Corrosion-preventive film and method for manufacturing the same

Abstract

In an alloy member using a magnesium-lithium alloy as the base material, the unevenness of the film thickness of the anticorrosion film applied to the surface of the base material and cracking of the film when dropped are suppressed, thereby improving the appearance and suppressing peeling of the paint film. [Solution] In the corrosion-resistant film 12 of the alloy member 10, which has a magnesium-lithium alloy as the base material 11, phosphorus is contained in an amorphous structure of 20% to 40% by mass, oxygen in an amount of 25% or more by mass, fluorine in an amount of 17% or less by mass, magnesium in an amount of 20% to 30% by mass, and nitrogen in an amount of 5% or less by mass.

Description

[Technical Field]

[0001] This invention relates to a corrosion-preventive film formed on the surface of a substrate made of a magnesium alloy, and a method for producing the corrosion-preventive film. [Background technology]

[0002] Magnesium-lithium alloys, which are primarily composed of magnesium and also contain lithium, are lightweight and possess excellent mechanical strength. Therefore, their application to a wide range of products is being explored. On the other hand, because magnesium alloys are prone to corrosion, it was necessary to form an anti-corrosion film on the surface of a magnesium alloy substrate. Patent Document 1 discloses a method for manufacturing a magnesium alloy product in which an anti-corrosion film is formed on the surface of the magnesium alloy by anodizing. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-102236 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, when the anticorrosion film obtained by the manufacturing method described in Patent Document 1 is applied to a substrate made of magnesium-lithium alloy, uneven film thickness occurs, particularly on substrates injected by die casting, resulting in a problem where a good painted appearance cannot be obtained. While forming a thicker anticorrosion film can reduce the appearance defects caused by uneven film thickness, a thicker anticorrosion film leads to the problem of paint peeling due to cracking of the anticorrosion film when the product is dropped. Therefore, the present invention aims to suppress both appearance defects caused by uneven film thickness and paint peeling due to cracking of the anticorrosion film formed on the surface of a magnesium-lithium alloy. [Means for solving the problem]

[0005] The first aspect of this disclosure is a corrosion-preventive film mainly composed of magnesium that covers and protects the surface of a substrate containing lithium, This corrosion-preventive film is characterized by containing 20% ​​to 40% by mass of phosphorus, 25% or more by mass of oxygen, 17% or less by mass of fluorine, 20% to 30% by mass of magnesium, and 5% or less by mass of nitrogen, and having an amorphous structure. The second part of this disclosure is a step of arranging an anode and a cathode in an electrolyte, A method for manufacturing an alloy member, comprising the step of applying a voltage between the anode and the cathode to form a corrosion-resistant film on the anode, The anode is a substrate mainly composed of magnesium and containing lithium. The electrolyte is characterized in that, when the fluoride ion concentration is X mol / L and the phosphate ion concentration is Y mol / L, the coordinates (X, Y) are located within the region enclosed by the coordinates [1] to [5] below. [1](1.9, 0.7) [2](5.8, 0.7) [3](10.0, 4.1) [4](4.4, 4.1) [5](1.9, 2.2) The third aspect of this disclosure is a substrate mainly composed of magnesium and containing lithium, An alloy member comprising a corrosion-resistant film provided on the substrate, The alloy member is characterized in that the corrosion protection film is the corrosion protection film according to the first disclosure described above. [Effects of the Invention]

[0006] According to this disclosure, an alloy member is provided in which unevenness in the thickness of the anticorrosion film applied to the surface of a magnesium-lithium alloy and cracking of the film when dropped are improved, resulting in an improved appearance and suppressed peeling of the coating. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic cross-sectional view of the alloy member according to this embodiment. [Figure 2] This is a flowchart of the manufacturing process for the alloy member according to this embodiment. [Figure 3] This is a schematic diagram of an anodic oxidation apparatus for producing a corrosion-preventive film according to this embodiment. [Figure 4] This is a schematic diagram of an imaging device to which the alloy member according to this embodiment is applied. [Figure 5] This figure shows the XRD analysis results of the corrosion protection films of the examples and comparative examples. [Figure 6] This is a schematic diagram illustrating the evaluation method for paint film peeling in the examples and comparative examples. [Modes for carrying out the invention]

[0008] The corrosion-preventive film of the present invention is a corrosion-preventive film formed on a substrate made of a magnesium-lithium alloy, and is characterized by containing predetermined amounts of phosphorus, oxygen, fluorine, and magnesium, and having an amorphous structure. Furthermore, the alloy member of the present invention is characterized by comprising a substrate made of a magnesium-lithium alloy and the corrosion-preventive film of the present invention, and preferably the corrosion-preventive film is coated with a paint film. The present invention will be described below with reference to embodiments.

[0009] <Alloy components> Figure 1 is a schematic diagram of the alloy member of the present invention, and is a cross-sectional view taken when cut in the lamination direction. The alloy member 10 of this embodiment comprises a base material 11, a corrosion-resistant film 12 provided on the base material 11, and a coating film 13 provided on the corrosion-resistant film 12. The use of the alloy member of this embodiment is not particularly limited, and it can be used as a structural material such as an exterior member, interior member, and sliding member of equipment having parts. Depending on the application, two or more films such as a primer and a topcoat layer may be provided on the corrosion-resistant film 12. Examples of coating films 13 include a heat-shielding film, a light-shielding film, and an anti-reflective film that have a heat-shielding function.

[0010] The inventors first found that by performing an anodic oxidation treatment for forming a corrosion prevention film 12 on the surface of the base material 11 in an electrolytic solution containing fluorine, ammonium, and phosphoric acid, which will be described later, the voltage during film formation can be reduced to a low voltage. Furthermore, by setting the component range of the formed corrosion prevention film 12 to an amorphous structure, it is possible to reduce film cracking and film thickness unevenness of the corrosion prevention film 12, and it has been found that the film can solve the problems of peeling of the coating film 13 applied to the surface of the corrosion prevention film 12 and poor appearance at the same time.

[0011] On the other hand, in the anodic oxidation treatment of conventional Patent Document 1 and the micro arc oxidation (Micro Arc Oxidation) treatment, the corrosion prevention film 12 can be made into an amorphous structure by increasing the voltage, and the film thickness unevenness could be suppressed. However, the film formed at a high voltage has many pores and cracks and does not become a dense film. Therefore, film cracking of the corrosion prevention film 12 may occur due to impacts during product dropping, etc., and coating film peeling may occur. As described above, by reducing the voltage during the anodic oxidation treatment and making the contained elements of the corrosion prevention film within a desired range to form an amorphous structure, it has been found that it is possible to achieve both prevention of coating film peeling due to film cracking of the corrosion prevention film and a good appearance with reduced film thickness unevenness.

[0012] [Base material] The base material 11 is made of a magnesium-lithium alloy (hereinafter, Mg-Li alloy) mainly composed of magnesium (Mg) and containing lithium (Li). In this specification, the main component means the element with the largest total mass among the contained elements when composed of a plurality of elements. Or, when composed of a plurality of compounds, it means the compound with the largest total mass among the contained compounds.

[0013] Among Mg-Li alloys, it is preferable that the sum of the Mg and Li content is 90% by mass or more for use as the base material 11. When the sum of the Mg and Li content is 90% by mass or more, it becomes lighter than magnesium alloys that do not contain Li. Mg-Li alloys are lightweight metallic materials and have superior vibration damping properties and specific strength compared to magnesium alloys that do not contain Li. Superior vibration damping means that vibrations are quickly dampened by rapidly converting vibration energy into thermal energy. Specific strength is the tensile strength per unit density, and the higher the specific strength, the lighter the component can be.

[0014] Mg-Li alloys may contain aluminum (Al) and zirconium (Zr) in addition to Mg and Li, and may also contain germanium (Ge) and / or beryllium (Be). Furthermore, in addition to the elements mentioned above, it is possible to contain at least one element selected from the group consisting of zinc (Zn), calcium (Ca), silicon (Si), and manganese (Mg), with the remainder being unavoidable impurities, magnesium, and lithium. Examples of unavoidable impurities include iron (Fe), cobalt (Co), and nickel (Ni).

[0015] The Li content in the Mg-Li alloy is preferably in the range of 0.5% by mass to 15% by mass. A Li content of 0.5% by mass or more allows for a lightweight alloy, while a Li content of 15% by mass or less provides sufficient vibration damping. Preferably, it is between 8% by mass and 14% by mass. Even more preferably, it is in the range where the α phase and β phase coexist, which is between 5% by mass and 11% by mass. Within this range, the corrosion resistance of the base material 11 is high.

[0016] The Al content in Mg-Li alloys is preferably in the range of 1% by mass to 8% by mass. In Mg-Li alloys, Al plays a role in increasing the fracture strength of the alloy. Therefore, when the Al content is within the above range, the mechanical strength of the Mg-Li alloy can be sufficiently high compared to when Al is not present. This is thought to be because Al and Mg react, and their compound, MgAl2, precipitates, thereby increasing the mechanical strength. A more preferable content is in the range of 4% by mass to 7% by mass.

[0017] The total content of germanium (Ge) and beryllium (Be) in Mg-Li alloys is in the range of 0.02% by mass or more and 0.4% by mass or less. In Mg-Li alloys, Ge and Be play a role in enhancing corrosion resistance by partially replacing Al. As mentioned above, in Mg-Li alloys containing Al, the mechanical strength increases due to the reaction between Al and Mg, but at that time, lithium-rich grain boundaries segregate in the matrix phase, making it susceptible to corrosion. However, by partially substituting Al with elements with smaller atomic radii than Al, such as Ge and Be, Ge and Be are actively positioned at the grain boundaries in place of Li, and segregation of Li at the grain boundaries can be suppressed. Therefore, corrosion resistance can be improved. The content of Ge alone is preferably in the range of 0.01% by mass or more and 0.4% by mass or less. More preferably, it is in the range of 0.01% by mass or less and 0.2% by mass or less. Also, the content of Be alone is preferably in the range of 0.02% by mass or more and 0.1% by mass or less. More preferably, the amount is in the range of 0.01% by mass or more and 0.05% by mass or less.

[0018] The Zr content in the Mg-Li alloy is preferably in the range of 0.6% by mass or more and 3.0% by mass or less. This is because it prevents the particle size of the base material 11 from becoming coarser.

[0019] In Mg-Li alloys, Zn, Ca, Si, and manganese (Mn) can increase the strength of the base material 11. The sum of the content of these elements is preferably in the range of 0.01% by mass or more and 5% by mass or less. If it is Zn, it is preferably contained at 3% by mass or less. More preferably at 0.2% by mass or more and 3% by mass or less. If it is Mn, it is preferably contained at 0.3% by mass or less. More preferably at 0.1% by mass or more and 0.3% by mass or less. If it is Si, it is preferably contained at 0.2% by mass or less. More preferably at 0.1% by mass or more and 0.2% by mass or less. If it is Ca, it is preferably contained at 3.0% by mass or less. More preferably at 0.1% by mass or more and 1.0% by mass or less.

[0020] The raw materials for Mg-Li alloys are not particularly limited. Commercially available options include, for example, "LZ91," "LAZ771," and "LAZ941" manufactured by Anli Materials Technology Co., Ltd.

[0021] The thickness of the base material 11 is not particularly limited, but from the viewpoint of ensuring sufficient rigidity, it is preferable that it be thicker than the thickness of the anticorrosion film 12.

[0022] [Corrosion-resistant film] The anticorrosion film 12 is provided on the substrate 11. The average thickness of the anticorrosion film 12 is 5 μm or more and 40 μm or less. If the thickness of the anticorrosion film 12 is 40 μm or less, peeling of the coating due to cracking of the anticorrosion film 12 when the product is dropped is suppressed. Also, if the thickness of the anticorrosion film 12 is 5 μm or more, unevenness in appearance due to uneven film thickness is suppressed.

[0023] The corrosion protection film 12 preferably contains at least Mg, phosphorus (P), fluorine (F), and oxygen (O). Furthermore, the content of each element is preferably 20% to 40% by mass for P, 25% or more by mass for O, 17% or less by mass for F, 20% to 30% by mass for Mg, and 5% or less by mass for nitrogen. By setting the content of each element in the corrosion protection film 12 within this range, the corrosion protection film 12 can be made amorphous, resulting in a dense film that suppresses both cracking and uneven film thickness. On the other hand, if the content of each element in the corrosion protection film 12 falls outside the above range, crystallization of the corrosion protection film 12 is more likely to occur, making it difficult to form an amorphous structure, which leads to cracking and uneven film thickness. The reason why film cracking can be suppressed when the anticorrosion film 12 has an amorphous structure is that the melting point within its component range is lowered, allowing it to melt at a lower temperature. This reduces the temperature difference until the molten material solidifies, decreasing the shrinkage rate, which is expected to reduce cracks and residual stress, thus making it less prone to cracking. This can also be inferred from the fact that the anticorrosion film 12 of this embodiment can be formed at a lower voltage. A preferred composition is one in which the mass ratio of F content to Mg content is 0.05 to 0.70, the mass ratio of P content is 0.8 to 1.41, and the mass ratio of oxygen content is 1.5 to 2.2.

[0024] <Method for manufacturing corrosion protection film> Figure 2 shows the manufacturing process flow of the alloy member 10 of this embodiment, and Figure 3 is a schematic diagram of an anodizing apparatus that produces a corrosion-preventive film 12 by anodizing the base material 11.

[0025] As shown in Figure 2, the alloy member 10 of this embodiment is prepared by (1) preparing an electrolyte and (2) pickling the substrate in parallel, and (3) performing an anodizing treatment, in which the substrate 11 is used as the anode to perform anodizing treatment and form a corrosion-resistant film 12. Then, in (4) painting, a coating film 13 is applied to the surface of the corrosion-resistant film 12. Depending on the cleanliness of the substrate to be coated, it is possible to omit (2) pickling the substrate. The process of (3) is described in detail below.

[0026] The anodic oxidation apparatus 30 shown in Figure 3 consists of an outer tank 32 that holds and temperature-controls the electrolyte 31 and an inner tank 33 that performs the electrical reaction. The outer tank 32 is equipped with a temperature control mechanism 34 that maintains a constant temperature of the electrolyte 31. The temperature of the electrolyte 31 can be set from a low temperature where the components do not condense to a high temperature where the components do not decompose. The optimal temperature is around 25°C, which does not require much energy to adjust the liquid temperature. Although the apparatus is described as a two-tank system, the corrosion-preventive film 12 can also be produced with a single-tank system.

[0027] The outer tank 32 and the inner tank 33 are connected by a magnetic pump 35, and the electrolyte 31 is circulated between them. In the formation of the anticorrosion film 12, exchange of electrolyte on the surface of the substrate 11 is important, but since the anodic oxidation reaction is an exothermic reaction, the electrolyte 31 on the surface undergoes self-convection, resulting in active exchange of electrolyte. Therefore, the circulation of electrolyte by the pump 35 is more for the removal of by-products generated in the electrolyte 31 than for exchange of electrolyte on the surface. In the anodic oxidation of the Mg-Li alloy surface, the anticorrosion film 12 is formed, and Li from the Mg-Li alloy is released into the solution as ions. These released lithium ions react with fluoride ions and phosphate ions, which are components of the electrolyte, to produce sparingly soluble salts. These sparingly soluble salts may remain in the electrolyte 31 as fine particles, potentially causing the electrolyte 31 to become cloudy. Therefore, a bag filter 36 is provided at the liquid outlet of the inner tank 33 to remove the fine particles generated in the electrolyte 31. It is preferable that the filter 36 can remove fine particles of 10 μm or larger. Furthermore, a filter may be installed within the piping system connected to the pump 35.

[0028] Next, an electrical circuit capable of forming a corrosion-resistant film 12 is formed. A carbon electrode that functions as a cathode 37 is placed inside the inner tank 33. The cathode material is not particularly limited as long as it is a material that is stable and conductive to the electrolyte 31. For example, platinum, stainless steel, and titanium can also be used.

[0029] Next, the anode 38, made of Mg-Li alloy, is set by being sandwiched in the conductive holding jig 39. Although a native oxide film is formed on the surface of the anode 38, it does not need to be removed beforehand because it will be replaced by a fluoride film, phosphate film, or fluorine phosphate film during the anodizing process. If oil stains are present on the surface of the anode 38 due to machining or other processes, it is necessary to go through a pre-cleaning process to remove the oil stains.

[0030] The material of the conductive holding jig 39 is a metal that has been pre-anodicized at a high voltage, using a metal with a higher anodizing voltage than the anode 38 used during anodizing. While pure Mg, AZ31, and AZ91 are acceptable materials, the system is not limited to these.

[0031] The conductive holding jig 39, which sandwiches the anode 38, is connected to the DC stabilized power supply 40 with wires so that it becomes the anode and the carbon plate becomes the cathode 37. Furthermore, the cathode 37 and the conductive holding jig 39, which are connected by wires, are immersed in the inner tank 33 to establish an anodic oxide film formation circuit. Then, a voltage is applied between the anode 38 and the cathode 37 to form a corrosion-resistant film 12.

[0032] Finally, the timing for stopping the current is determined by the cumulative current value applied to the Mg-Li alloy. To give a specific example, the amount of electricity required to grow the corrosion protection film 12 to a thickness of 1 μm is 100 cm². 2 The required energy is 42.5 coulombs per unit. The desired film thickness can be obtained by supplying the necessary amount of electricity and then switching off the power. Furthermore, if the current value during energization is stable, the desired film thickness can also be obtained by controlling the energization time.

[0033] Furthermore, the current setting can be determined by the surface area and current density of the anode 38. For example, 100 cm² 2 The current density is 5A / 100cm² relative to the anode 38 surface. 2When performing anodizing, the set current is 5A. If the current density is low, the anodizing process takes longer, resulting in lower productivity. Conversely, if the current density is high, the anodizing process takes shorter, improving productivity. However, if it is too high, voids and cracks in the formed anodized film may grow larger, potentially reducing its crack resistance. Therefore, the current density is set to 1A / 100cm². 2 More than 10A / 100cm 2 The following is preferable. By the above method, the corrosion-resistant film 12 of this embodiment can be obtained.

[0034] The manufacturing method for the Mg-Li alloy, which serves as the base material 11 for the anode 38, is not particularly limited, but examples include casting, thixotropy, and die casting. The base material 11 obtained by rapidly cooling molten metal in this way tends to have different surface structures in the plane depending on the molding shape, the direction of molten metal flow relative to the mold, and the temperature difference. This in-plane distribution of surface structure can also cause variations in the thickness of the anticorrosion film 12, but with the above manufacturing method, an alloy member with excellent appearance can be provided even for such an anode 38.

[0035] The electrolyte 31 used for anodizing is a liquid containing fluoride ions, ammonium molecules, and phosphate ions. Substances containing fluoride ions and ammonium molecules include acidic ammonium fluoride, neutral ammonium fluoride, hydrogen fluoride, and ammonia. Substances containing phosphate ions include, for example, phosphoric acid and triammonium phosphate trihydrate (including diammonium hydrogen phosphate and ammonium dihydrogen phosphate). The easiest way to prepare the electrolyte 31 is to dissolve desired amounts of ammonium fluoride and triammonium phosphate trihydrate in pure water. Care should be taken to ensure the pH of this electrolyte is between 5.7 and 7.5 to prevent the generation of high concentrations of hydrogen fluoride. Note that triammonium phosphate trihydrate has low solubility. Therefore, to increase the concentration of phosphate ions, phosphoric acid may be added to the electrolyte to shift the pH towards the acidic side, and then triammonium phosphate trihydrate may be added and dissolved.

[0036] The electrolyte 31 is a concentration range in which the coordinates (X, Y), where the fluoride ion concentration in the solution is X mol / L and the phosphate ion concentration is Y mol / L, are located within the region enclosed by the coordinates [1] to [5] below. [1](1.9, 0.7) [2](5.8, 0.7) [3](10.0, 4.1) [4](4.4, 4.1) [5](1.9, 2.2) Furthermore, at the above concentrations, the ratio of the phosphate ion concentration to the sum of the fluoride ion concentration and the phosphate ion concentration is preferably 11% or more and 54% or less. Note that the phosphate ion concentration shown here is calculated based on the assumption that 100% of the phosphoric acid added to the solution has dissociated and ionized (PO4). 3- The concentration shown is for when ( ). In actual electrolytes, phosphate ions are H2PO4 - HPO4 2- It exists in this form.

[0037] <Device> The alloy member of the present invention can be applied to a housing in a device comprising a housing and components provided within the housing. Below, a single-lens reflex digital camera is described as an example of a device to which the alloy member of the present invention is applied; however, the device is not limited to this, and may also be a smartphone or a compact digital camera.

[0038] Figure 4 shows the configuration of a single-lens reflex digital camera 50, which is an example of an imaging device. In Figure 4, the camera body 52 and the lens barrel 51, which is an optical component, are connected. The lens barrel 51 is a so-called interchangeable lens that can be attached to and detached from the camera body 52.

[0039] Light from the subject is received by the image sensor 60 and captured when it passes through an optical system consisting of multiple lenses 53, 55, etc., which are an example of components arranged on the optical axis of the imaging optical system within the housing of the lens barrel 51. Here, lens 55 is supported by the inner barrel 54 and is movablely supported relative to the outer barrel of the lens barrel 51 for focusing and zooming.

[0040] During the observation period before shooting, light from the subject is reflected by the main mirror 57, which is an example of a component inside the housing 65 of the camera body 52, passes through the prism 61, and the image is projected onto the photographer through the viewfinder lens 62. The main mirror 57 is, for example, a half-mirror, and the light that passes through the main mirror 57 is reflected by the sub-mirror 58 towards the AF (autofocus) unit 63, and this reflected light is used, for example, for distance measurement. The main mirror 57 is also attached and supported by the main mirror holder 66 by adhesive or the like. During shooting, the main mirror 57 and sub-mirror 58 are moved out of the optical path via a drive mechanism (not shown), the shutter 59 is opened, and the image of the light incident from the lens barrel 51 is projected onto the image sensor 60. The aperture 56 is configured to change the brightness and depth of field during shooting by changing the aperture area.

[0041] The alloy member 10 of the present invention can be used in at least a portion of the housing 64, 65, and in this case, it is positioned so that the coating film 13 is located on at least a portion of the outer circumference of the housing 64, 65. Since the alloy member 10 of the present invention suppresses peeling of the coating film due to cracking of the coating film 13, it is possible to provide a lighter imaging device with suppressed peeling of the coating film compared to conventional devices. [Examples]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0043] (Example 1) First, an electrolyte solution 31 was prepared by dissolving ammonium fluoride at a ratio of 146.7 g / L and triammonium phosphate trihydrate at a ratio of 146.4 g / L in pure water. The prepared electrolyte solution 31 was poured into the outer tank 32 of the anodic oxidation apparatus 30 shown in Figure 3, and the magnetic pump 35 was started. After the electrolyte solution 31 in the inner tank 33 overflowed and liquid circulation began, the temperature control mechanism 34 was started to stabilize the liquid temperature at 20°C. Furthermore, a carbon plate was immersed in the inner tank 33 as the cathode 37 and connected to the cathode of the power supply 40 with a wire.

[0044] As the base material 11 made of a Mg-Li alloy subjected to an anodic oxidation treatment, a die-cast substrate of "Ares" (composition: Mg-9%Li-4%Al-1%Zn, manufactured by Anritsu Material Technology Co., Ltd.) was prepared. The size was a thin plate of 150 mm × 100 mm × 1 mm. The die-casting was performed using "LMI450M" manufactured by Sodick Co., Ltd.

[0045] Next, a conduction holding jig 39 made of AZ31 material was prepared. The conduction holding jig 39 has a fixed hinge at the tip of an AZ31 round bar and has an operating hinge at a position 107 mm therefrom. The fixed hinge and the operating hinge are structured to shrink with an O-ring made by Biton. This conduction holding jig 39 was previously anodized in the above electrolytic solution 31 until no current flowed at a voltage of 100V. This treatment is to make it easier to transmit power to the conduction holding jig 39. The above base material 11 was sandwiched as the anode 38 in the conduction holding jig 39 after the pretreatment, connected to the anode of the DC stabilized power supply 40 with a conducting wire, and immersed and arranged in the inner tank 33 at a position facing the cathode 37.

[0046] The DC stabilized power supply 40 used "PAT160-100TMX" manufactured by Kikusui Electronics Industry Co., Ltd. The input current was 15.25 A (surface area: 305 cm 2 , current density: 5 A / 100 cm 2 ). The target film thickness was 20 μm, and the input current was set to 2593 coulombs. When the specified coulomb amount was reached, the current of the DC stabilized power supply 40 was stopped.

[0047] The anode 38 and the conduction holding jig 39 after the anodic oxidation treatment were taken out from the inner tank 33, washed with pure water to thoroughly wash away the electrolytic solution 31 adhering to the surface, and then dried in a clean oven at 60°C.

[0048] Finally, the surface of the anticorrosion film 12 was spray-coated using a one-component baking primer (product name: Panaco SMG) and an acrylic paint (product name: Armor Top) manufactured by Musashi Paint Co., Ltd. For the primer, thinner of product number Z-2854 (product name: Panaco MG Thinner) was used, diluted in a ratio of 2:1 (undiluted:thinner), and spray-coated to a thickness of 20 μm. After spraying, it was dried by air for 10 minutes, and then dried in a 160°C oven for 20 minutes. On the surface coated with primer, paint diluted with thinner of product number Z-2253 (product name: Armor Top Thinner) in a ratio of 2:1 (undiluted:thinner) was spray-coated to a thickness of 15 μm. After spraying, it was dried by air for 10 minutes, and then dried in a 160°C oven for 20 minutes to obtain an alloy member 10 with a painted film 13.

[0049] (Examples 2 to 11) As shown in Table 1, alloy members were fabricated in the same manner as in Example 1, except that the concentrations of fluoride ions and phosphate ions were adjusted by changing the composition and concentration of the materials constituting the electrolyte 31, and the input current value was changed. The voltage during the anodizing treatment was in the range of 60 to 70V.

[0050] (Comparative Examples 1 to 7) As shown in Table 1, alloy members were fabricated in the same manner as in Example 1, except that the concentration of the electrolyte 31 and the input current were changed. The voltage during the anodizing treatment of Comparative Examples 1 to 3 and Comparative Examples 6 and 7 was in the range of 70 to 80V, and the voltage during the anodizing treatment of Comparative Examples 4 and 5 was in the range of 230 to 250V.

[0051] <Rating> (Thickness of the protective coating) The film thickness of the corrosion-preventive coating on the alloy members of the examples and comparative examples was measured. The film thickness was evaluated using the eddy current type film thickness gauge "SWT-9000" (probe: NF-0.6) manufactured by Sanko Electronics Laboratory Co., Ltd. Film thickness was measured at five arbitrary points on the uniform surface, and the average value was calculated. The results are shown in Table 2.

[0052] (Component ratio of the corrosion protection film) To evaluate the component ratio of the corrosion protection film, elemental analysis was performed using EDS (energy-dispersive X-ray spectrometer). EDS elemental analysis was performed using a ZEISS SIGMA500 (FE-SEM) instrument. The elements targeted for EDS elemental analysis were Mg, P, F, O, Al, and Ca. The analysis conditions were an acceleration voltage of 10kV and a work distance of 8.5mm to 9mm. The measurement involved elemental composition analysis using EDS from the surface side of the anticorrosion film after anodizing. The average value across the entire image area at a magnification of 500x was used as the component ratio of the film. The results are shown in Table 2.

[0053] (Crystal structure of the corrosion protection film) To analyze the crystalline structure of the corrosion protection film, measurements were performed using X-ray diffraction at 25°C. The X-ray diffractometer used was Rigaku's "Ultima IV". A copper tube was used, and the measurement wavelength λ was set to 1.5418 Å. The tube voltage was 40 kV, and the tube current was 40 mA. First, diffraction patterns were acquired using the 2θ-θ method for 2θ in the range of 20° to 60°. The step size was 0.02°, and the scan speed was 2° / min (2 integrations). Next, background noise was removed from the acquired diffraction patterns. Then, each peak in the background-removed diffraction pattern was identified. Next, the α-phase and β-phase peaks of the Mg-Li alloy were extracted. Since these peaks originate from the substrate, we focused on identifying the peaks of the phosphoric acid and fluorine-derived films. The results are shown in Figure 5. As shown by the dashed lines, comparative examples 1 to 3 show peaks originating from the protective film (Mg2PO4F), indicating crystallization. On the other hand, the peaks of examples 1 to 8 are shown by solid lines, and no peaks originating from the protective film were detected. Furthermore, a broad waveform was observed from 20° to 40°, and since no crystal peaks originating from the protective film appeared, it was identified as an amorphous structure. The results of identifying the amorphous and crystalline structures in this way are shown in Table 2.

[0054] (Paint film peeling evaluation) Figure 6 shows an overview of the evaluation method for paint film peeling. Alloy members 10 of the examples and comparative examples were placed on a jig 71, and a weight 72 was dropped onto the painted surface of the alloy member 10 to check for paint film peeling. The jig 71 has an outer diameter of 60 mm, with concentric holes of an inner diameter of 30 mm, and a thickness of 10 mm. The weight 72 is cylindrical with a mass of 1000 g and an outer diameter of 18 mm, and has a spherical tip. The center of the weight 72 and the center of the jig 71 were aligned, and the weight was dropped vertically onto the alloy member 10 from a height H of 300 mm. The results are shown in Table 2. Samples with no peeling were marked with ○, samples with partial peeling in a point-like manner were marked with △, and samples with complete peeling across a surface were marked with ×.

[0055] (Appearance inconsistency evaluation) Appearance irregularities were judged based on whether the irregularities were visible to the naked eye on the alloy component 10 after painting. Areas with thicker anodic oxide films appeared white, while areas with thinner films appeared gray, resulting in variations in shading due to film thickness. While slight variations in shading were hidden after painting and not visible as appearance irregularities, significant variations in shading were visible even after painting and unsuitable for use as a product. The results are shown in Table 2.

[0056] [Table 1]

[0057] [Table 2]

[0058] As described above, in the example, the anticorrosion film in which the mass ratio of F to Mg is 0.05 to 0.70 and the mass ratio of P to Mg is 0.8 to 1.41 can achieve both suppression of coating peeling and suppression of uneven appearance. In Comparative Examples 1 to 3, the component range is outside that of this example, so the anticorrosion film crystallizes, resulting in either coating peeling or uneven appearance, or both. In Comparative Examples 4 to 5, the anticorrosion film has an amorphous structure due to the high voltage of the anodizing treatment, but the film does not densify at high voltage, so coating peeling occurs due to film cracking. In Comparative Examples 6 and 7, the ratio of F to P is heavily skewed to one side, resulting in uneven film on the high-concentration P side and film cracking on the high-concentration F side.

[0059] [Included components] This embodiment includes the following configuration. (Composition 1) A corrosion-preventive film mainly composed of magnesium that covers and protects the surface of a substrate containing lithium, A corrosion-preventive film characterized by containing 20% ​​to 40% by mass of phosphorus, 25% or more by mass of oxygen, 17% or less by mass of fluorine, 20% to 30% by mass of magnesium, and 5% or less by mass of nitrogen, and having an amorphous structure. (Configuration 2) The corrosion-preventive film according to configuration 1, characterized in that its thickness is 5 μm or more and 40 μm or less. (Composition 3) The corrosion-preventive film according to configuration 1 or 2, characterized in that the mass ratio of fluorine content to magnesium content is 0.05 or more and 0.70 or less, and the mass ratio of phosphorus content is 0.8 or more and 1.41 or less.

[0060] (Composition 4) The process involves placing an anode and a cathode in an electrolyte solution, A method for manufacturing an alloy member, comprising the step of applying a voltage between the anode and the cathode to form a corrosion-resistant film on the anode, The anode is a substrate mainly composed of magnesium and containing lithium. A method for manufacturing an alloy member, characterized in that the coordinates (X, Y) of the electrolyte, where the fluoride ion concentration is X mol / L and the phosphate ion concentration is Y mol / L, are located within the region enclosed by the coordinates [1] to [5] below. [1](1.9, 0.7) [2](5.8, 0.7) [3](10.0, 4.1) [4](4.4, 4.1) [5](1.9, 2.2) (Composition 5) In the aforementioned electrolyte, A method for manufacturing an alloy member according to configuration 4, characterized in that the ratio of the phosphate ion concentration to the sum of the fluoride ion concentration and the phosphate ion concentration is in the range of 11% to 54%.

[0061] (Composition 6) A base material mainly composed of magnesium and containing lithium, An alloy member comprising a corrosion-resistant film provided on the substrate, The alloy member is characterized in that the corrosion protection film is the corrosion protection film described in any one of configurations 1 to 3. (Composition 7) The alloy member according to configuration 6, characterized in that the sum of the magnesium content and the lithium content in the base material is 90% by mass or more. (Composition 8) The alloy member according to configuration 6 or 7, characterized in that the lithium content in the substrate is 0.5% by mass or more and 15% by mass or less. (Composition 9) The alloy member according to any one of configurations 6 to 8, characterized in that the base material contains aluminum in a range of 1% by mass or more and 8% by mass or less.

[0062] (Composition 10) The alloy member according to any one of configurations 6 to 9, characterized in that the base material contains at least one of germanium and beryllium in an amount of 0.02% by mass or more and 0.4% by mass or less. (Composition 11) The alloy member according to configuration 10, characterized in that the germanium content in the substrate is 0.01% by mass or more and 0.4% by mass or less, and the beryllium content is 0.02% by mass or more and 0.1% by mass or less. (Composition 12) The alloy member according to any one of configurations 6 to 11, characterized in that the base material contains zirconium in an amount of 0.6% by mass or more and 3.0% by mass or less.

[0063] (Composition 13) The alloy member according to any one of configurations 6 to 12, characterized in that the base material contains at least one element selected from zinc, calcium, silicon, and manganese in an amount of 0.01% by mass or more and 5% by mass or less. (Composition 14) The zinc content is 3% by mass or less, The calcium content is 3.0% by mass or less. The silicon content is 0.2% by mass or less, The manganese content is 0.3% by mass or less, The alloy member according to configuration 13, characterized in that the remainder consists of unavoidable impurities, magnesium, and lithium. (Composition 15) An alloy member according to any one of configurations 6 to 14, characterized in that the anticorrosion film is covered with a paint film.

[0064] (Composition 16) A device comprising a housing and components provided within the housing, The apparatus is characterized in that the housing includes an alloy member as described in any of configurations 6 to 15. [Explanation of Symbols]

[0065] 10: Alloy component, 11: Base material, 12: Anticorrosion film, 13: Paint film, 31: Electrolyte, 37: Cathode, 38: Anode

Claims

1. A corrosion-preventive film mainly composed of magnesium that covers and protects the surface of a substrate containing lithium, A corrosion-preventive film characterized by containing 20% ​​to 40% by mass of phosphorus, 25% or more by mass of oxygen, 17% or less by mass of fluorine, 20% to 30% by mass of magnesium, and 5% or less by mass of nitrogen, and having an amorphous structure.

2. The corrosion-preventive film according to claim 1, characterized in that its thickness is 5 μm or more and 40 μm or less.

3. The corrosion-preventive film according to claim 1, characterized in that the mass ratio of fluorine content to magnesium content is 0.05 or more and 0.70 or less, the mass ratio of phosphorus content is 0.8 or more and 1.41 or less, and the mass ratio of oxygen content is 1.5 or more and 2.2 or less.

4. A step of placing an anode and a cathode in an electrolyte, A method for manufacturing an alloy member, comprising the step of applying a voltage between the anode and the cathode to form a corrosion-preventive film on the anode, The anode is a substrate mainly composed of magnesium and containing lithium. A method for manufacturing an alloy member, characterized in that the coordinates (X, Y) of the electrolyte, where the fluoride ion concentration is X mol / L and the phosphate ion concentration is Y mol / L, are located within the region enclosed by the coordinates [1] to [5] below. ［１］（１．９、０．７） ［２］（５．８、０．７） ［３］（１０．０、４．１） ［４］（４．４、４．１） ［５］（１．９、２．２）

5. In the aforementioned electrolyte, The method for manufacturing an alloy member according to claim 4, characterized in that the ratio of the phosphate ion concentration to the sum of the fluoride ion concentration and the phosphate ion concentration is in the range of 11% to 54%.

6. A base material mainly composed of magnesium and containing lithium, An alloy member comprising a corrosion-resistant film provided on the substrate, The alloy member is characterized in that the corrosion-preventive film is the corrosion-preventive film described in claim 1.

7. The alloy member according to claim 6, characterized in that the sum of the magnesium content and the lithium content in the base material is 90% by mass or more.

8. The alloy member according to claim 6, characterized in that the lithium content in the substrate is 0.5% by mass or more and 15% by mass or less.

9. The alloy member according to claim 6, characterized in that the base material contains aluminum in a range of 1% by mass or more and 8% by mass or less.

10. The alloy member according to claim 6, characterized in that the base material contains at least one of germanium and beryllium in an amount of 0.02% by mass or more and 0.4% by mass or less.

11. The alloy member according to claim 10, characterized in that the germanium content in the substrate is 0.01% by mass or more and 0.4% by mass or less, and the beryllium content is 0.02% by mass or more and 0.1% by mass or less.

12. The alloy member according to claim 6, characterized in that the base material contains zirconium in an amount of 0.6% by mass or more and 3.0% by mass or less.

13. The alloy member according to claim 6, characterized in that the base material contains at least one element selected from zinc, calcium, silicon, and manganese in an amount of 0.01% by mass or more and 5% by mass or less.

14. The zinc content is 3% by mass or less, The calcium content is 3.0% by mass or less. The silicon content is 0.2% by mass or less, The manganese content is 0.3% by mass or less. The alloy member according to claim 13, characterized in that the remainder consists of unavoidable impurities, magnesium, and lithium.

15. The alloy member according to claim 6, characterized in that the anticorrosion film is covered with a paint film.

16. A device comprising a housing and components provided within the housing, The apparatus is characterized in that the housing includes the alloy member described in any one of claims 6 to 15.

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