JP2009120877A - Magnesium alloy parts - Google Patents

Abstract

A magnesium alloy member having a high metal texture is provided.
A magnesium alloy member comprising a base material made of a magnesium alloy and a coating layer formed on the base material. The base material has a metal texture on at least a part of its surface. As described above, the coating layer is transparent, and includes a surface processed portion on which fine unevenness processing is performed. By providing the surface processed portion, the metal texture can be effectively enhanced. Moreover, this member is excellent in anticorrosion property by providing a coating layer, and it is easy to feel the metal texture by a surface processed part because a coating layer is transparent. Examples of the uneven processing include hairline processing and diamond cut processing.
[Selection figure] None

Description

  The present invention relates to a magnesium alloy member having a coating layer on a base material made of a magnesium alloy. In particular, it relates to a magnesium alloy member having a high metal texture.

  Magnesium alloys containing various additive elements in magnesium have been used as materials for casings of portable electrical devices such as mobile phones and notebook computers and members of automobile parts. Since the magnesium alloy is an active metal, the surface of the member is subjected to surface treatment for the purpose of corrosion prevention (see, for example, Patent Documents 1 and 2).

  In addition, since magnesium alloys have a hexagonal crystal structure (hcp structure) and have poor plastic workability at room temperature, magnesium alloy members such as the above casings are mainly cast materials by die casting or thixomolding. It is. Recently, it has been studied to press the plate made of AZ31 alloy in the ASTM standard to form the casing. Patent Document 3 proposes a plate material made of an alloy equivalent to the AZ91 alloy in the ASTM standard and having excellent press workability.

JP 2002-285361 A JP 2004-149911 JP JP 2007-98470

  In recent years, it has been demanded that magnesium alloy members such as the above-described housings have a higher metallic feel and a higher-class feeling. However, Patent Documents 1 and 2 propose surface treatment agents that do not impair the metallic luster, but have not been studied for enhancing the metal texture. Patent Document 3 also does not mention enhancing the metal texture.

  Accordingly, an object of the present invention is to provide a magnesium alloy member having a high metal texture.

  The present invention achieves the above-mentioned object by having a surface processed portion that has been processed to enhance the metallic texture on at least a part of the surface of a base material made of a magnesium alloy. Specifically, the magnesium alloy member of the present invention comprises a base material made of a magnesium alloy and a coating layer formed on the base material, and the base material is formed on at least a part of the surface thereof. In order to obtain a metal texture, it has a surface processed portion that is finely textured. Moreover, the said coating layer is transparent.

  The magnesium alloy member of the present invention is provided with the above-mentioned surface processed portion, so that the metal texture can be effectively enhanced. Moreover, this invention member can have sufficient corrosion resistance by providing a coating layer. In particular, since the coating layer is transparent, light from the outside is easily transmitted through the coating layer and irregularly reflected by the surface processed portion, and the metal texture is easily felt from any direction. Therefore, the member of the present invention has high metal texture and excellent design properties while having desired corrosion resistance. Hereinafter, the present invention will be described in more detail.

<Base material>
"composition"
The magnesium alloy constituting the base material of the member of the present invention can be used in various compositions containing Mg with an additive element (remainder: Mg and impurities), and is not particularly limited. For example, Mg-Al, Mg-Zn, Mg-RE (rare earth element), Y-added alloy and the like can be mentioned. In particular, Mg-Al alloys containing Al are preferable because of high corrosion resistance. Examples of Mg-Al alloys include AZ alloys (Mg-Al-Zn alloys, Zn: 0.2 to 1.5 mass%) and AM alloys (Mg-Al-Mn alloys, Mn: 0.15 to 0.5 mass%), AS alloys (Mg-Al-Si alloys, Si: 0.6-1.4 mass%), Mg-Al-RE (rare earth elements) alloys, Bi-Sn, Examples thereof include an alloy to which one or more elements selected from the group consisting of Pb, Ca, and Be are added. The Al content is preferably 1.0% by mass or more and 11% by mass or less, and as the Al content increases, the mechanical properties such as corrosion resistance and strength are excellent. However, if too much, the plastic workability tends to decrease, so corrosion resistance, mechanical Considering characteristics and moldability, 8% by mass or more and 11% by mass or less is more preferable. In particular, Mg-Al alloys containing 8 to 11% by mass of Al and 0.2 to 1.5% by mass of Zn, typically AZ80 and AZ91, can be suitably used. These alloys are preferable because the surface of the base material is not easily discolored even after fine unevenness processing, and a metal texture such as metallic luster is easily obtained.

<Form>
Typically, the base material is a rolled material obtained by rolling a cast material, a processed material obtained by further subjecting the rolled material to heat treatment, leveler processing, polishing, etc., and further pressing or bending the rolled material or processed material. Examples thereof include a plastic processed material subjected to plastic processing such as forging. Substrates subjected to plastic working such as rolling and pressing have fine crystal grain size and excellent mechanical properties such as strength than cast materials, as well as internal and surface defects such as shrinkage and voids (pores) And has good surface properties. In addition, since the rolled material has fewer surface defects than the cast material, it is possible to reduce or eliminate the defect putty (defect correction) before forming the coating layer. Since the occurrence of defective products due to sufficient can be reduced, it can contribute to the improvement of product yield. Hereinafter, casting conditions and rolling conditions will be described.

"Production method"
[Casting conditions]
The cast material is preferably produced by a continuous casting method such as a twin roll method, in particular, a casting method described in WO / 2006/003899. Since the continuous casting method can be rapidly solidified, oxides and segregation can be reduced, and a cast material excellent in plastic workability such as rolling can be obtained. Further, by rolling the cast material, defects that adversely affect plastic processing such as subsequent press processing, for example, coarse crystal precipitates having a particle size of 10 μm or more can be eliminated. In particular, AZ-based alloys tend to generate crystal precipitates as the amount of Al increases, but rolling the above continuous cast material provides a rolled material with few defects regardless of the alloy composition. The obtained cast material may be subjected to heat treatment (solution treatment, heating temperature: 380 to 420 ° C., heating time: 60 to 600 minutes) or an aging treatment for homogenizing the composition. In particular, in the case of an AZ-based alloy, it is preferable to perform solution treatment for a long time when the content of Al is high. The size of the cast material is not particularly limited, but is preferably 10 mm or less because segregation is likely to occur if it is too thick.

[Rolling conditions]
Rolling is preferably performed in a plurality of passes under the conditions that the heating temperature of the object to be processed is 200 to 400 ° C., the heating temperature of the rolling roll is 150 to 250 ° C., and the rolling reduction per pass is 10 to 50%. Moreover, it is preferable to appropriately combine the above conditions so that a rolled material having a desired thickness can be obtained. By appropriately combining the above temperatures, the reduction ratio per pass, and the number of passes, for example, a workpiece having a thickness of 3 to 8 mm before rolling is rolled to a thickness of 1 mm or less, specifically 0.2 mm. Is possible. Known conditions such as controlled rolling disclosed in Patent Document 3 may be used.

  Intermediate heat treatment (heating temperature: 250 to 350 ° C, heating time: 20 to 60 minutes) is performed during the rolling process to remove strain, residual stress, texture, etc. If it reduces, it is preferable that a subsequent rolling can prevent inadvertent cracking, distortion and deformation, and can be rolled more smoothly. Moreover, it is preferable to apply a final heat treatment after the final rolling because a rolled material having excellent strength can be obtained. The rolled material before the final heat treatment has a crystal structure in which processing strain is sufficiently accumulated, and the strength can be improved by forming a fine recrystallized structure by the final heat treatment. In addition, the rolled material after the final heat treatment having such a recrystallized structure is difficult to coarsen crystal grains due to heating during press working. For example, in the case of an AZ-based alloy, the heating temperature of the final heat treatment is preferably increased as the Al amount is higher. When the Al amount is 8 to 11% by mass, 300 to 340 ° C., heating time: 10 to 30 Minutes are preferred. In these heat treatments, if the temperature is too high or the time is too long, the crystal grains become too coarse and the plastic workability such as press working is lowered.

Rolled material subjected to the above rolling has a small variation in crystal grain size, and since there are few segregations during casting (for example, intermetallic compounds such as Mg ₁₇ Al ₁₂ ), internal defects, surface defects, etc., high plastic workability The occurrence of cracks and cracks during processing is effectively reduced, and the surface properties are excellent.

[Preliminary machining after rolling and before plastic working]
The obtained rolled material is preferably subjected to leveler processing for correcting waviness of the rolled material, crystal grain orientation, and the like and polishing for smoothing the surface of the rolled material. The leveler processing is performed, for example, by passing the rolled material through a roller leveler, and the polishing processing is typically wet belt type polishing. The abrasive grains are preferably # 240 or more, more preferably # 320 or more, particularly # 600. The rolled material subjected to the preliminary processing and the plastic processed material obtained by performing plastic processing such as press processing on the rolled material are easily subjected to uneven processing described later.

[Plastic processing]
Plastic processing such as pressing, deep drawing, forging, blow, and bending is a temperature range where the mechanical properties of the rolled material do not change significantly due to recrystallization of the rolled material, specifically 250 It is preferable to carry out at a temperature of not higher than ° C., particularly 200 to 250 ° C. When plastic working is performed on a rolled material at such a temperature, the size of the crystal grain in the portion that is not plastically deformed hardly changes, so the strength of this portion hardly changes before and after the plastic working, and high strength is achieved. It is possible to maintain a high-strength plastic working material.

  The plastic working may be performed at any stage before or after the uneven process described later, after the uneven process, before the formation of the coating layer described later, or after the formation.

  A heat treatment may be performed after the plastic working to remove strain and residual stress introduced by the plastic working and to improve the mechanical characteristics. Examples of the heat treatment conditions include a heating temperature: 100 to 450 ° C. and a heating time: about 5 minutes to 40 hours.

<Surface processed part>
One feature of the member of the present invention is that at least a part of the surface of the substrate is provided with a surface processed portion on which fine unevenness is applied. This concavo-convex processing is processing that contributes to enhancing the metal texture, and specifically includes at least one of cutting processing, grinding processing, spraying processing, and corrosion processing using an acid. More specifically, at least one of hairline processing, diamond cut processing, spin cut processing, shot blast processing, and etching processing may be mentioned. The member of the present invention may be one type of these processes, or may be subjected to uneven processing combining a plurality of types.

  Specifically, the fine irregularities include those having a surface roughness Rmax (maximum height: distance from the lowest position to the highest position) of 1 μm or more and 200 μm or less. When the unevenness satisfying the above range is provided, the light from the outside directed to the member of the present invention is irregularly reflected on the surface of the member of the present invention, so that the metal texture can be sufficiently felt from any direction. it can. In a relatively smooth state of less than 1 μm, an excellent metallic luster can be obtained in the same way as in a mirror-finished state, but it is difficult to improve the metal texture, and in a rough state exceeding 200 μm, a metal texture is obtained It's hard to be done. The surface roughness is more preferably 1 μm or more and 50 μm or less in terms of Rmax. Note that the base material may be roughened to improve the adhesion between the base material and the coating layer, but this roughening is performed to the extent that the metallic luster is not impaired, and the metal texture is enhanced. It is considered impossible.

  The surface-treated portion may be only a part of the surface of the base material, or when the member of the present invention has front and back surfaces, only the front side (the entire surface on one side) or the entire surface (the entire surface). However, when the plastic processing is performed after the uneven processing, the uneven processing is preferably performed after the plastic processing when the unevenness is crushed by the plastic processing and the metal texture may be lowered. In particular, when the surface processed portion extends over one side or the entire front and back surfaces, the possibility of crushing irregularities due to plastic processing increases, and therefore it is preferable to perform the irregular processing after the plastic processing. Alternatively, when the plastic working is performed so that the unevenness of the surface processed portion is not crushed by devising the lubricant during the plastic working, the plastic working can also be performed after the uneven processing. For example, a material that has been subjected to uneven processing is sandwiched between fluororesin sheets such as Teflon (registered trademark), and press processing is performed. When such plastic working is performed, the surface shape of the member obtained after the plastic working can maintain the surface shape of the material before the plastic working substantially as it is. Therefore, for example, a member whose entire surface of the base material is a surface processed portion can be easily manufactured by using a material whose entire surface is subjected to uneven processing as a material.

<Coating layer>
One feature of the member of the present invention is that it has a transparent coating layer on its surface. By providing the transparent coating layer on the base material, it is easy to visually confirm the surface processed portion provided on the base material surface, and it is easy to feel the metal texture. The coating layer may be colored and transparent, but if it is colorless and transparent, the color and texture of the base metal itself of the base material can be felt, and the metal texture is more likely to be felt. In addition, transparent means the grade which can confirm a base material visually.

  The coating layer preferably has at least anticorrosion properties, and further has a decorative property, which is preferable because the commercial value can be increased. For example, the coating layer may have a multilayer structure including an anticorrosion layer having anticorrosion properties and a coating layer that functions for protection and decoration. The anticorrosion layer is disposed on the substrate side, and the coating layer is disposed on the anticorrosion layer.

  The anticorrosion layer is not particularly limited as long as it has a desired anticorrosion property. Typically, those formed by anticorrosion treatment (chemical conversion treatment or anodizing treatment) can be mentioned. When the anticorrosion treatment is performed, magnesium on the surface of the substrate is oxidized to produce an oxide of magnesium, and a layer made of this oxide functions as an anticorrosion layer. This anticorrosion layer may be formed before plastic working such as press working or after plastic working. If an anticorrosion layer is provided before plastic processing, this layer tends to function as a lubricant during plastic processing. Furthermore, since this anticorrosion layer is in a state in which fine cracks (cracks) have occurred, it is preferable because the constituent material of the coating layer enters the crack, and thus the adhesion to the coating layer is high.

  It is preferable that the anticorrosion layer has a small surface resistivity, specifically, 0.2 Ω · cm or less, since it can be grounded when the member of the present invention is an electronic device casing. In order to reduce the surface resistivity, for example, the thickness of the coating layer can be reduced. When the thickness of the anticorrosion layer is 2 μm or less, it tends to be a low resistance layer. Further, when the anticorrosion layer has a thickness of 2 μm or less, particularly 0.5 μm or less, a transparent feeling can be easily obtained. Note that a surface to be grounded in the housing or the like (which is often the back surface of the housing) is often not required to have a decorative property, and thus a coating layer may not be provided and only the anticorrosion layer may be provided. It is good to form a coating layer only in a desired part by performing masking etc. suitably in the part (for example, a part where it is desired that surface resistance is low) to make only an anticorrosion layer.

  The anticorrosion layer can be formed using a transparent surface treatment agent as described in Patent Document 1.

  The coating layer is not particularly limited as long as it is transparent, has excellent adhesion to the anticorrosion layer, and is excellent in corrosion resistance and surface hardness to some extent. For example, a known clear coating using a resin such as a transparent acrylic resin or a transparent fluororesin can be used. In order to form a coating layer using the above resin or the like, either a wet method (dipping method, spray coating, electrodeposition coating, etc.) or a dry method (PVD method, CVD method) may be used. By providing such a transparent coating layer, the member of the present invention can enhance the metal texture and the commercial value. The coating layer is preferably formed after plastic processing when there is a risk of damage due to plastic processing. In addition, the coating layer preferably has a thickness of 30 μm or less in consideration of good expression of the metal texture in the surface processed portion and ease of manufacture. When the thickness of the coating layer is increased, the reflected light from the outside interferes with each other, and the sharpness of the surface processed portion may be blurred, resulting in a thin metal texture.

  The magnesium alloy member of the present invention has a high metal texture and can increase commercial value.

Embodiments of the present invention will be described below.
[Test Example 1]
A press-molded body comprising a base material made of a magnesium alloy and a coating layer covering the surface thereof was produced, and a panel test was performed on the appearance.

  A base material is produced as follows. A rolled sheet having a thickness of 5.0 mm obtained by a twin roll continuous casting method having a composition of Mg-9.0% Al-1.0% Zn (all by mass%) (composition equivalent to AZ91 alloy) is prepared. Casting is performed under the conditions described in WO / 2006/003899. Rolling is performed in multiple passes under the conditions of a processing object (rolling object) heating temperature of 200 to 400 ° C., a rolling roll heating temperature of 150 to 250 ° C., and a rolling reduction per pass of 10 to 50%, and a thickness of 0.5 Prepare a rolled sheet of mm. The obtained rolled material is subjected to leveler processing and polishing processing in this order, and a hot press processing is performed on a cut piece cut into a desired size to obtain a box-shaped press material. The press working is performed by placing the cut piece on a die having a rectangular parallelepiped concave portion so as to cover the concave portion and pressing a rectangular parallelepiped punch. The punch has a rectangular parallelepiped shape of 60 × 90 mm, and the four corners contacting the cut piece have a predetermined roundness. In addition, a heater and a thermocouple are embedded in the die and punch, and the temperature during pressing can be adjusted to a desired temperature. Here, it is heated to 200 to 300 ° C.

  In addition, an intermediate heat treatment may be performed during rolling, or a final heat treatment may be performed after rolling to remove distortion introduced by rolling before the heat treatment. Alternatively, the cast material may be subjected to a solution treatment before rolling.

(Test Material 1-A)
The obtained box-shaped press material is subjected to diamond cutting with a processing radius of 50 mm, a depth of 0.02 mm (20 μm), and a pitch of 0.05 mm on the entire surface on the protruding side (about 60 × 90 mm). This processing is performed with a commercially available diamond cutting machine. By this step, a base material (press material (plastic working material)) in which the entire surface on the protruding side is a surface processed portion by diamond cutting is obtained.

  The base material is subjected to a base treatment to form a multi-layer coating layer (anticorrosion layer, coating layer) to obtain a magnesium alloy member having a base material having a surface processed portion and the coating layer. The base treatment is performed in the order of degreasing → acid etching → desmutting → surface adjustment. Thereafter, chemical conversion treatment → drying is performed to form an anticorrosion layer (thickness: about 0.5 μm). Wash with water between each step from degreasing to drying. The coating layer (thickness: about 20 μm) is formed by the procedure of spray application → baking. The coating layer is formed only on the outer surface side (outside of the box) of the base material, and is not formed on the inner surface side (inside of the box). Therefore, masking is performed on the inner surface side before forming the coating layer. Hereinafter, each step will be described in detail (the concentration of each solution indicates mass%). The material obtained by this step is designated as test material 1-A. In addition, when there is a defect on the substrate surface, putty filling and polishing may be appropriately performed.

Degreasing: 10% KOH and nonionic surfactant 0.2% solution under stirring, 60 ° C, 10 minutes Acid etching: 5% organic phosphoric acid solution stirring, 40 ° C, 1 minute Desmutting: Over 10% KOH solution Under sonic stirring, 60 ° C., 5 minutes Surface adjustment: 60 ° C. × 5 minutes under stirring with aqueous carbonate solution adjusted to pH 8 Chemical conversion treatment: P-type treatment solution manufactured by A company with 10% phosphoric acid as the main component + 1% KOH Used as a treatment liquid, with stirring, 30 ° C, 2 minutes Drying: 150 ° C, 5 minutes Spray coating: Spray application of colorless and transparent acrylic paint Baking: 150 ° C, 10 minutes

(Test Material 1-B)
A sample in which the base material and the coating layer are formed in the same manner except that the above-described box-shaped press material is not subjected to the diamond cutting process is referred to as test material 1-B.

  For the test materials 1-A and 1-B obtained, a panel test was conducted on any 10 people, and 9 out of 10 test materials 1-A had a higher metal texture and improved design. The answer was excellent. From this result, it can be seen that the metal texture of the magnesium alloy member having a surface processed portion subjected to diamond cutting on the surface of the base material and having a transparent coating layer is enhanced. The panel test target can also be selected according to the target layer of a product using a magnesium alloy member such as a personal computer or a mobile phone (for example, a group that likes PCs in their 20s). The same applies to the following test examples.

[Test Example 2]
Except for changing the diamond-cut processing of test material 1-A in Test Example 1 to hairline processing, a sample prepared in the same manner as test material 1-A was used as test material 2-A, and a panel test was performed on the appearance. .

  In this test, hairline processing with a surface roughness Rmax (maximum height) of 10 μm was performed. A panel test was conducted on any 10 persons for the obtained test material 2-A and the test material 1-B prepared in Test Example 1 (not subjected to hairline processing or diamond cutting). , 8 out of 10 respondents indicated that the test material 2-A had a higher metal texture and better design. From this result, it can be seen that the metal texture of the magnesium alloy member having the surface processed portion subjected to the hairline processing on the surface of the base material and having a transparent coating layer is enhanced.

[Test Example 3]
Except that the constituent material of the coating layer in the test material 1-A of Test Example 1 was changed, a sample produced in the same manner as the test material 1-A was used as the test material 3-A, and a panel test was performed on the appearance.

  In this test, the base treatment and the formation of the anticorrosion layer were performed on the substrate in the same procedure as in Test Example 1, and then a colorless transparent fluororesin (Sumiflon: Sumitomo Electric Industries, Ltd. registered trademark) was applied and dried. . By this step, a test material 3-A having a transparent coating layer having a thickness of 25 μm is obtained.

  A panel test was conducted on 10 test subjects for the test material 3-A obtained and the test material 1-B produced in Test Example 1 (not subjected to hairline processing or diamond cutting). , 9 out of 10 respondents indicated that the test material 3-A had a higher metal texture and better design.

[Test Example 4]
Except for changing the diamond-cut processing of test material 1-A in Test Example 1 to etching, samples prepared in the same way as Test material 1-A are used as test materials 4-1A and 4-2A. A test was conducted.

  The surface processed part of the test material 4-1A by etching was formed as follows. After applying a resist on the surface of the box-shaped press material, a predetermined pattern mask was placed on the surface for exposure, and the uncured portion was peeled off with a solvent to pattern the predetermined pattern. After that, dry etching with a depth of 10 μm is applied to the exposed part of the press material (material) with an ion milling device, and finally the resist is removed to form a surface (about 60 x 90 mm) on the protruding side of the press material. Unevenness of a predetermined pattern was provided.

  The surface processed part of the test material 4-2A by etching was formed as follows. After printing a predetermined pattern on the surface of the box-shaped press material by screen printing, the unprinted portion is etched with a depth of 20 μm with acid, and finally the printed portion is removed, and the protruding portion of the press material is removed. Irregularities with a predetermined pattern were provided on the surface (about 60 × 90 mm).

  Panel test was conducted for any 10 persons with respect to the obtained test materials 4-1A and 4-2A and test material 1-B prepared in Test Example 1 (not subjected to uneven processing such as etching processing). Carried out. As a result, 7 out of 10 respondents indicated that the test material 4-1A had a higher metal texture and superior design. In addition, 8 out of 10 respondents indicated that test material 4-2A had a higher metal texture and superior design.

  The above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the composition of the magnesium alloy, the conditions of casting, rolling, and plastic working, the plate thickness after casting and after rolling, the forming method of the uneven processing, the forming conditions, the forming material of the coating layer, the forming method, etc. may be appropriately changed. it can.

  Since the magnesium alloy member of the present invention has a high metal texture, it can be suitably used in a field that is desired to have excellent design properties such as a casing of portable electric equipment.

Claims (11)

A magnesium alloy member comprising a base material made of a magnesium alloy and a coating layer formed on the base material,
The base material has a surface processed portion on which fine unevenness is applied so that a metal texture is obtained on at least a part of the surface,
The magnesium alloy member, wherein the coating layer is transparent.   2. The magnesium alloy member according to claim 1, wherein the base material is made of a rolled material made of an Mg—Al-based magnesium alloy and contains 8% by mass to 11% by mass of Al.   3. The magnesium alloy member according to claim 2, wherein the base material is a press material obtained by pressing the rolled material.   4. The magnesium alloy member according to claim 1, wherein the uneven processing is at least one of cutting, grinding, spraying, and corrosion using acid.   5. The magnesium alloy member according to claim 4, wherein the uneven processing is at least one of hairline processing, diamond cut processing, spin cut processing, shot blast processing, and etching processing.   6. The magnesium alloy member according to claim 1, wherein the surface processed portion has a surface roughness Rmax of 1 μm or more and 200 μm or less.   The magnesium alloy according to any one of claims 1 to 6, wherein the coating layer includes an anticorrosion layer disposed on the substrate side and a coating layer disposed on the anticorrosion layer. Element.   8. The magnesium alloy member according to claim 7, wherein the anticorrosion layer includes a magnesium oxide.   9. The magnesium alloy member according to claim 7, wherein the anticorrosion layer has a thickness of 2 μm or less (excluding 0 μm).   The magnesium alloy member according to any one of claims 7 to 9, wherein the coating layer has a thickness of 30 µm or less (excluding 0 µm).   11. The magnesium alloy member according to claim 7, wherein the coating layer is made of a transparent resin.