Investigation of material flow, microstructure evolution, and texture development in dissimilar friction stir welding of Al6061 to Ti6Al4V

Abstract

Aluminium -Titanium dissimilar welds are widely used in defence and aerospace industries. Welding of Al to Ti is highly challenging due to the wide difference in thermo-mechanical properties. One of the most promising techniques for producing dissimilar welds is friction stir welding. In the present study, material flow, texture, and microstructural evolution of Ti-6Al-4 V and Al6061 dissimilar friction stir welded joints are elucidated at the Ti interface and centre of the stir zone (CSZ). Material flow pattern reveals the spread of fragments of Ti particles of around 80.3% at the interface and about 23% at the CSZ. The dispersion of Ti fragments in the stir zone resulted in better strength and hardness values of around 256 MPa and 345 HV, respectively, with failure of the specimens in the heat-affected zone of Al6061 side. The interface microstructure at Ti reveals plenty of equiaxed and recrystallized grains. The strengthening mechanism at the Ti interface is due to the dynamic recovery driven by adiabatic shear bands (ASBs) and twin-induced deformation. The electron backscattered diffraction results revealed the presence of 91% and 77% of strain-free recrystallized grains at the Ti interface and CSZ, respectively. The strong texture components of S {123} < 346 > in Al and D {0001} < 112̅0 > in Ti were also observed.