JP6350551B2 - Anodized film generation method - Google Patents

Description

The present invention, a metallic article to be treated was placed in the electrolytic solution as an anode, about the anodized film generation how the deposition of the anodic oxide film on the surface of the workpiece.

  Conventionally, a technique is known in which an anodized film is formed on a piston top surface (an object to be processed) of an internal combustion engine that is an aluminum molded article to improve heat insulation and reduce cooling loss (for example, Patent Documents 1 to 3). 2). The reason why the cooling loss can be reduced is that the heat conductivity and the heat capacity are reduced by the holes formed inside the anodized film, and it is difficult for heat to be conducted to the aluminum base material.

  The anodized film of Patent Document 1 is set to have a large porosity by adjusting the maximum voltage and the temperature of the electrolytic solution, and further, the surface is sealed with an inorganic sealing material such as boiling water or water glass, with a pore expansion treatment using acid. Processing is performed.

  On the surface of the anodized film of Patent Document 2, a coating layer is formed by plasma spraying a powder having low thermal conductivity and low heat capacity. Moreover, in order to improve the adhesiveness of an anodized film and a coating layer, the unevenness | corrugation is formed in the surface of the aluminum base material by the photo edging method.

JP 2012-46784 A JP 2012-72745 A

  However, since the anodized film of Patent Document 1 has a large porosity, there is a possibility that the pores cannot be sealed by the sealing treatment with boiling water. In this case, fuel and combustion gas penetrate | invade in an anodized film, and desired heat insulation performance cannot be ensured. On the other hand, in the case of sealing with an inorganic sealing material such as water glass, a separate coating device is required, resulting in an increase in manufacturing cost.

  Moreover, although patent document 2 is improving the adhesiveness of an anodized film and a coating layer by the photo edging method, since an anodized film and a coating layer become a different material, it is a severe environment like an internal combustion engine. Then, there exists a possibility that a coating layer may peel. In addition, since a photo edging process and a plasma spraying process are required, the manufacturing cost increases.

Therefore, the anodized film generation how the film can be formed an anodic oxide film by a simple method with high thermal insulation performance is desired.

  The characteristic configuration of the anodic oxide film generation method includes a first step of forming a first film on the object to be processed with an electrolytic solution containing chromic acid using a metal object as an anode, and after the first step. A second step of forming a second film on the object to be processed with an electrolyte containing at least one of sulfuric acid, oxalic acid, and phosphoric acid, using the object to be processed as an anode; It is in the point provided with the 3rd process which immerses a 2nd membrane | film | coat in acidic solution, and performs the hole expansion process of said 2nd membrane | film | coat, and the 4th process of sealing the surface of said 1st membrane | film | coat.

  In the anodic oxide film formed using sulfuric acid, oxalic acid, and phosphoric acid, the electrolyte anions enter (residual) the film, and the anodic oxide film formed using chromic acid contains the electrolyte. It is known that anions do not enter (residual) inside the coating. When the present inventors immerse both an anodized film in which an anion is not mixed and an anodized film in which an anion has entered in an acidic liquid, the anodized film in which the anion is mixed has an enlarged pore. The knowledge that it was promoted was obtained. This is presumed to be because the film in which anions are present is in an unstable state as compared with the film in which anions are not present, so that dissolution is likely to proceed with an acidic solution.

  Therefore, in this method, after forming the first film on the object to be processed using chromic acid as the electrolytic solution, the second film is formed using sulfuric acid or the like as the electrolytic solution. That is, since the anodized film grows in order from the surface of the substrate, a second film is formed between the first film and the object to be processed. Thus, when the anodized film is immersed in the acidic solution in the third step, the hole in the first film is hardly dissolved, but only the hole in the second film is dissolved and expanded. As a result, the thermal conductivity and heat capacity of the anodized film are reduced, making it difficult for heat to be conducted to the substrate.

  Moreover, since the hole part of the 1st membrane | film | coat is not expanded, if the hole sealing process by a boiling water process is performed in a 4th process, the surface of a hole part will be sealed reliably. As a result, when the object to be processed is a piston of an internal combustion engine to which high heat is exposed, the inconvenience that fuel and combustion gas enter the inside of the anodized film is solved. Moreover, since it can be manufactured by a normal anodizing process without providing a coating material on the anodized film, the manufacturing cost can be saved. Moreover, since both the first film and the second film are made of the same material that grows from the base material, they are difficult to peel even under a harsh environment like an internal combustion engine. Thus, this method forms a anodic oxide film having high heat insulation performance by a simple method.

  Another characteristic configuration is that the electrolytic solution used in the second step is sulfuric acid.

  In sulfuric acid, the rate at which anions enter the film thickness direction of the anodized film is close to 100%. For this reason, if sulfuric acid is used in the second step as in this method, when the anodized film is immersed in an acidic solution in the third step, the holes present in the film thickness direction of the second film are even in the film thickness direction. Expanded to Therefore, it is easy to control the hole diameter of the second film, and the heat insulation performance of the anodized film can be reliably improved.

It is a figure explaining an anodizing apparatus. It is a figure which shows the aluminum molded product which concerns on this embodiment. It is a figure explaining the anodic oxide film production | generation method which concerns on this embodiment. It is the SEM photograph which expanded the cross section of the anodic oxide film which concerns on a present Example. It is the SEM photograph which expanded the 1st membrane | film | coat of FIG. It is the SEM photograph which expanded the 2nd membrane | film | coat of FIG. 4 is an SEM photograph in which a cross section of a second film according to Comparative Example 1 is enlarged. 4 is an SEM photograph in which a cross section of an anodized film according to Comparative Example 2 is enlarged. It is the SEM photograph which expanded the cross section of the anodic oxide film which concerns on the comparative example 3. 10 is an enlarged SEM photograph showing the vicinity of the surface of the anodized film in FIG. 9.

  Hereinafter, embodiments of an aluminum molded article and an anodized film production method according to the present invention will be described with reference to the drawings. In the present embodiment, an example will be described in which the aluminum molded product 1 is anodized on the top of a piston of an internal combustion engine. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the invention.

(Aluminum molded product)
As shown in FIG. 1, an aluminum molded product 1 includes a base 2 containing aluminum (an example of an object to be processed; hereinafter referred to as “base 2”), and an anodization formed on the surface of the base 2. And a coating 3. The aluminum molded product 1 assumes the top of a piston of an internal combustion engine, the bore of a cylinder block that defines a combustion chamber, the bottom of a cylinder head, and the like. The aluminum molded product 1 is not particularly limited as long as it forms an anodized film on the base 2 containing aluminum.

  As the base material 2, for example, an aluminum casting material such as die casting, an aluminum forging material, or the like can be used. As aluminum, pure aluminum, aluminum alloy, or the like can be applied. As the kind of the aluminum alloy, an alloy with one kind or plural kinds of copper, manganese, silicon, magnesium, zinc, nickel, tin, lead, titanium, chromium, dicuronium and the like can be considered.

  An anodizing apparatus X used for producing the anodized film 3 includes a DC power source 4, a cathode 5, and an electrolytic cell 6 having an electrolytic solution 61 inside. Further, the base material 2 is placed in the electrolyte 61 together with the cathode 5 as the anode 7, and a direct current is passed between both electrodes, thereby forming the anodic oxide film 3 on the surface of the base material 2. As the electrolytic solution 61, dilute sulfuric acid, oxalic acid, phosphoric acid, chromic acid, and other organic acids are used alone or in combination of two or more. In addition, although lead, platinum, etc. are used for the cathode 5, it does not specifically limit. Further, the power source is not limited to the DC power source 4, and an AC power source or an AC / DC superimposed power source may be used, and is not particularly limited.

  The anodizing apparatus X includes an energization control unit 8 that controls energization to the DC power supply 4 and a temperature control unit 9 that controls the temperature of the electrolytic solution 61. The energization control unit 8 in the present embodiment selects one of constant current control and constant voltage control, and controls the current value, voltage value, and energization time. The energization control unit 8 may execute pulse control or AC / DC superimposition control. In the case of pulse control, the cell diameter of the anodized film 3 may be controlled by setting the duty ratio and frequency to predetermined values, and there is no particular limitation.

  The temperature control unit 9 adjusts the temperature of the electrolytic solution 61 in order to keep the temperature of the anodizing process constant. The treatment temperature is not particularly limited as long as it is a temperature at which the anodic oxide film 3 does not dissolve and disappear, but for example, it is adjusted in the range of −5 ° C. to 25 ° C.

  Further, the electrolytic cell 6 is provided with a stirring means (not shown) for stirring the electrolytic solution 61 so as to suppress variations in the temperature of the electrolytic solution 61 so that the temperature difference of the electrolytic solution 61 does not affect the substrate 2. It is. As the agitation means, for example, the electrolytic solution 61 is circulated by a pump, or agitation by air publishing can be considered.

  FIG. 2 shows a partially enlarged view of the aluminum molded product 1 formed by the anodizing apparatus X. The aluminum molded product 1 includes a base material 2 containing aluminum and an anodized film 3 formed on the surface of the base material 2. The anodic oxide film 3 includes a barrier layer 3A which is a thin film-like non-porous conductive film and a porous layer 3B which is an aggregate of hexagonal columnar cells. The porous layer 3B is formed between the first film 32 having the first hole 32a and the base material 2 and the first film 32, and has a second hole 31a having a larger hole diameter than the first film 32. And a coating 31.

  In this embodiment, since the hole diameter of the second film 31 is set larger than the hole diameter of the first film 32, the thermal conductivity and heat capacity of the anodized film 3 are reduced, and heat is not easily conducted to the base material 2. .

  Further, the first coating 32 is formed with a hole sealing portion 33 whose surface is sealed. That is, the first film 32 has a first hole portion 32a having a hole sealing portion 33 formed on the surface. Since the 1st membrane | film | coat 32 has a small hole diameter, for example, when the hole sealing process by boiling water is given, the hole sealing part 33 can be formed reliably. As a result, in the aluminum molded product 1 of the internal combustion engine exposed to high heat, the inconvenience that the fuel and the combustion gas enter the inside of the anodized film 3 is solved. Moreover, since it can be manufactured by a normal anodizing process without providing a coating material on the anodized film 3, the manufacturing cost can be saved. Moreover, since both the first film 32 and the second film 31 are composed of the same anodic oxide film 3, they are difficult to peel even under a harsh environment such as an internal combustion engine.

  The film thickness of the anodized film 3 is set to 50 μm to 200 μm. In order to increase the thermal resistance, 50 μm is adopted as the lower limit value, and 200 μm is adopted as the upper limit value so that the volume specific heat does not become too large. Further, the thickness of the first film 32 is configured to be smaller than the thickness of the second film 31. Although the details will be described later, the first film 32 is formed to have a thickness of 0.5 to 5 μm because chromic acid is used as the electrolytic solution 61 and it is difficult to increase the thickness. On the other hand, 3 A of barrier layers are several nm, and the 2nd membrane | film | coat 31 is set to 45 micrometers or more and less than 200 micrometers.

  If the thickness of the first film 32 is reduced in this way, for example, when hydrated and expanded with boiling water, the opposing wall surfaces sandwiching the first hole portion 32a are easily accessible, and the hole sealing portion 33 is easily formed. Can be formed. Further, by increasing the thickness of the second film 31, the thermal conductivity and heat capacity of the anodized film 3 can be further reduced.

  By the way, among the anions of the electrolytic solution 61, sulfate ions, oxalate ions, and phosphate ions should enter (residual) into the anodized film 3, and chromate ions should not enter (residual) into the anodized film 3. It has been known. When the present inventors immerse both the anodic oxide film 3 in which the anion is not mixed and the anodic oxide film 3 in which the anion has entered in the acidic liquid, the anodic oxide film 3 in which the anion is mixed becomes the pore portion. We learned that the expansion of This is presumed to be because the anodic oxide film 3 in which anions are present is in an unstable state as compared with the anodic oxide film 3 in which no anions are present, so that dissolution is likely to proceed with an acidic solution.

  Therefore, the first coating 32 is hardly mixed with the anion of the electrolytic solution 61, and the second coating 31 is mixed with the anion of the electrolytic solution 61. Thereby, the 2nd hole 31a of the 2nd membrane | film | coat 31 can be expanded using an acidic liquid, and the thermal conductivity and heat capacity of the anodic oxide membrane 3 can be reduced further. And since the 1st hole 32a does not enlarge the 1st membrane | film | coat 32 using an acidic liquid, the hole sealing part 33 can be formed easily.

  In particular, the anion mixed in the second film 31 is preferably a sulfate ion. In sulfuric acid, the ratio of anions entering in the film thickness direction of the anodized film 3 is close to 100%. For this reason, when the hole expansion process is performed with the acidic liquid, the second hole portions 31 a existing in the film thickness direction of the second coating 31 are uniformly expanded. Therefore, the hole diameter of the second film 31 can be easily controlled, and the heat insulating performance of the anodized film 3 can be reliably improved.

(Anodized film generation method)
Hereinafter, the method for producing an anodized film according to the present embodiment will be described with reference to FIG. An anodic oxide film production method includes a first step of forming a first film 32 on a base material 2 with an electrolytic solution 61 containing chromic acid using the base material 2 containing aluminum as an anode, and a base layer after the first step. A second step of forming the second film 31 on the substrate 2 with the electrolyte 61 containing at least one of sulfuric acid, oxalic acid, and phosphoric acid using the material 2 as an anode, and the first film 32 and the second film 31 Is immersed in an acidic solution, and a third process for expanding the pores of the second film 31 and a fourth process for sealing the surface of the first film 32 are provided. The first step and the second step may be executed by the same anodizing apparatus X or may be executed by different anodizing apparatuses X.

  First, the base material 2 is processed into a predetermined shape by roughing or surface polishing. Next, in the first step, using the electrolytic solution 61 containing chromic acid, the energization control unit 8 performs constant voltage control at a predetermined voltage value (for example, 40 V to 60 V). The reason for the constant voltage control is that the generation of Joule heat is suppressed and the temperature is hardly increased as compared with the constant current control in which the voltage continues to increase as the first film 32 grows. As a result, it is possible to prevent burns from occurring in the first film 32 having a small film thickness formed at the initial stage of film formation. Moreover, it is preferable that the temperature controller 9 maintains the temperature of the electrolytic solution 61 at a predetermined low temperature (for example, −5 ° C. to 10 ° C.) so that the first film 32 is not burnt.

  By the first step, the first film 32 having the first hole portion 32a that hardly contains chromate ions is generated on the barrier layer 3A. Next, in the second step, using the electrolytic solution 61 containing at least one of sulfuric acid, oxalic acid, and phosphoric acid, the energization control unit 8 performs constant current control at a predetermined current value (for example, 0.1 A to 5 A). Run. By using constant current control, it is easy to set the energization time in the energization control unit 8 necessary for forming a desired film thickness. This is because the film thickness of the second film 31 formed on the substrate 2 is proportional to the integrated value of the current value and the processing time.

  Next, in the third step, the first film 32 and the second film 31 are immersed in an acidic solution such as sulfuric acid or phosphoric acid, and the second hole 31a of the second film 31 is enlarged. At this time, the first hole 32a of the first film 32 hardly expands. As described above, the first coating 32 hardly contains anions (chromate ions) of the electrolytic solution 61, and the second coating 31 contains the anions (sulfate ions, etc.) of the electrolytic solution 61. Because. The processing time in the third step is set within a time during which the second film 31 is completely dissolved and does not disappear, with a predetermined thermal conductivity as a target value.

  Next, in the fourth step, a hole sealing process is performed using boiling water, nickel acetate, or the like to seal the first hole 32 a on the surface of the first coating 32. For example, in the case of boiling water treatment, the pores are sealed by hydration expansion. At this time, since the first film 32 has a small film thickness and the first hole 32a in the third step is not enlarged, the surface of the first hole 32a is reliably sealed.

  As a result, when the aluminum molded product 1 is a piston of an internal combustion engine to which high heat is exposed, the inconvenience that the fuel and the combustion gas enter the inside of the anodized film 3 is solved. Moreover, since it can be manufactured by a normal anodizing process without providing a coating material on the anodized film 3, the manufacturing cost can be saved. Moreover, since both the first film 32 and the second film 31 are made of the same aluminum oxide grown from the base material 2, they are difficult to peel even under a harsh environment like an internal combustion engine.

  Then, the anodic oxide film 3 (this example) manufactured with the anodic oxide film production | generation method which concerns on this embodiment is compared with the anodic oxide film (comparative example) manufactured with the other method. Comparative Example 1 is an example in which the first step and the second step are performed, and the third step and the fourth step are omitted. Comparative Example 2 is an example in which sulfuric acid is used as the electrolytic solution, and the above-described third step and fourth step are omitted. Comparative Example 3 is an example in which sulfuric acid is used as the electrolytic solution and the above-described third step and fourth step are performed. The processing conditions in each example are shown in Table 1 below.

  When the hole expansion process in the third step was performed as in this example or Comparative Example 3, phosphoric acid having a concentration of 5% was used as the acidic solution, and the process was performed at 25 ° C. for 40 minutes. When the hole sealing process of the fourth step was performed as in this example or Comparative Example 3, it was carried out for 60 minutes using boiling water. 4 to 6 show the anodized film 3 of this example, FIG. 7 shows the second film of Comparative Example 1, FIG. 8 shows the anodized film of Comparative Example 2, and FIGS. 9 to 10 show the anodized film of Comparative Example 3. An enlarged photo of is shown.

  As shown in FIGS. 4 and 5, it can be seen that the surface of the first film 32 of the present example is sealed by performing a hole sealing process. On the other hand, the second coating 31 also hydrates and expands by performing the hole sealing treatment. In this embodiment, the hole diameter of the second coating 31 is 54 nm, 61 nm, and 62 nm (see FIG. 6) by performing the hole enlargement process and the hole sealing process, and the first process and the second process are provided. In Comparative Example 1 in which the enlargement process and the hole sealing process were not performed, the pore diameters of the second film were 47 nm, 51 nm, and 59 nm (see FIG. 7). That is, the hole diameter of the second film 31 of this example is larger than the hole diameter of the second film of Comparative Example 1, despite being hydrated and expanded.

  As a result, the thermal conductivity of this example is 0.5 W / m · K, the thermal conductivity of Comparative Example 1 is 1.1 W / m · K, and the thermal insulation performance of this Example is higher than that of Comparative Example 1. It turns out that it is excellent in. On the other hand, the difference in thermal conductivity is larger than the difference between the hole diameter of the second film 31 of this example and the hole diameter of the second film of Comparative Example 1 because the second film 31 of this example hydrates and expands. This is probably because the density has decreased. As the density of the second coating 31 decreases, the heat capacity also decreases.

  Further, as in Comparative Example 2, when the anodizing treatment is performed only with sulfuric acid as the electrolytic solution and the pore enlargement treatment and the pore sealing treatment are not performed, the thermal conductivity is 1.1 W / m · K, It turns out that the direction of a present Example is excellent in the heat insulation performance compared with the comparative example 1. FIG. Thus, when the hole enlargement process is not performed as in Comparative Example 1 and Comparative Example 2, the thermal conductivity and the heat capacity cannot be reduced. In addition, when the hole sealing process is not performed, for example, as shown in FIG. 8 of Comparative Example 2, it can be seen that innumerable holes exist on the surface of the anodized film.

  In addition, as in Comparative Example 3, when anodizing is performed only with sulfuric acid as an electrolytic solution, and pore enlargement treatment and pore sealing treatment are performed, the pores near the surface of the anodized film are enlarged, Hole sealing due to hydration expansion could not be performed (see FIG. 9). This is also clear from the fact that the pore diameters near the surface of the anodized film remain as large as 26 nm, 29 nm, and 32 nm (see FIG. 10). As a result, fuel and combustion gas penetrate into the anodized film and the desired heat insulation performance cannot be ensured.

  Furthermore, in Comparative Example 3 in which sulfate ions were mixed in the entire anodized film, the film thickness before the hole enlargement treatment was 80.5 μm, but the film thickness after the hole enlargement treatment was significantly reduced to 65.3 μm. On the other hand, when the second film 31 mixed with sulfate ions is covered with the first film 32 not mixed with anions as in this embodiment, the film thickness before the hole enlargement process is 78.9 μm. On the other hand, the film thickness after the hole expansion treatment was hardly reduced to 73.9 μm. Thus, it was confirmed that in this example, when the hole enlargement process was performed, the first film 32 can suppress the dissolution of the entire anodized film 3 and maintain a desired film thickness. That is, in this embodiment, it is possible to increase the thermal resistivity calculated by dividing the film thickness by the thermal conductivity while ensuring the desired heat insulation performance.

[Other Embodiments]
(1) The base material 2 to be anodized may be a metal such as titanium or tantalum other than aluminum, or an alloy of these and other metals.
(2) As long as the first film 32 containing chromic acid as the electrolytic solution 61 is formed on the surface layer of the anodic oxide film 3, the second film 31 may be composed of two or more layers.

INDUSTRIAL APPLICABILITY The present invention can be used in a method for forming an anodized film on an aluminum molded product that requires a desired heat insulation performance.

1 Aluminum molded product 2 Base material (object to be treated)
3 Anodized film 6 Electrolytic tank 7 Anode 31 Second film 32 First film 33 Hole sealing portion 61 Electrolytic solution

Claims (2)

A first step of forming a first film on the object to be processed with an electrolytic solution containing chromic acid using a metal object to be processed as an anode;
After the first step, with the object to be treated as an anode, a second step of forming a second film on the object to be treated with an electrolyte containing at least one of sulfuric acid, oxalic acid, and phosphoric acid;
A third step of immersing the first film and the second film in an acidic solution, and subjecting the second film to a pore expansion treatment;
And a fourth step of sealing the surface of the first film.   The method for producing an anodized film according to claim 1, wherein the electrolytic solution used in the second step is sulfuric acid.

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