Honeycomb body formed of metallic foils, method for the production thereof and motor vehicle

1. A honeycomb body, comprising: at least one metallic smooth foil; and at least one metallic structured foil; said at least one smooth foil having a different mean roughness than said at least one structured foil, one of said at least one smooth foil or said at least one structured foil having a mean roughness Ra of 0.3 to 0.7 micrometers and the other of said at least one smooth foil or said at least one structured foil having a mean roughness Ra of 0.001 to 0.3 micrometers for reducing diffusion connections between said foils, wherein said at least one smooth foil having a mean roughness which is greater than the mean roughness of said at least one structured foil.

2. The honeycomb body according to claim 1 , wherein said at least one smooth foil has a mean roughness R a of 0.3 to 0.7 micrometers.

3. The honeycomb body according to claim 2 , wherein said at least one structured foil has a mean roughness R a of 0.001 to 0.3 micrometers.

4. The honeycomb body according to claim 1 , wherein said at least one structured foil has a mean roughness R a of 0.001 to 0.3 micrometers.

5. The honeycomb body according to claim 1 , wherein said roughnesses of said foils are measured transversely relative to a rolling direction.

6. The honeycomb body according to claim 1 , wherein said at least one smooth foil has two surfaces, oxide layers are disposed on said two surfaces of said at least one smooth foil and on said at least one structured foil, and said oxide layers on said two surfaces of said at least one smooth foil have a different first oxide layer thickness than said oxide layer on said at least one structured foil.

7. The honeycomb body according to claim 6 , wherein said oxide layers on said two surfaces of said at least one smooth foil have a greater first oxide layer thickness than said oxide layer on said at least one structured foil.

8. The honeycomb body according to claim 7 , wherein said first oxide layer thickness of said oxide layer on said at least one smooth foil lies in a range of from 60 to 80 nanometers.

9. The honeycomb body according to claim 1 , wherein at least one of said at least one smooth foil or said at least one structured foil contains 14 to 25% by weight of chromium and 3 to 7% by weight of aluminum.

10. The honeycomb body according to claim 1 , which further comprises connecting points produced between adjacent foils for brazing selectively in only predetermined regions.

11. The honeycomb body according to claim 1 , which further comprises an oxide layer disposed on said foils, and an additional coating at least partially covering said oxide layer.

12. A motor vehicle, comprising:

an internal combustion engine;

an exhaust system receiving exhaust gas from said internal combustion engine; and

a honeycomb body according to claim 1 associated with said exhaust system.

13. A method for producing a honeycomb body, the method comprising the following steps:

a) providing at least one smooth foil and at least one structured foil having different mean roughnesses, one of the at least one smooth foil or the at least one structured foil having a mean roughness Ra of 0.3 to 0.7 micrometers and the other of the at least one smooth foil or the at least one structured foil having a mean roughness Ra of 0.001 to 0.3 micrometers for reducing diffusion connections between the foils, wherein the least one smooth foil has a mean roughness which is greater than the mean roughness of the at least one structured foil;

b) forming an oxide layer with a first oxide layer thickness on the at least one smooth foil or on the at least one structured foil;

c) forming a honeycomb structure from the at least one smooth foil and the at least one structured foil;

d) inserting the honeycomb structure into a housing; and

e) forming technical joining connections at least at some of the foils.

14. The method according to claim 13 , which further comprises carrying out step b) at temperatures of at least 750° C. in air over a time period of 4 to 8 seconds.

15. A motor vehicle, comprising:

an internal combustion engine;

an exhaust system receiving exhaust gas from said internal combustion engine; and

a honeycomb body produced according to claim 13 and associated with said exhaust system.