JP2016003390A - Surface treatment method of aluminum material for heat release - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method of an aluminum material for heat release which can improve the heat release performance by improving the radiation amount.SOLUTION: A surface treatment method of an aluminum material for heat release is a method of surface-treating an aluminum material for heat release including an anodic oxidation treatment step of subjecting an aluminum material to an anodic oxidation treatment by using an electrolytic solution containing oxalic acid as the main agent and a sealing step of forming cobalt (II) sulfide (CoS) in pores formed in the surface of the aluminum material to seal the surface.

Description

  The present invention relates to a surface treatment method for a heat-dissipating aluminum material, and more particularly to a surface treatment method for a heat-dissipating aluminum material that can improve the heat dissipation performance by improving the radiation amount.

An aluminum material is a lightweight metal that has excellent thermal conductivity and good electrical conductivity. Furthermore, aluminum materials are widely used in various fields because surface treatment can improve corrosion resistance and mechanical performance. In particular, recently, due to such characteristics, it is frequently used as a material for automobile parts.
On the other hand, when an aluminum material is used as an automobile part, it is roughly divided when it is intended to reduce weight and when it is intended to improve heat dissipation. Therefore, conventionally, aluminum materials have been selectively used for parts that require weight reduction or heat dissipation.
However, with the improvement of automobile technology, the performance required for each component is increasing, and research for reducing the weight of aluminum material and improving the heat dissipation performance has been continued.
First, when aiming at weight reduction, various techniques for improving the properties of aluminum materials by adjusting the components of the aluminum alloy have been proposed and used.
On the other hand, when the purpose is to improve heat dissipation, it has been difficult to achieve with the technique of adjusting the components of the aluminum alloy. Therefore, technical research for improving heat dissipation by improving the surface treatment technology of aluminum material is underway.

Generally, an aluminum material is used after its corrosion resistance and wear resistance are improved by a surface treatment called anodizing. In addition, since a large number of pore layers are formed in the film formed by the anodizing treatment, various colors can be realized by coloring dyes or impregnated with functional substances using the pore layers. The surface is sealed by.
The anodizing treatment for surface treatment of an aluminum material generally employs a sulfuric acid method in which a 10-18 wt% sulfuric acid aqueous solution is used as an electrolytic solution. The reason for adopting this sulfuric acid method is that the electrolytic solution is the cheapest and the power consumption is small and economical. However, the anodic oxidation technology by the sulfuric acid method is a technology applied for the purpose of improving the wear resistance and corrosion resistance of the aluminum material, and is not a technology considering the heat dissipation of the aluminum material.
Therefore, in recent years, techniques have been proposed for improving the performance and characteristics of aluminum materials by variously changing the components of the electrolytic solution during anodization.
For example, without using sulfuric acid at all in the electrolyte, citric acid is the main agent, and by adding oxalic acid to the citric acid as an additive, the shape of the porous structure generated in the oxide film layer is regular. In addition, the technique for stably generating is disclosed in detail in “A composition method of an anodizing electrolytic solution of an aluminum alloy material and its composition (Patent Document 1)”.

However, in the invention described in Patent Document 1, the shape of the porous structure generated in the oxide film is regularly and stably generated, the residual phenomenon of the electrolytic solution is prevented, and the post-treatment process is greatly omitted. In addition to chemical and mechanical properties such as surface strength, corrosion resistance, wear resistance, insulation and heat resistance, it was possible to obtain the effect of improving electrical properties such as voltage resistance, but heat dissipation Not considered.
On the other hand, as a sealing process for finishing the surface of an anodized aluminum material, a boiling water sealing method (Boiling water), a low temperature sealing method (NiF ₂ ), or the like is generally used. However, such a sealing treatment method is intended to protect the oxide film formed on the surface of the aluminum material, and does not consider the heat dissipation of the aluminum material.

Korean Registered Patent No. 10-0606939

  The present invention has been made to solve the above-described problems, and the object of the present invention is to provide a heat-dissipating aluminum material that improves heat dissipation using surface treatment technology and sealing technology of the aluminum material. The object is to provide a surface treatment method.

  The surface treatment method for a heat-dissipating aluminum material according to the present invention, which has been made to achieve the above object, is a method for surface-treating a heat-dissipating aluminum material, and uses an electrolytic solution containing oxalic acid as a main agent. Anodization treatment step of anodizing the material, and a sealing step of sealing the surface by forming cobalt sulfide (CoS) in the pores formed on the surface of the aluminum material .

The oxalic acid concentration of the electrolytic solution in the anodizing treatment stage is 0.2 to 0.8 mol (M).
The temperature of the electrolytic solution in the anodizing treatment stage is 10 to 40 ° C.
The treatment time of the anodizing treatment stage is 30 minutes or more.

The sealing step includes a first immersion process in which the aluminum material treated in the anodizing treatment stage is immersed in a cobalt acetate immersion liquid, and a second immersion process in which the aluminum material processed in the first immersion process is immersed in an ammonium sulfide immersion liquid. Including.
The cobalt acetate immersion solution in the first immersion process has a cobalt acetate (Co (CH ₃ COO) ₂ ) concentration of 100 to 250 g / L.
The ammonium sulfide ((NH ₄ ) ₂ S) concentration of the ammonium sulfide immersion liquid in the second immersion process is 10 to 50 g / L.

According to the present invention, the heat dissipation of the aluminum material can be improved by using only oxalic acid as the electrolyte used in the anodizing treatment and making the hue of the oxide film close to black.
Moreover, the heat dissipation of the aluminum material can be improved by generating CoS in the pores of the anodized surface so that the hue of the surface of the aluminum material is closer to black.

It is a photograph which shows the surface of the oxide film manufactured by changing temperature and time in the conventional anodic oxidation process using a sulfuric acid electrolyte. It is a photograph which shows the surface of the oxide film manufactured by changing temperature and time in the anodizing process using the oxalic acid electrolyte solution which concerns on this invention. It is a graph which shows the relative radiation heat dissipation of the oxide film manufactured by changing temperature and time in the anodizing process using the conventional sulfuric acid electrolyte solution. It is a graph which shows the relative radiation heat dissipation of the oxide film manufactured by changing temperature and time in the anodic oxidation process using the oxalic-acid electrolyte which concerns on this invention. It is a figure which shows the surface photograph and relative radiation heat dissipation of the aluminum raw material which were sealed by various methods. It is a graph which shows the change of the emitted-heat amount by the density | concentration of the cobalt acetate used in the 1st immersion process in the sealing process by the black sealing method which concerns on this invention. It is a graph which shows the change of the emitted-heat amount by the density | concentration of the ammonium sulfide used in the 2nd immersion process in the sealing process by the black sealing method which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

In general, it is known that the aluminum material has a higher radiation amount and improved heat dissipation as the hue of the oxide film generated by the surface treatment is closer to black.
For this reason, the surface treatment method of the heat-dissipating aluminum material according to the present invention is intended to improve the anodizing treatment and sealing treatment applied to the aluminum material so that the surface of the aluminum material has a hue close to black.
In detail, the surface treatment method of the heat-dissipating aluminum material according to the present invention includes an anodizing step of anodizing the aluminum material using an electrolyte containing oxalic acid as a main agent, and an anodizing step. And a sealing step of sealing the surface by generating cobalt (II) sulfide (CoS) in pores formed on the surface of the aluminum material.

The anodizing stage is a stage in which the surface of the aluminum material is anodized to form an oxide film close to black, and the electrolytic solution is composed by adding only oxalic acid as the electrolyte during the anodizing process. Use liquid.
At this time, the concentration of oxalic acid is maintained at 0.2 to 0.8 mol (M). Preferably it is 0.3 mol (M). The reason is that since the saturation concentration of oxalic acid at 0 ° C. is 0.3 mol, the anodic oxidation treatment is performed when the concentration of oxalic acid is lower than 0.2 mol in consideration of the use temperature of the electrolytic solution. The amount of electric power required for the process increases, the density of pores formed on the surface of the oxide film decreases, and when the concentration of oxalic acid is higher than 0.8 mol, oxalic acid is no longer dissolved. It is. Therefore, the concentration of oxalic acid is preferably 0.2 to 0.8 mol (M).

On the other hand, the electrolytic solution used in the present embodiment preferably uses oxalic acid alone, but may further contain an acid used for general anodizing treatment while using oxalic acid as a main agent. For example, sulfuric acid, phosphoric acid, chromic acid and the like can be further dissolved in the electrolytic solution together with oxalic acid. At this time, the concentration of sulfuric acid, phosphoric acid, chromic acid, etc. is preferably maintained at 0.1 to 1 mol (M).
On the other hand, when the oxalic acid concentration of the electrolytic solution is maintained at 0.2 to 0.8 mol (M), it is preferable to maintain the current at 1 to 5 ASD and the voltage at 50 to 150 V during the anodizing treatment.
Moreover, it is good to maintain the temperature of electrolyte solution at 10-40 degreeC in the case of an anodizing process. Furthermore, the temperature of the electrolytic solution is more preferably maintained at 15 to 30 ° C. The reason is that, when anodizing is performed with an electrolytic solution in which oxalic acid is dissolved, the hue of the generated oxide film tends to be deeper as the temperature of the electrolytic solution is higher. However, if the temperature of the electrolyte exceeds 30 ° C, even if the temperature is further increased, the degree to which the hue of the oxide film becomes dark decreases, so that the hue of the oxide film becomes the maximum. Thus, maintaining the temperature of the electrolytic solution higher than 40 ° C. is a wasteful measure from the aspect of managing the temperature of the electrolytic solution.

The treatment time for the anodizing treatment is preferably maintained for 30 minutes or more. The reason for this is that the longer the anodization time, the thicker the oxide film that is formed, and the more the heat radiation tends to be improved. This is because, in particular, when the anodizing time exceeds 30 minutes, the heat dissipation amount shows the maximum value.
As described above, the reason for limiting the temperature of the electrolytic solution and the processing time during the anodizing treatment is that the effect has been proved by an experiment described later.

On the other hand, the sealing stage is a stage in which the oxide film generated by the anodizing treatment in the anodizing treatment step is sealed to make the surface hue of the aluminum material a hue close to black. This sealing step includes a first immersion process in which the aluminum material treated in the anodizing treatment stage is immersed in a cobalt acetate immersion liquid, and a second immersion process in which the aluminum material processed in the first immersion process is immersed in an ammonium sulfide immersion liquid. Process.
The cobalt acetate (Co (CH ₃ COO) ₂ ) concentration of the cobalt acetate immersion liquid in the first immersion process is 100 to 250 g / L, the temperature of the cobalt acetate immersion liquid is 20 to 50 ° C., and the immersion time is 10 to 10 ° C. It is preferable to maintain 30 minutes.
Moreover, the ammonium sulfide ((NH ₄ ) ₂ S) concentration of the ammonium sulfide immersion liquid in the second immersion process is 10 to 50 g / L, the temperature of the ammonium sulfide immersion liquid is 20 to 50 ° C., and the immersion time is 10 It is preferred to maintain ~ 30 minutes.
The reason for limiting the concentration, temperature and immersion time of the immersion liquid in the first immersion process and the second immersion process is that the effect has been proved by an experiment described later.

Hereinafter, the effects of the present invention will be proved by various experimental examples.
[Experiment 1]
Experimental Example 1 is a comparative example in which an aluminum material is anodized using an aqueous sulfuric acid solution as an electrolytic solution, and an aluminum material is anodized using an electrolytic solution composed by adding oxalic acid alone. The experiment according to the present invention is an experiment in which the surface of an oxide film formed on the surface of an aluminum material is compared after anodizing by changing the temperature of the electrolyte and the treatment time.
At this time, an electrolytic solution having a sulfuric acid concentration of 15 wt% was used in the comparative example, and an electrolytic solution having an oxalic acid concentration of 0.3 mol was used in the examples. In each of the comparative example and the example, the temperature of the electrolytic solution was 0 ° C., 15 ° C., and 30 ° C., and the treatment time was set to 10 minutes, 20 minutes, 30 minutes, and 40 minutes.
The results are shown in FIG. 1 and FIG.

FIG. 1 is a photograph showing the surface of an oxide film produced by changing the temperature and time in a conventional anodizing process using a sulfuric acid electrolyte, and FIG. 2 is an anodizing process using the oxalic acid electrolyte according to the present invention. It is a photograph which shows the surface of the oxide film manufactured by changing temperature and time in a process.
As can be seen from FIG. 1, in the case of the comparative example using sulfuric acid as the electrolytic solution, it was confirmed that the surface hue of the oxide film becomes darker as the temperature of the electrolytic solution is lower.
Moreover, in the comparative example, it was confirmed that the surface hue of an oxide film becomes dark, so that processing time becomes long.

On the other hand, as can be seen from FIG. 2, it was confirmed that in the examples of the present invention using oxalic acid as the electrolyte, the surface hue of the oxide film becomes darker as the temperature of the electrolyte is higher.
Moreover, in the case of the Example, it was confirmed that the surface hue of the oxide film became darker and darker as the treatment time became longer as in the comparative example. However, in the comparison between the case where the treatment time is 30 minutes and the case where the treatment time is 40 minutes, the surface hue of the aluminum material remains almost unchanged and is maintained at a similar level.
From this, in the case of the present invention using oxalic acid as the electrolytic solution, it is preferable to maintain the temperature of the electrolytic solution at 10 to 40 ° C. and to maintain at 15 to 30 ° C. in consideration of heat dissipation. More preferably, it was confirmed that the treatment time is preferably maintained at 30 minutes or more.

[Experiment 2]
In Experimental Example 2, the relative radiation heat release of the oxide film formed on the surface of the aluminum material manufactured in Comparative Example and Example used in Experimental Example 1 was measured. The results are shown in Table 1, FIG. 3 and FIG.
FIG. 3 is a graph showing the relative radiation heat dissipation of an oxide film produced by changing the temperature and time in a conventional anodizing process using a sulfuric acid electrolyte, and FIG. 4 shows the oxalic acid electrolyte according to the present invention. It is a graph which shows the relative radiation heat dissipation of the oxide film manufactured by changing temperature and time in the used anodizing process.

As can be seen from Table 1, FIG. 3 and FIG. 4, it was confirmed that the radiation heat radiation amount of the example was relatively higher than that of the comparative example when compared with the temperature and processing time of the same electrolytic solution.
Moreover, in the case of the Example, it was confirmed that the amount of radiant heat release increases as the temperature of the electrolytic solution increases and the treatment time increases. However, this is the case when the temperature of the electrolytic solution is 15 ° C. and 30 ° C., and when the processing time is 30 minutes and 40 minutes, the radiation heat dissipation amount may show the same value within the range of the measurement equipment error level. confirmed. From this result, considering the economics of the process, when anodizing treatment is performed using 0.3 mol of oxalic acid electrolyte, the temperature of the electrolyte can be set to 15 ° C. and the treatment time can be maintained at 30 minutes. It was judged to be the most suitable.

[Experiment 3]
Experimental Example 3 is an experiment for examining a difference in surface hue due to a sealing process on an aluminum material anodized using the oxalic acid electrolyte according to the present invention. An aluminum material that has been maintained at 15 ° C. with an oxalic acid 0.3 mol electrolyte solution and anodized for 60 minutes has not been sealed, a boiling water sealing method (Boiling Water), a low temperature sealing method The surface hue of the state treated with (NiF ₂ ) and the state of the sealing treatment of the present invention (hereinafter referred to as “black sealing method”) was observed, and the calorific value of the radiation method was measured.
The results are shown in FIG.
In this example, in the case of the boiling water sealing method, an aluminum material was immersed in deionized water at 95 ° C. for 30 minutes.
In the case of the low-temperature sealing method, an aluminum material was immersed in this immersion liquid for 30 minutes while maintaining an immersion liquid having a nickel fluoride (NiF ₂ ) concentration of 3 g / L at 25 ° C.
In the case of the black sealing method according to the present invention, first, an aluminum material is added to the immersion liquid for 20 minutes while maintaining the immersion liquid having a cobalt acetate (Co (CH ₃ COO) ₂ ) concentration of 200 g / L at 45 ° C. After dipping, the dipping solution having an ammonium sulfide ((NH ₄ ) ₂ ) S concentration of 30 g / L was dipped in this dipping solution for 25 minutes while maintaining at 25 ° C.

FIG. 5 is a view showing a surface photograph and a heat radiation amount of an aluminum material sealed by various methods. As can be seen from FIG. 5, the aluminum material sealed by the boiling water sealing method and the low-temperature sealing method also had a darker surface than the unsealed state. The surface hue became the darkest black.
In particular, from the results of measuring the radiation heat dissipation in FIG. 5, the aluminum material sealed by the boiling water sealing method is the same as before the sealing treatment, and the aluminum material sealed by the low temperature sealing method is Although the amount of radiation heat dissipation increased before the sealing treatment, the radiation heat dissipation amount was not as high as that of the aluminum material sealed by the black sealing method. That is, it was confirmed that when the surface of the aluminum material was sealed by the black sealing method, the radiation heat dissipation amount was significantly increased as compared with other sealing methods.

[Experimental Example 4]
Experimental Example 4 is an experiment in which, when a sealing process is performed by the black sealing method, a change in the heat release due to the cobalt acetate (Co (CH ₃ COO) ₂ ) concentration of the cobalt acetate immersion liquid in the first immersion process is examined. The amount of cobalt acetate (Co (CH ₃ COO) ₂ ) in the cobalt acetate immersion liquid used in the first immersion process in the stage of sealing the anodized aluminum material using the oxalic acid electrolyte was changed. Under the present circumstances, the temperature of all the cobalt acetate immersion liquids was maintained at 45 degreeC, and immersion time was maintained for 20 minutes. Next, in the second immersion process, an immersion liquid having an ammonium sulfide ((NH ₄ ) ₂ S) concentration of 30 g / L was maintained at 25 ° C. and immersed for 15 minutes. The results are shown in FIG.
As can be seen from FIG. 6, when the amount of cobalt acetate was 100, 200 and 250 g / L, it was confirmed that the heat dissipation amount was 400 W / m ² or more. From this result, it was confirmed that the cobalt acetate (Co (CH ₃ COO) ₂ ) concentration of the cobalt acetate immersion liquid in the first immersion process is preferably 100 to 250 g / L.

[Experimental Example 5]
Experimental Example 5 is an experiment in which a change in heat release due to a difference in ammonium sulfide ((NH ₄ ) ₂ S) concentration in the ammonium sulfide immersion liquid used in the second immersion process was examined when sealing treatment was performed by the black sealing method. is there. The aluminum material anodized with oxalic acid electrolyte was black sealed. First, as a first immersion process, an immersion liquid having a cobalt acetate (Co (CH ₃ COO) ₂ ) concentration of 200 g / L was maintained at 45 ° C. and immersed for 20 minutes. Next, in the second dipping process, the ammonium sulfide dipping solution was dipped while changing the amount of ammonium sulfide ((NH ₄ ) ₂ S). The temperature of all ammonium sulfide immersion liquids was maintained at 25 ° C., and the immersion time was maintained at 15 minutes. The results are shown in FIG.
As can be seen from FIG. 7, when the amount of ammonium sulfide was 10, 30, and 50 g / L, it was confirmed that the heat dissipation amount was 400 W / m ² or more. From this result, it was confirmed that the ammonium sulfide ((NH ₄ ) ₂ S) concentration of the ammonium sulfide immersion liquid is preferably maintained at 10 to 50 g / L in the second immersion process.

  As mentioned above, although this invention was demonstrated with reference to an accompanying drawing and an Example, this invention is not limited to these, It is limited by the claim which is mentioned later. Therefore, it is obvious that a person having ordinary knowledge in the technical field can variously modify and modify the present invention without departing from the technical idea of the claims.

Claims (7)

A method of surface-treating a heat-dissipating aluminum material,
Using an electrolytic solution containing oxalic acid as a main component, an anodizing step of anodizing an aluminum material;
A surface treatment method for a heat-dissipating aluminum material, comprising the step of sealing the surface by forming cobalt sulfide (II) (CoS) in pores formed on the surface of the aluminum material.   2. The surface treatment method for a heat-dissipating aluminum material according to claim 1, wherein an oxalic acid concentration of the electrolytic solution in the anodizing treatment step is 0.2 to 0.8 mol (M).   The surface treatment method for a heat-dissipating aluminum material according to claim 1, wherein the temperature of the electrolytic solution in the anodizing treatment stage is 10 to 40 ° C.   The surface treatment method for a heat-dissipating aluminum material according to claim 1, wherein a treatment time of the anodizing treatment stage is 30 minutes or more. The sealing step includes
A first dipping process in which the aluminum material treated in the anodizing step is dipped in a cobalt acetate dipping solution;
2. The surface treatment method for a heat-dissipating aluminum material according to claim 1, comprising a second dipping process in which the aluminum material treated in the first dipping process is dipped in an ammonium sulfide dipping solution. The surface treatment of a heat-dissipating aluminum material according to claim 5, wherein a concentration of cobalt acetate (Co (CH ₃ COO) ₂ ) in the cobalt acetate immersion liquid in the first immersion process is 100 to 250 g / L. Method. The surface treatment method of radiating aluminum material according to claim 5, wherein the ammonium sulfide of the ammonium sulphide immersion liquid in the second immersion step ((NH _{4) 2} S) concentration of 10 to 50 g / L .

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