KR102705184B1 - Method of treating surface of manesium alloy and surface treated manesium alloy - Google Patents

Abstract

A method for surface treating a magnesium alloy of the present invention may include a step of forming a composite polysilazane layer including at least one of an inorganic polysilazane and an organic polysilazane on the magnesium alloy, a step of coating an aluminum layer on the composite polysilazane layer, and a step of anodizing the aluminum layer so that the aluminum layer exhibits a predetermined color.

Description

Method of treating surface of magnesium alloy and surface treated magnesium alloy {METHOD OF TREATING SURFACE OF MANESIUM ALLOY AND SURFACE TREATED MANESIUM ALLOY}

The present invention relates to a method for surface treating a magnesium alloy and a surface-treated magnesium alloy. More specifically, the present invention relates to a method for surface treating a magnesium alloy to prevent surface corrosion of the magnesium alloy by an electrolyte and a surface-treated magnesium alloy.

Magnesium has the lowest specific gravity (1.74) among structural metal materials, and has the advantages of high specific strength, excellent castability, machinability, dimensional stability, and scratch resistance. In addition, due to its characteristics such as electromagnetic shielding and vibration damping, it is widely used in various technical fields, especially in fields that require lightness and strength, such as laptop computer cases, mobile phone cases, car seat frames, car interior materials, military supplies, and sports goods.

Magnesium has a standard electrode potential of 2.363 V _NHE , making it the most chemically active metal among commercial metals. Because of this, it is prone to corrosion when in contact with other metals or chemical solutions, and has poor corrosion resistance. Due to the above disadvantages, appropriate surface treatment is required to apply magnesium to electronic products, etc.

The technical problem to be solved by the present invention is to provide a method for surface treatment of a magnesium alloy to provide a magnesium alloy that has improved corrosion resistance, high safety that does not deteriorate even after long-term use, and improved appearance so that it can be used for various purposes.

Another technical problem to be achieved by the present invention is to provide a magnesium alloy surface-treated by a method for surface-treating a magnesium alloy having the aforementioned advantages.

According to one embodiment of the present invention for solving the above-described problem, a method for surface treating a magnesium alloy may include the steps of forming a composite polysilazane layer including at least one of an inorganic polysilazane and an organic polysilazane on the magnesium alloy, coating an aluminum layer on the composite polysilazane layer, and anodizing the aluminum layer so that the aluminum layer exhibits a predetermined color.

In one embodiment, prior to the step of forming the composite polysilazane layer, the method may further include a step of forming a chromium film on the surface of the magnesium alloy by anodizing or chromating the surface of the magnesium alloy.

In one embodiment, the composite polysilazane layer can include at least one of an inorganic polysilazane layer and an organic polysilazane layer.

In one embodiment, the step of forming the composite polysilazane layer may include the steps of forming a first inorganic polysilazane layer on the magnesium alloy, forming a first organic polysilazane layer on the first inorganic polysilazane layer, and forming a second inorganic polysilazane layer on the first organic polysilazane layer.

According to one embodiment of the present invention for solving the above-described problem, a surface-treated magnesium alloy may include a magnesium alloy, a composite polysilazane layer formed on the magnesium alloy and including at least one of an inorganic polysilazane and an organic polysilazane, and an aluminum layer formed on the composite polysilazane layer and anodized to exhibit a predetermined color.

According to one embodiment of the present invention for solving the above problem, a method for surface treating a magnesium alloy may include a step of forming a magnesium oxide film as an insulating layer on a surface of the magnesium alloy, a step of coating an aluminum layer on the magnesium oxide film, and a step of anodizing the aluminum layer so that the aluminum layer exhibits a predetermined color.

In one embodiment, the step of forming the magnesium oxide film can include treating the surface of the magnesium alloy with 10 to 30% (w/w) sodium hydroxide at a direct current (DC) constant voltage of 5 to 10 V for 3 to 15 minutes.

In one embodiment, prior to the step of forming the magnesium oxide film, a step of cleaning the surface of the magnesium alloy, chemically etching, and then sand blasting may be additionally performed.

In one embodiment, the anodizing step may include a step of anodizing the aluminum layer to form an oxide film having pores, a step of injecting a dye having the predetermined color into the pores, and a step of sealing the pores so that the dye does not escape from the pores.

In one embodiment, the sealing step can increase the wear resistance, chemical resistance, fingerprint resistance, and hydrophobicity of the surface-treated magnesium alloy.

In one embodiment, the sealing step can be performed by water-soluble silicone electrolytic sealing.

In one embodiment, the step of forming the oxide film having the pores may include the steps of chemically polishing the aluminum layer with a phosphoric acid aqueous solution, rinsing the chemically polished aluminum layer, ultrasonically cleaning the rinsed aluminum layer, anodizing the ultrasonically cleaned aluminum layer with a sulfuric acid aqueous solution, rinsing the anodized aluminum layer, and ultrasonically cleaning the aluminum layer.

According to one embodiment of the present invention for solving the above-described problem, a surface-treated magnesium alloy may include a magnesium alloy, a magnesium oxide film as an insulating layer formed on the magnesium alloy, and an aluminum layer (230) formed on the magnesium oxide film and anodized to exhibit a predetermined color.

In one embodiment, the thickness of the aluminum layer (230) may be 50 μm to 250 μm.

In one embodiment, the thickness of the aluminum layer (230) may be 10 ㎛ to 100 ㎛, and the depth of the pores formed by the anodizing treatment of the aluminum layer (230) may be 6 ㎛ to 50 ㎛.

A method for surface treating a magnesium alloy according to one embodiment of the present invention can improve the adhesion and bonding strength between a magnesium alloy layer and an aluminum layer by forming a composite polysilazane layer before coating an aluminum layer on the magnesium alloy, and in particular, when the magnesium alloy layer is an outer casing of an electronic device having a curved surface or rounded corners, it can improve the conventional problem of poor adhesion of the aluminum layer.

In addition, the method for surface treating a magnesium alloy according to one embodiment of the present invention can effectively prevent an anodizing electrolyte from penetrating into and corroding the magnesium alloy by forming a composite polysilazane layer before coating an aluminum layer on the magnesium alloy.

In addition, a method for surface treating a magnesium alloy according to one embodiment of the present invention is such that the magnesium alloy is first protected with a chemical film, and then a composite polysilazane layer is formed on the chemical film, thereby doubly protecting the magnesium alloy by the chemical film and the composite polysilazane layer, thereby more efficiently preventing penetration of an anodizing electrolyte.

In addition, the surface-treated magnesium alloy according to one embodiment of the present invention includes a composite polysilazane layer formed between the magnesium alloy and the aluminum layer, thereby providing a surface-treated magnesium alloy having the aforementioned advantages during the manufacturing process and improved adhesion of the aluminum layer.

In addition, a method for surface treating a magnesium alloy according to one embodiment of the present invention forms a magnesium oxide film as an insulating layer on the surface of the magnesium alloy, thereby reducing variables due to outgassing of the magnesium alloy, thereby preventing foreign matter defects and reduced adhesion during deposition of an aluminum layer.

In addition, a surface-treated magnesium alloy according to one embodiment of the present invention includes a magnesium oxide film as an insulating layer on a surface of a magnesium alloy and an aluminum layer anodized on the magnesium oxide film, and by appropriately controlling the thickness of the aluminum layer and the depth of pores formed by the anodizing treatment, the magnesium alloy can be prevented from being corroded when the aluminum layer is anodized.

FIG. 1 is a drawing showing a surface-treated magnesium alloy according to one embodiment of the present invention.
FIG. 2 is a schematic diagram of the internal structure of an anodized aluminum layer of a surface-treated magnesium alloy according to one embodiment of the present invention.
FIG. 3 is a drawing showing a surface-treated magnesium alloy according to one embodiment of the present invention.
FIG. 4 is a flow chart of a method for surface treating a surface-treated magnesium alloy according to one embodiment of the present invention.
FIGS. 5a and 5b are drawings showing corrosion reactions of a magnesium alloy before and after a salt water reaction, and FIGS. 6a to 6c are drawings showing corrosion prevention effects of a surface-treated magnesium alloy according to an embodiment of the present invention in a sulfuric acid aqueous solution.
FIGS. 7a and 7b are drawings showing adhesion tests for an aluminum layer coated on a magnesium alloy according to a comparative example, and FIGS. 8a to 8c are drawings showing adhesion tests for a surface-treated magnesium alloy according to an example of the present invention.
FIG. 9 is a drawing showing a surface-treated magnesium alloy (200) according to one embodiment of the present invention.
FIG. 10a is a flow chart of a method for surface treating a magnesium alloy according to one embodiment, and FIG. 10b is a detailed flow chart of a step (S230) of anodizing an aluminum layer.
Figure 11 shows the results of a corrosion test after a magnesium oxide film is formed according to another embodiment.
FIGS. 12a and 12b are experimental results showing the thickness and component analysis of a deposited aluminum layer of a surface-treated magnesium alloy according to one embodiment of the present invention.
FIG. 13 is a process diagram for surface treating a complex formation using a surface treatment method for a magnesium alloy according to one embodiment of the present invention.
FIG. 14 is an image of a cross-section of a magnesium alloy surface-treated by a method for surface-treating a magnesium alloy according to one embodiment of the present invention.
FIG. 15 is a diagram showing the results of measuring the thickness of the deposited aluminum layer by photographing a cross-section of a magnesium alloy after forming a magnesium oxide film on the surface of a magnesium alloy and coating an aluminum layer on the magnesium oxide film according to one embodiment of the present invention.
FIG. 16 is a photograph of a coating surface in the case where aluminum is coated by magnetron sputtering without forming a magnesium oxide film on the surface of the magnesium alloy, and FIG. 17 is a photograph of a magnesium alloy in which a magnesium oxide film as an insulating layer is formed on the magnesium alloy as described in FIGS. 10a and 10b, aluminum is coated on the magnesium oxide film, and then anodizing including water-soluble electrolytic sealing is performed on the aluminum layer.
FIG. 18(a) is an image taken after dropping a water droplet on the surface of a surface-treated magnesium alloy treated according to a conventional aluminum anodizing process, and FIG. 18(b) is an image taken after dropping a water droplet on the surface of a magnesium alloy to which water-soluble silicon electrolytic sealing has been applied according to the surface treatment method of a magnesium alloy according to the present invention described above with reference to FIGS. 10a and 10b.

Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In addition, the present invention is not limited to the embodiments below, and may be realized not only in a separate manner that can be recognized by a person skilled in the art, but also in any arbitrarily feasible combination. In addition, the scope of the present invention is not limited by the preferred embodiments. In addition, the embodiments are schematically illustrated in the drawings. In the present application, the same drawing reference numerals in these drawings represent identical or functionally similar elements.

FIG. 1 is a drawing showing a surface-treated magnesium alloy (100) according to one embodiment of the present invention.

Referring to FIG. 1, in one embodiment, a surface-treated magnesium alloy (100) may include a magnesium alloy (110), a composite polysilazane layer (120) formed on the magnesium alloy (110), and an aluminum layer (130) formed on the composite polysilazane layer (120). The surface-treated magnesium alloy (100) may be an outer shell of an electronic device, such as a portable or non-portable electronic device, for example, a mobile phone, a laptop, or a tablet. The electronic device may have sharp corners or rounded corners, and in particular, a vertex where three sides meet may have a rounded corner. Typically, when an outer shell of an electronic device having a curved surface or rounded corners is plated with aluminum, a problem may occur in which the adhesion of the aluminum coating, i.e., the aluminum layer, is reduced. In one embodiment, the magnesium alloy may be formed by die casting.

In one embodiment, the composite polysilazane layer (120) includes polysilazane, which is a compound having Si-N repeating units in a polymer backbone, and the composite polysilazane layer may include at least one of inorganic polysilazane and organic polysilazane. Polysilazane may be classified into inorganic polysilazane and organic polysilazane depending on whether or not carbon is included in a functional group substituted on a Si or N atom, for example, a methyl group or a vinyl group. The functional group substituted on a Si or N atom of the polysilazane is not limited, and various types of known polysilazane may be used. According to an embodiment of the present invention, before the aluminum layer (130) is coated on the magnesium alloy (110), a composite polysilazane layer (120) is formed as an intermediate adhesive layer between the magnesium alloy (110) and the aluminum layer (130), thereby improving the adhesion and bonding strength between the magnesium alloy and the aluminum layer. In particular, when the magnesium alloy is an outer casing material of an electronic device having a curved surface or rounded corners, there is an advantage in that the conventional problem of poor adhesion of the aluminum layer can be improved.

In one embodiment, the composite polysilazane layer (120) can include at least one of an inorganic polysilazane layer and an organic polysilazane layer. For example, an inorganic polysilazane layer can be formed on a magnesium alloy, an organic polysilazane layer can be formed on the inorganic polysilazane layer, and an aluminum layer can be coated on the organic polysilazane layer. Alternatively, an organic polysilazane layer can be formed on a magnesium alloy, an inorganic polysilazane layer can be formed on the organic polysilazane layer, and an aluminum layer can be coated on the inorganic polysilazane layer. Alternatively, a first inorganic polysilazane layer can be formed on a magnesium alloy, a first organic polysilazane layer can be formed on the first inorganic polysilazane layer, a second inorganic polysilazane layer can be formed on the first organic polysilazane layer, and an aluminum layer can be coated on the second inorganic polysilazane layer. Alternatively, the composite polysilazane layer may be a layer in which organic polysilazane layers and inorganic polysilazane layers are alternately laminated, for example, when a laminate of two layers of an inorganic polysilazane layer - an organic polysilazane layer is made as one set, n sets may be laminated. 1 ≤ n ≤ 100, or 2 ≤ n ≤ 20, or 2 ≤ n ≤ 5. In another embodiment, the layers may be laminated in the order of first inorganic polysilazane layer - first organic polysilazane layer - second inorganic polysilazane layer - second organic polysilazane layer - (...) - n-1th organic polysilazane layer - nth inorganic polysilazane layer. Alternatively, the layers may be laminated in the order of first organic polysilazane layer - first inorganic polysilazane layer - second organic polysilazane layer - second inorganic polysilazane layer - (...) - n-1th inorganic polysilazane layer - nth organic polysilazane layer. Here, 1 ≤ n ≤ 100 may be, or 2 ≤ n ≤ 20 may be, or 2 ≤ n ≤ 5 may be. In another embodiment, the composite polysilazane layer may be a layer formed of a mixture of inorganic polysilazane and organic polysilazane.

FIG. 2 is a schematic diagram of the internal structure of an anodized aluminum layer (130) of a surface-treated magnesium alloy (100) according to one embodiment of the present invention.

In one embodiment, the aluminum layer (130) may be a layer that is anodized to exhibit a predetermined color. The aluminum layer (130) is anodized to form an anodized film on the surface, and the anodized film includes fine pores (131) therein. A dye (132) is injected into the pores (131), so that the aluminum layer (130) can be provided in various colors desired by the customer. After the dye (132) is injected, the dye is prevented from escaping from the pores (131) by a sealing treatment (sealing treatment, 133) after the dye is injected. The predetermined color may be applied to various colors of dyes that can be used in a known anodizing process technology.

FIG. 3 is a drawing showing a surface-treated magnesium alloy (100') according to one embodiment of the present invention.

In one embodiment, the surface-treated magnesium alloy (100') further includes a chemical conversion film (140) formed on the magnesium alloy (110), and a composite polysilazane layer (120) may be formed on the chemical conversion film (140). The chemical conversion film (140) is a corrosion-resistant surface film that is produced by immersing a magnesium alloy in a chemical agent to cause a chemical reaction on the surface. The chemical conversion film may be produced by anodizing treatment or chromating treatment, and may be CrOHCrO ₄ , Cr(OH) ₃ or MgCrO depending on the type of chemical conversion solution, and preferably, may be a magnesium oxide (MgO) film. For a detailed description of the case where the chemical conversion film (140) is magnesium oxide, reference may be made to the descriptions of FIGS. 9 and 10 .

FIG. 4 is a flow chart of a method for surface treating a surface-treated magnesium alloy (100, 100') according to one embodiment of the present invention.

Referring to FIG. 4, a composite polysilazane layer (120) can be formed on a magnesium alloy (110) or on a magnesium alloy (110) on which a ignition film (140) is formed (S120). The composite polysilazane layer (120) can be formed by coating a polysilazane compound on the magnesium alloy (110). The polysilazane compound can include an organic polysilazane or an inorganic polysilazane. As a coating method, a spray coating method, a dip coating method, or a sol-gel coating method can be used. After coating the polysilazane compound on the surface of the magnesium alloy, the formed composite polysilazane layer is cured by drying in a drying oven. The coating method of the composite polysilazane layer is not limited thereto, and known coating methods can be applied. According to an embodiment of the present invention, since a composite polysilazane layer is formed on a magnesium alloy, when an aluminum layer formed on the composite polysilazane layer is anodized, the anodizing electrolyte can be effectively prevented from penetrating into the magnesium alloy and corroding the magnesium alloy.

In one embodiment, the step (S120) of forming a composite polysilazane layer may include the steps of forming a first inorganic polysilazane layer on the magnesium alloy (110), forming a first organic polysilazane layer on the first inorganic polysilazane layer, and forming a second inorganic polysilazane layer on the first organic polysilazane layer. Alternatively, the organic polysilazane layers and/or the inorganic polysilazane layers may be alternately laminated to form a composite polysilazane layer having various laminated forms described above with reference to FIG. 1. According to an embodiment of the present invention, by alternately forming organic polysilazane and inorganic polysilazane layers having different physical or chemical properties into a composite, the anodizing electrolyte can be more effectively prevented from penetrating into the magnesium alloy and causing corrosion, compared to the case where a polysilazane layer including only one type of polysilazane compound is formed or a single polysilazane layer formed of a polysilazane mixture is formed.

Optionally, before the step of forming the composite polysilazane layer (120), a step of forming a chemical film (140) on the surface of the magnesium alloy by anodizing or chromating the surface of the magnesium alloy may be further performed (S110). According to an embodiment of the present invention, by forming the chemical film (140) on the magnesium alloy (110) before forming the composite polysilazane layer (120), when anodizing an aluminum layer (130) formed on the composite polysilazane layer (120), it is possible to prevent an anodizing electrolyte from penetrating and corroding the magnesium alloy (110). In particular, when a magnesium alloy (110) is first protected with a chemical film (140) and a composite polysilazane layer (120) is formed on the chemical film (140), the magnesium alloy is doubly protected by the chemical film (140) and the composite polysilazane layer (120), so there is an advantage in that penetration of an anodizing electrolyte can be more efficiently prevented.

After the composite polysilazane layer (120) is formed, an aluminum layer (130) can be coated on the composite polysilazane layer (120) (S130). The aluminum layer (130) can be coated by magnetron sputtering. However, the aluminum layer can be coated by spin coating, sputtering, plating, chemical vapor deposition, or physical vapor deposition, and the coating method of the aluminum layer is not limited thereto, and known coating methods can be applied.

The aluminum layer (130) is coated with a thickness suitable for performing a coloring process to exhibit a predetermined color in the anodizing step. The thickness of the aluminum layer (130) may be 50 ㎛ to 250 ㎛. By setting the thickness to 50 ㎛ or more, when forming pores (131) to implement color in the coating, the magnesium alloy can be prevented from being corroded by the treatment solution, thereby enabling stable color implementation and ensuring reliability. In addition, by setting the thickness to 250 ㎛ or less, it is possible to prevent the coating from becoming unnecessarily thick, thereby increasing the cost and time of the coating and deteriorating the quality of the coating. In particular, when the thickness of the aluminum coating is 100 ㎛ or more, the texture and color desired by the customer can be implemented by various surface treatments. For example, when soft anodizing is performed on an aluminum layer, the thickness of the aluminum layer is preferably 10 ㎛ to 20 ㎛, and when hard anodizing is performed, the thickness of the aluminum layer is preferably 50 ㎛ to 100 ㎛.

In one embodiment, when the thickness of the aluminum layer is 10 ㎛ to 100 ㎛, the depth of the pores is formed to be 6 ㎛ to 50 ㎛, so that the aluminum layer can exhibit a predetermined color by anodizing. Alternatively, methods substantially the same as the step (S220) of coating the aluminum layer of the method for surface treating a magnesium alloy according to another embodiment described later in FIGS. 10a and 10b may be used.

Thereafter, the aluminum layer (130) can be anodized to exhibit a predetermined color (S140). Anodizing can be performed by allowing current to flow through the magnesium alloy (110) in which the aluminum layer (130) and the composite polysilazane layer (120) are formed as an anode in an electrolyte to form an oxide film on the surface. Sulfuric acid, oxalic acid, chromic acid, or phosphoric acid can be used as the electrolyte. However, the type of the electrolyte is not limited thereto, and known anodizing electrolytes can be applied. As described above with respect to FIG. 2, when an oxide film is formed by anodizing, fine pores (131) are formed in the oxide film. Thereafter, when a dye (132) is injected into the fine pores, the anodized aluminum layer (130) can exhibit a predetermined color desired by the customer, and after the dye (132) is injected, a sealing treatment (sealing, 133) can be performed to prevent the dye (132) from escaping from the pores (131). Alternatively, methods substantially the same as the step (S230) of anodizing the aluminum layer of the method for surface treating a magnesium alloy according to another embodiment described later in FIGS. 10a and 10b can be used.

FIGS. 5a and 5b are drawings showing corrosion reactions of a magnesium alloy before and after a salt water reaction, and FIGS. 6a to 6c are drawings showing corrosion prevention effects of a surface-treated magnesium alloy according to an embodiment of the present invention in a sulfuric acid aqueous solution.

Referring to FIGS. 5a and 5b, as comparative examples, drawings are provided showing the state of a magnesium alloy not coated with polysilazane before and after a salt water reaction (Comparative Example 1). FIG. 5a is a photograph showing the state of a die-casted magnesium alloy before a salt water reaction, and FIG. 5b is a photograph showing the state of a die-casted magnesium alloy after a salt water reaction. It can be confirmed that a significant corrosion reaction occurs when a die-casted magnesium alloy is reacted with salt water.

Referring to FIGS. 6a to 6c , FIG. 6b is a drawing showing, as a comparative example, the before and after reaction of a magnesium alloy that is not coated with polysilazane with a 20% (w/w) sulfuric acid aqueous solution (Comparative Example 2). FIG. 6a is a photograph showing the state before a die-casted magnesium alloy reacts with a 20% sulfuric acid aqueous solution, and FIG. 6b is a photograph showing the state after a die-casted magnesium alloy reacts with a 20% sulfuric acid aqueous solution. It can be confirmed that a significant corrosion reaction occurs when a die-casted magnesium alloy reacts with a 20% sulfuric acid aqueous solution. FIG. 6c is a photograph showing the after reaction of a magnesium alloy surface-treated according to an embodiment of the present invention with a 20% sulfuric acid aqueous solution (Example 1). The die-cast magnesium alloy was chromated to form a chemical film on the surface, then coated with polysilazane, and reacted with a 20% sulfuric acid aqueous solution. From this, it can be confirmed that when the magnesium alloy according to Comparative Example 2 reacted with a sulfuric acid aqueous solution, serious corrosion occurred on the surface, whereas when the magnesium alloy surface was coated with a chemical film and a polysilazane layer as in Example 1, surface corrosion was effectively prevented even when reacting with a sulfuric acid aqueous solution.

FIGS. 7a and 7b are drawings showing adhesion tests for an aluminum layer coated on a magnesium alloy according to a comparative example, and FIGS. 8a to 8c are drawings showing adhesion tests for a surface-treated magnesium alloy according to an example of the present invention.

Referring to FIGS. 7a and 7b, these are photographs showing the results of an adhesion test on a magnesium alloy that is not coated with polysilazane (Comparative Example 3). FIG. 7a is a photograph after coating an aluminum layer on a magnesium alloy, and FIG. 7b is a photograph showing the results after conducting an adhesion test on the coated aluminum layer. Referring to FIGS. 8a to 8c, these are drawings showing the results of an adhesion test on an aluminum layer coated on a magnesium alloy according to an embodiment of the present invention (Example 2). FIG. 8a is a photograph after coating inorganic polysilazane on a magnesium alloy, FIG. 8b is a photograph after coating an aluminum layer on a magnesium alloy coated with inorganic polysilazane, and FIG. 8c is a photograph showing the results after conducting an adhesion test on an aluminum layer of a magnesium alloy coated with inorganic polysilazane. From this, in the case of Comparative Example 3, where no inorganic polysilazane layer was formed between the magnesium alloy and the aluminum layer, the aluminum layer was peeled off after the adhesion test, resulting in a “bad” adhesion test result, whereas in the case of Example 2, where an inorganic polysilazane layer was formed between the magnesium alloy and the aluminum layer, the adhesion state of the aluminum layer was shown to be “good” after the adhesion test.

FIG. 9 is a drawing showing a surface-treated magnesium alloy (200) according to one embodiment of the present invention.

Referring to FIG. 9, in one embodiment, the surface-treated magnesium alloy (200) may include a magnesium alloy (210), a magnesium oxide film (240) formed on the magnesium alloy (210), and an aluminum layer (230) formed on the magnesium oxide film (240). With respect to the magnesium alloy (210) and the aluminum layer (230), reference may be made to the descriptions made with respect to the surface-treated magnesium alloy (100, 100') according to one embodiment in FIGS. 1 to 8. Additionally, the magnesium oxide film (240) may be a type of the aforementioned chemical film.

The thickness of the magnesium oxide film (240) may be 3 ㎛ to 20 ㎛. If the thickness is less than 3 ㎛, the magnesium alloy (210) is not sufficiently protected, which may cause corrosion or damage to the magnesium alloy during the anodizing process of the aluminum layer (230), and if the thickness exceeds 20 ㎛, the time required to form the film layer may be unnecessarily long and the coating quality may deteriorate.

The magnesium oxide film (240) can protect the magnesium alloy (210) without changing its properties even after surface treatment of the magnesium alloy (210), and does not contain hexavalent chromium or heavy metals. In addition, the magnesium oxide film (240) has insulating properties and can prevent the magnesium alloy (210) from being corroded by contact with an external aqueous solution. In addition, the adhesion of the aluminum layer (230) to the magnesium alloy (210) can be increased, and the corrosion resistance of the magnesium alloy product can be improved because the magnesium oxide film (240) protects the magnesium alloy (210).

In addition, in a conventional method of coating a magnesium alloy with aluminum, the quality of the aluminum coating deteriorated due to outgassing of the magnesium alloy at a temperature of 300°C or less, but according to the present embodiment, the magnesium oxide film can prevent foreign matter defects and reduced adhesion during deposition of the aluminum layer by reducing the variable due to vaporization, i.e. outgassing, generated from the magnesium alloy.

FIG. 10a is a flow chart of a method for surface treating a magnesium alloy according to one embodiment, and FIG. 10b is a detailed flow chart of a step (S230) of anodizing an aluminum layer.

Referring to Fig. 10a, a magnesium oxide (MgO) film is formed on the surface of a magnesium alloy (S210). To form the magnesium oxide film, the surface of the magnesium alloy is degreased with a sodium hydroxide aqueous solution. The degreased treatment is performed by heating a 50% (w/w) sodium hydroxide aqueous solution to 80 to 90 ℃ and immersing for 8 to 10 minutes (S210).

Next, the surface of the magnesium alloy can be oxidized by treating it with a sodium hydroxide aqueous solution, thereby forming a magnesium oxide film (insulating layer). For example, the surface of the magnesium alloy can be immersed in a sodium hydroxide aqueous solution. The concentration of the sodium hydroxide aqueous solution can be 10% to 50% (w/w), or 10% to 30% (w/w), or 20% (w/w), the temperature of the sodium hydroxide aqueous solution during the treatment is 25°C to 30°C, and the treatment is performed at a direct current (DC) constant voltage of 5 to 10 V for 3 to 15 minutes to form an insulating layer.

After forming the insulating layer, ultrasonic washing is performed at room temperature for 30 seconds. After that, it is dried at a temperature of 90°C to 100°C for 30 minutes. When the magnesium alloy is treated with a sodium hydroxide aqueous solution according to this embodiment, an insulating layer can be formed as a magnesium oxide film without changing the color of the surface of the magnesium alloy.

Here, a magnesium oxide film (insulating layer) was formed, ultrasonic washing was performed at room temperature for 30 seconds, and a sample was dried at a temperature of 90 to 100 ℃ for 30 minutes. As a result of a corrosion test conducted for 60 minutes in a 10% (w/w) sulfuric acid aqueous solution, it was confirmed that no corrosion reaction occurred. In addition, excellent salt water resistance was confirmed as a result of a salt water spray test conducted for 72 hours.

In another embodiment, before the step of forming a magnesium oxide film (S210), a step of cleaning the surface of the magnesium alloy, performing chemical etching, and then performing sand blasting may be additionally performed. By the chemical etching, a portion mixed in the surface layer of segregation (intermetallic chemical substance) oxide or release agent existing on the surface or between particles of the magnesium material may be removed, and a natural oxide film and corrosion products on the surface may be removed. In addition, the chemical etching may act as a polishing process for magnesium. If the chemical etching ability is reduced, that is, if the chemical etching is not performed properly, segregation (a shape in which the composition is unevenly distributed inside the solid material) may be formed or corrosion products may not be removed, and in particular, a corrosion portion may be characterized. In this state, the anodic oxide film treatment cannot be performed normally, and poor adhesion of the film occurs.

The specific conditions for chemical etching are as follows.

- Working conditions

Sodium hydroxide (NaOH) aqueous solution 100-150 (g/l, 100-150 g of sodium hydroxide dissolved per 1 L of water)

- Working temperature 60~70℃

- Aqueous solution stirring or air stirring method

- Working time 10-13 minutes

Additionally, in order to prevent deformation of the magnesium alloy product during the sandblasting process, the front and back surfaces can be sandblasted with uniform pressure.

After forming a magnesium oxide film, an aluminum layer is coated on the magnesium oxide film (S220). The step of coating the aluminum layer (S220) may use substantially the same methods as the step of coating the aluminum layer on the composite polysilazane layer (S130) in the method for surface treating a surface-treated magnesium alloy (100, 100') according to one embodiment (see FIG. 4). For example, the aluminum layer may use physical vapor deposition (PVD), preferably, magnetron sputtering. When the aluminum layer is formed by magnetron sputtering, the microstructure film formation speed of the aluminum layer is constant and can have high productivity. In addition, when the aluminum layer is formed by magnetron sputtering, the formed aluminum layer has a high deposition adhesion strength and a high-density uniform structure, which has the advantage of high film uniformity. In addition, the microstructure of the aluminum layer formed by magnetron sputtering exhibits a smooth surface and a dense microstructure. In addition, the purity of the aluminum coating formed by magnetron sputtering according to the present embodiment can be 99.9% or higher.

A specific method for coating aluminum by magnetron sputtering is as follows.

a. Target: Al 99.6% or higher

b. Cathode Magnetron Sputtering

c. PVD working vacuum level (Torr): 2.0*10 ⁴ ~ 5.0*10 ⁵ Torr

b. Ar Gas 100~1000 Sccm

e. Working vacuum (Torr): 2.0*10 ² ~ 8.0*10 ⁴ Torr

f. Process power: DC Power 20 Kw~160 Kw

g. Process time: 3 to 10 hours

Next, after coating the aluminum layer, the aluminum layer is anodized to exhibit a predetermined color (S230). The step of anodizing the aluminum layer (S230) may be substantially the same as the step of anodizing the aluminum layer (S140) in the method for surface treating a surface-treated magnesium alloy (100, 100') according to one embodiment (see FIG. 4) to exhibit a predetermined color.

Referring to Fig. 10b, when aluminum is anodized to form an oxide film, fine pores are formed within the oxide film (S231). The thickness of the anodized portion of the aluminum layer, that is, the thickness of the alumite layer, may be 3 ㎛ to 100 ㎛ from the surface of the surface-treated magnesium alloy. Specific experimental conditions for anodizing aluminum are as follows.

a. Step of chemically polishing the deposited aluminum layer

- 10% (w/w) phosphoric acid (H ₃ O ₄ P) aqueous solution

- Temperature of phosphoric acid solution: 80 ~ 95 ℃

- Working time: 10 to 20 seconds

b. Rinse step

c. Ultrasonic Wave (Ultrasonic Cleaning)

d. Hard alumite treatment step (anodizing)

- Anodizing the aluminum layer that performed steps a to c to form alumite

- 10% _sulfuric acid ( _H2SO4 ) solution

- Process power: voltage 10 to 15 V, current size (A) is automatic (constant voltage) per area

- Temperature of sulfuric acid solution: 10℃ or less

- Process time: 25 to 35 minutes

e. Washing: 5-stage room temperature washing

f. Ultrasonic cleaning: 30 seconds ultrasonic at room temperature

When pores are formed in the aluminum layer by anodizing treatment (S231), a dye is injected into the pores to implement the desired color of the customer (S232). The specific method is as follows.

a. Step of injecting a chemical dye of a predetermined color

- Process temperature: 45 ~ 55 ℃

- Process time: 25 minutes for Pink, Silver, Beige, 30 minutes for Blue, Red, 35 minutes for Black

b. Washing step

- Step 5: Running cold water

- Room temperature: 20±5 ℃

- 10~30 seconds

c. Ultrasonic cleaning step for 30 seconds at room temperature

After injecting a dye into a pore, a sealing treatment is performed to prevent the dye from escaping from the pore (S233). Unlike the existing electrolytic sealing treatment, when the water-soluble silicone electrolytic sealing method of the present invention is used, reliability, fingerprint resistance, excellent durability, environmental friendliness, and harmlessness to the human body can be obtained. Specifically, in the existing electrolytic sealing treatment, a dipping method is used, the sealing agent contains nickel (Ni) acetate as a main component, which is harmful to the human body, the process temperature is 90 to 98°C, the process time is 50 to 60 minutes, and nickel elution may occur after 10 to 15 minutes. In addition, although the Ni safe_standard reliability criterion was satisfied immediately after sealing, the Ni toxicity increases over time, showing an unsafe result. In addition, as a result of performing a salt spray test, the sealing was maintained after 72 hours of salt spray, but a corrosion reaction occurred after 100 hours or more.

In contrast, the water-soluble silicone electrolytic sealing method of the present invention shortens the work process time compared to the existing Ni (nickel) sealing conditions, is harmless to the human body and is environmentally friendly, and has excellent wear resistance, chemical resistance, fingerprint resistance, and hydrophobicity. In addition, as a result of performing a salt water spray test, the sealing was maintained when sprayed with salt water for 72 hours, and no corrosion reaction occurred even when performed for more than 720 hours.

The electrolytic solution used in the water-soluble silicone electrolytic sealing may be ion-exchanged water in which silicone solids are dissolved. The concentration of the silicone solids may be 10 mass% to 30 mass%, for example, 20 mass%. If the concentration of the silicone solids is lower than the threshold value, there is a possibility that the dye inside the seal may leak out, and the color of the surface-treated magnesium alloy may not be stably maintained. In addition, if the concentration is higher than the threshold value, silicone in excess of the required amount may be formed, which may impair the uniformity of the coating.

The specific process conditions for water-soluble silicone electrolytic sealing are as follows.

- Electrolytic sealing using silicon solids dissolved in ion exchange water (concentration: 20 mass%)

- Power supply: DC/AC constant voltage rectifier: current 25 ~ 35 V

- Process time: 15 to 20 seconds

- Process temperature: 20 ~ 25 ℃

Additionally, the aluminum layer after sealing can be washed five times at room temperature and dried at 160°C.

Figure 11 shows the results of a corrosion test after a magnesium oxide film is formed according to another embodiment.

According to the method for forming a magnesium oxide film described in Fig. 10a, a magnesium oxide film (insulating layer) was formed, ultrasonic washing was performed at room temperature for 30 seconds, and a sample dried at a temperature of 90 to 100° C. for 30 minutes was subjected to a corrosion test in a 10% (w/w) sulfuric acid aqueous solution for 60 minutes. Fig. 11(a) shows the result of reacting the surface of a magnesium alloy on which a magnesium oxide film was not formed in a 10% (w/w) sulfuric acid aqueous solution for 5 minutes, and it can be confirmed that the corrosion reaction by sulfuric acid progressed considerably. On the other hand, Fig. 11(b) shows the result of reacting the surface of a magnesium alloy on which an insulating film was formed by a magnesium oxide film according to the present invention in a 10% (w/w) sulfuric acid aqueous solution for 60 minutes, and it can be confirmed that the corrosion reaction did not progress.

FIGS. 12a and 12b are experimental results showing the thickness and component analysis of a deposited aluminum layer of a surface-treated magnesium alloy according to one embodiment of the present invention.

Referring to Fig. 12a, the thickness of the deposited aluminum layer was measured to be 175 ㎛. Referring to Fig. 12b, the weight percentage and atomic percentage of each element can be confirmed from the surface spectrum analysis results of Mg, Si, Fe, and Al.

FIG. 13 is a process diagram for surface treating a complex formation using a surface treatment method for a magnesium alloy according to one embodiment of the present invention.

Referring to Fig. 13, first, a notebook cover is prepared as a magnesium alloy (Fig. 13(a)), and the magnesium alloy is sandblasted (Fig. 13(b)). Then, a magnesium oxide film is formed on the surface of the magnesium alloy, and the magnesium oxide film functions as an insulating oxide film (Fig. 13(c)). Then, an aluminum layer is coated on the magnesium oxide film using magnetron sputtering (Figs. 13(d), (e)). Next, the aluminum layer is anodized to form an alumite film, and a sealing treatment is performed (Fig. 13(f)).

Fig. 14 is an image of a cross-section of a magnesium alloy surface-treated by a method of surface-treating a magnesium alloy according to one embodiment of the present invention. It can be confirmed that an insulating layer (MgO insulating oxide layer) which is a magnesium oxide layer is formed on the magnesium alloy, an aluminum layer (Al coating layer) is formed on the magnesium oxide layer, and an upper portion of the aluminum layer is an anodized and sealing layer (Anodizing + Sealing Layer).

FIG. 15 is a diagram showing the results of measuring the thickness of the deposited aluminum layer by photographing a cross-section of a magnesium alloy after forming a magnesium oxide film on the surface of a magnesium alloy and coating an aluminum layer on the magnesium oxide film according to one embodiment of the present invention.

FIG. 16 is a photograph of a coating surface in the case where aluminum is coated by magnetron sputtering without forming a magnesium oxide film on the surface of the magnesium alloy, and FIG. 17 is a photograph of a magnesium alloy in which a magnesium oxide film as an insulating layer is formed on the magnesium alloy as described in FIGS. 10a and 10b, aluminum is coated on the magnesium oxide film, and then anodizing including water-soluble electrolytic sealing is performed on the aluminum layer.

Referring to Fig. 16(a), it can be seen that the aluminum coating contains foreign matter, and referring to Fig. 16(b), it can be seen that outgassing occurred from the magnesium alloy during the aluminum layer forming process, and bubbles were formed in the coating. Referring to Fig. 16(c), poor adhesion occurred in the aluminum coating, and referring to Fig. 16(d), it can be seen that outgassing occurred from the aluminum alloy, forming bubbles and containing foreign matter. In contrast, it can be seen that the magnesium alloy surface-treated according to the present invention does not have a coating defect due to outgassing because it is treated with a magnesium oxide film, does not have foreign matter defects during the deposition of the aluminum layer, and does not have poor adhesion of the coating. Fig. 17(a) is coated in pink, and Fig. 17(b) is coated in gray. It is possible to provide a good coating in various colors according to the customer's needs without being limited by color.

FIG. 18(a) is an image taken after dropping a water droplet on the surface of a surface-treated magnesium alloy treated according to a conventional aluminum anodizing process, and FIG. 18(b) is an image taken after dropping a water droplet on the surface of a magnesium alloy to which water-soluble silicon electrolytic sealing has been applied according to the surface treatment method of a magnesium alloy according to the present invention described above with reference to FIGS. 10a and 10b.

Referring to FIG. 18, it can be confirmed that the surface of a magnesium alloy to which water-soluble silicon electrolytic sealing has been applied according to the surface treatment method of a magnesium alloy according to the present invention described above in FIGS. 10a and 10b has a smaller contact angle of a water droplet than the surface of a magnesium alloy treated according to a conventional aluminum anodizing process.

The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the term "comprises" and the like are intended to specify the presence of described features, numbers, steps, operations, components, or combinations thereof, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, or combinations thereof.

100: Surface treated magnesium alloy
110, 210: Magnesium alloy
120: Composite polysilazane layer
130, 230: Aluminum layer
140: Mars Film
240: Magnesium oxide film

Claims (15)

A method for surface treating a magnesium alloy (110),
The above method,
A step of forming a composite polysilazane layer (120) including at least one of an inorganic polysilazane and an organic polysilazane on the magnesium alloy (110);
A step of coating an aluminum layer (130) on the above composite polysilazane layer (120); and
It includes a step of anodizing the aluminum layer (130) so that the aluminum layer (130) exhibits a predetermined color.
The step of forming the above composite polysilazane layer is:
A step of forming a first inorganic polysilazane layer on the above magnesium alloy (110);
A step of forming a first organic polysilazane layer on the first inorganic polysilazane layer; and
A method for surface treating a magnesium alloy, comprising the step of forming a second inorganic polysilazane layer on the first organic polysilazane layer. In the first paragraph,
A method for surface treatment of a magnesium alloy, further comprising, before the step of forming the composite polysilazane layer (120), a step of anodizing or chromating the surface of the magnesium alloy to form a chemical film (140) on the surface of the magnesium alloy. delete delete As a surface-treated magnesium alloy (100),
The above surface-treated magnesium alloy (100) is
Magnesium alloy (110);
A composite polysilazane layer (120) comprising a first inorganic polysilazane layer formed on the magnesium alloy (110), a first organic polysilazane layer formed on the first inorganic polysilazane layer, and a second inorganic polysilazane layer formed on the first organic polysilazane layer; and
A surface-treated magnesium alloy including an aluminum layer (130) formed on the above composite polysilazane layer (120) and anodized to exhibit a predetermined color. A method for surface treating a magnesium alloy (210),
The above method,
A step of forming a magnesium oxide film (240) as an insulating layer on the surface of the above magnesium alloy (210);
A step of coating an aluminum layer (230) on the above magnesium oxide film (240); and
Including a step of anodizing the aluminum layer (230) so that the aluminum layer (230) exhibits a predetermined color,
The above anodizing process step is:
A step of forming an oxide film having pores by anodizing the above aluminum layer (230);
A step of injecting a dye having the predetermined color into the pore; and
Including a step of sealing the pores so that the dye does not escape from the pores,
A method for surface treating a magnesium alloy, wherein the sealing step is performed by using water-soluble silicon electrolytic sealing, which is performed at 20° C. to 25° C. for 15 to 20 seconds using ion-exchange water in which 10 to 30 mass% of silicon solids are dissolved. In paragraph 6,
The step of forming the above magnesium oxide film (240) is a method for surface treating a magnesium alloy, which comprises treating the surface of the magnesium alloy (210) with 10 to 30% (w/w) of sodium hydroxide at a direct current (DC) constant voltage of 5 to 10 V for 3 to 15 minutes. In paragraph 6,
A method for surface treatment of a magnesium alloy, wherein, before the step of forming the magnesium oxide film, a step of cleaning the surface of the magnesium alloy, chemical etching, and then sand blasting is additionally performed. delete In paragraph 6,
The above sealing step is a method for surface treating a magnesium alloy to increase the wear resistance, chemical resistance, fingerprint resistance and hydrophobicity of the surface-treated magnesium alloy. delete In paragraph 6,
The step of forming an oxide film having the above pores is:
A step of chemically polishing the above aluminum layer with a phosphoric acid aqueous solution;
A step of rinsing the chemically polished aluminum layer;
A step of ultrasonically cleaning the rinsed aluminum layer;
A step of anodizing the ultrasonically cleaned aluminum layer with a sulfuric acid solution;
A step of washing the anodized aluminum layer; and
A method for surface treatment of a magnesium alloy, comprising the step of ultrasonically cleaning the above aluminum layer. A magnesium alloy surface-treated according to the method for surface-treating a magnesium alloy according to Article 6,
The above surface-treated magnesium alloy (200) is
Magnesium alloy (210);
Magnesium oxide film (240) as an insulating layer formed on the above magnesium alloy (210); and
A surface-treated magnesium alloy including an aluminum layer (230) formed on the above magnesium oxide film (240) and anodized to exhibit a predetermined color. In Article 13,
Surface-treated magnesium alloy having a thickness of the aluminum layer (230) of 50 ㎛ to 250 ㎛. In Article 14,
A surface-treated magnesium alloy in which the thickness of the aluminum layer (230) is 10 ㎛ to 100 ㎛ and the depth of the pores formed by anodizing treatment of the aluminum layer (230) is 6 ㎛ to 50 ㎛.