Influence of welding parameters on interface evolution and mechanical properties of FSW Al/Ti lap joints

Friction stir welding (FSW) was performed to produce Al/Ti lap joints under various welding conditions. More heat was generated when rotational rate increased or traversing rate decreased. Two types of Al/Ti interfaces – mixed interface and diffusive interface – were formed under different welding conditions. The diffusive interface was formed with low heat input, and the mixed interface was formed more heat. The grains at the mixed interface were larger than those at the diffusive interface because of the higher heat input. Moreover, the microstructure of the mixed interface had a lower texture intensity compared with that of the diffusive interface, which was attributed to the enhanced continuous dynamic recrystallization (CDRX). TiAl₃ was formed at the diffusive interface. When the interface varied to the mixed interface as heat input increased, TiAl was fomed within the Al/Ti mixture following the formation of TiAl₃. In addition, TiAl₃ precipitates were observed in the diffusion layer. The hardness value of the mixed interface was higher than 350 HV, due to the larger amount of intermetallic compounds (IMCs). The lap shear strength reached a maximum value of 147 MPa with medium heat input and an interface that exits in a critical state between diffusive and mixed interfaces. All the specimens fractured at the interface, which was attributed to the presence of IMCs.