3.1. Hardness and tensile properties tests
Fig. 3 shows the Vickers hardness arrangement in cross section of BM and
FSWed joint. It reveals that an entire drop of hardness occurred after
FSW as compared with BM. A roughly symmetrical micro-hardness
distribution could be seen in welded joint, and two well pronounced
softening bands with a distance of 10 mm from the joint center located
in AS-HAZ and RS-HAZ, respectively. The softening band in AS-HAZ was
about 5 mm in breadth, which was wider than the other one in RS-HAZ (3
mm). The average values of hardness in BM, AS-HAZ, RS-HAZ and WNZ were
186 HV, 124 HV, 132 HV, and 158 HV, respectively.