Interfacial Microstructure and Mechanical Properties of Dissimilar Friction Stir Welds between 6061-T6 Aluminum and Ti-6%Al-4%V Alloys

Abstract

Friction stir welding (FSW) was performed about AA6061-T6 and Ti-6Al-4V alloy sheets. A unique shaped tool with circular truncated cone of probe was used. Mechanical properties and interfacial microstructure were evaluated using tensile test, hardness test, optical microscopy (OM), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM), respectively. Root area of probe in stir zone (SZ) reveals a mixture of finely recrystallized grains of Al and Ti particles pushed away from the base metal by strong stirring of probe. The joint interface of tip area of probe was relatively flat because stirring between aluminum and titanium alloy was not occurred due to the gap of the probe and titanium alloy front. It is considered that the insufficient stirring due to inclined side of the probe was contributed to the decrease of weld strength. After tensile test, fracture surface was analyzed by SEM. In the probe root area, dimples of Al were observed. In the probe tip area, the initial surface of titanium alloy plate was observed. However, in the middle area, similar amount of Ti and Al was detected. As result, it was confirmed that the fracture sequence was very complex and the fracture position was different according to the probe position.