Dissimilar friction stir welding of AA6061 and Ti6Al4V alloys: A study on microstructure and mechanical properties

Abstract

Intact Al/Ti joints were fabricated using W-Re pin tool at various welding speeds when the rotating speed was 1000 rpm. The temperature histories were recorded and tool wear was measured, in order to study the welding processes. The microstructure of the welds had a smaller grain size as the welding speed increased. The base materials were intermixed at a welding speed of 40 mm/min, forming the Al/Ti mechanical mixture and hook structure at/beside the interface. However, no obvious Al/Ti intermixing could be found in joints welded at 80 mm/min or more. Distinguishable amount of intermetallic compound (IMC) were depicted from the Al/Ti mixture in light of the SEM and EDS results. TiAl3 was further identified from the interface by TEM. The lowest hardness was tested at the boundary between HAZ and TMAZ, and the highest hardness was found at interface, due to the excessive IMCs in the Al/Ti mixture. The joints reached the maximum shear load of 4206 N at 80 mm/min. The specimens all failed along the interface with the characteristics of both brittle and plastic fracture.