JP6083020B2 - Surface treatment method of magnesium or magnesium alloy, acid detergent and chemical conversion treatment agent, and chemical conversion treatment structure of magnesium or magnesium alloy - Google Patents

Description

  The present invention relates to an improved surface treatment method for magnesium or a magnesium alloy.

  Magnesium or a magnesium alloy has features such as being lightweight and having high specific strength, being abundant as a natural resource, and being easier to recycle than resin materials and the like. Magnesium or magnesium alloys with such characteristics are widely used in aircraft, automobiles, agricultural machinery, tools, precision machinery, sports equipment, speaker diaphragms, portable equipment housings, medical equipment, spacecraft, weapons, etc. In recent years, it has been applied to applications such as portable information terminals, notebook personal computers, and cameras that can exhibit characteristics such as lightness, specific rigidity, electromagnetic wave shielding, heat dissipation, recycling, and thin moldability. The use of is increasing.

  However, since magnesium is easy to react with water, alcohol, acid, etc. and has low corrosion resistance, it is produced by casting such as die casting method or injection molding method, plastic processing such as press method using wrought material or forging. It is rarely used in the state, and surface treatment using various methods is necessary for improving corrosion resistance, countermeasures against electric corrosion, improving adhesion with paints, surface lubrication during plastic processing, etc. Accordingly, it is often used in a state of being further coated.

  Known surface treatment methods for magnesium or magnesium alloys include anodization, chemical conversion, plating, painting, and vapor phase (CVD, PVD), but chemical conversion with excellent corrosion resistance and film adhesion. Is widely used. Conventionally, hexavalent chromium has been used for chemical conversion treatment, but the use of hexavalent chromium has been avoided in consideration of the environment. Although the thing containing manganese was used as a non-chromium chemical conversion treatment agent, since manganese is a specific chemical substance, its use is being avoided from the viewpoint of occupational health. Then, the chemical conversion treatment agent for magnesium or magnesium alloy which does not contain chromium and manganese is proposed. For example, Patent Document 1 proposes a method of treating with a chemical conversion treatment aqueous solution containing a carbonate compound as a method of chemical conversion treatment with a treatment solution that does not contain chromium or manganese, while having excellent film corrosion resistance. Patent Document 2 discloses at least one vanadium compound (A), cobalt, as a metal surface treatment agent not containing chromium used for imparting excellent corrosion resistance, alkali resistance and interlayer adhesion to a metal material. Disclosed is a metal surface treatment agent containing a metal compound (B) containing at least one metal selected from the group consisting of nickel, zinc, magnesium, aluminum, calcium, strontium, barium and lithium. Yes.

JP 2003-221684 A JP 2004-183015 A

  However, the chemical conversion treatment film obtained by the chemical conversion treatment method described in Patent Document 1 has excellent performance as a coating base, but the chemical resistance of the chemical conversion treatment film alone is not high. Therefore, in the case of not only a coated product but also an automobile part or the like that requires a considerable level of corrosion resistance in terms of the corrosion resistance of an unpainted internal part or an unpainted part such as a part that is not sufficiently painted, Patent Document 1 When the described chemical conversion treatment method is used, there arises a problem that parts having satisfactory physical properties cannot be obtained. Therefore, although chemical conversion treatment by anodizing treatment method excellent in bare corrosion resistance is also performed, in this case, the process is complicated and processing equipment such as a rectifier is expensive, and generally about 3 to 5 times the chemical conversion treatment method. Cost is required.

  Further, in the chemical conversion treatment of magnesium or magnesium alloy using the metal surface treating agent described in Patent Document 2, there is a problem that the manufacturing cost increases because baking in the final process is required.

  Further, in the conventional chemical conversion treatment method of magnesium or magnesium alloy, the magnesium substrate is largely etched in the pretreatment process or the chemical conversion treatment process, so that the surface roughness becomes rough, and the resulting chemical conversion treatment structure exhibits a gray color tone. Therefore, the conventional chemical conversion treatment method for magnesium or magnesium alloy has a problem that it is difficult to apply to products having high design properties without being coated.

  SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and the surface treatment of magnesium or a magnesium alloy that can provide a magnesium or a magnesium alloy that has simple processing equipment, simple processes, low processing costs, and excellent design and corrosion resistance. It is an object of the present invention to provide a method, an acid detergent and a chemical conversion treatment agent, and a chemical conversion treatment structure of magnesium or a magnesium alloy produced by using them.

According to the first aspect of the present invention that meets the above-mentioned object, an acidic acid detergent containing a fluoride ion source is brought into contact with the surface of defatted magnesium or magnesium alloy, and magnesium fluoride is contained on the surface of the magnesium or magnesium alloy. A chemical conversion treatment agent containing phosphoric acid, strontium ions, and tungstate ions is brought into contact with Step A of forming the first transparent film, and the surface of the magnesium or magnesium alloy on which the first transparent film is formed. By providing a surface treatment method for magnesium or a magnesium alloy, comprising the step B of forming a second transparent film containing strontium phosphate, magnesium phosphate and magnesium tungstate on the surface of the first transparent film. It solves the problem.

  In the magnesium or magnesium alloy surface treatment method according to the first aspect of the present invention, the surface of the magnesium or magnesium alloy on which the first transparent film is formed between the step A and the step B is 80 ° C. or higher. The step of contacting the 3-6N alkali hydroxide solution of 3 to 10 minutes may be further included.

  In the magnesium or magnesium alloy surface treatment method according to the first aspect of the present invention, the acid detergent preferably has a fluoride ion concentration of 0.3 to 1 mol / L.

  In the surface treatment method of magnesium or a magnesium alloy according to the first aspect of the present invention, the acid detergent preferably contains an alkali fluoride, ammonium fluoride or ammonium hydrogen fluoride, and phosphoric acid.

  In the surface treatment method of magnesium or magnesium alloy according to the first aspect of the present invention, the acid detergent preferably has a pH of 2.0 to 4.0.

  In the surface treatment method of magnesium or a magnesium alloy according to the first aspect of the present invention, it is preferable that the temperature of the acid detergent in the step A is 25 to 60 ° C. and the treatment time is 1 minute or more and 10 minutes or less.

  In the magnesium or magnesium alloy surface treatment method according to the first aspect of the present invention, the chemical conversion treatment agent has a strontium ion concentration of 0.001 to 0.5 mol / L and a tungstate ion concentration of 0.1 to 20 mmol. / L is preferable.

  In the surface treatment method of magnesium or magnesium alloy according to the first aspect of the present invention, the chemical conversion treatment agent preferably has a pH of 2.8 to 3.2.

  In the surface treatment method of magnesium or magnesium alloy according to the first aspect of the present invention, it is preferable that the temperature of the chemical conversion treatment agent in Step B is 25 to 50 ° C. and the treatment time is 1 minute or more and 10 minutes or less.

  A second aspect of the present invention is an acid detergent used in an acid cleaning step which is a pretreatment of a chemical conversion treatment of magnesium or a magnesium alloy, comprising alkali fluoride, ammonium fluoride or ammonium hydrogen fluoride, and phosphoric acid. In addition, the above-mentioned problems are solved by providing an acid detergent having a fluoride ion concentration of 0.4 to 1 mol / L and a pH of 2.0 to 4.0.

A third aspect of the present invention is a chemical conversion treatment agent used for chemical conversion treatment of magnesium or a magnesium alloy having a transparent film containing magnesium fluoride formed on a surface thereof, and includes phosphoric acid, strontium ions, tungstate ions, A chemical conversion treatment agent having a strontium ion concentration of 0.001 to 0.5 mol / L, a tungstate ion concentration of 0.1 to 20 mmol / L, and a pH of 2.8 to 3.2 By doing so, the above-mentioned problems are solved.

  According to a fourth aspect of the present invention, there is provided a first transparent film containing magnesium fluoride formed on the surface of magnesium or a magnesium alloy, and strontium phosphate and magnesium phosphate formed on the surface of the first transparent film. And the said subject is solved by providing the chemical conversion treatment structure of magnesium or a magnesium alloy which has a 2nd transparent film containing magnesium tungstate.

  According to the surface treatment method of magnesium or magnesium alloy of the present invention, since surface treatment can be performed in a short time under mild conditions, the processing equipment and process are simple, the processing cost is low, and the object to be processed. Magnesium or magnesium alloy with excellent adhesion and high adhesion and high corrosion resistance can be obtained by optimizing the composition of the first and second films because the surface of magnesium or magnesium alloy is hardly roughened. Can do. Moreover, according to this invention, the acid detergent and chemical conversion treatment agent which can be used for the surface treatment of the above-mentioned magnesium or magnesium alloy are provided. Furthermore, according to the present invention, magnesium or a magnesium alloy having a transparent film formed on the surface, which has high designability and transparency, is chemically stable, has high adhesion and is dense, and has excellent corrosion resistance. A chemical conversion treatment structure is provided.

Subsequently, an embodiment of the present invention will be described to provide an understanding of the present invention. A surface treatment method of magnesium or a magnesium alloy according to an embodiment of the present invention (hereinafter sometimes referred to as “surface treatment method”) includes a fluoride ion source on the surface of degreased magnesium or magnesium alloy. A step A of contacting the acidic acid detergent containing, and forming a first transparent film containing magnesium fluoride on the surface of the magnesium or magnesium alloy; and the surface of the magnesium or magnesium alloy on which the first transparent film is formed, Process B for forming a second transparent film containing strontium phosphate, magnesium phosphate and magnesium tungstate on the surface of the first transparent film by chemical contact with phosphoric acid, strontium ions and tungstate ions Have

  Any known magnesium or magnesium alloy can be used without particular limitation as magnesium or a magnesium alloy (hereinafter abbreviated as “magnesium alloy or the like”) to which the surface treatment method is applied. Specific examples of magnesium or a magnesium alloy include magnesium, aluminum-magnesium, aluminum-magnesium-manganese, aluminum-magnesium-silicon, aluminum-zinc-magnesium, and the like. There are no particular limitations on the size and shape of the object to be processed made of these materials, and for example, it may be a plate shape, a rod shape, a wire, or a tube, or may be various parts processed into various shapes. Since it can form a film with excellent corrosion resistance by itself, it can be used without painting, such as electrical equipment parts such as mobile phones, notebook computers, and digital cameras, and automobile parts such as wheels, frames, and engine covers. This is particularly effective when applied to parts to be used.

  Machine cutting oil, buffing particles, etc. are attached to the surface of the magnesium alloy or the like that has been subjected to hairline processing or mirror polishing, and a process of removing these before chemical conversion treatment is indispensable. Any known method such as washing with an organic solvent, acid washing, or washing with an alkaline degreasing agent can be used for degreasing magnesium alloys, etc., but acid under severe conditions (eg, high concentration, high temperature, long time) can be used. Since degreasing by washing may cause the surface of the magnesium alloy or the like to be etched and increase the surface roughness, it is preferable to perform the degreasing in as short a time as possible using, for example, an alkaline degreasing agent. Specific examples of the degreasing method include a method of immersing in a 5N sodium hydroxide aqueous solution at 85 ° C. for 5 minutes.

  Next, for the purpose of removing the release agent and oxide layer from the surface of the magnesium alloy etc. after degreasing, the surface is immersed in an acid detergent containing acid to dissolve the surface. The process which forms the transparent film of 1 is performed (process A). The acid cleaning of the magnesium alloy after degreasing is performed by bringing the magnesium alloy after degreasing into contact with an acid detergent containing fluoride ions and phosphoric acid.

The acid detergent contains alkali fluoride (LiF, NaF, KF, RbF or CsF), ammonium fluoride (NH ₄ F) or ammonium hydrogen fluoride ((NH ₄ ) HF ₂ ) as a fluoride ion source. Fluoride ions react with magnesium ions eluted from a magnesium alloy or the like to produce magnesium fluoride, which is deposited on the surface of the magnesium alloy or the like to form a first transparent film. A preferred fluoride ion source includes ammonium hydrogen fluoride. The fluoride ion concentration is preferably 0.3 to 1 mol / L, more preferably 0.5 to 0.8 mol / L.

  Moreover, the acid detergent contains phosphoric acid as an acid. The pH of the acid detergent is preferably 2.0 to 4.0, more preferably 2.7 to 3.5, and the concentration of phosphoric acid is appropriately adjusted so that an acid detergent having a desired pH is obtained.

  The temperature of the acid detergent is preferably 25 to 60 ° C., and the treatment time with the acid detergent is preferably 1 minute or more and 10 minutes or less. Although it is ideal if the surface of a magnesium alloy or the like can be uniformly dissolved by acid treatment, the magnesium alloy has a heterogeneous metal structure. For example, AZ91D (Mg—Al—Zn 90), which is the most popular magnesium alloy, is used. : 9: 1), there are a plurality of phases such as α-Mg solid solution and β-Mg17Al12 compound phase. For this reason, a potential difference is generated between the metal structures, and the α-Mg solid solution having a low aluminum content is preferentially dissolved. Therefore, the surface roughness increases by acid cleaning, and the metallic luster due to hairline processing or mirror surface processing may be lost. However, by making the acid detergent as described above, the eluted magnesium and fluoride ions By forming a magnesium fluoride film, dissolution of the α-Mg solid solution can be suppressed. Therefore, the α-Mg solid solution is preferentially dissolved, so that an increase in surface roughness can be suppressed and acid cleaning can be performed while maintaining a metallic luster.

  After the treatment with the acid detergent, a treatment for removing smut formed on the surface of the magnesium alloy or the like on which the first transparent film is formed is performed as necessary. As a result of the α-Mg solid solution preferentially dissolved by acid cleaning, an aluminum-rich phase such as a β-Mg17Al12 compound phase remains on the surface as a smut. Since the smut is usually colored black or the like and impairs the aesthetic appearance of the surface of the magnesium alloy or the like, it must be removed using any known method. There are various methods for removing the smut. For example, the smut can be removed by bringing a surface of a magnesium alloy or the like after forming the first transparent film into contact with a 3-6N alkali hydroxide solution at 80 ° C. or higher for 1 to 10 minutes. Is called. As a specific example of the method preferably used, a method of immersing in a 5N sodium hydroxide aqueous solution at 85 ° C. for 5 minutes is the same as in the case of degreasing. As will be described later, when the smut removal treatment is performed by this method, generation of hydrogen gas accompanying dissolution of magnesium can be suppressed during the formation of the transparent film in the subsequent step B, smoothness is high, and corrosion resistance and adhesion are improved. An excellent transparent film can be obtained.

Next, a chemical conversion treatment agent containing phosphoric acid, strontium ions, and tungstate ions is brought into contact with the surface of the magnesium alloy or the like on which the first transparent film has been formed after removing the smut, if necessary. A second transparent film containing strontium phosphate, magnesium phosphate and magnesium tungstate is formed on the surface of the first transparent film (step B). The strontium ion concentration of the chemical conversion treatment agent is preferably 0.001 to 0.5 mol / L, and the tungstate ion concentration is preferably 0.1 to 20 mmol / L.
The pH of the chemical conversion treatment agent is preferably 2.8 to 3.2.
The chemical conversion treatment agent may contain an amine as necessary. The amine is considered to have an effect of improving the adhesion between the first transparent film containing magnesium alloy or the like or magnesium fluoride and the second transparent film. As the amine, any amine can be used as long as it has a certain degree of water solubility, but from the viewpoint of cost and ease of handling, lower monoalkyl such as n-propylamine, n-butylamine, allylamine and the like. Preferred examples include amines or monoaralkylamines, lower dialkylamines such as dimethylamine, diethylamine, dipropylamine and dibutylamine, cyclic amines such as pyrrolidine and piperidine, and lower trialkylamines such as triethylamine, tripropylamine and tributylamine. The concentration of the amine is not particularly limited as long as it does not affect the pH of the chemical conversion treatment agent, but is preferably 0.0005 to 0.1 mol / L.

  The temperature of the chemical conversion treatment agent is preferably 25 to 50 ° C., and the treatment time is preferably 1 minute or more and 10 minutes or less. In the conventional method, a method of forming an insoluble phosphate on the substrate surface by dissolving magnesium base with an acid chemical conversion treatment agent and reacting magnesium ions eluted with phosphoric acid in the chemical conversion treatment agent is used. . That is, it is represented by the following formula (in formula 3, M represents strontium or tungsten; the same applies hereinafter).

Mg + 2H ⁺ → Mg ²⁺ + H ₂ ↑ ... Magnesium elution reaction (Formula 1)
Mg ²⁺ + HPO ₄ ²⁻ → MgHPO ₄ ... Formation of insoluble phosphate (formula 2)
M ²⁺ + HPO ₄ ²⁻ → MHPO ₄ ... Formation of additive component phosphate (formula 3)

  However, in the chemical conversion treatment using the reactions of the above (formula 1) to (formula 3), hydrogen generation is accompanied when the magnesium base material is dissolved, so that a location where hydrogen bubbles are generated becomes a defect such as insufficient film formation. . This defect may cause a decrease in corrosion resistance. In order to improve the corrosion resistance, for example, measures such as increasing the film thickness by taking a long reaction time are often taken.

  When the desmutting step is performed by bringing a 3-6N alkali hydroxide solution at 80 ° C. or higher into contact for 1 to 10 minutes as in the surface treatment method according to the present embodiment, a magnesium hydroxide film is formed on the metal magnesium surface. It is formed. In this case, as shown in the following (Formula 4) and (Formula 5), it was found that a chemical conversion treatment film without hydrogen generation can be formed by reacting a hydroxide and phosphoric acid.

Mg ²⁺ + 2OH ⁻ → Mg (OH) ₂ ↓ ... Magnesium hydroxide formation (formula 4)
Mg (OH) ₂ + H ₃ PO ₄ → MgHPO ₄ ↓ + 2H ₂ O ... Formation of insoluble phosphate (formula 5)

  Furthermore, with the increase in pH due to neutralization of phosphoric acid according to (Formula 5), the phosphate of the additive component is precipitated and taken into the film. In this method, strontium or the like is added as an additive component, and it is considered that it is taken into the film by a reaction shown in the following formula (formula 6).

M ²⁺ + HPO ₄ ²⁻ → MHPO ₄ ... Formation of additive component phosphate (formula 6)
As described above, a dense film can be formed without generating hydrogen. Thereby, even when the film thickness is small, it becomes possible to impart higher corrosion resistance to the magnesium alloy than before.

Next, examples carried out for confirming the effects of the present invention will be described.
[1] Preparation of acid detergent 30 g of ammonium hydrogen fluoride (NH ₄ HF ₂ ) per liter of acid detergent and 50 g of 85% phosphoric acid per liter of acid detergent were diluted with water to obtain a predetermined amount of acid detergent.

[2] Preparation of chemical conversion treatment agent 50 g of strontium hydroxide octahydrate per liter of stock solution, 74 g of 85% phosphoric acid per liter of stock solution, 2 g of sodium tungstate dihydrate per liter of stock solution, 5 g of amine per liter of stock solution The compound was dissolved in water to obtain a stock solution having a predetermined weight. The specific gravity of the obtained stock solution was 1.058 ± 0.005 at 25 ° C., and the pH was 2.7 ± 0.2. The obtained undiluted | stock solution was diluted 5 times, 20 times, and 100 times with water, phosphoric acid was added as needed, and pH was adjusted to about 3.0.

[3] Method of surface treatment The magnesium alloy member whose surface was polished No. 2000 was immersed in a 5N (200 g / L) aqueous sodium hydroxide solution and subjected to alkali degreasing treatment at 85 ° C for 5 minutes. Next, the magnesium alloy member after the alkali degreasing treatment was washed with water, then immersed in the pickling solution prepared in [1], and pickled at 30 ° C. for 5 minutes. Next, the magnesium alloy member after the pickling treatment was washed with water, immersed in a 5N (200 g / L) sodium hydroxide aqueous solution, and treated at 85 ° C. for 5 minutes. Finally, the magnesium alloy member after the alkali treatment was washed with water, immersed in the chemical conversion treatment solution prepared in [2], treated at 35 ° C. for 5 minutes, washed with water and dried with hot air.

[4] Evaluation In order to evaluate the corrosion resistance in the unpainted state of the magnesium alloy member having the transparent film formed on the surface in this way, a neutral salt spray test was performed in accordance with JIS H8502-1999. The rating number was determined based on the state of occurrence of corrosion after 48, 96 and 96 hours. Also, paint adhesion is evaluated for a sample in which acrylic urethane-based clear coating (mixed with a small amount of green pigment to facilitate visual observation) is applied to the surface of the magnesium alloy member on which a transparent film is formed. Therefore, 100 square grid test (1mm wide grid pattern (10x10 square) is cut with a cutter, and adhesive tape is attached to it and peeled off. Observed.)

  Table 1 shows the composition of the chemical conversion treatment agent used in the experiments (Examples 1 to 3, Comparative Examples 1 to 6). In addition, except the comparative examples 5 and 6, the acid detergent prepared by said [1] was used as an acid detergent. In Comparative Example 5, the pickling treatment (35 ° C., 1 minute) was performed with an acid detergent containing an organic acid (oxalic acid 25 g / L + citric acid 30 g / L) and not containing fluoride ions. In Comparative Example 6, the magnesium alloy member polished No. 2000 was directly treated with the chemical conversion treatment agent without performing alkali degreasing and pickling treatments.

Table 2 below shows the results of the neutral salt spray test and the cross-cut test performed on Examples 1 to 3 and Comparative Examples 1 to 6. For Examples 1 to 3, excellent results were obtained for both corrosion resistance and paint adhesion, whereas the results of Comparative Examples 1 to 4 were either Sr concentration, WO ₄ concentration or pH, Sufficient corrosion resistance is obtained when a chemical conversion treatment agent deviating from a predetermined range (0.001 to 0.5 mol / L, 0.1 to 20 mmol / L, 2.8 to 3.2, respectively) is used. It shows no.

  Further, the results of Comparative Examples 5 and 6 indicate that when the acid detergent does not contain fluoride ions, the first transparent film containing magnesium fluoride is not formed, and thus sufficient corrosion resistance cannot be obtained.

  On the other hand, with respect to coating adhesion, a good result was observed that no peeling was observed for all of the examples and comparative examples. These results indicate that only the formed second transparent film contributes to the paint adhesion, regardless of the adhesion to the surface of the magnesium alloy member.

  No fogging or coloring was observed on the surfaces of the magnesium alloy members obtained in Examples 1 to 3, and the metallic luster and hairline of the magnesium alloy members before the surface treatment were maintained.

  About Example 1-3 and the comparative example 5, when the change of the surface roughness after a pickling process was measured, about Example 1-3, the surface roughness substantially the same as the surface treatment was observed. On the other hand, in Comparative Example 5, the surface roughness increased and the hairline almost disappeared. From these results, the acid detergent prepared in the above [1] not only improves the adhesion of the second transparent film formed by chemical conversion treatment to the surface of the magnesium alloy member, but also roughens the surface of the magnesium alloy member. It was found that the pickling treatment can be performed without any problems.

Claims (12)

A step A in which an acidic acid detergent containing a fluoride ion source is brought into contact with the surface of the degreased magnesium or magnesium alloy to form a first transparent film containing magnesium fluoride on the surface of the magnesium or magnesium alloy;
A chemical conversion treatment agent containing phosphoric acid, strontium ions, and tungstate ions is brought into contact with the surface of the magnesium or magnesium alloy on which the first transparent film is formed, and the surface of the first transparent film is coated with phosphorus. A surface treatment method of magnesium or a magnesium alloy, comprising a step B of forming a second transparent film containing strontium acid, magnesium phosphate and magnesium tungstate.   Between the step A and the step B, the method further includes a step of bringing a surface of the magnesium or magnesium alloy on which the first transparent film is formed into contact with a 3-6N alkali hydroxide solution at 80 ° C. or higher for 3 to 10 minutes. The surface treatment method of magnesium or a magnesium alloy according to claim 1.   The surface treatment method for magnesium or magnesium alloy according to claim 1 or 2, wherein the acid detergent has a fluoride ion concentration of 0.3 to 1 mol / L.   The surface treatment method for magnesium or a magnesium alloy according to any one of claims 1 to 3, wherein the acid detergent contains alkali fluoride, ammonium fluoride or ammonium hydrogen fluoride, and phosphoric acid.   The surface treatment method of magnesium or a magnesium alloy according to any one of claims 1 to 3, wherein the acid detergent has a pH of 2.0 to 4.0.   The surface treatment of magnesium or a magnesium alloy according to any one of claims 1 to 4, wherein the temperature of the acid detergent in the step A is 25 to 60 ° C and the treatment time is 1 minute or more and 10 minutes or less. Method.   The strontium ion concentration of the chemical conversion treatment agent is 0.001 to 0.5 mol / L, and the tungstate ion concentration is 0.1 to 20 mmol / L. The surface treatment method of the magnesium or magnesium alloy of description.   The surface treatment method for magnesium or a magnesium alloy according to any one of claims 1 to 7, wherein the chemical conversion treatment agent has a pH of 2.8 to 3.2.   The surface of magnesium or a magnesium alloy according to any one of claims 1 to 8, wherein a temperature of the chemical conversion treatment agent in the step B is 25 to 50 ° C and a treatment time is 1 minute or more and 10 minutes or less. Processing method.   An acid detergent used in an acid cleaning process, which is a pretreatment for a chemical conversion treatment of magnesium or a magnesium alloy, containing an alkali fluoride, ammonium fluoride or ammonium hydrogen fluoride, and phosphoric acid, and having a fluoride ion concentration of 0. An acid detergent having a pH of 4 to 1 mol / L and a pH of 2.0 to 4.0. A chemical conversion treatment agent used for chemical conversion treatment of magnesium or a magnesium alloy having a transparent film containing magnesium fluoride formed on a surface thereof, containing phosphoric acid, strontium ions, and tungstate ions, and having a strontium ion concentration of 0. The chemical conversion treatment agent characterized by being 001-0.5 mol / L, a tungstate ion concentration of 0.1-20 mmol / L, and a pH of 2.8-3.2.   A first transparent film containing magnesium fluoride formed on the surface of magnesium or a magnesium alloy, and a second transparent film containing strontium phosphate, magnesium phosphate and magnesium tungstate formed on the surface of the first transparent film A chemical conversion treatment structure of magnesium or magnesium alloy, characterized by having a transparent film.