KR100485831B1 - A aluminum material and method of ceramic coating manufacturing - Google Patents

Abstract

An aluminum material and a ceramic coating manufacturing method thereof are provided to secure low friction coefficient and to improve excellent sliding efficiency and heat resistance and corrosion resistance by treating a surface of a base material under high voltage and low current by plasma electrolytic oxidation. An electrolytic cell(1) keeps the temperature of 10~40 deg.C and receives alkali electrolyte(2) of 7.9~8.8pH containing alkali metal hydroxides with the concentration of 1~3g/L, alkali metal silicate with the concentration of 2~5g/L, alkali metal fluoride of 2~6g/L. An anode(3) made from aluminum or aluminum alloy and a cathode(4) made from stainless steel are dipped in the electrolytic cell. And then, a plasma electrolytic oxidation layer is formed on the surface of a base material by applying an alternating current of a pulse mode to the anode and the cathode according to a current value calculated by the following formula. Current value = D*S/n. D is current density. S is a surface area of the base material. N is the number over 3. The current is continuously applied without regulating the current value. An effective voltage value applied to the anode is kept over 450V all the time by intermittently regulating voltage in applying the current. The pulse mode 50 or 60Hz. The current density is 5~30A/dm^2. Watt-hour of an anode pulse mode of the pulse mode is larger than a cathode pulse mode.

Description

A aluminum material and method of ceramic coating manufacturing

The present invention relates to an aluminum material and a method for producing a ceramic coating of an aluminum material. More specifically, the present invention provides heat and corrosion resistance by forming a plasma electrolytic oxide film containing α-Al ₂ O ₃ as a main component in a surface layer of a substrate in an aluminum or aluminum alloy. In addition to the excellent surface roughness (R) is less friction with other materials and excellent sliding properties, and relates to an aluminum material having a high hardness and a ceramic coating method of the aluminum material.

In recent years, the plasma electrolytic oxidation method has attracted attention for the surface treatment of aluminum or aluminum alloy. According to the plasma electrolytic oxidation method, it is possible to change the surface layer of aluminum or aluminum alloy into a hard ceramic film composed of Al ₂ O ₃ . Therefore, characteristics such as corrosion resistance and wear resistance can be imparted to the aluminum material.

On the other hand, according to the invention described in U.S. Patent No. 5,616,229, in the application of plasma electrooxidation method to aluminum material, 60% of korandam, 30% of aluminosilicate and 8% of alumina are applied to the surface of the Juralmin (alloy 2014). A method of forming an Al ₂ O ₃ based ceramic film having a thickness of 65 μm is disclosed.

The ceramic coating method disclosed in the U.S. Patent discloses an aqueous solution containing potassium hydroxide and sodium tetrasilicate as an electrolyte, immersed in an electrolytic cell with juralmin as an anode (+) and stainless steel as a cathode (-), and an anode. A high voltage of at least 700 V is applied to the circuit to conduct an AC current, and as a half-wave current, the anode current raises the current from 0 to the maximum value within a quarter of one cycle, and then increases the current value to 40% or less of the maximum value. It adopts the current waveform which lowers.

By the above method, microarc is generated on the surface of the juralmin, and electrolytic oxidation proceeds on the surface of the juralmin to form an Al ₂ O ₃ based ceramic film.

However, in the method as described above, since the electrolytic oxidation treatment is performed three times using different devices to form the ceramic film, the structure of the electrolytic oxidation treatment apparatus is not only complicated, but also difficult to operate. The electrolyte was also unstable, and there was a problem that the formed ceramic film was also inferior in quality.

In addition, the plasma electrolytic oxidation method described in Japanese Patent Laid-Open No. 2002-508454 uses an electrolytic solution containing an alkali metal hydroxide, an alkali metal silicate, an alkali metal polyphosphate, and a peroxide compound, wherein an aluminum alloy is added to the anode electrode (+). After the arrangement, the current pulse mode in which the anode pulse mode and the cathode pulse mode intersect is energized between the anode pole (+) and the cathode pole (−).

In more detail, first, the current is energized with a current density of 160 to 180 A / dm ² at an initial stage of 5 to 90 seconds from the start of energization, and then the current density is reduced to 3 to 30 A / dm ² , where the desired thickness is obtained. Until no power is supplied, energization is continued to voluntarily reduce the power used.

 Therefore, according to the above method, in the initial stage of energization, one characteristic is that a very large current flows between the anode electrode (+) and the cathode electrode (-) to satisfy the high current density as described above. This is to increase the formation rate of the oxide film.

However, according to the above method, since a large amount of current is energized in the initial stage of energization, a strong micro-arc discharge occurs to increase the formation rate of the plasma electrolytic oxide film, but at the same time, the arc discharge is an aluminum alloy (anode electrode). Because it is not uniformly distributed on the surface of the burning phenomenon occurs in the surface where the arc discharge is concentrated, there is a problem that the surface of the resulting plasma electrolytic oxide film is uneven, the surface is uneven.

On the other hand, in the field of materials such as pistons and cylinder liners of internal combustion engines, parts of pumps and compressors, parts of hydraulic devices and air compressors, the tendency to manufacture such parts as lightweight aluminum materials for energy saving is being considered. In this case, the aluminum material is not only excellent in corrosion resistance, heat resistance, heat insulation, but also has a small surface roughness (R), so that the friction with other materials is low, the sliding property is excellent, and the hardness is high.

From this point of view, the aluminum material in which the surface layer portion is changed to an Al ₂ O ₃ based ceramic film by the above-described conventional plasma electrolytic oxidation method satisfies the corrosion resistance, heat resistance, and heat insulation sufficiently, but the surface roughness (R) is large and the sliding property is poor. There was a problem that the hardness was small.

In order to solve the above problems, the present invention relates to a method for producing an aluminum material and a ceramic coating of the aluminum material, and more specifically, to the surface layer of the base material in the aluminum or aluminum alloy as α-Al ₂ O ₃ as a main component By forming a ceramic film, not only has excellent heat resistance and corrosion resistance, but also has a low surface roughness (R), so that friction with other materials is low, and slidability is excellent. Its purpose is to provide a method.

In order to achieve the above object, the ceramic coating method of the aluminum material according to the present invention, the temperature is maintained at 10 ~ 40 ℃, alkali metal hydroxide of 1 ~ 3 g / L concentration, alkali of 2 ~ 5 g / L concentration An anode (3) formed of an aluminum or aluminum alloy substrate and a stainless steel in an electrolytic cell (1) containing an alkali electrolytic solution (2) having a pH of 7.9 to 8.8 containing a metal silicate and 2 to 6 g / L alkali metal polyphosphate After soaking the cathode electrode 4 formed of steel, a plasma electrolytic oxide film is applied to the surface layer of the substrate by energizing the anode electrode 3 and the cathode electrode 4 with an alternating current of a pulse mode consisting of an anode pulse mode and a cathode pulse mode. In the producing method,

Current value = D S / n. … … … … … … … … … … … … … … … … … … … Formula (1)

               (Where D is the current density, S is the surface area of the substrate, and n is the number of 3 or more)

The current value is calculated by Equation (1) to start the energization, after which the energization state is continued without adjusting the current value until the end of the energization, and the voltage is applied to the anode pole by intermittently adjusting the voltage during the energization process. The effective voltage value is always 450V or more, wherein the pulse mode is 50 or 60 Hz, and the current density (D) is 5 to 30 A / dm ² .

In addition, the pulse mode is characterized in that the amount of power in the anode pulse mode is larger than the amount of power in the cathode pulse mode.

In the pulse mode, the ON time of the anode pulse mode is longer than the ON time of the cathode pulse mode.

In addition, four surfaces of the anode electrode 3 are surrounded by four cathode electrodes 4.

In addition, the alkali metal hydroxide is characterized in that KOH.

In addition, the alkali metal silicate is characterized in that Na ₂ SiO ₂ .

In addition, the alkali metal polyphosphate is characterized in that any one of Na ₄ P ₂ O ₇ , Na ₂ PO ₄ , Na ₆ P ₆ O ₁₈ .

In addition, the n is characterized in that 3 to 7.

In addition, the aluminum material according to the present invention has a plasma electrolytic oxide film having α-Al ₂ O ₃ as a main component and a surface roughness (R) of 1.0 μm or less in the surface layer of the substrate in aluminum or aluminum alloy, so that it is excellent in heat resistance and corrosion resistance. As well as excellent sliding, it is characterized by a large hardness.

Hereinafter, an aluminum material and a ceramic coating method of manufacturing an aluminum material according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a cross-sectional structure in the surface layer portion of the aluminum material according to the present invention, Figure 2 is a view showing the surface of the plasma electrolytic oxide film formed by the ceramic coating method of the aluminum material according to the present invention, Figure 3 FIG. 4 is a schematic view showing an embodiment of an apparatus for manufacturing an aluminum material according to the present invention, and FIG. 4 is a diagram illustrating an arrangement relationship between an anode electrode (+) and a cathode electrode (−) employed in a method of manufacturing a ceramic coating of an aluminum material according to the present invention. 5 is a plan view showing an embodiment, Figure 5 is a plan view showing another embodiment of the arrangement relationship of the anode electrode (+) and the cathode electrode (-) adopted in the ceramic coating method of the aluminum material according to the present invention, Figure 6 Is a view showing an embodiment of the anode pulse mode (A mode) of the current adopted in the method of manufacturing a ceramic coating of aluminum material according to the present invention, Figure 7 is an aluminum according to the present invention Fig. 8 is a view showing an embodiment of the cathode pulse mode (C mode) of the current adopted in the ceramic coating method of ash, Fig. 8 is an AC pulse mode (AC mode) of the current adopted in the ceramic coating method of the aluminum material according to the present invention. 9 is a view showing an embodiment of, Figure 9 is a view for explaining the adjustment of the applied voltage adopted in the method of manufacturing a ceramic coating of aluminum material according to the present invention.

First, the basic principle of manufacturing the aluminum material according to the present invention by the plasma electrolytic oxidation method will be described.

First, in order to form a plasma electrolytic oxide film in the surface layer portion of the substrate, when the substrate is used as an anode (+) and immersed in the electrolyte, a constant alternating current high voltage is applied to the substrate and a constant current density (current) is applied. In addition to ionization and oxygen generation as electrolyte components, a large number of plasma filaments are generated on the contact surface between the substrate and the electrolyte.

On the other hand, at the front end of the plasma filament, that is, the surface of the substrate, a high temperature and a high pressure spot having a temperature of about 1000 to 10000 ° C. and a pressure of about 100 MPa are formed as many as the number of occurrences of the plasma filament. The surface of the substrate on which (spot) is formed changes into an oxide containing Al ₂ O ₃ as a main component and grows in a layered manner in the course of energization.

However, the above growth on the oxide layer is based on the premise that the tip of the plasma filament continues to reach the surface of the unreacted substrate positioned below the oxide layer.

 In addition, when the thickness on the oxide layer becomes thick, the resistance becomes large, so that the plasma filament becomes difficult to reach the surface of the above-mentioned unreacted substrate, and as a result, the plasma filament does not reach the surface of the unreacted substrate. It stops and the trace of a plasma filament remains as a hole on an oxide layer.

Therefore, in order to maintain growth on the oxide layer, it is necessary to continuously reach the surface of the unreacted substrate by reaching the set applied voltage to increase the current through which the current flows, thereby increasing the power. In the process of controlling voltage and current

On the other hand, according to the experiments of the applicant, when a large current was energized in the initial stage, a thick oxide layer phase was surely generated in a short time, but the thickness of the oxide layer phase was not uniform and the surface was severely rugged, and the applied voltage was low. Part of the surface was discolored.

Therefore, it was concluded that it was inappropriate to conduct a large current to form an oxide layer on which the surface was uniform and flat, and that the applied voltage should be set high to prevent discoloration.

As described above, in the plasma electrolytic oxidation, an oxide layer phase grows at a high temperature and high pressure spot generated at the tip of the plasma filament, which contributes to the formation reaction of the oxide by generating the high temperature and high pressure spot. Is the anode pulse mode.

On the other hand, the cathode pulse mode does not contribute to the formation reaction of the oxide, but generates a cathode discharge on the surface of the already formed oxide layer, thereby maintaining a high temperature and a high pressure spot at a higher temperature than when the anode pulse mode is energized.

Therefore, in the high temperature and high pressure spot generated in the energization of the anode pulse mode, if the temperature can be made higher and the pressure can be made higher, the oxide will continue to be produced, and the oxide is hardened under high temperature and high pressure. And compression deformation, it can be concluded that the surface on the growing oxide layer is planarized.

That is, it is effective to increase the applied voltage in order to exhibit the above functions in the anode pulse mode, and since the cathode discharge occurs on the surface of the oxide layer when the cathode pulse mode is energized, part of the surface of the oxide layer by the cathode discharge, That is, the cathode discharge contributes to the planarization of the oxide layer by removing the convex portions where discharge is likely to occur.

According to the above principle, in order to form a plasma electrolytic oxide film having a flat surface, it is concluded that plasma electrolytic oxidation should be performed at high voltage and low current.

Hereinafter, the aluminum material which concerns on this invention is demonstrated in detail.

1 is a micrograph (1000 times magnification) showing the cross-sectional structure of the surface layer portion of the aluminum material according to the present invention, Figure 2 is a micrograph (400 times magnification) of the surface of the plasma electrolytic oxide film formed by the manufacturing method of the aluminum material according to the present invention. to be.

As can be seen in Figure 1 or 2, the plasma electrolytic oxide film is formed by changing the surface electrolytic oxide film of the substrate by performing plasma electrolytic oxidation under the energization or operating conditions to be described later, and basically has a one-layer structure.

 In addition, according to FIG. 2, the surface of the plasma electrolytic oxide film has a surface state in which fine oil components are assembled in a state in which they are pressed to each other, and thus the distribution of micropores can be confirmed. The characteristics of the plasma electrolytic oxide film are as follows.

First of all, the surface is fairly flat, specifically, the surface roughness (R) measured by the method specified by the Korean Industrial Standard is 1.0 μm or less, even if the surface is rather rough, the electrolytic oxidation of the aluminum material according to the method of manufacturing the aluminum material according to the present invention. After the surface roughness (R) of the substrate can be made 1.0 μm or less.

On the other hand, as can be seen in Figure 2, the micropores are traces of the pores, the micropores are only distributed in the surface portion of the plasma electrolytic oxide film, and are extremely shallow holes.

Therefore, it can be said that the generated plasma electrolytic oxide film is in a substantially non-porous state even if it contains micropores distributed in the above-mentioned surface portion.

Here, when the thin film X-ray diffraction method is applied to the plasma electrolytic oxide film, the diffraction angle of crystalline Al ₂ O ₃ (α-Al ₂ O ₃ ) can be confirmed, and thus, the plasma electrolytic oxide film is basically α-Al ₂ O _3. It can be seen that consists of.

As described above, in the aluminum material produced by the method of manufacturing the aluminum coating ceramic according to the present invention, the plasma electrolytic oxide film formed on the surface layer portion of the base material has α-Al ₂ O ₃ as a main component, and its surface roughness (R) is 1.0 μm or less, in fact. It is characterized by consisting of a precision structure of a non-porous state.

Next, a method of manufacturing a ceramic coating of an aluminum material according to the present invention will be described in detail with reference to the drawings.

3 is a schematic view showing an embodiment of an apparatus for manufacturing an aluminum material according to the present invention, in which an electrolyte solution 2 is accommodated in an electrolytic cell 1, and a substrate is contained in the electrolyte solution 2. As the anode electrode 3, stainless steel is contained as the cathode electrode 4, and the anode electrode 3 and the cathode electrode 4 are each connected to a control device.

On the other hand, the control device converts the AC power of 50Hz or 60Hz supplied from the power source into a pulse mode including an anode pulse mode and a cathode pulse mode, and supplies the pulse mode to the anode electrode 3 to perform plasma electrolytic oxidation.

The electrolytic cell 1 is equipped with a cooler and an air discharge device, and temperature control and stirring of the electrolytic solution 2 are possible.

Here, the anode 3 is composed of aluminum or an aluminum alloy, but is not particularly limited as an aluminum alloy, for example, 2014 alloy, 2024 alloy (all Al-Cu-Mg), 6061 alloy, 6463 alloy ( Al-Mg-Si type | system | group, 7075 alloy, 7175 alloy (all Al-Zn-Mg type), 5052 alloy (Al-Mg type), etc. are mentioned.

In addition, for the anode electrode 3, it is suitable to make the surface as smooth as possible by processing the surface precisely when performing plasma electrolytic oxidation, but if the roughness of the surface roughness R is about 3 to 4 µm, Even if it is formed as a surface roughness (R) after the plasma electrolytic oxidation treatment of the aluminum material according to the present invention will be flattened to 1.0㎛ or less.

On the other hand, when the pH value of the electrolyte solution 2 is lower than 7 or higher than 9, the plasma filament is hardly generated, and the drainage process is complicated, so that the pH value of the electrolyte solution 2 is preferably about 7.9 to 8.8. When the organic material is included, the peeling resistance of the generated plasma electrolytic oxide film tends to be deteriorated, so that the organic material is removed.

In addition, there can be KOH, NaOH, etc. As the alkali metal hydroxide for the electrolyte (2), it is preferable to KOH is more suitable, as the alkali metal silicate employed for Na ₂ SiO _2, as the alkali metal Poly Lin acid Na ₄ One or two or more kinds of P ₂ O ₇ , Na ₂ PO ₄ , Na ₆ P ₆ O _18, and the like can be used.

On the other hand, the electrolyte solution 2 is dissolved in distilled or deionized water to adjust the components, and adjust the concentration of each component in consideration of the generation, hardness, etc. of the plasma electrolytic oxide film formed on the substrate.

Here, when KOH is used as the alkali metal hydroxide, the concentration is usually 1 to 3 g / L, and when Na ₂ SiO ₂ is used as the alkali metal silicate, the concentration is 2 to 5 g / L, and the alkali metal is used. Poly Lin when using acid as Na ₄ P ₂ O _7, it is preferred to independently control the concentration of 2 ~ 6 g / L.

Next, when the plasma electrolytic oxidation is started, the temperature of the electrolytic solution 2 starts to rise because a high temperature and high pressure spot occurs on the surface of the substrate, but in the present invention, the temperature of the electrolytic solution 2 is determined by the plasma electrolytic oxidation. The process maintains 10-40 ° C.

On the other hand, when the temperature of the electrolyte solution 2 is lower than 10 ° C., for example, various ions generated in the energization process are sealed in the oxygen film, making it difficult to generate plasma filaments, and when the temperature is higher than 40 ° C., Na ₂ SiO in the _two becomes solidified started to SiO ₂ is removed.

Therefore, as shown in Fig. 3, by installing a cooler having a temperature control function, two pipes 5a and 5b are provided in the cooler, and the electrolyte solution 2 is sucked into the cooler from one pipe 5a. The electrolyte 2 is cooled to a predetermined temperature in a cooler and then returned to the electrolytic cell 1 through the other pipe 5b. A heat exchanger can be used as the cooler.

In addition, an acid substrate 6 is provided on the bottom surface of the electrolytic cell 1 to connect the acid substrate 6 to an air discharge device to bubble air from the acid substrate 6 to the electrolyte 2. Preferably, the electrolyte 2 is stirred and homogenized, and the cooling effect of the anode electrode 3 is also promoted, and the quality of the plasma electrolytic oxide film can be improved.

Meanwhile, although FIG. 3 illustrates an embodiment in which the anode electrode 3 and the cathode electrode 4 are disposed so as to face each other on one surface, the anode electrode 3 and the cathode electrode 4 are shown in FIG. It is preferable to arrange | position in the form of FIG. 5, FIG. 4 and FIG. 5 are the top view which shows the mutual arrangement | positioning relationship of the anode electrode 3 and the cathode electrode 4. As shown in FIG.

In more detail, FIG. 4 shows an arrangement relationship in which four surfaces of the anode pole ₃ are surrounded by four cathode poles 4 ₁ , 4 ₂ , 4 ₃ , and 4 ₄ , and FIG. 5 shows the anode pole 3. ) Is shown in the center of the circular cathode electrode 4, in both cases the anode electrode 3 is surrounded by the cathode electrode (4).

As such, when the anode 3 is surrounded by the cathode 4, the current and voltage acting on the surface of the anode 3 during the plasma electrolytic oxidation are homogenized, so that a high temperature and high pressure spot caused by the plasma filament is uniform. In addition, since it is generated evenly distributed on the surface of the anode electrode 3, the production of high quality plasma electrolytic oxide film proceeds in a stable state.

Next, the energization conditions adopted in the ceramic coating method of manufacturing an aluminum material according to the present invention will be described in detail.

First, at the start of energization of the control device, the set current value is a value calculated by the above formula (1), and if the indication value of the ammeter at the start of energization is set to the set current value, the current value until the end of energization. Do not adjust and leave unchanged.

In addition, from the start of energization to the end of energization, the voltage of the anode 3 is continuously adjusted so that a voltage of 450 V or more is always applied. The supply of power to the anode 3 is performed by combining the anode pulse mode and the cathode pulse mode. Do it.

By adopting the above energizing conditions, the plasma electrolytic oxide film is formed or formed at an appropriate speed, and the surface roughness R of the surface thereof is flattened to 1.0 µm or less.

On the other hand, in the manufacture of the aluminum coating ceramic coating according to the present invention, the higher the current density, as described above, the faster the formation or formation rate of the film, the surface of the resulting plasma electrolytic oxide film becomes rough and surface discoloration (burning phenomenon) also If the current density is too low, the plasma electrolytic oxide film will not be formed or the production rate will be slow.

In addition, when the surface area of the anode electrode 3 is very large (25 dm ² or more), unless the current density is increased, the formation of the plasma electrolytic oxide film may not proceed smoothly in the center of the surface of the anode electrode 3, so that the anode When the area of the pole 3 is large, the current density is set high.

Therefore, in the manufacture of the ceramic coating of the aluminum material according to the present invention, the current density is arbitrarily selected in the range of 5 ~ 160 A / dm ² , it is preferable to select in the range of 5 ~ 30 A / dm ² , if the current density Usually, the production rate of the plasma electrolytic oxide film is about 2 ~ 4㎛ / min.

In the conventional method, the energization is started at the current value D · S multiplied by the surface area S and the current density D (A / dm ² ) by calculating the surface area S (dm ² ) of the anode electrode 3. The current value at the start is set to the value calculated based on equation (1).

More specifically, in the formula (1), if n is greater than or equal to 3, a number of 3 or more is selected, and when the current is started with a current value calculated by setting n to a value less than 3, the surface of the plasma electrolytic oxide film that is obtained becomes rough, n If the value becomes too large, the set current value at the start of energization becomes too small and the formation rate of the plasma electrolytic oxide film is slowed. Therefore, n is preferably set within the range of 3 to 7.

At this time, the generation of the plasma electrolytic oxide film proceeds at an appropriate speed, the surface of the resulting film is very flat, the surface roughness (R) is 1.0㎛ or less.

As described above, in the method of manufacturing the ceramic coating of the aluminum material according to the present invention, the current is supplied to the manufacturing apparatus at a current value lower than the current value D · S calculated in order to generate the plasma electrolytic oxide film at an appropriate speed.

Thereafter, even when the surface of the substrate is changed to the plasma electrolytic oxide film in the energization process, even if there is a reduction in the energization current accompanied by an increase in resistance, the current is maintained as it is until the termination of the energization without restoring or adjusting the set current value. Continue energizing as it is decreasing.

In addition, in order to maintain the voltage of the apparatus so that the effective voltage applied to the substrate is 450V or more in the above process, the voltage applied to the substrate is intermittently adjusted to be 450V or more at all times until the end of energization.

The reason why the voltage applied to the substrate is always maintained at 450 V or higher is due to the oxide (α-Al ₂ O ₃ ) produced by continuously maintaining the active state of the high temperature and high pressure spot generated on the surface of the substrate during energization. This is to promote the production of the oxide while applying a compressive force to produce a plasma electrolytic oxide film having a flat surface.

On the other hand, if the applied voltage is lower than 450V, the above-mentioned effect cannot be sufficiently obtained, and the surface roughness (R) of the film surface cannot be set to 1.0 μm or less, so 450V must be applied until the end of energization. It is not possible to produce a surface having a surface roughness R of 1.0 μm or less.

The energizing process is performed by preparing a current of a pulse mode including at least one anode pulse mode and at least one cathode pulse mode. An embodiment of the anode pulse mode of the current (hereinafter referred to as "A mode") In Fig. 6, one embodiment of the cathode pulse mode of current (hereinafter referred to as "C mode") is shown in Fig. 7, respectively.

The mode A of FIG. 6 is generated from a plurality of (three) positively polarized anode pulses, and one mode is configured by periodically arranging each pulse. The mode A is a plasma electrolytic oxide film while applying a compressive force by the energization. At the same time, the plasma electrolytic oxide film is refined to make the surface flat.

In addition, by adjusting the ON time (A) of one anode pulse in the A mode, the generation rate, the degree of refinement, the surface roughness (R), and the like of the plasma electrolytic oxide film can be changed.

For example, when the ON time A is extended, the active state of the high temperature / high pressure post is kept long, so that the rate of formation of the plasma electrolytic oxide film is increased and refined, and the amount of deformation of the oxide is increased, thereby to planarize the surface.

On the other hand, the C mode shown in FIG. 7 is composed of a plurality of polarized cathode pulses, and one mode is configured by periodically disposing each pulse. When the C mode is energized, the growth of the plasma electrolytic oxide film is stopped. In addition, a cathode discharge is generated to generate a high temperature on the surface of the plasma electrolytic oxide film that has already been generated, for example, a projection portion that concentrates transfer.

Therefore, a part of the plasma electrolytic oxide film is melted by the cathode discharge and at the same time, a compression action by an applied voltage of 450 V or more occurs in combination, thereby flattening the surface of the plasma electrolytic oxide film.

That is, the C mode acts to smooth the surface by acting on the projection of the surface of the plasma electrolytic oxide film generated in the A mode, and in the C mode, by adjusting the ON time C of one cathode pulse The surface roughness of the plasma electrolytic oxide film can be adjusted.

For example, when the ON time C is lengthened, the cathode discharge is kept long, so that the projections and the like on the surface can be reliably melted to increase the flatness of the surface.

On the other hand, the pulse mode of the electric current to be supplied is used by appropriately combining these on the basis of the A mode and the C mode. Of these combinations, the pulse mode of the waveform shown in FIG. 8 is appropriate.

The pulse mode is configured as one cross-pulse mode (hereinafter referred to as "AC mode") by exchanging one anode pulse and one cathode pulse, which is the surface of the plasma electrolytic oxide film generated when the AC mode is energized. Since the operation of the A mode and the C mode alternately works, a fine, homogeneous and flat plasma electrolytic oxide film can be reliably produced.

In addition, in the AC mode, the ON time of the anode pulse and the ON time of the cathode pulse are appropriately set, but in order to reliably form the plasma electrolytic oxide film, the sum of the ON time of the anode pulse is longer than the sum of the ON time of the cathode pulse. It is appropriate.

In other words, it is appropriate that the amount of power of the anode pulse, which is an integral value of the half wavelength, be larger than that of the cathode pulse.

By the way, in the present invention, since the set current value (D · S / n) at the start of power supply is energized, the set current value is not adjusted until the end of power supply. The conduction current is reduced and the amount of power introduced to the substrate is reduced.

 Here, when the amount of power introduced into the substrate is reduced, the generation of the plasma electrolytic oxide film does not proceed, and in some cases, the plasma electrolytic oxide film having a desired thickness is not formed. As a result, in the method of manufacturing the ceramic coating of the aluminum material according to the present invention, it is intermittent. To adjust the voltage applied to the anode pulse.

 More specifically, as shown in Fig. 9, a process of increasing the applied voltage is performed, and a new AC mode for processing of increasing the applied voltage is designed as follows.

That is, as shown in FIG. 9, the voltage of the anode pulse is increased from + V ₀ to + V (+ V> V ₀ ) and at the same time, the voltage of the cathode pulse is changed from -V ₀ to -V ′. Shall be.

At this time, the applied voltage is set by setting the + V and -V 'values so that the absolute value of the power increase amount ΔP on the half-wave side of the anode pulse and the power decrease amount (-ΔP) on the half-wave side of the cathode pulse are equal. After adjustment of, the AC mode becomes the waveform shown in FIG.

Here, the amount of power supplied by the AC mode increases on the anode pulse side and decreases on the cathode pulse side compared to before the adjustment of the applied voltage, but the sum is equal to the amount of power at the start of energization.

In addition, the adjustment of the applied voltage is performed at the following time points.

That is, when the energization is started at the set current value (D · S / n), intense foaming may be observed on the anode electrode 3, that is, on the surface of the substrate. However, as time passes, the plasma electrolytic oxide film is deposited on the surface of the substrate. When the plasma electrolytic oxide film is formed, the foaming phenomenon decreases at the same time, because the resistance of the surface of the substrate is increased, so that the current is suppressed and the plasma electrolytic oxidation is reduced.

In this case, the foaming phenomenon in the center portion of the substrate, which is generally a flat cross section, gradually decreases, and since the foaming phenomenon is confirmed until the end, the edge portion of the substrate where the current is easy to concentrate, the timing of adjusting the applied voltage Decide

For reference, an experimental example of the ceramic coating method of manufacturing an aluminum material according to the present invention will be described.

(1) mention

First, 5052 alloy, 6061 alloy, 7071 alloy and ADC12 alloy were selected as substrates, and the alloy was cut and polished to produce five 45 mm x 45 mm x 1 mm specimens. The surface area (s) of each specimen was 0.423dm ² It was set as.

Meanwhile, the micro-Vickers hardness (Hv) of each specimen was measured and the results are shown in Table 1, and the surface roughness (R) of each specimen was measured by the method specified in Korean Industrial Standard (KSMISO8503-3). The surface roughness (R) of was 3-4 micrometers.

(2) Preparation of Plasma Electrolytic Oxidation

KOH, Na ₂ SiO ₃ and Na ₂ HPO ₄ were dissolved in distilled water to prepare an electrolyte solution having a pH of 8.8 based on KOH concentration of 2 g / L, Na ₂ SiO ₃ concentration of 4 g / L, and Na ₂ HPO ₄ concentration of 5 g / L. .

The electrolyte solution is contained in the electrolytic cell shown in FIG. 3 and the specimen (+) and the stainless steel plate (-) are immersed therein, and the arrangement of the specimen (+) and the stainless steel plate (-) is shown in FIG. It adopts the form of enclosing (+) all directions with stainless steel plate (-).

On the other hand, by operating the air blower to blow air into the electrolyte at 0.1MPa to start bubbling (bubbling) at the same time by operating the cooler to set the temperature of the electrolyte solution to 15 ± 3 ℃.

In addition, the current density is 15 A / dm ² and n is 4, which is calculated by Equation (1), and the set current value is 1.58 A. In the pulse mode, the duration of the ON state of the anode pulse and the cathode pulse is 1.2 ms. AC mode is adopted.

(3) Conducting plasma electrolytic oxidation

The control device was operated to start the energization with a current value of 1.58A and an applied voltage of 450V, and the foaming state of the specimen surface was observed. When the foaming phenomenon calmly subsided in the center of the specimen surface, the applied voltage was raised to 550V.

At this time, the foaming phenomenon appeared at the center of the specimen surface again. Then, when the foaming phenomenon began to sink gradually, the electricity supply was stopped after 40 minutes from the start of energization, while the operation of raising the applied voltage was repeated. The value was not adjusted at all.

(4) results

The surface roughness (R) and the micro-Vickers hardness (Hv) of five points on the surface of each specimen obtained by the above experiments were measured, and the average values of the results are shown in Table 1.

TABLE 1

Kind of A1 alloy 5052 alloy 6061 alloy 7071 alloy ADC12 R (μmm) Surface of specimen after treatment 0.572 0.610 0.394 0.683 Surface of the test before treatment Both surface roughness (R) is 3 ~ 4 Hv Surface of specimen after treatment 898.6 1042.5 862 951.2 Surface of the test before treatment 132.1 133 128.3 134.4

As can be seen from Table 1, the surface of each specimen was changed to a very flat surface with a surface roughness (R) of 3 to 4 μm before treatment and a surface roughness (R) of 0.7 μm or less after treatment, and its hardness was also significantly larger than before treatment. Improved.

On the other hand, the thickness of the plasma electrolytic oxide film of each specimen was about 10㎛ and the thin film X-ray diffraction was performed on the plasma electrolytic oxide film of each specimen was confirmed that all basically composed of α-Al ₂ O ₃ .

Although the above-described embodiments have been described with respect to the most preferred examples of the present invention, it is not limited to the above embodiments, and various modifications are possible within the scope without departing from the technical spirit of the present invention. It is evident to those who have knowledge of.

According to the ceramic coating method for producing an aluminum material according to the present invention as described above, α-Al ₂ O ₃ is used as the main component by subjecting the surface layer of the substrate to electrolytic oxidation under high voltage and low current. The aluminum material in which the plasma electrolytic oxide film whose surface roughness R is 1.0 micrometer or less is formed.

 The aluminum material produced as described above has an effect of being able to be used as a sliding material that does not require oil under high heat or corrosion environment due to its low coefficient of friction and excellent sliding properties, and excellent heat resistance and corrosion resistance.

1 is a view showing a cross-sectional structure in the surface layer portion of the aluminum material according to the present invention.

2 is a view showing the surface of the plasma electrolytic oxide film formed by the ceramic coating method of the aluminum material according to the present invention.

3 is a schematic view showing one embodiment of an apparatus for producing an aluminum material according to the present invention.

Figure 4 is a plan view showing an embodiment of the arrangement relationship between the anode electrode and the cathode electrode adopted in the method for producing a ceramic coating of aluminum material according to the present invention.

Figure 5 is a plan view showing another embodiment of the arrangement relationship between the anode electrode and the cathode electrode adopted in the method for producing a ceramic coating of aluminum material according to the present invention.

Figure 6 is a view showing an embodiment of the anode pulse mode (A mode) of the current adopted in the method of manufacturing a ceramic coating of aluminum material according to the present invention.

7 is a view showing an embodiment of the cathode pulse mode (C mode) of the current adopted in the method of manufacturing a ceramic coating of aluminum material according to the present invention.

8 is a view showing an embodiment of the AC pulse mode (AC mode) of the current adopted in the method of manufacturing a ceramic coating of aluminum material according to the present invention.

9 is a view for explaining the regulation of the applied voltage adopted in the method of manufacturing a ceramic coating of aluminum material according to the present invention.

<Description of the symbols for the main parts of the drawings>

1: electrolyzer 2. electrolyte

3. Base material (anode pole) 4. Cathode pole

5a, 5b. Piping 6. Acid Board

Claims (9)

The temperature is maintained at 10 to 40 ° C., pH 7.9 to 1 to 3 g / L alkali metal hydroxides, 2 to 5 g / L alkali metal silicates, and 2 to 6 g / L alkali metalporinates. The anode electrode 3 made of aluminum or an aluminum alloy base material and the cathode electrode 4 made of stainless steel are dipped into the electrolytic cell 1 containing the alkaline electrolyte solution 2 of 8.8, and then the anode electrode 3 and In the method of producing a plasma electrolytic oxide film on the surface layer of a base material by energizing the cathode electrode 4 with the alternating current of the pulse mode consisting of an anode pulse mode and a cathode pulse mode, Current value = D S / n. … … … … … … … … … … … … … … … … … … … Formula (1)         (Where D is the current density, S is the surface area of the substrate, and n is the number of 3 or more) The current value is calculated by Equation (1) to start the energization, after which the energization state is continued without adjusting the current value until the end of the energization, and the voltage is applied to the anode pole by intermittently adjusting the voltage during the energization process. The effective voltage value is always 450V or more, wherein the pulse mode is 50 or 60 Hz and the current density (D) is 5 to 30 A / dm ² , and the pulse mode is that the amount of power in the anode pulse mode is greater than that in the cathode pulse mode. Ceramic coating method of the aluminum material characterized in that. delete The method of claim 1, The pulse mode is a method of manufacturing a ceramic coating of aluminum, characterized in that the ON time of the anode pulse mode longer than the ON time of the cathode pulse mode. The method of claim 1, The method of manufacturing a ceramic coating made of aluminum, characterized in that four surfaces of the anode electrode (3) are surrounded by four cathode electrodes (4). The method of claim 1, The alkali metal hydroxide is KOH ceramic coating method, characterized in that the KOH. The method of claim 1, The alkali metal silicate is Na ₂ SiO ₂ The ceramic coating method of the aluminum material, characterized in that. The method of claim 1, The alkali metal polyphosphate salt is a ceramic coating method of the aluminum material, characterized in that any one of Na ₄ P ₂ O ₇ , Na ₂ PO ₄ , Na ₆ P ₆ O ₁₈ . The method of claim 1, The n is a ceramic coating method of manufacturing an aluminum material, characterized in that 3 to 7. In the aluminum or aluminum alloy produced by the ceramic coating method of the aluminum material according to claim 1, a plasma electrolytic oxide film having α-Al ₂ O ₃ as a main component and a surface roughness R of 1.0 μm or less is formed on the surface layer of the substrate. Aluminum material with high hardness, good corrosion resistance, good sliding and high hardness.