Patent ID: 8479971

Claim:
A joining method comprising: a butting step in which metal members to be joined are butted against each other to form a butting portion between the metal members; a tab member disposing step in which a first tab member and a second tab member are disposed on both sides of the butting portion between the metal members; a first tab member joining step in which the butting portion between the metal members and the first tab member is friction stir welded from a first surface; a preliminary joining step in which the butting portion between the metal members is preliminarily friction stir welded from the first surface; a second tab member joining step in which the butting portion between the metal members and the second tab member is friction stir welded from the first surface; a first primary welding step in which the butting portion preliminarily joined between the metal members is friction stir welded using a first rotating tool with a first stirring pin from the first surface of the metal members, and the first rotating tool used in the first primary welding step reaches an end position on the first surface of the first tab member or the second tab member where the first rotating tool is moved up to withdraw the first stirring pin from the end position; and a second primary welding step in which the butting portion between the metal members is friction stir welded using a second rotating tool with a second stirring pin from a back surface of the metal members, opposite said first surface, wherein, in the second primary welding step, friction stir welding is performed while inserting the second stirring pin of the second: rotating tool into a plasticized region formed through the first primary welding step.