JP2007302922A - Method for treating surface of magnesium member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating the surface of a magnesium member having a grounding part and a non-grounding part through a highly efficient operation process. <P>SOLUTION: This surface treatment method comprises the steps of: forming a conductive chemical conversion coating 2 (figure (a)) by chemical-conversion-treating the whole surface of the magnesium member 1; subsequently masking the grounding part A1; anodizing the non-grounding part A2 to form an anodic oxide film 3 comprising porous cells (figure (b)); and finally coating the surface of the anodic oxide film 3 with a paint to form a paint film 5 (figure (c)). Then, the pores in the anodic oxide film 3 are plugged by the coating film 5. Thereby, the method can prevent the rust of the magnesium member 1 while securing grounding, in a continuous process. As a result, the operation process for treating the surface of the magnesium member 1 is simplified, and needs a shorter period of time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for treating a surface of a magnesium member, which is suitable for application to each part in an automobile, particularly a part (for example, a junction box) that comes into contact with a corrosive liquid such as moisture or salt water. Here, the magnesium member means a member made of magnesium or a magnesium alloy.

  FIG. 4 is a sectional view showing a first example (chemical conversion treatment method) of a conventional magnesium member surface treatment method, and FIG. 5 is a sectional view showing a second example (anodization treatment method) of a conventional magnesium member surface treatment method. It is.

  In recent years, the demand for magnesium (Mg), which is a low specific gravity metal, tends to increase in response to the growing demand for weight reduction for each part in an automobile. Magnesium is an electrochemically very basic metal, and corrosion of different metal contact sites becomes a problem. Therefore, chemical conversion treatment and anodizing treatment are mainly performed as a surface treatment for the purpose of anticorrosion.

  Here, the chemical conversion treatment is a chemical reaction between magnesium and a treatment solution, and as shown in FIG. 4, a protective coating made of a reaction product such as an oxide is formed on the surface of the magnesium member 1, that is, the chemical conversion coating 2. It is a processing method to do. Specifically, a method of contacting a high temperature sodium hydroxide solution (for example, see Patent Document 1), a method of treating with a pyrophosphate solution and an alkali hydroxide solution (for example, see Patent Document 2), acidic (hydrogen A method of contacting an aqueous liquid containing phosphoric acid, manganese ions and an amine compound under an ion index pH <7) has been proposed (for example, see Patent Document 3). And this chemical conversion process has the characteristics that the chemical conversion film 2 is thin and a very high corrosion resistance cannot be obtained.

On the other hand, the anodizing treatment is performed by electrochemically reacting magnesium as an anode, thereby forming a non-conductive porous oxide film, that is, an anodic oxide film 3 on the surface of the magnesium member 1 as shown in FIG. It is a processing method. In addition, this anodizing treatment is characterized in that the anodized film 3 is thick and has excellent corrosion resistance.
Japanese Patent Laid-Open No. 61-90776 JP-A-6-116740 Japanese Unexamined Patent Publication No. 7-126858

  However, when the earth location is included in the magnesium member 1, it is necessary to perform surface treatment on the magnesium member 1 while ensuring conduction at the earth location and placing importance on corrosion resistance at other locations (non-earth location). Accordingly, the work process of the surface treatment becomes complicated and the required time becomes long, and there is a disadvantage that the efficiency of the work process is poor.

  An object of this invention is to provide the surface treatment method of a magnesium member which can solve such inconvenience.

First, the invention of the magnesium member surface treatment method according to claim 1 is a surface treatment method of a magnesium member in which surface treatment is performed on a magnesium member composed of a grounded portion and a non-grounded portion, and is conducted to the surface of the magnesium member. It includes a chemical conversion treatment step for forming a chemical conversion coating and an anodization treatment step for forming an anodic oxidation coating at a non-ground portion of the magnesium member.
Further, in the invention of the surface treatment method for a magnesium member according to claim 2, the grounding portion of the magnesium member is masked in the anodizing treatment step.
The magnesium member surface treatment method according to claim 3 is characterized in that the chemical conversion film is extinguished in the anodizing step.
According to a fourth aspect of the present invention, there is provided a magnesium member surface treatment method including a sealing treatment step of closing a hole of the anodized film.
The magnesium member surface treatment method according to claim 5 is characterized in that a coating film is formed on the surface of the anodized film in the sealing treatment step.

  According to the present invention, corrosion prevention and grounding can be performed in a series of steps on a magnesium member composed of a grounded location and a non-grounded location. As a result, the surface treatment work process is simplified and the required time is shortened in the magnesium member composed of the ground part and the non-ground part, so that the work process can be made highly efficient.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a process diagram showing an embodiment of a surface treatment method for a magnesium member according to the present invention, wherein (a) is a sectional view showing a first process (chemical conversion treatment process), and (b) is a second process ( Sectional drawing which shows an anodizing process process, (c) is sectional drawing which shows a 3rd process (sealing process process).

  The magnesium member surface treatment method according to the present invention is performed according to the following procedure.

  First, in the first step (chemical conversion treatment step), as shown in FIG. 1 (a), the entire surface (the ground point A1 and the non-ground point) is applied to the magnesium member 1 composed of the ground point A1 and the non-ground point A2. A conductive (conductive) chemical conversion film 2 is formed on A2). For this purpose, for example, the entire surface of the magnesium member 1 is subjected to chemical conversion treatment by the method disclosed in Japanese Patent No. 3307882.

  Next, the process proceeds to the second step (anodizing treatment step), and as shown in FIG. 1 (b), the porous cell-like anodic oxide film 3 is formed on the surface of the magnesium member 1 except for the ground portion A1. . For this purpose, the ground portion A1 of the magnesium member 1 is masked, and in this state, the surface of the magnesium member 1 is anodized by, for example, a method disclosed in Japanese Patent Application Laid-Open No. 2005-103505. Then, the ground portion A1 in the surface of the magnesium member 1 is masked, so that the anodized film 3 is not formed. On the other hand, the non-earthed portion A2 of the surface of the magnesium member 1 is not masked, so that the anodized film 3 is formed. As described above, since the ground portion A1 is masked, only the non-ground portion A2 can be anodized quickly and easily.

  At this time, in the non-earth location A2, the chemical conversion film 2 is destroyed and disappears, and only the anodized film 3 is covered. The disappearance mechanism of the chemical conversion film 2 is as follows. That is, when anodizing treatment is performed, first, as a pretreatment, the surface is cleaned with a solution having a high oxidizing power such as hydrofluoric acid, and then, when anodized film 3 is formed, a strong alkali solution or the like is made reactive. Using a rich solution, the anodic oxide film 3 is formed by electrolysis in an energized state. Therefore, the very thin chemical conversion film 2 having a film thickness of about several hundred nm to several μm is destroyed and disappears in the above process.

  Finally, the process proceeds to the third step (sealing treatment step), and as shown in FIG. 1C, the pores of the porous cellular anodized film 3 are closed. For this purpose, the anodized film 3 is subjected to a sealing treatment. As a specific method of this sealing treatment, a method of coating the surface of the anodized film 3 to form the coating film 5 can be considered. For example, after undercoating, baking, intermediate coating, and baking with an epoxy paint, overcoating and baking with an acrylic paint may be performed. At this time, by setting the total coating thickness to a certain value (for example, 60 μm) or more, the holes of the anodized film 3 are closed by the coating film 5. Furthermore, the coating film 5 can enhance the corrosion resistance of the non-earthed portion A2 of the magnesium member 1.

  Here, the surface treatment process of the magnesium member 1 is completed.

  Thus, the corrosion prevention and grounding can be performed in a series of steps on the magnesium member 1 composed of the ground point A1 and the non-ground point A2. As a result, in the magnesium member 1 composed of the ground point A1 and the non-ground point A2, the work process of the surface treatment is simplified and the required time is shortened, so that the work process can be made highly efficient.

  In addition, although the chemical conversion film 2 is formed in the earth location A1, since this chemical conversion film 2 has electroconductivity, taking out of an earth can be performed without trouble.

  Examples of the present invention will be described below.

  2 is a perspective view of a junction box made of magnesium, and FIG. 3 is a perspective view of the junction box shown in FIG.

  In order to confirm the above-described effects, as shown in FIGS. 2 and 3, the surface treatment method (Example) of the present invention combining the chemical conversion treatment and the anodic oxidation treatment is applied to the hexagonal junction box 6 made of magnesium. did. The junction box 6 has a structure in which a flat top cover 6b is fastened to a bottomed rectangular tube-shaped box 6a with four screws 6c and energizes components in the box 6a. It is necessary to ground the fastening portion of one screw 6c. In addition, this example includes two types of coating film thicknesses in the third step: 40 μm or more (Example 1) and 60 μm or more (Example 2).

  For comparison, a hexagonal junction box 6 made of magnesium of the same size was subjected to a conventional surface treatment method only by chemical conversion treatment (Comparative Example 1) and a conventional surface treatment method only by anodization treatment (Comparative Example 2). .

  And about the comparative examples 1 and 2 and Examples 1 and 2, the salt spray test based on Japanese Industrial Standard (JIS Z 2371) was implemented, and the progress degree of corrosion was confirmed visually. Here, the bath temperature was 35 ° C., the test time was 240 hours (however, 48 hours for Comparative Examples 1 and 2), and a 5% NaCl aqueous solution was used as the salt solution.

  As a result, in Comparative Example 1, corrosion occurred when 24 hours passed, and the corrosion progressed violently after 48 hours. Further, in Comparative Example 2, no corrosion occurred even after 48 hours. Furthermore, in Examples 1 and 2, no corrosion occurred even after 48 hours. Therefore, it was confirmed that there was no problem in the corrosion resistance in Comparative Example 2 and Examples 1 and 2 while there was a problem in the corrosion resistance in Comparative Example 1.

  On the other hand, in Example 1, after 48 hours passed, corrosion started at the fastening portion of the screw 6c, and corrosion progressed over a wide range when 240 hours passed. On the other hand, in Example 2, even if 240 hours passed, corrosion was not seen by the fastening part of the screw 6c. Accordingly, it has been found that the corrosion resistance is further improved by increasing the thickness of the coating film to 60 μm or more.

  The present invention can be widely applied to various industrial fields such as automobiles, airplanes, trains, manufacturing plants, electrical appliances, and OA equipment.

It is process drawing which shows one Embodiment of the surface treatment method of the magnesium member which concerns on this invention, Comprising: (a) is sectional drawing which shows a 1st process (chemical conversion treatment process), (b) is a 2nd process (anodic oxidation process). (C) is sectional drawing which shows a 3rd process (sealing process process). It is a perspective view of the junction box made from magnesium. It is a perspective view of the open state of the junction box shown in FIG. It is sectional drawing which shows the 1st example (chemical conversion treatment method) of the surface treatment method of the conventional magnesium member. It is sectional drawing which shows the 2nd example (anodic oxidation method) of the surface treatment method of the conventional magnesium member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Magnesium member 2 ... Chemical conversion film 3 ... Anodized film 5 ... Coating film 6 ... Junction box A1 ... Ground location A2 ... Non-ground location

Claims (5)

A surface treatment method for a magnesium member, in which a surface treatment is performed on a magnesium member composed of a ground point and a non-ground point,
A chemical conversion treatment step of forming a conductive chemical film on the surface of the magnesium member;
A surface treatment method for a magnesium member, comprising: an anodizing treatment step of forming an anodized film at a non-earthed portion of the magnesium member. In the anodizing process,
The surface treatment method for a magnesium member according to claim 1, wherein a ground portion of the magnesium member is masked. In the anodizing process,
The surface treatment method for a magnesium member according to claim 1 or 2, wherein the chemical conversion film is extinguished.   The surface treatment method for a magnesium member according to any one of claims 1 to 3, further comprising a sealing treatment step of closing the pores of the anodized film. In the sealing treatment step,
The surface treatment method for a magnesium member according to claim 4, wherein a coating film is formed on the surface of the anodized film.

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