Method for the laser welding of a composite material to a component, and laser-weldable composite material for such a method

1. A method for the laser welding of a composite material (V) to a component ( 11 ) for the production of a solar collector element (E), the method comprising the steps of:

providing the composite material (V) comprising a strip-shaped substrate ( 1 ) composed of a metal having high reflectivity to laser radiation, said substrate having a first side (A) and a second side (B), wherein a dielectric coating ( 7 ) is situated at least on the first side (A), the dielectric coating ( 7 ) having a thickness (D B ) in the range of 140 nm to 210 nm; and

projecting a laser beam (L) at an acute orientation angle (μ) at least onto the first side (A) of the substrate ( 1 ) provided with the dielectric coating ( 7 ), in order to produce one of a continuous weld seam and discrete weld spots, wherein the laser beam (L) is radiated in onto the composite material (V) in such a way that the radiated-in energy of the laser beam (L) is absorbed to the extent of at least 15 percent.

2. The method according to claim 1 , characterized in that the laser beam (L) is focused optically, for example by means of lenses.

3. The method according to claim 2 , characterized in that the laser beam (L) is focused by lenses.

4. The method according to claim 1 , characterized in that the coating ( 7 ) is a ceramic coating.

5. The method according to claim 1 , characterized in that the coating ( 7 ) has a thickness (D B ) in the range of 170 nm to 195 nm.

6. The method according to claim 1 , characterized in that the coating ( 7 ) has a thickness (D B ) of less than 200 nm and the laser beam (L) is radiated in onto the composite material (V), in particular at an orientation angle (μ) in the range of 2° to 50°, in such a way that the radiated-in energy of the laser beam (L) is absorbed to the extent of at least 20 percent.

7. The method according to claim 1 , characterized in that the laser beam (L) is radiated in onto the composite material (V) at an orientation angle (μ) in the range of 2° to 50°.

8. The method according to claim 7 , characterized in that the orientation angle (μ) at which the laser beam (L) is radiated in onto the composite material (V) is less than 30°.

9. The method according to claim 7 , characterized in that the focused laser beam (L) is radiated in onto the composite material (V) at an orientation angle (μ) in the range of 7° to 17°.

10. The method according to claim 1 , characterized in that the laser beam (L) is linearly polarized in a single plane.

11. The method according to claim 10 , characterized in that the laser beam (L) is polarized in such a way that its light lies parallel to an incidence plane (W) perpendicular to the interface between composite material (V) and component ( 11 ).

12. The method according to claim 1 , characterized in that the coating ( 7 ) is substantially composed of aluminum oxide.

13. The method according to claim 1 , characterized in that the substrate ( 1 ) of the composite material (V) is composed of aluminum.

14. The method according to claim 12 , characterized in that the aluminum oxide of the coating ( 7 ) is formed from one of anodically oxidized, and electrolytically brightened and anodically oxidized, aluminum of which the substrate ( 1 ) is composed.

15. The method according to claim 1 , characterized in that the component ( 11 ) is a tube ( 11 ).

16. The method according to claim 1 , characterized in that the component ( 11 ) is composed of copper.

17. The method according to claim 1 , characterized in that the component ( 11 ) and the composite material (V) are connected along an abutment joint of the component ( 11 ) and of the composite material (V) by means of weld seams running on both sides of the component ( 11 ).

18. The method according to claim 1 , characterized in that each weld seam is formed from small molten balls ( 12 ) that are spaced apart from one another (distance a).

19. The method according to claim 18 , characterized in that the energy of the laser beam (L) for producing a small molten ball ( 12 ) acts over a time period of not more than approximately 10 ms.

20. The method according to claim 1 , characterized in that the power density of the laser beam (L) during welding does not exceed 10 6 W/cm 2 .

21. The method according to claim 1 , characterized in that an Nd:YAG laser is used for producing the laser beam (L).

22. The method according to claim 1 , characterized in that a dielectric coating ( 2 ) is situated on the second side (B) of the substrate ( 1 ).

23. The method according to claim 22 , characterized in that the coating ( 2 ) on the second side (B) of the substrate ( 1 ) is produced identically to the coating ( 7 ) situated on the first side (A) of the substrate ( 1 ).

24. The method according to claim 1 , characterized in that an optically active coating ( 3 ) is situated on the second side (B) of the substrate ( 1 ).

25. The method according to claim 24 , characterized in that the optically active coating ( 3 ) is a multilayer system ( 3 ) composed of at least three layers ( 4 , 5 , 6 ).

26. The method according to claim 25 , characterized in that, in the multilayer system ( 3 ), a topmost layer ( 4 ) is a dielectric layer, a middle layer ( 5 ) is a layer containing chromium oxide, and in that a bottommost layer ( 6 ) is composed of gold, silver, copper, chromium, aluminum and/or molybdenum.

27. The method according to claim 1 , characterized in that a distance (b) between an impingement point (P) of the laser beam (L) and a tangent point (Q), at which the coating ( 7 ) of the composite material (V) touches the component ( 11 ), embodied as a tube ( 11 ), is not greater than 10 percent of a radius (R) of the tube ( 11 ).