JP4686728B2 - Method for producing magnesium or magnesium alloy product having an anodized film on the surface - Google Patents

Description

  The present invention relates to a method for producing a product made of magnesium or a magnesium alloy having an anodized film with excellent corrosion resistance on the surface.

  Magnesium and magnesium alloys are lightest in practical metals, so they have high specific strength, good heat dissipation, and excellent recyclability compared to resins, so that they are widely used in recent years for electrical equipment and automotive parts. It has become to. Among them, it is suitably used as a casing for electrical equipment that has high performance requirements for reduction in size and weight, and has high requirements for design and recyclability. However, since magnesium and magnesium alloys are easily corroded, surface treatment or coating having corrosion resistance is required.

  Excellent corrosion resistance can be imparted by anodizing magnesium or a magnesium alloy. Typically, anodizing treatment with a prescription called Dow17 method or HAE method is generally performed, whereby an anodized film having practically sufficient corrosion resistance can be formed. Also, Japanese Patent Publication No. 11-502567 (Patent Document 1: WO96 / 28591) describes a method of anodic oxidation of magnesium or a magnesium alloy by immersing in an electrolyte containing ammonia and a phosphate compound. ing.

  In addition, it is described in the following publication that a certain degree of corrosion resistance can be imparted by chemical conversion treatment of magnesium or a magnesium alloy, and a conductive film can be formed. Japanese Unexamined Patent Publication No. 2000-96255 (Patent Document 2) describes a chemical conversion film containing a certain amount of calcium, manganese, and phosphorus and having an electrical resistivity of 0.1 Ω · cm or less. JP 2000-328261 A (Patent Document 3) discloses that after etching the surface of a magnesium alloy with an acidic aqueous solution having a pH of 1 to 5, it is brought into contact with an alkaline aqueous solution having a pH of 7 to 14 containing an organic phosphorus compound. Subsequently, a surface treatment method of a magnesium alloy that is brought into contact with a chemical conversion treatment liquid is described, and it is described that a product having a small surface resistance value can be obtained.

  As described above, the film formed by the chemical conversion treatment includes, for example, an electric film such as the film described in JP 2000-96255 A (Patent Document 2) and JP 2000-328261 A (Patent Document 3). Those having conductivity have recently been reported. However, compared with an anodizing treatment in which a strong oxide film is formed by energizing magnesium or a magnesium alloy, a film formed by a chemical conversion treatment simply immersed in a treatment solution has insufficient corrosion resistance. This problem is particularly important in the case of mobile device casings and the like in recent years because corrosion resistance in various environments is required. For this reason, when a film is formed by chemical conversion treatment, the present situation is that a plurality of layers are further coated thereon to ensure corrosion resistance. However, it is not always easy to apply a uniform coating to a casing of an electric device having a complicated shape, and a cost increase is great if a plurality of coating steps are performed.

  On the other hand, in the Dow 17 method, which is widely used as an anodizing treatment, the obtained anodized film contains chromium, and in the HAE method, manganese is contained. In many products obtained by chemical conversion treatment, the coating contains a heavy metal element. When the heavy metal element is contained in this manner, the heavy metal element is mixed into the magnesium or the magnesium alloy at the time of recycling, which is not preferable. In particular, since magnesium and magnesium alloys are characterized by excellent recyclability compared to plastics, the amount of heavy metal elements accumulated by the repeated number of recycling cannot be ignored. In addition, if the treatment liquid contains a heavy metal element, it is not preferable from the viewpoint of waste liquid treatment and preservation of the surrounding environment.

Japanese National Patent Publication No. 11-502567 JP 2000-96255 A JP 2000-328261 A

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a product made of magnesium or a magnesium alloy having an anodized film having excellent corrosion resistance on the surface. It is. The anodic oxide film obtained by the present invention can solve the above problems even if it does not contain a heavy metal element, and is therefore excellent from the viewpoints of recyclability and environmental conservation. Moreover, since the anodic oxide film can be formed even if the electrolytic solution used does not contain a heavy metal element, it is possible to contribute to environmental conservation around the factory and to reduce waste liquid treatment costs.

An object of the present invention is to provide an electrolytic solution containing 0.2 to 1 mol / L of a phosphate group, 0.2 to 5 mol / L of ammonia or ammonium ions, no fluorine element, and having a pH of 9 to 13. It is characterized by immersing magnesium or a magnesium alloy in the liquid and anodizing the surface while sparking during energization to form an anodized film in which a large number of holes originating from the energized spark are present on the surface This is achieved by providing a method for producing a product made of magnesium or a magnesium alloy having an anodized film on its surface. At this time , it is preferable that the electrolytic solution does not substantially contain a heavy metal element.

  As described above, in the conventional anodic oxidation treatment, the treatment liquid mostly contains heavy metal ions, and sometimes contains fluorine ions that make waste liquid treatment difficult. On the other hand, in the method for producing a product made of magnesium or magnesium alloy of the present invention, an anodized film having excellent performance can be obtained without containing such components. In recent years, since the regulation of discharge of heavy metal element-containing waste liquid is becoming stricter, it is important that the production method of the present invention is excellent from the viewpoint of environmental conservation.

  In the production method of the present invention, it is preferable to immerse magnesium or a magnesium alloy in an acidic aqueous solution before anodic oxidation, and then anodic oxidation by immersing in an electrolytic solution. A product exhibiting the effects of the present invention can be easily obtained by subjecting it to an anodic oxidation treatment after appropriate pretreatment.

  Conventionally, a film obtained by anodizing magnesium or a magnesium alloy is a film mainly composed of an oxide and is an insulator. Rather, because it is an insulator, it has been considered that no corrosion current flows through the magnesium or magnesium alloy main body and that the main body can be prevented from oxidative deterioration. However, as a result of intensive studies by the present inventor, a film having sufficient electrical conductivity while being an anodized film was found. In addition, it has also been clarified that the excellent corrosion resistance that the anodized film has conventionally had is maintained as it is.

In the present invention, it is preferable that the anodized film contains 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 does not contain fluorine element. is there. By containing oxidized magnesium as a main component, it can be presumed that the anodized film on the surface of magnesium or magnesium alloy has the corrosion resistance that should be inherent, but the reason for having such corrosion resistance is Not necessarily certain. It is also preferable that the product is made of a magnesium alloy containing aluminum, and the anodized film contains 5 to 20% by weight of an aluminum element. It can be presumed that by containing an appropriate amount of elements other than magnesium and oxygen, it will have good electrical conductivity without impairing corrosion resistance, but the reason for having such electrical conductivity is also Not sure. Further, the anodized film of the present invention exhibits excellent performance even if it does not contain a heavy metal element as contained in a conventional anodized film .

  In the production method of the present invention, it is preferable that after the anodizing treatment, the resin coating film is applied only once on the surface of the anodized film and heated at a temperature of 40 to 120 ° C. to dry the coating film. It is. Since an anodic oxide film having excellent corrosion resistance can be obtained, only a simple coating process is sufficient, and as a result, the manufacturing cost can be reduced.

  A product made of magnesium or a magnesium alloy obtained by the production method of the present invention has an anodized film having excellent corrosion resistance on its surface. Moreover, the product does not contain heavy metals and is suitable for recycling. Furthermore, since it can be anodized with an electrolytic solution that does not use heavy metal ions or fluorine ions, an excellent manufacturing method can be provided from the viewpoint of environmental conservation.

  Hereinafter, the present invention will be described in detail.

  The present invention is a method for producing a product made of magnesium or a magnesium alloy having an anodized film on its surface.

  Magnesium or a magnesium alloy used as a raw material may be one containing magnesium as a main component, and may be a metal made of magnesium alone or an alloy. Usually, a magnesium alloy is preferably used to impart formability, 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 elements alloys, Mg-Zn-rare earth elements alloys. Etc. In the examples of the present invention, an Mg—Al—Zn alloy was used, and the obtained anodic oxide film contained an aluminum element. Therefore, it is presumed that the magnesium alloy as the raw material is preferably one containing aluminum among the above-mentioned various alloys.

  The form of magnesium or magnesium alloy used for the anodizing treatment is not particularly limited. A molded product formed by a die casting method, a thixo mold method, a press molding method, a forging method, or the like can be used. At the time of molding, the mold release agent may remain inside the ridges or hollow portions formed near the surface of the molded product. In the case of anodizing, it is easy to reduce the remaining release agent compared to the case of chemical conversion. The release agent remaining in the product volatilizes when heated, and may cause swelling in the resin coating. Here, as a mold release agent used at the time of shaping | molding, the mold release agent which consists of a silicone compound is typical.

  Since a molded product made of magnesium or a magnesium alloy may have dirt on its surface due to organic substances such as a release agent attached during molding, it is preferable to perform a degreasing treatment. As the liquid for degreasing, an aqueous solution containing a surfactant or a chelating agent is preferably used.

  After degreasing as necessary, it is preferable to immerse in an acidic aqueous solution and then immerse in an electrolytic solution to perform anodization. By dipping in an acidic aqueous solution, the surface of magnesium or a magnesium alloy can be appropriately etched to remove an already formed insufficient oxide film and remaining organic contaminants. Although it does not specifically limit as acidic aqueous solution, Phosphoric acid aqueous solution has moderate acidity, and is suitable. When a phosphoric acid aqueous solution is used, magnesium phosphate may be formed on the surface simultaneously with etching. In addition, a degreasing treatment can be performed simultaneously by mixing a surfactant or a chelating agent with an acidic aqueous solution.

  It is also preferable that after the treatment with the acidic aqueous solution, the anodic oxidation treatment is performed after washing with an alkaline aqueous solution. Since a component (smut) that is insoluble in an acidic aqueous solution may adhere to the surface of magnesium or a magnesium alloy, it can be removed. As the alkaline aqueous solution, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferably used.

  After each treatment step such as the degreasing treatment, the acidic aqueous solution treatment, and the alkaline aqueous solution treatment, washing and drying may be performed as necessary. In this way, magnesium or a magnesium alloy that has been pretreated as necessary is immersed in the electrolytic solution.

  The electrolytic solution of the present invention is an alkaline aqueous solution containing phosphate radicals, specifically, an aqueous solution containing 0.1 to 1 mol / L of phosphate radicals and having a pH of 9 to 13. By containing an appropriate amount of phosphate group, an appropriate amount of phosphorus element is included in the anodic oxide film. Moreover, unnecessary elution of magnesium or a magnesium alloy can be prevented by making it alkaline.

  The phosphate group here is one included in the electrolyte as free phosphoric acid, phosphate, hydrogen phosphate, or dihydrogen phosphate. In addition, in the case of polyphosphoric acid obtained by condensation of phosphoric acid or a salt thereof, it is assumed that the phosphoric acid radicals are contained by the number of phosphate radicals obtained by hydrolysis thereof. In the case of a salt, it may be a metal salt or a non-metallic salt such as an ammonium salt. The phosphate group content is 0.1 to 1 mol / L. Preferably it is 0.15 mol / L or more, more preferably 0.2 mol / L or more. Moreover, it is 0.7 mol / L or less suitably, More preferably, it is 0.5 mol / L or less.

  The pH of the electrolyte is 9-13. Preferably it is 10 or more. Moreover, it is 12 or less suitably.

  Moreover, it is preferable that electrolyte solution contains 0.2-5 mol / L of ammonia or ammonium ion as those total amounts. As a result, the pH of the electrolytic solution is maintained at an appropriate alkaline level. The content of ammonia or ammonium ions is more preferably 0.5 mol / L or more, and even more preferably 1 mol / L or more. Further, it is more preferably 3 mol / L or less, and further preferably 2 mol / L or less.

  The electrolytic solution of the present invention may contain other components as long as the effects of the present invention are not impaired, but preferably does not substantially contain heavy metal elements. Here, the heavy metal element means a metal element having a specific gravity of more than 4 as a simple substance, and chromium, manganese and the like are exemplified as those contained in a typical electrolyte solution in a conventional anodizing treatment. In particular, it is preferable not to contain harmful chromium which has strict emission regulations. It is not usually a problem that a heavy metal contained in the magnesium alloy, for example, zinc, is dissolved in a trace amount and contained in the electrolytic solution. It is also preferable that the electrolytic solution of the present invention does not contain a fluorine element. This is because an aqueous solution containing elemental fluorine often becomes difficult to treat wastewater.

  Anodizing treatment is performed by immersing pretreated magnesium or a magnesium alloy in the electrolytic solution as necessary, and energizing it as an anode. The power source to be used is not particularly limited, and either a DC power source or an AC power source can be used, but it is preferable to use a DC power source. Further, when using a DC power supply, either a constant current power supply or a constant voltage power supply may be used, but it is preferable to use a constant current power supply. A cathode material is not specifically limited, For example, a stainless steel material etc. can be used conveniently. The surface area of the cathode is preferably larger than the surface area of magnesium or magnesium alloy to be anodized, more preferably 2 times or more, and usually 10 times or less.

The current density of the anode surface when using a constant-current power supply as a power source is usually 0.1 to 10 A / dm ^2. Preferably it is 0.2 A / dm ² or more, more preferably 0.5 A / dm ² or more. Further, it is preferably 5 A / dm ² or less, more preferably 2 A / dm ² or less. The energization time is usually 10 to 1000 seconds. Preferably it is 20 seconds or more, more preferably 50 seconds or more. Further, it is preferably 500 seconds or shorter, and more preferably 200 seconds or shorter. When energizing with a constant current power supply, although the applied voltage at the start of energization is low, the applied voltage increases with time. The applied voltage at the end of energization is usually 50 to 400 volts. Preferably it is 100 volts or more, more preferably 150 volts or more. Moreover, it is preferably 300 volts or less, and more preferably 250 volts or less. In the conventional anodic oxidation method Dow17 method and HAE method, the applied voltage is often set to less than 100 volts, whereas in the anodic oxidation treatment of the present invention, a relatively high voltage is set. preferable. As a result, the oxidation reaction easily proceeds even in a portion containing impurities such as a silicone release agent, and a film having good conductivity is easily formed on the entire surface of the magnesium or magnesium alloy. Moreover, since oxygen gas is actively generated from the surface of magnesium or a magnesium alloy with the oxidation reaction, the impurities are easily removed during the anodic oxidation treatment. The temperature of the electrolytic solution during energization is usually 5 to 70 ° C. It is preferably 10 ° C or higher. Moreover, it is 50 degrees C or less suitably, More preferably, it is 30 degrees C or less.

  After the energization is finished, the electrolytic solution adhering to the surface of the anodized film is removed by washing. In the cleaning, it is preferable to use not only water but also an acidic aqueous solution. Since the electrolytic solution is alkaline, the adhesion of the coating film is improved when resin coating is performed by washing with an 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, drying is performed to obtain a product made of magnesium or a magnesium alloy having an anodized film on the surface.

  As shown in FIG. 1, the anodic oxide film obtained by the present invention often has a large number of pores that are thought to be derived from sparks during energization. This is different from the chemical conversion coating. If the film thickness is too thin, the corrosion resistance may deteriorate, and if it is too thick, the electrical conductivity may decrease.

  The chemical composition of the anodic oxide film obtained in the present invention is not particularly limited, but those containing 35 to 65% by weight of magnesium element and 25 to 45% by weight of oxygen element are suitable. That is, it is preferable to contain oxidized magnesium as a main component, which is a product resulting from anodization of magnesium or a magnesium alloy. The content of magnesium element is more preferably 40% by weight or more, and further preferably 45% by weight or more. Further, it is more preferably 60% by weight or less, and further preferably 55% by weight or less. The content of oxygen element is more preferably 30% by weight or more. Further, it is more preferably 40% by weight or less.

  It is preferable that the anodized film contains 4 to 15% by weight of phosphorus element. The content of phosphorus element is more preferably 5% by weight or more, and further preferably 6% by weight or more. Moreover, it is 12 weight% or less more suitably, More preferably, it is 10 weight% or less. It is also preferable to contain 5 to 20% by weight of aluminum element. The aluminum element content is more preferably 7% by weight or more, and even more preferably 9% by weight or more. Further, it is more preferably 17% by weight or less, and further preferably 15% by weight or less. It can be presumed that by containing an appropriate amount of the above-mentioned elements other than magnesium and oxygen, it has good electrical conductivity without impairing corrosion resistance. The anodized film of the present invention may contain elements other than those described above as long as the effects of the present invention are not impaired. However, it is preferable that substantially no heavy metals, particularly chromium elements, are contained except for those originally contained in the raw material magnesium alloy. Moreover, it is preferable not to contain a fluorine element substantially.

  The use of the product made of magnesium or a magnesium alloy of the present invention having an anodized film on its surface is not particularly limited, and can be used for various electrical equipments and automotive parts. In use, an overcoat may be applied to the surface of the anodized film as necessary.

  The paint used is not particularly limited, and various kinds of paint used for painting a metal surface can be used. A resin coating film can be formed using a solvent-type paint, a water-based paint, a powder paint, or the like. Although it may be a thermosetting paint that requires high-temperature baking after coating, it may be a paint that only needs to volatilize the solvent and water at a relatively low temperature, but the latter, which is easy to operate, is preferably used. In order to make the appearance beautiful, it is preferable to use a transparent resin paint, and an appropriately colored one may be used. The coating method is not particularly limited, and a known method such as spray coating, immersion coating, electrodeposition coating, powder coating, or the like can be employed. In a product made of magnesium or a magnesium alloy of the present invention that preferably has a part that does not have a coating film, powder coating by spray coating or thermal spraying is suitably employed.

  After the anodizing treatment, it is preferable to form a coating film by coating the resin coating film only once on the surface of the anodized film. In many cases, a housing of an electric device has a complicated shape, and it is not always easy to form a uniform coating film. In many cases, the corrosion resistance is further improved by applying a plurality of times of coating. However, if the number of times of coating is large, the cost increases. In this respect, in products made of magnesium or a magnesium alloy of the present invention having good corrosion resistance, sufficiently good corrosion resistance is often obtained even by a single coating.

  When a solvent-type paint or a water-based paint is used, it is preferable to dry the coating film by heating at a temperature of 40 to 120 ° C. More preferably, it is 50 ° C. or higher and 100 ° C. or lower. In products made of the magnesium or magnesium alloy of the present invention having good corrosion resistance, it is often sufficient to use only resin coating that is dried and cured in a relatively low-temperature heating step, and as a result, manufacturing costs can be reduced. Become. The heating and drying method is not particularly limited, and a general-purpose oven or the like can be used.

  The product made of magnesium or magnesium alloy obtained by the present invention can be used for various applications. It can be used for casings of electric devices such as mobile phones, personal computers, video cameras, still cameras, optical disk players, displays (CRT, plasma, liquid crystal), projectors, automobile parts, and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, 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 into a size of 5 mm × 10 mm and embedded in an epoxy resin, and then the cut surface was polished to obtain a mirror surface. From the cross-sectional direction of the sample, an electron micrograph was taken using an X-ray microanalyzer “JXA-8900” manufactured by JEOL Ltd., and the film thickness was measured.

(2) Chemical composition analysis of anodized film Using X-ray microanalyzer “JXA-8900” manufactured by JEOL Ltd., the film composition was analyzed from two directions of the surface and cross section of the film. Measurements were made at three locations in each direction, and the chemical composition was determined from the average value. The measurement was performed under the conditions of an acceleration voltage of 15 kV and a sample irradiation current of 2 × 10 ⁻⁸ A. Data analysis was performed with ZAH correction.

(3) Measurement of resistance value on the surface of the anodic oxide film Using a low resistivity meter “Lorestar AP MCP-T400” manufactured by Mitsubishi Chemical Corporation, measurement was performed using a two-probe probe “MCP-TP01”. The resistance value (Ω) was measured by pressing the measuring terminal against the surface of the film at the center of the test piece. The probe has measuring terminals arranged at intervals of 10 mm, the terminal is gold-plated beryllium alloy, the tip shape is a cylindrical shape with a diameter of 2 mm, and the load for pressing the terminal against the surface of the film is the terminal 1 240g per piece.

(4) Hot water immersion test The test piece was immersed in warm water maintained at 70 ° C. for 24 hours. After 24 hours, take out the test piece, wipe off the moisture, and make a grid-like cut at an interval of about 1 mm so as to penetrate the resin coating and the anodized coating, and in accordance with JIS K5400 A tape peeling test was performed, and the peeling state of the coating film and the occurrence of other defects were observed with the naked eye.

(5) Salt spray test After making a cross-cut into the surface of the test piece so as to penetrate the resin coating and the anodic oxide coating, 5% salt spray is applied in accordance with JIS Z-2371. The test was conducted for 120 hours. After 120 hours, the test piece was taken out, and the occurrence of blisters from the crosscut portion and the presence or absence of other defects were observed with the naked eye.

Example 1
ASTM No. consisting of 90% magnesium, 9% aluminum and 1% zinc. An alloy plate having a size of 170 mm × 50 mm × 2 mm cast from a AZ91D magnesium alloy as a raw material 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 small amount of surfactant, and then washed with ion-exchanged water. Subsequently, the test piece surface was pretreated by immersing in an alkaline aqueous solution containing 18% by weight of sodium hydroxide and then washing with ion-exchanged water.

An aqueous solution of phosphoric acid and aqueous ammonia were mixed to prepare an electrolyte solution containing 0.25 mol / L of phosphate groups and 1.5 mol / L of ammonia or ammonium ions in the total amount, and kept at 20 ° C. The electrolyte had a pH of 11. The magnesium alloy test piece subjected to the pretreatment was immersed in this as an anode, and anodizing treatment was performed. As the cathode at this time, a SUS316L plate having a surface area four times that of the anode was used. A constant current power source was used, and current was supplied for 120 seconds so that the current density on the anode surface was 1 A / dm ² . Although the applied voltage was low at the start of energization, it increased to about 200 volts at the end of energization. After the energization, the ion-exchanged water, nitric acid aqueous solution, and ion-exchanged water were washed in this order and then dried.

  The photograph which observed the surface of the obtained anodic oxide film with the scanning electron microscope is shown in FIG. The presence of a large number of holes thought to be derived from sparks during energization was observed on the surface of the anodized film. The thickness of this anodized film was about 1.5 μm. The film thickness referred to here is an average distance from the surface of the thick part to the magnesium alloy surface of the base material in the film having local film thickness unevenness due to a large number of holes. The obtained anodized film contained 48.0% by weight of magnesium element, 33.5% by weight of oxygen element, 7.0% by weight of phosphorus element, and 11.2% by weight of aluminum element. The resistance value of the surface of the anodized film was 0.25Ω.

  The surface of the obtained anodic oxide film was air spray-coated with an acrylic silicone paint “ASCOAT 300J” manufactured by Cashew Co., Ltd. At this time, the acrylic silicone-based paint was applied only once on the surface of the anodized film without applying primer. After the application, the coating was heated by heating at 60 ° C. for 20 minutes to volatilize and remove the solvent. As a result, a coating film having a thickness of about 20 μm was formed on the surface of the anodized film.

  When the obtained test piece was subjected to a hot water immersion test and a salt spray test, no change in appearance was observed on the surface in any case. A photograph of the surface of the test piece after being subjected to the hot water immersion test is shown in FIG. 2, and a photograph of the surface of the test piece after being subjected to the salt spray test is shown in FIG.

Comparative Example 1
In this example, a chemical conversion treatment is performed using a commercially available chemical conversion treatment solution instead of anodizing. A treatment solution was prepared by diluting with Mion Chemical Co., Ltd. chemical conversion treatment solution “MC-1000” at a rate of 75 g / L with ion-exchanged water, and kept at 40 ° C. Although the details of the chemical composition of the chemical conversion treatment liquid are unknown, it is presumed to be a chemical conversion treatment liquid containing phosphate ions, manganese (or manganese oxide) ions and calcium ions. In this treatment solution, a magnesium alloy specimen subjected to the same pretreatment as in Example 1 was immersed for 30 seconds. After the immersion, it was washed with ion exchange water and then dried.

The film thickness of the obtained chemical conversion film was 0.1 μm or less, and was a thin film that was difficult to measure quantitatively. The conversion coating, as the content per unit area, 85 mg / ^{m 2} of calcium element, 95 mg / ^{m 2} of manganese, were those elemental phosphorus containing 220 mg / ^{m 2.} Moreover, the resistance value of the surface of this chemical conversion treatment film was 0.5Ω.
A resin coating film was formed in the same manner as in Example 1 on the surface of the obtained chemical conversion film. The appearance after subjecting the obtained test piece to the hot water immersion test is shown in FIG. 4, and the appearance after subjecting it to the salt spray test is shown in FIG. In any case, peeling of the resin coating was remarkably observed around the cuts made in the coating.

Comparative Example 2
This is an example in which a chemical conversion treatment was performed using a commercially available chemical conversion solution different from Comparative Example 1 instead of anodizing treatment. A treatment solution was prepared by diluting with Nihon Parkerizing Co., Ltd. chemical conversion treatment solution “MB-C10M” at a rate of 75 g / L with ion-exchanged water, and kept at 50 ° C. Although the details of the chemical composition of the chemical conversion treatment liquid are unknown, it is estimated that the chemical conversion treatment liquid contains 14% by weight of chromic anhydride and 0.7% by weight of hydrogen fluoride as main components. In this treatment solution, a magnesium alloy test piece subjected to the same pretreatment as in Example 1 was immersed for 60 seconds. After the immersion, it was washed with ion exchange water and then dried.

The film thickness of the obtained chemical conversion film was 0.1 μm or less, and was a thin film that was difficult to measure quantitatively. This chemical conversion film contained 190 mg / m ^{2 of} chromium element as the content per unit area. Moreover, the resistance value of the surface of this chemical conversion treatment film was 0.75Ω.

  A resin film was formed on the surface of the obtained chemical film in the same manner as in Example 1. When the obtained test piece was subjected to a hot water immersion test and a salt spray test, in both cases, peeling or swelling of the resin coating around the cuts made in the coating was not observed. However, after the hot water immersion test, it was observed that a plurality of dots (blisters) swelled in the form of dots in the coating film 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 was provided with excellent corrosion resistance. On the other hand, a product made of a magnesium alloy obtained by chemical conversion treatment as shown in Comparative Example 1 was insufficient in corrosion resistance although electrical conductivity was observed.

FIG. 1 is a photograph of the surface of the anodized film obtained in Example 1 observed with a scanning electron microscope. FIG. 2 is a photograph of the surface of the test piece of Example 1 after being subjected to a hot water immersion test. FIG. 3 is a photograph of the surface of the test piece of Example 1 after being subjected to a salt spray test. FIG. 4 is a photograph of the surface of the test piece of Comparative Example 1 after being subjected to the hot water immersion test. FIG. 5 is a photograph of the surface of the test piece of Comparative Example 1 after being subjected to a salt spray test.

Claims (5)

Magnesium or a magnesium alloy is contained in an electrolyte solution containing 0.2 to 1 mol / L of phosphate groups, 0.2 to 5 mol / L of ammonia or ammonium ions, no fluorine element, and having a pH of 9 to 13. An anodized film characterized by forming an anodized film in which a large number of pores derived from sparks are present on the surface by anodizing the surface while the electrode is immersed and sparking while energized. A method for producing a product comprising magnesium or a magnesium alloy on the surface. Product The method of preparation of the electrolyte solution is substantially free of heavy metal elements according to claim 1, wherein. The method for producing a product according to claim 1 or 2 , wherein the magnesium or the magnesium alloy is previously immersed in an acidic aqueous solution and then immersed in an electrolytic solution to be anodized. The anodized film, a magnesium element 35 to 65 wt%, the oxygen element 25-45 wt%, and the phosphorus element contained 4 to 15 wt%, and any one of claims 1 to 3 containing no fluorine element A manufacturing method of the product described. The method for producing a product according to claim 4 , wherein the product is made of a magnesium alloy containing aluminum, and the anodized film contains 5 to 20% by weight of an aluminum element.