JP2015096636A - Component producing method and surface treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a chemical coating of good quality on the surface of magnesium lithium alloy.SOLUTION: A component producing method comprises a step of exposing a surface 10a of base material 10 of magnesium lithium alloy to first acid 12 which does not comprise fluorine, and a step of fluorinating the surface 10a after exposed to second acid 13 to form a chemical coating 10x.

Description

  The present invention relates to a component manufacturing method and a surface treatment method.

  In mobile terminals such as mobile phones and notebook PCs (Personal Computers), a casing made of resin or aluminum alloy is used for weight reduction. Aluminum alloys have the advantage of being stronger than resins, but have the disadvantage of being heavier than resins.

  Therefore, a magnesium lithium alloy is attracting attention as an alloy that is lighter than an aluminum alloy. Magnesium lithium alloys are characterized by high strength and light weight by adding a small amount of lithium to magnesium, which is the main component.

  However, a magnesium lithium alloy containing highly reactive magnesium is difficult to handle because it is easily oxidized in the atmosphere as compared with an aluminum alloy. In order to prevent oxidation, it may be possible to form a chemical conversion film on the surface of the magnesium lithium alloy, but it is difficult to form a high-quality chemical conversion film that is compatible with corrosion resistance, paint adhesion, and the like.

JP 2003-328188 A JP 2011-58075 A

  In a component manufacturing method and a surface treatment method, an object is to form a high-quality chemical conversion film on the surface of a magnesium lithium alloy.

  According to one aspect of the following disclosure, the step of exposing the surface of the base material of the magnesium lithium alloy to a first acid not containing fluorine, and the step of exposing the surface to the first acid and then There is provided a method for producing a component, comprising: exposing the surface to a second acid; and exposing the surface to the second acid and then fluorinating the surface to form a chemical conversion film.

  According to the following disclosure, when free lithium on the surface of the magnesium lithium alloy is removed with a first acid that does not contain fluorine, the surface of the magnesium lithium alloy is fluorinated to form a chemical conversion film. Generation of powder due to lithium can be prevented.

  Further, by exposing the surface of the magnesium lithium alloy to a second acid containing fluorine, magnesium fluoride is formed on the surface, and this fluoride promotes the growth of the chemical conversion film. An excellent chemical conversion film can be formed.

FIG. 1 is a flowchart of a surface treatment method for a magnesium lithium alloy investigated by the present inventors. FIG. 2 is a diagram (part 1) obtained by observing the surface of the test piece. FIG. 3 is a diagram (part 2) obtained by observing the surface of the test piece. FIG. 4 is a diagram (part 3) obtained by observing the surface of the test piece. FIG. 5 is a perspective view showing an example of a component manufactured in the present embodiment. FIG. 6 is a flowchart of the component manufacturing method according to the present embodiment. FIG. 7 is a schematic cross-sectional view for explaining step S6 of the present embodiment. FIG. 8 is a schematic cross-sectional view for explaining the step S2 of the present embodiment. FIG. 9 is a schematic cross-sectional view for explaining step S3 of the present embodiment. FIG. 10 is a schematic cross-sectional view for explaining step S4 of the present embodiment. 11A and 11B are schematic cross-sectional views showing an example of processing performed on a component in the present embodiment. FIG. 12 is a diagram showing the results of an investigation conducted by the present inventor.

  Prior to the description of the present embodiment, items studied by the inventor will be described.

  As a method of forming a chemical conversion film on the surface of the magnesium lithium alloy, for example, there is a method of fluorinating the surface. This method will be described with reference to FIG.

  FIG. 1 is a flowchart of a surface treatment method for a magnesium lithium alloy investigated by the present inventors.

  First, in the first step S1, the surface of the test piece was degreased by immersing the test piece of magnesium lithium alloy in a strong alkaline aqueous solution (GF MG-15SX manufactured by Million Chemical Co., Ltd.) having a temperature of 75 ° C. for 5 minutes. . In this example, a rectangular LZ91 plate having a short side length of 25 mm and a long side length of 50 mm was used as a test piece. LZ91 is a magnesium lithium alloy containing 9% lithium, 1% zinc, and 90% magnesium. Further, GF F21 manufactured by Million Chemical Co., Ltd. was added as an additive to the strong alkaline aqueous solution.

  Next, the process proceeds to step S2, and the natural oxide film of magnesium or lithium formed on the surface of the test piece is etched and removed by immersing the test piece in an acid having a temperature of 40 ° C. for 1 minute. The surface of the piece was cleaned. This process of cleaning the surface is also called activation.

  In this example, GF MG-109 manufactured by Million Chemical Co. containing hydrofluoric acid was used as the acid. By using an acid containing fluorine in this way, magnesium in the test piece is fluorinated, and magnesium fluoride is formed on the surface of the test piece after activation.

  Subsequently, the process proceeds to step S3, and in order to remove the residue generated on the surface of the test piece by the above activation, the test piece is placed in a strong alkaline aqueous solution (GF MG-15SX manufactured by Million Chemical Co., Ltd.) having a temperature of 60 ° C. Soaked for 2 minutes. The residue removed in this step is a black material called smut, and this step is also called desmut treatment.

  And it moved to process S4 and said test piece was immersed in the chemical conversion liquid containing a fluorine. In this example, GR MC-1600 manufactured by Million Chemical Co., Ltd. was used as the chemical conversion treatment solution, and the test piece was immersed in the chemical conversion treatment solution for 2.5 minutes while maintaining the temperature of the chemical conversion treatment solution at 60 ° C. .

  By this chemical conversion treatment, magnesium which is a material of the test piece is fluorinated, and a chemical conversion film containing fluorine is formed on the surface of the test piece. In this example, by removing the natural oxide film from the surface of the test piece in step S2, the natural oxide film does not prevent the surface from being fluorinated, and a chemical film having a sufficient thickness can be formed.

  Furthermore, in step S2, since an acid containing fluorine is used to remove the natural oxide film, magnesium fluoride is generated in advance on the surface of the test piece before the chemical conversion film is formed. The growth of the chemical conversion film can be promoted.

  Then, it moved to process S5, the water | moisture content on the surface of the test piece was evaporated in the high temperature tank on the conditions which made temperature 80 degreeC and heating time 10 minutes, and dried the test piece.

  Thus, the surface treatment for the test piece is completed.

  The inventor of the present application observed the surface of the chemical conversion film. As a result, it was confirmed that a large amount of powder was deposited on the surface of the chemical conversion film. If powder deposits when forming a chemical conversion film on a magnesium lithium alloy housing, the conductive tape for grounding cannot be applied to the surface of the housing due to the powder, or the conductive tape is peeled off from the housing due to deterioration over time. Therefore, it is preferable to prevent the powder from precipitating as much as possible.

  In order to identify the cause of the generation of the powder, the inventor of the present application completed the activation (step S2), desmut treatment (step S3), and formation of the chemical conversion film (step S4) at the time when the surface of the test piece was finished. Was observed.

  The result is shown in FIG.

  In FIG. 2, “appearance” indicates the appearance of the test piece. Moreover, in order to confirm the generation | occurence | production state of powder, after sticking a transparent adhesive tape on the surface of a test piece and extract | collecting powder | flour, the adhesive tape was read with the scanner in the state which stuck the adhesive tape on the black mount. And the brightness value of the image file acquired by this was acquired with photo retouching software.

  “Luminance value” in FIG. 2 indicates the value obtained by the photo retouching software as described above, and when “luminance value” is 80 or more, it is determined that “powder generation” is present. This is because the brightness value is 80 or more when the presence of powder is obvious from the appearance.

  In addition, “reference value” in FIG. 2 indicates “luminance value” of an untreated test piece that has not been subjected to steps S1 to S5.

  Further, “tape” in FIG. 2 indicates an image of the adhesive tape read by the scanner as described above.

  As shown in FIG. 2, the powder is generated by activation (step S2) and formation of a chemical conversion film (step S4). The inventor considers the cause as follows.

  In a magnesium lithium alloy, not all lithium is present at the lattice points of magnesium, and there is free lithium separated from the lattice points. When the free lithium is activated (step S2) and exposed to an acid containing fluorine, lithium fluoride and lithium oxide are produced, which are considered to precipitate as powder.

  The powder appears to have been removed by the desmutting process (step S3).

  However, in the desmut treatment, it is considered that only the powder in the vicinity of the surface of the test piece is removed from the powder deposited at the time of activation (step S2), and the powder in a deep part from the surface is not removed.

  And, in the formation of the chemical conversion film (step S4), it is considered that the powder that could not be removed by the desmut treatment was deposited again.

  In order to reduce such powder, the inventor of the present application cleaned the test piece by ultrasonic cleaning after the formation of the chemical conversion film (step S4).

  FIG. 3 is a diagram obtained by observing the surface of the test piece after ultrasonic cleaning. In FIG. 3, images of the test pieces described in FIG. 2 are also shown.

  As shown in FIG. 3, it can be confirmed that the ultrasonic cleaning reduces the luminance value and removes the powder.

  On the other hand, the color of the chemical conversion film is mottled by ultrasonic cleaning. This is because a part of the chemical conversion film peeled off due to damage caused by ultrasonic cleaning. When the chemical film peels in this way, the magnesium lithium alloy cannot be protected by the chemical film, and the corrosion resistance of the magnesium lithium alloy decreases.

  Therefore, ultrasonic cleaning is not suitable for cleaning the chemical conversion film.

  Next, the inventor of the present application paid attention to the activation step S2 in which powder is first generated. In step S2, as described above, an acid containing fluorine is used, and lithium fluoride formed by reacting the fluorine with free lithium is considered to be one of the generation factors of the powder.

  Therefore, the inventor of the present application activated Step S2 using a nitric acid-based acid instead of the fluorine-containing acid. In this example, GF MG-109 manufactured by Orion Chemical Co., Ltd. was used as the nitric acid. This acid does not contain fluorine.

  Then, the surface of the test piece was observed when the activation (step S2), the desmut treatment (step S3), and the formation of the chemical conversion film (step S4) were completed.

  FIG. 4 is a diagram obtained by observing the surface of the test piece after performing each step in this manner.

  As shown in FIG. 4, the generation of powder in the step S2 can be suppressed by using a nitric acid acid in the activation step S2. This is presumably because the nitric acid does not contain fluorine, so that free lithium and fluorine react with each other so that lithium fluoride that causes powder is not generated.

  However, when such an acid containing no fluorine is used, the magnesium of the test piece is not fluorinated in the activation step S2, and magnesium fluoride is not formed on the surface of the test piece after activation. Magnesium fluoride plays a role in promoting the growth of the chemical conversion film as described above. Therefore, if there is no magnesium fluoride, the growth of the chemical conversion film becomes insufficient and the film thickness of the chemical conversion film becomes thin. . Therefore, also in this case, the magnesium lithium alloy cannot be protected by the chemical conversion film, and the corrosion resistance of the magnesium lithium alloy is lowered.

  Below, this embodiment which can suppress generation | occurrence | production of powder | flour without peeling or thinning of a chemical film is demonstrated.

(This embodiment)
In the present embodiment, a part made of a magnesium lithium alloy is manufactured as follows.

  FIG. 5 is a perspective view showing an example of a component manufactured in the present embodiment.

  This component 10 is an example of a base material made of a magnesium lithium alloy such as LZ91, and is, for example, a casing of an electronic device. The electronic device to which the component 10 is assembled is not particularly limited. For example, the component 10 can be assembled to a mobile terminal such as a notebook PC, a tablet PC, a mobile phone, and a smartphone.

  In order to protect the surface of the component 10 and improve the adhesion between the surface and the paint, in this embodiment, the surface of the component 10 is subjected to surface treatment in the following manner to form the surface. Form a film.

  FIG. 6 is a flowchart of the component manufacturing method according to the present embodiment. In FIG. 6, the same steps as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  First, in the first step S1, the surface of the component 10 is degreased by immersing the component 10 in a strong alkaline aqueous solution (GF MG-15SX manufactured by Million Chemical Co., Ltd.) having a temperature of 75 ° C. for 5 minutes. Note that GF F21 manufactured by Million Chemical Co., Ltd. may be added as an additive to the strong alkaline aqueous solution.

  Next, the process proceeds to step S6. FIG. 7 is a schematic cross-sectional view for explaining step S6.

  In this step, as shown in FIG. 7, by immersing a plurality of components 10 in the first acid 12 that does not contain fluorine stored in the liquid tank 11, the surface 10 a of the component 10 is made into the first acid 12. Expose and slightly etch the surface 10a.

  The first acid 12 is not particularly limited as long as it does not contain fluorine. In this example, GF MG-1091 manufactured by Million Chemical Co., which is a nitric acid, is used as the first acid 12. The temperature of the first acid 12 is, for example, 40 ° C., and the time for immersing the component 10 in the first acid 12 is, for example, 1 minute.

  As a result, the natural oxide film on the surface 10a is etched with the first acid 12, and the clean surface of the magnesium lithium alloy is exposed on the surface 10a.

  Furthermore, since the free lithium present on the surface 10a is also dissolved in the first acid 12, the amount of free lithium present on the surface 10a is reduced by performing this step.

  In addition, instead of processing the plurality of components 10 at once as described above, only one component 10 may be immersed in the first acid 12. The same applies to each step described later.

  Next, the process proceeds to step S2 in FIG. FIG. 8 is a schematic cross-sectional view for explaining step S2.

  In this step, as shown in FIG. 8, the component 10 is immersed in the second acid 13 containing fluorine stored in the liquid tank 11 in order to activate the surface 10a.

  As the second acid 13, there is GF MG-109 manufactured by Million Chemical Co., which contains hydrofluoric acid. The temperature of the second acid 13 is, for example, 40 ° C., and the time for immersing the component 10 in the second acid 13 is, for example, 1 minute.

  Thereby, the surface 10a of the component 10 is exposed to the second acid 13 to be further cleaned, and magnesium of the magnesium lithium alloy exposed on the surface 10a is fluorinated, and magnesium fluoride is formed on the surface 10a. It is formed.

  Here, in this embodiment, since free lithium is previously removed from the surface 10a in step S6, free lithium can be prevented from being fluorinated by the second acid 13 on the surface 10a. As a result, fluoride of free lithium that causes powder is hardly formed, and the amount of powder can be reduced as compared with the example of FIG.

  Next, the process proceeds to step S3 in FIG. FIG. 9 is a schematic cross-sectional view for explaining step S3.

  In this step, as shown in FIG. 9, the part 10 is immersed in a strong alkaline aqueous solution 14 to perform a desmut treatment on the part 10. Examples of the strong alkaline aqueous solution 14 include GF MG-15SX manufactured by Million Chemical Co., Ltd.

  The conditions for the desmut treatment are not particularly limited. In this example, the temperature of the strong alkaline aqueous solution 14 is set to 60 ° C., and the component 10 is immersed in the strong alkaline aqueous solution 14 for 2 minutes.

  By this desmut process, the smut generated in the above-described step S2 and step S6 is removed.

  Further, since the amount of powder generated in step S2 is reduced as described above, most of the powder can be removed by this desmut treatment, and the amount of powder left on the surface 10a after the desmut treatment is small. It becomes.

  Next, the process proceeds to step S4 in FIG. FIG. 10 is a schematic cross-sectional view for explaining step S4.

  In this step, as shown in FIG. 10, magnesium on the surface 10 a is fluorinated by immersing the component 10 in the chemical conversion solution 15 containing fluorine stored in the liquid tank 11, and the surface 10 a contains fluorine. A film 10x is formed.

  The chemical conversion treatment liquid 15 containing fluorine is not particularly limited. For example, any of hydrofluoric acid, sodium fluoride, hydrofluoric acid, sodium acid fluoride, potassium acid fluoride, ammonium acid fluoride, hydrofluoric acid and its salt, and hydrofluoric acid and its salt The solution can be used as the chemical conversion solution 15. In this embodiment, GR MC-1600 manufactured by Million Chemical Co., Ltd. is used as the chemical conversion treatment liquid 15.

  The temperature of the chemical conversion liquid 15 is, for example, 60 ° C., and the time for immersing the component 10 in the chemical conversion liquid 15 is, for example, 2.5 minutes.

  Here, since the natural oxide film is previously removed from the surface 10a in the step S6 as described above, the growth of the chemical film 10x is not inhibited by the natural oxide film, and the chemical film 10x having a sufficient thickness is formed. be able to.

  Moreover, since the growth of the chemical conversion film 10x is promoted by the magnesium fluoride formed in advance on the surface 10a in the step S2, the chemical conversion film 10x that is thick and excellent in corrosion resistance can be obtained.

  Furthermore, since generation | occurrence | production of the powder is suppressed in process S2 as mentioned above, the powder becomes difficult to appear even after formation of the chemical conversion film 10x.

  In addition, the thickness of the chemical conversion film 10x formed at this process is about 1 micrometer at maximum.

  Next, the process proceeds to step S5 in FIG. 6, and moisture on the surface 10a of the component 10 is evaporated in a high-temperature bath under the conditions of a temperature of 80 ° C. and a heating time of 10 minutes, and the surface 10a is dried.

  Thus, the basic process of the method for manufacturing the component 10 according to the present embodiment is completed.

  Thereafter, various processing is performed on the component 10 as necessary. FIGS. 11A and 11B are schematic cross-sectional views showing an example of processing performed on the component 10.

  In this example, as shown in FIG. 11A, a part R of the insulating chemical film 10x is removed by laser irradiation or the like, and the surface 10a of the component 10 is exposed.

  And as shown in FIG.11 (b), the electrically conductive tape 21 for earthing is affixed on the exposed surface 10a.

  The conductive tape 21 is a copper tape, for example, and plays a role of grounding the component 10 by electrically connecting an electronic component 22 such as a circuit board to the conductive component 10.

  The conductive tape 21 and the component 10 are bonded to each other with a conductive adhesive (not shown). In the present embodiment, almost no powder is generated on the chemical conversion film 10x as described above. The powder is difficult to wrap around the adhesive surface. Therefore, the adhesive force between the component 10 and the conductive tape 21 is prevented from being weakened by powder, and the component 10 and the conductive tape 21 can be firmly bonded.

  Next, an investigation conducted by the present inventor will be described with reference to FIG.

  FIG. 12 is a diagram showing the results of an investigation conducted by the inventor of the present application.

  In this investigation, it was examined how much the generation of powder is suppressed in this embodiment. In the investigation, a chemical conversion film was formed on the surface of the magnesium lithium alloy test piece according to the flowchart of FIG. As the test piece, a rectangular plate having a short side length of 25 mm and a long side length of 50 mm was used. The material of the test piece is LZ91.

  The meanings of the items “appearance”, “tape”, “luminance value”, and “occurrence of powder” in FIG. 12 are the same as those in FIG.

  As shown in FIG. 12, the luminance at the time of activation (step S2) is 95.1 also in this embodiment, and it appears that powder is generated in step S2. This is probably because free lithium that could not be removed by etching (step S6) was fluorinated in step S2 and appeared as powder.

  However, since most of the free lithium on the surface 10a, which is the cause of powder generation, is removed in step S6, the total amount of powder generated in step S2 is considered to be less than in the example of FIG.

  According to FIG. 12, the powder is removed by the desmut treatment (step S3), and is not deposited again even after the formation of the chemical conversion film (step S4). This is probably because the total amount of powder generated in step S2 was small as described above, and most of the powder was removed by the desmut treatment.

  From this result, it was confirmed that performing the etching in the step S6 before the activation in the step S2 as in the present embodiment is effective in reducing the powder appearing in the chemical conversion film.

  As described above, according to the present embodiment, free lithium on the surface 10a of the component 10 is removed with the first acid 12 that does not contain fluorine in step S6. Thereby, when the surface 10a is fluorinated with the second acid 13 containing fluorine in the step S4 to form the chemical conversion film 10x, it is possible to prevent the surface 10a from appearing due to free lithium.

  Further, by exposing the surface 10a of the component 10 to the second acid 13 containing fluorine in step S2, magnesium fluoride is formed on the surface 10a. This fluoride promotes the growth of the chemical conversion film 10x in step S4, and the chemical conversion film 10x having a large film thickness and excellent corrosion resistance can be formed. In this way, the thick chemical conversion film 10x is mechanically strong and has good adhesion to the paint applied thereon.

  The following additional notes are disclosed for each embodiment described above.

(Additional remark 1) The process of exposing the surface of the base material of a magnesium lithium alloy to the 1st acid which does not contain a fluorine,
Exposing the surface to a second acid containing fluorine after exposing the surface to the first acid;
After exposing the surface to the second acid, fluorinating the surface to form a chemical conversion film;
A method for manufacturing a component, comprising:

  (Additional remark 2) The said 1st acid contains nitric acid, The manufacturing method of the components of Additional remark 1 characterized by the above-mentioned.

  (Additional remark 3) Said 2nd acid contains hydrofluoric acid, The manufacturing method of the components of Additional remark 1 or Additional remark 2 characterized by the above-mentioned.

(Appendix 4) After forming the chemical conversion film, removing a part of the chemical conversion film to expose the surface;
The method for manufacturing a component according to any one of appendix 1 to appendix 3, further comprising a step of attaching a grounding conductive tape to the exposed surface.

  (Additional remark 5) The said base material is a housing | casing of an electronic device, The manufacturing method of the components in any one of Additional remark 1 thru | or Additional remark 4 characterized by the above-mentioned.

  (Supplementary Note 6) The supplementary notes 1 to 3, further comprising a step of performing a desmut treatment on the surface after the surface is exposed to the second acid and before forming the chemical conversion film. The method for manufacturing a part according to any one of appendix 5.

(Appendix 7) A step of exposing the surface of the base material of the magnesium lithium alloy to the first acid not containing fluorine;
Exposing the surface to a second acid containing fluorine after exposing the surface to the first acid;
After exposing the surface to the second acid, fluorinating the surface to form a chemical conversion film;
A surface treatment method characterized by comprising:

DESCRIPTION OF SYMBOLS 10 ... Parts, 10a ... Surface, 10x ... Chemical conversion film, 11 ... Liquid tank, 12 ... 1st acid, 13 ... 2nd acid, 14 ... Strong alkaline aqueous solution, 15 ... Chemical conversion treatment liquid, 21 ... Conductive tape, 22 ... electronic components.

Claims (5)

Exposing the surface of the base material of the magnesium lithium alloy to the first acid not containing fluorine;
Exposing the surface to a second acid containing fluorine after exposing the surface to the first acid;
After exposing the surface to the second acid, fluorinating the surface to form a chemical conversion film;
A method for manufacturing a component, comprising: After forming the chemical film, removing a part of the chemical film to expose the surface; and
The method for manufacturing a component according to claim 1, further comprising a step of attaching a conductive tape for grounding to the exposed surface.   The method for manufacturing a component according to claim 1, wherein the base material is a casing of an electronic device.   4. The method according to claim 1, further comprising a step of performing a desmut treatment on the surface after the surface is exposed to the second acid and before the chemical conversion film is formed. The manufacturing method of the components of any one of these. Exposing the surface of the base material of the magnesium lithium alloy to the first acid not containing fluorine;
Exposing the surface to a second acid containing fluorine after exposing the surface to the first acid;
After exposing the surface to the second acid, fluorinating the surface to form a chemical conversion film;
A surface treatment method characterized by comprising:

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