Tool geometry dependence of local texture in friction stir welds of 7050 aluminum plate

Friction stir welding employs tortuous thermomechanical deformation during solid state joining of materials. The severe textural heterogeneity both across the width and through the thickness of the weld nugget and surrounding regions has been previously reported. Much of the research into friction stir welding processes involves optimization of tool geometry. The present work investigates the character of crystallographic textures as a function of tool geometry. Three tool geometries are employed: a standard threaded pin, a non-threaded pin, and a coarse threaded pin. The gradients persist for the threaded weld tools but are significantly diminished with the non-threaded tool. Important differences exist in the structures that are discussed in relation to suspected material flow during friction stir joining.