KR101612707B1 - Eco-Friendly Chemical Conversion Treatment Methods of Magnesium Alloy - Google Patents

Abstract

The present invention relates to an environmentally friendly conversion treatment method of a magnesium alloy. The present invention provides an environmentally friendly conversion treatment method in which desired physical properties of a magnesium alloy are maintained without discharging a harmful substance. The environmentally friendly conversion treatment method of a magnesium alloy includes: a degreasing step of degreasing the magnesium alloy using ultrasonic waves after depositing the magnesium alloy in a degreasing solution; an etching step of etching the magnesium alloy using an etchant after the degreasing step is completed; a desmut step of performing a desmut process using a desmut solution after the etching step is completed; a conversion treatment step of performing conversion treatment during one to five minutes using a conversion treatment solution containing 3-6 wt% of sodium hydoxide, 6-12 wt% of phosphoric acid, 3-8 wt% of vanadium pentoxide, and 74-88 wt% of distilled water, after the desmut step is completed; a surface adjustment step of adjusting the surface using a surface adjustment solution after the conversion treatment step is completed; and a drying step of drying the magnesium alloy with hot air after the surface adjustment step is completed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an eco-friendly chemical conversion treatment method of Magnesium Alloy

The present invention relates to a process for treating an environmentally friendly magnesium alloy, and more particularly, to a process for chemical conversion of a magnesium alloy mainly used for parts for smart devices and the like, specifically an AZ91D magnesium alloy.

Since magnesium alloys generally have excellent mechanical properties to be used as structural materials, they have been widely used. Therefore, magnesium alloys have been widely used for parts and materials of transportation machines such as aircraft and automobiles. In recent years, Application to electric and electronic components has increased rapidly, and the use of magnesium alloys has been further expanded by the development of surface treatment methods to overcome corrosion resistance, which is the biggest disadvantage of magnesium alloys.

Furthermore, the demand for AZ91D magnesium alloy among the above magnesium alloys is continuously increasing due to widespread use of smart devices, but magnesium alloy itself is a thermodynamically active metal and rapidly corrodes from the surface due to oxygen and water molecules in the atmosphere The disadvantage is that the surface treatment technology for the method is becoming important.

Moreover, since magnesium has the lowest standard electrode potential among practical metals, corrosion resistance is very weak in all environments, and therefore, surface treatment for corrosion prevention is inevitable. In addition, surface treatment is also performed for the purpose of improving surface characteristics such as appearance and wear resistance of a product. The surface treatment process of such a magnesium alloy component is not limited to the use conditions such as surface conductivity, corrosion resistance, abrasion resistance, Whether or not other metals are assembled together, and the like. In general, processes such as chemical conversion treatment, anodic oxidation, electroplating, electroless plating and painting are becoming the means.

Among these methods, the most commonly used surface treatment methods are chemical treatment and anodic oxidation. All of the above surface treatment methods are carried out after pretreatment such as degreasing and pickling. Generally, after magnesium alloy parts are molded, they are pretreated for surface treatment, subjected to cleaning and surface conditioning treatment, .

Such a chemical conversion solution for magnesium alloy material, that is, a surface treatment solution, can be roughly divided into a chromate type and a non-chromate type.

Typical chromate type treatment liquids include a chromate chromate treatment liquid and a phosphoric acid chromating treatment liquid.

First, the chromate chromate-forming treatment liquid will be described.

The chromate chromate treatment liquid was put into practical use around 1950, and is still widely used for surface treatment of aircraft materials, building materials, and automobile parts.

This chromate chromate-imparting treatment liquid contains chromic acid and a fluoride as a reaction promoter as main components, and forms a chemical conversion coating containing hexavalent chromium on the surface of the metal material.

The chromate-phosphating solution is disclosed in U.S. Patent No. 2438877. It contains chromic acid, phosphoric acid, and hydrofluoric acid as its main components, and forms a chemical conversion coating mainly composed of chromium phosphate hydrated on the surface of the metal material do. Since this chemical conversion film does not contain hexavalent chromium, it is widely used for the coating treatment of beverage can lid materials and the like.

Although the chemical conversion coating formed by such a chromate type surface treatment liquid has excellent corrosion resistance and coating film adhesion property, since the harmful hexavalent chromium is contained in the treatment liquid, the treatment which does not contain any hexavalent chromium The use of liquids is required. With regard to the surface treatment liquid and the surface treatment method which do not contain hexavalent chrome, many inventions have been devised, but there are not so many techniques that are actually industrialized.

A typical example of the invention of the non-chromate type surface treatment liquid containing no chromium is the treatment liquid disclosed in Japanese Patent Laid-Open No. 52-131937.

The surface treatment liquid is an acidic aqueous coating solution containing zirconium or titanium or a mixture thereof, phosphoric acid and fluoride, and having a pH of about 1.5 to 4.0. When the surface of the metal material is treated using this surface treatment liquid, a chemical conversion film containing zirconium or titanium oxide as a main component is formed on the metal surface. This non-chromate type surface treatment liquid has an advantage that it does not contain hexavalent chromium and is widely used for surface treatment of aluminum can used in beverage cans such as beer.

Generally, it is a category of non-chromicizing agent called zirconium-based or titanium-based.

The treatment method disclosed in Japanese Patent Application Laid-Open No. 57-41376 is a method in which one or two or more kinds of titanium salts or zirconium salts, one or two or more kinds of imidazole derivatives, , An aqueous solution containing an oxidizing agent such as hydrogen peroxide, potassium permanganate or the like. The oxidizing agent promotes precipitation of titanium or zirconium. And is in the category of an improved technique of the non-chromium conversion agent called zirconium system or titanium system.

Examples of the non-chromate type treatment liquid include those disclosed in the following conventional techniques. Japanese Unexamined Patent Publication No. 56-136978 discloses a chemical conversion treatment solution comprising an aqueous solution containing a vanadium compound and at least one compound selected from the group of titanium salts, zirconium salts and zinc salts. Zirconium and vanadium combined with the titanium system.

Japanese Patent Application Laid-Open No. 2000-199077 discloses an acidic metal surface treatment liquid containing metal acetylacetonate, at least one compound selected from a water-soluble inorganic titanium compound and a water-soluble inorganic zirconium compound.

The treatment liquid is prepared by using vanadyl acetate, zirconium acetate, zinc acetate or the like, and the zirconium and the titanium-based compound are combined with the metal acetate.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method for environmentally friendly chemical conversion treatment while attracting physical properties of a desired magnesium alloy without discharging harmful substances.

The present invention
A degreasing step of degreasing the magnesium alloy by using ultrasound after immersing the magnesium alloy in the degreasing solution;
Etching with an etchant containing 3 to 8 wt% of NH ₄ HF _2, 3 to 8 wt% of NH ₄ OH, and 84 to 94 wt% of distilled water based on the total weight of the etchant after the defatting step is completed;
A desmutting step in which the etching step is finished and then desmutted into a desmut liquid;
After completion of the desmutting step, a solution containing 3 to 6% by weight of sodium hydroxide, 6 to 12% by weight of phosphoric acid, 3 to 8% by weight of vanadium pentoxide and 74 to 88% by weight of distilled water, A chemical conversion treatment step for chemical treatment for 1 to 5 minutes with the treatment liquid;
A surface adjusting step of surface-adjusting the surface adjustment liquid after the chemical conversion step is finished; And

And a drying step of hot air drying after the surface conditioning step is completed.

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According to the eco-friendly magnesium alloy treatment method of the present invention, a chemical conversion coating can be formed on a magnesium alloy substrate having high activity even by immersion treatment of an environmentally friendly method that does not discharge harmful substances, So that the electrical conductivity of the magnesium alloy can be maintained at 1.5 Ω or less.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing a method for chemical conversion treatment of a magnesium alloy according to the present invention. FIG.
FIG. 2 is a graph showing the results of XRD analysis of a coating layer of a magnesium alloy subjected to chemical conversion according to the present invention. FIG.
3 is a graph showing the results of a co-electromagnetically polarized test of the converted magnesium alloy according to the present invention.
4 is a view showing the evaluation results of an authorized testing institute for corrosion resistance of a magnesium alloy according to the present invention (Korea Construction & Living Environment Test Institute: KCL).
Fig. 5 is a view showing the evaluation results of an authorized testing institute (Korea Institute of Construction & Living Environment Test: KCL) for acid resistance of a magnesium alloy according to the present invention.
6 is a view showing the evaluation result of an authorized testing institution (KCL) of surface resistance of a magnesium alloy according to the present invention.
FIG. 7 is a view showing the evaluation result of an authorized testing institution (Korea Construction & Living Environment Test Institute: KCL) for adhesion of a magnesium alloy according to the present invention.

Hereinafter, the present invention will be described in detail.

The present invention relates to a degreasing step of degreasing a magnesium alloy by using ultrasonic waves after immersing the magnesium alloy in a degreasing solution; An etching step of etching the etching solution after the degreasing step is completed; A desmutting step in which the etching step is finished and then desmutted into a desmut liquid; After completion of the desmutting step, a solution containing 3 to 6% by weight of sodium hydroxide, 6 to 12% by weight of phosphoric acid, 3 to 8% by weight of vanadium pentoxide and 74 to 88% by weight of distilled water, A chemical conversion treatment step for chemical treatment for 1 to 5 minutes with the treatment liquid; A surface adjusting step of surface-adjusting the surface adjustment liquid after the chemical conversion step is finished; And a drying step of hot air drying after the surface conditioning step is completed.

The method for magnesium alloys formation treatment according to the present invention, in particular, an eco-friendly magnesium alloy formation treatment method, is characterized in that the surface of a magnesium alloy, a magnesium alloy specifically applied to a smart device such as an AZ91D magnesium alloy, , A surface treatment method that does not release harmful substances while maintaining physical properties such as conductivity, and the like, and is not particularly limited as long as it is a chemical conversion treatment method in a specific manner.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. However, the following description is only for the purpose of specifically describing the present invention and is not intended to limit the scope of the present invention by the following description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process diagram showing a method for chemical conversion treatment of a magnesium alloy according to the present invention. FIG.

As shown in FIG. 1, the chemical conversion treatment method, specifically the magnesium alloy conversion treatment method according to the present invention includes: a degreasing step of immersing a magnesium alloy in a degreasing solution and then degreasing it using ultrasonic waves;

An etching step of etching the etching solution after the degreasing step is completed;

A desmutting step in which the etching step is finished and then desmutted into a desmut liquid;

After completion of the desmutting step, a solution containing 3 to 6% by weight of sodium hydroxide, 6 to 12% by weight of phosphoric acid, 3 to 8% by weight of vanadium pentoxide and 74 to 88% by weight of distilled water, A chemical conversion treatment step for chemical treatment for 1 to 5 minutes with the treatment liquid;

A surface adjusting step of surface-adjusting the surface adjustment liquid after the chemical conversion step is finished; And

And a drying step of performing hot air drying after the surface conditioning step is completed.

Here, the magnesium alloy may be any conventional magnesium alloy, preferably an AZ91D magnesium alloy used in a smart device.

The degreasing step according to the present invention is a degreasing step that completely removes contaminants such as oxides, hydroxides, metal salts and / or oils adhering to the surface of a metal, specifically a magnesium alloy surface, and adheres to a metal surface and causes defective gloss, So that defects do not occur.

The degreasing step may be any method as long as the degreasing liquid is used to degrease the metal, specifically, the magnesium alloy.

The preferred degreasing method may include ultrasonic degreasing using ultrasound, and more preferably, degreasing performed by immersing the magnesium alloy for 3 to 10 minutes in a degreasing solution maintained in a temperature range of 50 to 100 캜.

At this time, the ultrasonic degreasing method using the ultrasonic waves can completely remove the oil penetrating the gap of the material made of the magnesium alloy.

If the degreasing time is less than 3 minutes, the oil penetrated into the fine gaps of the material during processing may remain, so oil-modified material may be formed on the surface and be changed to black. If the degreasing time exceeds 10 minutes, So that the foreign matter coming into the degreasing liquid is attached to the surface of the material again and is contaminated.

The degreasing solution may be any conventional degreasing solution. Preferably, the degreasing solution may contain 1 to 3% by weight of sodium hydroxide (NaOH) based on the total weight of the degreasing solution; 1.5 to 4% by weight of sodium carbonate (Na ₂ CO ₃ ), 0.001 to 0.01% by weight of a surfactant and 93 to 97% by weight of distilled water.

Here, the surfactant may be any of nonionic, cationic, and anionic surfactants.

Preferred surfactants include, but are not limited to, cocoamidopropyl betaine, lauryl betaine, capryl / capramidobetaine, monoalkyl phosphate, ethoxylated monoalkyl phosphate, alkylbenzenesulfonate salts or mixtures of at least one thereof But the present invention is not limited thereto.

The etching step according to the present invention is intended to prevent the adhesion of the plating from being poor due to the remaining thin oxide film and passive film on the surface of the magnesium alloy after the degreasing step.

Particularly, the etching step dissolves and removes the outermost surface layer, such as light contaminants such as machine oil and cutting oil, which can remain in the degreasing step, and the oxide film and the passive film, and removes the alkali remaining on the surface of the material, for example, The hydroxide layer formed during the degreasing can be neutralized.

The preferred etching step comprises treating the magnesium alloy having undergone the degreasing step with an etchant for 2 to 10 minutes at a temperature ranging from 50 to 100 < 0 > C.

The etchant is not particularly limited, but it is recommended that the etchant contains 3 to 8% by weight of NH ₄ HF _2, 3 to 8% by weight of NH ₄ OH, and 84 to 94% by weight of distilled water, based on the total weight of the etchant.

The desmutting step according to the present invention is used to enhance the adhesion of the plating film by reducing the surface tension between the magnesium alloy and the plating solution.

A preferred desmutting step comprises treating the magnesium alloy from which the etching step has been completed with a dismutant solution for 10 to 60 seconds at a temperature in the range of 50 to 100 占 폚.

The dismutant is not particularly limited, but it is recommended to use 5 to 10% by weight of sodium hydroxide (NaOH), 0.3 to 0.8% by weight of sodium fluoride (NaF), and _{4 to 6} % by weight of C ₄ H ₆ O ₆ 0.1 to 2.5% by weight and distilled water 87 to 93% by weight.

The chemical conversion treatment step according to the present invention is for improving the corrosion resistance of the magnesium alloy, and any chemical conversion treatment method commonly used in the art may be used for this purpose. Preferably, however, 3 to 6% by weight of sodium hydroxide (NaOH), 6 to 12% by weight of phosphoric acid (H ₃ PO ₄ ), 3 to 8% by weight of vanadium pentoxide (V ₂ O ₅ ) and And chemical treatment for 1 to 5 minutes with a chemical liquor containing 74 to 88% by weight of distilled water.

In this case, the conversion treatment temperature in the chemical conversion treatment step is not particularly limited, and is preferably carried out at room temperature. However, it is particularly preferably carried out in a temperature range of 23 to 27 ° C in the summer and 28 to 32 ° C in the winter season .

The surface conditioning step according to the present invention includes surface conditioning for 30 seconds to 2 minutes with the surface conditioning liquid after the chemical treatment step is finished.

The surface conditioning liquid may be any conventional surface conditioning liquid in the art, but preferably contains 2 to 6% by weight of sodium hydroxide (NaOH), ₆ % by weight of C ₆ H ₉ O ₇ Na 1 to 2.5% by weight and distilled water 92 to 96% by weight.

The drying step according to the present invention may be any drying method commonly used in the art.

It is preferable to use a hot air drying method in which the drying is carried out in a hot air drying, more preferably a temperature range of 120 to 180 ° C for 5 to 15 minutes.

Specifically, the magnesium alloys forming treatment method according to the present invention is characterized in that the degreasing step, the etching step, the dismutting step, the chemical treatment step and / or the surface adjusting step are additionally carried out by washing with water to the end of each step .

Here, the washing treatment step is used to remove the used solution from the magnesium alloy through each step.

Hereinafter, the present invention will be described in detail by way of examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[Example 1]

Firstly, an AZ91D magnesium alloy ingot, which had been subjected to a primary machining, was processed into 100 mm L x 50 mm W x 3 mm T, and then 15 g of NaOH, 22 g of Na ₂ CO ₃ , 0.05 ml of a surfactant containing monoalkyl phosphate and 962.95 g of distilled water were mixed Immersed in a degreasing solution, and degreased by ultrasonic treatment at a temperature of 75 캜 for 5 minutes.

The degreased magnesium alloy was then washed.

Then, the washed magnesium alloy was etched at a temperature of 70 ° C for 5 minutes with an etchant prepared by mixing 50 g of NH ₄ HF _2, 50 g of NH ₄ OH and 900 g of distilled water.

The etched magnesium alloy was then washed.

Then, the washed magnesium alloy was subjected to a dismantling process at a temperature of 70 DEG C for 30 seconds with a disodium salt solution prepared by mixing 80 g of NaOH, 5 g of NaF, 15 g of C ₄ H ₆ O ₆ and 900 g of distilled water.

Then, the desmutted magnesium alloy was washed.

Then, the washed magnesium alloy was chemically treated by immersing it in a chemical treatment solution prepared by mixing 48 g of NaOH, 90 ml of H ₃ PO ₄ , 50 g of V ₂ O ₅ and 812 g of distilled water at room temperature for 2 minutes.

Then, the converted magnesium alloy was washed.

Then, the washed magnesium alloy was surface-adjusted for 1 minute with a surface conditioning solution prepared by mixing 40 g of NaOH, 15 g of C ₆ H ₉ O ₇ Na and 945 g of distilled water.

Then, the surface-adjusted magnesium alloy was washed.

The washed magnesium alloy was then hot air dried at a temperature of 150 캜 for 10 minutes.

[Experiment 1]

The physical properties of the magnesium alloy treated according to the examples were measured, and the results are shown in Table 1 and Figs. 2 to 7.

Evaluation items unit Specific gravity (%) Development result Assessment Methods Corrosion resistance hrs 40 96 KS D 9502: 2009 Acid resistance hrs 15 48 KS M ISO 2812-1: 2012 conductivity m / Ωmm2 30 5.3 ASTM D 257: 2007 Adhesiveness time 15 Peeling KS M ISO 2409: 2008

As shown in Table 1 and FIG. 2 to FIG. 7, the magnesium alloy treated according to the embodiment of the present invention showed good corrosion resistance, acid resistance, conductivity, and adhesion.

As shown in FIGS. 2 and 3, when the crystal structure of the chemical conversion coating of the magnesium alloy treated according to the present invention is analyzed, MgO, K ₂ Mn ₂ O ₃ , MgAl ₂ O ₄ And so on.

In particular, oxides, such as MgO and MgAl ₂ O ₄ , produced are major constituents of the chemical conversion film which improves the corrosion resistance of the film. It was also found that K ₂ Mn ₂ O ₃ was formed on the magnesium alloy by the self-reaction of the magnesium alloy during the chemical conversion process.

As a result of electrochemical evaluation of the coating film formed on the magnesium alloy according to the present invention, the result of the electromagnetically polarized test in which the chemical conversion coating was formed in the 3.5% NaCl solution at 25 ° C at room temperature was compared with the resistance value of the magnesium alloy material not subjected to the chemical conversion coating It was found that the chemical conversion coating treated in the present invention exhibited a high value and could be used to protect the AZ91D magnesium alloy material from the corrosive environment.

As described above, those skilled in the art will understand that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are all illustrative and not restrictive. The scope of the present invention should be construed as being included in the scope of the present invention without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents.

Claims (4)

A degreasing step of degreasing the magnesium alloy by using ultrasound after immersing the magnesium alloy in the degreasing solution;
Etching with an etchant containing 3 to 8 wt% of NH ₄ HF _2, 3 to 8 wt% of NH ₄ OH, and 84 to 94 wt% of distilled water based on the total weight of the etchant after the defatting step is completed;
A desmutting step in which the etching step is finished and then desmutted into a desmut liquid;
After completion of the desmutting step, a solution containing 3 to 6% by weight of sodium hydroxide, 6 to 12% by weight of phosphoric acid, 3 to 8% by weight of vanadium pentoxide and 74 to 88% by weight of distilled water, A chemical conversion treatment step for chemical treatment for 1 to 5 minutes with the treatment liquid;
A surface adjusting step of surface-adjusting the surface adjustment liquid after the chemical conversion step is finished; And
And a drying step of hot air drying after the surface conditioning step is completed.
The method according to claim 1,
Wherein at least one of the degreasing step, the etching step, the desmutting step, the chemical treatment step, the surface adjusting step, or the at least one step selected from these steps further comprises a water washing step of washing with water after each step is finished. The method according to claim 1,
Wherein the chemical conversion treatment step is carried out in a temperature range of 23 to 27 占 폚 in the summer and a temperature range of 28 to 32 占 폚 in the winter season.
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