Influence of process on parameters on superplasticity of friction stir processed nugget in high strength Al-Cu-Li alloy

A parametric study was carried out to evaluate the influence of friction stir processing (FSP) parameters (tool rotation speed and feed rate) on the superplasticity of the weld nugget. Dynamically recrystallised AA 2095 thin sheets with a fine grain size of 2 μm were welded using four feed rates and three rotational speeds. High temperature tensile testing was employed to understand the significance of the FSP parameters and to optimise the parameters for maximum elongation. The tool rotation speed was found to be the most decisive parameter for controlling superplastic behaviour. A strain rate sensitivity of 0.68 was measured for the highest rotational speed at the optimum superplastic forming (SPF) temperature of 495°C. A maximum percentage 'elongation to failure' of 550% was achieved for the sheets subjected to FSP at 1000 rev min^-1 and 4.2 mm s^-1, compared with 475% obtained for the base metal at the optimum SPF temperature and strain rate of 495°C and 10^-3 s^-1, respectively.