JP2006183144A - Method for surface treatment of aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for surface treatment of an aluminum alloy capable of forming a uniform and dense zinc phosphate coating which has excellent corrosion resistance properties, on the surface of the aluminum alloy. <P>SOLUTION: The surface of the aluminum alloy adjusted by a surface adjustor containing a predetermined volume of zinc phosphate particles, copolymer containing carboxylic acid group, and natural hectorite and/or synthetic hectorite respectively, and then the surface of the resultant aluminum alloy is subjected to chemical processing by a zinc phosphate treating agent containing a predetermined volume of chelating agent that can chelate bond with iron ion, thereby the uniform and dense zinc phosphate coating can be formed on the surface of the aluminum alloy. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface treatment method for an aluminum alloy, and more particularly to a surface treatment method for an aluminum alloy capable of forming a uniform and dense zinc phosphate coating excellent in corrosion resistance on the surface of the aluminum alloy.

  Metal materials such as steel plates, galvanized steel plates, and aluminum alloys are used in various fields such as automobile bodies and other automobile parts, building materials, furniture, etc., and these metal materials are painted and then commercialized. Is done. The coating is performed mainly for the purpose of preventing the corrosion of the metal material in addition to improving the design properties of these metal materials, and as a pretreatment for coating, surface treatments such as degreasing, surface adjustment, and chemical conversion treatment are sequentially performed.

  The surface adjustment is a process necessary for forming a high-density chemical conversion film uniformly and rapidly on the entire surface of the metal material in the chemical conversion process of the next step. Specifically, by bringing the surface conditioner into contact with the surface of the metal material, the surface conditioner particles are adsorbed on the surface of the metal material, and the formation of the chemical conversion treatment film is promoted.

  By the way, in an automobile body and other automobile parts, an aluminum alloy is partially used, and the aluminum alloy is in contact with a cold-rolled steel sheet (hereinafter referred to as SPC) or an galvannealed steel sheet (hereinafter referred to as GA). Is used. In such a member, since aluminum is a base metal, aluminum is excessively dissolved in the chemical conversion treatment agent, and the chemical conversion film may not be formed normally.

  In response to this, by assembling an automobile body with an insulator sandwiched between an aluminum alloy and SPC or GA, it is possible to suppress excessive dissolution of aluminum in the chemical conversion treatment agent and to form a good chemical film on the aluminum alloy. Can be formed.

  However, when an insulator is used, electricity does not flow to the aluminum alloy at the time of electrodeposition coating in the next process, and thus it cannot be normally coated. For this reason, in the electrodeposition coating process, it is necessary to separately connect the aluminum alloy with an electric cable or the like. Furthermore, in the baking process after electrodeposition coating, the insulator shrinks, so that additional tightening is necessary. Therefore, it takes more man-hours than usual, and a special production line is indispensable.

  Moreover, when there is much content of copper in an aluminum alloy, the corrosion resistance as an aluminum alloy, especially yarn rust resistance and water-resistant adhesiveness will fall. This is because the potential difference between aluminum and copper is large, and aluminum is eluted significantly in a corrosive environment. Therefore, in order to ensure good corrosion resistance, it is necessary to reduce the copper content in the aluminum alloy, but this is not a good solution because it leads to an increase in cost.

Therefore, the development of a surface treatment method capable of forming a uniform and dense chemical conversion treatment film having excellent corrosion resistance on the surface of an aluminum alloy is an urgent issue imposed on those skilled in the art. The invention disclosed in Patent Document 1 can be cited as an effort to improve the chemical conversion treatment agent in order to solve such problems. In Patent Document 1, zinc ions are 0.1 to 2.0 g / l, nickel ions are 0.1 to 4.0 g / l, manganese ions are 0.1 to 3.0 g / l, and phosphoric acid. 5 to 40 g / l of ions, 0.1 to 15 g / l of nitrate ions, 0.01 to 0.5 g / l of nitrite ions, and 0.5 to 0.5 in terms of complex fluoride as fluoride. -1.0 g / l, an aqueous solution containing 0.3 to 0.5 g / l of a simple fluoride in terms of F, and a chelating agent capable of chelating with iron ions in terms of Fe A zinc phosphate treating agent characterized by containing 0.025 to 0.45 g / l has been proposed. According to this zinc phosphate treating agent, a uniform and dense zinc phosphate coating excellent in corrosion resistance is formed on the surface of an aluminum alloy having a copper content of 0.1% by weight or less, or on the ground surface thereof. Can be formed.
Japanese Patent No. 3366826

  The present invention, as a solution to the above problems, is an invention that has been addressed from both the improvement of the surface conditioner and the improvement of the chemical conversion treatment agent. On the surface of the aluminum alloy, the present invention is uniform and dense with excellent corrosion resistance. It aims at providing the surface treatment method of the aluminum alloy which can form a zinc phosphate membrane | film | coat.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the surface of the aluminum alloy was surface-adjusted with zinc phosphate particles, a carboxylic acid group-containing copolymer, and a surface conditioner containing a predetermined amount of natural hectorite and / or synthetic hectorite, and then chelated with iron ions. We found that a uniform and dense zinc phosphate coating with excellent corrosion resistance can be formed on the surface of an aluminum alloy by chemical conversion treatment with a zinc phosphate chemical conversion treatment containing a predetermined amount of a chelating agent capable of binding. The invention has been completed. More specifically, the present invention provides the following.

(1) The step of degreasing and washing the surface of the aluminum alloy, the step of adjusting the surface of the aluminum alloy that has been degreased and washed with a surface conditioner, and the surface of the aluminum alloy that has been surface-adjusted with phosphoric acid A surface treatment method for an aluminum alloy, comprising a chemical conversion treatment step with a zinc chemical conversion treatment agent, wherein the surface conditioner comprises ₅₀ ppm or more and 2000 ppm or less and less than 50 mass% of zinc phosphate particles having a D50 of 3 μm or less. A carboxylic acid group-containing copolymer obtained by copolymerizing a monomer composition containing an amount of acrylic acid and an amount of 2-acrylamido-2-methylpropanesulfonic acid exceeding 50% by mass; And a surface condition having a pH of 7 or more and 12 or less containing 3 to 200 ppm of natural hectorite and / or synthetic hectorite. The zinc phosphate chemical conversion treatment agent is 0.1 g / l or more and 2.0 g / l or less, nickel ion is 0.1 g / l or more and 4.0 g / l or less, and manganese ion is 0.00 g. 1 g / l to 3.0 g / l, phosphate ions from 5 g / l to 40 g / l, complex fluorides from F to 0.5 g / l to 1.0 g / l, simple fluorides from F Phosphoric acid comprising 0.3 g / l or more and 0.5 g / l or less, and an acidic aqueous solution containing a chelating agent capable of chelating with iron ions in an amount of 0.025 g / l or more and 0.45 g / l or less in terms of Fe A method for surface treatment of an aluminum alloy as a zinc chemical conversion treatment agent.

  (2) The surface treatment method for an aluminum alloy according to (1), wherein the content of copper in the aluminum alloy is 0.2% by weight or less.

  ADVANTAGE OF THE INVENTION According to this invention, the surface treatment method of the aluminum alloy which can form the uniform and precise zinc phosphate membrane | film | coat excellent in corrosion resistance on the surface of an aluminum alloy can be provided.

  Hereinafter, embodiments of the present invention will be described.

<Surface conditioner>
The surface conditioner used in the present invention is a surface conditioner containing zinc phosphate particles, a carboxylic acid group-containing copolymer, and a predetermined amount of natural hectorite and / or synthetic hectorite. More specifically, the zinc phosphate particles having a D ₅₀ of 3 μm or less contain 50 ppm or more and 2000 ppm or less of acrylic acid in an amount of less than 50% by mass and 2-acrylamido-2-methylpropanesulfonic acid in an amount of more than 50% by mass. 2 to 200 ppm of a carboxylic acid group-containing copolymer obtained by copolymerizing the monomer composition to be used, and 3 to 200 ppm of natural hectorite and / or synthetic hectorite and having a pH of 7 to 12 It is a surface conditioner.

  Conventionally known surface conditioners containing divalent or trivalent phosphate particles cannot form a sufficient amount of chemical conversion film on the surface of the aluminum alloy, whereas the surface used in the present invention. The adjusting agent can form a sufficient amount of the chemical conversion film. For this reason, according to the surface treatment method according to the present invention, sufficient corrosion resistance can be imparted to the aluminum alloy.

Zinc phosphate particles contained in the surface conditioning agent used in the present invention, D ₅₀ is at 3μm or less, smaller than the particle size of the zinc phosphate particles used in the conventional surface control agent. For this reason, sedimentation of the zinc phosphate particles in the surface conditioner is suppressed, and the stability is excellent. In addition, a large amount of surface conditioner particles can be adsorbed on the surface of the aluminum alloy, and the formation of the chemical conversion film can be promoted. Since the D ₅₀ of zinc phosphate particles in the case where 0.01μm or less, there is a fear that zinc phosphate particles aggregate due to excessive dispersion is undesirable. More preferably, they are 0.05 micrometer or more and 1 micrometer or less.

Here, D ₅₀ is called a 50% volume diameter, and when the cumulative curve is obtained based on the particle size distribution in the dispersion with the total volume of zinc phosphate particles being 100%, the cumulative curve is 50%. Means the particle size at the point of%. The D ₅₀ is, for example, a laser Doppler type particle size analyzer by using a particle size measuring apparatus such as (manufactured by Nikkiso Co., Ltd., trade name "Microtrac UPA150"), can be measured.

The zinc phosphate particles can be obtained by using zinc phosphate which is usually used as a raw material. Zinc phosphate includes tetrahydrate, dihydrate, monohydrate and anhydrous, and any zinc phosphate can be used in the surface conditioning agent according to the present invention. Usually, it is sufficient to use a white powdery tetrahydrate which is generally easily available. These zinc phosphates may be subjected to various surface treatments. For example, it may be surface-treated with a silane coupling agent, rosin, silicone compound, metal alkoxide such as silicon alkoxide or aluminum alkoxide. The shape of zinc phosphate is not particularly limited, and any shape such as a plate shape or a flake shape can be used. These zinc phosphates are refined by a conventionally known dispersion method using a disperser such as a bead mill, a high-pressure homogenizer, or an ultrasonic disperser to obtain zinc phosphate particles having a D ₅₀ of 3 μm or less.

  The content of zinc phosphate particles is 50 ppm or more and 2000 ppm or less, more preferably 60 ppm or more and 1500 ppm or less. When the content of the zinc phosphate particles is less than 50 ppm, only a small amount of the surface conditioner particles are adsorbed on the surface of the aluminum alloy, and the formation of the chemical conversion film cannot be promoted. Moreover, even if it exceeds 2000 ppm, the surface adjustment effect corresponding to the increase in the amount is not obtained and it is not economical.

  The surface conditioner used in the present invention includes a monomer composition containing less than 50% by weight of acrylic acid and more than 50% by weight of 2-acrylamido-2-methylpropanesulfonic acid. Polymerized carboxylic acid group-containing copolymers are included. This carboxylic acid group-containing copolymer acts as a dispersant and has the effect of promoting the formation of a chemical conversion film. For this reason, in the chemical conversion treatment of the next step, a uniform and dense chemical conversion treatment film can be formed, and excellent corrosion resistance can be imparted to the aluminum alloy.

  A carboxylic acid group-containing copolymer is obtained by peroxidizing a monomer composition containing less than 50% by weight of acrylic acid and more than 50% by weight of 2-acrylamido-2-methylpropanesulfonic acid. It can be easily obtained by a conventionally known method of copolymerization under a catalyst such as a product. When the content of acrylic acid is 50% by mass or more, or when the content of 2-acrylamido-2-methylpropanesulfonic acid is 50% by mass or less, a good chemical conversion film is formed on the surface of the aluminum alloy. It cannot be formed. The lower limit of the acrylic acid content is more preferably 20% by mass, and even more preferably 25% by mass. Moreover, as for the upper limit of content, it is more preferable that it is 45 mass%, and it is further more preferable that it is 40 mass%. On the other hand, the lower limit of the content of 2-acrylamido-2-methylpropanesulfonic acid is more preferably 55% by mass, and further preferably 60% by mass. Moreover, as for the upper limit of content, it is more preferable that it is 80 mass%, and it is further more preferable that it is 75 mass%.

  The said monomer composition may contain another monomer in the range which does not inhibit the effect of this invention. Examples of other monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, Hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypentyl acrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxypentyl methacrylate, Examples include vinyl acetate. These monomers may be blended alone in the monomer composition, or two or more may be blended in the monomer composition.

  The content of the carboxylic acid group-containing copolymer is 2 ppm to 200 ppm, more preferably 4 ppm to 100 ppm. When the content of the carboxylic acid group-containing copolymer is less than 2 ppm, the dispersion force is insufficient and the particle size of the zinc phosphate particles is increased, and at the same time, the stability of the surface conditioner is lowered and may be precipitated. There is. Moreover, when content exceeds 200 ppm, the surface adjustment effect corresponding to the increase in the quantity is not acquired, and it is not economical.

  Furthermore, the surface conditioning agent used in the present invention contains natural hectorite and / or synthetic hectorite. Natural hectorite and synthetic hectorite may be used alone or in combination of two or more. By including natural hectorite and / or synthetic hectorite in the surface conditioner, more excellent dispersion stability can be imparted, and sedimentation of zinc phosphate particles can be prevented.

  Natural hectorite is a trioctahedral clay mineral belonging to the montmorillonite family represented by Chemical Formula 1. As a commercial item of natural hectorite, BENTON EW, BENTON AD (made by ELEMENTIS) etc. are mentioned, for example.

  Synthetic hectorite has a crystal three-layer structure, and approximates hectorite belonging to the unrestricted layer expansion type trioctahedral having an expansion lattice, and is represented by Chemical Formula 2. Examples of commercially available synthetic hectorite include Laporte Industries Ltd. The brand names Laponite B, S, RD, RDS, XLG, XLS, and the like are available. These are white powders and easily form sols or gels when water is added. Other commercially available products include Lucentite SWN manufactured by Corp Chemical.

  In Chemical Formula 2, 0 <a ≦ 6, 0 <b ≦ 6, 4 <a + b <8, 0 ≦ c <4, and x = 12-2a-b. M is almost Na. Synthetic hectorite is composed of magnesium, silicon, sodium, trace amounts of lithium and fluorine as main components.

  The content of natural hectorite and / or synthetic hectorite is 3 ppm or more and 200 ppm or less, more preferably 20 ppm or more and 100 ppm or less. When the content of natural hectorite and / or synthetic hectorite is less than 3 ppm, the precipitation of zinc phosphate particles may not be effectively prevented. Moreover, when content exceeds 200 ppm, the surface adjustment effect corresponding to the increase in the quantity is not acquired, and it is not economical.

  The pH of the surface conditioner used in the present invention is 7 or more and 12 or less. When the pH is less than 7, the zinc phosphate particles are easily dissolved and may become unstable. Moreover, when pH exceeds 12, in the chemical conversion treatment of a next process, the raise of pH of a chemical conversion treatment agent is caused and there exists a possibility of causing a chemical conversion treatment defect.

  The surface conditioner used in the present invention can be further blended with other dispersants, dispersion media, thickeners and the like as long as the effects of the present invention are not impaired. When adjusting the surface of an aluminum alloy using such a surface conditioner, the surface conditioner is brought into contact with the surface of the aluminum alloy. The contact method is not particularly limited, and a conventionally known method such as an immersion method or a spray method can be employed.

<Zinc phosphate chemical conversion treatment agent>
The zinc phosphate chemical conversion treatment agent used in the present invention has a zinc ion of 0.1 g / l or more and 2.0 g / l or less, a nickel ion of 0.1 g / l or more and 4.0 g / l or less, and a manganese ion of 0.00 g / l or less. 1 g / l to 3.0 g / l, phosphate ions from 5 g / l to 40 g / l, complex fluorides from F to 0.5 g / l to 1.0 g / l, simple fluorides from F Phosphoric acid comprising 0.3 g / l or more and 0.5 g / l or less, and an acidic aqueous solution containing a chelating agent capable of chelating with iron ions in an amount of 0.025 g / l or more and 0.45 g / l or less in terms of Fe It is a zinc chemical conversion treatment agent.

  In zinc phosphate chemical conversion treatment, by containing divalent or trivalent iron ions in the chemical conversion treatment agent, there is an effect of forming a uniform and dense zinc phosphate coating on the iron-based surface or zinc-based surface. It is known. The zinc phosphate chemical conversion treatment agent used in the present invention contains a chelating agent capable of chelating with iron ions, and this chelating agent chelates the eluted iron ions from the iron-based surface. For this reason, a fixed amount of iron ions can be stably held in the chemical conversion treatment agent, and the effect of iron ions as described above can be expressed in the formation of a zinc phosphate film on the aluminum-based surface.

  The zinc ion concentration is 0.1 g / l or more and 2.0 g / l or less, more preferably 0.3 g / l or more and 1.5 g / l or less. When the zinc ion concentration is less than 0.1 g / l, a uniform zinc phosphate coating is not formed on the aluminum-based surface, and there are many skeins, and a blue-colored coating is formed in part. In addition, when the zinc ion concentration exceeds 2.0 g / l, a uniform zinc phosphate film is formed, but it is easily dissolved in alkali. Especially in the subsequent step of cationic electrodeposition coating, an alkaline atmosphere Because it is exposed to the bottom, it feels bad. When the zinc phosphate coating dissolves, the warm salt resistance decreases, and particularly in the case of an iron-based surface, the cab resistance (ie, the ability to prevent rust corrosion) is reduced. The desired performance cannot be obtained.

  The nickel ion concentration is 0.1 g / l or more and 4.0 g / l or less, more preferably 0.1 g / l or more and 2.0 g / l or less. When the nickel ion concentration is less than 0.1 g / l, the corrosion resistance of iron decreases, and when it exceeds 4.0 g / l, the corrosion resistance of aluminum decreases.

  The manganese ion concentration is 0.1 g / l or more and 3.0 g / l or less, more preferably 0.6 g / l or more and 3.0 g / l or less. When the manganese ion concentration is less than 0.1 g / l, the effect of improving the adhesion between the zinc-based surface and the coating film and the resistance to warm salt water is insufficient. Moreover, when it exceeds 3.0 g / l, the effect corresponding to the increase in the quantity cannot be expected, and it is economically disadvantageous.

  The phosphate ion concentration is 5 g / l or more and 40 g / l or less, more preferably 10 g / l or more and 30 g / l or less. When the phosphate ion concentration is less than 5 g / l, it is easy to form a non-uniform zinc phosphate film, and when it exceeds 40 g / l, improvement in the effect commensurate with the increase in the amount cannot be expected. It is economically disadvantageous.

  Among the fluorides, the concentration of the complex fluoride is 0.5 g / l or more and 1.0 g / l or less in terms of F. When the concentration of the complex fluoride is less than 0.5 g / l in terms of F, a uniform zinc phosphate film is not formed on the aluminum-based surface, and excellent corrosion resistance cannot be obtained. On the other hand, if it exceeds 1.0 g / l, the iron-based surface is excessively etched, the amount of zinc phosphate film is reduced, and excellent corrosion resistance cannot be obtained.

  Among fluorides, the concentration of simple fluoride is 0.3 g / l or more and 0.5 g / l or less in terms of F. When the concentration of simple fluoride is less than 0.3 g / l in terms of F, a zinc phosphate film is not sufficiently formed on the aluminum surface, and excellent yarn rust resistance cannot be obtained. In addition, when it exceeds 0.5 g / l, the increase in the etching amount of the aluminum-based surface promotes the generation of by-products mainly composed of Al, F, and Na on the aluminum-based surface, and has excellent yarn resistance. Rust and water adhesion cannot be obtained.

  Here, examples of the zinc ion supply source include zinc oxide, zinc carbonate, and zinc nitrate. Examples of the nickel ion supply source include nickel carbonate, nickel nitrate, nickel chloride, nickel phosphate, and nickel hydroxide. Examples of the manganese ion supply source include manganese carbonate, manganese nitrate, and chloride. Examples include manganese and manganese phosphate. Furthermore, examples of the phosphate ion supply source include phosphoric acid, zinc phosphate, and manganese phosphate.

Examples of the complex fluoride include SiF ₆ and BF _4. Examples of the supply source of SiF ₆ include hydrofluoric acid, nickel silicofluoride, zinc silicofluoride, Examples thereof include manganese hydrofluoride, iron silicofluoride, magnesium silicofluoride, and calcium silicofluoride. Examples of the supply source of BF ₄ include borohydrofluoric acid, nickel borohydrofluoride, zinc borofluoride, manganese borofluoride, iron borofluoride, and magnesium borofluoride. And calcium borohydrofluoride.

  Among fluorides, simple fluorides that supply free fluorine ions include, for example, hydrofluoric acid, potassium fluoride, sodium fluoride, ammonium fluoride, acidic potassium fluoride, acidic sodium fluoride, ammonium fluoride. And ammonium ammonium fluoride. Aluminum ions eluted from the aluminum alloy are combined with free fluorine ions in the chemical conversion treatment agent to form complex ions and promote the formation of a zinc phosphate coating.

  Furthermore, the zinc phosphate chemical conversion treatment agent according to the present invention contains a chelating agent capable of chelate bonding with iron ions in an amount of 0.025 g / l to 0.45 g / l in terms of Fe. In this way, by adding a chelating agent capable of chelate bonding with iron ions to the zinc phosphate chemical conversion treatment agent, iron ions eluted from the iron-based surface can be retained in the chemical conversion treatment agent, and the coating is uniform and dense. A highly functional zinc phosphate coating can be formed. Specific examples of the chelating agent include citric acid, tartaric acid, EDTA, gluconic acid, succinic acid, tannic acid, malic acid, and compounds and derivatives thereof.

  When the content of the chelating agent is less than 0.025 g / l, the coating performance of the zinc phosphate coating on the aluminum-based surface is lowered, and a uniform and dense zinc phosphate coating with high coverage cannot be formed. . On the other hand, when it exceeds 0.45 g / l, the amount of zinc phosphate film decreases, and excellent yarn rust resistance cannot be obtained.

  The pH of the zinc phosphate chemical conversion treatment agent is 2.0 or more and 5.0 or less, more preferably 3.0 or more and 4.0 or less. The pH can be adjusted with NaOH, an aqueous ammonia solution, nitric acid or the like. When the aluminum alloy is subjected to chemical conversion treatment, a zinc phosphate treating agent is brought into contact with the aluminum alloy. The contact temperature is preferably 40 ° C. or higher and 60 ° C. or lower, more preferably 42 ° C. or higher and 48 ° C. or lower. Examples of the contact method include a spray method and a dipping method, and both the spray treatment time and the dipping time are from 1 minute to 10 minutes, and more preferably from 1.5 minutes to 3 minutes. As another contact method, the zinc phosphate treating agent may be brought into contact with the aluminum alloy by a flow coating method or a roll coating method. The aluminum alloy that has been subjected to chemical conversion treatment is subjected to a drying step after being washed with water. The drying temperature is 80 ° C. or higher and 120 ° C. or lower.

<Aluminum alloy>
The content of copper in the aluminum alloy used in the present invention is 0.2% by weight or less. When the content of copper in the aluminum alloy is large, the corrosion resistance is lowered. For example, even in Patent Document 1, the copper content needs to be 0.1% by weight or less. In contrast, in the surface treatment method according to the present invention, excellent corrosion resistance can be imparted even when the copper content is 0.2% by weight.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Examples 1-7, Comparative Examples 1-5>
[Material to be processed]
In any of Examples 1 to 7 and Comparative Examples 1 to 5, the same aluminum alloy was used as a processing target material. Specifically, an aluminum alloy having a copper content of 0.01% by weight or less, 0.1% by weight, or 0.2% by weight was used. The size of the aluminum alloy was 70 mm × 150 mm, and the thickness was 0.8 mm. These aluminum alloys were ground on a # 180 sandpaper using a double action sander (“905B4D” manufactured by Compact Tool Co., Ltd.) to obtain a material to be processed. Further, a material to be treated was obtained by contacting and conducting SPC having the same size and thickness as those of the aluminum alloy to these aluminum alloys whose entire surface was ground. That is, for the three types of aluminum alloys having different copper contents, the materials subjected to contact conduction with SPC and the materials not subjected to contact conduction were used as materials to be treated.

  FIG. 1 shows a material to be treated in which an aluminum alloy and SPC are brought into contact with each other. This material to be processed was created by the following procedure. First, the SPC 20 was arranged with an interval of approximately 20 mm on both sides of the aluminum alloy 10, and these were hung by the hanger 40. Next, a material to be processed in which the aluminum alloy 10 and the SPC 20 are brought into contact with each other by providing holes in the upper portions of the aluminum alloy 10 and the SPC 20, connecting these holes with the aluminum wire 30, and connecting the aluminum alloy 10 and the SPC 20. It was.

[Processing process]
In any of Examples 1 to 7 and Comparative Examples 1 to 5, (a) degreasing, (b) water washing, (c) surface conditioning, (d) chemical conversion treatment, (e) water washing, (f) pure water washing, (g ) Drying, (h) Electrodeposition coating. In the water washing step of (b) and (e), tap water was sprayed on the material to be treated at room temperature for 15 seconds, and in the (f) pure water washing step, ion exchange water was sprayed on the material to be treated at room temperature for 15 seconds. In the (g) drying step, the material to be treated was dried at 80 ° C. for 5 minutes. Note that (a) degreasing, (c) surface adjustment, (d) chemical conversion treatment, and (h) electrodeposition coating steps were performed as follows.

[Degreasing]
In any of Examples 1 to 7 and Comparative Examples 1 to 5, the same degreasing treatment was performed for each of the above-described processing target materials. Specifically, an alkaline degreasing agent (trade name “Surf Cleaner SD250”) manufactured by Nippon Paint Co., Ltd., in an aqueous solution containing 1.5% by weight of A agent and 0.9% by weight of B agent, The material to be treated was immersed and degreased at 43 ° C. for 2 minutes.

[Surface adjustment]
In Examples 1 to 7, a surface conditioner (hereinafter referred to as “surface conditioner 1”) containing zinc phosphate particles, a carboxylic acid group-containing copolymer, and natural hectorite and / or synthetic hectorite in respective predetermined amounts. The surface was adjusted using this. Specifically, first, as the adjustment of the surface conditioning agent 1, 0.3 parts by mass of natural hectorite “BENTON EW” (manufactured by ELEMENTIS) is added to 87.7 parts by mass of water, and 3000 rpm is used using a disper. The mixture was stirred for 30 minutes to obtain a pregel. 2 masses of commercially available “Aron A-6020” (40% by mass of acrylic acid, 60% by mass of 2-acrylamido-2-methylpropanesulfonic acid, carboxylic acid group-containing copolymer, manufactured by Toagosei Co., Ltd.) And 50 parts by mass of zinc phosphate particles were added, and the pH was adjusted to 9.0 with caustic soda to obtain a surface conditioner (zinc phosphate particle concentration 1500 ppm, carboxylic acid group-containing copolymer concentration 60 ppm, natural hector Light concentration 45 ppm). Next, the material to be treated was immersed in the obtained surface conditioning agent 1, and surface conditioning was performed at room temperature for 30 seconds.

  In Comparative Examples 1 to 5, surface adjustment was performed using a titanium colloid-based surface conditioner instead of the zinc phosphate-based surface conditioner as in the examples. Specifically, an aqueous solution containing 0.1% by weight of a surface treatment agent (trade name “Surffine 5N-10” for building bath) manufactured by Nippon Paint Co., Ltd. (hereinafter referred to as “Surface Conditioner 2”) The material to be treated was dipped in and the surface was adjusted at room temperature for 30 seconds. In addition, the solid content was set to be substantially equal between the surface conditioner 1 and the surface conditioner 2.

However, about Example 7 and Comparative Example 5, after carrying out degreasing and water washing, it was immersed in the chemical conversion treatment agent which does not contain zinc ion, nickel ion, and manganese ion for 60 seconds at 43 degreeC, and then surface adjustment was performed. The reason for performing such an operation is as follows. In the case where the surface conditioning agent 1 is used for the surface conditioning, even if the chemical conversion treatment is performed in a state where the aluminum material and the SPC are brought into contact with each other, the decrease in the zinc phosphate film is not remarkable. For this reason, these operations were carried out in order to determine the limit value at which the performance can be maintained on the low film amount side. The reason for immersing in the chemical conversion treatment agent not containing metal ions is to make the etching amount of the aluminum material equivalent to that when the chemical conversion treatment is performed in a state where the aluminum material and the SPC are in contact conduction. That is, in order to reduce the coating amount, when the treatment is performed in a short time using a normal chemical conversion treatment agent, the coating amount is small but the etching amount is small. In this case, it cannot be said that the state in which the aluminum material and the SPC are brought into contact with each other can be simulated. Therefore, the etching amount is controlled by a chemical conversion treatment agent that does not contain metal ions. The etching amount was set to about 0.5 g / m ² .

[Chemical conversion treatment]
In any of Examples 1 to 7 and Comparative Examples 1 to 5, chemical conversion treatment was performed by immersing at 43 ° C. for 2 minutes using the same chemical conversion treatment agent. Specifically, as a chemical conversion treatment agent, zinc ion is 1.0 g / l, nickel ion is 1.0 g / l, manganese ion is 1.3 g / l, phosphate ion is 20 g / l, and complex fluoride is F. Chemical conversion treatment containing 0.5 g / l in terms of conversion, 0.35 g / l of simple fluoride in terms of F, and 0.025 g / l in terms of Fe that contains a chelating agent capable of chelating with iron ions The agent was used. The total acidity of the chemical conversion treatment agent was adjusted to 22.2 pt and the free acidity to 0.5 pt. As described above, in Example 7 and Comparative Example 5, the chemical conversion treatment time was set short. Specifically, it was 10 seconds in Example 7, and 20 seconds in Comparative Example 5.

[Electrodeposition coating]
In any of Examples 1 to 7 and Comparative Examples 1 to 5, the same electrodeposition coating was performed. Specifically, cationic electrodeposition coating was performed using a cationic electrodeposition paint (trade name “Power Top V50 Gray”) manufactured by Nippon Paint Co., Ltd. The coating conditions were set so that the coating thickness after baking and drying was 25 μm. After electrodeposition coating, baking was performed at 170 ° C. for 25 minutes to form a cationic electrodeposition coating film on the surface of the aluminum alloy that had been subjected to surface adjustment and chemical conversion treatment.

[Intermediate coating]
An intermediate coating material (trade name “Orga P-5A N-2.0”) manufactured by Nippon Paint Co., Ltd. was spray-coated on the electrodeposition coating film, and baked at a temperature of 140 ° C. for 20 minutes. The film thickness after baking and drying of the formed intermediate coating film was 35 μm.

[Top coating]
A top coat (trade name “Super Rack M-95HB YR-511P”) manufactured by Nippon Paint Co., Ltd. was spray-coated on the intermediate coating film, and baked at a temperature of 140 ° C. for 20 minutes. The film thickness after baking and drying of the formed top coat film was 15 μm.

<Evaluation>
[Yarn rust resistance]
A crosscut (cut length: 20 cm) was put into the coating film of the 3-coated plate using a sharp cutter, and salt water spraying according to JIS-Z2371 was carried out for 24 hours. Next, letting it stand for 240 hours in a humid atmosphere at a temperature of 40 ° C. and a relative humidity of 70 to 75% is one cycle, and the swelling from the cross-cut portion after four cycles was visually confirmed and evaluated according to the following criteria. .

○ ... Almost no swelling is seen.
Δ: Slight swelling is observed.
X: Swelling is remarkable.

[Water-resistant adhesion]
The test plate on which the zinc phosphate coating and the cationic electrodeposition coating were formed was immersed in warm water at 40 ° C. for 240 hours and then cooled to room temperature. Thereafter, a cross-cut adhesion test was performed, and the degree of peeling was visually evaluated according to the following criteria.

○ ... No peeling.
Δ: Edge defect of cut portion is observed.
X: Peeling is observed.

[Chemical conversion film weight]
The chemical conversion film weight was obtained by immersing a chemical conversion-treated test plate in a 30% nitric acid aqueous solution at room temperature for 1 minute to dissolve the chemical conversion film, and measuring and calculating the weight before and after dissolution.

  Table 1 shows the evaluation results of the yarn rust resistance and water resistance adhesion performed on Examples 1 to 7 and Comparative Examples 1 to 5.

The evaluation results in Table 1 are summarized as follows. First, when the aluminum alloy and SPC are brought into contact with each other, good corrosion resistance cannot be obtained in the comparative example, whereas in the example, the copper content in the aluminum alloy is in the range of 0.2% by weight or less. Good corrosion resistance can be obtained. Second, when the copper content in the aluminum alloy is 0.2% by weight, good corrosion resistance cannot be obtained in the comparative example, but in the examples, there is no contact conduction between the aluminum alloy and the SPC. Good corrosion resistance can be obtained. Third, when the zinc phosphate coating has a low coating amount of 0.3 g / m ² , good corrosion resistance cannot be obtained in the comparative example, whereas good corrosion resistance can be obtained in the examples. Therefore, according to the present invention, it was confirmed that a uniform and dense zinc phosphate film excellent in corrosion resistance can be formed on the surface of the aluminum alloy.

It is drawing which shows the process target raw material which made the aluminum alloy and SPC contact-conductive.

Explanation of symbols

10 Aluminum alloy 20 SPC
30 Aluminum wire 40 Hanger

Claims (2)

A step of degreasing and washing the surface of the aluminum alloy, a step of surface-adjusting the surface of the aluminum alloy that has been degreased and washed with water, and a zinc phosphate conversion treatment on the surface of the aluminum alloy that has been surface-adjusted A surface treatment method of an aluminum alloy, comprising a chemical conversion treatment with an agent,
The surface _{modifier, D 50} is 3μm or less of zinc phosphate particles 50ppm or 2000ppm or less is, the amount of 2-acrylamido-2-methylpropanesulfonic acid of more than 50 wt% acrylic acid content of less than 50 wt% 2 to 200 ppm and a carboxylic acid group-containing copolymer obtained by copolymerization of a monomer composition containing a natural hectorite and / or synthetic hectorite to a pH of 7 to 12 The following surface conditioner
The zinc phosphate chemical conversion treatment agent includes zinc ions of 0.1 g / l or more and 2.0 g / l or less, nickel ions of 0.1 g / l or more and 4.0 g / l or less, and manganese ions of 0.1 g / l or more. 3.0 g / l or less, phosphate ion from 5 g / l to 40 g / l, complex fluoride from 0.5 g / l to 1.0 g / l in terms of F, simple fluoride from 0.3 g in terms of F / L to 0.5 g / l and a zinc phosphate chemical conversion treatment comprising an acidic aqueous solution containing a chelating agent capable of chelating with iron ions in an amount of 0.025 g / l to 0.45 g / l in terms of Fe A method for surface treatment of an aluminum alloy.   The surface treatment method for an aluminum alloy according to claim 1, wherein the content of copper in the aluminum alloy is 0.2 wt% or less.

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