Seamless composite metal tube and method of manufacturing the same
A seamless composite metal tube comprises an inner layer ( 1 ) consisting of copper or a copper alloy, an outer layer ( 5 ) consisting of aluminium or an aluminium alloy, and at least three different intermediate intermetallic layers ( 2, 3, 4 ) each consisting of copper and aluminium, wherein the concentration of copper decreases from the inner layer ( 1 ) to the outer layer ( 5 ) in the radial direction of the tube.
1. A seamless composite metal tube comprising an inner layer consisting of copper or a copper alloy, an outer layer consisting of aluminium or an aluminium alloy, and at least three different intermediate intermetallic layers each consisting of copper and aluminium, wherein the concentration of copper decreases from the inner layer to the outer layer in the radial direction of the tube.
2. The seamless composite metal tube according to claim 1 , wherein the inner intermediate intermetallic layer comprises 79-85 wt % of copper and 21-15 wt % of aluminium, the middle intermediate intermetallic layer comprises 69-73 wt % of copper and 31-27 wt % of aluminium, and the outer intermediate intermetallic layer comprises 50-55 wt % of copper and 50-45 wt % of aluminium.
3. The seamless composite metal tube according to claim 1 , wherein the inner intermediate intermetallic layer consists of copper and aluminium being in the γ-phase, the middle intermediate intermetallic layer consists of copper and aluminium being in the η-phase, and the outer intermediate intermetallic layer consists of copper and aluminium being in the θ-phase.
4. The seamless composite metal tube according to of claim 1 , wherein each of the intermediate intermetallic layers has a thickness in the radial direction of the tube between 0.5 μm to 4.0 μm, and/or the sum of the thicknesses of the intermediate intermetallic layers in the radial direction of the tube is between 1.5 μm to 12 μm.
5. The seamless composite metal tube according to claim 1 , wherein the thickness of the outer intermediate intermetallic layer is at least twice as much as the thickness of the inner intermediate intermetallic layer in the radial direction of the tube.
6. The seamless composite metal tube according to claim 1 , wherein the thickness ratio of the inner layer and the outer layer in the radial direction of the tube is between 0.1 and 0.8.
7. A method of manufacturing a seamless composite metal tube comprising the steps of:
heat-activating the outer surface of a seamless tube made of copper or a copper alloy, and
extruding a tubular layer of aluminium or an aluminium alloy directly onto the heat-activated outer surface of the seamless tube made of copper or a copper alloy thereby producing a seamless composite metal tube.
8. Method according to claim 7 , wherein the produced seamless composite metal tube is a seamless composite metal tube comprising an inner layer consisting of copper or a copper alloy, an outer layer consisting of aluminium or an aluminium alloy, and at least three different intermediate intermetallic layers each consisting of copper and aluminium, wherein the concentration of copper decreases from the inner layer to the outer layer in the radial direction of the tube.
9. The method according to claim 7 , wherein the step of extruding is performed by continuously passing the seamless tube made of copper or a copper alloy through an extrusion die and continuously extruding the tubular layer of aluminium or an aluminium alloy by means of the extrusion die.
10. The method according to claim 7 , wherein the temperature of the heat-activated outer surface is between 350 degrees to 450 degrees C.
11. The method according to claim 7 , wherein the heat-activating is performed by induction heating under a protective atmosphere.
12. The method according to claim 7 , wherein the extrusion temperature of the aluminium or aluminium alloy is between 400 degrees to 550 degrees C.
13. The method according to claim 7 , further comprising, subsequent to the step of extruding, the step of cooling the composite metal tube by forced convection.
14. The method according to claim 13 , wherein a cooling time is set in a range from 5 to 60 sec.
15. The method according to claim 13 , further comprising, subsequent to the step of cooling, the step of passing the composite metal tube through a diameter reducing device or a diameter and wall thickness reducing device for reducing its outer diameter or its outer diameter and wall thickness by cold working.
16. The method according to claim 7 , wherein the heat-activating is performed by induction heating under a protective nitrogen atmosphere.
17. The method according to claim 7 , further comprising:
subsequent to the step of extruding, the step of cooling the composite metal tube by forced convection by means of a cooling tube comprising internal fluid spray nozzles and/or fluid spray passages for spraying water onto the composite metal tube when being passed through the interior of the cooling tube.
18. The method according to claim 7 , further comprising:
subsequent to the step of extruding, the step of cooling the composite metal tube by forced convection by means of a cooling tube comprising internal fluid spray nozzles and/or fluid spray passages for spraying water onto the composite metal tube when being passed through the interior of the cooling tube, wherein the composite metal tube is cooled down to below 80 degrees C.
19. The method according to claim 13 , wherein a cooling rate is between 5 to 100 degrees C./sec.