Butt welding method and friction stir welding tool

A method for butt welding a first material piece of metal to a second material piece of metal at opposed longitudinal edges, using a friction stir welding tool wherein the second material piece has a greater material thickness than the first material piece and the first material piece is made of a material having at least one of a higher tensile strength, a higher melting temperature, a higher yield strength and a higher modulus of elasticity than the second material piece, comprising the following steps:

• a) Providing a thickened longitudinal edge at the first material piece for locally increasing the material thickness of the first material piece at the longitudinal edge, wherein the thickening of the longitudinal edge is at least partly produced by one of simple folding, beading or winding of the first material piece or is at least partly produced by folding the first material piece on itself at its edge, and
• b) Friction stir welding of the two material pieces along the longitudinal edges facing each other at their front, wherein the friction stir welding tool includes a rotating pin which in the region of the opposed longitudinal edges penetrates essentially only into the second material piece, and wherein the first material piece is made of a steel and the second material piece is made of one of a light metal, transition metal and their alloys.

A method for butt welding a first material piece of metal to a second material piece of metal at opposed longitudinal edges, using a friction stir welding tool wherein the second material piece has a greater material thickness than the first material piece and the first material piece is made of a material having at least one of a higher tensile strength, a higher melting temperature, a higher yield strength and a higher modulus of elasticity than the second material piece, comprising the following steps:

• a) Providing a thickened longitudinal edge at the first material piece for locally increasing the material thickness of the first material piece at the longitudinal edge, wherein the thickening of the longitudinal edge is at least partly produced by one of simple folding, beading or winding of the first material piece or is at least partly produced by folding the first material piece on itself at its edge, wherein the second material piece remains unfolded, and
• b) Friction stir welding of the two material pieces along the longitudinal edges facing each other at their front, wherein the thickness extends along a direction which is substantially parallel to an axis of rotation of the friction stir welding tool used for friction stir welding, wherein the friction stir welding tool has a pin which is pressed only into the second material piece.