Lightweight alloy surface treatment method using femtosecond laser

Abstract

A lightweight alloy surface treatment method is provided. Therefore, excellent physical properties such as corrosion resistance, abrasion resistance, voltage resistance and high hardness are provided, a light modulation effect such as light scattering can be induced without deterioration in the durability of the physical properties such that, depending on the viewing angle, various colors and / or patterns can be visually recognized to impart aesthetic appeal to viewers and / or, when in close contact with the surface of another component, airtightness and adhesion can be provided, and thus wide adoption in various products is possible.

Description

Method for surface treatment of lightweight alloys using femtosecond laser

[0001] The present invention relates to a method for treating a lightweight alloy surface, and more specifically, to a method for treating a lightweight alloy surface using a laser.

[0002] Anodizing is a compound word of anode and oxidizing (Ano-dizing). The oxide film formed by the anodizing process is known to prevent rust on the metal surface and improve wear resistance, heat resistance, adhesion, and aesthetics. In general, metals such as aluminum alloys, titanium alloys, and magnesium alloys naturally form a thin oxide film with high corrosion resistance due to their high reactivity with air in the atmosphere. However, the naturally formed oxide film has limitations in uniformity and corrosion resistance. Therefore, the anodizing surface treatment method is widely used to artificially form an oxide film with uniformity and high corrosion resistance.

[0003] Anodized surface-treated metal alloys have excellent wear resistance, heat resistance, and corrosion resistance, and are therefore frequently used as materials for components of various devices.

[0004] Meanwhile, recently, there has been a growing demand for functional properties such as corrosion resistance, wear resistance, adhesion, voltage resistance, and hardness achieved through anodizing, along with design and aesthetics revealed on the surface. Furthermore, there is a growing demand for anodized metal alloys that can achieve high airtightness during assembly between anodized metal alloy parts and other components, as well as at the interface between the two parts. This is leading to a growing demand for the surfaces of anodized metal alloy parts to possess various additional functions, such as aesthetics and airtightness.

[0005] Accordingly, in line with this trend, attempts are ongoing to add design and aesthetics by applying coloring agents to anodized surfaces. However, these coloring agents can be removed during product use. Furthermore, while various treatments are being applied to ensure airtightness, sufficient airtightness is difficult to achieve. Furthermore, when used in harsh environments requiring corrosion resistance after being treated for various functions, such as aesthetics or airtightness, the design, aesthetics, and airtightness imparted can easily be lost.

[0006] The present invention has been devised in consideration of the above points, and the purpose of the present invention is to provide a method for surface treatment of a lightweight alloy using a laser, which has a metal alloy surface having functionality such as corrosion resistance, wear resistance, and voltage resistance, and at the same time, has additional functions such as designability, aesthetics, and airtightness and adhesion at the interface formed with other parts, and has durability such that the additional functions such as designability, aesthetics, and airtightness can be maintained for a long period of time, and a lightweight alloy having a structured surface realized through the method.

[0007] Another purpose of the present invention is to provide a method for surface treatment of a lightweight alloy using a laser, which prevents the durability of functional properties such as corrosion resistance, wear resistance, and voltage resistance from deteriorating due to additional functions such as added aesthetics or design, and airtightness and adhesion at the interface formed with other parts, and a lightweight alloy having a structured surface.

[0008] In order to solve the above-described problem, the present invention provides a method for surface treatment of a metal alloy to impart aesthetic properties, comprising (1) a step of irradiating a laser onto a base material surface of a metal alloy to implement a structured surface having a predetermined pattern, and (2) a step of anodizing the structured surface.

[0009] According to one embodiment of the present invention, a pretreatment process including an alkaline degreasing process on the metal alloy surface may be further performed prior to step (1).

[0010] Additionally, a pretreatment process including alkaline degreasing, alkaline etching, and smut removal processes on the metal alloy surface may be further performed between steps (1) and (2).

[0011] Additionally, in step (1), the laser can be irradiated with a pulse width of 500 fs or less.

[0012] Additionally, the energy per pulse of the laser investigated in step (1) may be 100 mJ or less.

[0013] In addition, the thickness of the heat-affected zone formed by the heat generated by the laser irradiation being transferred from the surface of the part being cut to the base material side can be controlled to be 10㎛ or less.

[0014] In addition, the structured surface includes a plurality of grooves extending in a first direction and spaced parallel to each other at equal intervals in a second direction to exhibit a light scattering effect, and the cutting depth of the grooves may be 700 nm or more.

[0015] Additionally, the structured surface can be utilized as a protrusion higher than the product reference surface, and can be utilized as a groove shape that digs downwards below the reference surface.

[0016] Additionally, the anodic oxidation layer formed through the anodic oxidation in step (2) may have a thickness of 2 to 15 μm.

[0017]

[0018] In addition, the present invention provides a lightweight alloy having a structured surface having a predetermined pattern formed in at least one area, and a lightweight alloy having a structured surface on which an anodic oxidation layer is formed with a predetermined thickness from the structured surface.

[0019] According to one embodiment of the present invention, the predetermined pattern is formed by laser irradiation, and the heat generated by the laser irradiation formed in the thickness direction of the base material side from the structured surface is transferred to the base material side, and the thickness of the heat-affected zone formed may be 10 µm or less.

[0020] The method for surface treatment of a metal alloy according to the present invention imparts functional properties such as corrosion resistance, wear resistance, voltage resistance, and high hardness to the surface of a metal alloy by using an anodizing treatment, and at the same time, can induce a light modulation effect such as light scattering without a separate coloring agent treatment, so that various colors and / or patterns can be recognized depending on the viewing angle, thereby providing aesthetic appeal to the viewer. In addition, since the light modulation effect is generated due to the structured surface formed on the surface of the metal alloy, the aesthetic appeal can be fundamentally prevented from being degraded when the colorant is removed due to a separate coloring agent addition method. In addition, additional functionality can be imparted, such as improving airtightness and adhesion by increasing the surface area of ​​the surface that comes into contact with other parts such as a gasket. Furthermore, since the formation of a structured surface on the surface of the metal alloy can prevent the durability of properties such as corrosion resistance, wear resistance, and voltage resistance from being degraded, the method can be widely adopted in various products that require additional functions such as aesthetics and airtightness in addition to these properties.

[0021] FIG. 1 is a schematic diagram illustrating a process of forming a structured surface by irradiating a laser on a metal alloy surface according to one embodiment of the manufacturing method of the present invention.

[0022] Figure 2 is a cross-sectional schematic diagram along the X-X' boundary line for part A of Figure 1.

[0023] Figure 3 is a cross-sectional schematic diagram showing an example of forming independently structured surfaces on one material surface and the other material surface to improve adhesion and airtightness with a gasket inserted between two materials.

[0024] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0025]

[0026] A method for surface treatment of a lightweight alloy according to one embodiment of the present invention can be performed by including (1) a step of irradiating a laser onto a surface of a base material, which is a metal alloy, to implement a structured surface having a predetermined pattern, and (2) a step of anodizing the structured surface.

[0027]

[0028] Referring to FIGS. 1 and 2, as step (1) of the present invention, a step of irradiating a laser onto the surface of a base material (10) which is a metal alloy is performed to implement a structured surface (S) having a predetermined pattern.

[0029] The above metal alloy can be used without limitation if it is a known metal alloy. For example, the metal alloy can be a titanium alloy, a magnesium alloy, an aluminum alloy, etc., and the present invention is not particularly limited to a specific alloy series for each alloying element belonging to each metal alloy. For example, the aluminum alloy can be a 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, or 6000 series alloy.

[0030]

[0031] In addition, the structured surface (S) performs the function of imparting design and aesthetics such as color, texture, and pattern through color difference to the metal alloy as the incident light exhibits various light modulation effects such as reflection and light scattering, and / or the function of imparting airtightness and adhesion to other surfaces that are in close contact with the structured surface (S).

[0032] The above structured surface (S) may be a surface formed with a known pattern capable of exhibiting various light modulation effects, such as reflection and light scattering of incident light, and the present invention is not particularly limited thereto. In addition, the structured surface (S) may be a surface formed with a known pattern capable of increasing a surface area to enhance airtightness and adhesion with another surface to which it is in close contact, and the present invention is not particularly limited thereto. For example, the structured surface (S) may have a pattern in which a plurality of grooves (10a) having a predetermined width and extending in a first direction are arranged in parallel at a predetermined interval in a second direction different from the first direction, as illustrated in FIG. 1. Alternatively, the structured surface (S) may be formed with a plurality of concentric circles centered on a point as grooves having a predetermined width, and each concentric circle may be spaced apart at a predetermined interval. In this case, the predetermined pattern may mean a certain regularity, but is not limited thereto. In addition, the predetermined pattern may be a continuous pattern or a non-continuous pattern. In addition, the structured surface (S) may have a cutting depth (c) of 700 nm or more of a plurality of grooves (10a) forming such a predetermined pattern, which may be advantageous in exhibiting a light scattering effect and / or airtightness / adhesion with another surface to which it is adhered.

[0033]

[0034] This structured surface (S) can be implemented by irradiating a laser according to a desired pattern on the surface of a base material (10) which is a metal alloy. The laser can be used without limitation as long as it is a laser that can form a groove (10a) with a predetermined width (b) and cutting depth (c) on the surface of the metal alloy. However, preferably, the laser can be irradiated with a pulse width of 500 fs or less, through which the size of the beam spot area (B) can be adjusted to be smaller, and a nanoscale pattern of less than 1 μm can be implemented on the surface of the metal alloy, and even a complex pattern can be implemented with high precision. A fine pattern in the nanoscale can induce light scattering compared to a pattern formed in a scale of several microns or tens or several times microns, and thus allows the recognition of various colors such as rainbow colors depending on the viewing angle, which is advantageous in imparting aesthetics. In addition, the heat-affected zone (e), which corresponds to the combined area of ​​the remelted area (d) where the heat generated by the laser irradiation remelts the base material (10) side from the etched surface and the area that has not yet melted but has received heat, may depend on the time that the laser stays at the point where it is irradiated. A shorter pulse width can significantly reduce the time that the heat caused by the laser can be transferred to the base material side, and thus the thickness of the heat-affected zone (e), which corresponds to the area affected by the transferred heat, can be significantly reduced. The heat-affected zone (e) has a great influence on the durability of the anodized layer formed to a predetermined thickness from the surface toward the base material (10) in step (2) described below, and as the thickness of the heat-affected zone (e) increases, the durability of the anodized layer may decrease. However, a laser irradiated with a pulse width of 500 fs or less can remove the metal alloy at the irradiated point while minimizing thermal processing, thereby drastically reducing the time for the heat caused by the laser irradiation to be transferred to the base material side, which is advantageous in reducing the thickness of the heat-affected zone (e).If the pulse width exceeds 500 fs, it is difficult to implement a nanoscale pattern of less than 1 μm, and even if the pattern is implemented as finely as possible, the pattern is likely to collapse, and as the metal alloy is removed after forming a molten zone at the point where the laser is irradiated, the time until the laser irradiation point moves is extended, which increases the thickness of the heat-affected zone (e), and this can reduce the durability of the formed anodic oxidation layer.

[0035] The above-mentioned laser having a pulse width of 500 fs or less can be irradiated by a known laser device, and for example, a laser device known as a femtosecond laser can be used without limitation. However, when forming a pattern with a nanosecond laser or a picosecond laser, the width of the pattern reaches several micrometers to tens of micrometers, making it difficult to implement a precise nanoscale pattern, and it is difficult to maintain the edge of the pattern. In addition, since the metal alloy is melted and then removed at the laser irradiation point, the time for the heat generated by the laser irradiation to be transferred from the surface of the irradiation point to the base material is greatly extended, so the molten area (d) also increases, and the thickness of the heat-affected zone (e) inevitably becomes thicker than 100 μm.

[0036] Accordingly, according to one embodiment of the present invention, a laser having a pulse width of 500 fs or less, more preferably an energy per pulse of the laser of 100 mJ or less, and even more preferably 50 mJ or less can be irradiated, and thereby it is advantageous to control the thickness of the heat-affected zone (10a) generated to 10 μm or less, and by satisfying the thickness of the heat-affected zone (10a) to 10 μm or less, it is possible to prevent a decrease in the durability of the anodic oxidation layer formed in step (2) described below.

[0037]

[0038] According to one embodiment of the present invention, a pretreatment process including an alkaline degreasing process on the surface of the metal alloy can be further performed before step (1), and through this, the structured surface to be formed in step (1) can be formed precisely as intended. If the alkaline degreasing process is not performed, the structured surface formed upon laser irradiation may include a part with a blurred edge, and it may be difficult to sufficiently express the intended physical properties. The alkaline degreasing can be performed by appropriately employing an alkaline degreasing solution and degreasing conditions performed as a surface pretreatment of the metal alloy, and the present invention is not particularly limited thereto.

[0039]

[0040] Next, in step (2) according to the present invention, a step of anodizing the structured surface is performed.

[0041] According to one embodiment of the present invention, a pretreatment process may be performed on the structured surface prior to anodizing. The pretreatment process may be performed without limitation as long as it is a known pretreatment process performed prior to anodizing a metal alloy. For example, the pretreatment process may include alkaline degreasing, alkaline etching, and smut removal processes, and may further include water rinsing between each process. In addition, since each process belonging to the pretreatment process can be performed using known solutions and conditions, the present invention is not particularly limited thereto, and a detailed description thereof will be omitted.

[0042]

[0043] After performing the pretreatment process, at least the structured surface (S) of the surface of the metal alloy is subjected to anodization. The anodization can be performed through a known anodization method for a metal alloy, such as a sulfuric acid method, an oxalic acid method, or a sulfuric acid-oxalic acid mixed acid method, and the specific method and conditions for anodization according to each method can be performed by appropriately adopting and changing known conditions, and therefore the present invention is not specifically limited thereto.

[0044] For example, the above anodic oxidation may be performed so that the thickness of the formed anodic oxidation layer is 2 to 15 μm, but is not limited thereto.

[0045]

[0046] The metal alloy implemented through the surface treatment method described above includes a structured surface (S) having a predetermined pattern, and an anodic oxidation layer can be formed from the structured surface (S) to a predetermined thickness, and by generating various light modulation effects due to the structured surface (S), the metal alloy surface can be implemented to display various colors or have a specific pattern, so that it can have both functional characteristics and aesthetic characteristics due to the anodic oxidation layer.

[0047]

[0048] The present invention will be described in more detail through the following examples, but the following examples do not limit the scope of the present invention, and should be interpreted as helping to understand the present invention.

[0049]

[0050] <Example 1>

[0051] Al1050 metal alloy specimens were prepared. The prepared specimens were immersed in a 40°C alkaline degreasing solution containing 7 wt% of an alkaline degreasing component (METEX PS MINCO) for 2 minutes, and then washed. The surface of the prepared specimen was irradiated with a femtosecond laser device with a pulse width of 500 fs and a pulse energy of 25 mJ to form a structured surface with a valley width of 3 μm, a cutting depth of 2 μm, and a valley-to-valley gap of 4 μm, so as to have a structured surface pattern as shown in Fig. 1.

[0052] Afterwards, a pretreatment process of alkaline degreasing, washing, alkaline etching, washing, smut removal, and washing was performed on the metal alloy with the structured surface formed. At this time, alkaline degreasing was performed by immersing the specimen in a 40°C alkaline degreasing solution containing 7 wt% of an alkaline degreasing component (METEX PS MINCO) for 2 minutes, and then washing. Afterwards, the alkaline-degreasing specimen was immersed in a 5 wt% sodium hydroxide solution at 60°C for 35 seconds, and then washed, and then alkaline etching was performed. Afterwards, the alkali-etched specimen was immersed in a 20 wt% nitric acid solution at 25°C for 2 minutes, and then washed, and then the smut removal process was performed.

[0053] Afterwards, in order to perform anodization treatment, the metal alloy was placed in an electrolytic cell containing a 16 vol% sulfuric acid aqueous solution as an electrolyte, and anodization was performed for 30 minutes under conditions of 30°C and 50 V constant voltage to manufacture a metal alloy having a structured surface on which anodization layer was formed.

[0054]

[0055] <Example 2>

[0056] A metal alloy having a structured surface on which an anodic oxide layer was formed was manufactured by performing the same process as in Example 1, but changing the irradiated laser to a nanosecond laser device and changing the pulse width of the laser to 5 ns.

[0057]

[0058] <Comparative Example 1>

[0059] A metal alloy was manufactured in the same manner as in Example 1, but without forming a structured surface, and with an anodic oxidation layer formed thereon.

[0060]

[0061] <Experimental Example>

[0062] The following physical properties were evaluated for Examples 1 to 2 and Comparative Example 1, and the results are shown in Table 1 below.

[0063]

[0064] 1. Measurement of heat affected zone thickness

[0065] Before anodizing, the cross-section of the metal alloy was cut, polished, and etched to highlight the heat-affected zone, and the thickness of the discolored area was measured.

[0066]

[0067] 2. Whether the light scattering effect occurs

[0068] After placing a light source on the surface of a metal alloy, we observed the surface of the metal alloy from various angles to see whether the surface was observed in rainbow colors.

[0069]

[0070] 3. Durability evaluation of the anodic oxidation layer

[0071] The durability of the anodic oxidation layer was evaluated through the corrosion resistance of the film. Specifically, the corrosion resistance of the film was evaluated by a salt spray test. In the salt spray test, the measurement specimen was placed at an angle in the tester, the internal temperature was maintained at 60±2℃, and the specimen was exposed to NaCl with a concentration of 5±0.5% and pH 6.5~7.2 for 3,000 hours to check for corrosion and peeling / delamination of the anodic oxidation layer.

[0072]

[0073] Example 1 Example 2 Comparative Example 1 Laser pulse width 500 fs 5 ns 20 ns Structured surface Valley width 3 ㎛ 3 ~ 4 ㎛ No structured surface Valley depth 2 ㎛ 3 ㎛ Valley spacing 4 ㎛ 5 ㎛ Heat affected zone thickness 7.8 ㎛ 30.7 ㎛ 45 ㎛ Light scattering effect Rainbow color observed Rainbow color not observed Rainbow color not observed Anodized layer durability Corrosion No corrosion Corrosion occurred Corrosion occurred Corrosion did not occur Peeling Peeling did not occur Partial peeling occurred Peeling did not occur

[0074] As can be seen in Table 1, in the case of Example 1, which formed a structured surface with a laser pulse width of 500 fs, it was possible to implement a fine pattern capable of exhibiting a light scattering effect, and at the same time, the thickness of the heat-affected zone was thin at 7.8 μm. In addition, as a result of evaluating the durability of the anodic oxidation layer, no corrosion occurred, so it can be expected that the durability of the anodic oxidation layer was not reduced due to the heat-affected zone.

[0075] However, in the case of Example 2, it can be confirmed that the implementation of a fine pattern capable of exhibiting a light scattering effect was not smoothly achieved as a structured surface was formed using a laser with a pulse width of 5 ns through a nanosecond laser. In addition, it can be confirmed that the durability of the anodic oxidation layer was significantly reduced in Example 2 as the heat-affected zone thickness reached 30.7 ㎛.

[0076]

[0077] Although one embodiment of the present invention has been described above, the spirit of the present invention is not limited to the embodiment presented in this specification, and a person skilled in the art who understands the spirit of the present invention will be able to easily propose other embodiments by adding, changing, deleting, or adding components within the scope of the same spirit, but this will also be considered to fall within the spirit of the present invention.

Claims

1. (1) A step of irradiating a laser onto the surface of a base material, which is a metal alloy, to implement a structured surface having a predetermined pattern; and (2) A method for surface treatment of a lightweight alloy using a laser, including a step of performing anodizing treatment on a structured surface.

2. In paragraph 1, (1) A method for surface treatment of a lightweight alloy using a laser, wherein a pretreatment process including an alkaline degreasing process is further performed on the surface of the metal alloy prior to the step.

3. In paragraph 1, (1) A method for surface treatment of a lightweight alloy using a laser irradiated with a pulse width of 500 fs or less in step (1).

4. In paragraph 2, (1) A method for surface treatment of a lightweight alloy using a laser having an energy per pulse of 100 mJ or less investigated in step (1).

5. In paragraph 1, A method for surface treatment of a lightweight alloy using a laser, wherein the structured surface extends in a first direction to exhibit a light scattering effect and includes a plurality of grooves spaced in parallel at equal intervals in a second direction, and the cutting depth of the grooves is 700 nm or more.

6. In paragraph 1, (2) A method for surface treatment of a lightweight alloy using a laser, wherein the anodic oxidation layer formed through the anodic oxidation step has a thickness of 2 ㎛ to 15 ㎛.

7. A lightweight alloy having a structured surface having a predetermined pattern formed in at least one area, A lightweight alloy having a structured surface on which an anodic oxide layer is formed to a predetermined thickness from the above structured surface.

8. In paragraph 7, A lightweight alloy having a structured surface in which the above-described pattern is formed by laser irradiation, and the heat generated by laser irradiation formed in the thickness direction of the base material from the structured surface is transferred to the base material side, and the thickness of the heat-affected zone formed is 10㎛ or less.

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