Improvement of microstructure and mechanical properties of dissimilar friction stir welded aluminum/titanium joints via aluminum oxide nanopowder

Aluminum oxide nanopowder has been fabricated and characterized successfully to improve the properties of friction stir welded aluminum/titanium joints, which pose a great challenge due to the great difference in mechanical properties. Intermetallic compounds (IMCs) of large sizes formed at the welding interface are a significant problem that deteriorates joint strength due to the uncontrollable thermal effect generated in the joint. Therefore, friction stir processing was integrated with friction stir welding, in which a dissimilar lap joint of AA6061-T6 and Ti6Al4V was reinforced with γ-Al₂O₃ nanoparticles of about 8 nm in diameter. First, several attempts were conducted to determine the most effective parameters in the welding process of the aluminum/titanium reinforced joint and then the effects of γ-Al₂O₃ nanopowder on microstructure, mechanical properties, and weldability were analyzed and compared to a welded joint without reinforcing powder. Sound joints have been successfully produced using welding speed of 25 mm/min, and tool rotational speed of 600 rpm. Lap shear fracture load and displacement of the Al/Ti joint increased from 3.5 KN and 1.25 mm to 3.7 KN and 2.45 mm, respectively, while the hardness of the reinforced joint increased from 384 HV to 391 HV at the Al/Ti weld interface with a remarkable improvement at the Al and Ti sides.