METAL MATERIAL AND METHOD FOR PRODUCING THE SAME

Abstract

[Problem] Provided are a metal material including a passive film on a surface and having corrosion resistance while having a small contact resistance, and a method for producing the metal material. Examples of the metal material include a material that is preferable as a material of a separator and a current collector plate in a fuel cell.

[Solution] Conductive particles 3 are embedded in and caused to adhere to a metal substrate 1 including, on a surface thereof, a passive film 2, in a state where the conductive particles 3 penetrate the passive film 2 in a thickness direction, and the surface of the metal substrate is covered with a coating film having conductivity and corrosion resistance. To cause the conductive particles to adhere in such a manner, the conductive particles 3 may be scattered on the metal substrate 1 on which the passive film 2 is formed, and the conductive particles 3 may be pushed into the surface of the metal substrate 1 by pressing with a roll or the like.

Claims

1. A sewing machine needle clamping device for attaching a sewing machine metal material, wherein conductive particles adhere to a metal substrate including, on a surface thereof, a passive film, in a state where the conductive particles penetrate the passive film in a thickness direction, and the surface of the metal substrate is covered with a coating film having conductivity and corrosion resistance.

2. A metal material, wherein WC particles being conductive particles adhere to Al or an Al alloy being a metal substrate including, on a surface thereof, a passive film, in a state where the conductive particles penetrate the passive film in a thickness direction.

3. The metal material according to claim 2, wherein the surface of the metal substrate is covered with a coating film having conductivity and corrosion resistance.

4. The metal material according to claim 3, wherein the surface is covered by a graphite coating.

5. The metal material according to claim 3, wherein the metal material is used as a fuel cell component.

6. The metal material according to claim 2, wherein the metal material is a plate-shaped metal material formed with a groove by press working to be used as a fuel cell component, and a particle size of the WC particles is 10 μm or less.

7. A method for producing a metal material, comprising: pushing, into a surface of a metal substrate including a passive film, conductive particles having a particle size larger than a thickness of the passive film to cause the conductive particles to adhere to the metal substrate in a state where the conductive particles penetrate the passive film in a thickness direction.

8. The method for producing a metal material according to claim 7, comprising: scattering the conductive particles on the surface of the metal substrate, and performing pressing to push the conductive particles into the surface of the metal substrate.

9. The method for producing a metal material according to claim 8, comprising: scattering the conductive particles together with a viscous fluid on the surface of the metal substrate when the pressing is performed.

10. The method for producing a metal material according to claim 9, wherein lubricating oil or lubricating grease is used as the viscous fluid.

11. The method for producing a metal material according to claim 7, comprising: after pushing the conductive particles into the surface of the metal substrate, forming a coating film having conductivity and corrosion resistance on the surface of the metal substrate.

12. The method for producing a metal material according to claim 7, wherein the method is a method for producing a metal material to be used as a fuel cell component, and the method comprises pushing WC particles being conductive particles having a particle size of 10 μm or less into a surface of plate-shaped Al or an Al alloy being a metal substrate including a passive film, and then forming a groove in the metal substrate by press working, and forming a coating film having conductivity and corrosion resistance on the surface.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0054] FIGS. 1A and 1B are micrographs of a surface (uncoated) of a metal material according to the invention. FIG. 1A is a micrograph of an Al substrate in which WC particles are embedded, and FIG. 1B is a micrograph of an Al—Mg—Ti alloy as a substrate in which WC particles are embedded in the surface of the substrate.

[0055] FIG. 2 is an image diagram illustrating a cross section of a metal material according to the invention. It is noted that proportions of thickness, size, and the like of each part are not accurately represented.

[0056] FIG. 3 is an image diagram illustrating a method for producing a metal material according to the invention. Again, the dimensional relationship of each part is not accurate.

[0057] FIGS. 4A and 4B are image diagrams of a cross section near a coating film of a metal material (including the coating film) according to the invention. Again, the dimensional relationship of each part is not accurate. FIG. 4A illustrates an example of a thick coating film, and FIG. 4B illustrates an example of a thin coating film.

[0058] FIG. 5 is a diagram illustrating essential points of a contact resistance test performed on the metal material and the like according to the invention.

[0059] FIGS. 6A to 6E are micrographs of lateral cross sections of the metal material according to the invention in which a plurality of grooves are formed by press working. FIGS. 6A and 6B illustrate a metal material in which WC particles having a maximum particle size of 150 μm are embedded in the surface, FIGS. 6C and 6D illustrate a metal material in which WC particles having a particle size of 36 to 106 μm are embedded in the surface, and FIG. 6E illustrates a metal material in which WC particles having a maximum particle size of 8.5 μm are embedded in the surface.

DESCRIPTION OF EMBODIMENTS

[0060] Examples of the invention will be described below.

[0061] The present inventors have manufactured and tested a novel metal material test piece using a general aluminum plate as a raw material, with the aim of reducing the contact resistance of the plate while taking advantage of the corrosion resistance of a passive film (Al2O3) on the surface of the aluminum plate without removing the passive film. The details are described below.

[0062] 1) A commercially available Al plate (1000 series, thickness 0.3 mm) is purchased and cut to obtain a 50 mm×50 mm plate-shaped Al substrate.

[0063] 2) Lubricating oil is applied to the surface of the Al substrate (one side surface, an upper surface when the plate is placed horizontally). WC particles are dispersed in the lubricating oil in an amount of 10 wt. %. WC particles have excellent conductivity and a high hardness of about HB 3000. Here, WC particles having an average particle size of 80 μm were used.

[0064] 3) The Al substrate as described in 2) is rolled by using a small rolling mill. FIG. 3 is an image diagram illustrating a rolling process. Reference numeral 1 denotes an Al substrate (metal substrate), reference numeral 2 denotes a passive film, reference numeral 3 denotes WC particles (conductive particles), reference numerals 11a and 11b denote rolling rolls, and reference numeral 12 denotes lubricating oil.

[0065] 4) By the above-mentioned rolling, a metal material test piece is obtained in which the WC particles 3 are embedded in the Al substrate 1 in a state as illustrated in FIG. 2. FIG. 1A is a micrograph of a surface 85 of the test piece, in which white masses in the image are WC particles. The passive film 2 having a thickness of about 0.5 μm or less exists on the surface of the Al substrate 1, however, many of the WC particles 3 pierce the passive film 2 and reach the Al substrate 1, and such WC particles 3 penetrate the Al substrate 1 in a state where they are in contact with the Al substrate 1 and are exposed to the outside (a side facing the outside air).

[0066] 5) After the above rolling is completed, the lubricating oil is removed from the metal material test piece.

[0067] 6) A graphite coating is applied on the surface of the Al substrate 1, that is, on the passive film 2 on which the WC particles 3 are scattered. The graphite coating is a coating containing graphite particles and the like in a resin component that forms a base. As illustrated in FIG. 4A or FIG. 4B, the thickness of a coating film 4 formed by the coating can be appropriately set, however, here, as illustrated in FIG. 4A, the coating film 4 has a thickness of about 10 μm (preferably about 1 to 20 μm) that covers the passive film 2 and the WC particles 3. For the graphite coating, the corrosion resistance is increased by selecting the resin component, and the conductivity is appropriately set by selecting the amount of graphite and the like.

[0068] The contact resistance value of the manufactured metal material test piece was measured. The measurement was performed using the test pieces obtained by the above 4) and 6) (referred to as Example 1 and Example 2, respectively), an Al substrate alone purchased and cut to the above-mentioned size (Comparative Example 1), and the Al substrate alone coated with the same graphite coating as in 6) above (Comparative Example 2), with a contact load set to 7 kgf/cm2. As a result, the contact resistance values of the test pieces of Examples 1 and 2 were 1/100 or less of those of the test pieces of Comparative Examples 1 and 2.

[0069] It is thought that, as described above, the Al substrate 1 includes the passive film on the surface, and thus, the contact resistance of the Al substrate alone is large, as indicated by Comparative Examples 1 and 2, however, as indicated by Examples 1 and 2, the metal material test piece to which the WC particles 3 are adhered has a structure in which the Al substrate 1 in the interior and the highly conductive WC particles 3 (and the coating film 4 in Example 2) are connected in a state where the electric resistance is low, and thus, the contact resistance is low.

[0070] The contact resistance of the above-described metal material test piece and the like was further measured in a state where the metal material test piece was combined with a copper electrode, a gas diffusion layer (GDL), and hard carbon, as illustrated in FIG. 5. That is, the metal material test piece was arranged at a position of a current collector plate in a fuel cell, and the contact resistance in relation to the other components was measured.

[0071] The measurement was performed by arranging, at the position of the metal material (a metal substrate 1, including the coating film 4 depending on the test piece) in FIG. 5, each of the test pieces of Examples 1 and 2 or each of the test pieces of Comparative Examples 1 and 2 and applying a contact load of 7 kgf/cm2. Then, as illustrated in the drawing, a resistance value Ra between the copper electrode and the Al substrate and a resistance value Rb between the hard carbon and the Al substrate are measured.

[0072] Table 1 shows the resistance values obtained in the measurement in FIG. 5. In Comparative Example 1 relating to the Al substrate alone to which the WC particles 3 are not adhered or the like, and in Comparative Example 2 in which only the graphite coating of the above 6) was applied to the Al substrate alone, Ra and Rb are both high, however, in Examples 1 and 2 relating to the metal material obtained by the above 4) and 6), both Ra and Rb are considerably lower.

TABLE-US-00001 TABLE 1 Electric resistance value Ra Rb Item (mΩ*cm.sup.2) (mΩ*cm.sup.2) (Comparative Example 1) 2292 2189 Aluminum plate (Comparative Example 2) 2056 2000 Aluminum plate + graphite coating film (Example 1) 55.6 8.8 Aluminum plate + rolled WC particles (Example 2) 96.4 27.2 Aluminum plate + rolled WC particles + graphite coating film

[0073] For mass production of a metal material like the metal material test pieces of Examples 1 and 2 as a separator or a current collector plate for a fuel cell (especially a PEFC), or the like, it is preferable to use a long coil as the Al substrate and continuously perform the above process 3) with a large rolling mill. For example, a coil having a thickness of 0.3 mm and a width of 320 mm is used as the Al substrate, a surface of the Al substrate is spray-coated with a rolling oil containing WC particles having an average particle size of 1 to 100 μm (preferably a maximum particle size of 10 μm), and the Al substrate is rolled to a thickness of 0.25 mm by applying a rolling load of about 5 to 15 tons with respect to the coil width. Afterwards, the above-mentioned process 6) is performed using an appropriate graphite coating. It is necessary that the graphite coating has corrosion resistance and conductivity in accordance with the application, does not easily peel off after application to the surface of the Al substrate including the passive film and the WC particles, and does not cause the development of cracks and continuous holes.

[0074] To use the metal material obtained in this way as a fuel cell separator or the like, it is necessary to further form a groove serving as a gas flow path by press working. The press working is performed after forming the coating film as described above or before forming the coating film. The Al substrate has excellent workability and the coating film thickness of the graphite coating can be thin, and thus, the forming of the groove on the metal material is relatively easy and a fine groove having a width of about 0.4 mm can be formed at low cost.

[0075] In another example described below, press working was performed on a metal material to obtain a groove shape.

[0076] First, a metal material test piece in which the WC particles 3 are embedded in the Al substrate 1 is prepared in the manner described in 1) to 5) above. The same Al substrate (thickness of 0.3 mm) as in 1) above was used, however, three types of WC particles having different particle sizes were used as described below. Afterwards, the metal material test piece is subjected to press (servo press) working to form a plurality of grooves in parallel having a groove width of 0.5 mm. These grooves correspond to grooves used as a gas flow path in the fuel cell separator.

[0077] FIGS. 6A to 6E are micrographs of lateral cross sections of the metal material test piece in which the grooves were formed by press working. FIG. 6A is a micrograph of a case where the maximum particle size of the embedded WC particles is 150 μm, FIG. 6C is a micrograph of a case where the particle size of the embedded WC particles is 36 to 106 μm, and FIG. 6E is a micrograph of a case where the maximum particle size of the embedded WC particles is 8.5 μm.

[0078] In the example of FIG. 6A in which the maximum particle size of the WC particles was 150 μm, a crack occurred in a part (a portion thinned by the press working) of the metal material test piece as shown in FIG. 6B. In the example of FIG. 6C in which the particle size of the embedded WC particles was 36 to 106 μm, a crack occurred similarly in a part as shown in FIG. 6D. Such cracking may be caused by a loss in continuity in the Al substrate due to presence of large WC particles in the thinned portion of the metal material test piece.

[0079] On the other hand, in the example of FIG. 6E in which the maximum particle size of the WC particles was 8.5 μm, there was no crack even in the thinned portion. When a groove having a similar width is formed in an Al substrate having a similar thickness, it is considered that the maximum particle size of the WC particles needs to be 10 μm or less.

[0080] In the above description, the metal material is produced by embedding WC particles in the Al substrate. However, a metal material having a similar function can be produced from another material. That is, a metal material having corrosion resistance and low contact resistance can also be produced by using another metal (having a passive film) such as an Al alloy, a copper alloy, or stainless steel as the metal substrate instead of the Al substrate, and using other conductive particles instead of the WC particles. Similarly, instead of the graphite coating used to reinforce the corrosion resistance, another coating having corrosion resistance and conductivity can be used.

[0081] For example, an Al—Mg alloy or an Al—Mg—Ti alloy may be used as the Al alloy.

[0082] FIG. 1B is a micrograph of the surface of such an Al—Mg—Ti alloy in which WC particles are adhered to the surface of the Al—Mg—Ti alloy in the manner described in 1) to 4) above. Similarly to FIG. 1A, white masses in the image are WC particles.