JP3777461B2 - Corrosion-resistant magnesium alloy and its manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnesium alloy with improved corrosion resistance and a method for producing the same, and relates to a highly corrosion-resistant magnesium alloy that can be used in a wide range of fields such as space, aeronautical materials, electronic equipment materials, and automobile members, and a method for producing the same. Is.
[0002]
[Prior art]
Magnesium alloys have the lowest density among practical metals and are excellent in specific strength characteristics. For this reason, in the automotive industry, where reduction of CO ₂ emissions is an urgent issue, many attempts have been made in recent years to reduce the weight of the vehicle by manufacturing many parts such as door frames, instrument panels, and steering wheels using magnesium alloys. Has been done. With the application of the Home Appliance Recycling Law, attempts to use magnesium alloy as a housing for electronic devices such as personal computers and mobile phones as an alternative to resin materials are steadily becoming practical.
[0003]
However, since magnesium is the most electrically basic metal among practical metals, there is a problem that it is susceptible to chemical corrosion even in the air. Therefore, in order to use a magnesium alloy for the member, surface treatment for the purpose of corrosion prevention is necessary.
[0004]
Conventionally, as a surface treatment of a magnesium alloy, a synthetic resin film is applied by electrodeposition coating to the surface of the magnesium alloy that has been subjected to chemical conversion treatment / anodic oxidation treatment (Japanese Patent Laid-Open No. 7-109598) and chemical conversion treatment / anodic oxidation treatment. Excellent corrosion resistance, such as a technique (Japanese Patent Laid-Open No. 63-250498), a method of casting a magnesium alloy in a state where a metal such as Al is previously applied to a mold and a core (Japanese Patent Laid-Open No. 63-285255), etc. A surface treatment method has been proposed.
[0005]
However, both methods have limitations such as a limitation on the type of material applied to the surface and inferior wear resistance. The fields where magnesium alloys are expected to be used in addition to electronic equipment casings and automobile parts include furniture that is closely related to daily life, such as tableware and tools, and industrial parts that require wear resistance. There is an urgent need to develop a method for forming a surface coating that is not only excellent, but also excellent in wear resistance and the like.
[0006]
Examples of the surface coating having abrasion resistance include a surface coating using fluorine processing. Fluorine processing surface treatment technology for magnesium alloy includes a method of forming a magnesium fluoride layer on the surface of the magnesium alloy (Japanese Patent Laid-Open No. 2000-212725), and a method of applying a fluorine-containing ceramic film to the magnesium alloy by a sol-gel method ( Japanese Patent Laid-Open No. 10-204647) has been proposed.
[0007]
Although the inventions disclosed in the above two publications can produce a surface coating having wear resistance, in the method of coating a magnesium fluoride layer on the surface of a magnesium alloy, a sputtering device, a vapor deposition device, an ion plate are used as equipment. Vacuum equipment such as a ting device is required, and the processing cost is high. Further, in the method of applying the fluorine-containing ceramic film to the magnesium alloy by the sol-gel method, the firing temperature of the ceramic is relatively high, 250 ° C. to 500 ° C., and the magnesium alloy as a base material is deformed. There is a problem.
[Problems to be solved by the invention]
[0008]
The present invention has been made in view of the present situation regarding the above-described corrosion-resistant magnesium alloy and a method for producing the same, and its purpose is to have ethylene tetrafluoride as a main component by coating with a resin which is a relatively inexpensive process. To provide a magnesium alloy having corrosion resistance and wear resistance by firing a resin obtained by dispersing resin fine powder in a thermosetting resin on a magnesium alloy at a relatively low temperature of 150 ° C. to 400 ° C. is there.
[0009]
Another object is to provide a magnesium alloy surface coating in which the firing temperature, color, and thermal conductivity can be freely selected by selecting the characteristics of the thermosetting resin.
[0011]
[Means for Solving the Problems]
In the corrosion-resistant magnesium alloy according to claim 1 of the present invention , ethylene tetrafluoride is mainly contained in a magnesium alloy obtained by applying a base treatment comprising applying a primer mainly composed of a urethane resin to the surface of the magnesium alloy. It is characterized by being obtained by applying a resin as a component and baking at 150 ° C. to 400 ° C. for 5 minutes or more.
[0014]
The method for producing a corrosion-resistant magnesium alloy according to claim 2 of the present invention is obtained by applying a base treatment comprising applying a primer mainly composed of a urethane resin to the surface of the magnesium alloy, and applying the base treatment. A magnesium alloy coated with a primer mainly composed of a urethane resin is coated with a resin in which a fine resin powder mainly composed of tetrafluoroethylene is dispersed in a thermosetting resin at 150 ° C. to 400 ° C. It is produced by baking for 5 minutes or more.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a corrosion-resistant magnesium alloy using resin fine powder mainly composed of tetrafluoroethylene according to the present invention and a method for producing the same will be described with reference to the accompanying drawings. In order to achieve the above-mentioned object, the inventors have applied a method of applying and baking a thermosetting resin containing a resin fine powder mainly composed of tetrafluoroethylene on a magnesium alloy surface, In order to improve the properties, attention was paid to a method of applying a resin primer.
[0017]
As a conventional coating method using fluorine, a method of forming a magnesium fluoride layer on the surface of a magnesium alloy using a vacuum deposition method or the like, and a method of firing a ceramic film containing fluorine are known.
[0018]
The former method uses a vacuum process such as a vacuum deposition method or a sputtering method when forming a magnesium fluoride film on the surface of the magnesium alloy, and thus has a problem of requiring many steps and costs for the surface treatment. In the latter method, a high temperature of 250 ° C. to 500 ° C. is required when the ceramic film is applied to the surface of the magnesium alloy. The magnesium alloy has an hcp structure, and the material is deformed at room temperature due to slippage of the (001) plane (bottom surface). On the other hand, when the temperature is set to 250 ° C. or more, the movement of other sliding surfaces ({1010} (column surface sliding), {1011} (conical surface sliding)) is also activated, and the crystal grain size accompanying the increase in thermal diffusion. Due to a synergistic effect such as coarsening, the material is deformed with a small amount of stress. Here, the temperature dependence of the tensile strength of AZ91 magnesium alloy (Mg-9 wt% Al-1 wt% Zn) which is a typical magnesium alloy is shown in FIG. The magnesium alloy used in the experiment is a sample that has been extruded at a processing temperature of 400 ° C. and an extrusion ratio of 100: 1. It can be confirmed that the tensile strength of the AZ91 magnesium alloy decreases to about half or less compared to the strength at room temperature at 200 ° C or higher. For this reason, it is difficult to utilize the magnesium alloy member for which surface accuracy is required.
[0019]
In view of the above problems, the inventors have made ethylene tetrafluoride as a main component as a method of applying fluorine processing with excellent manufacturing resistance at an inexpensive manufacturing cost and at a relatively low temperature of about 200 ° C. We focused on baking the fine resin powder on the magnesium surface. The inventor applied a thermosetting resin (for example, amino resin) containing 5% or more of tetrafluoroethylene resin fine powder on the surface of the magnesium alloy and fired at 180 ° C. for 10 minutes or more, thereby improving the dimensional accuracy of the magnesium alloy. It was confirmed that the fluorine processing can be applied to the surface of the magnesium alloy without any damage.
[0020]
However, due to the poor wettability between the thermosetting resin and the magnesium alloy, we faced a new problem that the peelability of the prepared coating film was significantly reduced.
[0021]
As a means for solving this problem, the inventors maintained adhesion by applying a resin-based primer having good wettability with the magnesium alloy and the thermosetting resin to the surface of the magnesium alloy before the surface treatment. In the meantime, we devised a technique to apply a fluororesin having corrosion resistance and wear resistance to the surface of magnesium alloy. In particular, the present inventors have succeeded in forming a surface film having good adhesion by applying a resin-based primer mainly composed of a urethane resin to the surface of the magnesium alloy. Thus, the inventors have obtained knowledge for firing a thermosetting resin containing a tetrafluororesin powder in a state having good adhesion to the magnesium alloy surface by a low-cost and low-temperature process. . The present invention is based on the above findings.
[0022]
Hereinafter, the present invention will be described in detail. FIG. 2 is a flowchart showing a process flow for producing the corrosion-resistant magnesium alloy according to the present invention. This process consists of (1) roughening and cleaning the surface of the magnesium alloy as the base material, (2) applying a resin-based primer, and (3) thermosetting containing a resin powder mainly composed of tetrafluoroethylene. It consists of application of resin and (4) baking of paint.
[0023]
In the above, after the surface of the magnesium alloy base material roughened by shot peening, etching treatment, etc. is washed by degreasing, etc., the base material is pretreated by applying a resin primer to the base material surface at room temperature. I do. When the thickness of the resin-based primer is set to 10 μm or more, surface treatment with good peeling characteristics is possible.
[0024]
In particular, by applying a resin-based primer containing a urethane resin as a main component to a magnesium alloy base material, a surface treatment having good peeling characteristics is possible.
[0025]
By applying a thermosetting resin containing a resin powder containing tetrafluoroethylene as a main component to a magnesium alloy substrate for 20 μm or more and baking at a firing temperature of 150 ° C. to 400 ° C. for 5 minutes or more, magnesium An alloy surface coating can be formed. When firing a fluororesin at a target low temperature of about 150 ° C., a resin having a low firing temperature such as an amino resin is used as the thermosetting resin, and baking is performed for 10 minutes or more. preferable.
[0026]
For surface treatment that does not require accuracy, a surface treatment that guarantees heat resistance of 200 ° C. or higher by using a resin mainly composed of a thermosetting resin having a relatively high baking temperature, such as polyamide-imide. A film can also be formed.
[0027]
In the present invention, the magnesium alloy refers to all alloys having magnesium as a main component, and the ratio of the additive element is allowed. The resin-based primer refers to all primers mainly composed of acrylic resin, urethane resin, acrylic urethane resin, vinyl chloride resin, chlorinated rubber resin, fluororesin, epoxy resin, carboxylic acid resin and the like. The urethane resin used as a resin-based primer refers to all resins mainly composed of a urethane resin, and the size of other additives is allowed. Furthermore, the resin powder containing tetrafluoroethylene as a main component refers to all resin fine powders containing tetrafluoroethylene, and the ratio of other additive substances is allowed. The thermosetting resin refers to all thermosetting resins such as phenol resin, epoxy resin, acrylic resin, polyamide resin, polyurethane resin, carboxylic acid resin, amino resin, and polyamideimide resin.
[0028]
[Example 1]
The surface of a commercial AZ91D magnesium alloy (Mg-8.7 wt% Al-0.7 wt% Zn-0.17 wt% Mn) cast product after surface roughening by shot peening and surface cleaning by degreasing treatment A urethane resin-based primer composed mainly of oil-modified urethane resin 38 wt%, toluene 10 wt%, 1 butanol 10 wt%, and butyl acetate 7 wt% was applied. A resin containing tetrafluoroethylene resin powder in an amino resin (thermosetting resin) was applied to the surface of the magnesium alloy and then baked at 180 ° C. for 10 minutes. In addition, a salt spray test was conducted to investigate the corrosion characteristics of the prepared samples.
[0029]
3 (a) and 3 (b) show the AZ91D magnesium alloy base material before coating and the base material after coating, respectively. According to this figure, it can be confirmed that the fluororesin can be uniformly applied to the entire surface of the sample by the method of this example. The applied fluororesin had a thickness of about 80 μm.
[0030]
[Example 2]
The surface of a commercial AZ91D magnesium alloy (Mg-8.7 wt% Al-0.7 wt% Zn-0.17 wt% Mn) cast product after surface roughening by shot peening and surface cleaning by degreasing treatment A urethane resin-based primer composed mainly of oil-modified urethane resin 38 wt%, toluene 10 wt%, 1 butanol 10 wt%, and butyl acetate 7 wt% was applied. A resin containing tetrafluoroethylene resin powder in an amino resin (thermosetting resin) was applied to the surface of the magnesium alloy and then baked at 180 ° C. for 10 minutes. On the other hand, apart from the urethane resin-based primer, a typical metal product primer, a carboxylic acid-based primer (18% by weight of carboxylic acid-based resin, 21% by weight of polyester resin, 28% by weight of ketones, 26% by weight of aromatic hydrocarbons) A sample with a surface coating formed on the surface was also prepared, and a salt spray test was conducted to investigate the corrosion characteristics of the prepared sample.
[0031]
FIG. 4 shows the surface state of the sample after the 100 hour salt spray test. 4A shows an overview of the surface of the sample using the urethane resin-based primer, and FIG. 4B shows an overview of the surface of the sample using the carboxylic acid-based resin primer. The surface condition of the sample using the urethane resin primer was almost the same as the condition of the sample surface before the corrosion test, whereas the progress of corrosion can be confirmed on the surface of the sample using the carboxylic acid resin primer. . This result shows that the adhesion of the magnesium alloy base material and the surface coating was improved by applying the urethane resin primer, and the sample surface did not peel during the salt spray test, preventing the progress of corrosion. ing.
[0032]
As described above, according to this example, it can be confirmed that the corrosion resistance is remarkably improved by forming the surface treatment film on the surface of the magnesium alloy casting.
[0033]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a magnesium alloy having corrosion resistance and wear resistance. The corrosion-resistant magnesium alloy produced according to the present invention can be applied to a wide range of fields such as tableware, tools, and other appliances closely attached to daily life, and has a very wide range of uses.
[Brief description of the drawings]
FIG. 1 is a graph showing the temperature dependence of the tensile strength of an AZ91 magnesium alloy (Mg-9 wt% Al-1 wt% Zn).
FIG. 2 is a flowchart showing a manufacturing procedure of a corrosion-resistant magnesium alloy according to the present invention.
FIGS. 3A and 3B are diagrams showing an AZ91D magnesium alloy cast product before and after surface treatment, in which FIG. 3A is a diagram before the surface treatment, and FIG.
FIG. 4 is a view showing a AZ91D magnesium alloy casting after a salt spray test, (a) is a view showing the surface of a sample using a urethane resin primer, and (b) is a carboxylic acid resin primer. The figure which shows the surface of a sample.

Claims (2)

A resin mainly composed of tetrafluoroethylene is applied to a magnesium alloy obtained by applying a base treatment consisting of applying a primer mainly composed of a urethane resin on the surface of the magnesium alloy, A corrosion-resistant magnesium alloy obtained by firing for 5 minutes or more at ° C. A magnesium alloy surface is coated with a primer composed mainly of a urethane resin, and a magnesium alloy coated with a primer composed mainly of a urethane resin, which is obtained by applying the primer. Corrosion resistance characterized by being formed by applying a resin in which resin fine powder containing ethylene fluoride as a main component is dispersed in a thermosetting resin and baking at 150 ° C. to 400 ° C. for 5 minutes or longer. Magnesium alloy manufacturing method.

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