AA2014 aluminum alloy (Al-Cu alloy) has been widely utilized in fabrication of lightweight structures like aircraft structures, demanding high strength to weight ratio and good corrosion resistance. The fusion welding of these alloys will lead to solidification problems such as hot cracking. Friction stir welding is a new solid state welding process, in which the material being welded does not melt and recast. Lot of research works have been carried out by many researchers to optimize process parameters and establish empirical relationships to predict tensile strength of friction stir welded butt joints of aluminum alloys. However, very few investigations have been carried out on friction stir welded lap joints of aluminum alloys. Hence, in this investigation, an attempt has been made to optimize friction stir lap welding (FSLW) parameters to attain maximum tensile strength using statistical tools such as design of experiment (DoE), analysis of variance (ANOVA), response graph and contour plots. By this method, it is found that maximum tensile shear fracture load of 12.76 kN can be achieved if a joint is made using tool rotational speed of 900 rpm, welding speed of 110 mm/min, tool shoulder diameter of 12 mm and tool tilt angle of 1.5°.
 Thomas W. M., Nicholas E. D., Needam J. C., Murch M. G., Templesmith P., Dawes C. J. GB Patent application No: 9125978.8, December 1191 and US Patent No. 5460317, October 1995.
 Irving B., Why aren’t airplanes welded? Welding Journal 76(1) (1997) 31-41.
 MIL-HDBK-5H, Metallic materials and elements for aerospace vehicle structure (1998) 8-27, 37, 108, 148.
 Fadaeifard F., Matori K. A., Toozandehjani M., Influence of rotational speed on mechanical properties of friction stir lap welded 6061-T6 Al alloy, Trans. Nonferrous Met .Soc. Chinna 24 (2014) 1004-1011.
 Urso G. D., Giardini C., The influence of process parameters and tool geometry on mechanical properties of friction stir welded aluminum lap joints, Int. J. Mater. Form. 3 (1) (2010) 1011-1014.
 Yazdanian S., Chen Z. W., Effect of friction stir lap welding conditions on joint strength of aluminum alloy 6060, Materials science anf Engineering 4 (2009) 012021
 Soundrarajan V., Yarrapareddy E., Kovacevic R., Investigation of the friction stir lap welding of aluminum alloys AA5182 and AA6022, Journal of Materials Engineering Performance 16 (2007) 477-484.
 Kimapong K., Watanabe T., Effect of welding process parameters on mechanical property of FSW lap joint between aluminum alloy and steel, Materials Transactions, 46 (10) (2005) 2211-2217.
 Cen Z.W, Yazdanian S., Friction stir lap welding: material flow, Joint structure and strength, Jour. Of Acheivements in Materials and Manufacturing Engineering 55 (2012) 629-637
 Babu S., Janakiram G. D., Venkatakrishnan P. V., Madusudhana Reddy G., Prasad Rao K., Microstructure and mechanical properties of frition stir lap welded aluminum alloy AA2014, J. Mater. Sci. Technol., 28 (5) (2012) 414-426.
 Galvao I., Verdera D., Gesto D., Loureiro A., Rodrigues D. M., Influence of aluminum alloy type on dissimilar friction stir lap welding of aluminum to copper, Journal of Material Processing Technology 213 (2013) 1920-1928.
 Buffa G., Campanile G., Fratini L., Prisco A., Friction stir lap joints: Influence of process parameters on the metallurgical and mechanical properties, Mater. Science and Engineering A, 519 (2009)19-26.
 Cen Y. C, Nakata K., Friction stir lap joining aluminum and magnesium alloys, Scripta materialia 58 (2008) 433-436.
 Salari E., Khodabandeh A., Friction stir lap welding of 5456 aluminum alloy with different sheet thickness: process optimization and microstructure evaluation, The Int. Jou of Adv Manu. Tech., 82 (2016) 39-48
 Shirazi H., Kheirandish Sh., Safarkhanian M. A, Effect of process parameters on the macrostructure and defect formation in friction stir lap welding of AA5456 aluminum alloy, Jour. Of Measurement, 76 (2015) 62-69.
 Zhengwei Li, Yumei Yue, Shude Ji, Peng Chai, Zhenlu Zhou, Joint features and mechanical properties of friction stir lap welded alclad 2024 aluminum alloy assisted by external stationary shoulder, Material & Design, 90 (2016) 238-247.
 Jamshidi H., Serajzadeh S., Kokabi A., Theoretical and experimental investigation in to friction stir welding of AA5086, Int. j. Adv. Manu. tech. 52 (2011) 531-544.
 Khuri A. I., Cornel l. J., Response surfaces; design and analysis. Marcel Dekker, New York (1996)
 Gunaraj V., Murugan N., Application of response surface methodology for predicting weld beadqualityin submerged arc welding of pipes. J Mater Process Technol, 88 (1999) 266-275.
 Tien C.L., Lin S.W., Optimization of process parameters of titanium dioxide films by response Surface Methodology. Opt Common 266 (2006) 574-581.
 Cao X. Jahazi M., Effect of tool rotational speed and probe length on lap joint quality of friction stir welded magnesium alloy, Materials & Design, 32 (2011) 1-11.
 Ghosh M., Kumar K., Mishra R.S., Mater. Sci. Eng. A (2011) 528, 8111.
 Mishra R. S., Ma Z. Y., Friction stir welding and processing, Mater. Sci. Eng. R 50 (2005) 1-78.
 Nandan R., Debroy T., Bhadesahia H. K. D. H., Recent advances in friction-stir welding - Process, weldment structure and properties, Prog. Mater. Sci. 53 (2008) 980.
 Buffa G., Hua J., Shivapuri R., Fratni I., A continuum based fem model for friction stir welding-model development, Mater. Sci. Eng A, (2006) 419, 381.
 Zhao Y., Lin S., Wu L., Qu F., The influence of pin geometry on bonding and mechanical properties in friction stir weld 2014 Al alloy, Mater. letter 59(23) (2005) 2948-2952.