Abstract: A friction stir welding tool for welding high-strength materials with one or more of the following features: 1) a curved transition geometry structure at the shoulder face and probe interface; 2) a tool material selected on the basis of an ultimate tensile strength determined at or above the temperature of the tool processing temperature; 3) a compressive stress at the point of crack fatigue introduced by mechanical or chemical means; and 4) a threaded probe with a) a major to minor thread diameter ratio that increases toward the distal end of the probe and/or b) with a curved thread root.

Abstract: A radiused corner support plate is used to form a corner void when making L- and T-corner welds that are filled with plasticized work piece material during friction stir welding to form a filleted corner weld. An improved friction stir welding tool uses either disrupting features such as crossed rectangular grooves in the distal tip end or a curved tip region or both to improve plasticized work piece material flow below the distal end and in the region of the fillet.