Abstract: A joining method of a pair of workpieces, each workpiece having a non-flat portion and an abutting surface continuous to the non-flat portion, wherein the method provides an extension portion on each of the workpieces, the extension portion having a surface continuous with the non-flat portion and the abutting surface and projecting outward from the workpiece, and holding the workpieces so as to form a joining line between the non-flat portions of the respective workpieces by bringing the abutting surfaces thereof into contact with each other. Also disclosed is a joining tool having a substantially cylindrical shoulder portion and a projection projecting outward from a tip surface of the shoulder portion.

Abstract: A friction stir welding performed by preparing a pair of members to be welded, each including an abutment surface and a margin portion provided in an extended manner, the margin portion including a welding surface that is continuous to the abutment surface by using a welding tool for performing friction stir welding. The welding tool integrally includes a columnar shoulder portion and a probe portion formed on a leading end surface of the shoulder portion, the probe portion having a diameter smaller than a diameter of the shoulder portion. The abutment surfaces and the welding surfaces are brought into contact with each other so as to form a continuous welding line therebetween.

Abstract: A joining method of a pair of workpieces, each workpiece having a non-flat portion and an abutting surface continuous to the non-flat portion, wherein the method provides an extension portion on each of the workpieces, the extension portion having a surface continuous with the non-flat portion and the abutting surface and projecting outward from the workpiece, and holding the workpieces so as to form a joining line between the non-flat portions of the respective workpieces by bringing the abutting surfaces thereof into contact with each other. Also disclosed is a joining tool having a substantially cylindrical shoulder portion and a projection projecting outward from a tip surface of the shoulder portion.