JPS6033360A - Treatment of magnesium or magnesium alloy - Google Patents

Abstract

PURPOSE:To impart sufficient corrosion resistance without generating public nuisance, by successively treating magnesium or a magnesium alloy with an aqueous solution containing a metal ion and a phosphate radical, an aqueous solution of alkali metal silicate and silicone. CONSTITUTION:Magnesium or a magnesium alloy is immersed in an aqueous solution containing a metal ion and a phosphaste radical such as an aqueous Ca (H2PO4) solution while the treated one is subsequently immersed in an aqueous solution containing alkali metal silicate such as sodium silicate and sufficiently washed with water and dried. In the next step, a diluted solution of an org. solvent souting containing a paint grade silicone resin is applied to the surface film obtained by the above mentioned treatments by an immersion or spraying method and, after drying, silicone treatment is applied. A strong film is formed to magnesium or its alloy by the above mentioned surface treating method and excellent corrosion resistance can be imparted and there is no possibility for generating public nuisance.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for treating the surface of magnesium or a magnesium alloy.

Prior Art As a chemical conversion treatment for imparting corrosion resistance to the surface of magnesium or a magnesium alloy, immersion treatment with an aqueous sodium dichromate solution has been most widely used in the past. This treatment has also been highly evaluated as a base treatment for Zolimer to be coated on when corrosion resistance is insufficient with chemical conversion treatment alone. JISH8651 Type 1 A corresponds to this treatment method, but since treatment waste liquid containing chromium may cause pollution, there has been a desire to develop a surface treatment method that does not use chromium.

Treatment methods that do not use chromium include depositing cationic salts on the surface of magnesium or magnesium alloys to form a coating, but this method only provides a porous coating and therefore does not provide sufficient corrosion resistance. It is difficult to achieve.

OBJECTS OF THE INVENTION The object of the present invention is to provide
The object of the present invention is to provide a method for surface treatment of magnesium or magnesium alloy that can provide sufficient corrosion resistance.

According to the present invention, there is provided a method for surface treating magnesium or a magnesium alloy, in which magnesium or a magnesium alloy is immersed in an aqueous solution containing metal ions and phosphate groups, and then treated with an alkali metal. It is characterized in that it is immersed in an aqueous solution containing a silicate, and the surface coating thus obtained is further treated with silicone.

Detailed Description of the Structure of the Invention In the method of the present invention, magnesium or a magnesium alloy is first immersed in an aqueous solution containing metal ions and phosphate groups. As the treatment liquid, it is preferable to use an aqueous solution of metal dihydrogen phosphate. An example of such a salt is Ca(H2PO4).

If the desired metal is not available in the trihydrogen phosphate form,
By dissolving other forms of water-soluble gold salts and dihydrogen phosphates in water, an aqueous solution containing desired metal ions and phosphate groups can be obtained.

For example, when it is desired to obtain an aqueous solution of Ba ions and phosphate radicals, BaCl2.2H20 and NH4H2PO4 can be used. Examples of useful metal ions include Ca
, Ba, Mn, etc.

In order to fully form a good phosphate film on the surface of magnesium or a magnesium base metal, it is necessary that the treatment liquid has sufficient etching action, and for this purpose it is preferable that the treatment liquid further contains phosphoric acid.

However, since the presence of excessive free phosphoric acid deteriorates the produced film, care must be taken not to add an excessive amount. Moreover, it is preferable that the treatment liquid further contains nitrite as a reaction accelerator.

For example, the treatment liquid contains a water-soluble barium salt in an amount of 10 to 100 j; l/l as B a C1-2. Contains H5HO4 (9
85%) and 1 to 5 fl/13 Na as a reaction accelerator.
Contains zNO2ft.

The soaking is preferably carried out at a temperature of 20 DEG to 100 DEG C. for 5 to 60 minutes, but it is advantageous to thoroughly degrease and clean the surface of the magnesium or magnesium alloy before soaking.

In the method of the invention, the magnesium or magnesium alloy is then immersed in an aqueous solution containing an alkali metal silicate. This treatment replaces a portion of the phosphate in the phosphate film formed above with silicate.
This is done to ensure extremely high affinity with silicone during the next silicone treatment, and the immersion is preferably carried out at a temperature of 70 to 100°C for 5 to 60 minutes. The treatment solution used for this treatment may be, for example, an aqueous solution containing 5 to 20% by weight of sodium silicate (18 parts by weight of Na2O, 236 parts by weight of 5IO).

After treatment, wash thoroughly with water and dry.

The resulting coating is then subjected to silicone treatment. This treatment is performed for the purpose of sealing the porous chemical conversion coating. Useful treatment agents include, for example, silicone coating resins such as Toray Silicone SR2405 Resin (trade name), Tone Silicone 5R2410 Resin (trade name), and Toray Silicone 5H200 Oil (trade name).
There are silicone oils such as Toray Silicone SRX 310 (trade name). When using a silicone resin, it is usually diluted with an organic solvent such as toluene or xylene that has a dissolving power for the silicone resin to form a solution.

When using such a dilute solution of silicone resin, 1
Make a solution with a concentration of ~60% by weight, and add 1 to 10% at room temperature.
Apply by dipping for seconds or by spraying, at room temperature
The desired silicone treatment is obtained by drying at a temperature of 0.000C and three-dimensional crosslinking of the resin. On the other hand, when using silicone oil, 1
751 It is better to soak at 50 to 250°C for 10 to 300 seconds.

Magnesium or magnesium alloys surface-treated in this way can have a strong coating and therefore have very good corrosion resistance.

Example The present invention will be further explained below with reference to Examples.

A magnesium alloy plate (AZ91B Guicast alloy) was treated as follows.

(1) Phosphate treatment 76g/l! of chloride, 18 g/l of phosphorous ammonium dihydrogen, 49/l of sodium nitrite and 3
The above magnesium alloy was immersed in an aqueous solution containing g/l phosphoric acid (85%) for 15 minutes at room temperature. Barium phosphate was deposited on the surface of the magnesium alloy.

(2) Silicate Treatment The phosphate-treated magnesium alloy was immersed in an aqueous IJ solution at 80° C. for 15 minutes. During soaking, the coating changed from dark gray to whitish gray as the reaction progressed.

(3) Silicone treatment Toray Silicone 5R2410 resin was mixed with toluene to form a solution with a concentration of 5% by weight, and the magnesium alloy after the silicate treatment was immersed in this solution for 10 seconds at palm temperature, and then dried at room temperature. The resin was left to harden for one day. The obtained magnesium alloy plate was designated as sample 1.

(4) Comparative Example For comparison, after performing the phosphate treatment in (1) above,
3) subjected to silicone treatment (referred to as sample 2),
Sample 3 was subjected to only the silicone treatment in (3) above.
), chromate treatment only according to JISH86511 type A (sample 4), JIS H86
After chromate treatment with 511 type A, the above (3)
(specimen 5), and chromate treatment according to JISH 86511 type A, followed by primer treatment using epoxy paint (sample 5).
(referred to as sample 6) were prepared.

The primer treatment with the epoxy paint described above was carried out as follows. Namely, 65% by weight of epoxy paint, Eponics 73HB primer (trade name of Dainippon Paint Co., Ltd., weight mixing ratio of curing agent to main agent: 80:20) and 3.
A mixed solution was prepared using a 5% by weight diluent and Ebonix HB thinner (trade name of Dainippon Paint Co., Ltd.), and a magnesium alloy plate was immersed in this for 30 seconds at room temperature, and then left at room temperature for 2 days to completely cure the resin. I let it happen.

(5) Corrosion resistance test Each of the above samples was placed at an angle of 15° above the normal line, and the JIS
Z2371 was subjected to a salt spray test according to the specified conditions. A 5% sodium chloride solution was used.

The results obtained are summarized in Table 1 below.

Note: * Amount of silicone resin or epoxy paint adhered.

※※Snacks during 12 days of exposure.

Claims (1)

[Claims] 1. When surface-treating magnesium or a magnesium alloy, magnesium or a magnesium alloy is immersed in an aqueous solution containing metal ions and phosphate groups, and then immersed in an aqueous solution containing an alkali metal silicate. A method characterized by further siliconizing the surface coating.