Patent ID: 6840426

Claim:
A friction stir welding method for friction stir welding a first member and a second member, said first member having a first plate, a second plate disposed substantially parallel to said first plate, and a third plate connecting an end portion of said first plate and said second plate, said third plate being disposed substantially orthogonal to said first plate, comprising the steps of: arranging a recessed portion in connection portion between said third plate and said first plate; opening said recessed portion directed toward an outer side of a thickness direction of said first member and toward said end portion of said first member; overlapping an end portion of said second member to said recessed portion, to provide an overlapped portion; and in a condition where said first member and said second member in said overlapped portion are supported, and in a condition where a rotary tool is inserted into said overlapped portion from said outer side, carrying out friction stir welding of said overlapped portion.