KR100300764B1 - Surface treatment method of magnesium and magnesium alloy with excellent corrosion resistance - Google Patents

Abstract

The present invention relates to a surface treatment method of magnesium and magnesium alloy, and more particularly, in the surface treatment method of Mg and Mg alloy to clean and surface the surface of Mg and Mg alloy, and then anodize and paint on the surface. The step of immersing the washed and pickled Mg and Mg alloy in pure water or deionized water of 90 ℃ or more, or the step of immersing in water of 90 ℃ or more added 0.1 ~ 0.5Vol.% Of Tri-ethanol amine, characterized in that it further comprises It relates to a surface treatment method of magnesium and magnesium alloy excellent in corrosion resistance.

Prior to the anodization of Mg and Mg alloys by the present invention as described above, hydration hydroxides are formed on the surface when immersed in pure water or deionized water or hot water to which amine is added. By acting as the current flows uniformly, the film is uniformly produced, thereby significantly improving the corrosion resistance, coating film adhesion, and wear resistance of the film.

Description

[Name of invention]

Surface treatment method of magnesium and magnesium alloy with excellent corrosion resistance

Detailed description of the invention

[Purpose of invention]

[Technical field to which the invention belongs and the prior art in that field]

The present invention relates to a surface treatment method of magnesium and magnesium alloys, and more particularly, by forming a hydroxide layer on the surface of magnesium and magnesium alloys before anodizing the surfaces of magnesium and magnesium alloys. It relates to a surface treatment method of magnesium and magnesium alloy to form an oxide film to have excellent corrosion resistance.

Mg alloys are generally divided into two groups: relatively old metals of Mg-Al- (Zn)-(Mn) and relatively new alloys of Mg-Zn-Zr, die cast and sealant. It is molded by casting, forging, extrusion, etc., and is widely used in aircraft parts, automobile parts, precision optical parts, OA devices, electronic and electronic material parts, information and communication devices, leisure, and sporting goods.

Thus, Mg alloy, which is the lightest among the practical metal materials and has been greatly spotlighted with the development of aircraft, has the disadvantage of low strength but low impact value and abundant activity, thereby reducing corrosion resistance.

Thus, the corrosion-resistant Mg alloys have been studied for a long time. In the treatment method, the cleaned and pickled Mg and Mg alloys are immersed in pure water or deionized water of 90 ° C. or higher, or 0.1 to 0.5 Vol.% Of Tri. It provides a method for surface treatment of magnesium and magnesium alloy excellent corrosion resistance characterized in that it further comprises the step of immersing in water of more than 90 ℃ ethanol amine added.

In addition, the coating is characterized by coating the resin by electrophoretic electrodeposition to the base coating, and to the top coating by electrostatic, spray coating or flow deposition coating thereon.

The reason for the use in the hot-water washing when 0.1 ~ 0.5Vol.% Of Tri-ethanol amine of Mg and Mg alloy added are 0.5Vol.% Or more in Mg (OH) ₂ formed of the hydrothermal reaction and MgO · nH ₂ Compounds with Mg due to amine (Amine) on the stable product of O is easy to form, it is difficult to produce a pure and stable Mg oxide or hydroxide, the reaction time takes too much at 0.1Vol.% Or less and is pure This is because the production of stable Mg oxides or hydroxides is difficult.

The reason why the temperature of the washing water is 90 ° C or higher is because water reacts most actively with the counterpart metallic material at this temperature or higher, and it is possible to grow stable Mg (OH) ₂ in a short time. .

On the other hand, looking at the mechanism for the formation of the hydroxide layer, which is the subject of the present invention, by depositing Mg and Mg alloy in hot water or more than 90 ℃ to which pure water or deionized water or 0.1 ~ 0.5Vol.% Of tri-amine is added,

Mg + 2H ₂ O → Mg (OH) ₂ + H ₂ ↑ + ΔG (ΔG = -84.0 Kcal / mol)

As the reaction occurs, free energy decreases, and hydroxides and oxides have a more stable structure than metals.

This reaction is influenced by the temperature of the reaction solution, and the stronger Mg (OH) ₂ is formed on the surface of the Mg and Mg alloy in hot water of 90 ° C. or higher.

The reason why the hydroxide layer formed in this way flows the electrolytic current uniformly is that if anodization is performed on the surface of Mg and Mg alloy as it is, the shape defects such as pinholes and bubbles present on the surface are electrolyzed and the defects gradually increase. As a result of concentration of current in these defects, it is impossible to cure a uniform anodized film.However, when Mg (OH) ₂ is coated on the surface, a hydroxide layer is formed even on defects present on the surface of Mg and Mg alloy. Concentration is eliminated to form a uniform anodized film.

Hereinafter, an Example is given and this invention is demonstrated in detail.

Example 1

AZ91 ash 5mm thick, 50mm wide and 100mm long was sufficiently cleaned in ethyl alcohol using an ultrasonic cleaner and then immersed in a mixed solution of 20 vol.% Acetate and 5wt.% Sodium acetate for 1 minute to produce irregular oxides, corrosion products and other surfaces. Contaminants were removed and this treated sample was taken as A.

Next, this sample A was subjected to pretreatment, which is the subject of the present application, as follows.

Deionized water was boiled and sample A was deposited for 1, 3, and 5 minutes at this rate, and these were defined as B, C, and D, respectively.

In addition, the sample A was deposited for 1, 3, and 5 minutes in a 90 ° C solution to which 0.3% by volume of Tri-ethanol-amine was added, thereby making E, F, and G, respectively.

Since the anodizing method, MIL Type 5 (DOW 12), H.A.E. Two types of (Herry A.Evonglide) methods were selected to be anodized a and b.

By either anodization, the current density and the electrolysis time were adjusted so that the average film thickness was about 15 mu m.

In addition, the weight of each sample was measured with the precision of 1/1000 g of precision electron blue flat in the state of sample A, B, C, D, E, F, G.

In the same manner, the weight after the completion of the anodization a, b was measured, and only the anodic oxide films of a and b were completely dissolved in a 90 ° C. thermal bath mixed with phosphoric acid and chromic acid, and then weighed. The weight of the sample before anodization was W ₀ , the weight after anodization was W ₁ , and only the anodized film was dissolved, and the weight of the remaining Mg alloy material was W ₂ , and the film formation efficiency CR (Coating Ratio) was Calculated as follows, CR has the following formula.

CR (Coating Ratio) = film thickness (W ₁ -W ₂ ) / metal consumption (W ₀ -W ₂ )

As a result of confirming the improvement of the corrosion resistance, the occurrence status of each sample for 48 hours by the salt spray test defined by KSD (Korean Industrial Standard) was obtained as shown in Table 3.

In addition, in order to confirm the improvement of coating adhesion, Cationic Epoxy resin is coated on the anodized film by electrophoretic electrodeposition, and the undercoat is coated on top of it, and the top coat is applied by electrostatic, spray coating or flow deposition coating. The evaluation was made by a neck test and the results are shown in Table 4.

Example 2

Mg now using two kinds (Mg: 99.8%) of cast material 5 × 50 × 100 mm plate pre-treatment and anodization under the same conditions as Mg alloy (AZ91) and then tested in the same manner as in Example 1 The results shown in Tables 5, 6 and 7 were obtained.

Claims (2)

In the method for surface treatment of Mg and Mg alloys, in which the surface of Mg and Mg alloys is cleaned and pickled, anodized and coated thereon, the cleaned and pickled Mg and Mg alloys are pure or deionized water of 90 ° C. or higher. The method for surface treatment of magnesium and magnesium alloys having excellent corrosion resistance, further comprising the step of immersing in water or at least 90 ° C. to which Tri-ethanol amine is added at 0.1˜0.5 Vol.%. 2. The magnesium and magnesium alloy having excellent corrosion resistance according to claim 1, wherein the coating is coated with a resin by electrophoretic electrodeposition, and the top coating is applied by electrostatic, spray coating, or flow deposition coating. Surface treatment method.