Mechanically activated effect of friction stir processing in Al–Ti reaction

The kinetics of the Al–Ti reaction during isothermal annealing and friction stir processing (FSP) was studied. The Al–Ti reaction was diffusion controlled during annealing at 525–550 °C and interfacial-reaction controlled at 575–650 °C, whereas the reaction during FSP with tool rotation rates of 1000 and 2000 rpm was interfacial-reaction controlled. The reaction rate constant k during FSP is substantially enhanced compared with that during annealing. This is attributed to the decrease in activation energy caused by severe deformation during FSP. The effective temperature was proposed to show the contribution of the mechanically activated effect of FSP, and was calculated to be 710 and 716 °C for FSP with rotation rates of 1000 and 2000 rpm.