Magnesium alloy and surface treatment method therefor, and chemical conversion treatment liquid used for surface treatment method

Abstract

Provided are: a magnesium alloy which reduces environmental loads without using a raw material containing any of phosphorus and nitrogen, and is excellent in coating performance and bare corrosion resistance, wherein a coating film capable of achieving low electric resistance is formed on the magnesium alloy; a surface treatment method for the magnesium alloy; and a chemical conversion treatment liquid used for the surface treatment method.　The chemical conversion treatment method involves bringing a magnesium alloy into contact with a chemical conversion treatment liquid which contains 300-6000 ppm of vanadium, 50-1000 ppm of zirconium, and 500-6000 ppm of an organic acid, does not contain a raw material containing any of phosphorus and nitrogen, and is prepared at a pH of 1.8-4.5. The magnesium alloy has a coating film formed on the surface of the magnesium alloy, wherein the coating film has vanadium and zirconium, the total adhesion amount of vanadium and zirconium is 20-70 mg / m2, the ratio of the adhesion amount of vanadium to said total adhesion amount of vanadium and zirconium falls within the range of 0.19-0.98, and none of phosphorus, nitrogen, and a functional group having any of phosphorus and nitrogen is detected.

Description

Magnesium alloy, surface treatment method thereof, and chemical conversion treatment solution used in the surface treatment method

[0001] The present invention relates to a magnesium alloy, a surface treatment method therefor, and a chemical conversion treatment solution used in the surface treatment method. More specifically, the present invention relates to a magnesium alloy that has excellent corrosion resistance, excellent coating performance when coated on the surface, and can reduce surface electrical resistance, a surface treatment method therefor, and a chemical conversion treatment solution used in the surface treatment method.

[0002] Magnesium alloys are excellent in physical strength, light weight, recyclability, electromagnetic wave shielding, heat dissipation, dimensional stability, etc. Among them, AZ-based magnesium alloys containing aluminum and zinc and LZ-based magnesium alloys containing lithium have improved ductility similar to alloys of iron and aluminum, and are used in a variety of fields as materials with excellent mechanical properties and castability.

[0003] Therefore, as a surface treatment method for improving the corrosion resistance of these magnesium alloys and realizing low electrical resistance, the present inventors have proposed a method for performing surface treatment of magnesium alloys using an inorganic acid treatment solution containing aluminum and zinc metal ions (see, for example, Patent Documents 1, 2, and 3).

[0004] JP 2011-58074 A JP 2011-58075 A JP 2020-152940 A

[0005] However, in order to achieve excellent performance from any of the above conventional surface treatment methods, it is necessary to use a chemical conversion treatment solution containing raw materials containing phosphorus and nitrogen, such as phosphoric acid or nitric acid, and according to a planetary boundary assessment, the outflow of these phosphorus and nitrogen into the ocean has been determined to have "exceeded the unstable range." Therefore, there is an urgent need to implement a surface treatment method that uses a chemical conversion treatment solution prepared using raw materials that do not contain phosphorus and nitrogen, but it has not yet been possible to achieve results using a chemical conversion treatment solution prepared using raw materials that do not contain phosphorus and nitrogen that are equivalent to those obtained when using a chemical conversion treatment solution prepared using raw materials that contain phosphorus and nitrogen.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a magnesium alloy that reduces the environmental load by using raw materials that do not contain phosphorus or nitrogen, and that forms a coating that is excellent in paintability and bare corrosion resistance and can achieve low electrical resistance; a surface treatment method for forming such a magnesium alloy; and a chemical conversion treatment liquid that uses raw materials that do not contain phosphorus or nitrogen and is used in the surface treatment method.

[0007] The magnesium alloy of the present invention, which solves the above-mentioned problems, is a magnesium alloy that has been chemically treated without using raw materials containing phosphorus and nitrogen in all steps including a pretreatment step to a chemical conversion treatment step, and a coating containing vanadium and zirconium is formed on the surface of the magnesium alloy, and the total amount of vanadium and zirconium deposited is 20 to 70 mg / m ２ The ratio of the amount of vanadium attached to the total amount of vanadium and zirconium attached is in the range of 0.19 to 0.98, and neither phosphorus nor nitrogen, nor functional groups having either of them, are detected.

[0008] The magnesium alloy was measured using a cylindrical two-point probe (contact surface area of ​​one point: 3.14 mm) with a pin spacing of 10 mm and a pin tip diameter of 2 mm. ２ ) may be pressed against the surface of the magnesium alloy with a load of 240 g, and the surface electrical resistance measured by an ammeter may be 1.0 Ω or less.

[0009] The magnesium alloy may have a rating number of 8 or more according to a 24-hour neutral salt spray test method in accordance with JIS Z 2371.

[0010] The magnesium alloy may be one in which an epoxy resin is applied to the surface of the magnesium alloy with a bar coater to a thickness of 20±5 μm, dried, and then a 40 mm×40 mm cross cut is made at an angle of 60 degrees.Then, using a salt spray testing device, a test piece is placed in a test tank in an atmosphere sprayed with a neutral sodium chloride solution, and after 800 hours, the test piece is removed, washed with water, wiped off the surface water, and left for 30 minutes, after which the maximum bulge width on one side of the coating film from the cut is 3.0 mm or less.

[0011] The surface treatment method for magnesium alloys of the present invention, which solves the above-mentioned problems, is a surface treatment method for obtaining the above-mentioned magnesium alloy, and includes a chemical conversion treatment step of contacting a magnesium alloy with a chemical conversion treatment solution containing 300 to 6000 ppm of vanadium, 50 to 1000 ppm of zirconium, and 500 to 6000 ppm of an organic acid, not containing raw materials containing phosphorus and nitrogen, and adjusted to a pH of 1.8 to 4.5, to form a coating on the surface of the magnesium alloy that contains vanadium and zirconium, and in which neither phosphorus nor nitrogen, nor functional groups containing either of these, are detected.

[0012] The chemical conversion treatment solution of the present invention, which solves the above-mentioned problems, is a chemical conversion treatment solution for obtaining the above-mentioned magnesium alloy, which contains 300 to 6000 ppm of vanadium, 50 to 1000 ppm of zirconium, and 500 to 6000 ppm of an organic acid, does not contain raw materials containing phosphorus or nitrogen, and is adjusted to a pH of 1.8 to 4.5.

[0013] The magnesium alloy to be treated in the present invention is not particularly limited, but examples thereof include Mg-Al-Zn, Mg-Al, and Mg-Zn magnesium alloys containing aluminum or zinc in magnesium. Among these, AZ91 material containing 9% aluminum and 1% zinc is suitable for use in terms of mechanical properties, castability, etc.

[0014] In addition, the surface layer of the magnesium alloy may have segregated trace elements added, or may have dirt or oils attached during processing or transportation. Therefore, as is done in ordinary chemical conversion treatments, the magnesium alloy is used after removing the surface oxide layer and segregated layer through processes such as degreasing, washing, etching, and desmutting, as necessary.

[0015] The degreasing process is carried out to remove cutting oil and machine oil adhering to the surface of the magnesium alloy and to soften and remove the mold release agent. Various conventionally used degreasing agents can be used in this degreasing process, including metasilicates, carbonates, chelating agents, surfactants, etc. The degreasing process is carried out by immersing the magnesium alloy in these degreasing agents or by cleaning the surface of the magnesium alloy with these degreasing agents. However, the degreasing agents used in this degreasing process should be those that do not contain phosphorus or nitrogen in their raw materials.

[0016] The etching step is carried out after the degreasing step and a water rinsing step. This etching step may be carried out in several stages with water rinsing steps in between. For example, the first etching step is carried out to remove the release agent remaining on the surface of the magnesium alloy, deposits, and uneven layers. The etching solution used in this etching step can be any of various conventionally used solutions, including various inorganic and organic acids. The etching step is carried out by immersing the magnesium alloy in such an etching solution or by cleaning the surface of the magnesium alloy with such an etching solution. However, the etching solution used in this etching step does not contain phosphorus or nitrogen in its raw materials.

[0017] Since smut may precipitate on the surface of the magnesium alloy during the etching process, in such cases, a desmutting process may be performed after rinsing with water. The desmutting process is performed to remove smut precipitated on the surface of the magnesium alloy substrate and to form a passivation film by reacting with metal ions (e.g., magnesium ions) that constitute the magnesium alloy. Various desmutting agents that have been used in the desmutting process can be used, including various alkali metal hydroxides and chelating agents. The desmutting process is performed by immersing the magnesium alloy in such a desmutting agent or by cleaning the surface of the magnesium alloy with such a desmutting agent. However, the desmutting agent used in the desmutting process must be one that does not contain phosphorus or nitrogen in its raw materials.

[0018] The chemical conversion treatment solution may contain water as a solvent, 300 to 6000 ppm of vanadium, 50 to 1000 ppm of zirconium, and 500 to 6000 ppm of organic acid, and be adjusted to a pH of 1.8 to 4.5. In this case, the chemical conversion treatment solution should be free of phosphorus and nitrogen in the raw materials. By not including phosphorus and nitrogen in the raw materials, the chemical conversion treatment solution reduces its environmental impact. The use of raw materials free of phosphorus and nitrogen applies not only to chemical conversion treatment solutions, but also to treatment solutions used in pretreatment steps of chemical conversion treatment processes, such as the degreasing agent used in the degreasing process and the etching solution used in the etching process, as described above. This also applies to treatment solutions used in all processes, including the pretreatment step of chemical conversion treatment through the chemical conversion treatment process.

[0019] The vanadium in the chemical conversion treatment solution is not particularly limited as long as it can produce vanadium ions in the chemical conversion treatment solution. For example, vanadium oxide (VO ２ , V ２ O ３ , V ２ O ５ ), vanadium chloride (VCl ２ , VCl ３ , VCl ４ ), vanadium sulfate (VSO ４ ), vanadium acetate (V(CH ３ COO) ３ ), sodium vanadate (Na ３ VO ４ ), sodium metavanadate (NaVO ３ ), potassium metavanadate (KVO ３ ), vanadium oxychloride (VOCl ２ , VOCl ３ ), vanadium oxysulfate (VOSO ４ ) or the like can be used. This vanadium is added to the chemical conversion treatment solution so that the concentration of vanadium ions is 300 to 6000 ppm (mg / L). However, the vanadium used in this chemical conversion treatment solution does not contain phosphorus or nitrogen in the raw material.

[0020] The zirconium in the chemical conversion treatment solution is not particularly limited as long as it can produce zirconium ions in the chemical conversion treatment solution. For example, zirconium hydroxide (Zr(OH) ４ ), zirconium sulfate (Zr(SO ４ ) ２ ), hydrofluoric acid (H ２ ZrF ６ ), Sodium zirconate fluoride (Na ２ ZrF ６ ), potassium zirconium fluoride (K ２ ZrF ６ ), etc. can be used. This zirconium is added to the chemical conversion treatment solution so that the concentration of zirconium ions is 50 to 1000 ppm (mg / L). However, the zirconium used in this chemical conversion treatment solution does not contain phosphorus or nitrogen in the raw material.

[0021] As the organic acid for the chemical conversion treatment solution, various organic acids having functional groups such as carboxyl groups or hydroxyl groups can be used. Specific examples include citric acid, malic acid, lactic acid, and gluconic acid. These organic acids may be used alone or in combination of two or more. The organic acid is added to the chemical conversion treatment solution at a concentration of 500 to 6000 ppm (mg / L). However, the organic acid used in this chemical conversion treatment solution should not contain phosphorus or nitrogen in its raw materials.

[0022] The pH of the chemical conversion treatment solution is adjusted by adding an acid or alkali so that it falls within the range of 1.8 to 4.5. In this case, as long as the pH can be adjusted to 1.8 to 4.5 using the organic acid, it is not necessary to add any particular acid or alkali. The organic acids listed above can be used as the acid used to adjust the pH, as long as the concentration in the chemical conversion treatment solution is within the range of 500 to 6000 ppm (mg / L). In other cases, inorganic acids such as hydrochloric acid and sulfuric acid can be used, and alkalis such as sodium hydroxide and potassium hydroxide can be used. However, the acid or alkali used to adjust the pH must be one that does not contain phosphorus or nitrogen in its raw materials.

[0023] In order to carry out the surface treatment method of the magnesium alloy of the present invention using the chemical conversion treatment solution thus constituted, it is preferable to carry out the above-mentioned degreasing step, etching step, and smut removal step, and then carry out the chemical conversion treatment step of forming a chemical conversion coating using this chemical conversion treatment solution.

[0024] The chemical conversion treatment process using a chemical conversion treatment solution can be carried out by a common method that allows the treatment solution to come into contact with the surface of the magnesium alloy for a certain period of time, such as immersing the magnesium alloy in the chemical conversion treatment solution. When using the immersion method, the chemical conversion treatment solution is preferably kept at a temperature of 35 to 70°C, preferably about 40 to 60°C. This is to ensure a rapid and effective chemical reaction between the magnesium alloy and the components of the chemical conversion treatment solution. The immersion time is preferably 0.5 to 5 minutes, more preferably about 1 minute. This is to ensure a sufficient chemical conversion treatment film is formed on the surface of the magnesium alloy. Immersion times of less than 0.5 minutes can result in insufficient coating weight and reduced corrosion resistance, while immersion times of more than 5 minutes can result in excessive treatment, resulting in increased surface electrical resistance and reduced coating adhesion.

[0025] The degreasing step, etching step, desmutting step, and chemical conversion treatment step are each carried out separately, with water rinsing being carried out between each step.

[0026] By the chemical conversion treatment process, the surface of the magnesium alloy is coated with 5 to 41 mg / m ２ Vanadium is deposited in an amount of 1 to 33 mg / m ２ A coating can be formed in which a further amount of zirconium is deposited, with the ratio of vanadium to the total amount of deposited vanadium and zirconium being 0.19 to 0.98. For magnesium alloys surface-treated in this manner, the treatment solutions used in all processes from the pretreatment step to the chemical conversion treatment step do not contain phosphorus or nitrogen as raw materials, so the coating formed after treatment also does not contain phosphorus or nitrogen, thereby reducing the environmental load. Furthermore, the coating formed on the surface of the magnesium alloy exhibits excellent corrosion resistance.

[0027] The magnesium alloy was a cylindrical probe with a pin distance of 10 mm and a pin tip diameter of 2 mm (contact surface area of ​​each probe: 3.14 mm ２ The surface electrical resistance value of an ammeter measured when a 240 g load of a probe A (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) is pressed against the surface can be reduced to 1.0 Ω or less. The 240 g load is assumed to be the fixing force when the magnesium alloy is earthed by screw fixing. Furthermore, the coating formed on the surface of the magnesium alloy has a rating number of 8 or higher in the 24-hour neutral salt spray test method according to JIS Z 2371, thereby providing excellent bare corrosion resistance.

[0028] Therefore, magnesium alloys obtained by surface treatment using the method of the present invention can be effectively used as housing parts for various electronic devices, such as mobile phones, notebook computers, portable translators, video cameras, and digital cameras, which require not only corrosion resistance but also high electromagnetic wave shielding properties and low surface electrical resistance for grounding from the substrate.

[0029] Furthermore, when a magnesium alloy thus obtained is painted in a subsequent coating process, it is possible to improve paint film adhesion and enhance paint film performance without using phosphorus or nitrogen. For example, the magnesium alloy is coated on the surface with an epoxy resin using a bar coater to a thickness of 20±5 μm, dried, and then a 40 mm×40 mm cross-cut is made at an angle of 60 degrees. A test piece is then placed in a test tank using a salt spray tester in an atmosphere sprayed with a neutral sodium chloride solution. After 800 hours, the test piece is removed, washed with water, wiped off the surface water, and left for 30 minutes. The maximum bulging width of the paint film on one side from the cut is 3.0 mm or less.

[0030] Therefore, the magnesium alloy obtained by surface treatment using the method of the present invention can improve the adhesion of a coating film applied to the outer surface of a casing while the casing is grounded, thereby enhancing the performance of the coating film, and can therefore be suitably used in various types of transportation equipment, such as automobiles and railway vehicles, where weight reduction is desired.

[0031] As described above, according to the present invention, the magnesium alloy has a surface containing 5 to 41 mg / m ２ Vanadium is deposited in an amount of 1 to 33 mg / m ２ The ratio of vanadium to the total amount of vanadium and zirconium attached is 0.19 to 0.98, and no phosphorus or nitrogen is detected. Therefore, the material exhibits excellent corrosion resistance while reducing the environmental load.

[0032] The magnesium alloy according to the present invention was also tested using a cylindrical two-point probe (contact surface area of ​​one point: 3.14 mm) with a pin spacing of 10 mm and a pin tip diameter of 2 mm. ２ ) has a surface electrical resistance of 1.0 Ω or less when pressed against the surface with a load of 240 g, and has a rating number of 8 or more according to the 24-hour neutral salt spray test method of JIS Z 2371, making it possible to use it in electronic device housing parts that require electromagnetic wave shielding properties or that need to be earthed from the substrate.

[0033] Furthermore, an epoxy resin is applied to the surface of a magnesium alloy using a bar coater to a thickness of 20±5 μm, and then dried. 40 mm x 40 mm cross cuts are made at 60 degrees, and then a salt spray testing device is used to spray a neutral sodium chloride solution onto the test piece. After 800 hours, the test piece is removed, washed with water, and the water on the surface is wiped off. After leaving the test piece for 30 minutes, the maximum bulge width on one side of the coating film from the cut is 3.0 mm or less. Therefore, when a coating is applied to the surface of this magnesium alloy, the adhesion of the coating can be improved.

[0034] (Examples 1 to 10, Comparative Examples 1 to 5) As the object to be treated, a die-cast plate material made of a magnesium alloy ("AZ91D material" manufactured by Paltec Co., Ltd.: 9 mass % aluminum, 1 mass % zinc, the remainder being magnesium) measuring 75 mm in length, 50 mm in width, and 2 mm in thickness was prepared as a test piece.

[0035] First, the test piece was degreased by immersing it for 3 minutes in an aqueous degreasing solution (3% aqueous solution of Granda Cleaner 2026, product name, manufactured by Million Chemical Co., Ltd.) that did not use raw materials containing phosphorus or nitrogen and whose liquid temperature was kept at 50°C.

[0036] The degreased test piece was rinsed with water and then subjected to an etching process using an etching solution that did not contain raw materials containing phosphorus or nitrogen (a 10% aqueous solution of Grandafiner MG-108, a product name manufactured by Million Chemical Co., Ltd.) This etching process was performed by immersing the test piece in the etching solution, the temperature of which was maintained at 60°C, for 60 seconds.

[0037] Next, the test piece was washed with water and then immersed for 7 minutes in a smut removal treatment solution (45% aqueous solution of Grandafiner MG-15SX, product name, manufactured by Million Chemical Co., Ltd.) that did not contain raw materials containing phosphorus or nitrogen and whose liquid temperature was kept at 60°C, to perform a smut removal treatment.

[0038] Next, the test pieces were washed with water and then chemically treated in each of the chemical conversion treatment solutions shown in Table 1 under the conditions shown in Table 1.

[0039]

[0040] After the chemical conversion treatment, the test specimens were washed with water and then dried. The amounts of vanadium and zirconium adhering to the surfaces of the test specimens thus obtained were measured. The measurements were performed using a scanning X-ray fluorescence analyzer (ZSX Primus III+, manufactured by Rigaku Corporation). The absence of phosphorus, nitrogen, and functional groups containing these was also confirmed. The surface electrical resistivity of each test specimen was measured. The bare corrosion resistance was also evaluated. Furthermore, the coating performance was also evaluated. The results are shown in Table 2.

[0041]

[0042] The evaluations in the present examples and comparative examples were carried out as follows.

[0043] - Surface electrical resistance value - The surface electrical resistance value was measured using a Loresta EP2 probe A probe (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: pin spacing 10 mm, pin tip diameter 2.0 mm (contact surface area of ​​one needle 3.14 mm２ The surface electrical resistance was measured by pressing pins against the center, top, and bottom of the surface of the test piece using a pressure of 240 g (spring pressure 240 g). Measurements were carried out on three test pieces, and measurements were taken at the three locations per test piece, and the maximum value of the measurements at a total of nine locations was calculated.

[0044] The 240 g measurement was taken by pressing the pins of a two-point probe against the surface of the test piece until they retracted against the spring pressure.

[0045] The measured value of 240 g is based on the assumption that the earth is fixed to the surface of the component with a screw.

[0046] - Bare corrosion resistance test - Test pieces were placed in a test tank set at 35°C, sprayed with 5% salt water, and removed after 24 hours using the salt spray test method (SST test) in accordance with JIS Z 2371. After the surface was washed with water and dried, the rating number was measured, and a value of 8 or higher was considered a pass.

[0047] - Coating film corrosion resistance test - An epoxy primer (primer MG-GUARD#1-SP, manufactured by Dai Nippon Toryo Co., Ltd.) was applied to the surface of a test piece using a bar coater to a film thickness of 20.0±5.0 mm, and then baked at 160°C for 20 minutes and allowed to cool. After that, a 40 mm x 40 mm cross cut at an angle of 60 degrees was made in the formed coating film.

[0048] This test piece was placed in a test tank set at 35°C and sprayed with 5% saline solution according to the salt spray test method (SST test) in accordance with JIS Z 2371. After 800 hours, the test piece was removed. The surface was washed with water, the moisture was wiped off, and the piece was left for 30 minutes, after which the maximum bulging width of the coating film on one side from the cut was measured. A value of 3.0 mm or less was considered a pass.

[0049] From the results in Table 2, it was confirmed that the test pieces according to the present invention had low surface electrical resistivity and excellent bare corrosion resistance and coating film performance, despite not using raw materials containing phosphorus and nitrogen.

[0050] The present invention can be embodied in various other forms without departing from its spirit or essential characteristics. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited to the text of the specification. Furthermore, all modifications and variations within the scope of the claims are within the scope of the present invention.

Claims

1. A magnesium alloy that has been subjected to chemical conversion treatment without using a raw material containing phosphorus and nitrogen in all processes including from a pretreatment process to a chemical conversion treatment process, wherein a film having vanadium and zirconium is formed on the surface of the magnesium alloy, and the total amount of vanadium and zirconium adhered is 20 to 70 mg / m ２ and the ratio of the amount of vanadium adhered to the total amount of vanadium and zirconium adhered is in the range of 0.19 to 0.98, and neither phosphorus and nitrogen nor any functional group having any of them is detected. A magnesium alloy characterized by this.

2. A columnar two-probe probe with a 10 mm pitch between pins and a 2 mm tip diameter of the pin (contact surface area of one pin: 3.14 mm ２ ), wherein the surface electrical resistance value of the ammeter is 1.0 Ω or less when pressed against the surface of the magnesium alloy with a load of 240 g. The magnesium alloy according to claim 1.

3. The magnesium alloy according to claim 1 or 2, wherein the rating number according to the 24-hour neutral salt spray test method specified in JIS Z 2371 is 8 or more.

4. After applying and drying an epoxy resin with a bar coater to a thickness of 20 ± 5 μm on the surface of the magnesium alloy, making 40 mm × 40 mm cross-cuts intersecting at 60 degrees, placing the test piece in a test tank in an atmosphere where a neutral sodium chloride solution is sprayed using a salt spray test apparatus, taking out the test piece after 800 hours, washing it with water, wiping off the water on the surface, leaving it to stand for 30 minutes, and the maximum value of the swelling width on one side of the coating film from the cut part is 3.0 mm or less. The magnesium alloy according to claim 1 or 2.

5. A columnar two-probe probe with a 10 mm distance between pins and a 2 mm diameter at the tip of the pin (contact surface area of one pin: 3.14 mm ２ ), when pressed against the surface of the magnesium alloy with a load of 240 g, the surface electrical resistance value of the ammeter is 1.0 Ω or less, and the rating number according to the 24-hour neutral salt spray test method according to JIS Z 2371 is 8 or more. After applying and drying an epoxy resin on the surface of the magnesium alloy with a bar coater to a thickness of 20 ± 5 μm, making a 40 mm × 40 mm cross cut that intersects at 60 degrees, placing the test piece in the test tank in an atmosphere where a neutral sodium chloride solution is sprayed using a salt spray test apparatus, taking out the test piece after 800 hours, washing with water, wiping off the water on the surface, leaving it for 30 minutes, and the maximum value of the swelling width on one side of the coating film from the cut part is 3.0 mm or less. The magnesium alloy according to claim 1.

6. A chemical conversion treatment method for obtaining the magnesium alloy according to claim 1, comprising: a chemical conversion treatment step of contacting the magnesium alloy with a chemical conversion treatment solution containing 300 to 6000 ppm of vanadium, 50 to 1000 ppm of zirconium, 500 to 6000 ppm of an organic acid, not containing raw materials containing phosphorus and nitrogen, and adjusted to pH 1.8 to 4.5, and forming a film on the surface of the magnesium alloy, in which neither vanadium nor zirconium, nor phosphorus and nitrogen, nor any functional groups having any of these are detected. A chemical conversion treatment method for a magnesium alloy.

7. A chemical conversion treatment solution for obtaining the magnesium alloy according to claim 1, containing 300 to 6000 ppm of vanadium, 50 to 1000 ppm of zirconium, 500 to 6000 ppm of an organic acid, not containing raw materials containing phosphorus and nitrogen, and adjusted to pH 1.8 to 4.

5. A chemical conversion treatment solution for a magnesium alloy.

8. The chemical conversion treatment solution according to claim 7, wherein the organic acid is citric acid and / or malic acid.

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