Friction stir welding method for metal material and metal material welded body obtained thereby

A friction stir welding method for a metal material longitudinally welding the members to be butted and then welded, each of the members having rectangular sectional shape to be welded, the welding method comprising:

• preparing members to be welded having rectangular sectional shape each having four side surfaces and formed with excess thickness portions and a welding tool provided with a probe for welding the members to be welded while rotating the welding tool in a manner of abutting against the members to be welded, the excess thickness portions being formed so as to protrude on extension surfaces of side surfaces of the rectangular member which at least includes an excess thickness portion formed at least one side surface of an extension surface of a first side of the four side surfaces of the rectangular members and on welding step for welding the rectangular members each having four side surfaces and a terminating side one surface of an extension surface of another surface subsequent to the welding of the first side surface;
• performing a first welding to the members to be welded so as to weld the four butt surfaces of the members to be welded along one side and terminating the butt welding by using the welding tool along the one side surfaces and terminating the first welding immediately before the excess thickness portions;
• inserting the welding tool from the excess thickness portion to cause plastic flow of the metal material subsequent to the butt welding along the one side to thereby fill a probe hole remaining in the first welding step after removing the probe from the first welding side surface of the members to be welded;
• performing second welding continuously from the filling step along a lateral side continuous to the one side mentioned previously in the preparing step of the members to be welded after removing the prove from the next welding side surface of the members to be welded;
• performing another first welding, as a first welding of a second welding step, of welding the butt surfaces of the members to be welded along another side opposite to the previous one side after termination of the second welding and terminating the butt welding along the another side immediately before a next excess thickness portion;
• inserting the welding tool from a next excess thickness portion to cause plastic flow of a material subsequent to the butt welding along the another side opposing to the previous one side to thereby fill a probe hole remaining after the another first welding as first welding of the second welding step;
• and
• performing another second welding, as second welding of the second welding step, of butt-welding continuously from the another filling step, along another lateral side continuous to the another side,
• wherein in the second welding step and the another second welding step, the butt welding along the lateral side is terminated at a center portion of the lateral side by stopping the welding tool in mid-course or by stopping the welding tool after turning back the welding tool from a lateral edge.

A friction stir welding method for a metal material for longitudinally welding butted members to be welded having rectangular sectional shape, the welding method comprising:

• preparing members to be welded having rectangular sectional shape each having four sides and formed with excess thickness portions and a welding tool provided with a probe for welding the members to be welded while rotating the welding tool in a manner of abutting against the members to be welded, the excess thickness portions being formed so as to protrude on extension surfaces of side weld end portions of four butting side surfaces of the members to be welded, respectively;
• performing a first welding to the members to be welded so as to weld the four butting side surfaces of the members to be welded along one side and terminating the butt welding by using the welding tool along the one side surfaces of the members to be welded and terminating the first welding immediately before first excess thickness portions;
• inserting the welding tool from the excess thickness portion to cause plastic flow of the metal material subsequent to the butt-welding along the one side to thereby fill a probe hole remaining in the first welding step after removing the probe from the members;
• performing second welding continuously from the filling step along a lateral side continuous to the one side mentioned previously in the preparing step of the members to be welded, and terminating the butt-welding to the continuous lateral side immediately before a second excess thickness portion;
• inserting the welding tool from the second excess thickness portion to cause plastic flow of a material subsequent to the butt welding along the another side opposing to the previous one side to thereby fill a probe hole remaining after the another first welding;
• performing a third welding of welding the butting surfaces of the members to be welded along another side opposite to the previous one side after the termination of filling the probe hole remaining in the second welding and terminating the butt welding along the another side immediately before a third excess thickness portion;
• inserting the welding tool from the third excess thickness portion to cause plastic flow of a material subsequent to the butt welding along the another side to thereby fill a prove hole remaining the another side surface after the third welding step;
• and
• welding the butt surfaces of the members to be welded along another lateral side opposite to the previous lateral side continuously from the another-side probe hole filling step, and terminating the butt welding along the another lateral side at a center portion of the another lateral side by stopping the welding tool in mid-course or by stopping the welding tool after turning back the welding tool from a lateral edge.