JP7464394B2 - Metallic materials - Google Patents

Description

This disclosure relates to metal components.

There is an industrial demand for metal components with liquid-repellent surfaces.

A known liquid-repellent surface is a rough surface with low surface free energy and a fine uneven structure, and is a liquid-repellent surface that is called a slippery liquid-infused porous surface (SLIPS), which is made up of a lubricating oil film applied on top of the rough surface.

A rough surface with low surface free energy improves wetting of the lubricant and prevents the liquid from adhering strongly to the solid surface, so that droplets adhering to the lubricant film have high mobility and slide off easily at even a slight incline.

Because of these characteristics, SLIPS is not only useful as a liquid-repellent, stain-resistant, and corrosion-resistant surface, but is also believed to be capable of applications that were difficult with conventional super-water-repellent and super-oleophobic surfaces, such as anti-icing surfaces that prevent ice from adhering, biofouling-resistant surfaces that prevent the adhesion of biological liquids such as blood, and water harvesting technology that utilizes the high cohesiveness of droplets on a lubricating oil film.

Representative examples of substances with low surface free energy include fluorine-based resins such as polytetrafluoroethylene (PTFE; critical interfacial tension γ _C =18 mNm ⁻¹ ), but their applications are limited.

On the other hand, there is a great industrial demand for liquid repellency on the surfaces of various metal oxides. Although the surface free energy of metal oxides is very high compared to other substances, it is _known that _the surface free energy can be significantly reduced by modifying the surface with a self-assembled organic monolayer (SAM) consisting of a long-chain perfluoroalkyl group having -CF ₃ (γ _C =6 mNm ^-1 ) at the end or a long-chain alkyl group having -CH 3 (γ C =24 mNm ^-1 ). Among them, phosphonic acid derivatives, which have been widely used in recent years, are themselves very stable compounds and form SAMs with higher density and stability than silane coupling agents, which have been known for a long time.

As disclosed in Patent Document 1, it is known that the impact resistance, wear resistance, and corrosion resistance of steel materials for automobile engine parts and the like can be improved by a surface treatment method for steel materials in which the steel materials are plasma-nitrided and then nitrogen ions are implanted to bring the nitrogen concentration on the steel material surface to 30 atomic % or more.

JP 2003-073800 A

The chemicals used to form the above SAMs are expensive, and strict solution management is required when coating with SAMs using the liquid phase method, while expensive equipment is required when using the gas phase method.

Therefore, if it were possible to manufacture metal components with liquid-repellent surfaces without the need for surface treatment using SAM or the like, it would be possible to simplify the processing process and significantly reduce costs when it comes to large-scale industrialization.

However, it has been thought that surface treatment with SAM or other methods to reduce the surface free energy of the metal oxide surface is essential to allow the adhering liquid to slide off.

In fact, the present inventors have found that even if lubricants made of fluorine-based polymers or silicone oils, which are well known as lubricants for SLIPS, are used, it is not possible to prevent even water adhesion unless surface treatment is performed using SAM or the like.

The present disclosure aims to provide a metal component having a water-repellent and corrosion-resistant surface without the need for surface treatment with SAM or the like.

The present inventors have found that the above object can be achieved by the following means:
<<Aspect 1>>
A metal component having a porous surface, the porous surface being directly coated with a hydrocarbon-based oil containing zinc dialkyldithiophosphate (ZnDTP).
Aspect 2
2. The metal component according to claim 1, wherein the porous surface is an oxidized surface.
Aspect 3
3. The metal member according to claim 2, wherein the porous surface is an anodized surface.
Aspect 4
The metal member according to any one of aspects 1 to 3, wherein the metal member is a member made of Al, Ti, Fe, or Mg, or an alloy of any of these metals, or a stainless steel member.
Aspect 5
A metal member according to any one of aspects 1 to 4, wherein the concentration of the zinc dialkyldithiophosphate (ZnDTP) is 0.1% by mass to 30.0% by mass with respect to the hydrocarbon-based oil.
Aspect 6
The metal member according to any one of Aspects 1 to 5, wherein the hydrocarbon-based oil is an engine oil.
Aspect 7
The metal member according to any one of aspects 1 to 6, which is an automobile member.
Aspect 8
The metal member according to aspect 7, which is used in a portion to which engine oil is supplied.
Aspect 9
The metal member according to aspect 7 or 8, which is an intercooler member.

According to the present disclosure, it is possible to provide a metal component having a water-repellent and corrosion-resistant surface without the need for surface treatment using SAM or the like.

FIG. 1A is a scanning electron microscope (SEM) image of the surface of an aluminum plate having a porous surface. FIG. 1B is a scanning electron microscope (SEM) image of the surface of an aluminum plate having a hierarchically structured porous surface. FIG. 1C is a diagram showing the contact angle of a water droplet or an automobile engine oil droplet with respect to the surface of each of the aluminum plates of Reference Examples 1 to 4. FIG. 2A is a graph showing the relationship between the rotation speed of the aluminum plate and the remaining amount of automobile engine oil (rotation time: 60 seconds) for each of the aluminum plates of Examples 1 and 2 and Comparative Example 5. FIG. 2B is a graph showing the relationship between the rotation speed of the aluminum plate and the falling angle of a 10 μL water droplet (rotation time: 60 seconds) for each of the aluminum plates of Examples 1 and 2 and Comparative Example 5. FIG. 2C is a graph showing the relationship between the remaining amount of automobile engine oil and the falling angle of a 10 μL water droplet (rotation time: 10, 60, 300 seconds) for each of the aluminum plates of Examples 1 and 2 and Comparative Example 5. FIG. 3 is a graph showing the relationship between the immersion time in the mixed liquid and the sliding angle of a 10 μL water droplet for the aluminum plates of Examples 1 and 2 and Comparative Examples 5 and 7. FIG. 4 is a graph showing the weight change after the corrosion resistance test for the aluminum plates of Examples 1 and 2 and Comparative Examples 1 to 6. FIG. 5A is a scanning electron microscope (SEM) image of the surface of an aluminum plate that was not subjected to hierarchical structuring and was anodized before a corrosion resistance test. FIG. 5B is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Comparative Example 5 after the corrosion resistance test. FIG. 5C is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Comparative Example 3 after the corrosion resistance test. FIG. 5D is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Example 1 after the corrosion resistance test. FIG. 5E is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Comparative Example 1 after a corrosion resistance test. FIG. 6A is a scanning electron microscope (SEM) image of the surface of a hierarchically structured and anodized aluminum plate before a corrosion resistance test. FIG. 6B is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Comparative Example 6 after the corrosion resistance test. FIG. 6C is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Comparative Example 4 after the corrosion resistance test. FIG. 6D is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Example 2 after the corrosion resistance test. FIG. 6E is a scanning electron microscope (SEM) image of the surface of the aluminum plate of Comparative Example 2 after the corrosion resistance test. FIG. 7 is a diagram showing a method for producing the aluminum plate of Reference Example 5. FIG. 8A is a diagram showing the surface state of the aluminum plate of Reference Example 5 and the contact angle when a 10 μL water droplet was placed on it. FIG. 8B is a diagram showing the surface state of the aluminum plate of Reference Example 6 and the contact angle when a 10 μL water droplet was placed on it. FIG. 9A is a graph showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aluminum plate of Reference Example 5 after immersion in and cleaning with automobile engine oil. FIG. 9B is a graph showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aluminum plate of Reference Example 5 after immersion in and cleaning with automobile engine oil. FIG. 9C is a graph showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aluminum plate of Reference Example 5 after immersion in and cleaning with automobile engine oil. FIG. 10 is a graph showing the results of electrochemical measurements on the aluminum plates of Examples 3 to 5 and Comparative Example 8. FIG. 11 is a graph showing the results of electrochemical measurements on the aluminum plates of Example 3 and Comparative Examples 8 to 10.

The following describes in detail the embodiments of the present disclosure. Note that the present disclosure is not limited to the following embodiments, and can be modified in various ways within the scope of the disclosure.

The metal member of the present disclosure has a porous surface, and the porous surface is directly coated with a hydrocarbon-based oil containing zinc dialkyldithiophosphate (ZnDTP).

Metallic parts
In the present disclosure, the metal member has a porous surface.

Here, the porous surface refers to a porous coating formed on the surface of a metal member, and may be, for example, an oxidized surface having an oxide of the same metal as the metal member. More specifically, the porous surface may be an anodized surface.

The anodized surface can be obtained by anodizing the metal member, for example, when the metal member is an Al member, by anodizing, more specifically, by surface treatment in which an oxide film (Al ₂ O ₃ ) is generated by electrolytic treatment using Al as the anode (positive electrode). The anodizing can be performed based on, for example, JIS H8601 or JIS H8603, but other methods may also be used.

The thickness and pore size of the porous surface are not particularly limited.

The thickness of the porous surface can be adjusted as appropriate depending on the application of the metal component.

The shape of the porous surface is not limited as long as it is a liquid slippery surface (SLIPS). The pore size (diameter) of each hole in the porous surface may be 1 nm or more and 5 μm or less. The porous surface may have a microscale uneven structure, a nanoscale uneven structure, or a structure in which these are mixed, and may further have a hierarchical structure of these.

For example, when the porous surface has a microscale uneven structure, the pore size (diameter) of each hole in the porous surface may be 0.1 μm or more and 5 μm or less, but is preferably 0.1 μm or more and 0.5 μm or less.

In addition, when the porous surface has a nanoscale uneven structure, the pore size (diameter) of each pore in the porous surface may be 1 nm or more and 100 nm or less, but is preferably 30 nm or more and 100 nm or less.

The material of the metal member may be any metal capable of forming a porous surface, for example the metal member may be Al, Ti, Fe, or Mg, or an alloy of any of these metals, or a stainless steel member.

The metal component can be a component for any application, for example a vehicle component, more specifically an automobile component.

When the metal component is an automobile component, it is preferably used in a portion to which engine oil is supplied. This is because, when the metal component of the present disclosure is applied to such a portion, even if engine oil as a hydrocarbon-based oil is detached from the surface of the metal component, engine oil can always be supplied to the metal component.

When the metal member is an automotive component, the metal member can be an intercooler component. An intercooler is a device into which high-temperature air flows, and depending on the configuration of the automobile, exhaust gases may also flow, and therefore has components that are more susceptible to corrosion than other devices installed in an automobile. Examples of such components include heat exchangers. Therefore, by applying the metal member of the present disclosure to such components, the corrosion resistance of the intercooler can be improved.

<Hydrocarbon oil>
The hydrocarbon-based oil contains at least zinc dialkyldithiophosphate (ZnDTP). The hydrocarbon-based oil may be a paraffinic oil or a polyalphorefin. The hydrocarbon-based oil may be, for example, a lubricating oil, specifically an engine oil, more specifically an engine oil for an automobile.

When zinc dialkyldithiophosphate (ZnDTP) is contained in a hydrocarbon oil, it provides water repellency to the surface of a metal component. More specifically, it is believed that when a hydrocarbon oil containing zinc dialkyldithiophosphate (ZnDTP) is applied to a metal component, it chemically adsorbs to the surface of the metal component to form a liquid repellent coating.

The concentration of zinc dialkyldithiophosphate (ZnDTP) may be 0.1% to 30.0% by mass relative to the hydrocarbon oil. The concentration of zinc dialkyldithiophosphate (ZnDTP) may be 0.1% by mass or more, 1.0% by mass or more, 2.0% by mass or more, or 5.0% by mass or more, and may be 30.0% by mass or less, 20.0% by mass or less, 10.0% by mass or less, or 5.0% by mass or less.

Reference Examples 1 to 4
Metal members of Reference Examples 1 to 4 were produced as follows, and the liquid repellency of each example was evaluated.

Reference Example 1
A 99.5% aluminum (Al) plate was cut into a size of 20 mm x 50 mm, and degreased with acetone for 10 minutes by ultrasonic cleaning. It was then immersed in a 1.0 M NaOH aqueous solution (60°C) for 120 seconds to remove the oxide film, and further immersed in a 1.0 M _HNO3 aqueous solution (60°C) for 180 seconds to remove smut generated in the previous process.

Next, anodization was performed in a 0.3 M _{H2SO4 aqueous} solution (15°C) at an inter-plate voltage of 25 V for 180 seconds to form an anodized film with nanometer-scale pores. This was performed in a two-electrode system with the above substrate as the working electrode and another Al plate as the counter electrode.

Thereafter, the pore diameter was expanded by immersing the sample in a 5 wt % H ₃ PO ₄ aqueous solution (30° C.) for 15 minutes.

Finally, the surface was cleaned by oxygen plasma treatment for 4 minutes to obtain an aluminum plate with a porous anodized surface.

Reference Example 2
An aluminum plate having a hierarchical structure was obtained in the same manner as in Reference Example 1, except that chemical etching was performed before anodization to form micrometer-scale etch pits.

Reference Example 3
The aluminum plate of Reference Example 1 was subjected to oxygen plasma treatment, then immersed in a 1 mM ethanol solution of _CF3 ( _CF2 ) _7PO (OH) ₂ (perfluorooctylphosphonic acid; FOPA) for 2 days, and finally subjected to heat treatment in an air atmosphere (100°C) for 1 hour, thereby forming a self-assembled organic monolayer (SAM) on the surface of the aluminum plate of Reference Example 1.

Reference Example 4
A self-assembled organic monolayer (SAM) was formed on the surface of the aluminum plate of Reference Example 2 having a hierarchical structure in the same manner as in Reference Example 3, except that the aluminum plate of Reference Example 2 was used instead of the aluminum plate of Reference Example 1.

<Measurement of Liquid Repellency>
(Measuring method)
For each of the aluminum plates of Reference Examples 1 to 4, the contact angle of a water droplet or an automobile engine oil droplet was measured.

For the aluminum plates of Reference Examples 1 and 3, which do not have a hierarchical structure, static contact angles were measured, and for the aluminum plates of Reference Examples 2 and 4, which have a hierarchical structure, dynamic contact angles, that is, advancing contact angle and contact angle hysteresis, were measured.

(result)
The configurations and evaluation results of Reference Examples 1 to 4 are shown in Table 1 and Figures 1A to 1C. In the table, the values in parentheses () in the contact angle column indicate the contact angle hysteresis.

Fig. 1A is a scanning electron microscope (SEM) image of the aluminum plate of Reference Example 1. As shown in Fig. 1A, a porous Al ₂ O ₃ coating is formed by anodizing on the surface of the aluminum plate of Reference Example 1. Also, as shown in Fig. 1B, a hierarchical structure is formed on the surface of the aluminum plate of Reference Example 2 by etching micrometer-scale pits and a porous Al ₂ O ₃ coating.

As shown in Table 1 and Figure 1C, the aluminum plates of Reference Examples 1 and 2, which did not form a self-assembled organic monolayer (SAM), had contact angles with water droplets of 4.6 ± 1.2 and ~0, respectively, and were superhydrophilic. In contrast, the aluminum plates of Reference Examples 3 and 4, which did form a self-assembled organic monolayer (SAM), had contact angles with water droplets of 129.1 ± 0.8 and 161.7 ± 1.0, respectively, and were highly water-repellent.

The aluminum plate of Reference Example 4, which has a hierarchical structure and has a self-assembled organic monolayer (SAM) formed on its surface, exhibited a large contact angle of 158.2±1.5, and had high liquid repellency against automobile engine oil droplets, whereas Reference Examples 1 to 3 had contact angles of 90° or less, and had low liquid repellency.

This shows that at least for the aluminum plates of Reference Examples 1 to 3, automobile engine oil can be formed as an oil film.

Examples 1 and 2, and Comparative Examples 5 to 7
Aluminum plates of Examples 1 and 2 and Comparative Examples 5 to 7 were prepared and their performance was evaluated as follows.

<Examples 1 and 2, and Comparative Examples 5 and 6>
100 μL of automobile engine oil was measured out and applied to the surface of each of the aluminum plates of Reference Examples 1 to 4, and allowed to stand for 10 minutes or more to obtain the aluminum plates of Examples 1 and 2 and Comparative Examples 5 and 6.

As shown in the evaluation of the liquid repellency of automobile engine oil in Reference Example 4 above, automobile engine oil does not spread sufficiently on the surface of the aluminum plate of Reference Example 4, which has a hierarchical structure and is coated with a SAM. Therefore, the aluminum plate was first immersed in engine oil for 48 hours to deteriorate the oil repellency, and then automobile engine oil was applied.

Comparative Example 7
The aluminum plate of Comparative Example 7 was obtained in the same manner as in Example 1, except that automobile engine oil was applied to an aluminum plate that had not been subjected to any of the following: hierarchical structuring by etching, porosity by anodization, or SAM coating.

Evaluation of the stability of SLIPS in an environment where shear stress is applied to automotive engine oil
(Evaluation method)
The aluminum plates of Examples 1 and 2 and Comparative Example 5 were evaluated for the retention and liquid sliding properties of automobile engine oil in an environment where shear force is applied to the automobile engine oil. This was aimed at simulating the deterioration of SLIPS in an environment where lubricating oil is lost due to gravity, wind, etc.

As an evaluation method, first, the aluminum plates of Examples 1 and 2 and Comparative Example 5 were rotated using a spin coater at a rotation speed of 500 rpm to 7000 rpm and a rotation time of 10 seconds to 300 seconds. After that, the weight of the remaining automobile engine oil and the falling angle of a 10 μL water droplet were measured.

(result)
The measurement results are shown in Figures 2A to 2C. Note that Figure 2A is a graph showing the relationship between the rotation speed of the aluminum plate and the remaining amount of automobile engine oil (rotation time: 60 seconds) for each of the aluminum plates of Examples 1 and 2 and Comparative Example 5, Figure 2B is a graph showing the relationship between the rotation speed of the aluminum plate and the falling angle of a 10 μL water droplet (rotation time: 60 seconds) for each of the aluminum plates of Examples 1 and 2 and Comparative Example 5, and Figure 2C is a graph showing the relationship between the remaining amount of automobile engine oil and the falling angle of a 10 μL water droplet (rotation time: 10, 60, 300 seconds) for each of the aluminum plates of Examples 1 and 2 and Comparative Example 5.

As shown in Figure 2A, for both aluminum plates, as the rotation speed increased and the centrifugal force applied to the automobile engine oil increased, the amount of automobile engine oil remaining decreased accordingly.

This residual amount was particularly large in the aluminum plate of Example 2, which had a hierarchical structure. This is thought to be because the aluminum plate with a hierarchical structure has micrometer-scale irregularities, which allowed the automobile engine oil to be retained therein.

In addition, when comparing the aluminum plates of Example 1 and Comparative Example 5, which did not have a hierarchical structure, there was no significant difference in the amount of remaining automobile engine oil.

As shown in Figure 2B, it was confirmed that even in the aluminum plate of Example 1, which does not have a hierarchical structure and is not coated with a SAM, water droplets attached to the porous surface slide off at a certain sliding angle by applying automobile engine oil to the surface. The surface of the aluminum plate of Example 1 itself is hydrophilic as shown in Figure 1C, so it is believed that it cannot function as a SLIPS by itself.

Comparing the aluminum plates of Examples 1 and 2 and Comparative Example 5, the water droplet sliding angle increases as the rotation speed increases, i.e., the water repellency decreases, but the aluminum plate that was most susceptible to the decrease was the aluminum plate of Example 2, which had a hierarchical structure and was not coated with a SAM, while the aluminum plate that maintained the smallest water droplet sliding angle, i.e., maintained the water repellency, was the aluminum plate of Example 1, which did not have a hierarchical structure and was not coated with a SAM.

The reason why the water droplet sliding angle was particularly likely to increase on the aluminum plate of Example 2 is thought to be that the originally smooth lubricating oil film began to reflect the roughness of the rough surface as the lubricating oil was lost, causing the lubricating oil film to become rough and increasing the contact area with the water droplet.

When examining the relationship between the remaining amount of automobile engine oil and the sliding angle of a 10 μL water droplet, when the remaining amount of lubricating oil was the same, the aluminum plate of Example 1, which did not have a hierarchical structure and was not coated with a SAM, showed the smallest water droplet sliding angle (good water repellency).

As shown in Figure 2C, the surfaces formed by directly applying automobile engine oil to aluminum plates without a SAM coating, as in Examples 1 and 2, not only allow water droplets to slide off easily, like the surface formed by applying a SAM coating to an aluminum plate, as in Comparative Example 5, but also maintain the highest stability in an environment where the lubricating oil is subjected to shear forces.

Evaluation of the Stability of SLIPS in Water
(Evaluation method)
Acetic acid and 10 g/L NaCl aqueous solution (pH = 3) were stirred at 1000 rpm to prepare a mixture. The aluminum plates of Examples 1 and 2 and Comparative Examples 3 and 7 were immersed in the mixture and removed after a predetermined time. Then, the falling angle of a 10 μL water droplet on the aluminum plate of each example was measured. The amount of automobile engine oil applied to the aluminum plate of each example was 3.75 μL/ ^cm2 .

(result)
FIG. 3 is a graph showing the relationship between the immersion time in the mixed liquid and the sliding angle of a 10 μL water droplet for the aluminum plates of Examples 1 and 2 and Comparative Examples 5 and 7.

As shown in Figure 3, the water droplet sliding angle exceeded the measurement limit of 20° within a few days in all cases, but the aluminum plate of Example 1, which had no SAM coating, maintained a small water droplet sliding angle for the longest period of time (i.e., maintained high water repellency). On the other hand, the aluminum plate of Example 2, which has a hierarchical structure and has no SAM coating, was most susceptible to increased water droplet sliding (i.e., decreased water repellency), and exceeded 20° in a shorter period of time than the aluminum plate of Comparative Example 7, i.e., a smooth aluminum plate that was neither hierarchically nor porous and was coated with automobile engine oil.

From this, it can be said that when forming SLIPS by directly applying automobile engine oil to an aluminum plate without a SAM coating, higher underwater stability can be obtained by not forming a hierarchical structure.

<Corrosion resistance test>
The aluminum plates of Examples 1 and 2 and Comparative Examples 1 to 6 were evaluated for corrosion resistance as follows.

(Test method)
The aluminum plate of each example was immersed in the above-mentioned mixed solution for 5 days, and then the change in weight and surface morphology of the substrate were observed.

(result)
The results are shown in Table 1, and in FIGS. 4, 5A to 5E, and 6A to 6E.

In Table 1, "◯" indicates that the corrosion resistance was good, and "×" indicates that the corrosion resistance was not good.

Figure 4 is a graph showing the weight change after the corrosion resistance test for the aluminum plates of Examples 1 and 2 and Comparative Examples 1 to 6.

As shown in Figure 4, the aluminum plates of Comparative Examples 1, 2, 3, and 4, which were not coated with automobile engine oil, all lost weight by about 0.5 mg/ ^cm2 to 1.5 mg/ ^cm2 . This is due to the dissolution of aluminum due to corrosion.

On the other hand, in the aluminum plates of Examples 1 and 2 and Comparative Examples 5 and 6 to which automobile engine oil was applied, the weight change was 0.1 mg/ ^cm2 or less, and weight loss due to corrosion was suppressed. The aluminum plates of Example 2, Comparative Example 5, and Comparative Example 6 showed a slight increase in weight after the corrosion resistance test. This is because a small amount of white product remained even when these aluminum plates were washed with an organic solvent such as acetone after the corrosion test. The white product is considered to be a reaction product between the mixed solution and a neutralizer contained as an additive in the automobile engine oil.

These results show that applying automobile engine oil to a porous aluminum plate provides corrosion resistance equivalent to that achieved by applying a SAM coating to a porous aluminum plate.

The surface condition of the aluminum plates of Example 1, Example 2, Comparative Example 5, and Comparative Example 6 after the corrosion resistance test was observed using a scanning microscope.

Figure 5A is a scanning electron microscope (SEM) image of the surface of an aluminum plate that was anodized without hierarchical structuring before the corrosion resistance test, and Figures 5B to 5E are scanning electron microscope (SEM) images of the surfaces of the aluminum plates of Comparative Example 5, Comparative Example 3, Example 1, and Comparative Example 1, respectively, after the corrosion resistance test.

Referring to Figures 5A, B, and D, when comparing the aluminum plates of Comparative Example 5 and Example 1, which were made porous and had automobile engine oil applied to the surface, it can be said that the porous film remained the same as before the corrosion resistance test regardless of whether or not the SAM coating was applied, and the pore structure was maintained.

In contrast, as shown in Figure 5C, in Comparative Example 3, where only SAM coating was performed and no automobile engine oil was applied to the surface, the anodized surface dissolved and the pore structure disappeared. In Comparative Example 1, where no SAM coating was performed and no automobile engine oil was applied, not only the anodized surface but also the base aluminum plate was significantly dissolved.

Figure 6A is a scanning electron microscope (SEM) image of the surface of an aluminum plate that has been hierarchically structured and anodized before the corrosion resistance test, and Figures 6B to 6E are scanning electron microscope (SEM) images of the surfaces of the aluminum plates of Comparative Example 6, Comparative Example 4, Example 2, and Comparative Example 2, respectively, after the corrosion resistance test.

Referring to Figures 6A, B, and D, when comparing the aluminum plates of Comparative Example 6 and Example 2, which have a hierarchical structure, are porous, and have automobile engine oil applied to the surface, it can be said that the porous film remains the same as before the corrosion resistance test, regardless of whether or not there is a SAM coating, and the pore structure is maintained.

In contrast, as shown in Figure 6C, in Comparative Example 4, where only SAM coating was performed and no automobile engine oil was applied to the surface, the anodized surface dissolved and the pore structure disappeared. In Comparative Example 2, where no SAM coating was performed and no automobile engine oil was applied, not only the anodized surface but also the base aluminum plate was significantly dissolved.

From these results, it can be said that, in both cases where a hierarchical structure is present and where it is not, applying automobile engine oil directly to the surface of a porous aluminum plate provides corrosion resistance equivalent to that of a porous aluminum plate with a SAM coating applied to the surface.

Reference Examples 5 and 6
In order to clarify the reason why applying automobile engine oil directly to the surface of a porous aluminum plate gave corrosion resistance equivalent to that of a porous aluminum plate having a SAM coating applied thereto, the aluminum plate was washed with an organic solvent after being applied with automobile engine oil, and then subjected to surface analysis by static contact angle measurement and X-ray photoelectron spectroscopy (XPS).

Reference Example 5
As shown in Fig. 7, automobile engine oil was applied (12.5 µL/ ^cm2 ) onto an aluminum plate having a porous surface and allowed to stand for 24 hours. The aluminum plate was then ultrasonically cleaned in heptane and dried to obtain an aluminum plate of Reference Example 5.

Reference Example 6
An aluminum plate of Reference Example 6 was obtained in the same manner as in Reference Example 5, except that no automobile engine oil was applied.

<Evaluation of the surface condition of aluminum sheets>
(Evaluation method, etc.)
The surface conditions of the aluminum plates of Reference Examples 5 and 6 were observed with a scanning electron microscope (SEM). A 10 μL water droplet was placed on each of these aluminum plates, and the contact angle was measured. The aluminum plate of Reference Example 5 was also analyzed by X-ray photoelectron spectroscopy (XPS) after immersion in and cleaning with automobile engine oil.

(result)
8A and 8B are diagrams showing the surface state of the aluminum plates of Reference Examples 5 and 6, respectively, and the contact angle when a 10 μL water droplet was placed on them.

As shown in Figure 8A, in Reference Example 5, the nanopores on the porous surface are clearly observed even after immersion in automobile engine oil, indicating that the automobile engine oil has been removed by washing, and no change in pore size is observed.

However, as shown in Figure 8B, the water droplet contact angle in Reference Example 6, where engine oil was not applied, was 20° or less, making the surface hydrophilic, whereas as shown in Figure 8A, in Reference Example 5, after immersion in engine oil and washing, the contact angle was 110° or more, clearly showing a change to a water-repellent surface.

This is probably due to additives in automobile engine oil being chemically adsorbed onto the surface, resulting in surface modification.

Figures 9A to 9C are graphs showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the surface of the aluminum plate of Reference Example 5 after immersion in and cleaning with automobile engine oil.

Zn, which was not present before immersion in automobile engine oil, remained after immersion in automobile engine oil and cleaning. In the S2p spectrum shown in Figure 9B, a sulfate ion peak resulting from anodic oxidation in sulfuric acid was observed at around 171 eV, but in addition, a peak at 164 eV thought to be derived from the additive zinc dialkyldithiophosphate (ZnDTP) also appeared after immersion in engine oil and cleaning.

From the above results, it is believed that the zinc dialkyldithiophosphate (ZnDTP) in the automobile engine oil was adsorbed onto the surface of the aluminum plate of Reference Example 5, modifying the surface, thereby reducing the surface free energy and creating a stable SLIPS state even without a SAM, leading to a significant improvement in corrosion resistance.

Examples 3 to 5 and Comparative Examples 8 to 10
Aluminum plates according to Examples 3 to 5 and Comparative Examples 8 to 10 were prepared and their corrosion resistance was evaluated in the following manner.

Example 3
An aluminum plate having a porous anodized surface was prepared in the same manner as in Reference Example 1. An oil containing zinc dialkyldithiophosphate (ZnDTP) added to a base oil was applied onto the aluminum plate to prepare an aluminum plate of Example 3. The amount of zinc dialkyldithiophosphate (ZnDTP) in the oil was 2 mass% relative to the total amount of the oil.

Examples 4 and 5
Aluminum plates of Examples 4 and 5 were produced in the same manner as in Example 3, except that the amount of zinc dialkyldithiophosphate (ZnDTP) in the oil was 10 mass % and 20 mass %, respectively.

Comparative Example 8
An aluminum plate having a porous anodized surface was prepared in the same manner as in Reference Example 1. A base oil was applied onto this aluminum plate to prepare an aluminum plate of Comparative Example 8.

Comparative Example 9
An aluminum plate of Comparative Example 9 was produced in the same manner as in Example 3, except that an oil in which calcium sulfonate was added to a base oil was used instead of zinc dialkyldithiophosphate (ZnDTP). The amount of calcium sulfonate in the oil was 1 mass% with respect to the total amount of the oil.

Comparative Example 10
An aluminum plate of Comparative Example 10 was prepared in the same manner as in Comparative Example 9, except that the amount of calcium sulfonate in the oil was 10 mass%.

<Evaluation of corrosion resistance>
(Evaluation method)
The corrosion resistance of the aluminum plates of Examples 3 to 5 and Comparative Examples 8 to 10 was evaluated by electrochemical measurement. As the corrosive solution, a mixed solution (pH = 3) prepared by stirring acetic acid and a 10 g/L NaCl aqueous solution at 1000 rpm was used.

(result)
FIG. 10 is a graph showing the results of electrochemical measurements on the aluminum plates of Examples 3 to 5 and Comparative Example 8.

As shown in Figure 10, the aluminum plate of Comparative Example 8, which was coated with base oil without zinc dialkyldithiophosphate (ZnDTP), had a large anode current density and did not achieve sufficient corrosion inhibition. In contrast, the aluminum plates of Examples 3 to 5, which were coated with oil in which zinc dialkyldithiophosphate (ZnDTP) was added to the base oil, had a current density that was four or more orders of magnitude lower than that of the aluminum plate of Comparative Example 8, indicating excellent corrosion resistance.

Figure 11 is a graph showing the results of electrochemical measurements on the aluminum plates of Example 3 and Comparative Examples 8 to 10.

As shown in Figure 11, the aluminum plates of Comparative Example 8, in which base oil was applied, and Comparative Examples 9 and 10, in which calcium sulfonate was added instead of zinc dialkyldithiophosphate (ZnDTP), had a large anode current density and did not achieve a sufficient corrosion inhibition effect.

Claims (5)

The anodized coating has an anodized coating, and the anodized coating is coated with a hydrocarbon oil containing zinc dialkyldithiophosphate (ZnDTP) without a SAM coating, and has a hierarchical structure of a microscale uneven structure and a nanoscale uneven structure.
Metal parts. 2. The metallic component according to claim 1 , wherein the metallic component is a component of Al, Ti, Fe, or Mg, or an alloy of any of these metals, or stainless steel. 3. The metal member according to claim 1 , wherein the concentration of the zinc dialkyldithiophosphate (ZnDTP) is 0.1% by mass to 30.0% by mass relative to the hydrocarbon-based oil. The metal member according to any one of claims 1 to 3 , which is an automotive member. The metal member according to claim 4 , which is an intercooler member.

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