KR101809154B1 - Composition of 3+ ion chromate agent for aluminum die-casting, aluminum die-cast comprising the film and method for preparing the same - Google Patents

Abstract

The present invention relates to a trivalent chromate composition having excellent corrosion resistance of a surface with respect to a die-casting cast of an aluminum alloy material and adhesion with paint, a die-casting cast with the composition, and a method for manufacturing the same, wherein the composition comprises: 5-15 wt% of a trivalent chromium compound; 0.1-5 wt% of an acid; 0.1-3 wt% of a phosphoric acid compound; 5-10 wt% of a metallic compound; 1-3 wt% of an alkali agent; and the remainder consisting of water.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a composition for forming a trivalent chromate film for die casting of aluminum and an aluminum alloy, an aluminum die cast including a trivalent chromate film and a method for producing the same. BACKGROUND OF THE INVENTION METHOD FOR PREPARING THE SAME}

The present invention relates to a composition for forming a trivalent chromate film having excellent corrosion resistance to a surface of a casting for die casting and adhesion to a paint in an aluminum alloy material, an aluminum die casting method using the composition, and an aluminum diecast obtained thereby.

Die casting is a casting method using non-ferrous metals and metals used in casting. It is also called "die casting". A method of obtaining the same casting as a mold by injecting molten metal into a steel mold machined precisely machined to exactly match the required casting shape is called a precision casting method and the product obtained through this method is called die casting casting.

Such a die casting uses a die casting machine to inject molten metal into the die by air pressure, water pressure, hydraulic pressure, etc. to cool and solidify the die casting casting. The most important advantage of such die casting is that it is not necessary to finely polish it because of its accurate dimensions, it has excellent mechanical properties and is capable of mass production.

Such die casting is a major material parts industry that is the basis of all industries, and various parts of die casting materials are utilized in various fields from aircraft, automobile to children's toys. For example, automobile parts made of aluminum have been increasing in recent years as a result of the weight reduction of automobiles. In addition, aluminum die casting is rapidly increasing in areas such as mobile phones, laptops, and cameras that require further weight reduction.

Examples of the metal used in the die casting include zinc, aluminum, tin, copper, magnesium, and alloys thereof. Of these, the die casting casting of aluminum or an alloy thereof can be subjected to a surface treatment such as formation of a metal coating layer on the surface thereof in order to ensure corrosion resistance and to ensure adhesion with the coating in forming a coating layer on the surface.

On the other hand, in order to form the metal coating layer, it is general to perform pretreatment of polishing and cleaning the surface of aluminum. The aluminum surface is smoothed and cleaned through the polishing and cleaning processes, thereby maintaining good adhesion between the aluminum surface and the metal coating layer.

On the other hand, surface treatment of aluminum materials includes anodizing, chemical conversion coating, electroplating, electroless plating, vacuum plating and the like. Representative surface treatments of aluminum include anodizing and chromate treatment.

The anodizing treatment may be carried out by dipping the aluminum or aluminum alloy anodic oxide coating disclosed in Korean Patent Application No. 1998-018460 in an aqueous solution containing a water-soluble fluorinated surfactant, A method in which an anodic oxide film of a metal is treated with an activation treatment bath containing a metal salt and an acid and dyeing treatment is carried out.

As the coating liquid composition, a trivalent chromium chromate coating solution composition in which a trivalent chromium salt and a phosphoric acid-based compound disclosed in Korean Patent Application No. 2003-0086079 are mixed and one or two or more metal-based compounds are added, Discloses a transition coating solution based on trivalent chromium, which comprises a trivalent chromium cation, a fluorometallate anion, a guanidinium ion, and at least one organic corrosion-resistant additive, and other optional components, as disclosed in U.S. Pat. No. 2015-7029666.

On the other hand, Korean Patent Application No. 1997-000743 discloses a solution in which CrO ₃ , HF, Na, (NH ₄ ) ₂ Cr ₂ O ₇ , and sodium fluoride are mixed, but hexavalent chromium and fluorine components are used , They are globally regulated as a component which has harmful effects on the human body and adverse effects on the environment.

Korean Patent Application No. 2007-0029767 discloses a trivalent chromate concentrate containing a trivalent chromium material, a ligand, a carboxylic acid and water, but it has been found that the surface of a zinc alloy layer containing a zinc layer or zinc , And a trivalent chromate coating film is formed thicker than 100 nm. In addition, it uses a high concentration of chromium components and a working temperature of 60 DEG C or higher, which is a technology that causes a working environment and a cost burden.

Such a composition must be soaked at a temperature of 40 to 80 DEG C for at least 2 minutes, resulting in a high treatment temperature and a long treatment time, resulting in a decrease in productivity and an increase in processing cost.

Disclosed is a trivalent chromate-containing composition for forming a trivalent chromium-containing coating film that does not contain hexavalent chromium and has a uniform appearance and good corrosion resistance on the surface of aluminum or aluminum alloy, An aluminum die cast having a trivalent chromate film formed by the above composition, and a process for producing the same.

The present invention relates to a composition for forming a trivalent chromate film for aluminum or aluminum alloy die casting, which comprises 5 to 15% by weight of a trivalent chromium compound, 0.1 to 3% by weight of an oxidizing agent, 0.1 to 3% by weight of a phosphoric acid compound, % Of an alkali agent, 1 to 3 wt% of an alkali agent, 0.1 to 4 wt% of a surfactant, and the remainder.

The trivalent chromium compound may be at least one selected from the group consisting of chromium nitrate, chromium sulfate, chromium acetate and chromium chloride.

The oxidizing agent may be at least one selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, maleic acid, acetic acid and oxalic acid.

The phosphoric acid compound is selected from the group consisting of sodium phosphate (NaH ₂ PO ₄ ), sodium phosphate dibasic (Na ₂ HPO ₄ ), sodium phosphate dibasic (Na ₃ PO ₄ ) and sodium hypophosphite (NaH ₂ PO ₂ ) And may be at least one selected.

The metal compound may be selected from the group consisting of manganese sulfate, cobalt nitrate, cobalt chloride, cobalt sulfate, nickel chloride, nickel sulfate, nickel nitrate, and metal alkoxide, such as tantalum ethoxide, titanium tetraisopropoxide, But may be at least one selected from the group consisting of titanium butoxide, zirconium butoxide, and zirconium ethoxide.

The alkali agent may be at least one selected from the group consisting of ammonia hydroxide, sodium hydroxide, and potassium hydroxide.

The surfactant may be an anionic surfactant, and the anionic surfactant may be selected from the group consisting of potassium lauryl phosphate, sodium dioctylsulfonate, sodium alkylsulphate having 12 to 15 carbon atoms, And disodium ethoxylated nonylphenyl ester of sulfosuccinic acid of succinic acid.

The pH of the composition for forming a chromate film is preferably 3 to 5.

The present invention provides a method for producing an aluminum die cast, wherein aluminum and an aluminum alloy are immersed in the composition for forming a trivalent chromate film having a temperature of 20 to 30 DEG C for 1 to 2 minutes and then dried, Trivalent chromate and a metal phosphate film.

The composition for forming the trivalent chromate film preferably has a pH of 3 to 5. [

The present invention also provides an aluminum or aluminum alloy die-cast having an aluminum or aluminum alloy and a coating comprising a trivalent chromate component and a metal phosphate component on the aluminum or aluminum alloy surface to provide an aluminum die-cast.

The trivalent chromate composition for aluminum and aluminum alloy die casting of the present invention does not contain hexavalent chromium, and the content of the trivalent chromium compound is low, thereby being eco-friendly.

The metal material treated with the trivalent chromate composition of the present invention is excellent in corrosion resistance and also has excellent paint adhesion.

In addition, the chromate composition of the present invention can be formed at a low temperature near room temperature for a short time to form a coating layer, which is economical because the processing temperature and time can be reduced.

Furthermore, the method for producing a trivalent chromate composition for aluminum and aluminum alloy die casting of the present invention is excellent in reproducibility and is simple in manufacturing process.

Fig. 1 is a photograph of the surface of a specimen after 40 hours of a salt spray test for the specimen of Example 2. Fig.

In one embodiment, the present invention provides a coating solution composition for aluminum and aluminum alloy die casting, which provides corrosion resistance equivalent to that of hexavalent chromium used to provide excellent corrosion resistance, and does not include hexavalent chromium And can form a trivalent chromate film containing trivalent chromium.

A chromate coating refers to a chromateable coating, and the basic idea is to thinly form an insoluble salt containing a chromium component on the surface of the metal. That is, the trivalent chromate for aluminum or aluminum alloy die casting uses a trivalent chromium compound to form a film of insoluble chromium salt on the aluminum plating material.

To this end, the present invention aims to provide a trivalent chromate composition, wherein the composition for forming a trivalent chromate film according to the present invention comprises a trivalent chromium compound and an oxidizing agent.

The most basic reaction formula of the chromate coating by forming a film on the aluminum plating material by the oxidation reaction is shown in the following reaction formula (1).

Al + Cr ^{3 +} + oxidizing agent → Cr ₂ O ₃ + Al ³⁺ (1)

That is, by the above reaction, water-soluble Cr ^{3 +} forms insoluble Cr ₂ O ₃ on Al by the oxidation reaction. Therefore, the chromate composition according to the present invention comprises a trivalent chromium compound and an oxidizing agent.

As the trivalent chromium compound, at least one compound selected from the group consisting of chromium nitrate, chromium sulfate, chromium acetate and chromium chloride can be used.

As the trivalent chromium compound, chromium sulfate, chromium chloride, or chromium nitrate may be used in an amount of 5 to 15% by weight based on the total weight of the composition. If the concentration of the trivalent chromium is less than 5 wt%, the thickness of the chromate film is formed thinly on the aluminum or aluminum alloy under the same conditions, and the corrosion resistance may be weakened. On the contrary, when the concentration of trivalent chromium exceeds 15 wt%, the trivalent chromium compound powder does not completely dissolve but precipitates and precipitates. In this case, when the trivalent chromate composition of the present invention is coated on the aluminum or aluminum alloy plating material, the trivalent chromium compound powder may remain on the surface of the plating material. Furthermore, it is more preferable that the trivalent chromium compound is contained in an amount of 8 to 13% by weight based on the total weight of the composition.

The oxidizing agent, that is, the acid included in the present invention, as seen from the formula (1), oxidizes the surface of Al or Al alloy to form insoluble chromium of Cr ₂ O ₃ , and further acts as a pH adjusting agent . As the oxidizing agent, any type of acid can be used as long as it can provide an oxidizing power, and various types of acids can be used. For example, nitric acid, sulfuric acid, hydrochloric acid, maleic acid, acetic acid or oxalic acid may be used. Or a mixture of two or more of them may be used.

The amount of the oxidizing agent may be 0.1 to 3% by weight, more preferably 1 to 1.5% by weight. If the content of the oxidizing agent is less than 0.1% by weight, the oxidation reaction on the surface of the Al or Al alloy is weakened and the insoluble salt of Cr ₂ O ₃ is not sufficiently formed on the surface of the coating film, The excessive oxidation reaction of the surface increases the surface roughness and fails to form a uniform coating film.

The trivalent chromate composition of the present invention further comprises a phosphoric acid compound. The phosphoric acid compound forms a phosphate film together with the trivalent chromate film formed by the trivalent chromate film of the present invention so that the trivalent chromate film and the phosphate film coexist, thereby providing excellent corrosion resistance and film adhesion. More specifically, the phosphoric acid compound reacts with the metal compound added to the composition of the present invention to form a phosphate metal compound to form a coating of an insoluble salt.

The phosphoric acid compound is not particularly limited, but may be selected from the group consisting of NaH ₂ PO ₄ , Na ₂ HPO ₄ , Sodium Phosphate (Na ₃ PO ₄ ) and Sodium hypophosphite (NaH ₂ PO ₂ ). These may be used singly or in combination of two or more.

The phosphoric acid compound is preferably contained in an amount of 0.1 to 5% by weight based on the total weight of the trivalent chromate composition of the present invention. If it is less than 0.1% by weight, the effect of the chemical conversion coating can not be exhibited due to insufficient formation of the insoluble salt of the metal phosphate compound. If it exceeds 5% by weight, the corrosion resistance of the trivalent chromate coating of the present invention Lt; / RTI >

The trivalent chromate composition of the present invention also includes a metal compound. The metal compound reacts with the phosphoric acid group of the phosphoric acid compound to form an insoluble phosphate film, wherein the metal compound provides a metal ion.

Therefore, the metal compound according to the present invention can be suitably used in the present invention as long as it provides a metal ion capable of forming an insoluble phosphate by reacting with a phosphoric acid group. Suitable metal compounds that can be used in the present invention include manganese sulfate, cobalt nitrate, cobalt chloride, cobalt sulfate, nickel chloride, nickel sulfate, nickel nitrate, and metal alkoxide such as tantalum ethoxide, titanium tetraisopropoxide Titanium tetraisopropoxide, Titanium buto-xide, Zirconium butoxide and Zirco-nium ethoxide may be used alone or in combination. .

The metal compound is preferably contained in an amount of 5 to 10% by weight based on the total weight of the trivalent chromate solution composition of the present invention. Since the metal compound has little interferences with each other in the ion state and the addition amount itself is not so large, the metal compound does not adversely affect the liquid stability within a short time such as the formation of the precipitate. However, when the amount of the additive is less than 5% by weight, the coating formed by the reaction with the phosphoric acid compound is too thin, so that the hiding power is decreased or the coating is peeled off. And the improvement in corrosion resistance can not be expected. And more preferably in the range of 7 to 10% by weight.

In order to form insoluble chromium on the surface of the Al or Al alloy by the trivalent chromate composition of the present invention, it is preferable that the pH is in the range of 3-5. However, the trivalent chromate composition of the present invention contains an acid such as a phosphate compound together with an oxidizing agent, and the trivalent chromate composition has a lower pH than the above range. Accordingly, it is preferable that the pH of the trivalent chromate composition of the present invention is raised to the range of 3-5 by adding an alkali agent as a pH adjusting agent.

The alkaline agent as the pH adjusting agent may be used in an amount of 1 to 3% by weight based on the total composition. By adding an alkaline agent to the above range, the pH of the composition due to the use of the oxidizing agent can be raised to the above range.

Examples of the pH adjuster that can be used in the present invention include ammonia hydroxide, sodium hydroxide, and potassium hydroxide, and they may be used alone or in combination. Ammonia water, sodium hydroxide and potassium hydroxide react with the trivalent chromium compound as a composition of the present invention to generate chromium hydrate primarily to cause precipitation of an insoluble salt and to dissolve in an acidic solution having a pH range of 3 to 5 .

The trivalent chromate composition of the present invention may further comprise a surfactant. The trivalent chromate composition of the present invention is very complex in constitutional components. Therefore, in order to prevent precipitation of the pre-use due to unnecessary reaction between components in the solution or deterioration of the performance of the solution during long-term storage, the surfactant may be added as needed.

The surfactant may be an anionic surfactant, for example, potassium lauryl phosphate, sodium dioctylsulfonate, sodium alkylsulfate having 12 to 15 carbon atoms, One or more selected from disodium ethoxylated nonylphenyl ester of sulfosuccinic acid of sulfosuccinic acid can be used.

The surfactant may be contained in an amount of 0.1 to 4% by weight based on the total amount of the composition. The addition of the anionic surfactant in an amount of 0.1% by weight or more is preferable because it can prevent the formation of a precipitate of the composition, thereby ensuring long-term storage stability of a uniform composition. If the content is more than 4% by weight, Which is not preferable in terms of economy. More preferably, the surfactant may be included in the range of 0.3 to 2% by weight.

As the surfactant, it is most preferable to use a disodium ethoxylated nonylphenyl ester of sulfosuccinic acid of sulfo succinic acid in an amount of 0.3 to 2% by weight based on the total amount of the composition.

The trivalent chromate composition of the present invention is prepared by diluting each component as described above with pure water (deionized water). For example, the content of the composition is preferably 4 to 10% by weight, more preferably 8 to 10% by weight based on the total weight of the composition diluent. If the composition is less than 4% by weight based on the total amount of the composition diluent, the thickness of the coating formed under the same conditions is too small to exhibit sufficient corrosion resistance, and if it exceeds 10% by weight, It is not preferable in view of the above.

The composition of the present invention can be prepared by gradually adding each composition component as described above to water (pure water). At this time, it is preferable that the composition is kept in a uniform aqueous solution state so that the layer separation phenomenon does not occur. Accordingly, the trivalent chromate composition of the present invention having excellent performance can be produced.

The corrosion resistance and adhesion can be improved by coating the aluminum or aluminum alloy surface with the trivalent chromate coating composition as described above.

The aluminum or aluminum alloy may be coated by applying a general method such as immersing the aluminum or aluminum alloy in the trivalent chromate coating composition. At this time, the composition is not necessarily limited thereto, but it is preferably maintained at a temperature of 20-30 ° C, and can be performed by immersing the composition in the composition for 1 minute to 2 minutes.

Example

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are illustrative of the present invention, and the present invention is not limited thereto.

Example  1 to 7 and Comparative Example  One

As the aluminum alloy plating material, the surface of an aluminum alloy material (ALDC-12 type: an alloy material for aluminum die casting) used as a back-bone (frame) of a mobile phone is etched, the smut generated in the etching process is completely removed , Washed and dried to prepare a sample.

A trivalent chromate coating composition having the composition shown in Table 1 was prepared.

The prepared specimen was immersed in the trivalent chromate coating composition for 1 minute to prepare a trivalent chromated aluminum plated material.

The trivalent chromate treatment was performed at a pH of the composition of 3.5 to 4 and the temperature was maintained at 30 캜.

The thus obtained trivalent chromate-treated specimen was again washed with water and dried, and the corrosion resistance and electrical resistance were measured and evaluated. The results are also shown in Table 1.

The corrosion resistance evaluation was carried out by a 40-hour salt spray test (domestic test standard: KS D-9502) on the specimens, and visual observation was carried out to record the time of corrosion.

In addition, the electrical resistance was measured with respect to the specimen after the 40-hour salt spray test.

division Example Comparative Example One 2 3 4 5 6 7 One Three
chrome
coating
Composition
(unit:
weight%) Three
chrome
compound Chromium sulfate 5 7 9 11 13 9 9 SurTec
650
Chromital TCP Chromium nitrate - - - - - 6 - Chromium chloride - - - - - - 6 Oxidant Sulfuric acid One 1.5 - 1.5 2 One One Oxalic acid - - 2 - One - - Phosphate compound Sodium hypophosphite 2 One 2 2 One 1.5 1.5 metal
compound Nickel sulfate 10 7 - - 5 5 10 Cobalt sulfate - 3 10 5 5 5 3 Titanium isopropoxide - - - 5 2 2 2 pH adjusting agent Ammonia water (25%) 0.20 0.22 0.19 0.20 0.25 0.23 0.26 Surfactants Aerosole-103 0.2 0.3 0.2 0.4 0.5 0.7 0.4 Water (deionized water) The remainder (remaining amount for 100% of total weight) Properties
evaluation Corrosion resistance (hr) 52 56 48 46 47 51 45 48 Electrical resistance
(Ω after 40 hr salt water spray test) 0.6 0.4 0.9 0.8 0.6 0.9 0.9 0.9

Corrosion resistance test by salt water spraying usually requires no corrosion after 40 hours, and electric resistance is required to be within 1 ?.

As shown in Table 1, when the compositions of Examples 1 to 7 were applied, all required corrosion resistance and electric resistance characteristics were satisfied. In the case of Example 2, the surface state after the corrosion resistance test showed no corrosion until 56 hours as shown in Fig. Therefore, as shown in Table 1, the corrosion resistance of Example 2 was evaluated to be at least 56 hours. 1 is a photograph of the surface state of a specimen after 40 hours of a salt spray test.

Further, as a result of measuring the electrical resistance value of the surface after 40 hours of the salt spray test, as shown in Table 1 above, the best result was also obtained with 0.4?. However, considering the relationship with other embodiments, the increase in the content of the trivalent chromium compound did not tend to increase the corrosion resistance. From this, it is judged that the combination of the appropriate content ratio of the trivalent chromium compound with the oxidizing agent and the composite coating metal compound shows excellent corrosion resistance and electric resistance characteristics of Example 2.

Claims (12)

A composition for forming a trivalent chromate film for aluminum or aluminum alloy die casting,
5 to 15% by weight trivalent chromium compound;
0.1 to 3% by weight of at least one oxidizing agent selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, maleic acid, acetic acid and oxalic acid;
0.1 to 3% by weight of a phosphoric acid compound;
5 to 10% by weight of a metal compound;
1 to 3% by weight of an alkali agent;
0.1 to 4% by weight of a surfactant; And
Remainder water
Wherein the composition is free of hexavalent chromium and fluorine components and has a pH of 3 to 5. The composition for forming a trivalent chromate film according to claim 1,
The composition for forming a trivalent chromate film according to claim 1, wherein the trivalent chromium compound is at least one selected from the group consisting of chromium nitrate, chromium sulfate, chromium acetate, and chromium chloride.
delete The method of claim 1, wherein the phosphate compound has a first acid soda (NaH ₂ PO _4), secondary phosphate soda (Na ₂ HPO _4), the third phosphoric acid soda (Na ₃ PO _4), and hypophosphorous acid soda (NaH ₂ PO ₂ ). ≪ / RTI >
The method according to claim 1, wherein the metal compound is at least one selected from the group consisting of manganese sulfate, cobalt nitrate, cobalt chloride, cobalt sulfate, nickel chloride, nickel sulfate, nickel nitrate, and metal alkoxide: tantalum ethoxide, titanium tetraisopropoxide Wherein the composition is at least one selected from the group consisting of titanium tetraisopropoxide, titanium butoxide, zirconium butoxide and zirconium ethoxide.
The composition according to claim 1, wherein the alkali agent is at least one selected from the group consisting of ammonia hydroxide, sodium hydroxide, and potassium hydroxide.
The composition for forming a trivalent chromate film according to claim 1, wherein the surfactant is an anionic surfactant.
The method of claim 7, wherein the anionic surfactant is selected from the group consisting of Potassium Lauryl phosphate, Sodium Dioctylsulfonate, Sodium Alkylsulfate having 12 to 15 carbon atoms, Wherein the composition is at least one selected from the group consisting of disodium ethoxylated nonylphenyl ester of sulfosuccinic acid.
delete Aluminum or aluminum alloy is immersed in the composition for forming a chromate film of any one of claims 1, 2 and 4 to 8 having a temperature of 20 to 30 占 폚 for 1 to 2 minutes, A process for producing an aluminum or aluminum alloy die cast in which a trivalent chromate and a metal phosphate coating are formed on an aluminum or aluminum alloy surface. delete delete

Images