PSI - Issue 17

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

496

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

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i.e. generating heat and providing material flow. The friction between the non-consumable rotating tool and workpiece along with the plastic deformation of the workpiece generates heat that softens the workpiece material, however, no melting takes place. The plasticized material flows around the tool pin, mixes and joint formation takes place primarily due to solid state diffusion. Comparatively low working temperature range helps in reducing thermal contractions due to solidification and cooling, thus distortions can be reduced. Also the process becomes much simpler by eradicating the use of shielding gas or filler material. The aerospace, automotive and ship-building industries persistently need to manufacture joints from dissimilar metals in order to produce lightweight and mechanically-sound structures (Jonckheere et al., 2013; Lim et al., 2004; Kadaganchi et al., 2015). The low solution treated 2xxx and 6xxx series aluminum alloys provide high formability and their prompt age hardening feature helps in strengthening the formed component. These diverse features make them useful for fabricating different components useful for transportation, automobile, aviation and other applications. For the adequate joint strength using FSW, the selection of tool pin profiles, process parameters becomes important in order to avoid formation of defects like tunneling, voids, etc. which generally appears due to improper heat input, flow and/or mixing of materials (Heidarzadeh et al., 2012; Kadaganchi et al., 2015; Zhao et al., 2005). Jonckheere et al. (2013) carried out similar and dissimilar FSW of 4.7 mm thick plates of AA2014-T6 and AA6061-T6 alloys with tool rotational speeds of 500 and 1500 rpm at 90 mm/min using threaded tool pin with three flat faces. They reported the formation of larger softened zone at high rotational speeds as compared to low rotational speeds. Raturi et al. (2019) used 6.1 mm thick plates of AA6061-T6 and AA7075-T651 for dissimilar FSW joints using different tool pin profiles, tool rotational speed (660, 900, 1200, 1700 rpm), welding speed (36, 63, 98, 132 mm/min) and with and without application of preheat. They reported that the rotational speed and pin profiles are the dominating factors in terms of better joint strength. Lim et al. (2004) investigated the tensile behavior of 4 mm thick friction stir welded AA6061 T651 plates obtained at different rotational (1000 to 2500 rpm) and welding speeds (0.1 to 0.4 m/min). Decreased tensile elongation was reported by them for low welding and high rotational speeds, presumed due to clustering and coarsening of Mg 2 Si precipitates. Better tensile results for 4 mm thick AA6061-T6 friction stir welded plates using square pin profile were obtained by Heidarzadeh et al. (2012) at 920 rpm tool rotation and 78 mm/min welding speed. Kadaganchi et al. (2015) observed rotational speed, welding speed, tilt angle and tool pin profile as most influencing factors while joining 5 mm thick AA2014-T6 plates by FSW. They have observed that the metallurgical transformations due to high heat input (combination of high rotational and low welding speed) can adversely affect the mechanical properties. Zhao et al. (2005) considered tool pin geometry as the pivotal element to obtain favorable welding structure and mechanical properties. They affirmed threaded pin geometries to be helpful in material transportation at accelerated rate as well as benefited in heat generation for same process parameters. The present experimental investigation was intended to appraise the tensile, impact strength and fracture behavior of friction stir welded joints between AA6061-T6 and AA2014-T6. Two different pin profiles were used to prepare joints at varied tool rotational and welding speeds. The welding process parameter combinations were chosen such that reasonably satisfactory welding achieved. The tensile strength and impact toughness of the welded joints were carried out. The metallurgical observations of the weld zone, fractographic studies were also carried out.

Nomenclature TIF

threaded with three intermittent flat faces tool pin truncated square pyramidal (trapezoidal) shaped tool pin

TPZ

AS RS SZ

advancing side retreating side

stir zone TMAZ thermo-mechanically affected zone HAZ heat affected zone