JP6659961B2 - Magnesium alloy substrate, electronic device, and method of forming corrosion-resistant coating - Google Patents

Description

  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 provided with a corrosion-resistant coating used for electronic devices such as a mobile phone and a notebook computer, an electronic device, and a corrosion-resistant coating And a method for forming the same.

  The inside of a housing of an electric product such as a notebook computer has a structure in which internal components such as a mechanical drive unit and a power supply are arranged. In such an electronic device, it is necessary to protect the internal structure from external impacts, pressures, and the like, so that the housing is required to have mechanical strength. Furthermore, in the case of a mobile device that is supposed to be carried among electronic devices, the housing material requires lightness in addition to the mechanical strength.

  Conventional metal casings are often made of pressed or cut products of iron and aluminum alloys, but in recent years, press-worked lightweight and high-rigidity magnesium alloys have been used. . AZ31B is marketed as a magnesium alloy for press working, and a magnesium alloy containing lithium has been developed in addition thereto (for example, see Patent Document 1). These materials are very active compared to iron and aluminum alloys, and therefore have poor corrosion resistance.

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

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

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

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

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

  Therefore, an object of the present invention is to provide a magnesium alloy substrate, an electronic device, and a method for forming a corrosion-resistant coating, in which the corrosion resistance of the magnesium alloy substrate is improved more than before.

  In one embodiment, the magnesium alloy substrate includes a substrate made of a magnesium alloy, and a first coating mainly containing 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 containing Si and F as main components provided on the surface of the first coating.

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

  Further, in another aspect, the method for forming a corrosion-resistant coating comprises immersing a substrate made of a magnesium alloy in an aqueous solution of sodium silicate 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 solution of sodium fluorosilicate to form a second coating.

  As one aspect, it becomes possible to improve the corrosion resistance of the magnesium alloy base more than before.

It is an explanatory view of a magnesium alloy substrate of an embodiment of the invention. It is a flow figure of a formation process of a corrosion-resistant film of an embodiment of the invention. FIG. 3 is a flowchart of a process of forming a corrosion-resistant film according to Example 1 of the present invention. 1 is a schematic perspective view showing a notebook computer to which a first embodiment of the present invention is applied. It is explanatory drawing of the state which carried out the press working in the shape of a front cover. It is explanatory drawing of the state which pressed in the back cover shape. It is explanatory drawing of the state which carried out the press work in the shape of an upper cover. FIG. 4 is an explanatory diagram of a state in which a lower cover is pressed;

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

  In this case, as shown in FIG. 1B, the second coating 13 may cover the surface of the base 11 at the pinhole portion 14 of the first coating 11 on which the first coating is not formed. good.

  As the magnesium alloy, any alloy containing Mg as the maximum component may be used. For example, an alloy containing lithium such as Mg (90 wt%), Li (9 wt%) and Zn (1 wt%) or AZ91 @ Mg (90 wt%) ), Al (9 wt%), Zn (1 wt%), and a magnesium alloy not containing 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 electronic devices such as a mobile phone and a notebook PC.

  In order to form such a corrosion-resistant coating, first, as shown in FIG. 2, a substrate 11 made of a magnesium alloy is immersed in an aqueous solution of sodium silicate to form a substrate 11 made of a reaction product of the magnesium alloy and sodium silicate. One coating 12 is formed. The first coating 12 contains Si and O as main components, but slightly contains 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 has been formed is immersed in an aqueous solution of sodium fluorosilicate to form a second coating 13. The first coating 12 is a fluoride coating containing Si and F as main components, but slightly contains Mg (Li), O which is a constituent element of the base 11, and Na which is a component of sodium fluorosilicate. I have. Usually, between the step of forming the first coating 12 and the step of forming the second coating 13, there is provided a step of washing the magnesium alloy substrate 11 on which the first coating 12 has been formed and then drying it.

As the sodium silicate, either sodium orthosilicate (Na ₄ SiO ₄ ) or sodium metasilicate (Na ₂ SiO ₃ ) may be used, and a mixture of these 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 sodium silicate solution is preferably in the range of 3 wt% to 10 wt%. If the concentration is too small, it takes too much time for forming a film, and the throughput is reduced. The concentration of sodium fluorosilicate in the aqueous sodium fluorosilicate solution is preferably in the range of 0.5 wt% to 3 wt%. It should be noted that sodium fluorosilicate is hardly soluble in water, and dissolves at about 0.67 g in 100 ml of water at 20 ° C.

  Although the corrosion resistance treatment of the magnesium alloy can be provided to the sheet material before the press working or the like, it is preferable to form the corrosion resistant film after the mechanical processing such as the press. Also, the thickness of the corrosion-resistant coating can be changed by changing the immersion temperature and time. Further, other chemical conversion treatment, plating treatment, and the like can be performed on the corrosion-resistant treatment 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, it is more excellent in corrosion resistance 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, a process for forming a corrosion-resistant film according to the first embodiment of the present invention will be described. Before that, a method for evaluating corrosion resistance will be described.

Table 1 is an explanatory diagram of the temperature / humidity cycle test conditions for the sample, and the test for one cycle 24 hours is repeated five cycles.

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

Next, with reference to FIG. 3, a description will be given of a process of forming a corrosion-resistant film according to Example 1 of the present invention. First,
a. An AZ91 alloy of Mg (90 wt%), Al (9 wt%), and Zn (1 wt%) is used as a magnesium alloy, and pressed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm after press working is degreased with an alkaline solution. Here, Granda Finer MG-15SX + Granda Finer Additive F21 is used as an alkaline chemical for degreasing in the degreasing treatment. Then
c. It is immersed in a 5 wt% sodium orthosilicate (Na ₄ SiO ₄ ) aqueous solution at 80 ° C. for 1 minute. Then
d. Wash and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The corrosion resistance evaluation result after subjecting the sample on which the corrosion resistant coating was formed to the above-described corrosion resistance test was JIS score 10 points, ΔE was 2, and was 5 points. The thickness of the film formed in step c is about 1.0 μm, and the thickness of the film formed in step e is about 0.5 μm.

  4 to 7 are explanatory diagrams of a notebook computer to which the corrosion-resistant coating 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 by the 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, and an upper cover 25 and a lower cover 26 that support the main body 21. FIG. 5 is an explanatory view showing a state where the front cover is pressed, FIG. 6 is an explanatory view showing a state where the back cover is pressed, and FIG. 7 is an explanatory view showing a state where the upper cover is pressed. FIG. 8 is an explanatory view of a state where the lower cover is pressed. A notebook computer is formed by forming a corrosion-resistant coating on all or some of these covers.

Next, Example 2 of the present invention will be described. Production was carried out under the same conditions except that sodium orthosilicate in Step c of Example 1 was changed to sodium metasilicate. That is, first,
a. The AZ91 alloy is used as a magnesium alloy, and press processing is performed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm after press working is degreased with an alkaline solution. Then
c. It is immersed in a 5 wt% sodium metasilicate (Na ₂ SiO ₃ ) aqueous solution at 80 ° C. for 1 minute. Then
d. Wash and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The corrosion resistance evaluation result after subjecting the sample on which the corrosion resistant coating was formed to the above-described corrosion resistance test was a JIS score of 10 points and a ΔE of 3, which was 5 points.

Next, Example 3 of the present invention will be described. Production was performed under the same conditions except that sodium orthosilicate in Step c of Example 1 was changed to a mixture of sodium orthosilicate and sodium metasilicate. That is, first,
a. The AZ91 alloy is used as a magnesium alloy, and press processing is performed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm after press working is degreased with an alkaline solution. Then
c. Immerse in a 5 wt% sodium silicate (50 wt% sodium orthosilicate + 50 wt% sodium metasilicate) aqueous solution at 80 ° C. for 1 minute. Then
d. Wash and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The corrosion resistance evaluation result after subjecting the sample on which the corrosion resistant coating was formed to the above-described corrosion resistance test was a JIS score of 10 points and a ΔE of 3, which was 5 points.

Next, Example 4 of the present invention will be described. Production was performed under the same conditions except that the immersion time in the aqueous sodium orthosilicate solution in Step c of Example 1 was changed to 30 seconds. That is, first,
a. The AZ91 alloy is used as a magnesium alloy, and press processing is performed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm after press working is degreased with an alkaline solution. Then
c. It is immersed in a 5 wt% sodium orthosilicate aqueous solution at 80 ° C. for 30 seconds. Then
d. Wash and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The sample on which the corrosion-resistant coating was formed was subjected to the above-described corrosion resistance test. The corrosion resistance evaluation result was 9 points in JIS and ΔE was 7, which was 4 points.

Next, Example 5 of the present invention will be described. Production was performed under the same conditions except that the immersion time in the aqueous solution of sodium fluorosilicate in Step e of Example 1 was changed to 15 seconds. That is, first,
a. The AZ91 alloy is used as a magnesium alloy, and press processing is performed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm after press working is degreased with an alkaline solution. Then
c. It is immersed in a 5 wt% sodium orthosilicate aqueous solution at 80 ° C. for 1 minute. Then
d. Wash and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 15 seconds. Then, f. Wash and dry.
The sample on which the corrosion-resistant coating was formed was subjected to the above-described corrosion resistance test. The corrosion resistance evaluation result was 9 points in JIS and ΔE was 11, which was 3 points.

Next, Example 6 of the present invention will be described. Production was performed 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%. That is, first,
a. The AZ91 alloy is used as a magnesium alloy, and press processing is performed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm 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 and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The sample on which the corrosion-resistant coating was formed was subjected to the above-described corrosion resistance test, and the corrosion resistance evaluation result was 8 points in JIS and 7 in ΔE, which was 3 points.

Next, Example 7 of the present invention will be described. Production was performed under the same conditions except that the concentration of the aqueous solution of sodium fluorosilicate in Step e of Example 1 was changed to 3% by weight. That is, first,
a. The AZ91 alloy is used as a magnesium alloy, and press processing is performed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm 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 and dry. Then
e. It is immersed in a 3 wt% aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The sample on which the corrosion-resistant coating was formed was subjected to the above-described corrosion resistance test. The corrosion resistance evaluation result was 8 points in JIS and ΔE was 5, which was 3 points.

Next, Example 8 of the present invention will be described. Production was performed under the same conditions except that Al in the composition of the magnesium alloy in Step a of Example 1 was changed to Li. That is, first,
a. An alloy of Mg (90 wt%), Li (9 wt%), and Zn (1 wt%) is used as a magnesium alloy, and is pressed into a notebook PC housing shape. Then
b. A sample cut into a shape of 50 × 100 mm 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 and dry. Then
e. It is immersed in a 1% by weight aqueous solution of sodium fluorosilicate at 60 ° C. for 30 seconds. Then, f. Wash and dry.
The corrosion resistance evaluation result after subjecting the sample on which the corrosion resistant coating was formed to the above-described corrosion resistance test was JIS score 10 points, ΔE was 2, and 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 performed without forming a corrosion resistant film. Since no corrosion resistant coating was formed, the JIS score was not evaluated, and only the ΔE was evaluated. As a result, the ΔE was 37, which was 1 point.
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 embodiment of the present invention, first, sodium silicate is reacted with Mg or Li, which is an alkali metal contained in the Mg alloy, to form a first material having good adhesion to a substrate containing Si and O as main components. 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 supplementary notes are added to the embodiments of the present invention including Examples 1 to 8.
(Supplementary Note 1) A first coating mainly composed of Si and O, which is a reaction product of a magnesium alloy, a sodium silicate provided on the surface of the base, and the magnesium alloy, and a first coating. A magnesium alloy substrate having, on a surface thereof, a second coating made of a reaction product of sodium fluorosilicate containing Si and F as main components.
(Supplementary note 2) The magnesium alloy base according to supplementary note 1, wherein the second coating covers a surface of the base at 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.
(Supplementary Note 4) An electronic device using the magnesium alloy substrate according to any one of Supplementary Notes 1 to 3 as an electronic device housing.
(Supplementary Note 5) A step of immersing a base made of a magnesium alloy in an aqueous solution of sodium silicate to form a first coating made of a reaction product of the magnesium alloy and the sodium silicate, and forming the first coating. Dipping the substrate in an aqueous solution of sodium fluorosilicate to form a second coating.
(Supplementary Note 6) A supplementary note 5 comprising, between the step of forming the first film and the step of forming the second film, washing and drying the magnesium alloy substrate on which the first film is formed. 3. The method for forming a corrosion-resistant film according to 1.
(Supplementary Note 7) The method for forming a corrosion-resistant coating according to Supplementary Note 5 or 6, wherein the sodium silicate is either sodium orthosilicate or sodium metasilicate, or a mixture thereof.
(Supplementary note 8) The method for forming a corrosion-resistant coating according to any one of Supplementary notes 5 to 7, wherein the magnesium alloy contains lithium.
(Supplementary note 9) The method for forming a corrosion-resistant coating according to any one of Supplementary notes 5 to 8, wherein the 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 according to any one of Supplementary notes 5 to 9, wherein the concentration of sodium fluorosilicate in the aqueous sodium fluorosilicate solution is 0.5 wt% to 3 wt%.
(Supplementary Note 11) The corrosion-resistant coating according to any one of Supplementary Notes 5 to 10, wherein the base made of the magnesium alloy is press-processed as a housing for an electronic device before the step of dipping in a sodium silicate aqueous solution. Formation method.

DESCRIPTION OF SYMBOLS 11 Base 12 First coating 13 Second coating 14 Pinhole section 20 Notebook personal computer 21 Main body 22 Housing 23 Front cover 24 Back cover 25 Upper cover 26 Lower cover 27 Liquid crystal panel

Claims (5)

A base made of a magnesium alloy; a first coating mainly composed of Si and O, which are reaction products of sodium silicate and the magnesium alloy provided on the surface of the base;
A magnesium alloy substrate comprising: a second film formed on the surface of the first film and comprising a reaction product of sodium fluorosilicate containing Si and F as main components.   2. The magnesium alloy substrate according to claim 1, wherein the second coating covers a surface of the substrate at 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 housing. Dipping a substrate made of a magnesium alloy in an aqueous solution of sodium silicate to form a first coating made of a reaction product of the magnesium alloy and the sodium silicate;
Dipping the substrate having the first coating formed thereon in an aqueous solution of sodium fluorosilicate to form a second coating. The method for forming a corrosion-resistant coating according to claim 4, wherein the base made of the magnesium alloy is press-processed as a housing for an electronic device before the step of dipping in a sodium silicate aqueous solution.

Images