Influence of cooling media in achieving grain refinement of AA2014 alloy using friction stir processing

The present paper studies the influence of different cooling media (water and cryogenic media) on microstructure, mechanical, and corrosion behavior of friction stir processing of AA2014. From the electron backscattered diffraction results, it was observed that the grain size in stir zone of air-cooled friction stir processing, dry ice-cooled friction stir processing, and underwater friction stir processing are 4.9 mu m, 3.5 mu m, and 0.9 mu m respectively, and the fraction of high angle grain boundaries are more in underwater friction stir processing sample compared to other conditions. The ultra-fine grained structure (0.9 mu m) was achieved in underwater friction stir processing due to uniform heat dissipation from the processing zone to the water. Mechanical properties such as hardness and strength were improved in underwater friction stir processing compared to other conditions. The fine precipitates formed in the underwater friction stir processing sample were distributed randomly at grain boundaries, and hence corrosion resistance was improved in underwater friction stir processing sample compared to other conditions.