KR102170244B1 - Coating method for inorganic polysilazane on the surface of magnesium alloy and magnesium alloy formed thereby - Google Patents

Abstract

The present invention relates to a coating method and an alloy formed thereby, and more specifically, by plasma electrolytic oxidation treatment on the surface of a magnesium alloy, and then applying inorganic polysilizane to improve the hardness and prevent fingerprints while maintaining the natural texture of the magnesium alloy metal. It relates to a method of coating an inorganic polysilazane on a surface of a magnesium alloy, and a magnesium alloy formed thereby.
To this end, the present invention provides a surface treatment step for plasma electrolytic oxidation treatment of a magnesium alloy surface by applying a + voltage and a-voltage to the magnesium alloy oppositely disposed in an electrolytic cell containing an electrolyte solution; A paint coating step of applying a paint containing inorganic polysilazane on the surface of the magnesium alloy subjected to plasma electrolytic oxidation through the surface treatment step; And a paint curing step of curing the paint applied on the magnesium alloy through the paint application step.

Description

Inorganic polysilazane coating method on the surface of magnesium alloy, and magnesium alloy formed by the method {COATING METHOD FOR INORGANIC POLYSILAZANE ON THE SURFACE OF MAGNESIUM ALLOY AND MAGNESIUM ALLOY FORMED THEREBY}

The present invention relates to a coating method and an alloy formed thereby, and more specifically, by plasma electrolytic oxidation treatment on the surface of a magnesium alloy, and then applying inorganic polysilizane to improve the hardness and prevent fingerprints while maintaining the natural texture of the magnesium alloy metal. It relates to a method of coating an inorganic polysilazane on a surface of a magnesium alloy, and a magnesium alloy formed thereby.

In general, magnesium alloys are lightweight and high-strength, so their application range has been greatly expanded in recent years, but they have a weakness in that they are easy to corrode due to their high chemical reactivity, and various surface treatment methods have been applied to solve this problem.

Among them, anodizing is the most common method, but since the anodic oxidation film has a thin thickness and low hardness, it is easy to break, so recently Plasma Electrolytic Oxidation (PEO) has replaced anodic oxidation. It is attracting attention as a new means to do.

PEO is a method of obtaining a dense and hard corrosion-resistant oxide film with a thickness of up to several hundred μm by applying a much higher voltage/current than anodization.It is much more environmentally friendly than anodic oxidation because it uses a low concentration neutral/alkali electrolyte instead of poisons such as sulfuric acid or chromic acid.

Because the quality of the PEO film is determined by the composition of the alloy, the type of electrolyte, electrical variables (type/mode of power source, strength of current/voltage, frequency, duty cycle, etc.), temperature of the electrolyte, reaction time, and type of additives. , By appropriately adjusting these conditions, it is aimed at providing excellent corrosion resistance to the film by removing or minimizing micropores or microcracks, and providing abrasion resistance by increasing the hardness of the film, while reducing frictional resistance.

However, even after the magnesium alloy has been PEO-treated as described, many studies are still needed to expand its application range in consideration of the characteristics of various industrial fields.

Korean Patent Publication No. 10-1451412 Korean Patent Publication No. 10-0931258

Journal of the Korean Metals and Materials Society (Korean J. Met. Mater.), Vol. 55, No. 5 (2017), pp. 296~307

The present invention was conceived to solve the problems of the prior art, and by applying an inorganic polysilizane after plasma electrolytic oxidation treatment on the surface of a magnesium alloy, it is possible to improve hardness and prevent fingerprints while maintaining the natural texture of the metal. It is an object of the present invention to provide a method of coating an inorganic polysilazane on a surface of a magnesium alloy and a magnesium alloy formed thereby.

In order to achieve the above object, the present invention provides a surface treatment step for plasma electrolytic oxidation treatment of a magnesium alloy surface by applying a + voltage and a-voltage to the magnesium alloy oppositely disposed in the electrolytic cell containing the electrolyte; A paint coating step of applying a paint containing inorganic polysilazane on the surface of the magnesium alloy subjected to plasma electrolytic oxidation through the surface treatment step; It characterized in that it comprises a; paint curing step of curing the paint applied on the magnesium alloy through the paint coating step.

In addition, after the surface treatment step, it further includes an edge cutting step of cutting the edge of the panel-shaped magnesium alloy subjected to plasma electrolytic oxidation treatment, and the + voltage applied in the surface treatment step is 400V~1KV, and the electrolytic cell used The outer surface is characterized by being surrounded by a conductor.

In addition, in the surface treatment step, an electrolyte stirring step of stirring the electrolyte with a stirrer to facilitate plasma electrolytic oxidation treatment on the surface of the magnesium alloy, and temperature sensing of the electrolyte solution to achieve a uniform plasma electrolytic oxidation treatment on the surface of the magnesium alloy It characterized in that it comprises a step of cooling the electrolyte to keep it constant through the sensor and the cooler.

In addition, the paint application step includes the steps of horizontally disposing a magnesium alloy subjected to plasma electrolytic oxidation in a spin coater, and entirely applying a paint containing inorganic polysilazane on a surface of the magnesium alloy disposed in the spin coater, Including the step of sealing the coated magnesium alloy and the spin coater with a cover, and rotating the surface of the coated magnesium alloy with a spin coater, or plasma electrolytic oxidation treatment according to a dip coating method The resulting magnesium alloy is immersed in the paint, and 0.1 ml to 4.0 ml of the paint is applied per 10 cm ² of the magnesium alloy treated with plasma electrolytic oxidation.

In addition, in the coating material curing step, the coating material applied on the magnesium alloy is cured for 50 to 80 minutes in an atmosphere of 110°C to 130°C.

The inorganic polysilazane coating method on the surface of the magnesium alloy according to the present invention as described above and the magnesium alloy formed thereby are subjected to plasma electrolytic oxidation treatment on the surface of the magnesium alloy and then coated with inorganic polysilazane to preserve the natural texture of the metal while maintaining the hardness. Enhancement, fingerprint prevention, etc. can be enabled.

1 is a flow chart showing an inorganic polysilazane coating method on the surface of a magnesium alloy according to the present invention
2 is a diagram showing a schematic structure for a PEO reaction
3 is a diagram showing a PEO reaction phenomenon according to a change in voltage/current
4 is a diagram showing the generation and change of an oxide film in a PEO reaction process
5 is a diagram showing the chemical structure of an inorganic polysilazane
6 is a diagram showing a curing mechanism of inorganic polysilazane
7 is a view showing the structure when the substrate surface and inorganic polysilazane are combined
8 is a schematic diagram showing a state in which a paint is coated on a PEO-treated magnesium alloy according to the present invention
9 is a photograph taken by SEM of the surface of the magnesium alloy of the present invention according to the coating amount

The terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Accordingly, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention, and do not represent all the technical ideas of the present invention, so that they can be replaced at the time of application It should be understood that there may be various equivalents and variations.

Hereinafter, a method of coating an inorganic polysilazane on a surface of a magnesium alloy according to the present invention and a magnesium alloy formed thereby will be described with reference to the drawings.

1 is a flowchart illustrating a method of coating inorganic polysilazane on a surface of a magnesium alloy according to the present invention.

The inorganic polysilazane coating method on the surface of the magnesium alloy according to the present invention basically includes a surface treatment step, a paint application step, and a paint hardening step.

More specifically, the inorganic polysilazane coating method on the surface of the magnesium alloy according to the present invention applies a + voltage and a-voltage to the magnesium alloy oppositely disposed in the electrolytic cell containing the electrolyte, thereby plasma electrolytic oxidation (PEO: Plasma). Through a surface treatment step for electrolytic oxidation) treatment, a paint application step of applying a paint containing inorganic polysilazane on the surface of the magnesium alloy treated with plasma electrolytic oxidation through the surface treatment step, and a paint application step. It comprises a paint hardening step of hardening the paint applied on the magnesium alloy.

2 is a diagram showing a schematic structure for a PEO reaction, FIG. 3 is a diagram showing a PEO reaction phenomenon according to a change in voltage/current, and FIG. 4 is a diagram showing the generation and change of an oxide film in the PEO reaction process. .

The mechanism of PEO treatment on the magnesium alloy in the surface treatment step will be described below with reference to Non-Patent Document 1 and FIGS. 2 to 4.

PEO is a kind of electrolytic reaction as shown in FIG. 2, and the anode generates oxygen (O ^2- → O ₂ ), electrode metal dissolution (Me ⁰ → Me ⁿ⁺ ), and metal oxide generation (Me ⁿ⁺ + O). ^2- → MeO) reaction occurs, and hydrogen generation (2H ⁺ → H ₂ ) in the cathode, and cation precipitation (Cat ^{n +} → Cat ⁰ ) in the electrolyte occurs.

3 and 4, two types of reactions occur in the electrode, one of which is the generation of gas (oxygen) indicated by ⓐ, and the other is the generation of oxide indicated by ⓑ, and FIGS. 4 corresponds to 1:1, so looking at it together, the 0-U ₄ section of ⓑ in FIG. 3 corresponds to FIG. 4 (a), that is, in the 0-U ₄ section where the voltage is relatively low, it is caused by the electrolysis of H ₂ O. Oxygen and Mg react to form a thin oxide film, and this oxide film does not cover the entire surface. When it reaches U ₄ , which corresponds to the corrosion potential, dissolution of the base metal occurs.

Section U ₄ -U ₅ of FIG. 3 ⓑ corresponds to the growth of the porous (column) oxide film in FIG. 4 (b), that is, when the voltage reaches the threshold U ₅ , the insulation of the oxide film is destroyed (dielectric breakdown) and the oxide film surface As shown in FIG. 4 (c) throughout, small sparks float quickly, and as U ₆ approaches, thermal ionization by high-temperature plasma begins, resulting in larger and slower arc discharge.

Sections U ₆ -U ₇ of FIG. 3 ⓑ correspond to FIG. 4 (d). After U ₆ , thermal ionization is partially suppressed due to negative charges accumulated in the thick oxide film, and a partial shorting with the metal base occurs. As the power is relatively reduced, the duration of the arc discharge becomes short, in other words, a micro-discharge, commonly referred to as a micro-arc, occurs.

The micro-arc gradually melts the oxide film, thereby causing elution, resolidification, and oxidation reactions of the base metal, and the oxide film gradually becomes thick and dense, and in this process, the surface becomes heterogeneous, and bubbles are trapped in the film to form a porous film. In this case, the incorporation of components of the electrolyte into the oxide film also occurs.

After U ₇ of FIG. 3 ⓑ, since the arc due to micro-discharge penetrates the film and reaches the metal base, it is converted into a strong arc, so that destructive phenomena such as thermal cracking of the film may occur.

Figure 4 (e) shows a three-layer structure film at the end of the PEO reaction, that is, a thin and dense inner layer at the matrix/oxide interface called a barrier layer, and a relatively dense intermediate layer ( functional layer) and a fragile outer layer (technology layer) with a large number of micropores and microcracks, but there are cases where the outer layer is not visible, and the A-type, B-type, and C-type discharges It refers to a discharge near the surface, a discharge reaching a metal matrix, and a discharge in micropores, respectively.

For reference, arc discharge means that hot electrons are discharged from the part corresponding to the cathode of the electrode, and the electrode and the cathode are connected to the plasma, so that the voltage decreases and the current increases rapidly.At this time, the shape of the plasma becomes an arc ( Arc) is called arc discharge and means the final form of gas discharge.

In the surface treatment step, the + voltage applied to the magnesium alloy for the PEO reaction may be preferably set to 400V~1KV. For example, below 400V, the oxide film is formed in the 0-U ₄ section of ⓑ in FIG. This is because even if this is not achieved or only a thin oxide film is formed or a thin oxide film is formed, the entire surface of the magnesium alloy cannot be covered, and the magnesium alloy exceeding 1KV may be severely damaged.

In addition, the outer surface of the electrolyzer used in the surface treatment step may be surrounded by a conductor, which prevents electromagnetic waves harmful to the human body from leaking out of the electrolyzer when a high voltage such as 400V~1KV is applied to the magnesium alloy in the electrolyzer. This is to provide a function of facilitating grounding when high voltage flows out of the electrolyzer.

In addition, the surface treatment step includes a stirring step of stirring the electrolyte with a stirrer to facilitate plasma electrolytic oxidation treatment on the surface of the magnesium alloy, so that a difference in concentration of the electrolyte may be prevented from occurring during PEO treatment.

As a constant temperature is also an important condition for an important PEO reaction, the surface treatment step includes an electrolyte cooling step of maintaining a constant temperature of the electrolyte through a temperature sensor and a cooler so that a uniform plasma electrolytic oxidation treatment is performed on the surface of the magnesium alloy. Accordingly, the temperature sensor detects a situation in which the temperature of the electrolyte solution increases during the PEO reaction, and operates the cooler to maintain the temperature of the electrolyte solution in the electrolyzer at a certain level.

In addition, after the surface treatment step, an edge cutting step of cutting the edge of the panel-type magnesium alloy subjected to plasma electrolytic oxidation treatment may be further included, and this edge cutting step is mainly performed on the edge of the magnesium alloy during the PEO treatment. This is performed to ensure the quality of the PEO-treated magnesium alloy in consideration of the fact that a crack may occur in the edge due to the occurrence of discharge.

In the paint application step, in particular, a paint containing inorganic polysilazane is used, and the description of the inorganic polysilazane is as follows.

5 is a diagram showing the chemical structure of an inorganic polysilazane.

Polysilazane is classified into inorganic polysilazane and organic polysilazane depending on the presence or absence of carbon in a functional group (methyl, vinyl group) substituted on Si or N atoms. Until now, organic-inorganic polysilazane It is mainly used as a ceramic precursor to form silicon, silicon nitride, and silicon nitride carbide layers, and it is possible to form a thin film relatively easily by a solution process, and the yield is 80% or more after high-temperature pyrolysis at 1,000℃ or higher, saving process cost and time. There is an advantage of being. In addition, it has excellent adhesion to the substrate, so it can be applied to various substrates, and has excellent features such as scratch resistance, corrosion resistance, chemical resistance, heat resistance, and durability.

In particular, inorganic polysilazane (Perhydropolysilazane) has a molecular structure of Si-N, Si-H, and NH, so it easily reacts with surrounding oxygen and moisture during high-temperature heat treatment or moist heat treatment, resulting in glass and glass by thermal decomposition or hydrolysis. Since it can be converted to SiO ₂ with similar properties, it is transparent and has high density, high hardness, chemical resistance and optical properties compared to organic silanes such as TMO (Tetramethyl orthosilicate) or TEOS (Tetraethyl orthosilicate) after conversion to a silica film. In recent years, it is expanding its application range to automobiles, textiles, coatings, ceramic composite materials, and aerospace industries.

The paint application step includes horizontally placing a plasma electrolytically oxidized magnesium alloy in a spin coater, applying a paint containing inorganic polysilazane as a whole on the surface of the magnesium alloy disposed in the spin coater, and It may include sealing the coated magnesium alloy and the spin coater with a cover, and rotating the surface of the coated magnesium alloy with the spin coater.

In addition to the process as described in the coating coating step, a coating material may be applied by immersing a magnesium alloy subjected to plasma electrolytic oxidation according to a dip coating method in the coating material.

6 is a diagram showing a curing mechanism of inorganic polysilazane, and FIG. 7 is a diagram showing a structure when a substrate surface and inorganic polysilazane are combined.

6 and 7, when inorganic polysilazane meets oxygen (O ₂ ) and water vapor (H ₂ O) in the air, ammonia (NH ₃ ) and hydrogen (H ₂ ) gases fly away, while Si and O It has a net structure made of only rho, and when a paint containing inorganic polysilazane is applied to the surface of the PEO-treated magnesium alloy, a structure as shown in FIG. 7 is formed.

Here, in the coating process, it is preferable to apply 0.1 ml to 4.0 ml of the coating per 10 cm ² of the magnesium alloy treated with plasma electrolytic oxidation so that the coating is coated on the entire surface of the alloy and does not flow down.

According to the coating coating step as described above, if the PEO-treated magnesium alloy is horizontally seated on a spin coater, then the paint containing inorganic polysilazane is applied and the spin coater is rotated while sealing it with a cover. Compared to the method, the paint can be evenly applied on the PEO-treated magnesium alloy by centrifugal force.

8 is a schematic diagram showing a state in which a paint is coated on a PEO-treated magnesium alloy according to the present invention.

When the coating is passed through the curing step, the surface of the magnesium alloy is changed as shown in FIG. 8 to secure hardness, and has scratch resistance and fingerprint resistance.

And, in the paint curing step, the paint applied on the magnesium alloy is cured for 50 to 80 minutes in an atmosphere of 110°C to 130°C. In the case of natural drying, the paint applied on the magnesium alloy must be dried too long for several days and applied to the paint coating layer exceeding 130°C. As cracks may occur during the drying process, the above drying conditions are most preferable.

9 is a photograph taken by SEM of the surface of the magnesium alloy of the present invention according to the coating amount.

Referring to FIG. 9, (a) is an SEM photograph of the surface of the magnesium alloy without coating, and (b), (c), (d), and (e) are of the magnesium alloy having an area of 10 cm ² . This is a photograph taken by SEM after applying and passing 0.5 ml, 1.0 ml, 1.5 ml, and 2.0 ml of paint on the surface, respectively, and the surface condition of the magnesium alloy coated with inorganic polysilazane after PEO treatment according to the present invention is shown in SEM ( As a result of checking through Scanning Electron Microscopy), as shown in photos (b) to (e), while maintaining the original texture of the metal, it was possible to improve the surface hardness and secure the characteristics of fingerprint-free.

In the description of the present invention with reference to the accompanying drawings above, a specific shape and direction have been mainly described, but the present invention can be variously modified and changed by those skilled in the art, and such modifications and changes are included in the scope of the present invention. Should be interpreted as.

Claims (11)

A surface treatment step for plasma electrolytic oxidation treatment of the magnesium alloy surface by applying a + voltage and a-voltage to the magnesium alloy oppositely disposed in the electrolytic cell containing the electrolyte solution;
A paint coating step of applying a paint containing inorganic polysilazane on the surface of the magnesium alloy subjected to plasma electrolytic oxidation through the surface treatment step;
Including; a paint curing step of curing the paint applied on the magnesium alloy through the paint application step,
In the surface treatment step,
An electrolyte stirring step of stirring the electrolyte with a stirrer to facilitate plasma electrolytic oxidation treatment on the surface of the magnesium alloy; and
An electrolyte cooling step of maintaining a constant temperature of the electrolyte through a temperature sensing sensor and a cooler so that a uniform plasma electrolytic oxidation treatment is performed on the surface of the magnesium alloy,
After the surface treatment step, further comprising an edge cutting step of cutting the edge of the panel-type magnesium alloy subjected to plasma electrolytic oxidation,
The paint application step,
Placing a plasma electrolytically oxidized magnesium alloy horizontally in a spin coater,
Applying a coating material containing inorganic polysilazane as a whole on the surface of the magnesium alloy disposed in the spin coater; and
Sealing the magnesium alloy coated with the paint and the spin coater with a cover,
Inorganic polysilazane coating method on the surface of the magnesium alloy comprising the step of rotating the surface of the magnesium alloy coated with the paint with a spin coater.
delete The method according to claim 1,
Inorganic polysilazane coating method on the surface of the magnesium alloy, characterized in that the + voltage applied in the surface treatment step is 400V to 1KV.
The method according to claim 1,
Inorganic polysilazane coating method on the surface of the magnesium alloy, characterized in that the outer surface of the electrolytic bath used in the surface treatment step is surrounded by a conductor.
delete delete delete delete The method according to claim 1,
In the paint application step, the inorganic polysilazane coating method on the surface of the magnesium alloy, characterized in that 0.1 ml to 4.0 ml of the paint per 10 cm ² of the plasma electrolytic oxidation treatment is applied.
The method according to claim 1,
In the paint curing step, the inorganic polysilazane coating method on the surface of the magnesium alloy, characterized in that curing the paint applied on the magnesium alloy for 50 to 80 minutes in an atmosphere of 110 ℃ ~ 130 ℃.
Magnesium alloy formed by the method according to any one of claims 1, 3, 4, 9 and 10.

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