Issue 37

C. Patil et alii, Frattura ed Integrità Strutturale, 37 (2016) 325-332; DOI: 10.3221/IGF-ESIS.37.43 326 shoulder and the work piece. This heat causes the latter to reach a visco-plastic state that allows traversing of the tool along the weld line. The plasticized material is transferred from the leading edge of the tool to the trailing edge of the tool probe and is forged by the intimate contact of the tool shoulder and the pin profile. It leaves a solid phase bond between the two pieces [6]. The Fig. 1describes the basic principle of the FSW process. Caroline et al [7] has welded AA2014-T 6 and AA7075-T 6 aluminium alloys for various welding parameters. Torque, Temperature, macrograph and micro hardness were measured and concluded that torque, temperature and hardness profile depend on the amount material mixture in the stir zone. S. Rajakumar et.al [8] studied the influence of process parameters on friction stir welding of Al 7075 alloy and concluded that higher tool rotation speed resulted in higher heat generation which caused slower cooling rate and leads to formation of coarse grains which in turn produced lower hardness. Moreira et al [9] produced FSW of AA6082- T 6 with AA6061-T 6 . The welds exhibited intermediate properties and the tensile tests failures occurred near the weld edge line where a minimum value of hardness was observed. Khodir et al [10] studied the microstructure and mechanical properties of dissimilar joints of 2024-T 3 to 7075-T 6 Al alloy and observed that the rise in welding speed caused formation of kissing bond and pores especially when the 2024 Al alloy plate was located on the retreating side. Minimum hardness was observed in the HAZ of both sides and their values increased with welding speed. Shen et al [11] used AA 7075 plates of 2 mm thickness, for various rotational speeds and the dwell time. They investigated the microstructure and the mechanical properties of the refilled friction Stir Spot Welding of AA7075. The keyhole of the weld was refilled successfully, the microstructure of the weld exhibits variations in the grain additionally, they observed, and defects associated to the material flow, such as hook, voids, bonding ligament and incomplete refill. Vladvoj et al [12] presents the results of microstructure analysis, hardness measurements and tensile tests of FS-welded sheets of two aluminium alloys AA5083 and AA7075.Ericsson and Sandstrom [13] investigated the influence of welding speed on fatigue behavior of FSW, MIG and TIG process. Moreira et al. [14] investigated the fatigue behavior of joints of FSW and metal inert gas (MIG) welding. Squillace et al. [15] investigated the microstructure and pitting corrosion resistance in TIG and FSW joints for 2024-T3 alloy. Munoz et al. [16] investigated the microstructure and mechanical properties of FSW and TIG for Al- Mg-Sc alloy. Taban et al [17] studied the microstructure and mechanical properties in MIG, TIG and FSW joints for 5083- H321 aluminum alloy. This paper presents the effect variable rotational speed and transverse speed on hardness properties of similar FSW joints of AA7075-T 651 and dissimilar FSW joints of AA7075-T 651 -AA6061-T 6 and also comparison between FSW and TIG welding were studied. Figure 1 : Working Principle of Friction Stir Welding. M ATERIALS AND EXPERIMENTAL METHODS Materials luminium alloys AA7075-T 651 and AA6061-T 6 sheet was cut on shear machine and brought to required size of 150 mm x 70 mm x 6.35 mm for FSW & TIG welding. The FSW tool employed was square trapezoidal pin of H13 tool steel material with dimensions of 4mm bottom face and 6mm top face, 20mm flat shoulder diameter and 6mm pin height. The chemical composition of base material is as shown in Tab. I. A