KR100855358B1 - Chemical Coating Solutions for Magnesium Alloys, Environmental-affinitive Surface Treating Methods Using the Same, and Magnesium Alloy Substrates thereby - Google Patents

Abstract

The present invention relates to a chemical treatment solution for magnesium alloys and an environmentally friendly surface treatment method of magnesium alloys using the same and a magnesium alloy substrate according to the present invention, according to the present invention 0.1 to 10% by weight of potassium permanganate, 5 to 30% by weight of potassium diphosphate And 0.1 to 10% by weight of potassium triphosphate, and a chemical treatment solution for magnesium alloy having a pH of 7.2 to 10.0; A surface treatment method of a magnesium alloy including a chemical conversion treatment step of depositing a magnesium alloy substrate on the chemical conversion treatment solution having a temperature of 50 to 60 ° C. for 0.5 to 5 minutes to form a uniform phosphate film on the surface thereof; In addition, a magnesium alloy substrate having a phosphate coating formed on its surface is provided by the surface treatment method. The chemical treatment solution for magnesium alloy according to the present invention has excellent mechanical properties, but has a dense chemical coating layer on a magnesium alloy material having a high corrosion resistance. According to the surface treatment method according to the present invention, since the magnesium alloy material has high corrosion resistance, high electrical conductivity, and beautiful appearance, the magnesium alloy is used as a lightweight portable part or product and structural part having conductivity for electrical, electronic and information communication. It is effective and productive, and is particularly useful as an environmentally friendly product because it does not use serious environmentally harmful substances such as chromates.

 Magnesium alloy, chemical conversion, environmental friendliness, non-chromate, phosphate coating, lightweight alloy

Description

Chemical Coating Solutions for Magnesium Alloys and Environmentally Friendly Surface Treatment Methods of Magnesium Alloys Using the Same and Magnesium Alloy Substrates {Chemical Coating Solutions for Magnesium Alloys, Environmental-affinitive Surface Treating Methods Using the Same, and Magnesium Alloy Substrates}

1 is a process flow chart illustrating an environmentally friendly surface treatment method of a magnesium alloy according to the present invention.

Figure 2 is a micrograph of the surface of the magnesium alloy substrate after the degreasing step in the environmentally friendly surface treatment method of magnesium alloy according to the present invention.

3A and 3B are micrographs of the surface of the magnesium alloy substrate after the surface adjustment process in the environmentally friendly surface treatment method of the magnesium alloy according to the present invention, respectively.

4 is a photomicrograph of the surface magnesium alloy substrate surface after phosphate film formation in the chemical conversion treatment step in the environmentally friendly surface treatment method of the magnesium alloy according to the present invention.

The present invention relates to a chemical conversion treatment solution for magnesium alloys, an environmentally friendly surface treatment method of magnesium alloys using the same, and a magnesium alloy base material according thereto, and more particularly, excellent corrosion resistance and rust-preventing properties for magnesium alloys, Chemical treatment solution for magnesium alloy for imparting conductivity, good appearance and paint adhesion, environmentally friendly surface treatment method of magnesium alloy using the same, and magnesium alloy base material treated accordingly It is about.

Magnesium is a metal found in 1808 by British chemist H. Davie reducing magnesia alba with potassium metal. It is a very rich mineral on the ground. Its appearance is silver white and its boiling point is almost the same as that of aluminum. Mainly used as an alloy with.

Magnesium is not produced naturally in the free state, but it is widely and largely present on earth in the form of carbonate, sulfate, silicate, etc., and its main output ore is magnesite, canalite, dolomite, talc, serpentine and asbestos. And the like, and is also contained in fluorite, hornblende and the like.

Magnesium is the eighth most abundant lightweight metal on the planet, and is the lightest mechanical structural material with superior strength, dimensional stability, machinability and vibration absorption.

In recent years, magnesium alloy has been in the spotlight as a new material of the 21st century dream because magnesium has superior strength and rigidity, good workability and thinness compared to conventional plastic, and it is designed, precision mold, precision processing, metal It is a high-precision, high value-added product that requires technology in various fields such as engineering and painting, and its use and market size are rapidly expanding in the fields of automotive, aerospace, electricity and electronics.

Magnesium alloys have recently been used in light weight and high strength electronics such as computers, OA devices, video, audio and MD / CD player cases, television frames, mobile phones, notebook computers, MP3s, digital cameras, TV cameras, liquid crystal projectors, and the like. As information and communication parts, it is applied to vehicle parts such as steering wheel, center fascia, engine cylinder head, ventilation fan, etc., and as high-quality lightweight sporting goods such as fishing and mountain climbing, and as new materials in aerospace field. It is expected to expand rapidly.

Looking specifically at the properties of the magnesium alloy, it is the lightest among the practical metals (specific gravity: Mg 1, Al 1.5, Zn 3.6, Cu 4.9, Fe 4.4), and has a very high conductivity, unlike copper and carbon conductive paints As it is a bulk type, electromagnetic shielding effect is perfect, and vibration absorption is excellent, so it can be used in repetitive or intermittent motion parts to prevent deformation or destruction of mechanical devices, extend the service life, and reduce noise. It has little dimensional change and high dimensional stability due to temperature change, so it can be applied to harsh use conditions, and has the same strength (specific strength) or strength per weight as compared to steel, aluminum, and other alloys (non-steel of magnesium alloy) 1.5 times higher than that of steel), better impact resistance against impact and less cutting resistance compared to Al alloys and mild steels. The processing power is about 1/10 of steel and about 1/3 of Al, so it has good processability, low specific gravity and heat capacity, and low heat and melting heat compared to Al alloy. It does not react with iron, making it suitable for die casting.

Table 1 below compares the physical properties of AZ91D (Al 9%, Zn 1%) as a typical example of magnesium alloy with other materials.

material magnesium aluminum zinc plastic steel division AZ91D ADC12 ZDC2 ABS ABS (GF30%) Carbon steel Tensile Strength (kg / ㎡) 23.9 33.5 29 9.8 12 517 0.2% 15.3 17 - - - - % Elongation 3 2.5 10 60 2.7 22 Hardness (HB) 63 - - - - - Shear strength (Kg / ㎡) 14.1 20 22 - - - Specific gravity (g / cm 3) 1.81 2.7 6.6 1.03 1.3 7.86 Specific Intensity (δ / p) 13.2 12.41 - 9.51 9.23 80 Melting Point (℃) 595 580 387 - - 1520 Specific heat (kcal / ℃) - 0.23 - 0.35 - - Thermal expansion rate (㎛ / m) 27.4 21 27 - - - Thermal Conductivity (W / m ℃) 79 100 113 0.91 - 42

AZ91-based alloys are widely used for magnesium die-casting, and other elongation and toughness AM60, or AS41 and AS21, which have good creep properties, are mainly used.

However, magnesium has the lowest standard potential among practical metals, so it is very easy to oxidize in the atmosphere. Therefore, magnesium alloy has the drawback that the corrosion resistance is very weak, so the surface treatment to increase the corrosion resistance is inevitable, which is an important problem.

In addition to the purpose of improving the corrosion resistance, the surface treatment of the magnesium alloy is also performed for the purpose of improving the surface function such as the appearance characteristics and the wear resistance characteristics of the product, and the surface treatment of the magnesium alloy component (material) is performed in terms of surface conductivity, corrosion resistance, Characteristic functionalities such as wear resistance and the like are given to the magnesium alloy.

The surface treatment of the magnesium alloy is applied to a specific surface treatment process suitable for the conditions of use of the product, the type of magnesium alloy, and whether or not other metals are assembled together, a typical surface treatment method is chemical coating (chemical coating) treatment), anodization, electroplating, electroless plating, painting and the like.

The most widely used surface treatment methods are chemical conversion and plating. All of the above surface treatment methods are carried out after the pretreatment process such as degreasing and pickling.In general, after molding magnesium alloy parts, the surface treatment is performed as a pretreatment for surface treatment, followed by cleaning, surface adjustment treatment, and chemical conversion or plating. It may be shipped or repainted to finish.

The above chemical conversion treatment is a chemical treatment method for making a kind of chemical coating on the metal surface. It is used for anticorrosive and primer coating, metal coloring, etc. Apply. On the other hand, the plating is applied to the product which is required for the appearance and strength of the product appearance and abrasion resistance is often used as a coating film.

Conventionally, a method of depositing magnesium alloy in a chemical treatment solution containing hexavalent chromium has been widely used as a general chemical conversion treatment of magnesium alloy, but hexavalent chromium, which is a heavy metal, is not only fatal to the human body but also causes serious environmental pollution problems. Due to the problem, strict regulations on the working environment and wastewater treatment are applied, and chromate treatment will be legally prohibited in the near future.

Therefore, as a conventional non-chromate chemical conversion method for replacing the conventional chromate treatment, a phosphate treatment method for adding a metal such as zirconium, titanium, or zinc to magnesium phosphate has been proposed, but a long treatment that takes a long time In addition to the lack of practicality due to the process, there is a problem in that sufficient corrosion resistance, rust resistance and coating film adhesion cannot be imparted.

In addition, Japanese Laid-Open Patent Publication No. 7-126858 proposes a manganese phosphate treatment method performed by adding an aliphatic amine, an aromatic amine and a heterocyclic amine compound in addition to divalent manganese ions and phosphate ions. There is a concern that it may cause other environmental pollution problems, there is a problem that the composition of the treatment liquid is complicated, the bathtub management is very complicated and difficult.

In addition, Japanese Patent Application Laid-Open No. 8-35073 proposes a chemical conversion treatment method using permanganate ions, but there is a problem that the coating film adhesion is not stable because the chemical conversion treatment solution does not contain a phosphate bond.

In addition, Korean Patent Laid-Open Publication No. 2002-0077150 proposes a chemical treatment solution and a surface treatment method for magnesium alloys containing first phosphoric acid, orthophosphoric acid and potassium permanganate and having a pH of 1.5 to 7. However, in this method, the pH of the chemical treatment solution is preferably in the range of pH 2.0 to 4.0, which is a strong acid treatment condition. When the pH of the chemical treatment solution exceeds 7, the precipitation amount of the film becomes extremely low due to the decrease in the oxidation power of permanganate ions. It is reported that coating film adhesion cannot be obtained and is inappropriate. In addition, this method, despite the advantages of simple tub management and easy handling, there is a problem that the yield is low due to the relatively low phosphate ion concentration, the yield is low, and the corrosion resistance and film strength is still not satisfactory enough.

Therefore, the first object of the present invention is an environmentally friendly magnesium that is capable of imparting sufficient corrosion resistance, corrosion resistance, and coating film adhesion, such as non-chromate-based and chromate-based coatings, which do not contain heavy metal hexavalent chromium, which are harmful to humans and the environment. It is to provide a chemical conversion treatment liquid for the alloy.

A second object of the present invention is to provide a chemical treatment solution for magnesium alloys which is simple and easy to be treated at room temperature to mid temperature under relatively mild weak alkali conditions.

A third object of the present invention is to provide a chemical treatment solution for magnesium alloy having a simple treatment liquid composition.

A fourth object of the present invention is to impart excellent corrosion resistance and conductivity to a magnesium alloy substrate of complex shape by die-casting or thixo-trophic molding, and optionally an excellent coating film. In order to provide adhesiveness, it is to provide an effective, economical and environmentally friendly magnesium alloy surface treatment method using the chemical conversion treatment liquid according to the first to third objects described above.

A fifth object of the present invention is to provide a magnesium alloy substrate on which a chemical conversion coating film is formed by the surface treatment method according to the fourth object of the present invention.

According to one preferred aspect of the present invention for smoothly achieving the first to third objects of the present invention, 0.1 to 10% by weight of potassium permanganate, 5 to 30% by weight of potassium diphosphate, and 0.1% of potassium triphosphate The chemical conversion treatment liquid for magnesium alloys containing -10 weight% and pH 7.2-10.0, Preferably pH 8.0-9.0 is provided.

According to another preferred aspect of the present invention for smoothly achieving the first to third objects of the present invention, citric acid, acetic acid, acetic acid, There is provided a chemical conversion treatment solution for magnesium alloy further comprising at least one compound selected from the group consisting of nitric acid, nitrous acid, sodium, and potassium salt.

According to a preferred embodiment of the present invention for smoothly achieving the fourth object of the present invention, 0.1 to 10% by weight of potassium permanganate, 5 to 30% by weight of potassium diphosphate, and 0.1 to 10% by weight of potassium triphosphate, and a magnesium alloy substrate for 0.5 to 5 minutes by depositing a magnesium alloy substrate in a chemical solution for magnesium alloy at a temperature of pH 7.2 to 10.0, preferably at a temperature of 8.0 to 9.0, and forming a uniform phosphate film on the surface thereof. Provided is a method for surface treatment of a magnesium alloy comprising the step.

According to a preferred aspect of the present invention for smoothly achieving the fifth object of the present invention, a magnesium alloy substrate having a phosphate coating formed on its surface is provided by the surface treatment method of the magnesium alloy of the above aspect.

Hereinafter, the present invention will be described in detail.

Surface treatment methods for imparting corrosion resistance to magnesium alloys include electroplating, anodizing, and chemical conversion, but magnesium alloy surface treatment with sufficient satisfactory degree of good corrosion resistance and good mass productivity has not yet been activated. It is not true.

Magnesium is only have an unstable corrosion resistance in the air as the active metal chloride ion (Cl ^{-) -} corrosion resistance significantly, since the passivation film is easily damaged by the penetration, such as the halogen compound or its anion, or an oxidizing atmosphere such as a chlorine ion (Cl) Since there is a problem of deterioration, there are many restrictions on its use.

Corrosion of the magnesium alloy occurs mainly in the part where the galvanic cell is formed between the magnesium base and the precipitated phase or impurities present in the base and serves as a positive electrode. Therefore, the presence of impurities such as Fe, Ni, Cu, and the like adversely affects the corrosion resistance of the magnesium alloy in a brine atmosphere. The commercialized by minimizing the content of such impurities is AZ91 series magnesium alloy, although the corrosion resistance has been greatly improved by the development of this alloy, it is still inferior to the light alloy material such as aluminum alloy.

Magnesium alloy is passivated by forming Mg (OH) ₂ hydroxide film which is very stable in strong alkalinity, but corrosion occurs easily in all other areas except strong alkalinity. In particular, corrosion of the magnesium is accelerated localized corrosion caused by the halogen element is the corrosion ball (腐蝕孔) oxidation of the magnesium occurs increasing the concentration of Mg ^{+ 2.}

To achieve electrical neutrality

_{^{Mg 2 + + H 2 O +}} Cl - → Mg (OH) Cl + H +

The reaction of the furnace is accelerated and acidification is accelerated by the generation of hydrogen ions, which accelerates the corrosion of magnesium.

Therefore, the present invention is to improve the corrosion resistance by forming a stable passivation film of phosphate in the magnesium alloy material in order to prevent the corrosion behavior of the magnesium alloy.

In general, chemical conversion treatment refers to forming a thin film of an oxide film or an inorganic salt by chemical treatment on a metal surface, and is widely used to give corrosion resistance to a metal surface due to its low production cost and excellent workability. In addition, it is also widely applied as a primer for coating.

The chemical conversion film formed by the chemical conversion treatment gives other physical and chemical properties superior to the underlying metal, such as rust resistance, coating and paint formation properties, protection of the underlying metal, coloring, and the like. It is an excellent surface treatment method.

The most widely used magnesium alloys (AZ91; Al 9%, Zn 0.7%, Mn 0.15%, other elements 0.006%; AZ61; AZ31, etc.), with the development of the electronics and telecommunications industry, have high specific strength, inelasticity, It has castability, processability, and excellent electromagnetic shielding, and has been spotlighted as a portable notebook computer including a mobile phone, a lightweight component material, and the like, and magnesium alloy has excellent mechanical properties as a structural material. As a result, its use is so wide that it is limited to the use of parts in transportation systems such as aircraft and automobiles, and in recent years, the application of light weight products for electric and electronic communication and other electric and electronic component materials has increased rapidly. With the development of surface treatment method to overcome the corrosion resistance which is the biggest disadvantage of magnesium alloy in recent years, For area it has expanded more rapidly.

Chemical conversion of magnesium alloy can be roughly divided into chromate treatment to form the chromate coating and non-chromate treatment to form the phosphate coating. In recent years, various kinds of environmentally friendly non-chromate treatments, especially various phosphate coating treatments, which do not use chromates, have been actively attempted because of limitations or restrictions.

The present invention relates to a surface treatment method of a magnesium alloy including a chemical conversion treatment process using a more environmentally friendly permanganic acid phosphate as a non-chromate salt, and the chemical conversion treatment in the present invention includes a deposition method, a brush method, a spray method, Although it may be applied by a roller treatment method or the like, a deposition method may be more preferable in terms of process efficiency.

Magnesium alloy surface treatment method comprising the process using the chemical conversion treatment according to the present invention, so that the ultra-light magnesium alloy can be used in a variety of parts material, degreasing, etching, neutralization, surface adjustment, chemical film formation, and sealing It consists of a process and provides high corrosion resistance and conductivity to a magnesium alloy base material or a base by forming a dense chemical conversion layer on the surface of a magnesium alloy base material or a base material.

Here, the release agent or heat-deformation layer in the die casting or thixomolding process, which is a high temperature process of magnesium alloy, has a uniform appearance by degreasing and etching as a pretreatment process of chemical conversion, and then passes through a neutralization process, followed by a chemical conversion process. This improves the corrosion resistance of the surface of the magnesium alloy substrate and imparts good conductivity.

1 is a process flow diagram illustrating a method for environmentally friendly surface treatment of a magnesium alloy according to the present invention, which includes acidic degreasing, neutralization, etching, surface adjustment, chemical conversion, neutralization, sealing of a magnesium base (ie, known) or a substrate; It is shown that it consists of a drying process, it will be described sequentially.

For example, the surface of the die casting casting may be Al ₂ O ₃ to facilitate separation between the mold and the casting. Or a release agent of SiO ₂ component is used. After die casting, the thermally deformable release agent component remaining on the surface by mechanical polishing or barrel polishing and the like, and the burrs present on the surface of the casting are removed.

First, the degreasing process uniforms the processing layer (chill (work hardening layer, release agent attaching part, etc.) on the surface of the die casting casting (or molded product by thixomolding)), and the organic and inorganic impurities and fine impurities remaining on the surface of the casting or the molding. As a step of removing the acid, acidic degreasing is used.

Cleaning the magnesium alloy will cause fatal damage to the surface of the magnesium alloy if it contains a small amount of the material that causes corrosion. Therefore, the degreasing of the magnesium alloy is used in combination with an appropriate concentration of corrosion inhibitors, surfactants, acidic degreasing agents commonly known in the art in the sulfuric acid base. Specifically, an acidic degreasing agent containing 0.2 to 10% by weight of nitrate (NO ₃ ⁻ ), 0.01 to 2% by weight of fluoride (F ⁻ ), surfactant and 0.1 to 5% by weight of a complexing agent at a working temperature of 10 to 50 ° C. Degrease for 1 to 120 seconds.

Subsequently, after the degreasing step, the neutralization step removes the release agent and magnesium compound (smut) reacted in the degreasing step in a neutralization bath of caustic soda base, which can be removed by immersion but can be removed by ultrasonic method (10-40). It may be desirable to use an ultrasonic wave that can improve the cleaning power due to vibration caused by vi).

In addition, the neutralization process also serves to prevent the progress of local corrosion by acid in the presence of pores, which are defects in die casting, in the degreasing process, and is a neutralization process using alkaline substances.

The neutralization process employs an alkaline surface conditioning solution containing 3-30% by weight sodium hydroxide, 1-20% by weight sodium triphosphate and a surfactant, and having a specific gravity of heavy Beau 3-30. For example, neutralize for 10 seconds to 10 minutes, preferably 1 to 5 minutes in a temperature range of 30 to 90 ° C, preferably 50 to 85 ° C in an ultrasonic irradiation apparatus installation bath having a frequency of 10 to 50 kHz, preferably 10 to 40 kHz. In addition to soaking in the bath, ultrasonic irradiation can also be used to remove the smut. The hydroxyl ions (OH ^-) may replace used as such a compound, sodium hydroxide is potassium hydroxide or ammonium hydroxide include, and phosphate ions (PO ₄ ^-) in Sodium tripolyphosphate compounds include the tripolyphosphate, potassium phosphate, sodium fatigue It may alternatively be used with sodium phosphate or the like, and 0.1 to 5 mol of hydroxyl ions (OH ⁻ ) and 0.05 to 5 mol of phosphate ions (PO ₄ ⁻ ) are contained.

The etching process following the neutralization process is an optimal process for uniformly removing the activated inorganic material, the processing layer (chill) and the smut in the degreasing process to obtain a fine and homogeneous surface in a short time. This is a process that removes inorganic substances at the same time as surface activation prior to chemical conversion process, and has a great effect on corrosion resistance and surface homogenization after chemical conversion.

As an etchant, a fluoride and a nitrate are mix | blended with a sulfuric acid base at appropriate concentration, and it is used. Specifically, the surface is immersed for 1 to 10 minutes in an etching bath containing 0.01 to 10% by weight sulfuric acid, 0.2 to 1M fluoride (F-), and 1 to 10% by weight of a surfactant and a chelating agent. It may be etched to have a uniform surface energy.

Subsequently, in consideration of the characteristics of the magnesium that corrosion proceeds at pH 11.5 or less, a surface adjustment process, which is a neutralization, surface activation, and homogenization treatment process, is performed to make the surface of the magnesium alloy strongly alkaline. The surface adjustment process is a pretreatment process prior to the chemical conversion process, which makes the energy potential equal to form a uniform film during chemical conversion process, and makes the etching surface uniform or homogeneous and removes smut by using acidic and alkaline chemicals. It provides a beautiful surface appearance, and also increases the activity before chemical conversion. In order to obtain a more beautiful surface appearance after the chemical conversion treatment, various chemicals known in the art are added to the caustic soda base to adjust the surface properties of the magnesium alloy substrate.

The surface adjustment process described above uses an alkaline surface adjustment solution containing 3-20% by weight of sodium hydroxide, 1-15% by weight of sodium triphosphate and a surfactant, and having a specific gravity of heavy beam (Be ') 3-30. Optionally, in the temperature range of 30-90 degreeC, Preferably it is 50-85 degreeC in the ultrasonic irradiation apparatus installation bath of frequency 10-50 Hz, Preferably 10-40 Hz, Preferably it is 1- The smut can also be removed by soaking in a surface adjustment bath for 5 minutes and by ultrasonic irradiation. The hydroxyl ions (OH ^-) may replace used as such a compound, sodium hydroxide is potassium hydroxide or ammonium hydroxide include, and phosphate ions (PO ₄ ^-) in Sodium tripolyphosphate compounds include the tripolyphosphate, potassium phosphate, sodium fatigue It may alternatively be used with sodium phosphate or the like, and 0.1 to 5 mol of hydroxyl ions (OH ⁻ ) and 0.05 to 5 mol of phosphate ions (PO ₄ ⁻ ) are contained.

The chemical conversion process, which is a key step in the surface treatment method according to the present invention, forms a uniform and dense phosphate film to impart high corrosion resistance and conductivity to the magnesium alloy. Specifically, the chemical conversion treatment process for forming the permanganate-phosphate coating enhances the corrosion resistance of the magnesium alloy, improves the appearance, and imparts color.

The chemical conversion treatment solution for magnesium alloy according to the present invention is 0.1 to 10% by weight of potassium permanganate, preferably 0.2 to 2% by weight, 5 to 30% by weight of potassium diphosphate, preferably 10 to 20% by weight, and potassium triphosphate 0.1 It contains 10 to 10 weight%, Preferably it is 0.2 to 2 weight%, pH 7.2-10.0, Preferably it is pH 8.0-9.0.

Optionally, if necessary, further, at least one compound selected from the group consisting of citric acid, acetic acid, lactic acid, nitric acid, nitrous acid, sodium, and potassium salt in the above-mentioned chemical conversion solution for magnesium alloy for imparting color and functionality. You may.

In addition, the pH control can be controlled by the phosphoric acid, and when the pH is low by adjusting the amount of phosphoric acid, the chemical conversion surface of the magnesium alloy has a bright color appearance, and when the pH is high, a dark yellow appearance is obtained. On the other hand, when pH 8.3-pH 8.5, the pale yellow (ivory) phosphate film used for coating base material will be obtained.

The chemical conversion process is performed by depositing a magnesium alloy substrate for 0.5 to 15 minutes, preferably 0.5 to 5 minutes, in the chemical conversion treatment solution for magnesium alloy according to the present invention maintained at a temperature of 30 to 60 ° C, preferably 50 to 60 ° C. A uniform and dense phosphate film is formed on the surface.

The neutralization process following the chemical conversion process is intended to remove the local reaction layer generated during the chemical conversion process, thereby uniforming the beautiful appearance and conductivity.

The neutralization process comprises 0.1 to 5% by weight of sodium hydroxide, potassium hydroxide or ammonium hydroxide and 0.05 to 5% by weight of sodium triphosphate, potassium triphosphate, sodium diphosphate and sodium pyrophosphate, and a surfactant (Be ') Scoop is removed using an alkaline neutralizing solution having a specific gravity of 1 to 10. The hydroxyl ions (OH ^-) is 0.001~0.55㏖, phosphate ion (PO ₄ ^-) which it is incorporated degree 0.001~0.5㏖.

Neutralization conditions are deposited for 1 to 10 seconds in the temperature range of about 30 to 50 ° C.

Subsequently, the sealing process performed is performed by converting a hydrophilic surface into a hydrophobic surface using NR-303 (Million Chemical Co., Ltd.), which is a paraffinic organic sealing agent, and the like, by water penetration. It is a treatment process to impart anticorrosive properties.

Finally. The drying process is carried out, followed by drying by hot blowing for 10 to 90 minutes at a drying temperature of 60 to 150 캜.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Examples 1 to 7: Application of Surface Treatment Methods

First, since magnesium die-casting alloy is a substrate having a lot of fine cracks, processing altered layers, and internal pores, five specimens (45x72mm, portable telephone external case) were simultaneously fabricated for the characteristics test in each example. Measurement was made for. In addition, in order to completely remove residual chemicals in the final washing step after the chemical conversion treatment was washed 2 to 5 times and isothermal blowing in a general drying furnace.

Magnesium alloy substrates used as structural materials are die cast and shaped by machining, and then shaped into finished products by buffing, finishing, and trimming, and then applied to provide corrosion resistance and conductivity. The surface treatment method according to the invention was applied.

(A) degreasing process

A solution composition containing 1 M nitric acid, 0.03 M fluoride, 0.01 wt% surfactant, 0.02 wt% corrosion inhibitor, and 3 wt% of other buffers was deposited for 1-30 seconds in a temperature range of 5-40 ° C. to remove release agents and organics. It was.

(B) neutralization process

A solution composition containing 1.5 M hydroxide OH (OH ⁻ ), 0.28 M phosphoric acid (PO ₄ ^{3 −} ), 0.05 wt% surfactant, and 3 wt% of other complexing agents for 0.5-5 minutes in a temperature range of 50-90 ° C. Dipping removed the smut (reaction product).

In the neutralization step, ultrasonic waves of 10 to 50 Hz were used to smooth the desorption of the surface product.

(C) etching process

0.1 to 5 minutes in a temperature range of 10 to 30 ° C. in a solution composition containing 0.3% by weight sulfuric acid (98%), 1.1M fluoride (F ⁻ ), 0.02% by weight surfactant, and 5% by weight of other complexing agents It was deposited during to remove the material heat deformation layer and the inorganic material.

(D) surface adjustment process

A solution composition containing 1.2 M hydroxide OH (OH ⁻ ), 0.20 M phosphoric acid (PO ₄ ^{3 −} ), 0.03 wt% surfactant, and 8 wt% of other complexing agents for 1-5 minutes in a temperature range of 50-85 ° C. It was deposited to remove the smut (reaction product).

In the surface adjustment process, ultrasonic waves of 10 to 50 Hz were used in order to smooth the desorption of the surface product.

(E) chemical conversion process

To a solution containing 0.5 wt% potassium permanganate, 15 wt% potassium diphosphate, 0.6 wt% potassium triphosphate, and 0.02 wt% surfactant, adjusted to pH 8.0-9.0 with phosphoric acid and 0.5-5 at a temperature range of 50-60 ° C. It was deposited for minutes to form a uniform and dense phosphate coating.

(F) neutralization process

A solution composition containing 0.8 M hydroxide OH (OH ⁻ ), 0.1 M phosphoric acid (PO ₄ ^{3 −} ), 0.05 wt% surfactant, and 1 wt% of other complexing agents for 1 to 10 seconds in a temperature range of 30 to 50 ° C. It was deposited to remove the reaction byproducts of the phosphate coating.

(G) Sealing process

Sealing was performed by converting the hydrophilic surface into hydrophobic using a sealing agent having an organic sealer content of 0.05% by weight, thereby imparting anticorrosive characteristics by penetration of moisture.

(H) drying process

Hot drying was performed for 10 to 90 minutes, preferably 10 to 50 minutes, at a high temperature of 60 to 150 ° C. to remove moisture of the chemically treated product on the deposited magnesium alloy.

The specific treatment conditions of Examples 1 to 7 and the test evaluation (determination) method for the surface treated magnesium alloy were performed as follows, and the results are shown in Tables 3 and 4, respectively.

-Test evaluation method-

1. Corrosion resistance test

NaCl, a method of confirming general corrosion resistance, was dissolved in distilled water to confirm corrosion resistance through a salt spray test (KSD 9502).

The conditions of the salt spray test adjusted the tank temperature to 35 ± 2 ℃ and spray pressure is 1.1 ~ 1.25kgf / ㎠ Was maintained. NaCl concentration in the brine at this time was 5 ± 0.5% and pH was 7 ± 0.2. Corrosion degree was evaluated by the rating number (Rating No.) shown in Table 3 below (10 for corrosion 0%, 0 for corrosion of 50% or more). Since the product may have a large number of casting defects, the material under the coating layer exhibits severe corrosion even when local pitting is progressed. In the case of local corrosion, the material was judged objectively compared to the same specimen.

2. Acid Resistance Test

The corrosion resistance test in acidic atmosphere of pH 4.6 was performed as a neutral salt spray test accelerated processing method according to JIS H 8503. The solution used in the acid resistance test is a solution made by mixing pH 7 and pH 4. When the acid solution comes into contact with air, there is a difference in pH due to the contamination of the solution. The temperature of 25 ° C was maintained.

The acid resistance evaluation criteria are also applied in the same manner as the salt spray test evaluation criteria described above.

Rating No. Evaluation Criteria Rating number Corrosion area ratio (%) Corrosion area (mm2) 1 mm round spot /1.57㎡ Spot 10 0 0 0 0 9.8 0.02 or less 0.75 0.3 0.3 9.5 0.03 to 0.05 1.25 One 0.5 9.3 0.05-0.07 1.75 1.7 0.7 9 0.07 to 0.10 2.5 2 1 to 3 8 0.10 to 0.25 6.25 6 4 to 8 7 0.25 to 0.50 12.5 12 9-15 6 0.50 to 1.0 25 24 16-31 5 1.0 to 2.5 62.5 59 32-79 4 2.5 to 5.0 125 119 80-159 3 5.0-10 250 240 160-318 2 10-25 625 480 319-796 One 25-50 1,250 960 792-1,592 0 50 or more 1,251 961 1,593

3. Conductivity measurement

Four-point probe (VEECO MODEL FPP-5000) was used to measure the surface resistance (this method uses four probes to flow two probes and measures the voltage drop of the other two probes. Calculated as specific resistance or sheet resistance).

The sheet resistance of the chemically treated product of magnesium alloy should have a conductivity of less than 1.5 cm / Ω, and in the case of a mobile phone case, the inside should be conductive and the outside should be non-conductive.

4. Color

The standard for determining the color of the chemical conversion product is not particularly defined, but if the color of the chemical conversion product is dark, it is not preferable because the dark color of the lower limb is reflected in the coating process, resulting in a crude and inferior appearance.

The color after the chemical treatment is affected by various external environments such as the concentration of the chemical treatment solution, the treatment time, the influence of pretreatment, and the temperature, but also has a great influence on the characteristics of the product. It was found to have no effect.

5. Surface Smut and Adhesion Test

The formation of Smut is formed by an abnormal phenomenon of chemical reaction by unstable chemical conversion treatment. If the stool is formed, it will adversely affect the adhesion during the electrodeposition of the paint in the post-process, and will seriously damage the reliability of the product. The presence of the scotch was confirmed by a change in color after 10 times rubbing alcohol on a cotton swab.

Adhesion test was conducted on the basis of KSD 0254 (X-cutting 1mm, 0% once, 1% or less in three consecutive tests).

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Degreasing 5 seconds deposition, 25 ° C 10 second deposition, 25 ° C Chinese 2 minutes deposition, temperature 75 ℃, ultrasonic 28 kHz etching 1 minute deposition, 25 ℃ 2 minutes deposition, 25 ℃ 1 minute, 25 ℃ 3 minutes, 25 ℃ Surface adjustment 2 minutes deposition, temperature 80 ℃, ultrasonic 28 kHz Chemical treatment 80 sec 55 ℃ pH 8.5 120 sec 55 ℃ pH 8.5 80 sec 55 ℃ pH 8.5 120 sec 55 ℃ pH8.5 120 sec 55 ° C, pH8.0 120 sec 55 ° C, pH8.0 180 sec 55 ° C, pH8.5 Chinese 2-3 seconds deposition, temperature 50 ℃ shilling 100 sec immersion, temperature 40 ℃ dry 80-90 degreeC, 40 minutes, convection ventilation drying,

Judgment result Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Corrosion Resistance Rating No. (48hr standard) 60 hr 72 hr 60 hr 72 hr 48 hr 48 hr 48 hr 8.8 9.6 8.2 9.4 7.6 8.1 7.6 Resistance (Ω) 0.6 to 1.2 0.6 to 1.2 0.4 to 1.1 0.4 to 1.1 0.4 to 1.2 0.4 to 1.2 0.2 to 0.8 Acid Resistance Rating No. (48hr standard) 48 hr 60 hr 60 hr 60 hr 48 hr 48 hr 48 hr 8.0 9.2 8.0 8.8 7.0 7.6 7.2 color Ivory Ivory Ivory Ivory Light gray Light gray Ivory Paint adhesion 10 tests (0%) 10 tests (0%) 10 tests (0%) 10 tests (0%) 10 tests (0%) 10 tests (0%) 10 tests (0%) Exterior Great Great Great Great usually usually usually Smut presence No discoloration No discoloration No discoloration No discoloration No discoloration No discoloration No discoloration

Comparative Examples 1 and 2:

Using a chemical conversion solution of pH 2.9 consisting of KMnO ₄ 5.0 g / l, monophosphate 50 g / l, orthophosphoric acid 2.0 g / l, and residues, and a chemical conversion solution of pH 5.9 using 10% sodium hydroxide. Except for 2 minutes at 55 ° C bath temperature was treated in the same manner as in Examples 1 to 7 to obtain a chemically treated magnesium alloy specimen having a dark brown and light brown appearance, respectively, Comparative Example 1 And 2.

As a result of the same test as in Example, the specimens of 1 and 2 had the same high electrical conductivity as the Example, but the corrosion resistance test showed that about 18% and 24% of corrosion were observed, respectively. Rated No. 2 was evaluated.

On the other hand, Figure 2 is a micrograph (SEM, x500) of the surface of the magnesium alloy substrate after the degreasing step in Example 2 in the environmentally friendly surface treatment method of magnesium alloy according to the present invention, the reaction product of magnesium in the degreasing process Excessive smut is generated, which adversely affects staining, surface resistance, and paint adhesion of the product and must be removed before chemical treatment.

3A and 3B are micrographs (SEM, x500) of the surface of the magnesium alloy substrate after the surface adjustment process in Example 2 in the method for environmentally friendly surface treatment of the magnesium alloy according to the present invention, each treated for 1 minute of etching. And the surface texture after the etching two-minute treated substrate is subjected to a surface adjustment step.

The longer the etching time of the magnesium alloy, the less porosity of the surface, but inferior in dimensional stability, increased internal crack generation concerns, coarse pores may protrude, may cause blister during the painting work. In addition, the etching time should be different according to die casting, other casting and plate processing methods. Especially, if the internal filling rate is high, the etching time should be high, and if the internal filling rate is low, the etching time should be high. Due to the risk of surface damage caused by the product, it is necessary to appropriately apply differently within the time and concentration conditions mentioned above.

Corrosion resistance and electrical conductivity of phosphate chemically coated products are determined by pretreatment conditions and surface appearance. In particular, the chemical conversion of magnesium alloy, which proceeds very quickly, has excellent corrosion resistance when forming a film having excellent sealing property without dense film formation and the presence of fine pores. In particular, in order to eliminate the effects of local pitting, sealing of micropores and cracks has the greatest effect on the corrosion resistance of magnesium surfaces.

In general, the corrosion resistance of magnesium chemical treatment is proportional to concentration, temperature and treatment time.

FIG. 4 is a micrograph (SEM, x500) of a surface magnesium alloy substrate surface after formation of a phosphate film in the chemical conversion treatment step of Example 2 in the environmentally friendly surface treatment method of the magnesium alloy according to the present invention. It then shows a uniform appearance surface shape of the finished product. In particular, the corrosion resistance drops sharply when there is a smut or non-uniform shape (pores or cracks) on the surface.

According to the surface treatment method of the magnesium alloy using the chemical treatment solution for magnesium alloy according to the present invention, not only the chemical conversion treatment can impart high corrosion resistance and conductivity to magnesium embedded parts, but also form a coating film having high surface resistance. Of course it is possible.

The chemical conversion treatment solution for magnesium alloy according to the present invention has excellent mechanical properties, but can form a dense chemical conversion layer on a magnesium alloy material, which is a super-light-weight alloy with high corrosiveness. The salt spray corrosion resistance test and acid resistance test on high magnesium alloy substrates provide very good corrosion resistance and high acid resistance of 48hr or more and high electrical conductivity of 1.5Ω or less, and do not form oxide film. Lightweight portable parts, products, and structural parts that make magnesium alloys effective and productive, and are particularly useful as export products for Europe and other eco-friendly products in the domestic industry because they do not use serious environmentally harmful substances such as chromates. Do.

Claims (15)

A chemical coating forming solution for magnesium alloy containing 0.1 to 10% by weight of potassium permanganate, 5 to 30% by weight of potassium diphosphate, and 0.1 to 10% by weight of potassium triphosphate. The chemical conversion treatment liquid for magnesium alloy according to claim 1, further comprising at least one compound selected from the group consisting of citric acid, acetic acid, acetic acid, nitric acid, nitrous acid, sodium, and potassium salt in the chemical conversion treatment liquid. The chemical conversion treatment liquid for magnesium alloy according to claim 1 or 2, wherein the chemical conversion treatment solution further contains a phosphoric acid for pH adjustment. Magnesium alloy substrate containing 0.1-10% by weight of potassium permanganate, 5-30% by weight of potassium diphosphate, and 0.1-10% by weight of potassium triphosphate and a temperature of 30-60 ° C. with a pH of 7.2-10.0. And a chemical conversion treatment step of contacting the chemical conversion solution for the alloy to form a uniform phosphate film on the surface thereof. 5. The surface treatment method of a magnesium alloy according to claim 4, wherein said contact of the magnesium alloy substrate with said chemical conversion treatment liquid for magnesium alloy is carried out by dipping for 0.5 to 15 minutes. The surface treatment method of a magnesium alloy according to claim 4 or 5, wherein the pH adjustment of the chemical conversion treatment liquid for magnesium alloy is performed by phosphoric acid. The etching bath according to claim 4 or 5, wherein prior to the above-mentioned chemical conversion step, 1 to a etching bath at 5 to 40 DEG C containing 0.01 to 10 wt% sulfuric acid and 0.2 to 1 M fluoride (F-). Magnesium alloy surface treatment method to perform the etching step of immersion for 10 minutes. The method according to claim 7, wherein between the etching step and the chemical conversion step, 0.1 to 5 mol of hydroxide ions (OH ⁻ ) and 0.05 to 5 mol of phosphate ions (PO ₄ ⁻ ) are included. A surface treatment method of magnesium alloy, which performs a surface adjustment step of removing smut by immersion for 1 to 5 minutes in an alkaline surface adjustment bath having a specific gravity of 30 to 90 ° C. The method of claim 8, wherein prior to the etching step, the magnesium alloy substrate is immersed in an acidic degreaser bath at 10 to 50 DEG C for 0.2 to 10 wt% nitrate and 0.01 to 2 wt% fluoride for 1 to 120 seconds. Surface treatment method of magnesium alloy to perform a degreasing step. 10. The method of claim 9 further comprising, between said degreasing step and the etching step, the hydroxyl ions (OH ^-) 0.1~5㏖ and phosphate ions (PO ₄ ^-) include 0.05~5㏖ and mediator Ume (Be ') 3~30 The surface treatment method of magnesium alloy which performs the neutralization step of removing smut by immersing for 1-5 minutes in the alkaline neutralization bath of 30-90 degreeC which has a specific gravity of. The surface treatment method of a magnesium alloy according to claim 8, wherein ultrasonic irradiation with a frequency of 10 to 50 Hz is performed in parallel. 10. The method according to claim 8, wherein the chemical conversion treatment step comprises following the chemical conversion step and comprising 0.001 to 0.55 mol of hydroxyl ions (OH ⁻ ) and 0.001 to 0.5 mol of phosphate ions (PO ₄ ⁻ ). A surface treatment method of a magnesium alloy, which is carried out by dipping in an alkaline neutralization bath having a specific gravity for 1 to 10 seconds to remove a smut remaining on the surface after chemical conversion. 13. The method of claim 12, wherein the sealing step of converting the hydrophilic surface into hydrophobic using a hydrophobic organic sealer is performed. The surface treatment method of a magnesium alloy according to claim 13, further comprising a drying step of hot blowing at a drying temperature of 60 to 150 DEG C for 10 to 90 minutes subsequent to the sealing step. Magnesium alloy substrate surface-treated by the surface treatment method according to claim 4.

Images