JP2009228087A - Magnesium alloy coating film and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium alloy coating film which has self-restoring property and excellent corrosion resistance and with which the application range of the conventional magnesium alloy can be enlarged, and to provide a method for producing the same. <P>SOLUTION: The magnesium alloy coating film has a porous layer on which an organic restoring material is supported. As the organic restoring material, casein, citric acid or oxalic acid can be used. The porous layer can be formed from the assembly of fine particles or a porous resin in which pores communicate with one another. As the fine particles, particles of titania (TiO<SB>2</SB>), silica (SiO<SB>2</SB>) or alumina (Al<SB>2</SB>O<SB>3</SB>) can be used. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnesium alloy film having self-repairing properties and excellent corrosion resistance, and a method for producing the same.

  Magnesium is the lightest structural metal, but its strength is low. Therefore, magnesium alloy, which is practically alloyed and enhanced in strength, is used for automobile parts, PC housings, mobile phones, aircraft parts, etc. Has been. Since such a magnesium alloy is inferior in corrosion resistance if it is a metal substrate, it usually requires anticorrosion treatment and has been subjected to chromate treatment. However, due to environmental hygiene problems, anticorrosion treatments that replace chromate treatments have been proposed.

  For example, Patent Document 1 proposes a zirconium phosphate laminated molecular anticorrosion film formed by a phosphoric acid molecular layer composed of a phosphoric acid group and / or a phosphoric acid derivative and a zirconium molecular layer composed of zirconium. And it is disclosed that this zirconium phosphate laminated molecular anticorrosion film is applied not only to magnesium metal but also to aluminum metal, aluminum alloy, magnesium alloy, titanium metal or titanium alloy.

  Further, Patent Document 2 has a problem that, when a magnesium alloy is chromated, the color of its surface changes and the metallic luster is lost. This is a colorless and transparent solution that can suppress the corrosion of the magnesium alloy. An anticorrosive coating composition for magnesium alloys has been proposed. That is, oxide particles selected from the group consisting of aluminum oxide, zinc oxide, tin (IV) oxide, and silicon dioxide, oxide particles (a) having an average particle diameter of 20 to 50 nm, acrylic resin ( An anticorrosive coating composition for magnesium alloys containing b) and a silane coupling agent (c) has been proposed.

JP 2003-293175 A JP 2006-137861 A

  However, the zirconium phosphate laminated molecular anticorrosion film proposed in Patent Document 1 has a description of the corrosion resistance when it is provided on an aluminum alloy, but there is actually an improvement in corrosion resistance relative to the magnesium alloy. There is no description. The anticorrosive coating composition for magnesium alloy proposed in Patent Document 2 has the advantage that the acrylic resin coating film in which the oxide is dispersed can improve the corrosion resistance several times as compared with the acrylic-only coating film. In addition, adjustment of additives for improving the adhesion between the acrylic resin coating film and the magnesium alloy, coating treatment, and the like are required, and there is a problem in workability.

  In addition, such a conventional magnesium alloy corrosion resistant coating does not have self-repairing properties such that the coating itself repairs the damaged portion of the coating. By improving the corrosion resistance of the magnesium alloy and expanding the application range of the magnesium alloy with the corrosion-resistant coating of the magnesium alloy having self-healing properties, it is possible to improve energy efficiency by reducing the weight and contribute to environmental conservation. It is to be.

  In view of such conventional problems and social demands, the present invention provides a magnesium alloy coating having a self-repairing property, excellent corrosion resistance, and capable of expanding the application range of conventional magnesium alloys, and a method for producing the same. The purpose is to provide.

The magnesium alloy coating according to the present invention has a porous layer carrying an organic restorative material. The organic restoration material can be casein, citric acid or oxalic acid, and the porous layer can be made of a porous resin in which aggregates of fine particles or pores communicate with each other. The fine particles may be titania (TiO ₂ ), silica (SiO ₂ ), or alumina (Al ₂ O ₃ ) fine particles.

  By forming the magnesium alloy coating of the present invention on the surface of the magnesium alloy, a magnesium alloy having excellent corrosion resistance can be obtained, and a lightweight automotive component having excellent corrosion resistance can be produced using the magnesium alloy. it can.

  The method for producing a magnesium alloy coating according to the present invention is performed by first forming an oxide fine particle layer on the surface of the magnesium alloy and then supporting casein on the formed oxide fine particle layer.

  In the above invention, casein is supported by adjusting the hydrogen ion index (pH) of the casein aqueous solution.

  The magnesium alloy coating according to the present invention has self-repairing properties and excellent corrosion resistance, and can be widely used for automobile parts, personal computer casings, mobile phones, aircraft parts, and the like.

  Hereinafter, the best mode for carrying out the present invention will be described. The magnesium alloy coating according to the present invention has a porous layer carrying an organic restorative material. That is, this magnesium alloy film is a film formed on the surface of the magnesium alloy 20 and having a thickness of 1 to 2 μm, for example, as shown in FIG. The organic restoration material 13 is supported on the porous layer 10 in which the pores 12 formed between 11 communicate with each other. Note that the thickness of the coating is optimally selected depending on the material constituting the porous layer 10 and the material of the organic restorative material 13, but can be 0.5 to 3 μm.

  As described above, the porous layer 10 can be porous having the pores 12 formed by the fine particles 11, but the communication from the surface of the porous layer 10 to the joint portion with the magnesium alloy 20 is possible. Any material having the fine pores 12 may be used. Therefore, it may be composed of a porous resin having such a structure. The thickness of the porous layer 10 is selected in consideration of the material and the material of the organic restorative material 13 to be combined, and can be set to 0.5 to 3 μm.

When the porous layer 10 is formed by stacking the fine particles 11, the fine particles 11 having an average particle diameter of 10 to 500 nm can be used. An optimum average particle diameter is selected depending on the material and properties of the fine particles 11 used. The fine particles 11 can be oxide fine particles. For example, titania (TiO ₂ ), silica (SiO ₂ ), or alumina (Al ₂ O ₃ ) fine particles can be used. As the shape of the fine particles 11, a spherical shape can be used. However, the shape of the fine particles 11 is preferably needle-shaped rather than spherical.

The fine particles 11 can be subjected to a surface treatment, and an appropriate surface treatment can be selected depending on the fine particles used. This surface treatment may impart water repellency to the fine particles 11 or may impart hydrophilicity. For example, in the case of titania, water repellency can be imparted by treatment with aluminum hydroxide (Al (OH) ₃ ). In addition, it is possible to impart hydrophilicity by further performing stearic acid treatment on aluminum hydroxide (Al (OH) ₃ ) treatment. These surface treatments are more effective in improving the corrosion resistance than when no surface treatment is performed. When the water-repellent surface treatment is compared with the hydrophilic surface treatment, the water-repellent surface treatment is better.

  The organic restorative material 13 may be any material that penetrates into the pores 12 of the porous layer 10 and aggregates and solidifies under certain conditions, and has reactivity with the magnesium alloy. For example, casein, citric acid, and oxalic acid can be used. Casein is preferably an aqueous solution because the aggregation state and the dispersion state can be changed by the hydrogen ion index (pH). Thereby, the outstanding self-repairing property can be exhibited.

  2 and 3 show the results of observation of the magnesium alloy coating film with a scanning electron microscope (SEM) and component analysis tests with an energy dispersive characteristic X-ray detector (EDS) attached thereto. FIG. 2 shows a surface portion of the magnesium alloy coating formed on the surface of the magnesium alloy AZ31, and FIG. 3 shows a cross-sectional portion of the magnesium alloy coating.

  This magnesium alloy film is an example in which casein is supported as the organic restorative material 13 in the porous layer 10 formed by laminating titania (average particle size 270 nm) as the fine particles 11. Casein was supported by readjusting a casein aqueous solution adjusted to pH 12 to pH 5 during film formation. JSM-6340F manufactured by JEOL Ltd. was used as the scanning electron microscope. EDS analysis was performed on the bar portion shown in the SEM photograph. The horizontal axis of the EDS analysis graph indicates the distance from the left end of the bar portion, and the vertical axis indicates the intensity.

  As shown in the EDS analysis graph of FIG. 2, the present magnesium alloy film has the carbon component C due to casein distributed throughout. And the high peak of the carbon component C which is observed in the center part of an EDS analysis graph is observed. The high peak of the carbon component C is an aggregate or film of casein, as can be seen from the SEM photograph. Moreover, since the film | membrane by titania is not formed in the black part of a SEM photograph, the magnesium which is a base material elutes and the high peak of magnesium component Mg is observed.

  Further, as shown in the EDS analysis graph of FIG. 3, a high peak of the carbon component C is also observed at the boundary portion between the magnesium alloy film and the magnesium alloy 20, and casein passes through the pores 12 in the porous layer 10. Thus, it can be seen that the surface of the magnesium alloy 20 is well distributed. Moreover, it turns out that the thickness of the magnesium alloy film of this example is 1-2 micrometers.

  Such a magnesium alloy film has a self-repairing property and high corrosion resistance. 4 to 6 show the self-repair status of the magnesium alloy coating. 4-6 is an example of the magnesium alloy film of the same structure as the magnesium alloy film shown in FIG. 2 or FIG. FIG. 4 is an SEM photograph of a sample in which a blade was pressed against the magnesium alloy film with a pressure of 10 g to provide a scratch. 5 and 6 are SEM photographs when the scratched sample was immersed in a 0.0005M saline solution and subjected to a corrosion test. FIG. 5 shows 4 hours after immersion, and FIG. 6 shows immersion. It is a SEM photograph 48 hours later.

  According to FIG. 4, the width of the scratch is about 10 μm, and it can be seen that the titania fine particles are completely scraped off at the center of the scratch. It can also be seen that the scraped titania fine particles are swollen beside the scratches.

  According to FIG. 5, the lump of titania particles drowned by the scratch is almost disappeared, the scratch is covered with a translucent film-like material, and there is a lump at every part of the scratch. It is observed that According to EDS analysis, the translucent film was casein, and the bulk was titania. According to FIG. 6, it can be observed that the thickness of the translucent film at the scratched portion increases and covers the entire scratched surface.

  That is, in the present magnesium alloy coating, the organic restoration material 13 (casein) carried on the porous layer 10 melts and covers the scratches, and the titania fine particles transferred with the organic restoration material 13 or porous The titania particles that collapsed from the stratum corneum 10 fill the scratches and repair the scratches. Thus, this magnesium alloy film has a self-repairing property and exhibits high corrosion resistance.

  FIG. 7 illustrates the corrosion resistance of the magnesium alloy coating. In FIG. 7, the horizontal axis represents the immersion time of the sample in the corrosion test solution, and the vertical axis represents the corrosion resistance ratio. The parameters in the figure indicate, for example, that pH12 → pH5 indicates that casein was supported by re-adjusting the casein aqueous solution adjusted to pH 12 to pH 5 during film formation. As the corrosion test solution, a saline solution having a concentration of 0.0005M was used. Corrosion resistance ratio is determined by the AC impedance measurement method described later. Corrosion resistance ratio = (corrosion resistance at each immersion time) / (corrosion resistance immediately after immersion). This is obtained by taking the correction into consideration.

  According to FIG. 7, it can be seen that the corrosion resistance of the magnesium alloy coating was improved by adjusting the casein aqueous solution to pH 12 → pH 5, pH 12 → pH 6, and pH 12 → pH 7. In particular, when the pH is 12 → pH 5, the corrosion resistance is remarkably improved. Next, pH12 → pH6, pH12 → pH7. However, in the case of pH 12 → pH 10 and pH 12 → pH 4, the corrosion resistance ratio is hardly changed. That is, in order to support the casein on the porous layer 10, it is necessary to optimally adjust the pH of the casein aqueous solution. In addition, the casein can be selected to be in an aggregated state or a dispersed state depending on the pH of the casein aqueous solution. Therefore, it is necessary to carry the casein on the porous layer 10 in an appropriate aggregated state. There is.

  FIG. 8 shows the results of the corrosion potential measurement test. As can be seen from FIG. 8, in the case of pH 12 → pH 5 and pH 12 → pH 6, the corrosion potential is almost constant and stable. In the case of pH12 → pH7, it is almost constant and stable, but the corrosion potential gradually increases after 20 hours after immersion. On the other hand, in the case of pH 12 → pH 4, the corrosion potential increases after the immersion, and the corrosion potential starts to oscillate after 20 hours have elapsed after the immersion. That is, according to the corrosion potential measurement test results, as in the case of FIG. 7, the casein carried on the porous layer 10 in the aqueous solution having a pH of 5 to 7 is excellent in corrosion resistance, and in particular at the pH of 5. It can be seen that the corrosion resistance is high.

  The present invention has been described above. The magnesium alloy film according to the present invention has self-repairing properties and excellent corrosion resistance. A magnesium alloy provided with such a rust-preventing coating has excellent corrosion resistance and can expand the application range of the magnesium alloy. Moreover, the rust preventive film having such self-repairing property and excellent corrosion resistance can be applied not only to the magnesium alloy but also to other alloys such as a zinc alloy. For example, a zinc alloy having excellent corrosion resistance can be obtained by forming a porous layer carrying casein on the surface of the zinc alloy as in the case of the magnesium alloy.

  The corrosion resistance test of the magnesium alloy coating according to the present invention was performed. The corrosion resistance test was performed by measuring the corrosion resistance and the corrosion potential using the apparatus shown in FIG. The corrosion test solution was a saline solution having a concentration of 0.0005 M, and the solution temperature was maintained at 35 ° C. and air saturation was performed. A test piece that had been subjected to film formation was immersed therein, and after the corrosion potential was stabilized, measurement was performed using a potentiostat and a frequency response analyzer. ± 10 mV alternating current was applied to the test piece in a range from 0.1 Hz to 20 kHz, and the impedance and phase difference were measured. The difference in impedance measured in the low frequency range and the high frequency range was taken as the corrosion resistance. Platinum was used for the counter electrode, and a silver / silver chloride electrode was used for the reference electrode. The test area was 6 mm in diameter.

  The test piece was produced as follows. That is, after polishing and drying 12 × 12 × 1mm magnesium alloy AZ31, it was immersed in ion-exchanged water at a rate of 10 mm / sec in an aqueous solution adjusted to titania (JR-800 manufactured by Teika Co., Ltd.) to a concentration of 1 wt%. And hold for 3 min. Next, the sample is pulled up at a speed of 10 mm / sec, dried by heating at 80 ° C. for 10 minutes, and allowed to cool for 1 minute. The dipping operation was repeated again, and the sample pulled up from the aqueous solution was dried by heating at 120 ° C. for 30 minutes to form the porous layer 10.

  Next, the sample on which the porous layer 10 is formed is dipped in a casein aqueous solution adjusted in advance to a concentration of 1 wt% and pH 12, and the aqueous solution is adjusted to a predetermined pH within 5 minutes and held for 4 hours. After 4 hours, the sample was pulled up, washed with water, and then dried with hot air, so that casein (organic restoration material 13) was supported on the porous layer 10. In carrying the organic restorative material 13, the casein aqueous solution was kept at 35 ° C. and air saturated.

  FIG. 10 shows the test results. In FIG. 10, the horizontal axis represents the immersion time, the vertical axis represents the corrosion resistance, and the parameter represents the pH of the casein aqueous solution when the organic restorative material 13 is supported. According to FIG. 10, it can be seen that the magnesium alloy film in which casein is supported at pH 5 has high corrosion resistance.

  A salt water immersion test was conducted to examine the effect of the material of the fine particles 11 forming the porous layer 10 on the corrosion of the magnesium alloy 20. In the salt water immersion test, a saline solution having a concentration of 0.005% was used. The test time was 24 hours. Table 1 shows the fine particles 11 used in the salt water immersion test and the test results. The remarks in Table 1 show the surface properties, solvent, source of the fine particles 11 used in the test. The particle shape was spherical except for those described as acicular particles. Note that a pure magnesium (99.95%) plate was used as the test piece.

When the corrosion rates shown in Table 1 are compared, the corrosion rate when using fine particles 11 of alumina (Al ₂ O ₃ ) and silica (SiO ₂ ) is the same as that of titania (TiO ₂ ), and the fine particles of alumina and silica It can be seen that 11 has the same ability to inhibit corrosion of magnesium alloy as the fine particles 11 of titania. Further, it can be seen that their ability to inhibit corrosion is affected by the average particle diameter, shape or surface properties of the fine particles 11.

  A salt water immersion test was conducted to examine the effect of the organic restorative material 13 supported on the porous layer 10 on the corrosion of the magnesium alloy 20. The organic restorative material 13 was dissolved in 500 ppm in a salt water corrosion solution and subjected to a salt water immersion test. The test conditions for this test are the same as in Example 2. The test results are shown in Table 3. Comparing the corrosion rates shown in Table 3, it can be seen that citric acid has a corrosion inhibiting ability for magnesium alloys similar to casein, and oxalic acid also has a high corrosion inhibiting ability.

It is sectional drawing which shows the structure of the magnesium alloy film which concerns on this invention. It is a figure which shows the form and component distribution of the surface part of the Example of the magnesium alloy film which concerns on this invention. It is a figure which shows the form and component distribution of the cross-sectional part of the magnesium alloy film shown in FIG. It is a figure which shows the form of the part which gave the scratch to the magnesium alloy film which concerns on this invention. FIG. 5 is a view showing a form of a scratched portion after 4 hours have passed after the magnesium alloy film of FIG. 4 is immersed in salt water. It is a figure which shows the form of the part which gave the crack after 48-hour progress, after immersing the magnesium alloy film of FIG. 4 in salt water. It is a graph which shows the influence of the pH concentration of the casein aqueous solution at the time of carrying | supporting the corrosion resistance ratio with respect to the salt water corrosion test of the magnesium alloy film which concerns on this invention, and casein. It is a graph which shows the corrosion potential with respect to the salt water corrosion test of the magnesium alloy film which concerns on this invention. It is a figure which shows the structure of the test apparatus which measured the corrosion resistance or the corrosion potential in the salt water corrosion test. It is a graph which shows the test result in a salt water corrosion test.

Explanation of symbols

10 Porous layer
11 Fine particles
12 pores
13 Organic restoration materials
20 Magnesium alloy

Claims (7)

  A magnesium alloy film having a porous layer carrying an organic restorative material.   2. The magnesium alloy coating according to claim 1, wherein the organic restorative material is casein, citric acid or oxalic acid.   The magnesium alloy coating according to claim 1 or 2, wherein the porous layer is made of a porous resin in which fine particle aggregates or pores communicate with each other. The magnesium alloy coating according to claim 3, wherein the fine particles are fine particles of titania (TiO ₂ ), silica (SiO ₂ ), or alumina (Al ₂ O ₃ ).   The magnesium alloy which has a magnesium alloy film in any one of Claims 1-4. First, an oxide fine particle layer is formed on the magnesium alloy surface,
Next, a method for producing a magnesium alloy film in which casein is supported on the formed oxide fine particle layer.   7. The method for producing a magnesium alloy coating according to claim 6, wherein the casein is supported by adjusting a hydrogen ion index (pH) of the casein aqueous solution.

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