Aluminum alloy pipe having multistage formability

1. An aluminum alloy pipe, which is composed of an aluminum alloy comprising

2.0% (% by mass, the same hereinafter) to 3.0% of Mg,

0.20% or less of Si,

0.30% or less of Fe,

0.8% or less (including 0%) of Mn,

0.35% or less (including 0%) of Cr, and

0.2% or less (including 0%) of Ti,

with the balance being Al and inevitable impurities,

wherein the aluminum alloy pipe has no welded portion, wherein the aluminum alloy pipe has a 0.2% yield strength of 60 MPa or more and 160 MPa or less and an average crystal grain diameter of 150 μm or less, and wherein the aluminum alloy pipe has multistage formability.

2. The aluminum alloy pipe according to claim 1 , wherein a distribution density of an intermetallic compound with a maximum length of 5 μm or more is 500/mm 2 or less.

3. The aluminum alloy pipe according to claim 1 , wherein a thickness of a pipe wall at a portion that comes to the outside after bending is larger than a thickness of a pipe wall at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

4. The aluminum alloy pipe according to claim 1 , wherein a wall surface that comes to the inside after bending, and a wall surface that comes to the outside after bending, each have an approximately linear side, and wherein a length of the side at a portion that comes to the outside after bending, is longer than a length of the side at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

5. The aluminum alloy pipe according to claim 1 , which is flanged.

6. An aluminum alloy pipe, which is composed of an aluminum alloy comprising

2.0% to 3.0% of Mg,

0.10% or less of Si,

0.15% or less of Fe,

0.8% or less (including 0%) of Mn,

0.35% or less (including 0%) of Cr, and

0.2% or less (including 0%) or Ti,

with the balance being Al and inevitable impurities,

wherein the aluminum alloy pipe has no welded portion,

wherein the aluminum alloy pipe has a 0.2% yield strength of 60 MPa or more and 140 MPa or less and an average crystal grain diameter of 150 μm or less, and

wherein the aluminum alloy pipe has multistage formability.

7. The aluminum alloy pipe according to claim 6 , wherein a distribution density of an intermetallic compound with a maximum length of 5 μm or more is 500/mm 2 or less.

8. The aluminum alloy pipe according to claim 6 , wherein a thickness of a pipe wall at a portion that comes to the outside after bending is larger than a thickness of a pipe wall at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

9. The aluminum alloy pipe according to claim 6 , wherein a wall surface that comes to the inside after bending, and a wall surface that comes to the outside after bending, each have an approximately linear side, and wherein a length of the side at a portion that comes to the outside after bending, is longer than a length of the side at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

10. The aluminum alloy pipe according to claim 6 , which is flanged.

11. An aluminum alloy pipe, which is composed of an aluminum alloy comprising

2.0% (% by mass, the same hereinafter) to 3.0% of Mg,

0.20% or less of Si,

0.30% or less of Fe,

0.8% or less (including 0%) of Mn,

0.35% or less (including 0%) of Cr, and

0.2% or less (including 0%) of Ti,

with the balance being Al and inevitable impurities,

wherein the aluminum alloy pipe has no welded portion, wherein the aluminum alloy pipe has a 0.2% yield strength of 60 MPa or more and 160 MPa or less and an average crystal grain diameter of 150 μm or less, and wherein the aluminum alloy pipe has multistage formability;

wherein the test to determine multistage formability is:

bending a sample of the alloy using a draw bender of 150 mm bend radius and 90 degrees bend angle;

hot mandrel extruding the alloy at an extrusion ratio of 47 at 490° C. and 5 m/minute into round cylindrical pipes of outer diameter 80 mm and thickness 4 mm;

annealing the cylindrical pipes 360° C. for 2 hours;

bending the alloy pipe using a draw bender of 150 mm bend radius and 90 degree bend angle;

cutting a test piece from the bent portion,

pressing the test piece to measure a height h (mm) of the test piece at which cracks occur; calculating flattening ratio L=(H−h)/H, wherein H (mm) denotes the initial height of the test piece;

and determining that a sample has multistage formability when a sample has a flattening ratio of 60% or greater.

12. The aluminum alloy pipe according to claim 11 , wherein a distribution density of an intermetallic compound with a maximum length of 5 μm or more is 500/mm 2 or less.

13. The aluminum alloy pipe according to claim 11 , wherein a thickness of a pipe wall at a portion that comes to the outside after bending is larger than a thickness of a pipe wall at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

14. The aluminum alloy pipe according to claim 11 , wherein a wall surface that comes to the inside after bending, and a wall surface that comes to the outside after bending, each have an approximately linear side, and wherein a length of the side at a portion that comes to the outside after bending, is longer than a length of the side at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

15. The aluminum alloy pipe according to claim 11 , which is flanged.

16. An aluminum alloy pipe, which is composed of an aluminum alloy comprising

2.0% to 3.0% of Mg,

0.10% or less of Si,

0.15% or less of Fe,

0.8% or less (including 0%) of Mn,

0.35% or less (including 0%) of Cr, and

0.2% or less (including 0%) or Ti,

with the balance being Al and inevitable impurities,

wherein the aluminum alloy pipe has a 0.2% yield strength of 60 MPa or more and 140 MPa or less and an average crystal grain diameter of 150 μm or less,

wherein the aluminum alloy pipe has no welded portion, and

wherein the aluminum alloy pipe has multistage formability;

wherein the test to determine multistage formability is:

bending a sample of the alloy using a draw bender of 150 mm bend radius and 90 degrees bend angle;

hot mandrel extruding the alloy at an extrusion ratio of 47 at 490° C. and 5 m/minute into round cylindrical pipes of outer diameter 80 mm and thickness 4 mm;

annealing the cylindrical pipes 360° C. for 2 hours;

bending the alloy pipe using a draw bender of 150 mm bend radius and 90 degree bend angle;

cutting a test piece from the bent portion,

pressing the test piece to measure a height h (mm) of the test piece at which cracks occur; calculating flattening ratio L=(H−h)/H, wherein H (mm) denotes the initial height of the test piece;

and determining that a sample has multistage formability when a sample has a flattening ratio of 60% or greater.

17. The aluminum alloy pipe according to claim 16 , wherein a distribution density of an intermetallic compound with a maximum length of 5 μm or more is 500/mm 2 less.

18. The aluminum alloy pipe according to claim 16 , wherein a thickness of a pipe wall at a portion that comes to the outside after bending is larger than a thickness of a pipe wall at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

19. The aluminum alloy pipe according to claim 16 , wherein a wall surface that comes to the inside after bending, and a wall surface that comes to the outside after bending, each have an approximately linear side, and wherein a length of the side at a portion that comes to the outside after bending, is longer than a length of the side at a portion that comes to the inside after bending, in a cross section of the pipe in a pipe's circumference direction.

20. The aluminum alloy pipe according to claim 16 , which is flanged.