Patent ID: 8672212

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 a butting portion between the metal members and the first tab member is friction stir welded from a back surface; a preliminary joining step in which the butting portion between the metal members is preliminarily friction stir welded from the back surface; a second tab member joining step in which a butting portion between the metal members and the second tab member is friction stir welded from the back surface; a pilot bore forming step in which a pilot bore is formed at the back surface of either one of the first tab member and the second tab member; a first primary welding step in which the butting portion between the metal members is friction stir welded using a first rotating tool with a first stirring pin from a first surface of the metal members, opposite said back surface; and a second primary welding step in which a second stirring pin of a second rotating tool is inserted into said pilot bore, and the butting portion preliminarily joined between metal members is friction stir welded from the back surface of the metal members, 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.