PSI - Issue 17

Madhav Raturi et al. / Procedia Structural Integrity 17 (2019) 495–502

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Madhav Raturi et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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FE-SEM images of the fractured surfaces (Fig. 5 and Fig. 6) represent the ductile failure as the thorough distribution of dimple structures can be observed. Fractographs shown in Fig. 5 indicates the presence of numerous distributed dimples over the surfaces indicating ductile dominated failure. Dimples with deep feature and thick edges with sufficiently high number of micro pores resulted in better mechanical properties. The density of the dimples is almost same and also the EDS mapping showed the close chemical composition, however, slightly higher amount of oxygen presence was noted in Fig. 5(a) compared to Fig. 5(b). A similar observation of failure surfaces for joints prepared with TPZ tool pin can be noted from Fig. 6 wherein presence of dimples over the fracture surface was observed. The TPZ pin profiles facilitated flow of plasticized material due to non-circular flat faces. Additionally this profile helped in breaking up of oxides and obtaining fine grain structure in the nugget zone. For the joints obtained using TPZ pin profile at high heat input (1200 rpm, 36 mm/min) fracture occurred through the SZ during tensile test. However, even though the fracture was through the SZ but still it offers higher joint strength when compared to the joints obtained with same pin profile (TPZ) with 660 rpm, 36 mm/min and 900 rpm, 63 mm/min in which fracture occurred outside the SZ. The probable cause for fracture propagating through the SZ might be due to the oxide inclusion as the EDS analysis of fracture surface showed comparatively high percentage of oxygen.

(a)

(b)

Fig. 5. Macrographs of fractured surface; FE-SEM image and EDS mapping at fractured surface of AA6061-AA2014 dissimilar friction stir welded joints using TIF pin profile at (a) 660 rpm tool rotation, 63 mm/min welding speed; (b)1200 rpm tool rotation, 98 mm/min welding speed.

It may also be noted from Fig. 4(c) that among TIF and TPZ tool pins, slightly better tensile strength was accomplished using TIF pin profile when combined with different set of process parameters. The threads incorporated in TIF pin profile results in smooth transition of microstructure while moving from TMAZ towards SZ whereas for the weld obtained using TPZ pin profile, showed sharp boundaries within the different recognized