Fig. 5 OM image of FSW joint on cross section
The detail statistical information of grain structure of BM, WNZ and softening band in AS-HAZ were further investigated by EBSD. The detailed statistical fractions of recrystallized, sub-structured, deformed structure were calculated and listed in the corresponding figures. According to the EBSD maps shown in Fig. 6, it can be found that BM and AS-HAZ mainly consisted of grains elongated along the rolling direction, many sub-grains inside grains as well as some small recrystallized grains in grain boundaries were distinguishable (Fig. 6a and 6c). In WNZ, the grain size dramatically decreased and the intragranular sub-grains entirely vanished (Fig. 6e), presenting a complete recrystallized equiaxed-grained structure (Fig. 6f).