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

Abstract

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.