JP5103034B2 - Method for forming a coating film of magnesium alloy - Google Patents

Description

The present invention relates to a method for forming a coating film of a magnesium alloy, and more particularly to a method for forming a coating film in which the surface of a magnesium alloy is surface-treated in an aqueous solution containing phosphate ions and directly coated on the surface-treated surface .

  From the viewpoints of energy problems, environmental problems, resource saving measures, recycling problems, etc., magnesium alloys that are lightweight, excellent in specific strength, and excellent in recyclability have attracted attention, and are used for home appliances or IT-related equipment, Application to automobile parts is spreading.

  However, magnesium alloys have a problem that they are inferior in corrosion resistance compared to aluminum, iron and the like. Therefore, various surface treatment methods and coating methods have been proposed to improve the corrosion resistance of magnesium alloys.

  For example, as a chemical conversion treatment method for a magnesium alloy, there is a non-chromium chemical conversion treatment method (see, for example, Patent Document 1 and Patent Document 2). In addition, after etching treatment, a surface treatment with an alkaline aqueous solution containing an organophosphorus compound (see, for example, Patent Document 3), orthophosphoric acid, and at least one metal ion selected from Zn, Mn and Ca are contained. There are a method of surface treatment with an acidic aqueous solution (for example, see Patent Document 4) and a method of chemical conversion treatment with a solution containing calcium ions, manganese ions and phosphate ions (for example, see Patent Document 5). Further, after etching treatment or after etching treatment, a chemical conversion treatment with a treatment liquid containing phosphate ions and permanganate ions (for example, see Patent Document 6), phosphoric acid, calcium compound, titanium compound, A method of chemical conversion treatment with a treatment liquid containing at least one metal compound selected from a zirconium compound and a strontium compound (see, for example, Patent Document 7), phosphoric acid and / or phosphate compound, and permanganate compound There exists a method (for example, refer patent document 8) of performing a chemical conversion treatment with the containing processing liquid.

  Generally, aluminum-containing magnesium alloys used for extruded materials and rolled materials typified by AZ31B have a lower aluminum content than cast magnesium-containing magnesium alloys typified by AZ91D. Sex is quite big. Therefore, in the etching process that is always performed for the purpose of removing the oxide film and removing the release agent and lubricant that have entered the surface of the aluminum-containing magnesium alloy, the same process as that performed with the AZ91 material is performed with the AZ31 material. If it is performed, the etching becomes excessive and the surface becomes excessively rough. When the chemical conversion film forming treatment is performed on the excessively rough surface in this way, the chemical conversion film is excessively deposited and the film mass becomes excessive, and the excessively deposited component remains on the surface as a fine powder. It becomes. Moreover, when coating is performed on the surface of such a chemical conversion coating, the adhesion, particularly the water-resistant adhesion, is significantly lowered depending on the type of coating.

JP-A-11-131255 JP 2000-096255 A JP 2000-328261 A JP 2001-288580 A JP 2003-286582 A JP 2002-294466 A JP 2003-003273 A JP 2003-277944 A

The present invention is, without the need for an etching process, the surface of the magnesium alloys containing small amounts of aluminum, corrosion resistance, can form a good chemical conversion film on the coating film adhesion, the film-forming method of the magnesium alloy It is intended to provide.

As a result of intensive studies to achieve the above object, the present inventors treated the surface of a magnesium alloy that has not been subjected to etching treatment with an aqueous solution containing 1 to 10% by mass of phosphoric acid in terms of phosphate ion concentration. As a result, the inventors have found that the above object can be achieved and completed the present invention.

That is, the method for forming a coating film of a magnesium alloy according to the present invention comprises degreasing the surface of a magnesium alloy containing 1 to 5% by mass of aluminum with xylene, and then performing phosphoric acid on the surface of the magnesium alloy without performing an etching treatment. An aqueous solution containing 1 to 10% by mass of phosphoric acid in terms of ion concentration is contacted at a temperature of room temperature to 70 ° C. for 10 seconds to 10 minutes, and is directly coated on the surface of the surface-treated magnesium alloy. It is characterized by that.

With the magnesium alloy coating film forming method of the present invention, a chemical conversion coating film excellent in corrosion resistance and coating film adhesion can be formed on the surface of the magnesium alloy without the need for etching treatment.

Below, the coating-film formation method of this invention is demonstrated concretely. In the present invention, the type of the magnesium alloy that forms the chemical conversion coating on the surface is not particularly limited as long as it is a magnesium alloy containing 1 to 5% by mass of aluminum . For example, the expansion of AZ21, AZ31B, AZ31C, etc. mention may be made of the use of magnesium alloy. The magnesium alloy coating film forming method of the present invention is particularly suitable for forming a chemical conversion film having excellent corrosion resistance and coating film adhesion on the surface of AZ21, AZ31B, AZ31C and the like.

  In addition, the method for forming the magnesium alloy member for forming the chemical conversion coating on the surface in the present invention is not particularly limited. Extrusion processing, rolling processing, drawing processing, die casting method, thixo molding method, press molding method, forging method, casting The law etc. can be mentioned.

  In the present invention, the etching treatment of the magnesium alloy surface is not necessary, but it is preferable to perform a degreasing treatment before the chemical conversion treatment. The degreasing treatment is performed by bringing a degreasing solution into contact with the surface of the magnesium alloy. Examples of methods for bringing the degreasing solution into contact with the surface of the magnesium alloy include conventionally known dipping methods and spray methods, and any method can be applied in the present invention.

In the present invention, xylene is used as the degreasing liquid. The temperature and time when the degreasing solution is brought into contact with the surface of the magnesium alloy are not particularly limited, but it is preferable to make the contact within the range of 35 to 70 ° C. for 30 seconds to 10 minutes depending on the degree of contamination of the magnesium alloy surface. Yes.

And phosphoric acid used in the present invention include orthophosphoric acid, phosphonic acid, pyrophosphoric acid, and tripolyphosphate. An aqueous solution containing 1 to 10% by mass of phosphoric acid in terms of phosphate ion concentration is a value obtained by dividing the weight of PO ₄ ^{--- in} phosphoric acid by the amount of the total solution and multiplying it by 100. For example, phosphoric acid when using a are use in an amount of from 1.03 to 10.3 wt%.

  In the present invention, examples of the method for bringing the chemical conversion treatment liquid into contact with the surface of the magnesium alloy include conventionally known dipping methods, spraying methods, and the like, and any method can be applied in the present invention.

The temperature and time at which the chemical conversion solution is brought into contact with the surface of the magnesium alloy vary depending on the type of phosphoric acid , the concentration of the aqueous solution, the pH, the type of magnesium alloy that is the object to be treated, and the like. Generally speaking, if the concentration of the chemical conversion treatment liquid is high, a desired degree of chemical conversion treatment is completed at a relatively low temperature in a relatively short time. If the temperature of the chemical conversion treatment liquid is high, the concentration of the chemical conversion treatment liquid is relatively low. In addition, a desired degree of chemical conversion treatment is completed in a relatively short time, and if the treatment time is long, the chemical conversion treatment is completed at a relatively low chemical conversion solution concentration and at a relatively low temperature. For example, the contact is performed at a temperature of room temperature to 70 ° C. for 10 seconds to 10 minutes.

  In the present invention, it is desirable to provide a water washing step between each step. The water washing in the water washing step is performed by bringing a magnesium alloy, which is an object to be treated, into contact with water. The degree of water washing (contact time, water purity / temperature, number of stages of water washing, dilution rate, etc.) is not particularly limited, taking into account the concentration of each processing solution, the degree of influence when mixed in the next process, etc. What is necessary is just to set suitably.

  After the formation of the chemical conversion coating according to the present invention, it is desirable to dry in order to evaporate water remaining on the surface. Of course, when applying with a water-based paint, drying is not essential since the coating itself is possible even if moisture remains on the surface. However, since moisture may enter the paint and affect the concentration of the paint, it is desirable to provide a drying step in this case as well. The drying is not particularly limited and may be natural drying, for example, but is preferably oven drying with a hot air heater or an infrared heater.

Film forming method Oite resulting magnesium alloy member of the present invention has excellent corrosion resistance it is, contemplates further improvement of corrosion resistance, or contemplates improving the appearance of the magnesium alloy member , painting is made. The paint used for coating is not particularly limited, and may be either water-based or solvent-based. The coating method is not particularly limited, and any conventionally known coating method such as spray coating, dip coating, or electrodeposition coating can be applied.

  Hereinafter, the present invention will be described more specifically based on examples and comparative examples.

Examples 1-2 and Comparative Example 1
A 5 mm × 70 mm × 150 mm member produced from an aluminum-containing magnesium alloy extruded member of ASTM AZ31B was used as the processing target member. In the degreasing treatment, xylene was used as a degreasing agent, and the oil on the surface of the member was washed away with a brush and allowed to air dry.

  In Examples 1-2, phosphoric acid aqueous solution (chemical conversion liquid A) having a phosphoric acid concentration of 5 mass% or phosphoric acid aqueous solution (chemical conversion liquid B) having a phosphoric acid concentration of 1 mass% was used as the chemical conversion liquid. The liquid temperature was kept at 23 ° C., and the above-mentioned members were immersed in them for 1 minute to carry out a chemical conversion treatment. In Comparative Example 1, no chemical conversion treatment was performed. The conditions of chemical conversion treatment for Examples 1-2 and Comparative Example 1 were as shown in Table 1.

Coating Example An epoxy resin paint (MG-PR-E, manufactured by Dainippon Paint Co., Ltd.) is formed on the surface of each member with a chemical conversion coating obtained in Examples 1 and 2 and Comparative Example 1 by a film thickness of 20 μm. After being allowed to stand for 20 minutes, an acrylic-melamine resin-based paint (MG-Top, manufactured by Dainippon Paint Co., Ltd.) is applied to a film thickness of 20 μm by wet-on-wet by an air spray method. This was baked at 180 ° C. for 20 minutes.

  About each coating film obtained by the coating example, the following coating film performance was evaluated by the following method. The results were as shown in Table 2.

(A) Coating film appearance The coating film appearance was visually evaluated according to the following criteria.
○: Good.
Δ: Slight repellency is observed.
X: There are many repellents.

(B) Coating film adhesion In accordance with the cross-cut tape method of JIS K 5400 8.5.2, a cross-cut pattern is drawn on the coating film with a knife and divided into 100 parts. I tried to peel off. The presence or absence and degree of peeling of the coating film were visually evaluated according to the following criteria.
○: No abnormality is observed at all.
(Triangle | delta): Peeling of a coating film is 20% or less.
*: Peeling of a coating film exceeds 20%.

(C) Salt spray resistance A cross-cut is made on the surface of the coating film with a knife, a salt spray test (SST) is performed for 500 hours in accordance with JIS Z 2371, and the peeling width of the coating film at the cross-cut portion is measured. It was evaluated according to the criteria.
○: Peel width is ± 2.5 mm or less.
Δ: Peel width is ± 5 mm or less.
X: The peeling width exceeds ± 5 mm.

Claims (1)

After degreasing the surface of the magnesium alloy containing 1 to 5% by mass of aluminum with xylene, the surface of the magnesium alloy contains 1 to 10% by mass of phosphoric acid in terms of phosphate ion concentration without performing an etching process. A method for forming a coating film of a magnesium alloy, wherein the aqueous solution is subjected to a surface treatment by bringing the aqueous solution into contact at a temperature of room temperature to 70 ° C. for 10 seconds to 10 minutes, and directly coating the surface of the surface-treated magnesium alloy.