Papers by Author: Yutaka S. Sato

Abstract: The authors have developed a new friction-stir welding (FSW) tool that enables to weld high-softening-temperature materials (HSTMs), such as steels, titanium and zirconium alloys. The new tool is made of a Co-based heat-resistant alloy strengthened by precipitating intermetallics, Co₃(Al,W), with a L1₂ structure at high temperatures. The Co-based alloy tool exhibits yield strengths higher than 500 MPa at 1000 deg C, so it might have a great potential as a tool material for FSW of HSTMs. In this study, the feasibility of using the Co-based alloy tool with various HSTMs was examined. Changes in the tool shape during FSW and the weld appearances produced with the Co-based alloy tool will be briefly shown.

Abstract: The principal features of material flow during friction stir welding (FSW) were illustrated via textural measurements in magnesium alloys. The straining state in the stir zone was demonstrated to be close to the simple-shear deformation with the shear plane/direction aligned with the local surface of the welding tool. Due to the unique nature of FSW process as well as specific character of the welding tool geometry, texture distribution in the stir zone was shown to be inherently inhomogeneous. The impact of this effect on mechanical properties is briefly considered.

Abstract: The “stop-action” technique was employed to study grain structure evolution during friction-stir welding of AZ31 magnesium alloy. The grain structure formation was found to be mainly governed by the combination of the continuous and discontinuous recrystallization but also involved geometric effect of strain and local grain boundary migration. Orientation measurements showed that the deformation mode was very close to the simple shear associated with the rotating pin and material flow arose mainly from basal slip.