Tube coupling and a method for forming a tube coupling

1. A tube coupling defining an axial direction, a radial direction and a circumferential direction, the tube coupling comprising:

an aluminum tube; and

a copper tube extending between a first end portion and a second end portion along the axial direction, the copper tube positioned within the aluminum tube at the first end portion of the copper tube, the copper tube and the aluminum tube defining a metallurgical joint therebetween at the first end portion of the copper tube, the metallurgical joint comprising a eutectic region and an intermetallic region, the eutectic region of the metallurgical joint extending along the radial direction between the aluminum tube and the intermetallic region of the metallurgical joint, the intermetallic region of the metallurgical joint extending along the radial direction between the eutectic region of the metallurgical joint and the copper tube,

wherein the eutectic region and the intermetallic region of the metallurgical joint extend about the copper tube along the circumferential direction wherein the eutectic region of the metallurgical joint comprises more than thirty percent copper by weight and less than forty percent copper by weight and the eutectic region of the metallurgical joint comprises less than seventy percent aluminum by weight and more than sixty percent aluminum by weight, the intermetallic region of the metallurgical joint comprises more than fifty percent copper by weight and less than sixty percent copper by weight and the intermetallic region of the metallurgical joint comprises less than fifty percent aluminum by weight and more than forty percent aluminum by weight.

2. The tube coupling of claim 1 , wherein the eutectic region of the metallurgical joint defines a length along the axial direction, the length of the eutectic region being greater than one sixteenth of an inch, the intermetallic region of the metallurgical joint defining a length along the axial direction, the length of the intermetallic region being greater than one sixteenth of an inch.

3. The tube coupling of claim 1 , wherein the eutectic region of the metallurgical joint defines a thickness along the radial direction, the thickness of the eutectic region being greater than one ten-thousandths of an inch, the intermetallic region of the metallurgical joint defining a thickness along the radial direction, the thickness of the intermetallic region being less than the thickness of the eutectic region.

4. An evaporator for a hot water heater appliance comprising the tube coupling of claim 1 .

5. A method for forming a tube coupling, comprising:

positioning a copper tube adjacent an aluminum tube such that the copper tube extends between a first end portion and a second end portion along the axial direction and is in axial alignment with the aluminum tube;

heating at least one of the copper tube and the aluminum tube to at least a eutectic temperature of aluminum and copper;

urging the copper tube and the aluminum tube together such that the first end portion of the copper tube is disposed within the aluminum tube;

cooling the copper tube and the aluminum tube in order to form a metallurgical joint between the copper tube and the aluminum tube; and

annealing the copper tube and the aluminum tube after said step of cooling, the metallurgical joint having a eutectic region and an intermetallic region after said step of annealing, the eutectic region of the metallurgical joint positioned between the aluminum tube and the intermetallic region of the metallurgical joint along a radial direction of the tube coupling, the intermetallic region of the metallurgical joint positioned between the eutectic region of the metallurgical joint and the copper tube along the radial direction of the tube coupling, the eutectic region and the intermetallic region of the metallurgical joint extending about the copper tube along the circumferential direction wherein the eutectic region of the metallurgical joint comprises more than thirty percent copper by weight and less than forty percent copper by weight and the eutectic region of the metallurgical joint comprises less than seventy percent aluminum by weight and more than sixty percent aluminum by weight after said step of annealing, the intermetallic region of the metallurgical joint comprising more than fifty percent copper by weight and less than sixty percent copper by weight and the intermetallic region of the metallurgical joint comprises less than fifty percent aluminum by weight and more than forty percent aluminum by weight after said step of annealing.

6. The method of claim 5 , wherein said step of annealing comprises heating the copper tube and the aluminum tube to a particular temperature and maintaining the copper tube and the aluminum tube at the particular temperature for a period of time.

7. The method of claim 6 , wherein said step of annealing comprises heating the copper tube and the aluminum tube to the particular temperature in an inert atmosphere.

8. The method of claim 6 , wherein the particular temperature is greater than five hundred degrees Fahrenheit and less than seven hundred degrees Fahrenheit.

9. The method of claim 8 , wherein the period of time is greater than thirty minutes and less than twenty-four hours.

10. The method of claim 6 , wherein the period of time is greater than thirty minutes and less than twenty-four hours.

11. The method of claim 5 , wherein the eutectic region of the metallurgical joint defines a thickness along the radial direction, the thickness of the eutectic region being greater than one ten-thousandths of an inch after said step of annealing, the intermetallic region of the metallurgical joint defining a thickness along the radial direction, the thickness of the intermetallic region being less than the thickness of the eutectic region after said step of annealing.

12. The method of claim 11 , wherein the thickness of the intermetallic region is less than one tenth of the thickness of the eutectic region after said step of annealing.

13. The method of claim 5 , further comprising mounting the aluminum tube to an evaporator of a hot water heater appliance.

14. The method of claim 13 , Wherein said step of mounting comprises brazing the aluminum tube to the evaporator of the hot water heater appliance.

15. An evaporator for a hot water heater appliance, comprising

an aluminum evaporator conduit having an opening, the opening of the aluminum evaporator conduit configured for directing refrigerant therethrough; and

a jumper tube positioned adjacent the aluminum evaporator conduit, the jumper tube defining an axial direction and a radial direction, the jumper tube comprising

an aluminum tube mounted to the aluminum evaporator conduit at the opening of the aluminum evaporator conduit; and

a copper tube extending between a first end portion and a second end portion along the axial direction, the copper tube positioned within the aluminum tube at the first end portion of the copper tube, the copper tube and the aluminum tube defining a metallurgical joint therebetween at the first end portion of the copper tube, the metallurgical joint comprising a eutectic region and an intermetallic region, the eutectic region of the metallurgical joint positioned between the aluminum tube and the intermetallic region of the metallurgical joint along the radial direction, the intermetallic region of the metallurgical joint positioned between the eutectic region of the metallurgical joint and the copper tube along the radial direction,

wherein the eutectic region and the intermetallic region of the metallurgical joint extend about the copper tube along the circumferential direction wherein the eutectic region of the metallurgical joint comprises more than thirty percent copper by weight and less than forty percent copper by weight and the eutectic region of the metallurgical joint comprises less than seventy percent aluminum by weight and more than sixty percent aluminum by weight, the intermetallic region of the metallurgical joint comprises more than fifty percent copper by weight and less than sixty percent copper by weight and the intermetallic region of the metallurgical joint comprises less than fifty percent aluminum by weight and more than forty percent aluminum by weight.

16. The evaporator of claim 15 , wherein the eutectic region of the metallurgical joint defines a length along the axial direction, the length of the eutectic region being greater than one sixteenth of an inch, the intermetallic region of the metallurgical joint defining a length along the axial direction, the length of the intermetallic region being greater than one sixteenth of an inch.

17. The evaporator of claim 15 , wherein the eutectic region of the metallurgical joint defines a thickness along the radial direction, the thickness of the eutectic region being greater than one ten-thousandths of an inch, the intermetallic region of the metallurgical joint defining a thickness along the radial direction, the thickness of the intermetallic region being less than the thickness of the eutectic region.