxygen elements. It is inferred that it contains the oxidized magnesium as a main component and has the corrosion resistance which an anodized film on the surface of magnesium or magnesium alloy should have originally, but the reason for having such corrosion resistance is not necessarily clear. Moreover, it is suitable that the said anodizing film contains 4 to 15 weight% of the phosphorus element, and it is preferable to contain 5 to 20 weight% of the aluminum element. It may be inferred that by containing an appropriate amount of elements other than magnesium and oxygen and having good electrical conductivity without impairing the corrosion resistance, the reason for having such electrical conductivity is also not clear. In addition, the anodized film of the present invention exhibits excellent performance even if it does not contain the heavy metal element contained in the conventional anodized film.

A preferred embodiment of the present invention comprises a magnesium or magnesium alloy in which all of the magnesium or magnesium alloy surfaces are covered with anodized film, and resin coating is applied only to a part of the anodized film surface and the anodized film of the remaining part is exposed. Product. By forming the exposed portion of the anodic oxide film in this way, it is possible to provide a product having a beautiful appearance and excellent friction resistance by resin coating while ensuring electromagnetic shielding properties or grounding characteristics. Specifically, the case where the electrical coating is not applied to the inner surface of the case and the outer surface of the case is coated with the resin is particularly preferred.

An object of the present invention is also characterized by immersing magnesium or magnesium alloy in an electrolyte solution containing 0.1 to 1 mol / L of phosphoric acid group, having a pH of 8 to 14, and subjecting the surface to anodizing. It is also achieved by providing a method for producing a product made of the magnesium or magnesium alloy. At this time, it is preferable that the electrolyte contains 0.2 to 5 mol / L of ammonia or ammonium ions.

As described above, in the anodic oxidation treatment to date, most of the treatment liquids contain heavy metal ions, and sometimes contain fluorine ions which make the waste liquid treatment difficult. On the other hand, in the manufacturing method of the product which consists of magnesium or magnesium alloy of this invention, even if it does not contain such a component, the anodic oxide film excellent in performance can be obtained. Since the restriction of the discharge of heavy metal element-containing waste liquids in recent years tends to be strict, it is important that the manufacturing method of the present invention is excellent in terms of environmental conservation.

In the production method of the present invention, in anodizing, magnesium or magnesium alloy is preferably immersed in an acidic aqueous solution, and then immersed in an electrolytic solution to be anodized. After appropriately pretreatment, it is then subjected to anodization so that a product having the effect of the present invention can be easily obtained.

Moreover, in the manufacturing method of this invention, after anodizing, it is preferable to coat a resin coating film only once on the surface of an anodizing film, and to heat at a temperature of 40-120 degreeC, and to dry a coating film. Since an anodic oxide film excellent in corrosion resistance can be obtained, only a simple coating process is sufficient, and as a result, manufacturing cost can be reduced.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

This invention is a product which consists of magnesium or magnesium alloy which has a conductive anodizing film on the surface whose resistance value of the film surface measured between two terminals 10 mm apart from each other is 100 ohms or less.

Magnesium or a magnesium alloy as a raw material may be made of magnesium as a main component, or may be a metal composed of magnesium alone or an alloy. Typically, magnesium alloys are suitably used to impart moldability, mechanical strength, ductility, and the like. Examples of magnesium alloys include Mg-Al alloys, Mg-Al-Zn alloys, Mg-Al-Mn alloys, Mg-Zn-Zr alloys, Mg-rare earth element alloys, and Mg-Zn-rare earth element alloys. Can be mentioned. In the Example of this invention, Mg-Al-Zn type alloy is used, and the aluminum oxide was contained in the obtained anodizing film. Therefore, as a magnesium alloy of a raw material, it is guessed that it is preferable to contain aluminum among the said various alloys.

The form of magnesium or magnesium alloy provided for anodizing is not particularly limited. Molded articles molded by a die cast method, thixo mold method, press molding method, forging method, or the like can be used. At the time of shaping | molding, a mold release agent may remain in the wrinkles or hollow part formed in the vicinity of the surface of a molded article. In the case of anodizing, it is easy to reduce the residual amount of the releasing agent as compared with the case of chemical conversion. The release agent which remains in a product may volatilize when heated, and may generate blisters in a resin coating film. Here, the mold release agent which consists of a silicone compound is typical as a mold release agent used at the time of shaping | molding.

Since the molded article which consists of magnesium or a magnesium alloy may have contamination on the surface from organic substances, such as a mold release agent adhering at the time of shaping | molding, it is preferable to perform a degreasing treatment. As a liquid for degreasing, the aqueous solution containing surfactant or a chelating agent is used suitably.

After degreasing as needed, it is preferable to immerse in an acidic aqueous solution, and then immerse in an electrolytic solution to perform anodization. The surface of the magnesium or magnesium alloy may be appropriately etched by immersing in an acidic aqueous solution to remove contamination of an already formed insufficient oxide film or remaining organic matter. Although it does not specifically limit as acidic aqueous solution, The aqueous solution of phosphoric acid has preferable acidity and is preferable. In the case of using an aqueous solution of phosphoric acid, magnesium phosphate may be formed on the surface simultaneously with etching. Moreover, surfactant or a chelating agent can be mix | blended with acidic aqueous solution, and degreasing treatment can also be performed simultaneously.

Furthermore, after treating with an acidic aqueous solution in this way, it is preferable to wash | clean with alkaline aqueous solution, and to apply to anodizing. In an acidic aqueous solution, an insoluble component [smut] may be attached to the surface of magnesium or magnesium alloy, and thus it is possible to remove it. As alkaline aqueous solution, the sodium hydroxide aqueous solution or the potassium hydroxide aqueous solution is used suitably.

After each treatment process such as the above degreasing treatment, acidic aqueous solution treatment and alkaline aqueous solution treatment, washing with water or drying may be carried out as necessary. In this way, magnesium or magnesium alloy to which pretreatment was performed as needed is immersed in electrolyte solution.

It is preferable that the electrolyte solution of this invention is an alkaline aqueous solution containing a phosphoric acid group, More specifically, the aqueous solution which contains 0.1-1 mol / L of phosphoric acid groups, and whose pH is 8-14 is preferable. By containing an appropriate amount of phosphoric acid groups, an appropriate amount of phosphorus element is included in the anodic oxide film. Furthermore, by making it alkaline, it is possible to prevent unnecessary elution of magnesium or magnesium alloy.

The phosphate group referred to here is one contained in the electrolyte as free phosphoric acid, phosphate, hydrogen phosphate, and dihydrogen phosphate. In the case of polyphosphoric acid or salts thereof obtained by condensation of phosphoric acid, it is assumed that the phosphoric acid groups contain as many phosphoric acid groups as those obtained by hydrolysis. In the case of a salt, a metal salt may be sufficient and a nonmetal salt, such as an ammonium salt, may be sufficient. It is preferable that content of a phosphoric acid group is 0.1-1 mol / L. More preferably, it is 0.15 mol / L or more, More preferably, it is 0.2 mol / L or more. More preferably, it is 0.7 mol / L or less, More preferably, it is 0.5 mol / L or less.

It is preferable that pH of electrolyte solution is 8-14. More preferably, pH is 9 or more, More preferably, it is 10 or more. More preferably, pH is 13 or less, More preferably, it is 12 or less.

Moreover, it is preferable that electrolyte solution contains 0.2-5 mol / L of ammonia or ammonium ion as these total amounts. Thereby, pH of electrolyte solution is maintained at moderate alkalinity. The content of ammonia or ammonium ion is more preferably 0.5 mol / L or more, and still more preferably 1 mol / L or more. More preferably, it is 3 mol / L or less, More preferably, it is 2 mol / L or less.

Although the electrolyte solution of this invention may contain another component in the range which does not impair the effect of this invention, it is preferable that it does not contain a heavy metal element substantially. Herein, the heavy metal element refers to a metal element having a specific gravity of more than 4 as a single element, and is contained in a typical electrolyte solution in the conventional anodizing treatment, and examples thereof include chromium and manganese. In particular, it is desirable to have strict emission regulations and not contain harmful chromium. In addition, it is usually not a problem that heavy metals contained in the magnesium alloy, for example, zinc are eluted in small amounts and contained in the electrolyte solution. Moreover, it is also preferable that the electrolyte solution of this invention does not contain a fluorine element. This is because the aqueous solution containing elemental fluorine is often difficult to treat wastewater.

In the electrolyte solution, anodizing treatment is performed by immersing pretreated magnesium or magnesium alloy as necessary and energizing it as an anode. Although the power supply to be used is not specifically limited, Although a DC power supply or an AC power supply can be used, it is preferable to use a DC power supply. In addition, when using a DC power supply, you may use either a constant current power supply or a constant voltage power supply, but it is preferable to use a constant current power supply. A negative electrode material is not specifically limited, For example, a stainless steel material etc. can be used suitably. The surface area of the negative electrode is preferably larger than the surface area of the magnesium or magnesium alloy to be anodized, more preferably twice or more, and usually 10 times or less.

When the constant current power source is used as the power source, the current density on the surface of the anode is usually 0.1 to 10 A / dm 2. It is suitably 0.2 A / dm 2 or more, and more preferably 0.5 A / dm 2 or more. Moreover, it is 5 A / dm <2> or less suitably, More preferably, it is 2 A / dm <2> or less. The energization time is usually 10 to 1000 seconds. It is suitably 20 seconds or more, More preferably, it is 50 seconds or more. Moreover, it is 500 second or less suitably, More preferably, it is 200 second or less. When energizing with a constant current power supply, the applied voltage at the start of energization is low, but as time passes, the applied voltage increases. The applied voltage at the end of energization is usually 50 to 400 volts. Preferably it is 100 volts or more, More preferably, it is 150 volts or more. Moreover, it is suitably 300 volts or less, More preferably, it is 250 volts or less. Although the applied voltage is often set to less than 100 volts in the conventional Dow17 method or the HAE method, which is a conventional anodization method, it is preferable to set it to a relatively high voltage in the anodization process of the present invention. As a result, even in a portion containing impurities such as a silicone releasing agent, the oxidation reaction can easily proceed, and a film with good conductivity can be easily formed on the entire surface of the magnesium or magnesium alloy. In addition, since oxygen gas is vigorously generated from the surface of the magnesium or magnesium alloy due to the oxidation reaction, the impurities are easily removed during the anodic oxidation treatment. The temperature of the electrolytic solution during energization is 5-70 degreeC normally. It is 10 degreeC or more suitably. More preferably, it is 50 degrees C or less, More preferably, it is 30 degrees C or less.

After the energization ends, the electrolyte solution adhered to the surface of the anodized film is removed by washing. In washing, it is preferable to wash using not only water but acidic aqueous solution. Since electrolyte solution is alkaline, adhesiveness of a coating film improves when resin coating is performed by washing | cleaning with acidic aqueous solution. As the acidic aqueous solution, nitric acid aqueous solution, hydrochloric acid aqueous solution, sulfuric acid aqueous solution and the like can be used. After washing, it is dried and the product which consists of magnesium or magnesium alloy which has an anodizing film on the surface is obtained.

The product made of the magnesium or magnesium alloy of the present invention has a conductive anodized film having a resistance of 100? Or less on the surface of the coating surface measured between two terminals 10 mm apart from each other. The resistance value is a resistance value (Ω) measured by pressing the terminals to any two points 10 mm apart from each other on the surface of the anodized film, and the product of the present invention preferably has a resistance value equal to or less than the above value at at least one surface thereof. . Since the resistance value of a magnesium or magnesium alloy main body is small, the value correlated substantially with the electrical resistance of the thickness direction of the anodizing film which exists between a measuring terminal and a magnesium or magnesium alloy main body. Therefore, the resistance value is a numerical value corresponding to the performance required for the product in terms of electromagnetic shielding properties or grounding characteristics. It is 10 ohms or less suitably, More preferably, it is 1 ohms or less, and 0.5 ohms or less is optimal. In addition, in the case of AZ91D, the resistance value of the surface of the molded article which consists of untreated magnesium or magnesium alloy is a value of about 0.02-0.1 ohm normally.

In the anodic oxide film obtained in the present invention, as shown in Fig. 1, a large number of voids, which are thought to be derived from sparks during energization, are often present on the surface. This differs from the chemical conversion coating. It is preferable that the film thickness of an anodizing film is 0.01-10 micrometers. More preferably, it is 0.1 micrometer or more, More preferably, it is 0.5 micrometer or more. Moreover, More preferably, it is 5 micrometers or less, More preferably, it is 3 micrometers or less. If the film thickness is too thin, the corrosion resistance may deteriorate. If the film thickness is too thick, the electrical conductivity may decrease, and the electromagnetic shielding property or the grounding property may decrease.

Although the chemical composition of the anodic oxide film obtained by this invention is not specifically limited, It is preferable to contain 35-65 weight% of magnesium elements, and 25-45 weight% of oxygen elements. That is, it is preferable to contain, as a main component, oxidized magnesium, which is a result of the anodization of magnesium or magnesium alloy. The content of the magnesium element is more preferably 40% by weight or more, and still more preferably 45% by weight or more. More preferably, it is 60 weight% or less, More preferably, it is 55 weight% or less. The content of the oxygen element is more preferably 30% by weight or more. Moreover, More preferably, it is 40 weight% or less.

It is preferable that the said anodic oxide film contains 4-15 weight% of phosphorus elements. The content of phosphorus element is more preferably 5% by weight or more, and even more preferably 6% by weight or more. More preferably, it is 12 weight% or less, More preferably, it is 10 weight% or less. Moreover, it is preferable to contain 5-20 weight% of aluminum elements. Content of an aluminum element becomes like this. More preferably, it is 7 weight% or more, More preferably, it is 9 weight% or more. More preferably, it is 17 weight% or less, More preferably, it is 15 weight% or less. By containing an appropriate amount of the above elements other than magnesium and oxygen, it can be inferred to have good electrical conductivity without impairing the corrosion resistance. The anodizing film of the present invention may contain elements other than those described above within the range of not impairing the effects of the present invention. However, it is preferable that substantially no heavy metal, especially chromium element is contained, except that the magnesium alloy which is a raw material originally contains. Moreover, it is preferable that substantially no fluorine element is included.

The use of the product which consists of the magnesium or magnesium alloy of this invention which has an anodizing film on the surface is not specifically limited, It can be used for various electrical equipment, automobile parts, etc. In use, a coating of the anodized film may be applied to the surface of the anodized film as necessary, but in order to take advantage of the characteristics of the anodized film of the present invention having good electrical conductivity, the whole product should not be covered with a coating made of an insulating film.

The coating material to be used is not particularly limited, and various coating materials used for coating the metal surface can be used. A resin coating film can be formed using a solvent type coating material, an aqueous coating material, a powder coating material, etc. Although sufficient coating is possible only by volatilizing a solvent or water at a relatively low temperature or a thermosetting paint requiring high temperature sintering after application, it is preferable to use the latter which is easy to operate. Moreover, in order to make an external appearance beautiful, it is preferable to use a transparent resin paint, and you may use suitably colored thing. A coating method is not specifically limited, either, A well-known method, such as spray coating, immersion coating, electrodeposition coating, powder coating, can be employ | adopted. In the product which consists of the magnesium or magnesium alloy of this invention in which it is preferable to have a part which does not have a coating film in part, powder coating by spray coating or the spraying method is employ | adopted suitably.

 After anodizing, it is preferable to coat the resin coating film only once on the surface of the anodizing film to form a coating film. In electrical equipment cases and the like, they often have complicated shapes, and it is not always easy to form a homogeneous coating film. In many cases, the corrosion resistance is further improved by applying a plurality of coatings, but the increase in the cost also increases when the number of coatings is large. For this reason, in the product which consists of the magnesium or magnesium alloy of this invention which is favorable in corrosion resistance, sufficient corrosion resistance can be obtained by only one coating in many cases.

When using a solvent type coating or an aqueous coating, it is preferable to heat at 40-120 degreeC, and to dry a coating film. More preferably, they are 50 degreeC or more and 100 degrees C or less. In the product which consists of the magnesium or magnesium alloy of this invention which is favorable in corrosion resistance, it is often sufficient only by resin coating hardened | cured at the comparatively low temperature heating process, and as a result, manufacturing cost can be reduced. The heat drying method is not particularly limited, and a general-purpose oven or the like can be used.

A preferred embodiment of the present invention comprises a magnesium or magnesium alloy in which all of the magnesium or magnesium alloy surfaces are covered with anodized film, and resin coating is applied only to a part of the anodized film surface and the anodized film of the remaining part is exposed. Product. Thus, the whole surface of magnesium or magnesium alloy is coat | covered with an anodizing film, and the corrosion resistance of the whole product can be ensured. However, all here is substantially everything, and there may be some parts in which the anodic oxide film is not formed, such as the contact part connected to the power supply during the anodic oxidation treatment. In addition, the resin coating is applied only to a part of the surface of the anodized film, and the anodized film of the remaining part is exposed, so that the appearance is beautiful and the friction resistance is excellent by the resin coating while ensuring electromagnetic shielding or grounding properties. It can be provided.

A particularly suitable embodiment is an electrical equipment case in which resin coating is not applied to the inner surface of the case and resin coating is applied to the outer surface of the case. By coating the outer surface of the case, not only the appearance can be made beautiful but also the damage during use can be prevented. On the other hand, since the conductive anodization film is exposed on the inner surface of the case, it is possible to easily secure the ground from the electrical wiring and effectively shield the electromagnetic waves from the electronic circuits inside the case.

The product which consists of magnesium or magnesium alloy of this invention obtained in this way can be used for various uses. It can be used for electronic device cases such as mobile phones, personal computers, video cameras, still cameras, optical disk players, displays (CRT, plasma, liquid crystal), projectors, and automobile parts.

1 is a photograph of the surface of the anodized film obtained in Example 1 observed with a scanning electron microscope.

2 is a photograph of the surface of the test piece of Example 1 after being provided in the warm water immersion test.

3 is a photograph of the surface of a test piece of Example 1 after being subjected to a salt spray test.

4 is a photograph of the surface of a test piece of Comparative Example 3 after being provided in a warm water immersion test.

5 is a photograph of the surface of a test piece of Comparative Example 3 after being provided in a salt spray test.

Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these. The test method in this Example was performed according to the following method.

(1) Film thickness measurement of anodized film

The test piece was cut | disconnected to the dimension of 5 mm x 10 mm, and it buried in the epoxy resin, and the cut surface was grind | polished, and the mirror surface was obtained. From the cross-sectional direction of a sample, the electron micrograph was image | photographed using the Nippon Denshi Corporation X-ray micro analyzer "JXA-8900", and the film thickness was measured.

(2) chemical composition analysis of anodized film

The film composition was analyzed from two directions of the film surface and the cross section using the X-ray micro analyzer "JXA-8900" by Nippon Denshi Corporation. Measurement was carried out in three places in each direction, and the chemical composition was determined from these average values. The measurement was performed under the conditions of an acceleration voltage of 15 kV and a sample irradiation current of 2x10 ^-8 A. Data analysis was performed by ZAH correction.

(3) Resistance measurement on the surface of anodized film

It was measured using a two-probe probe "MCP-TP01" using a low-resistance meter "Lolesta AP MCP-T400" manufactured by Mitsubishi Chemical Corporation. The resistance value (Ω) was measured by pressing the measurement terminal on the film surface at the center of the test piece. The probe is a measuring terminal arranged at intervals of 10 mm, the terminal is gold-plated beryllium alloy, its tip shape is a cylindrical shape with a diameter of 2 mm, the load for pressing the terminal to the film surface is 240g per one terminal .

(4) hot water immersion test

The test piece was immersed in hot water maintained at 70 degreeC for 24 hours. After 24 hours, the test piece was extracted, the moisture was wiped off, and a checkerboard cut was inserted at intervals of about 1 mm to penetrate the resin coating film and the anodizing film, and the tape peeling test was conducted in accordance with JIS K5400. Peeling or other defects were visually observed.

(5) salt spray test

A cross-shaped cut (crosscut) was put on the surface of the test piece so as to penetrate the resin coating film and the anodized film, and then a 5% salt spray test was conducted for 120 hours in accordance with JIS Z-2371. After 120 hours, the test pieces were extracted and visually observed the occurrence of blisters from the crosscut portion or the presence of other defects.

Example 1

ASTM No. consisting of 90% magnesium, 9% aluminum and 1% zinc. Using a magnesium alloy of AZ91D as a raw material, an alloy plate having a size of 170 mm x 50 mm x 2 mm cast by a hot chamber method was used as a test piece. The test piece was immersed in an acidic aqueous solution containing 2.2% by weight of phosphoric acid and a trace amount of surfactant, and then washed with ion-exchanged water. Subsequently, it was immersed in the alkaline aqueous solution containing 18 weight% sodium hydroxide, and then washed with ion-exchange water, and the test piece surface was pretreated.

Aqueous phosphoric acid solution and ammonia water were mixed, an electrolyte solution containing 1.5 mol / L of phosphoric acid groups in a total amount of 0.25 mol / L and ammonia or ammonium ions was prepared, and maintained at 20 ° C. PH of this electrolyte solution was 11. Among them, the magnesium alloy test piece subjected to the pretreatment was immersed as an anode and subjected to anodization. As the negative electrode at this time, a SUS316L plate having a surface area four times that of the positive electrode was used. Using a constant current power source, the current density on the surface of the anode was 1 A / dm 2, and the current was supplied for 120 seconds. The low applied voltage at the start of energization rose to about 200 volts at the end of energization. After the energization was completed, the mixture was washed in the order of ion-exchanged water, aqueous nitric acid solution, and ion-exchanged water, followed by drying.

The photograph which observed the obtained anodic oxide film surface with the scanning electron microscope is shown in FIG. On the surface of the anodic oxide film, the presence of a large number of pores, which are thought to be derived from sparks during energization, were recognized. The film thickness of this anodic oxide film was about 1.5 micrometers. The film thickness here is an average distance in the magnesium alloy surface of a base material from the surface of a thick part in the film which has a local film thickness nonuniformity because it has many voids. The resulting anodic oxide film contained 48.0% by weight of magnesium, 33.5% by weight of oxygen, 7.0% by weight of phosphorus and 11.2% by weight of aluminum. The resistance value of the anodized film surface was 0.25?.

The surface of the anodic oxide film thus obtained was air-sprayed with an acrylic silicone paint "Ascote 300J" manufactured by Kyushu Chemical Co., Ltd. At this time, the acrylic silicone paint was applied only once to the surface of the anodized film without primer coating in coating. After coating, the mixture was heated at 60 ° C. for 20 minutes to evaporate the solvent to cure the coating film. As a result, a coating film having a thickness of about 20 μm was formed on the surface of the anodized film.

The obtained test piece was subjected to the hot water immersion test and the salt spray test, and in either case, no change in appearance was observed on the surface. The photograph of the test piece surface after being provided for the hot water immersion test is shown in FIG. 2, and the photograph of the test piece surface after being provided for the salt spray test is shown in FIG.

Comparative Example 1

Aqueous phosphoric acid solution and ammonia water were mixed, an electrolyte solution containing 0.88 mol / L of phosphoric acid groups in a total amount of 0.08 mol / L and ammonia or ammonium ions was prepared, and maintained at 20 ° C. PH of this electrolyte solution was 11. Among them, the magnesium alloy test piece subjected to the pretreatment as in Example 1 was immersed as an anode, and anodized. As a negative electrode at this time, the same thing as Example 1 was used. Although the voltage applied at the anode surface was 1 A / dm 2 using a constant current power source, the voltage was low at the start of energization for 120 seconds, but rose to about 200 volts at the end of energization. After the energization was completed, the mixture was washed in the order of ion-exchanged water, aqueous nitric acid solution, and ion-exchanged water, followed by drying.

The film thickness of the anodic oxide film thus obtained was about 1.5 mu m, and contained 54.8 wt% magnesium element, 37.7 wt% oxygen element, 3.2 wt% phosphorus element, and 4.3 wt% aluminum element. The resistivity on the surface of the anodized film exceeded 10 ⁷ Ω, which is the measurement limit of the resistivity meter used for the measurement.

On the obtained anodized film surface, a resin coating film was formed in the same manner as in Example 1. The obtained test piece was subjected to the hot water immersion test and the salt spray test, and in either case, no change in appearance was observed on the surface.

Comparative Example 2

It is the example which tested the well-known anodized film formation method called Dow17 method. An electrolyte solution containing 300 g / L of acidic ammonium fluoride, 100 g / L of sodium dichromate and 90 g / L of phosphoric acid was prepared and maintained at 75 ° C. Among them, the magnesium alloy test piece subjected to the pretreatment as in Example 1 was immersed as an anode, and anodized. As a negative electrode at this time, the same thing as Example 1 was used. Using a constant current power source, the current density was 4 A / dm 2 at the surface of the positive electrode, and energized for 300 seconds. At the end of energization it rose to about 70 volts. After the end of energization, it was washed with ion-exchanged water and dried.

The film thickness of the anodic oxide film thus obtained was about 1.5 µm, 26.0 weight% of magnesium element, 25.7 weight% of oxygen element, 11.2 weight% of phosphorus element, 1.0 weight% of aluminum element, 23.4 weight% of fluorine element, It contained 9.2 weight% of chromium elements and 3.6 weight% of sodium elements. The resistivity on the surface of the anodized film exceeded 10 ⁷ Ω, the measurement limit of the resistivity meter used for the measurement.

Comparative Example 3

Instead of anodizing, the chemical conversion treatment is carried out using a commercial chemical treatment solution. The treatment liquid was prepared by diluting it with ion-exchange water so that the conversion treatment solution "MC-1000" made from Million Chemical Co., Ltd. may be contained at a ratio of 75 g / L, and maintained at 40 degreeC. Although the detailed chemical composition of this chemical conversion liquid is unclear, it is estimated that it is a chemical conversion liquid containing phosphate ion, manganese (or manganese oxide) ion, and calcium ion. In this processing liquid, the magnesium alloy test piece subjected to the pretreatment as in Example 1 was immersed for 30 seconds. After immersion, it was washed with ion-exchanged water and dried.

The film thickness of the obtained chemical conversion treatment film was 0.1 micrometer or less, and was thin film thickness which is difficult to measure quantitatively. This chemical conversion film contained 85 mg / m 2 of calcium elements, 95 mg / m 2 of manganese elements, and 220 mg / m 2 of phosphorus elements as content per unit area. Moreover, the resistance value of this chemical conversion coating surface was 0.5 ohms.

On the obtained chemical conversion film surface, the resin coating film was formed like Example 1. The external appearance after the obtained test piece was provided to the hot water immersion test is shown in FIG. 4, and the external appearance after being provided to the salt spray test is shown in FIG. In either case, peeling of the resin coating film was remarkably recognized around the cutting | disconnection which put into the film.

Comparative Example 4

Instead of the anodizing treatment, a chemical conversion treatment is performed using a commercially available chemical treatment solution different from Comparative Example 3. The treatment liquid was prepared by diluting with Nippon Parka Co., Ltd. chemical conversion treatment liquid "MB-C10M" in 75 g / L ratio, and preparing the process liquid, and maintaining it at 50 degreeC. Although the detailed chemical composition of this chemical conversion treatment liquid is unclear, it is estimated that it is a chemical conversion treatment liquid containing 14 weight% of chromic anhydride and 0.7 weight% of hydrogen fluoride as a main component. In this treatment liquid, the magnesium alloy test piece subjected to the same pretreatment as in Example 1 was immersed for 60 seconds. After immersion, it was washed with ion-exchanged water and dried.

The film thickness of the obtained chemical conversion treatment film was 0.1 micrometer or less, and was thin film thickness which is difficult to measure quantitatively. This chemical conversion film contained 190 mg / m <2> of chromium element as content per unit area. Moreover, the resistance value of this chemical conversion coating surface was 0.75 ohms.

On the obtained chemical conversion film surface, the resin film was formed like Example 1. The obtained test piece was subjected to the hot water immersion test and the salt spray test, and in either case, no peeling or blistering of the resin coating film around the cut put into the film was recognized. However, after the hot water immersion test, it was observed that a plurality of dots (bubbles) bulging in dots were generated in the coating film at a portion near the edge of the test piece.

As described above, the product made of the magnesium alloy of the present invention obtained by anodizing in Example 1 had both electrical conductivity and excellent corrosion resistance. In contrast, a product made of a magnesium alloy obtained by conventional anodizing treatment as disclosed in Comparative Examples 1 or 2 was excellent in corrosion resistance, but electrical conductivity was not recognized. On the other hand, the product which consists of magnesium alloy obtained by the chemical conversion treatment as disclosed in the comparative example 3 was recognized electrical conductivity, but corrosion resistance was not enough.

The product made of the magnesium or magnesium alloy of the present invention has an anodized film having electrical conductivity and excellent corrosion resistance on its surface. Therefore, it is used as a product which consists of magnesium or a magnesium alloy which is excellent in electromagnetic shielding property or grounding property, and is especially useful as an electrical equipment case. Moreover, the product does not contain heavy metals and is suitable for recycling. In addition, since the anodic oxidation treatment can be performed with an electrolyte solution that does not use heavy metal ions or fluorine ions, it is possible to provide an excellent production method in terms of environmental conservation.

Claims (13)

A film measured between two terminals containing 35 to 65% by weight of magnesium element, 25 to 45% by weight of oxygen element and 4 to 15% by weight of phosphorus element and having a thickness of 0.01 to 10 µm and 10 mm apart from each other. A product made of magnesium or a magnesium alloy having a conductive anodized film having a surface resistance of 100 Ω or less. delete delete The product of claim 1, wherein the anodized film contains 5 to 20 wt% of an aluminum element. delete 2. A product according to claim 1, wherein the entire surface of the magnesium or magnesium alloy is covered with anodized film, the resin coating is applied to only a part of the surface of the anodized film, and the remaining anodized film is exposed. . The product made of magnesium or a magnesium alloy according to claim 6, wherein the inner surface of the case is not coated with resin, and the outer surface of the case is a resin case coated with resin. A method for producing a product according to claim 1, comprising 0.1 to 1 mol / L of phosphoric acid groups, immersing magnesium or a magnesium alloy in an electrolyte solution having a pH of 8 to 14, and anodizing the surface thereof. The method of claim 8, wherein the electrolyte contains 0.2 to 5 mol / L of ammonia or ammonium ions. The method for producing a product according to claim 8 or 9, wherein the magnesium or magnesium alloy is previously immersed in an acidic aqueous solution and then immersed in an electrolyte solution. The method for producing a product according to claim 8 or 9, wherein, after anodizing, the resin coating film is coated only once on the surface of the anodizing film, and the coating film is dried by heating at a temperature of 40 to 120 ° C. A product according to claim 1, wherein the conductive anodization film does not contain elemental fluorine. The method for producing a product according to claim 8, wherein the electrolyte solution does not contain fluorine element.

Images