Experimental and finite element analysis of progressive failure in friction stir welded AA6061-AA7075 joints

In the present study, an in-situ analysis of crack initiation and propagation during tensile loading was captured using high speed camera for dissimilar friction stir weld joint of AA6061-T6 and AA7075-T651 prepared with plain cylindrical (CYL) and threaded with three intermittent flat faces (TIF) tool pins. To study notch sensitivity, experiment was also carried out for notch tensile sample creating notch at weld center. Joint failures were further predicted by finite element (FE) method. Results indicate that for joints obtained with CYL tool pin, crack initiated from vicinity of tunnel region however, propagated through the boundary of stir zone (SZ) and thermo-mechanically affected zone. FE results also indicate that the stresses and strain were confined near tunnel region which act as crack initiation site. For joints obtained with TIF tool pin, no tunnel/void was noticed in the SZ and the sample failed from the heat affected zone on the advancing side (AA6061-T6) of the joints. For notch tensile specimen, the specimen exhibited minimum elongation when compared with tensile specimen and notch strength ratio > 1 indicated that the joint was notch insensitive or in other words, notch strengthened. FE result indicated that the higher stresses were confined near the notch root from where crack initiated and propagated through the SZ. Fractographic analysis showed the presence of dimples, micro-voids with some shear failure marks for all joints indicating the ductile fracture. (C) 2019 The Authors. Published by Elsevier B.V.