Joining method

1. A joining method of joining a first metal member with a second metal member by friction stir welding using a joining rotating tool which includes a stirring pin, at least an edge of each of the first metal member and the second metal member being formed to have a U-shaped cross section with a first horizontal plate projecting from a base edge of a first side surface of a vertical plate, and with a second horizontal plate projecting from a top edge of the first side surface of the vertical plate, the second metal member including a projecting part projecting from the top edge of the vertical plate in a longitudinal direction of the vertical plate,

the joining method comprising:

an abutting step of forming an abutted part by abutting a front surface of the first horizontal plate of the first metal member against a second side surface of the vertical plate of the second metal member with a second side surface of the vertical plate of the first metal member and a front surface of the first horizontal plate of the second metal member made flush with each other; and

a joining step of performing friction stir welding to the abutted part between the first metal member and second metal member by inserting the stirring pin from the projecting part and moving the joining rotating tool along an inner corner at the top edge of the vertical plate of the second metal member while making only the stirring pin in contact with the first metal member and the second metal member.

2. A joining method of joining a first metal member with a second metal member by friction stir welding using a joining rotating tool which includes a stirring pin, at least an edge of each of the first metal member and the second metal member being formed to have a U-shaped cross section with a first horizontal plate projecting from a base edge of a first side surface of a vertical plate and with a second horizontal plate projecting from a top edge of the first side surface of the vertical plate, the first metal member including a projecting part projecting outward from a front surface of the first horizontal plate,

the joining method comprising:

an abutting step of forming an abutted part by abutting the front surface of the first horizontal plate of the first metal member against a second side surface of the vertical plate of the second metal member with a second side surface of the vertical plate of the first metal member and a front surface of the first horizontal plate of the second metal member made flush with each other and with the projecting part of the first horizontal plate of the first metal member engaged with the top edge of the vertical plate of the second metal member; and

a joining step of performing friction stir welding to the abutted part between the first metal member and the second metal member by inserting the stirring pin from the projecting part and moving the joining rotating tool along an inner corner at the top edge of the vertical plate of the second metal member while making only the stirring pin in contact with the first metal member and the second metal member.

3. The joining method set forth in claim 2 ,

wherein the second metal member includes a notch part in the top edge of the vertical plate, and

wherein in the abutting step the projecting part of the first metal member is engaged with the notch part of the second metal member.

4. A joining method of joining a first metal member with a second metal member by friction stir welding using a joining rotating tool which includes a stirring pin, at least an edge of each of the first metal member and the second metal member being formed to have a U-shaped cross section with a first horizontal plate projecting from a base edge of a first side surface of a vertical plate and with a second horizontal plate projecting from a top edge of the vertical plate, the first metal member including a first projecting part projecting outward from a front surface of the first horizontal plate, the second metal member including a second projecting part projecting from a top edge of the vertical plate in a longitudinal direction of the vertical plate,

the joining method comprising:

an abutting step of forming an abutted part by abutting the front surface of the first horizontal plate of the first metal member against a second side surface of the vertical plate of the second metal member with a second side surface of the vertical plate of the first metal member and a front surface of the first horizontal plate of the second metal member made flush with each other and with the first projecting part of the first horizontal plate of the first metal member abutted against the second projecting part of the top edge of the vertical plate of the second metal member; and

a joining step of performing friction stir welding to the abutted part between the first metal member and the second metal member by inserting the stirring pin from the first projecting part and the second projecting part and moving the joining rotating tool along an inner corner at the top edge of the vertical plate of the second metal member while making only the stirring pin in contact with the first metal member and the second metal member.

5. The joining method as set forth in claim 1 ,

wherein the first metal member and the second metal member are each an extruded member.

6. The joining method as set forth in claim 2 ,

wherein the first metal member and the second metal member are each an extruded member.

7. The joining method as set forth in claim 4 ,

wherein the first metal member and the second metal member are each an extruded member.