| 摘要 |
A method for forming a good weld portion by two processes when members having different thicknesses are abutted and friction stir welded is provided. In a method for friction stir welding a butt portion(30) having a height difference formed by abutting a first member(10) with a higher height and a second member(20) with a lower height to one another, the friction stir welding method comprises: forming a convex on the top surface of the second member by moving the rotating convex forming tool relatively with respect to the first and second members and moving a metal of the first member side to a top surface(20a) of the second member side while rotating a rotating convex forming tool(100) using a round-bar shaped convex forming tool having a front end portion(101) whose end face(110) is substantially flat; and performing friction stir welding by inserting a rotating tool for friction stir welding from an upper side of the convex of the second member and the first member and moving the rotating tool relatively with respect to the first and second members in a state in which a boundary between a large diameter portion of the rotating tool and a small diameter portion at the front end of the rotating tool is positioned within a height range of the convex.
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