Composite material and method of producing the same, and composite metal material and method of producing the same

1. A method of producing a composite metal material, the method comprising:

(a) mixing at least a first carbon material and a particulate metal material Z into an elastomer, and dispersing the first carbon material and the metal material Z by applying a shear force to obtain a composite elastomer, the metal material Z having a melting point lower than a melting point of the first carbon material;

(b) heat-treating the composite elastomer in an atmosphere containing oxygen to vaporize the elastomer included in the composite elastomer to obtain an intermediate composite material including a second carbon material, wherein the second carbon material is derived from the first carbon material, and the metal material Z;

(c) heat-treating the intermediate composite material together with a substance including an element Y having a melting point lower than the melting point of the metal material Z to vaporize the substance including the element Y; and

(d) casting a composite material obtained by the step (c) in a die having a desired shape either directly or after mixing the composite material into a molten matrix metal material to obtain the composite metal material,

wherein:

the metal material Z is aluminum or an alloy containing aluminum as a major component;

the element Y is magnesium;

the heat treatment temperature in the step (b) is set at a point lower than the vaporization temperature of the substance including the element Y;

the heat treatment temperature in the step (c) is set at a point higher than the heat treatment temperature in the step (b), the heat treatment temperature in the step (c) is set at a point equal to or higher than the vaporization temperature of the substance including the element Y, and the heat treatment temperature in the step (c) is set at a point lower than the vaporization temperatures of the metal material Z and the first carbon material;

a surface of the first carbon material activated in the step (a) bonds to oxygen present in the atmosphere inside a furnace by the heat treatment in the step (b) to obtain the second carbon material having a surface oxidized;

the composite metal material has a compressive yield strength mean value of 320 MPa or more; and

the casting in the step (d) is selected from the group consisting of a metal mold casting method, a diecasting method, a low-pressure casting method, a high-pressure casting method, a thixocasting method, and a centrifugal casting method.

2. The method of producing a composite metal material as defined in claim 1 , wherein, in the step (c), the substance including the element Y is disposed in a heat treatment furnace together with the second carbon material and vaporized by the heat treatment.

3. The method of producing a composite metal material as defined in claim 1 , wherein the first carbon material is carbon black.

4. The method of producing a composite metal material as defined in claim 1 , wherein the first carbon material is carbon fiber.

5. The method of producing a composite metal material as defined in claim 4 , wherein the carbon fiber is carbon nanofiber.

6. The method of producing a composite metal material as defined in claim 5 , wherein the carbon nanofibers have an average diameter of 0.5 to 500 nm.

7. The method of producing a composite metal material as defined in claim 1 , wherein the elastomer has a molecular weight of 5,000 to 5,000,000.

8. The method of producing a composite metal material as defined in claim 1 , wherein at least one of a main chain, a side chain, and a terminal chain of the elastomer includes at least one unsaturated bond or group having affinity to carbon nanofibers selected from the group consisting of a double bond, a triple bond, α-hydrogen, a carbonyl group, a carboxyl group, a hydroxyl group, an amino group, a nitrile group, a ketone group, an amide group, an epoxy group, an ester group, a vinyl group, a halogen group, a urethane group, a biuret group, an allophanate group, and a urea group.

9. The method of producing a composite metal material as defined in claim 1 , wherein a network component of the elastomer in an uncrosslinked form has a spin spin relaxation time (T 2 n ) of 100 to 3,000 μsec, measured at 30° C. by a Hahn-echo method using a pulsed nuclear magnetic resonance (NMR) technique.

10. The method of producing a composite metal material as defined in claim 1 , wherein a network component of the elastomer in a crosslinked form has a spin-spin relaxation time (T 2 n ) of 100 to 2,000 μsec, measured at 30° C. by a Hahn-echo method using a pulsed nuclear magnetic resonance (NMR) technique.

11. The method of producing a composite metal material as defined in claim 1 , wherein the elastomer is natural rubber or nitrile butadiene rubber.

12. The method of producing a composite metal material as defined in claim 1 , wherein the step (a) is performed by using an open roll method with a roll interval of 0.5 mm or less.

13. The method of producing a composite metal material as defined in claim 12 , wherein two rolls used in the open-roll method have a surface velocity ratio of 1.05 to 3.00.

14. The method of producing a composite metal material as defined in claim 1 , wherein the step (a) is performed by using an internal mixing method.

15. The method of producing a composite metal material as defined in claim 1 , wherein the step (a) is performed by using a multi-screw extrusion kneading method.

16. The method of producing a composite metal material as defined in claim 1 , wherein the step (a) is performed at 0 to 50° C.

17. The method of producing a composite metal material as defined in claim 1 , wherein the substance including the element Y is mixed with the elastomer in the step (a).