JP2002082041A - Surface activity determining agent for magnesium member and evaluating method for corrosion resistance of surface of magnesium member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluating method capable of easily evaluating the degree of corrosion resistance of the surface of a magnesium member in a short time and a surface activity determining agent for the magnesium member for use in the evaluating method. SOLUTION: The surface activity determining agent for a magnesium member contains water, a pH indicator which discolors within the range of pH 9 to 11, and a thickener which when mixed with water can form a high-viscosity solution. The evaluating method for the corrosion resistance of the surface of a magnesium member includes applying the surface activity determining agent to the surface of the magnesium member, and evaluating the corrosion resistance of the surface of the magnesium member according to whether or not the determining agent discolors and to the time required for the discoloring to occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface activity determining agent for magnesium or a magnesium alloy (both are collectively referred to as a magnesium material in this specification), and a method for determining the surface of a magnesium material using the surface activity determining agent. The present invention relates to an evaluation method capable of easily and quickly evaluating corrosion resistance.

[0002]

2. Description of the Related Art Magnesium is the lightest and most specific metal in practical metals, and its properties are used to make interior and exterior parts for automobiles and motorcycles, parts for home appliances, storage containers for suitcases, etc. , Sports equipment, optical equipment parts,
Furthermore, application to new fields of the electronics industry such as computer and sound has been tried and put to practical use.

However, since the magnesium material is an electrochemically active metal material, it has been difficult to use the magnesium material as it is in terms of corrosion resistance. As a surface treatment method for improving the corrosion resistance of a magnesium material, a chemical conversion treatment and an anodic oxidation treatment have been conventionally performed. Since the chemical conversion treatment is simple, it is widely used as a base treatment for coating. In particular,
When a film is formed by anodic oxidation treatment and then sealing treatment is performed, a relatively uniform film is formed, so that it is used as a rust preventive treatment or a base treatment for coating. In addition, painting has been implemented.

[0004]

As a method for judging the effect of corrosion resistance by the surface treatment applied to the surface of a magnesium material, a salt spray test method (JIS) is generally used.
Z 2371, 1994). However, this test method has to be performed for several hours to several hundreds of hours depending on the degree of corrosion resistance of the film, that is, it has a disadvantage that it requires a long time and the equipment is expensive.

An object of the present invention is to provide an evaluation method which does not have the above-mentioned drawbacks, that is, which can easily and quickly evaluate the degree of corrosion resistance of a magnesium material surface.
Another object of the present invention is to provide a surface activity determining agent for a magnesium material used in the evaluation method.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, in wet corrosion of a magnesium material, magnesium reacts with water to produce magnesium hydroxide. Magnesium hydroxide is p
The present inventors have found that the above-mentioned problems can be achieved by utilizing the phenomenon of strong alkalinity around H11, and completed the present invention.

That is, the surface activity-determining agent for magnesium material of the present invention has a p-value that changes color in water and in the pH range of 9 to 11.
A thickening agent containing an H indicator and optionally further forming a high-viscosity liquid by mixing with water, and / or a solvent for promoting dissolution of the pH indicator in the surface activity determining agent for magnesium material; And / or additionally contains a corrosion promoter capable of promoting corrosion of the magnesium material surface.

Further, the method for evaluating the corrosion resistance of the surface of a magnesium material according to the present invention comprises applying the above-mentioned surface activity evaluation agent for a magnesium material to the surface of the magnesium material, and discoloring the surface activity evaluation agent entirely or locally after application. It is characterized in that the corrosion resistance of the magnesium material surface is evaluated based on the determination of the presence or absence and the measurement of the time until discoloration occurs.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Since the surface activity determining agent for magnesium material of the present invention contains water, when this surface activity determining agent is applied to the surface of a magnesium material, it depends on the degree of corrosion resistance of the film on the surface of the magnesium material. Immediately after the application or after a predetermined time, corrosion occurs on at least a part of the surface of the magnesium material, and the corrosion generates magnesium hydroxide having a strong alkalinity of about pH11.

[0010] The surface activity-determining agent of the present invention has a pH of 9 to
Since it contains a pH indicator that changes color within the range of 11, the surface activity evaluation agent of the present invention changes color due to the formation of magnesium hydroxide. Accordingly, the activity and the corrosion resistance of the surface of the magnesium material can be easily determined by containing the water and the pH indicator which changes color within a pH range of 9 to 11 in the surface activity determination agent of the present invention. Furthermore, as a remarkable phenomenon, the discoloration reaction by this surface activity determination agent has extremely high sensitivity to the detection of corrosion. It can be detected easily and quickly. Of course, if the film on the surface of the magnesium material is excellent in corrosion resistance, no corrosion occurs and no discoloration occurs even after a predetermined time.

The surface activity determining agent of the present invention preferably contains a thickener capable of forming a high viscosity liquid when mixed with water. When a thickener is contained, the surface activity determining agent of the present invention becomes a high viscosity liquid, so that magnesium hydroxide generated by corrosion does not diffuse much in the surface activity determining agent, and as a result, the surface activity determining agent is determined. A high pH portion is generated in the agent, which facilitates determination of discoloration of the surface activity determination agent, and facilitates determination of activity and corrosion resistance of the magnesium material surface.

Further, when a thickener is contained as described above, magnesium hydroxide produced by corrosion does not diffuse so much in the surface activity determining agent, so that it is easy to determine a local anode corrosion point. become. The local corrosion point is iron on the magnesium material surface which is more noble than magnesium,
This is seen when trace amounts of impurities such as nickel and copper are present. Such a local corrosion point cannot be detected by a conventional salt spray test method or the like, and is made possible for the first time in the present invention. Further, the strong alkalinity exhibited by magnesium hydroxide generated by such wet corrosion of a magnesium material is not observed by wet corrosion of zinc or aluminum.

In the surface activity evaluation agent of the present invention, the pH
There is no problem when the indicator is water-soluble, but when the indicator is hardly soluble or insoluble in water, the pH in the surface activity determination agent
The pH indicator is dissolved in the solvent and then mixed with water to facilitate dissolution of the indicator. Furthermore, in order to shorten the evaluation time of the corrosion resistance of the magnesium material surface, it is preferable that the surface activity determining agent contains a corrosion accelerator capable of promoting corrosion of the magnesium material surface. Therefore, the surface activity evaluation agent of the present invention can further promote the corrosion of the pH indicator in the surface activity evaluation agent for magnesium material, such as ethyl alcohol, and / or the magnesium material surface, if desired. It is preferable to additionally contain a corrosion promoter, for example, sodium chloride.

The pH indicator used in the surface activity evaluation agent of the present invention is in the range of pH 9-11, preferably pH 9.2-1.
0.7, more preferably pH 9.3 to 10.5
The pH indicator changes its color within the range of, for example, p-xylenol blue, thymol blue, phenolphthalein, α-naphtholbenzein, thymolphthalein, nile blue, salicyl yellow and the like. When these pH indicators are hardly soluble or insoluble in water, they are dissolved in a solvent such as ethyl alcohol and then mixed with water and a thickener.

The thickener which can be used in the surface activity determining agent of the present invention is a thickener capable of forming a high viscosity liquid by mixing with water, and examples thereof include polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, Examples include a polyacrylic acid compound, gelatin, and a water-absorbing gel. When these thickeners are present in the surface activity determining agent, the surface activity determining agent of the present invention becomes a high viscosity liquid.
The viscosity is preferably a viscosity suitable for application or spraying, and a viscosity such that magnesium hydroxide generated by corrosion does not diffuse so much in the surface activity determination agent.

In the surface activity evaluation agent of the present invention, water,
The relative amounts of the pH indicator, thickener, solvent and corrosion promoter are:
Since it varies depending on the type of pH indicator, thickener, solvent and corrosion promoter used, the desired viscosity of the surface activity determining agent, and the like, it cannot be said unconditionally. However, functionally, the relative amount of the pH indicator is such that the concentration of the pH indicator can be exerted in the surface activity determination agent. If the amount is too small, the pH indicator cannot be exhibited, and if the amount is too large, the effect increases. Is not obtained, but the cost is high. Generally, for example, the amount is 0.001 to 1 part by mass per 100 parts by mass of water.

When a thickener is contained, the relative amount of the thickener is such that the viscosity of the surface activity judging agent can be adjusted to a desired viscosity, and there is a considerable difference depending on the type of the thickener. However, for example, it is 50 parts by mass or less per 100 parts by mass of water. Therefore, in the surface activity evaluation agent of the present invention, the relative amount of the thickener is 0 to 50 parts by mass, for example, 1 to 50 parts by mass per 100 parts by mass of water. Department.

When a solvent is contained, the relative amount of the solvent is such that the dissolution of the pH indicator in the surface activity determining agent is promoted to produce a stable surface activity determining agent,
For example, the amount is 5 parts by mass or less per 100 parts by mass of water. Therefore, in the surface activity evaluation agent of the present invention, the relative amount of the solvent is 0 to 5 parts by mass, for example, 0.1 to 5 parts by mass per 100 parts by mass of water.
Parts by weight.

When a corrosion accelerator is contained, it is preferable that the relative amount of the corrosion accelerator promotes the degree of corrosion of the magnesium material surface within a range in which the activity and corrosion resistance of the magnesium material surface can be reliably determined. For example, the amount is 20 parts by mass or less per 100 parts by mass of water. Therefore, in the surface activity evaluation agent of the present invention, the relative amount of the solvent is 0 to 20 parts by mass, for example, 1 to 20 parts by mass per 100 parts by mass of water. It is.

The surface activity-determining agent of the present invention may be added to water or a high-viscosity liquid comprising water and a thickening agent or a high-viscosity liquid comprising water, a thickening agent and a corrosion promoter, to a pH indicator or a solvent. It can be prepared by adding a pH indicator dissolved therein and stirring and mixing. In addition, the evaluation method of the present invention, sprayer, brush,
Using a roller brush, a spatula, or the like, apply the above-described surface activity determination agent to the surface of the magnesium material, determine whether or not the surface activity determination agent after application is entirely or locally discolored, and until discoloration occurs. This can be done by measuring the time.

For example, JIS H8651, 1995
When the surface activity determining agent of the present invention is applied to a magnesium material having a strong corrosion-resistant coating as specified as MX3 per year, no discoloration is exhibited even after a long period of application. However, when the surface activity determining agent of the present invention is applied to a magnesium material provided with a chemical conversion coating of such an extent as to be used for temporary rust prevention as specified in MX1 in JISH 8651, 1995, After 2 minutes, discoloration of the surface activity determining agent (discoloration of the indicator) occurs. on the other hand,
When the surface activity determining agent of the present invention is applied to a magnesium material whose surface has been removed by lightly polishing the surface of the magnesium material, discoloration of the surface activity determining agent (discoloration of the indicator) occurs immediately after application. As described above, the surface of the magnesium material is corroded by moisture, indicating that the pH of the portion has changed to the alkali side.

Although the judgment results obtained by the evaluation method of the present invention do not have a perfect correlation with the judgment results obtained by the salt spray test method (JIS Z 2371, 1994), the judgment results tend to be proportional to the results. Therefore, the evaluation method of the present invention can easily and quickly evaluate the degree of corrosion resistance (or corrosion sensitivity) of the magnesium material surface. Further, by observing the discolored portion of the surface activity determining agent (the discolored portion of the indicator), a local corrosion active site can be detected. In addition, the evaluation method of the present invention uses magnesium metal, AZ
It can be applied to all magnesium materials such as those based on AM and AM.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Example 1 1 mL of a 1 part by weight solution of phenolphthalein in ethyl alcohol was mixed with 30 parts by weight of an aqueous solution of polyvinyl alcohol
It was added to 00 mL and stirred and mixed to obtain a surface activity evaluation agent for magnesium material. This surface activity evaluation agent was a high viscosity solution.

As test specimens, (1) AZ91D-based magnesium die-cast product whose surface is polished, (2) A
(3) The surface of the AZ91D-based magnesium die-cast product is JIS H 865 as it is (the release material is adhered during casting).
1. Chemical conversion treatment (sodium dichromate + nitric acid) as specified in 1995 as MX1; (4) A
JIS for surface of Z91D-based magnesium die-cast products
H8651, a chemical conversion treatment (sodium dichromate + magnesium fluoride system) as specified in 1995 as MX3; and (5) AZ91D magnesium die-cast product with iron powder having a diameter of about 1 μm on the surface. Those which adhered in a shape (observed by EPMA) were selected, and the surface activity determining agent was applied to their surfaces with a brush, and the discoloration was observed.

As a result of observation, (1) was discolored to pink immediately after application, and (2) was discolored to pink about 30 seconds after application, but there was some unevenness in color development in some parts. , (3) was discolored pink after about 60 seconds of application, and (4) no discoloration was observed even after 300 seconds of application. The tendency (order) of the discoloration occurrence in (1) to (4) is based on a salt spray test (JIS Z 2371, 1).
(994)). In addition, although the discoloration of (5) showed the same discoloration as that of (2) as a whole, a local dark color was observed in the spot-like portion of the iron powder 5 seconds after application.

As is clear from the above observation results, the evaluation method of the present invention using the surface activity determining agent of the present invention makes it possible to determine the presence or absence of a corrosion-resistant coating such as a chemical conversion coating on the surface of a magnesium material, and to evaluate the corrosion resistance. Quantitative determination becomes extremely easy. Further, even on the surface of the cast product where the release agent remains adhered, as in the test specimen of (2) above, the local residual state can be easily visually judged. Further, a local anode corrosion point can be easily determined.

[0027]

By performing the evaluation method of the present invention using the surface activity evaluation agent of the present invention, the degree of corrosion resistance on the surface of the magnesium material can be easily and quickly evaluated.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masahiro Hyakutake 1333-2, Hara-shi, Ageo-shi, Saitama F-term (reference) 2M042 AA05 BC02 CA03 CB06 DA08 FA12 FB02 2G050 AA01 BA02 BA03 DA01 EA02 EB10 2G055 AA01 BA11 CA01 FA09

Claims (6)

[Claims] 1. A surface activity-determining agent for a magnesium material comprising water and a pH indicator that changes color within a pH range of 9 to 11. 2. The surface activity judging agent according to claim 1, further comprising a thickener capable of forming a high-viscosity liquid when mixed with water. 3. The p in a surface activity evaluation agent for magnesium material.
The surface activity-determining agent for a magnesium material according to claim 1 or 2, further comprising a solvent for promoting dissolution of the H indicator. 4. The method according to claim 1, further comprising a corrosion promoter capable of promoting corrosion of the surface of the magnesium material.
4. The agent for determining a surface activity for a magnesium material according to 2 or 3. 5. 100 parts by weight of water, 0.001 to 1 part by weight of a pH indicator which changes color within a pH range of 9 to 11, 0 to 50 parts by weight of a thickener capable of forming a high-viscosity liquid when mixed with water, Solvent 0
The surface activity evaluation agent for a magnesium material according to claim 1, 2, 3 or 4, which comprises 0 to 5 parts by mass and 0 to 20 parts by mass of a corrosion accelerator. 6. The surface activity evaluation agent for magnesium material according to claim 1, 2, 3, 4, or 5 is applied to the surface of the magnesium material, and the surface activity evaluation agent after application is totally or locally discolored. A method for evaluating the corrosion resistance of the surface of a magnesium material, comprising evaluating the corrosion resistance of the surface of the magnesium material based on the determination of the time and measurement of the time until discoloration occurs.