Acoustic diaphragm and method for manufacturing acoustic diaphragm

Abstract

To provide an acoustic diaphragm capable of preventing rust from a cut surface formed by trimming and improving acoustic properties, and a method for manufacturing the same.SOLUTION: Since a cut surface 7 of the periphery of a diaphragm 6 can be covered with aluminium oxide in an aluminum high content layer 8 having a high aluminum content by using fusion for cutting while melting the periphery of the diaphragm without punching the periphery of the diaphragm when trimming a diaphragm base material formed of magnesium and aluminum containing magnesium alloy, rust from the cut surface 7 is prevented, and the diaphragm 6 excellent in acoustic properties is formed by surrounding the periphery with the aluminium oxide having high hardness.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] The present invention relates to an acoustic diaphragm having excellent corrosion resistance and acoustic characteristics, and a method for manufacturing the acoustic diaphragm. [Background technology]

[0002] Various materials are used for acoustic diaphragms, including aluminum, titanium, magnesium, paper, and resin. Light metals such as aluminum, titanium, and magnesium are practical metal materials that are light and have moderate hardness, providing excellent properties. For this reason, these light metals are preferred as materials for acoustic diaphragms, and the use of light metal materials allows for the production of diaphragms that exhibit good acoustic properties even in the high-frequency range.

[0003] Magnesium is the lightest of all light metals, making it a desirable material for acoustic diaphragms. However, because it is a base metal with a low standard electrode potential, it has the disadvantage of being highly reactive and poor in corrosion resistance. For this reason, when using magnesium alloys containing magnesium as materials for acoustic diaphragms, it is necessary to apply a corrosion-preventive surface treatment to the surface of the magnesium alloy to prevent the progression of corrosion. Conventionally, surface treatments include electrodeposition coating after anodizing, and coating with paint after chemical conversion treatment, and these may be used alone or in combination.

[0004] A magnesium acoustic diaphragm is manufactured, for example, by first pressing a magnesium base material into the shape of a diaphragm, then surface-treating the magnesium base material formed into the shape of the diaphragm, and then performing a trimming process to punch out the magnesium base material that has been surface-treated and has become a molded product.In this manufacturing method, in which the magnesium base material formed into the shape of a diaphragm is surface-treated and then trimmed using a trimming mold, the base material that has not been surface-treated is revealed on the cut surface of the magnesium diaphragm formed by the trimming process.

[0005] Patent Document 1 describes a speaker device in which the cut surface of the trimmed magnesium diaphragm near its periphery is coated with adhesive, with the aim of improving the rust resistance of the cut surface of the trimmed magnesium diaphragm without surface treatment. Patent Document 2 describes a speaker diaphragm consisting of a magnesium diaphragm and a resin edge, which aims to avoid bonding with adhesive and also to eliminate the need for edge processing of the outer cut surface of the magnesium diaphragm, and in which the inner peripheral edge of the edge has a structure with a clamping groove into which the outer peripheral edge of the magnesium diaphragm fits tightly, and the edge is formed integrally with the magnesium diaphragm by insert molding. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-94422 [Patent Document 2] JP 2005-260619 Summary of the Invention [Problem to be solved by the invention]

[0007] In the speaker device of Patent Document 1, there may be a portion of the cut surface that is not covered with adhesive that is left behind after trimming. Similarly, with the speaker diaphragm of Patent Document 2, there are cases where portions of the outer periphery of the magnesium diaphragm do not fit tightly into the clamping grooves of the edge. In such cases, there is a problem in that the portions not covered with adhesive or the portions not fitting tightly into the clamping grooves become rusting points, from which corrosion progresses. Similarly, when a magnesium alloy containing magnesium as its main component is used, the edge of the outer cut surface of the magnesium diaphragm becomes rusting points, from which corrosion progresses. An object of the present invention is to provide an acoustic diaphragm having good acoustic characteristics that can prevent corrosion from the cut surface formed by trimming a magnesium alloy diaphragm, and a method for manufacturing the same. [Means for solving the problem]

[0008] The present invention, which is provided to solve the above problems, is as follows. [1] An acoustic diaphragm made of a magnesium alloy containing magnesium and aluminum, characterized in that the peripheral cut surfaces are formed by melt cutting. [2] The acoustic diaphragm according to [1], wherein the cut surface is formed by melting using high-energy particles or discharged energy. [3] The acoustic diaphragm according to [2], wherein a high aluminum content layer having a higher aluminum content than other portions is formed on the cut surface.

[0009] In trimming diaphragms made of magnesium alloys containing aluminum, a high-aluminum content layer is formed on the cut surface by melt cutting. The aluminum oxide formed on the cut surface by oxidation of aluminum acts as a passivating layer, improving the corrosion resistance of the cut surface compared to when a trimming mold is used. Therefore, the progression of corrosion due to rust from the cut surface can be prevented without surface treatment of the cut surface formed during trimming. Furthermore, the aluminum oxide formed by oxidizing the high aluminum content layer formed on the cut surface of the diaphragm is harder than other parts, so by surrounding the periphery with a high aluminum content layer, the diaphragm has less deflection and excellent acoustic properties.

[0010] [4] The acoustic diaphragm according to [1], wherein the cut surface is formed by laser cutting. By using laser cutting, the diaphragm can be trimmed with high precision.

[0011] [5] The acoustic diaphragm according to claim 1, wherein the magnesium alloy has a magnesium content of 80 to 97% and an aluminum content of 2 to 10%. Magnesium is the lightest of all light metals and has high internal loss, so using a magnesium alloy with a high magnesium content results in an acoustic diaphragm with excellent acoustic properties. Furthermore, by setting the aluminum content to 2-10%, a high-aluminum layer is formed on the cut surface, which helps prevent rust.

[0012] [6] A method for manufacturing an acoustic diaphragm according to [1], comprising a melt-cutting step of forming a peripheral cut surface by melt-cutting. [7] The method for manufacturing an acoustic diaphragm according to [6], wherein the cutting step uses a laser to form the cut surface. By trimming the diaphragm using laser cutting or other methods to form a cut surface around the diaphragm, the aluminum-rich layer formed on the cut surface can be oxidized to form aluminum oxide, which acts as a passivation layer. This eliminates the need for surface treatment of the cut surface after trimming, improving the manufacturing efficiency of the diaphragm.

[0013] [8] The method for manufacturing an acoustic diaphragm according to [6], wherein the cutting step forms the cut surface by irradiating a laser multiple times along the outer shape of the diaphragm. [9] The method for manufacturing an acoustic diaphragm according to [6], wherein the thickness of the portion of the diaphragm that is irradiated with the laser in the melt-cutting step is 20 to 200 μm. In the fusion cutting process, by irradiating the laser multiple times, the thickness of the high aluminum content layer formed on the cut surface can be made thicker than when cutting with a single laser irradiation. By thickening the high aluminum content layer formed around the diaphragm, the corrosion resistance of the cut surface and the acoustic characteristics of the diaphragm are improved. [Effects of the Invention]

[0014] The present invention allows the peripheral cut surfaces to be formed by fusion cutting, thereby covering the cut surfaces formed around the diaphragm with a high aluminum content layer, thereby preventing rust due to corrosion of the cut surfaces without requiring surface treatment to impart corrosion resistance to the cut surfaces formed by trimming. Furthermore, since the aluminum oxide layer formed by oxidation of the high aluminum content layer is harder than other parts of the diaphragm, by forming a high aluminum content layer on the fusion cut surface, the cut surface of the diaphragm becomes harder than before fusion cutting, resulting in a diaphragm with less deflection and better acoustic characteristics. [Brief explanation of the drawings]

[0015] [Figure 1] 10 is a flowchart of a conventional method for manufacturing a speaker having a diaphragm. [Figure 2] 3 is a flowchart of a method for manufacturing a speaker including a diaphragm according to an embodiment of the present invention. [Figure 3] 4A to 4C are cross-sectional views illustrating the formation of a diaphragm. [Figure 4A] FIG. 10 is a cross-sectional view illustrating trimming by punching. [Figure 4B] FIG. 10 is a cross-sectional view illustrating trimming by melt cutting. [Figure 5A] FIG. 2 is a front view of the diaphragm of the present invention. [Figure 5B] FIG. 5B is a cross-sectional view taken along the line AA in FIG. 5A. [Figure 6] FIG. 2 is a schematic diagram showing a method of irradiating a test piece with a laser in Example 1. [Figure 7A] 1 is a photograph, shown as a substitute for a drawing, showing the surface of a magnesium alloy test piece after laser irradiation. [Figure 7B] 1 is a photograph, substituted for a drawing, showing the surface of a pure magnesium test piece after laser irradiation. [Figure 7C] 1 is a photograph, substituted for a drawing, showing the surface of an aluminum alloy test piece after laser irradiation. [Figure 8A] 1 is a graph showing the results of elemental analysis of a magnesium alloy test piece. [Figure 8B] 1 is a graph showing the results of elemental analysis of a magnesium alloy test piece. [Figure 9] 1 is a graph showing the results of elemental analysis of a test piece of pure magnesium. [Figure 10] 1 is a graph showing the results of elemental analysis of a test piece of an aluminum alloy. [Figure 11A] 1 is a photograph, shown in place of a drawing, illustrating the state of a magnesium foil before a salt spray test. [Figure 11B] 1 is a photograph, substituted for a drawing, showing the state of a magnesium foil after a salt spray test. [Figure 12] FIG. 10 is a schematic diagram showing a laser melt-cutting method for a test piece in Example 2. [Figure 13A] 1 is a photograph, used as a substitute for a drawing, of a test piece including a cut surface of a magnesium alloy. [Figure 13B] 1 is a graph showing the aluminum concentration in a test piece including a cut surface of a magnesium alloy. [Figure 13C] 1 is a graph showing the magnesium concentration in a test piece including a cut surface of a magnesium alloy. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same components are assigned the same numbers, and their descriptions will be omitted where appropriate. In addition, in the XYZ coordinate system showing relative directions in each drawing, the directions parallel to the surface of the foil used as the base material are defined as the X direction, the Y direction, and the thickness direction perpendicular to the surface of the foil is defined as the Z direction.

[0017] FIG. 1 is a flowchart of a conventional method for manufacturing a speaker equipped with an acoustic diaphragm. First, in molding step S10, a magnesium alloy substrate is molded using a press molding machine equipped with upper and lower dies 1 to form diaphragm substrate 2 having a predetermined shape (see FIG. 3). Note that while FIG. 3 shows an example in which diaphragm substrate 2 is molded into a so-called dome shape, the shape is not limited to this and may be molded into other shapes such as a cone shape.

[0018] Next, a surface treatment step S20 is performed to enhance the corrosion resistance (rust prevention) of the formed diaphragm substrate 2. For example, an anodized film is formed on the surface of the diaphragm substrate 2 by anodizing, thereby enhancing the corrosion resistance of the surface of the diaphragm substrate 2.

[0019] In the punching and trimming step S31, the diaphragm substrate 2 is formed into a predetermined shape and then surface-treated, and is then punched out to produce the diaphragm 5. 4A is an explanatory diagram that schematically illustrates the punching and trimming step S31. Conventionally, as shown in the figure, a diaphragm 5 is produced by punching a diaphragm substrate 2 into a predetermined outer shape using a trimming die 3. This method is excellent in terms of manufacturing efficiency because it allows multiple diaphragms 5 to be produced simultaneously from the diaphragm substrate 2. However, when a magnesium alloy, which is easily oxidized, is used as the substrate, the punching and trimming step S31 leaves a cut surface that is not surface-treated, and rust is likely to form on the cut surface, which is prone to corrosion.

[0020] Therefore, in order to prevent corrosion from the cut surfaces, a cut surface treatment step S32 is required. For example, the cut surface treatment step S32 involves covering the cut surfaces with a corrosion-resistant film. Note that the treatment step S32 for treating the cut surfaces formed around the peripheries of multiple diaphragms 5 formed from a single diaphragm substrate 2 requires more time and effort than the surface treatment step S20 for the diaphragm substrate 2 before the punching and trimming step S31.

[0021] In the speaker manufacturing process S40, the diaphragm 5 manufactured through the molding process S10, the surface treatment process S20, the punching and trimming process S31 and the cut surface treatment process S32 is attached to a speaker body to complete a speaker device.

[0022] Fig. 2 is a flowchart of a method for manufacturing a speaker equipped with the acoustic diaphragm of this embodiment. The molding step S10, surface treatment step S20, and speaker manufacturing step S40 are the same as the conventional manufacturing method shown in Fig. 1. The manufacturing method of this embodiment trims the diaphragm substrate 2 by fusion cutting using high-energy particles or discharged energy, and differs from the conventional manufacturing method shown in Fig. 1 in that it includes a fusion cutting trimming step (fusion cutting step) S30.

[0023] In addition, when using laser cutting instead of conventional punching to trim the speaker diaphragm, a different device is required, resulting in excessive manufacturing costs. For this reason, trimming of the speaker diaphragm has traditionally been performed using the punching and trimming process S31 described above. After the punching and trimming process S31, a processing process S32 is performed to improve the corrosion resistance of the cut surface formed around the diaphragm 5.

[0024] The inventors discovered that when a magnesium alloy containing magnesium and aluminum is used as the substrate, forming the end face using a laser results in the formation of a high-aluminum layer on the cut surface, which has a higher aluminum content than the remaining portion. The high-aluminum layer formed on the cut surface becomes aluminum oxide and functions as a passivation, making the subsequent processing step S32 unnecessary. Based on the above findings, the inventors came up with the idea of ​​an acoustic diaphragm made of a magnesium alloy according to the present invention, in which the peripheral cut surface is formed by fusion cutting using a laser or the like, which has not been used conventionally, as a means for trimming the diaphragm.

[0025] The melt cutting trimming step S30 is performed using, for example, an energy emission unit 4 shown in FIG. 4B instead of the trimming die 3 shown in FIG. 4A. A laser can be used as the energy particles emitted from the energy emission unit 4. The melt cutting trimming step S30 using a laser is appropriately referred to as laser melt cutting.

[0026] By performing laser cutting as the cutting trimming step S30, trimming can be performed with high precision. Note that the cutting trimming step S30 is a step of melting a portion of the diaphragm substrate 2 to cut the diaphragm substrate 2. In addition to laser cutting, other methods include wire cutting, in which the diaphragm substrate 2 is melted using a wire heated by passing a current for cutting, and discharge cutting (plasma cutting, arc cutting), in which an arc discharge is generated from the energy emitting unit 4 to melt the diaphragm substrate 2.

[0027] Fig. 5A is a front view of diaphragm 6 of this embodiment obtained by fusion cutting trimming step S30. Fig. 5B is a cross-sectional view taken along line AA in Fig. 5A. As shown in these figures, cut surface 7 of diaphragm 6 formed by melting diaphragm substrate 2 in melt-cutting trimming step S30 is covered with high-aluminum content layer 8, which has a higher aluminum content than other portions. This is thought to be because the magnesium and aluminum contained in magnesium alloys have similar melting points of 650°C and 660.3°C, respectively, while aluminum has a melting point of 2470°C, which is higher than magnesium's boiling point of 1091°C. In other words, it can be assumed that during melt-cutting, much of the magnesium evaporates, while much of the aluminum remains on cut surface 7, resulting in the formation of high-aluminum content layer 8, which has a high aluminum content, on cut surface 7.

[0028] As will be shown in the examples described later, the high aluminum content layer 8 formed in the fusion cut trimming step S30 has excellent corrosion resistance. The high aluminum content layer 8 covering the cut surface 7 formed in the fusion cut trimming step S30 is oxidized to become an aluminum oxide layer, so there is no need to subsequently perform a surface treatment on the cut surface 7 to impart corrosion resistance. Therefore, the manufacturing method of this embodiment does not require the time-consuming cut surface treatment step S32, and the manufacturing process can be simplified.

[0029] Furthermore, in the melt cutting trimming step S30, the high aluminum content layer 8 covering the cut surface 7 formed around the periphery of the diaphragm 6 becomes aluminum oxide, and is therefore harder than other parts of the diaphragm 6. In this way, the high hardness high aluminum content layer 8 is formed so as to cover the cut surface 7 around the periphery of the diaphragm 6, thereby improving the acoustic characteristics of the diaphragm 6. In other words, the formation of an aluminum oxide layer around the periphery of the diaphragm 6, which is harder (has a higher Vickers hardness) than other parts, resulting from the oxidation of the high aluminum content layer 8, improves the hardness of the diaphragm 6 as a whole, reduces deflection, and improves sound quality.

[0030] Furthermore, by covering the periphery of the diaphragm 6 with a layer of aluminum oxide, which has high hardness, it is possible to manufacture a diaphragm 6 with sufficient strength using a magnesium alloy substrate with a thinner plate thickness than conventional ones. Therefore, by reducing the weight, it is also possible to improve the acoustic characteristics of the acoustic diaphragm 6.

[0031] Magnesium has the advantage of high internal loss and sound velocity, which allows it to achieve excellent acoustic properties. However, it is prone to oxidation and rust more easily than aluminum or titanium. Therefore, by using a magnesium alloy containing aluminum and performing trimming by melt cutting, corrosion due to rust from the cut surface formed during trimming can be suppressed.

[0032] When a laser is used in the melt cutting trimming step S30, it is preferable to cut the magnesium alloy substrate by irradiating the laser multiple times along the outer shape of the diaphragm. By irradiating the magnesium alloy substrate multiple times with the laser, the width and thickness of the high aluminum content layer 8 formed around the periphery of the diaphragm 6 increases. This increases the effect of the high aluminum content layer 8 in hardening the diaphragm 6, further improving the sound quality characteristics of the diaphragm 6.

[0033] In the fusion trimming step S30, when fusion cutting is performed using a laser on diaphragm 6 made of a magnesium alloy containing aluminum, the thickness of the portion of the magnesium alloy base material that is irradiated with the laser is, for example, about 10 to 250 μm.

[0034] In the melt cutting and trimming step S30, for example, the laser is irradiated about 1 to 2 times when the thickness of the portion to be irradiated is 10 to 30 μm, about 1 to 4 times when the thickness of the portion is 30 to 80 μm, about 4 to 8 times when the thickness of the portion is 80 to 150 μm, and about 8 to 15 times when the thickness of the portion is 150 to 250 μm to form the cut surface 7. The number of times the laser is irradiated can be adjusted depending on the size, output, irradiation angle, etc. of the laser.

[0035] The substrate is made of a magnesium alloy, such as an Mg-Al-Zn alloy or an Mg-Al alloy.

[0036] Specific examples of Mg-Al-Zn alloys include AZ31A, AZ31B, AZ31C, AZ61A, AZ80A, and AZ91. Specific examples of Mg-Al alloys include AM100A. To impart the excellent properties of magnesium to the diaphragm, the magnesium content in the magnesium alloy is preferably 80 to 97%, and even more preferably 85 to 97%. Furthermore, to form a high aluminum content layer on the cut surface and improve corrosion resistance, the magnesium content in the magnesium alloy is preferably 2 to 10%.

[0037] In addition, from the viewpoint of improving the design, the acoustic diaphragm described in this embodiment may be colored by electro-deposition coating or spray coating on the surface of a magnesium base material on which a hydroxide layer or the like is formed to provide anti-rust properties. [Example]

[0038] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 The following equipment was used to measure the effect of laser irradiation on a magnesium alloy. In this example, a laser was irradiated onto a portion of the surface of a magnesium alloy foil material to form a laser irradiated area 18A whose surface condition corresponds to the cut surface 7 formed by laser cutting. (device) Green laser (MD-T1000) (Laser irradiation conditions) Travel speed 200mm / sec, output 50%, irradiation twice at 0.02mm intervals (Test piece) Dimensions: 30mm length x 30mm width x 200μm thickness (Type of test piece) Magnesium alloy: AZ31 (magnesium alloy containing 3% Al and 1% Zn) Pure magnesium Aluminum alloy: A5052 (aluminum alloy containing 2.2-2.8% Mg)

[0039] 6 is a schematic diagram showing the laser irradiation method for the test piece in this example. As shown in the figure, in this example, laser irradiation was performed by irradiating the XY plane of the test piece 12 with a laser 21 at a predetermined output repeatedly at intervals of 0.02 mm in the Y direction while moving the laser irradiation means 20 in the X direction at a predetermined speed, thereby forming the laser irradiation area 18A.

[0040] 7A, 7B, and 7C are photographs showing laser-irradiated areas 18A on the surfaces of magnesium alloy AZ31 (hereinafter referred to as AZ31), pure magnesium, and aluminum alloy A5052 (hereinafter referred to as A5052) test pieces after laser irradiation. As shown in these figures, it was confirmed that linear grooves were formed in the laser-irradiated areas 18A of the AZ31, pure magnesium, and A5052 test pieces. The element distribution state in the laser irradiated area 18A of each test piece before and after laser irradiation was measured by line analysis at an acceleration voltage of 10 kV, and the effects of laser irradiation on AZ31, pure magnesium, and A5052 were evaluated.

[0041] Figures 8A and 8B show the measurement results of the laser-irradiated region 18A on the surface of the AZ31 test piece shown in Figure 7A. From the measurement results shown in Figures 8A and 8B, the distributions of magnesium, oxygen, and aluminum in the laser-irradiated region 18A were calculated to show the ratios to the values ​​of each element measured in the untreated region. The results are shown in Table 1. [Table 1] The results shown in Table 1 show that laser irradiation of AZ31 increases the ratio of aluminum to magnesium compared to before irradiation.

[0042] Figure 9 shows the measurement results of the laser irradiated region 18A on the surface of the pure magnesium test piece shown in Figure 7B. From the measurement results shown in Figure 9, the distribution of magnesium and oxygen in the laser irradiated region 18A was calculated to show the ratios to the values ​​of each element measured in the untreated region. Table 2 shows the results. [Table 2] As shown in Table 2, it was found that the ratio of oxygen to magnesium was reduced by laser irradiation. From these results, it is thought that irradiating pure magnesium with a laser removes the magnesium oxide layer on the surface, causing the magnesium to appear on the surface.

[0043] Fig. 10 shows the measurement results of the laser-irradiated region 18A on the surface of the aluminum alloy A5052 test piece shown in Fig. 7C. From the measurement results shown in Fig. 10, the distribution of aluminum and oxygen in the laser-irradiated region 18A was calculated to show the ratios to the values ​​of each element measured in the untreated region. The results are shown in Table 3. [Table 3]

[0044] As shown in Table 3, when an aluminum alloy containing aluminum as the main component was irradiated with a laser, the proportion of oxygen increased. This suggests that the laser irradiation oxidized the aluminum, forming aluminum oxide, which functions as a passive state.

[0045] (Corrosion resistance test) 6, the laser irradiation region 18A was formed for the magnesium alloy AZ31 by irradiating the laser 21 under the same conditions using the above-mentioned equipment and test piece. That is, a 200 μm thick foil of the magnesium alloy AZ31 was used as the test piece, and its surface was polished to remove carbides and other materials that had adhered during rolling. After that, a part of the surface of the foil was irradiated with the laser to melt and remove about 30 μm of the material surface, thereby forming the laser irradiation region 18A.

[0046] (Salt spray test (continuous spray test)) A salt spray test was performed on the above test pieces using the following method, and the rust condition was observed before and after the salt spray test for the laser-irradiated area 18A where laser irradiation was performed and the untreated area where the foil material surface was left in its original state.

[0047] Test method: Conforms to JI Process SZ 2371 salt spray test method. Test conditions: Neutral salt spray (pH 6.5-7.2), spray chamber temperature 35±2°C, water temperature in air-saturated container 47±2°C, salt spray duration 2 hours Testing equipment: Suga Testing Machine Co., Ltd., Salt spray testing machine process STP-90V2

[0048] 11A and 11B are photographs showing the state of the magnesium foil test piece of the example before and after the salt spray test. In each figure, the laser-irradiated area 18A formed by laser irradiation is indicated by a dashed line. The laser-irradiated area 18A corresponds to the high-aluminum content layer 8 formed on the cut surface 7 (see FIGS. 5A and 5B), and the area outside the dashed line is the untreated area.

[0049] The salt spray test showed that no rust was observed in the laser-irradiated area 18A, while rust occurred in the untreated area. This result shows that laser irradiation improves the corrosion resistance of the magnesium alloy AZ31.

[0050] Example 2 The following equipment was used to measure the effect of laser cutting on magnesium alloys: In this example, a laser was irradiated onto the surface to melt-cut the magnesium alloy foil material, forming a laser irradiated area 18A on the cut surface 7.

[0051] (device) Green laser (MD-T1000) (Laser irradiation conditions) Travel speed: 200mm / sec, output: 80%, irradiated three times (Test piece) Dimensions: 30mm length x 30mm width x 50μm thickness (Type of test piece) Magnesium alloy: AZ31 (magnesium alloy containing 3% Al and 1% Zn)

[0052] 12 is a schematic diagram showing the laser irradiation method for the test piece in this example. As shown in the figure, in this example, while moving the laser irradiation means 20 in the X direction at a predetermined speed, a laser 21 was irradiated with a predetermined output onto the XY plane of the test piece 12 to melt and cut the test piece 12, forming a laser irradiation area 18B on the cut surface.

[0053] Using the above-mentioned device and conditions, a 50 μm thick magnesium alloy AZ31 test piece 12 was irradiated with a laser 21 to be cut. The test piece, including the cut surface, was photographed using a mapping mode of a scanning electron microscope along the irradiation direction of the laser 21 used during cutting, i.e., the thickness direction (Z direction) of the magnesium alloy substrate that was the test piece 12.

[0054] Figure 13A is a photograph of test piece 12 including laser-irradiated region 18B. Figures 13B and 13C are photographs showing, in that order, the aluminum and magnesium contents of test piece 12 including laser-irradiated region 18B. In Figure 13B, the bright white areas indicate areas with a high aluminum content. In Figure 13C, the magnesium content is indicated by a scale in the lower left corner of the photograph.

[0055] As shown in Figure 13B, a high-aluminum content layer with a higher aluminum content than the other parts was formed in the laser-irradiated region 18B that was cut by the laser. Furthermore, as shown in Figure 13C, it was found that the magnesium content in the laser-irradiated region 18B was lower than in the other parts. This is presumably because, during laser cutting, magnesium, which has a low boiling point, evaporated near the cut surface, while aluminum, which has a high boiling point, remained unevaporated. This resulted in the formation of a high-aluminum content layer 8 with a higher aluminum content than the other parts in the laser-irradiated region 18B that was formed on the cut surface by laser cutting.

[0056] In the present invention, the term "high aluminum content layer" refers to a layered portion having a higher aluminum content than other portions. The presence or absence of the high aluminum content layer can be confirmed by taking an image using a scanning electron microscope in mapping mode. When a high aluminum content layer is formed, a bright layered portion appears, indicating a higher aluminum content than other portions, as shown in Figure 13B.

[0057] The results of Examples 1 and 2 show that, unlike punching trimming using a die, melt cutting using a laser or the like forms a corrosion-resistant cut surface covered with a high-aluminum content layer. The improvement in corrosion resistance due to melt cutting is presumably due to the formation of a non-conductive film of aluminum oxide on the laser-irradiated surface, where the high-aluminum content layer is oxidized, and this non-conductive film suppresses the occurrence of rust.

[0058] As described above, it has been found that laser cutting of magnesium alloys containing aluminum forms a high-aluminum content layer on the cut surface, and the aluminum is oxidized to become passivated as magnesium oxide. In other words, laser cutting of magnesium alloys forms a high-aluminum content layer on the cut surface, which can suppress corrosion due to rust on the cut surface. Therefore, diaphragms trimmed by cutting have excellent durability and are less susceptible to rust on the cut surface, without the need for surface treatment on the cut surface after trimming. [Industrial Applicability]

[0059] The present invention is effective as an acoustic diaphragm that is excellent in acoustic characteristics and that is inhibited from rusting from cut surfaces due to trimming. [Explanation of symbols]

[0060] 1: Mold 2: Vibration plate base material 3: Trimming mold 4: Energy release section 5: Vibration plate 6: Vibration plate 7: Cut surface 8: High aluminum content layer 12: Test piece 20: Laser irradiation means 21: Laser 18A, 18B: Laser irradiation area

Claims

1. 1. An acoustic diaphragm made of a magnesium alloy containing magnesium and aluminum, characterized in that the peripheral cut surfaces are formed by melt cutting.

2. 2. The acoustic diaphragm according to claim 1, wherein the cut surface is formed by fusion cutting using high-energy particles or discharged energy.

3. 3. The acoustic diaphragm according to claim 2, wherein a high aluminum content layer having a higher aluminum content than other portions is formed on the cut surface.

4. 2. The acoustic diaphragm according to claim 1, wherein the cut surface is formed by laser cutting.

5. 2. The acoustic diaphragm according to claim 1, wherein the magnesium alloy has a magnesium content of 80 to 97% and an aluminum content of 2 to 10%.

6. A method for manufacturing the acoustic diaphragm according to claim 1, A method for manufacturing an acoustic diaphragm, comprising a fusion cutting process for forming a peripheral cut surface by fusion cutting.

7. The method for manufacturing an acoustic diaphragm according to claim 6 , wherein the cutting step forms the cut surface using a laser.

8. The method for manufacturing an acoustic diaphragm according to claim 6 , wherein the cutting step forms the cut surface by irradiating a laser multiple times along the outer shape of the diaphragm.

9. 7. The method for manufacturing an acoustic diaphragm according to claim 6, wherein the thickness of the portion of the diaphragm that is irradiated with the laser in the melting step is 20 to 200 μm.

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