Issue 37

C. Patil et alii, Frattura ed Integrità Strutturale, 37 (2016) 325-332; DOI: 10.3221/IGF-ESIS.37.43 331 grain coarsening and softening could also take place in the HAZ. The reducing in the weld hardness can be attributed to the dissolution of precipitates and subsequently the weld cooling rates do not favor nucleation and growth of all precipitates. The variation in hardness values in the microstructural weld zones are shown in Fig. 7. Due to the high temperature required for fusion welding, the heat affected zone region was large as well as and the subsequent melting and solidification that occur, voids are common defects found in fusion welds. The presence of voids (Fig.-7b) in the TIG welds contributes to the reduced hardness (Fig. 5-6) observed during testing in respect of friction stirs welds. C ONCLUSION he minimum hardness was recorded in the weld metal for TIG welding of about 50.1BHN for similar joint and 70.7 BHN for dissimilar joints. While for FSW joint the minimum hardness was recorded about 70.1 BHN and maximum hardness about 121BHN as compared with 170BHN for the base alloy. A hardness value has mixed result with respect to rotations speed and transverse speed for similar FSW joints. But in case of dissimilar FSW joints hardness value decreases with increase rotations speed and transverse speed. Hardness was strongly affected by precipitate distribution.The voids presence in the TIG welds contributes to the reduced hardness. It is observed that of FSW joints has more hardness than TIG joints. R EFERENCES [1] Thomas, W.M., et al., Friction stir butt welding, International patent application PCT/GB92, Patent Application GB9125978.8, 6, (1991). [2] Muthukrishnan, M., Marimuthu, K., Some Studies on Mechanical Properties of Friction Stir Butt Welded Al-6082- T6 Plates, IEEE, (2010). [3] Yan-hua Zhao, T., San-bao Lin, Lin Wu, Fu-xingqu, The influence of pin geometry on bonding and mechanical properties in friction stir weld 2014 Al alloy, Materials Letters, 59 (2005) 2948 – 2952. [4] Mishra, R. S., Mahoney, M. W., Friction stir welding and processing Materials Park, OH, ASM International, (2007). [5] Jonhson, R., Kallee, S., Friction stir welding, Materials World, 7(12) (1999) 751-753. [6] Patil, H.S., Soman, S.N., Experimental study on the effect of welding speed and tool pin profiles on AA6082-O aluminium friction stir welded butt joints, International Journal of Engineering, Science and Technology, 2(5) (2010) 268-275. [7] Caroline, J., Bruno, D., Anne, D., Aude, S., Torque, temperature and hardening precipitation evolution in dissimilar friction stir welds between 6061-T6 and 2014-T6 aluminum alloys. Journal of Materials Processing Technology, 213 (2013) 826– 837. [8] Rajakumar, S., Muralidharan, C., Balasubramanian, V., Influence of friction stir welding process and tool parameters on strength properties of AA7075-T6 aluminium alloy joints, Materials and Design, 32 (2011) 535–549. [9] Moreira, P.M.G.P., Santos, T., Tavares, S.M.O., Richter-Trummer, V., Vilaca, P., de Castro, P.M.S.T., Mechanical and metallurgical characterization of friction stir welding joints of AA6061-T6 with AA6082-T6, Materials and Design, 30 (2009) 180–187. [10] Khodir, S. A., Shibayanagi, T., Friction stir welding of dissimilar AA2024 and AA7075 aluminum alloys, Material Science and Engineering B, 148 (2008) 82–87. [11] Zhikangshen, Xinqi, Y., Zhang, Z., Cui, L., Li, T., Microstructure and failure mechanisms of refill friction stir spot welded 7075-T6 aluminum alloy joints, Materials and Design, 44 (2013) 476–486. [12] Vladvoj, M., Jorge F. P., Microstructure and Properties of Friction Stir Welded Aluminium Alloys, Metal, (2005) 1-8. [13] Ericsson, M., Sandstrom, R., Influence of welding speed on the fatigue of friction stir welds and comparison with MIG and TIG, J. Fatigue, 25 (2003) 1379- 1387. [14] Moreira, P.M.G.P., Defigueiredo, M.A.V., De Castro, P.M.S.T., Fatigue behaviour of FSW and MIG weldments for aluminum alloys. J. Theoretical Appl. Fracture mech., 48 (2007) 169-177. [15] Squillace, A., De Fenzo, G., Giorleo, F., Bellucci, A comparison between FSW and TIG welding techniques: modifications of microstructure and pitting corrosion resistance in AA 2024-T3 butt joints, Journal of Materials Processing Technology, 152 (2004) 97-105. T