FRICTION STIR WELDING TOOL, FRICTION STIR WELDING DEVICE, AND FRICTION STIR WELDING METHOD

1 . A friction stir welding tool comprising:

a first face which is rotated about an axis relative to a joined portion in a state in which the first face comes into contact with the joined portion of a workpiece and in which an arithmetic mean roughness Ra value is greater than or equal to 0.8 μm and less than or equal to 25 μm; and

a second face which is formed to continue to the first face, which is rotated about the axis relative to the joined portion in a state in which the second face comes into contact with the joined portion, and in which an arithmetic mean roughness Ra value is smaller than that of the first face.

2 . The friction stir welding tool according to claim 1 , wherein the arithmetic mean roughness Ra value of the first face is greater than or equal to 1.6 μm and less than or equal to 25 μm.

3 . The friction stir welding tool according to claim 1 , wherein the arithmetic mean roughness Ra value of the first face is greater than or equal to 3.2 μm and less than or equal to 25 μm.

4 . The friction stir welding tool according to claim 1 , further comprising:

a probe inserted into the joined portion of the workpiece at a time of joining, having a columnar shape formed about an axis, and rotating about the axis; and

a shoulder with a columnar shape formed about the axis, rotated together with the probe, and having a shoulder surface pressed against a surface of the workpiece at the time of joining,

wherein the first face and the second face are formed in an outer circumferential surface of the probe to be adjacent to each other in the circumferential direction.

5 . The friction stir welding tool according to claim 1 , wherein a spiral groove with a spiral shape extending to one direction along the axis as going toward the circumferential direction of the probe is formed in the second face.

6 . The friction stir welding tool according to claim 1 , comprising:

a probe inserted into the joined portion of the workpiece at a time of joining, having a columnar shape formed about an axis, and rotating about the axis; and

a shoulder with a columnar shape formed about the axis, rotated together with the probe, and having a shoulder surface pressed against a surface of the workpiece at the time of joining,

wherein the first face and the second face are formed in the shoulder surface to be adjacent to each other in the circumferential direction.

7 . The friction stir welding tool according to claim 6 , wherein a spiral groove with a spiral shape is formed extending outward in a radial direction of the axis as going toward the front of a direction of rotation of the shoulder in the circumferential direction in the shoulder surface,

the first face is a surface of the shoulder surface other than a position at which the spiral groove is formed, and

the second face is an inner surface of the spiral groove.

8 . A friction stir welding device comprising:

the friction stir welding tool according to claim 1 ; and

a device main body configured to hold the friction stir welding tool and to rotate the friction stir welding tool relative to the workpiece.

9 . A friction stir welding method comprising:

a tool contact step of bringing a first face of a friction stir welding tool of which an arithmetic mean roughness Ra value is greater than or equal to 0.8 μm and less than or equal to 25 μm into contact with a joined portion of a workpiece and bringing a second face of the friction stir welding tool, which continues to the first face and of which an arithmetic mean roughness Ra value is smaller than that of the first face, into contact with the joined portion; and

a rotating step of rotating the first face and the second face relative to the joined portion.