Abstract: Sections 1 and 2 each in the form of a welded pipe (square pipe) are provided. The sections 1 and 2 are brought into abutment with each other so that the respective end faces 3a and 3b abut each other at a predetermined angle .beta. between each section and its axial direction. The sections 1 and 2 are arranged symmetrically with respect to each other. Acute end portions of the abutted portion are chamfered to from a plane part. Corners of the sections 1 and 2 are rounded. In such a combined state of both sections, the abutted portion is welded in the circumferential direction to form a weld bead. As a result, penetration of weld metal to the section 1 and that to the section 2 become equal to each other. Thus, it becomes possible to fabricate a welded structure having a uniform weld bead and having improved strength and reliability of welded portions.

Abstract: A joint member is used for positioning a first square tubular section made of aluminum or aluminum alloy and a second square tubular section made of aluminum or aluminum alloy with the sections' end portions butting against each other so as to weld the butt end portions together. The joint member includes an angle retainment portion and first and second anchorage portions. The angle retainment portion is applied onto the outer or inner surfaces of walls of the first and second square tubular sections, the walls intersecting each other with an angle equal to or smaller than 180.degree. when the first and second tubular sections are caused to butt against each other. The first and second anchorage portions branch off and extend from the angle retainment portion so as to fixedly hold the walls of the first and second square tubular sections, respectively, in cooperation with the angle retainment portion.

Abstract: A method of vertical welding of aluminum and aluminum alloys comprising welding Al or an Al alloy while oscillating in a welding groove an electrode in a closed pattern corresponding substantially to the groove shape, wherein the welding is conducted by using a welding current higher by 10 to 150 A than the base welding current at least during the course of oscillation of the electrode along the groove face of one of the materials to be welded while the electrode is pursuing courses of oscillation along both groove faces of the materials to be welded.