The Effect of Rotation Speed and Dwell Time on the Mechanical Properties and Microstructure of Dissimilar Aluminum-Titanium Alloys by FSSW Process

Friction Stir Spot Welding (FSSW) is a novel solid-state joining process developed by Mazda and Kawaski and patented in 2003. It utilizes a profiled rotating pin that plunges into the joint and penetrates the material surface to the tool's shoulder and material is softened by heat-input generated by friction on contact area. FSSW has several advantages over fusion joining processes, as it is could be more cost effective, durable and reliable than conventional spot welding processes. In addition, joints made by FSSW process have high shear tensile strength without adding weight than rivets, bolts, nuts and fasteners. Recently, many researches have applied FSSW for joining of similar as well as dissimilar alloys such as; Al-Al, Mg-Mg, Al-Cu, and Al-Mg alloys. This study focuses on FSSW of aluminum alloy with grade 5 titanium (AA 6061; Ti-6Al-4V), and the relationship between the welding parameters of; tool rotation speed and dwell time on the mechanical properties and microstructure of welded joint, which it is investigated by empirical observation utilizing SEM-EDS analysis, shear tensile and Vickers hardness tests. Tow-level factorial design was conducted for welding parameters. It is observed that the joint quality, mechanical behavior and microstructural evolution in the welded regions are considerably affected by the welding parameters. The microhardness profiles of titanium have significantly affected by heat-input. Additionally, maximum shear load was produced at 1000 rpm and 10 sec dwell time. SEM-EDS analyses detected the formation of Intermetallic Compounds (IMC) of AlTi3 patterns near to Thermomechancial Affected Zone (TMAZ). Keywords: Friction Stir Spot Welding, Aluminum Alloy, Titanium Alloy, Lap-joint, Welding Parameters