Friction stir welding process for large metallic components

A method for forming a metallic component comprising:

• positioning a first metallic plate and a second metallic plate in an abutting arrangement, the first metallic plate and the second metallic plate having corresponding faying surfaces at a point of abutment;
• attaching a backing plate spanning the point of abutment adjacent the faying surfaces;
• friction stir welding the first metallic plate to the second metallic plate to form a friction stir weld along the faying surfaces, the backing plate receiving an end of a friction stir welding tool during the friction stir welding, the friction stir welding tool forming a weld root in the backing plate;
• removing the backing plate, including the weld root, prior to exposure to elevated temperatures including an elevated temperature forming, a heat treatment and an aging to form a welded blank;
• forming the welded blank into a component form;
• and
• the heat treatment and the aging of the component form;
• wherein the removing the backing plate including the weld root prior to the elevated temperature forming, the heat treatment and the aging results in a stable microstructure in the component form having no abnormal grain growth during the heat treatment and the aging and the second metallic plate include an F temper.