In the current work friction stir processing of the Ti-6Al-4V alloy was carried out. Various process parameters (tool traverse speed and tool rotation speed) were studied for successful FSP of Ti-6Al-4V. The process parameters were identified using macrostructure observation on the surface of processed plate and microstructure evolution in the stir zone (SZ) of the FSP specimen. The effect of tool traverse speed and tool rotation speed on microstructure evolution in the SZ, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) were studied. The microstructure transformation from initial elongated α structure to prior β grains, with α layer grain boundary consisting of mixture of acicular α′ and very fine lamellar α/β colonies, was observed at SZ. This was the case for wide range of variations in parameters except for the tool rotation speed of 600 rpm and traverse speed of 60 and 100 mm/min. Under this combination of parameters, the bands of DRX α and transformed β structure were observed to evolve at SZ.

Investigation of Process Parameters for Friction Stir Processing (FSP) of Ti-6Al-4V Alloy

Multipass friction stir processing (MFSP) of the Ti-6Al-4V alloy was carried out at 600 tool rpm and 80 mm/min traverse speed. After first pass, the initial elongated α structure transformed to prior β grains, consisting of a mixture of acicular α'and very fine lamellar α colonies along with α layer grain boundary in stir zone (SZ). This subsequently transformed to equiaxed α grain via dynamic recrystallization (DRX) process. With the increase in the number of FSP passes the fraction of equiaxed α grains was found to increase, reaching almost fully equiaxed α structure in SZ upon completion of the fifth pass. Flow properties of MFSP Ti-6Al-4V alloy were investigated by differential strain rate test carried out at 927°C. There appears no significant variation in the strain rate sensitivity index (m ≥ 0.3) values between as received Ti-6Al-4V alloy and MFSP Ti-6Al-4V alloy specimens.

Digvijay Sheed

Papers

Investigation of Process Parameters for Friction Stir Processing (FSP) of Ti-6Al-4V Alloy

Multipass-friction Stir Processing (MFSP) of Ti-6Al-4V Alloy and Investigation of Flow Properties