Influence of probe offset distance on interfacial microstructure and mechanical properties of friction stir butt welded joint of Ti6Al4V and A6061 dissimilar alloys

• Friction stir butt welding of titanium alloy Ti6Al4V and aluminum alloy A6061-T6.
• Probe offset distance affects interfacial microstructure of the joint.
• Probe offset distance affects the mechanical properties of joint and fracture position.
• Joining mechanism of Ti6Al4V/A6061 dissimilar alloys by FSW is proposed.

Friction stir butt welding of titanium alloy Ti6Al4V and aluminum alloy A6061-T6 with 2 mm thickness was conducted by offsetting probe edge into the titanium alloy at rotation speed of 750 rpm and 1000 rpm and welding speed of 120 mm/min. The effect of probe offset distance on the interfacial microstructure and mechanical properties of the butt joint was investigated. When the probe offset distance is not sufficient, the two alloys cannot be completely joined together, i.e. there exists no bonding or kissing bonding at the root part of joint interface. However, when the probe offset distance is too large, a great amount of intermetallic compounds are formed at the joint interface and its adjacency, leading to fracturing roughly along the joint interface during a tensile test. In a proper range of probe offset distance, sound dissimilar butt joints are produced, which have comparatively high tensile strength and fracture in heat affected zone of the aluminum alloy during a tensile test.