KR101618741B1 - Method for surface treatment of magnesium alloy sheet - Google Patents

Abstract

The present invention relates to a surface treatment method for improving the corrosion resistance of a magnesium alloy sheet material. According to an embodiment of the present invention, the magnesium alloy sheet material is cleaned using ultrasonic waves. Thereafter, the cleaned magnesium alloy plate material is placed in the reaction chamber, the pressure inside the reaction chamber is lowered to maintain the first vacuum state, a plasma is generated in the reaction chamber in the first vacuum state, The surface of the magnesium alloy sheet material is cleaned. Subsequently, the organic coating material is introduced into the reaction chamber in the second vacuum state, and the surface of the magnesium alloy plate cleaned with the organic coating material is coated by again generating plasma.

Magnesium alloy, Surface treatment, Coating, Corrosion resistance, Low vacuum, Plasma

Description

[0001] METHOD FOR SURFACE TREATMENT OF MAGNESIUM ALLOY SHEET [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method of a magnesium alloy sheet material, and more particularly, to a surface coating method of a magnesium alloy sheet material for suppressing surface corrosion of a magnesium alloy sheet material.

Magnesium alloy has excellent machinability, high vibration damping ability, excellent absorbency against vibration and impact, excellent electromagnetic wave shielding property, light weight, high non-strength, etc., and it is possible to form into thin plate from the viewpoint of processing.

Particularly, magnesium has a low specific gravity and a high specific strength in practical metals and is used in various industrial fields such as those used for manufacturing electronic parts and automobile parts through a casting method such as die casting.

In particular, the automotive industry is accelerating the development of related technologies in order to satisfy exhaust emission regulations according to the international environmental treaties centered on developed countries such as the United States, Japan, and Europe. In other words, one of the most practical techniques for dealing with emission regulation is vehicle lightening technology, and accordingly, the use of lightweight materials such as aluminum and magnesium is increasing to lighten the vehicle.

In general, when the vehicle is lightened by 1%, it is known that the fuel consumption is increased by 1%. The light weight of the vehicle plays an important role in improving the fuel efficiency. Thus, in order to improve the fuel efficiency and reduce the exhaust gas emission, It is recognized as an important technology in the industrial field.

Most of the magnesium alloy, AZ91 magnesium alloy, which is a casting material having aluminum and zinc contents of about 9% by weight and about 1% by weight, respectively, is present. However, recently, aluminum and zinc contents are about 3% by weight and about 1% As a result of the production of AZ31 magnesium alloy sheet, there is a growing interest in the development of automobile parts using rolled materials.

The AZ31 magnesium alloy has many advantages over the AZ91 alloy because of its high mechanical strength and relatively easy molding. However, all magnesium alloys have a disadvantage that they are highly active metals among practical metals and easily corroded in the presence of air and humidity.

Therefore, surface treatment is indispensable to suppress the corrosion of the magnesium alloy. Specifically, the final step of the magnesium alloy product is painted to secure corrosion resistance, or to improve the corrosion resistance through surface treatment such as chemical treatment, anodic oxidation, plating, and coating.

However, such a corrosion-resistant surface treatment is a surface treatment method for connection with an article, and it is difficult to apply the surface treatment method for temporary anticorrosion which occurs in the distribution process of the magnesium alloy in terms of the treatment cost and the post- .

In addition, the wet process of chemical conversion treatment, anodic oxidation, and plating is difficult to treat the waste liquid generated during the process and has a large burden of environmental pollution. In order to solve the environmental problem, the method using the discharge in the electrolyte solution also consumes a large amount of power It has disadvantages. In addition, the dry coating has a disadvantage that the vacuum exhausting and coating process is relatively expensive, and the processing area is limited.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface treatment method for improving the corrosion resistance of a magnesium alloy sheet material.

According to an embodiment of the present invention, there is provided a method for surface treatment of a magnesium alloy plate, the method comprising: an ultrasonic cleaning step of washing a magnesium alloy plate using ultrasonic waves; a step of positioning the washed magnesium alloy plate in a reaction chamber, A plasma cleaning step of keeping the magnesium alloy sheet material in a first vacuum state and generating a plasma in the reaction chamber in the first vacuum state to clean the surface of the magnesium alloy sheet material; Coating the surface of the magnesium alloy sheet washed with the organic coating material by introducing the magnesium alloy sheet into the chamber and again generating plasma.

In the polymer coating step, the organic coating material may flow into the reaction chamber of the second vacuum state and be spontaneously vaporized, wherein the organic coating material may be toluene. Further, the organic coating material may be heated and vaporized and then introduced into the reaction chamber in the second vacuum state.

The washing of the magnesium alloy sheet material in the ultrasonic cleaning step may be performed in acetone and pure water. In the plasma cleaning step, the reaction chamber may be maintained in the first vacuum state by using a rotary pump And oxygen gas may be used as a plasma forming gas for generating the plasma in the plasma cleaning step.

In the polymer coating step, an RF power of 150 W or more may be supplied to generate the plasma, and the pressure in the first vacuum state and the pressure in the second vacuum state may be 10 ^-3 Torr and 0.5 Torr, respectively.

According to the embodiment of the present invention, the corrosion resistance of the magnesium alloy sheet material can be improved while simplifying the surface treatment process.

In addition, productivity can be improved through rapid surface treatment process speed, and environmental pollution problems can be suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be easily understood by those skilled in the art.

FIG. 1 is a flow chart showing a method of surface-treating a magnesium alloy sheet according to an embodiment of the present invention, and shows a process of performing polymer coating on the surface to improve the corrosion resistance of the magnesium alloy sheet. FIG. FIG. 2 is a schematic configuration diagram of a low-vacuum polymer coating apparatus that performs surface treatment of a magnesium alloy sheet according to an embodiment. FIG.

Referring to FIG. 1, a method of surface-treating a magnesium alloy sheet according to an embodiment of the present invention includes ultrasonic cleaning of a magnesium alloy sheet material (S10), charging a washed magnesium alloy sheet into a reaction chamber, (S20) and performing a polymer coating through a low vacuum plasma polymerization process (S30).

The step S10 of ultrasonic cleaning the magnesium alloy sheet material is a step for removing contaminants and the like on the surface of the magnesium alloy sheet material. In this embodiment, acetone and pure water may be used in ultrasonic cleaning, but the present invention is not limited thereto .

The ultrasonically cleaned magnesium alloy sheet is subjected to a cleaning step (S20) and a polymer coating step (S30) in a low vacuum polymer coating apparatus.

Referring to FIG. 2, the low-vacuum polymer coating apparatus according to the present embodiment includes a reaction chamber 1, a vacuum pump 2, a valve for low-vacuum exhaust 15, a RF power supply 3, (4) and a shower ring (6). In addition, the low-vacuum polymer coating apparatus includes a coating material storage unit 7, a mixing gas storage unit 8, a pretreatment gas storage unit 9, a coating material conditioner 10, a mixing gas conditioner 11 A pretreatment gas regulator 12, a nitrogen gas reservoir 13, and a nitrogen gas valve 14.

The ultrasonically cleaned magnesium alloy sheet material is charged into the reaction chamber 1 and placed on the electrode 4. Then, the reaction chamber 1 is closed, and the vacuum pump 2 is used to evacuate to a vacuum degree as low as possible through the low vacuum exhaust pump 15. [ In this embodiment, the inside of the reaction chamber 1 is evacuated to a vacuum of about 10 ^-3 Torr by using the vacuum pump 2. In this embodiment, since a low vacuum state is used, a low vacuum rotary pump is used, and a device for maintaining a high vacuum state is not required, so that the entire configuration can be simplified.

When vacuum exhaust is completed up to the limit of the vacuum pump 2 and a low vacuum state is formed, the gas is used as a pretreatment gas from the pretreatment gas reservoir 9 through the pretreatment gas regulator 12 into the reaction chamber 1 Oxygen gas is supplied. At this time, the oxygen gas flows into the reaction chamber 1 through the shower ring 6. Then, power is supplied through the RF power supply 3 to generate plasma, and the generated plasma is used for cleaning for a predetermined time according to the state of the magnesium plate. On the other hand, in this embodiment, oxygen is used as the pretreatment gas in the cleaning step S20, but the present invention is not limited thereto.

After the cleaning step S20, the oxygen gas supply is stopped, and a polymer coating step S30 is performed to coat the surface of the magnesium alloy plate 5.

The coating material is supplied from the mixing gas reservoir 8 in which the coating material is prepared and the auxiliary helium gas for plasma activation is prepared through the coating material controller 11 and the mixing gas controller 12, Into the reaction chamber 1. At this time, the coating material gas and the mixing gas are introduced into the reaction chamber 1 through the shower ring 6.

Meanwhile, in this embodiment, the coating material is formed of an organic material in a liquid state, and a material having a low boiling point at a low pressure may be used as a liquid organic material. In this case, the organic substances in the liquid state are introduced into the reaction chamber 1 in a low vacuum state and naturally vaporized to be coated on the magnesium alloy plate 5. (Not shown) capable of heating the coating material reservoir 11 may be installed if the boiling point of the liquid organic material is not sufficiently low enough to cause spontaneous vaporization in the reaction chamber 1 in a low vacuum state . In this case, the organic substances in the liquid state are vaporized by being heated through the additional heating system, and can be introduced into the reaction chamber 1 in a low vacuum state in a gaseous state and coated on the magnesium alloy plate. Thus, the organic coating material can be vaporized and supplied stably by using a liquid organic material having a low boiling point at a low pressure as a coating material or additionally providing a heating system.

When the coating material and the mixing gas are stably supplied, power is supplied through the RF power supply 3 to generate a plasma, whereby a coating film on the polymer is formed on the magnesium alloy sheet material 5 to be treated . At this time, the corrosion resistance of the coated surface of the magnesium alloy sheet material can be determined according to the magnitude of the RF power supplied through the RF power supply 3. In this embodiment, RF power of 150 W or more is supplied in order to obtain corrosion resistance higher than a certain level .

When the coating progresses for a predetermined time, the power supply from the RF power supply 3 is sequentially stopped, and the supply of the coating material and the mixing gas is stopped. Thereafter, nitrogen gas is introduced into the reaction chamber 1 through the nitrogen gas valve 14 in the nitrogen gas storage part 13 to convert the internal pressure of the reaction chamber 1 to atmospheric pressure. Then, the magnesium alloy plate material (5).

3A and 3B are diagrams showing the surface structure of the magnesium alloy sheet before and after the polymer coating. Referring to FIG. 3A and FIG. 3B, on the magnesium alloy sheet having the magnesium natural oxide film 16 formed thereon, ) Are formed.

As described above, according to the surface treatment method of the magnesium alloy sheet according to this embodiment, the process can be simplified without using the high vacuum exhaust system, and the liquid organic material that can be spontaneously vaporized in a low vacuum state due to low boiling point at low pressure can be coated By using the polymer coating as a material, the process can be carried out easily and quickly.

[Experimental Example]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the results of experiments conducted in accordance with an embodiment of the present invention.

In this experiment, AZ31 magnesium alloy sheet was used to fabricate test specimens. Ultrasonic washing was performed for 5 minutes in acetone and pure water, respectively. After the ultrasonic cleaning, the test piece was charged into a reaction chamber in a low vacuum state. The inside of the reaction chamber was evacuated to a low vacuum state of 10 ^-3 Torr by using a rotary pump. After exhausting to the pressure, 10 sccm flow rate, and a power of 250 W was supplied to the RF power supply to generate plasma, which was then cleaned for 5 minutes.

After stopping the supply of the RF power source and stopping the supply of the oxygen gas, helium gas was supplied at a flow rate of 10 sccm, and the coating material was supplied to maintain the vacuum degree at 0.5 Torr. At this time, toluene was used as a coating material.

After the completion of the coating process, the supply of power and gas was stopped, nitrogen gas was introduced into the reaction chamber to regulate the pressure inside the reaction chamber to atmospheric pressure, Was recovered.

Vacuum pretreatment
(Cleaning step) Coating material RF  power Helium flow rate Vacuum degree Coating time 250W

O2 10 sccm

5min toluene 50W 10 sccm 0.5 Torr 3min 150W 300W

Table 1 shows the process conditions for the polymer coating in this experiment, and it was compared with the case where the RF power was not supplied by repeatedly changing the RF power of the coating to 50W, 150W, and 300W.

Fig. 4 is a photograph showing the results of the saline spray test on the recovered test specimens. Fig. 4 shows photographs before and after spraying each of the samples when 50 W, 150 W and 300 W were supplied without RF power supply. It can be seen that the corrosion resistance of the surface of the magnesium alloy sheet is improved when the RF power is supplied and the plasma is used to coat the test piece which is not supplied with the RF power. In particular, when the RF power is supplied at 150 W and 300 W And the corrosion resistance is remarkably improved.

As described above, according to the present invention, corrosion resistance can be improved by forming and coating an RF plasma in a vacuum state of a magnesium alloy plate subjected to cleaning and cleaning, and the process can be simplified and the production speed can be improved. Further, unlike the conventional wet surface treatment process, there is no problem of environmental pollution because no solution is used.

Although the present invention has been described by way of preferred embodiments with reference to the accompanying drawings, the present invention is not limited to the above embodiments. That is, those skilled in the art can easily understand that various modifications and variations are possible without departing from the scope and spirit of the following claims.

1 is a flowchart showing a method of coating a surface of a magnesium alloy sheet according to an embodiment of the present invention.

2 is a schematic block diagram of a low-vacuum polymer coating apparatus according to an embodiment of the present invention.

FIG. 3 is a view showing the structure of a magnesium alloy sheet surface before and after a polymer coating according to an embodiment of the present invention. FIG.

4 is a photograph showing a result of evaluation of corrosion resistance according to an embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

1: reaction chamber 2: vacuum pump

3: RF power supply 4: Electrode

5: Magnesium alloy plate 6: Shower ring

7: coating material storage part 8: mixing gas storage part

9: pretreatment gas reservoir 10: coating material conditioner

11: Mixing gas regulator 12: Pretreatment gas regulator

13: Nitrogen gas storage part 14: Nitrogen gas valve

15: Low vacuum exhaust valve 16: Magnesium natural oxide film

17: polymer coating film

Claims (9)

An ultrasonic washing step of washing the magnesium alloy plate using ultrasonic waves; The method of claim 1, further comprising: placing the washed magnesium alloy sheet material in a reaction chamber, lowering a pressure inside the reaction chamber to maintain the first vacuum state, generating a plasma in the reaction chamber in the first vacuum state, A plasma cleaning step of cleaning the surface of the alloy sheet material; And A polymer coating step of flowing an organic coating material into the reaction chamber in a second vacuum state and coating the surface of the magnesium alloy sheet cleaned with the organic coating material by generating a plasma; Lt; / RTI > Wherein oxygen gas is used as a plasma composition gas for generating the plasma in the plasma cleaning step. The method of claim 1, In the polymer coating step, the organic coating material flows into the reaction chamber in the second vacuum state and is spontaneously vaporized. 3. The method of claim 2, Wherein the organic coating material is toluene. The method of claim 1, In the polymer coating step, the organic coating material is heated and vaporized and then introduced into the reaction chamber in the second vacuum state. The method of claim 1, Wherein the cleaning of the magnesium alloy sheet material in the ultrasonic cleaning step is performed in acetone and pure water. The method of claim 1, Wherein in the plasma cleaning step, the reaction chamber is maintained in the first vacuum state by using a rotary pump. delete The method of claim 1, Wherein the plasma is generated by supplying an RF power of 150 W or more in the polymer coating step. The method of claim 1, Wherein the pressure of the first vacuum state in the plasma cleaning step is 10 ^-3 Torr and the pressure of the second vacuum state in the polymer coating step is 0.5 Torr.

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