Microstructure evolution along thickness in double-side friction stir welded 7085 Al alloy

The microstructure evolution in the weld zone of double-side friction stir welded (DS-FSWed) 7085-T7452 Al alloy was investigated by the electron backscatter diffraction method. The results indicate that DS-FSW process results in substantial grain refinement. The misorientation angle distribution shows a very high volume fraction of high angle grain boundary (HAGB) (above 75%) under DS-FSW condition at rotational rate of 300 r/min. The fraction of HAGB rapidly decreases with increasing the rotational rate from 300 to 950 r/min, and the obvious growth of grain in the weld nugget zone (WNZ) is presented. The average grain sizes in the elongated grains of thermal-mechanical affected zone (TMAZ) and partially equiaxed and coarser grains of thermal affected zone (HAZ) are 7.3 and 15.7 μm with the fractions of HAGBs less than 43% and 30%, respectively. The intensities of (100), (110) and (111) pole figures in the WNZ obviously decrease when compared with those in the BM and present significantly difference along the thickness direction of plate.