JP4609779B2 - Magnesium alloy member and method for forming highly corrosion-resistant film thereof - Google Patents

Description

  The present invention relates to a method for forming a highly corrosion-resistant film of a magnesium alloy and a magnesium product produced using the method.

  Magnesium is expected to be put to practical use because its density is about 2/3 that of aluminum and its strength when made into a thin plate is strong. However, since magnesium and its alloys are very rusting, surface treatment for rust prevention is required. Currently, painting is mainly used for the surface treatment of magnesium alloy, but surface treatment with a metallic texture is also required, and surface treatment by plating is attracting attention.

  As a method for forming an aluminum film, hot dipping is generally used, but since the melting point of magnesium (650 ° C.) is lower than the melting point of aluminum (660.2 ° C.), the base magnesium dissolves during plating. Vapor deposition is well known as another film forming method, but it takes a long time to form a film having a sufficient corrosion resistance on magnesium because the film forming speed is slow. On the other hand, although there are few examples of practical use, there is an electroaluminum plating method as a method for forming aluminum at a low temperature in a short time. The electroaluminum plating method has been studied for a long time since the plating film does not contain heavy metals that affect the environment and the human body. Since the potential of aluminum electrodeposition in an aqueous solution is lower than the potential of hydrogen generation, when plating is performed from an aqueous solution, electrolysis of water occurs in preference to electrodeposition of aluminum. Therefore, electroaluminum plating from an aqueous solution is impossible, and nonaqueous solvents such as tetrahydrofuran, diethyl ether, and toluene are used as the solvent. An aluminum halide or alkylaluminum is used as a solute serving as an aluminum source. Since these solutes easily react with moisture and easily absorb moisture in the air, it is important to control the atmosphere in electroaluminum plating.

The surface of aluminum can be formed into a film having high corrosion resistance by anodizing. Moreover, the film which has various external appearances can be formed by coloring after anodization.
Japanese Patent No. 2751530 JP 2006-233315 A

  Since an oxide film is formed by natural oxidation on the surface of the magnesium alloy, it is important to remove the oxide film by pretreatment in order to plate the magnesium alloy. However, as described above, since the electroaluminum plating solution has a characteristic that it is easily affected by moisture, it must be plated in a state where the object to be plated is sufficiently dried. Accordingly, it is necessary to perform a pretreatment that removes the oxide film and does not generate a natural oxide film by drying.

  Patent Document 1 reports a method of forming a plating film having a four-layer structure of zinc / copper / nickel / aluminum on a magnesium alloy using zinc / copper plating as an antioxidant film. These plating processes use a liquid containing chromic acid and other substances in the pretreatment for removing the magnesium oxide film, and the copper plating process uses a liquid containing hydrocyanic acid. There is a problem with safety.

  Patent Document 2 discloses a method for forming a plating film having a nickel / aluminum two-layer structure by performing nickel plating using a pretreatment process that does not use harmful substances such as hydrocyanic acid and chromic acid, and further performing electroaluminum plating. Although it has been reported, since the corrosiveness of the aluminum plating solution is strong, the magnesium alloy substrate is eluted through the pinholes of the nickel plating film, and as a result, the adhesion of the nickel plating film may be lowered.

  In addition, although the aluminum plating film can be easily removed with an alkaline solution, the above-described film configuration has a problem that it is difficult to remove the copper or nickel plating film used as the antioxidant film and it is difficult to recycle the magnesium alloy. .

  The purpose of this patent is to provide a plating film that has a high corrosion resistance and is rich in metal texture and color variation by using a method that does not use harmful substances on the magnesium alloy, and also has good recyclability. And

  In the present invention, the above-mentioned problems have been solved by forming a conductive anodized film on a magnesium alloy by forming a conductive anodized film and further forming a zinc film / aluminum film double-layer plating film structure. Conductive anodizing treatment of magnesium alloy and electrogalvanizing were used as pretreatment for electroaluminum plating. By forming the conductive anodic oxide film, the reaction between the electrogalvanizing solution and the magnesium material can be prevented. Furthermore, by performing zinc plating as the aluminum plating base, it is possible to prevent a reaction between the highly corrosive aluminum plating solution and the magnesium material. The galvanized film has a silver color similar to that of the aluminum plated film, and there is no noticeable color tone change even if zinc is exposed when scratched. Further, since the AZ-based magnesium alloy contains zinc and aluminum, it can be recycled without peeling off the plating film at the time of disposal. During recycling, the anodized film of the aluminum plating film can be easily removed by dissolving with an alkali.

That is, the first invention of the present application is directed to a magnesium alloy, a conductive anodic oxide film having a thickness of 5 μm or less formed from the magnesium alloy, and a galvanized film having a thickness of 10 to 15 μm formed on the conductive anodic oxide film. a magnesium alloy member having a electroplated aluminum film having a thickness of 10~100μm formed on the galvanized coating, the oxide film formed from the electroplated aluminum coating.

In the second invention of the present application, a conductive anodic oxide film having a thickness of 5 μm or less is formed on a magnesium alloy, a galvanized film having a thickness of 10 to 15 μm is formed thereon, and the thickness is further formed thereon. forming an electrical aluminum plating film 10 to 100 [mu] m, a high corrosion resistant coating method for forming a magnesium alloy member to form an oxide film by oxidizing the surface of the electroplated aluminum coating.

  The thickness of the conductive anodic oxide film is preferably 5 μm or less. When the film thickness exceeds 5 μm, conductivity is lost and electrogalvanization cannot be performed.

  The galvanized film thickness is preferably 5 to 15 μm. When the galvanized film thickness is less than 5 μm, the aluminum plating solution reacts with the magnesium alloy substrate through the pinholes of the galvanized film during aluminum plating. On the other hand, when the film thickness is 15 μm or more, the internal stress of the plating film increases, so that the adhesiveness decreases. The zinc film may be formed by a method other than plating.

  The aluminum plating film thickness is preferably 10 to 100 μm. If the film thickness is less than 10 μm, pinholes in the aluminum plating film become prominent, and there is a risk of eroding the galvanized magnesium alloy substrate during subsequent surface oxidation. Further, when the film thickness exceeds 100 μm, the nodule electrodeposition on the sample edge becomes remarkable.

  The thickness of the aluminum oxide film is preferably 100 nm or more. If the thickness is less than 100 nm, the aluminum plating film is oxidized and the appearance is likely to be uneven.

  By using the present invention, it is possible to obtain a film having a metallic luster and color variation on the magnesium alloy and having good corrosion resistance.

  An example of the highly corrosion resistant coating for magnesium alloy of the present invention will be described below. The zinc plating and aluminum plating solutions are not limited to those described in the embodiments, and any plating solution can be applied.

(Comparative Example 1)
A 60 mm × 60 mm × 1 mm thick magnesium alloy (AZ31) plate was used as the sample to be plated. Using a plating solution prepared by melting 1.0 mol of anhydrous aluminum chloride against 5.0 mol of dimethylsulfone, direct electroaluminum plating was performed on the sample without pretreatment (leaving the oxide layer of the magnesium alloy on the surface). However, the deposit was black powder and did not form a film.

(Comparative Example 2)
A conductive anodic oxide film having a thickness of about 1 μm was formed using a phosphoric acid-based chemical, and electroaluminum plating was performed in the same manner as in Comparative Example 1. As a result, as shown in FIG. 1, the electrodeposit was formed in a white film shape, but was easily peeled off from the substrate. Note that the natural oxide film of the magnesium alloy plate has a negligible thickness (at most several tens of squares) compared to the anodic oxide film, and thus is not removed by pretreatment.

Example 1
A conductive anodic oxide film having a thickness of about 1 μm is formed under the same conditions as in Comparative Example 2, a zinc plating film having a thickness of about 10 μm is formed using a zinc sulfate plating bath, and the same electroaluminum plating solution as in Comparative Example 1 is formed thereon. Thus, an aluminum plating film was formed at a current density of 3 A / dm ² . As a result, a white aluminum plating film as shown in FIG. 2 was obtained. FIG. 3 shows a cross-sectional photograph thereof. The thickness of the aluminum plating at this time is about 10 μm. As a result of a cross-cut adhesion test (JIS K 5400), the coating did not peel off as shown in FIG. FIG. 5 shows the result of component analysis by GD-OES after the surface of the aluminum plating film was oxidized with boiling water at 100 ° C. for 1 hour to form an oxide film having a thickness of about 500 nm. It can be seen that the structure is Al / Zn / Mg from the surface (sputtering time 0 second) side from the peak of the issuing intensity. The salt spray test results are shown in FIG. Although discoloration of the film was observed, no rust was observed over 96 hours, indicating good corrosion resistance.

(Comparative Example 3)
A conductive anodic oxide film having a film thickness of about 10 μm was formed using the same chemical conversion solution as in Comparative Example 2, and the same electrogalvanization and electroaluminum plating as in Example 1 were performed thereon, but the anodic oxide film was too thick. Therefore, there was no conductivity and no film was formed.

Appearance of aluminum plating film of comparative example Example of aluminum plating film appearance Cross-sectional photograph of the magnesium alloy member in Fig. 2 Cross-cut adhesion test results GD-OES results Salt spray test results

Claims (2)

Magnesium alloy, conductive anodic oxide film having a thickness of 5 μm or less formed from the magnesium alloy, galvanized film having a thickness of 10 to 15 μm formed on the conductive anodic oxide film, and formed on the galvanized film magnesium alloy member, characterized in that it comprises an electric aluminum plating film thickness 10~100μm that, the oxide film formed from the electroplated aluminum coating.
A conductive anodic oxide film having a thickness of 5 μm or less is formed on the magnesium alloy, a galvanized film having a thickness of 10 to 15 μm is formed thereon, and an electroaluminum plating having a thickness of 10 to 100 μm is formed thereon. to form a film, high corrosion resistant coating method for forming a magnesium alloy member characterized by oxidizing the surface of the electroplated aluminum film to form an oxide film.