Fig. 1. (a) Optical image of the cross-sectional FSP GW83 K alloys. (b) The corresponding microhardness evolution map. (c-e) Optical microstructure of SZ, TZ, and BM in the retreating size. (f) (0002) plane pole figure of SZ, BM, and TZ. The PD, TD, and ND denote the processing, transverse, and normal direction of the plate, respectively.

Fig. 2. (a) Schematic illustration of friction-stir processing and the sampling position of two laminate structure samples. (b) Optical image of the grain structure evolution of the BS and TS samples. (c) Statistical grain size distribution of the fine grain and coarse grain in the BS and TS samples.

Fig. 3. (a) Engineering tensile stress-strain curve for the CG, BS, FG, and TS samples at room temperature. (b) Strain hardening rate ($\text{ }\!\!\theta\!\!\text{ }=\text{d }\!\!\sigma\!\!\text{ }/\text{d }\!\!\varepsilon\!\!\text{ }$) vs. strain curves for all samples. (c) Strengths predicted from ROM versus volume fraction of fine grain and the measured strength of the BS and TS samples. (d) Uniform elongation predicted from ROM versus volume fraction of fine grain and the measured elongation of the BS and TS samples.

Fig. 4. Detailed characterization of slip transfer and non-slip transfer in (a) the FG and (b) CG samples at the tensile strain of 8 %. Comparison of (c) the number of slip transfer and (d) frequency of different slip traces between the FG and CG samples. More than 150 grains’ slip activities have been observed and summarized.