JP2018024912A - Magnesium alloy substrate, electronic apparatus, and formation method of anticorrosive coating sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance of a magnesium alloy substrate furthermore than hitherto, concerning the magnesium alloy substrate, an electronic apparatus, and a formation method of an anticorrosive coating sheet.SOLUTION: A first coating sheet mainly composed of Si and O which are reaction products between sodium silicate and a magnesium alloy is provided on the surface of a substrate comprising the magnesium alloy, and a second coating sheet comprising a reaction product of sodium fluorosilicate mainly composed of Si and F is provided on the surface of the first coating sheet.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a magnesium alloy substrate, an electronic device, and a method for forming a corrosion-resistant coating. For example, a magnesium alloy substrate, an electronic device, and a corrosion-resistant coating provided with a corrosion-resistant coating used for electronic devices such as mobile phones and laptop computers. It is related with the formation method of this.

  The inside of a casing of an electric product such as a notebook personal computer has a structure in which internal components such as a mechanical drive unit and a power source are arranged. Such an electronic device needs to protect the internal structure from an impact, pressure, or the like received from the outside, so that the casing is required to have mechanical strength. Furthermore, in the case of a mobile device that is assumed to be carried among electronic devices, the casing material is required to be light in addition to the mechanical strength.

  Conventionally, metal and aluminum alloy press-worked products and machined products have been widely used, but in recent years, lightweight and highly rigid magnesium alloys that have been press-worked have come to be used. . As a magnesium alloy for press working, AZ31B is marketed, and in addition, a magnesium alloy containing lithium has been developed (for example, see Patent Document 1). Since these materials are very active as compared with iron and aluminum alloys, they are inferior in corrosion resistance.

  Therefore, in order to improve the corrosion resistance of the magnesium alloy, an antioxidant coating is formed on the surface. The coating is formed with a thickness of about 0.5 μm to 20 μm depending on productivity, cost, appearance, and the like. Examples of coating types include plating, chemical conversion treatment, and anodizing.

  For example, a coating is applied to the surface of the housing such as metal plating (for example, see Non-Patent Document 1), chemical conversion treatment (for example, see Patent Document 2 or Patent Document 3), or zinc diffusion film (for example, see Patent Document 4). Methods have been proposed for forming and improving the corrosion resistance of the surface.

JP 09-041066 A JP-A-10-040369 JP 2009-221507 A JP 2000-160320 A

Journal of Aluminum Society No. 9, p. 121 (1993)

  However, there is a problem that sufficient corrosion resistance cannot always be obtained even when a film is formed on the surface of the magnesium alloy with the above-described metal plating or zinc diffusion film. As a result of earnest research, this is because when a new metal layer or metal compound layer film is formed on the surface of the magnesium alloy, the film is formed without improving the adhesion of the film on the surface of the magnesium alloy. I came to the conclusion.

  Accordingly, it is an object of the present invention to improve the corrosion resistance of a magnesium alloy substrate more than before in a magnesium alloy substrate, an electronic device, and a method for forming a corrosion-resistant film.

  In one embodiment, the magnesium alloy substrate includes a substrate made of a magnesium alloy, and a first coating mainly comprising Si and O, which are reaction products of sodium silicate and the magnesium alloy provided on the surface of the substrate. And a second coating made of a reaction product of sodium fluorosilicate having Si and F as main components provided on the surface of the first coating.

  In another aspect, the electronic device uses the above-described magnesium alloy substrate as an electronic device casing.

  Furthermore, in another aspect, the method for forming a corrosion-resistant coating includes immersing a substrate made of a magnesium alloy in an aqueous sodium silicate solution to form a first coating made of a reaction product of the magnesium alloy and the sodium silicate. And a step of immersing the substrate on which the first coating is formed in an aqueous sodium fluorosilicate solution to form a second coating.

  As one aspect, the corrosion resistance of the magnesium alloy substrate can be improved more than before.

It is explanatory drawing of the magnesium alloy base | substrate of embodiment of this invention. It is a flowchart of the formation process of the corrosion-resistant film of embodiment of this invention. It is a flowchart of the formation process of the corrosion-resistant film of Example 1 of this invention. It is a schematic perspective view which shows the notebook computer to which Example 1 of this invention is applied. It is explanatory drawing of the state pressed into the shape of a front cover. It is explanatory drawing of the state pressed into the shape of a back cover. It is explanatory drawing of the state pressed into the upper cover shape. It is explanatory drawing of the state pressed into the shape of a lower cover.

Here, with reference to FIG.1 and FIG.2, embodiment of this invention is described. As a result of intensive studies to solve the above problems, the present inventors have found that the corrosion resistance is improved by forming a corrosion-resistant film of an inorganic compound that reacts with alkali metal ions such as Mg on the surface of the magnesium alloy substrate. It was. FIG. 1 is an explanatory diagram of a magnesium alloy substrate, and FIG. 2 is an explanatory diagram of a process for forming a corrosion-resistant coating. As shown in FIG. 1 (a), a magnesium alloy substrate according to an embodiment of the present invention includes a sodium silicate (Na ₂ SiO ₃ , Na ₄ SiO ₄ ) and a magnesium alloy provided on the surface of a substrate 11 made of a magnesium alloy. The first film 12 containing Si and O, which are reaction products of the above, as main components is provided. Since the first coating 12 is a reaction product with the magnesium alloy, the adhesion with the substrate 11 is improved. A second coating 13 made of a reaction product using sodium fluorosilicate (Na ₂ SiF ₆ ) containing Si and F as main components is provided on the surface of the first coating 12.

  In this case, as shown in FIG. 1B, the second film 13 may cover the surface of the substrate 11 in the pinhole portion 14 of the first film 11 where the first film is not formed. good.

  As a magnesium alloy, Mg may be an alloy having the largest component, such as an alloy containing lithium such as Mg (90 wt%), Li (9 wt%), Zn (1 wt%), or AZ91 {Mg (90 wt%). ), Al (9 wt%), Zn (1 wt%)}, or a magnesium alloy that does not contain Li. Note that a magnesium alloy containing Li is desirable for weight reduction.

  Such a magnesium alloy substrate provided with a corrosion-resistant coating is suitable as a housing for an electronic device such as a mobile phone or a notebook PC.

  In order to form such a corrosion-resistant film, as shown in FIG. 2, first, a base 11 made of a magnesium alloy is immersed in an aqueous solution of sodium silicate, and a reaction product of a magnesium alloy and sodium silicate is first formed. 1 coating 12 is formed. The first coating 12 contains Si and O as main components, but contains some Mg (Li), which is a constituent element of the base 11, and Na, which is a component of sodium silicate.

  Next, the substrate 11 on which the first coating 12 is formed is immersed in an aqueous sodium fluorosilicate solution to form a second coating 13. The first coating 12 is a fluoride coating mainly composed of Si and F, but contains a little of Mg (Li), which is a constituent element of the substrate 11, O, and Na which is a component of sodium fluorosilicate. Yes. Usually, between the formation process of the 1st coating film 12 and the formation process of the 2nd coating film 13, the process of drying after washing the magnesium alloy base | substrate 11 in which the 1st coating film 12 was formed is provided.

As sodium silicate, any of sodium orthosilicate (Na ₄ SiO ₄ ) or sodium metasilicate (Na ₂ SiO ₃ ) may be used, and a mixture thereof may be used. Sodium orthosilicate (Na ₄ SiO ₄ ) forms a hydrate of Na ₂ SiO _{3 in} aqueous solution.

  The concentration of sodium silicate in the aqueous solution of sodium silicate is preferably in the range of 3 wt% to 10 wt%. If it is too thin, it takes too much time to form a film and the throughput decreases. The concentration of sodium fluorosilicate in the sodium fluorosilicate aqueous solution is preferably in the range of 0.5 wt% to 3 wt%. In addition, sodium fluorosilicate is hardly soluble in water, and dissolves at about 0.67 g per 100 ml of water at 20 ° C.

  Although the corrosion resistance treatment of the magnesium alloy can be provided to a plate material before press working or the like, it is preferable to form a corrosion resistant coating after machining such as pressing. Further, the thickness of the corrosion-resistant coating can be changed by changing the immersion temperature and time. Furthermore, other chemical conversion treatments, plating treatments, and the like can be performed on the corrosion-resistant treatment coating film.

  According to the embodiment of the present invention, by forming a plurality of chemical conversion treatment films composed of a reaction product with sodium silicate and a reaction product of sodium fluorosilicate on the surface of the magnesium alloy, the corrosion resistance is better than before. A magnesium alloy corrosion resistant coating can be obtained.

表１は、サンプルに対する温湿度サイクル試験条件の説明図であり、この１サイクル２４時間の試験を５サイクル繰り返す。 Next, although the formation process of the corrosion-resistant coating film of Example 1 of this invention is demonstrated, the corrosion resistance evaluation method is demonstrated before that.

Table 1 is an explanatory diagram of the temperature and humidity cycle test conditions for the sample, and this one cycle 24 hour test is repeated 5 cycles.

After this temperature / humidity cycle test, the JIS score and surface state of the fifth test specified in JIS K5400 were measured with a spectrocolorimeter (CM-5 manufactured by Konica Minolta) at 10 points, and the color difference (ΔE) from before the temperature / humidity test. The evaluation shown in Table 2 was given. An evaluation of 3 or more was accepted.

Next, with reference to FIG. 3, the formation process of the corrosion-resistant film of Example 1 of this invention is demonstrated. First,
a. An AZ91 alloy of Mg (90 wt%), Al (9 wt%), and Zn (1 wt%) is used as the magnesium alloy, and press processing is performed on the case shape of the notebook PC. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Here, Grandafiner MG-15SX + Grandafiner additive F21 is used as an alkaline chemical solution for the degreasing process in the degreasing process. Then
c. Immerse in an aqueous solution of 5 wt% sodium orthosilicate (Na ₄ SiO ₄ ) at 80 ° C. for 1 minute. Then
d. Wash with water and dry. Then
e. Immerse in a 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample in which the corrosion-resistant film was formed was subjected to the above-described corrosion resistance test, the corrosion resistance evaluation result was JIS score 10 points and ΔE was 2, which was 5 points. Note that the thickness of the film formed in the step c is about 1.0 μm, and the thickness of the film formed in the step e is about 0.5 μm.

  4 to 7 are explanatory diagrams of a notebook computer to which the corrosion-resistant film of Example 1 is applied. FIG. 4 is a schematic perspective view showing a notebook computer. In the notebook computer 20, at least a part of the surface of the main body 21 is covered with a housing 22. The housing 22 includes a front cover 23 and a back cover 24 that support the liquid crystal panel 27 of the liquid crystal monitor unit, and an upper cover 25 and a lower cover 26 that support the main body 21. FIG. 5 is an explanatory diagram of a state pressed into a front cover shape, FIG. 6 is an explanatory diagram of a state pressed into a back cover shape, and FIG. 7 is an explanatory diagram of a state pressed into an upper cover shape. FIG. 8 is an explanatory view showing a state where the lower cover is pressed. A notebook personal computer is formed by forming a corrosion-resistant film on all or a part of these covers.

Next, Example 2 of the present invention will be described, and it was produced under the same conditions except that sodium orthosilicate in Step c of Example 1 was changed to sodium metasilicate. First of all,
a. An AZ91 alloy is used as the magnesium alloy, and the notebook PC is pressed into a casing shape. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in an aqueous solution of 5 wt% sodium metasilicate (Na ₂ SiO ₃ ) at 80 ° C. for 1 minute. Then
d. Wash with water and dry. Then
e. Immerse in a 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample which formed the corrosion-resistant film was subjected to the above-mentioned corrosion resistance test, the corrosion resistance evaluation result was JIS score 10 points and ΔE was 3, which was 5 points.

Next, although Example 3 of this invention is demonstrated, it manufactured on the same conditions except having changed the sodium orthosilicate in the process c of Example 1 into the mixture of sodium orthosilicate and sodium metasilicate. First of all,
a. An AZ91 alloy is used as the magnesium alloy, and the notebook PC is pressed into a casing shape. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in an aqueous solution of 5 wt% sodium silicate (50 wt% sodium orthosilicate + 50 wt% sodium metasilicate) at 80 ° C. for 1 minute. Then
d. Wash with water and dry. Then
e. Immerse in a 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample which formed the corrosion-resistant film was subjected to the above-mentioned corrosion resistance test, the corrosion resistance evaluation result was JIS score 10 points and ΔE was 3, which was 5 points.

Next, Example 4 of the present invention will be described. It was manufactured under the same conditions except that the immersion time in the sodium orthosilicate aqueous solution in Step c of Example 1 was changed to 30 seconds. First of all,
a. An AZ91 alloy is used as the magnesium alloy, and the notebook PC is pressed into a casing shape. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in a 5 wt% sodium orthosilicate aqueous solution at 80 ° C. for 30 seconds. Then
d. Wash with water and dry. Then
e. Immerse in a 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample which formed the corrosion-resistant film was subjected to the above-mentioned corrosion resistance test, the evaluation result of the corrosion resistance was 9 points for JIS and 7 was ΔE, which was 4 points.

Next, Example 5 of the present invention will be described, but it was produced under the same conditions except that the immersion time in the sodium fluorosilicate aqueous solution in Step e of Example 1 was changed to 15 seconds. First of all,
a. An AZ91 alloy is used as the magnesium alloy, and the notebook PC is pressed into a casing shape. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in an aqueous solution of 5 wt% sodium orthosilicate at 80 ° C. for 1 minute. Then
d. Wash with water and dry. Then
e. Immerse in 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 15 seconds. F. Wash with water and dry.
Thus, after the sample which formed the corrosion-resistant film was subjected to the above-mentioned corrosion resistance test, the corrosion resistance evaluation result was JIS score 9 and ΔE was 11, which was 3 points.

Next, Example 6 of the present invention will be described, and it was produced under the same conditions except that the concentration of the sodium orthosilicate aqueous solution in Step c of Example 1 was changed to 3 wt%. First of all,
a. An AZ91 alloy is used as the magnesium alloy, and the notebook PC is pressed into a casing shape. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in 3 wt% sodium orthosilicate at 80 ° C. for 30 seconds. Then
d. Wash with water and dry. Then
e. Immerse in a 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample which formed the corrosion-resistant film was subjected to the above-mentioned corrosion resistance test, the corrosion resistance evaluation result was JIS score of 8 points and ΔE was 7, which was 3 points of evaluation.

Next, Example 7 of the present invention will be described. It was manufactured under the same conditions except that the concentration of the sodium fluorosilicate aqueous solution in Step e of Example 1 was changed to 3 wt%. First of all,
a. An AZ91 alloy is used as the magnesium alloy, and the notebook PC is pressed into a casing shape. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in 5 wt% sodium orthosilicate at 80 ° C. for 30 seconds. Then
d. Wash with water and dry. Then
e. Immerse in 3 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample which formed the corrosion-resistant film was subjected to the above-mentioned corrosion resistance test, the corrosion resistance evaluation result was JIS score of 8 points and ΔE was 5 which was 3 points of evaluation.

Next, Example 8 of the present invention will be described. It was manufactured under the same conditions except that Al in the composition of the magnesium alloy in step a of Example 1 was changed to Li. First of all,
a. An alloy of Mg (90 wt%), Li (9 wt%), and Zn (1 wt%) is used as the magnesium alloy, and press processing is performed on the shape of the notebook PC casing. Then
b. A sample cut into a 50 × 100 mm shape after press working is degreased with an alkaline solution. Then
c. Immerse in 5 wt% sodium orthosilicate at 80 ° C. for 30 seconds. Then
d. Wash with water and dry. Then
e. Immerse in a 1 wt% sodium fluorosilicate aqueous solution at 60 ° C. for 30 seconds. F. Wash with water and dry.
Thus, after the sample in which the corrosion-resistant film was formed was subjected to the above-described corrosion resistance test, the corrosion resistance evaluation result was JIS score 10 points and ΔE was 2, which was 5 points.

Here, a comparative example will be described for comparison with each embodiment of the present invention.
(Comparative Example 1) An AZ91 alloy was used as a magnesium alloy, and only a degreasing was performed, and a corrosion resistance test was not performed without forming a corrosion resistant film. Since no corrosion-resistant film was formed, the JIS score was not evaluated, and as a result of evaluation using only ΔE, ΔE was 37, which was 1 rating.
(Comparative Example 2) The sample prepared in Comparative Example 1 was galvanized and subjected to a corrosion resistance test. As a result, the JIS score was 3 stores, ΔE was 22, and the evaluation was 1 point.

  In each of the embodiments of the present invention, first, sodium silicate is reacted with Mg or Li, which are alkali metals contained in an Mg alloy, so that the first adhesive having good adhesion to a substrate mainly composed of Si and O is used. Form a corrosion resistant coating. Next, since the fluoride-based second corrosion-resistant film is formed on the first corrosion-resistant film, the JIS corrosion resistance test can be cleared.

Here, the following additional notes are attached to the embodiment of the present invention including Examples 1 to 8.
(Supplementary Note 1) A first coating containing Si and O as main components, which are reaction products of a base made of a magnesium alloy, a sodium silicate provided on the surface of the base and the magnesium alloy, and the first coating A magnesium alloy substrate having a second coating film comprising a reaction product of sodium fluorosilicate having Si and F as main components provided on the surface.
(Supplementary note 2) The magnesium alloy substrate according to supplementary note 1, wherein the second coating covers the surface of the substrate in the first pinhole portion where the first coating is not formed.
(Supplementary Note 3) The magnesium alloy substrate according to Supplementary Note 1 or 2, wherein the magnesium alloy contains lithium.
(Appendix 4) An electronic device using the magnesium alloy substrate according to any one of appendices 1 to 3 as an electronic device casing.
(Supplementary Note 5) A step of immersing a base made of a magnesium alloy in an aqueous sodium silicate solution to form a first film made of a reaction product of the magnesium alloy and the sodium silicate, and forming the first film And a step of immersing the substrate in an aqueous sodium fluorosilicate solution to form a second coating.
(Additional remark 6) Between the formation process of the said 1st film and the formation process of the said 2nd film, it has the process of drying, after washing | cleaning the said magnesium alloy base | substrate which formed the said 1st film. A method for forming a corrosion-resistant film as described in 1. above.
(Additional remark 7) The formation method of the corrosion-resistant film of Additional remark 5 or Additional remark 6 whose said sodium silicate is either orthosilicate sodium or sodium metasilicate, and those mixtures.
(Appendix 8) The method for forming a corrosion-resistant coating film according to any one of appendices 5 to 7, wherein the magnesium alloy contains lithium.
(Supplementary note 9) The method for forming a corrosion-resistant coating film according to any one of supplementary notes 5 to 8, wherein a concentration of sodium silicate in the aqueous sodium silicate solution is 3 wt% to 10 wt%.
(Supplementary note 10) The method for forming a corrosion-resistant coating film according to any one of supplementary notes 5 to 9, wherein a concentration of sodium fluorosilicate in the sodium fluorosilicate aqueous solution is 0.5 wt% to 3 wt%.
(Supplementary note 11) The corrosion-resistant coating film according to any one of supplementary notes 5 to 10, wherein the base made of the magnesium alloy is pressed as a casing for an electronic device before the step of immersing in a sodium silicate aqueous solution. Forming method.

DESCRIPTION OF SYMBOLS 11 Base 12 1st film 13 2nd film 14 Pinhole part 20 Notebook personal computer 21 Main body 22 Case 23 Front cover 24 Back cover 25 Upper cover 26 Lower cover 27 Liquid crystal panel

Claims (5)

A base film made of a magnesium alloy; a first coating mainly comprising Si and O, which are reaction products of sodium silicate and the magnesium alloy provided on the surface of the base body;
A magnesium alloy substrate having a second coating made of a reaction product of sodium fluorosilicate containing Si and F as main components provided on the surface of the first coating.   2. The magnesium alloy substrate according to claim 1, wherein the second coating covers a surface of the substrate in the first pinhole portion where the first coating is not formed. 3.   An electronic device using the magnesium alloy substrate according to claim 1 or 2 as an electronic device casing. Immersing a base made of a magnesium alloy in an aqueous sodium silicate solution to form a first film made of a reaction product of the magnesium alloy and the sodium silicate;
Forming a second coating by immersing the substrate on which the first coating has been formed in a sodium fluorosilicate aqueous solution. The method for forming a corrosion-resistant coating film according to claim 4, wherein the substrate made of the magnesium alloy is pressed as a housing for electronic equipment before the step of immersing in the sodium silicate aqueous solution.

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