抄録
Friction stir processing (FSP) has been proposed by applying friction stir welding, FSW, as a method for controlling the microstructures to improve mechanical properties. In this study, microstructure of a 7075 aluminum alloy subjected to multipass FSP, MP-FSP, are assessed to obtain fundamental knowledge on MP-FSP. The MP-FSP has been applied to 7075 aluminum alloy plates with T6 and O tempers, and microstructural characterization has been made by means of optical and scanning electron microscopies together with EDX and EBSD analyses. In addition, micro hardness measurement has been carried out. From microstructural observation, a new zone, PBZ (Pass Boundary Zone), has been discovered between stir zones, SZs. The PBZ is composed of two types of (fine-equiaxed and coarse-elongated) grains, where the coarse elongated grain contains many sub-grains. Hardnesses in PBZ are decreased and increased in T6 and O, respectively, by MP-FSP, and are intermediate between those in BM (base metal) and SZ in both tempers.
