Effect of post-process and in-process cooling on wide-area stir zone processed via friction stir processing with pin overlapping

In the current investigation, the influence of post-process and in-process cooling on microstructural, mechanical and electrochemical behavior of wide-area stir zone (WSZ) processed with overlapping friction stir processing (OL-FSP) was studied. The WSZ was successfully prepared in Al5083 aluminum alloy using multi-pass friction stir processing (FSP) with 50% pin overlapping under both cooling conditions. The post-process cooling FSP (PP-FSP) used solid CO2 as cooling media, whereas the in-process cooling FSP (IP-FSP) used water as cooling media. The microstructural investigations revealed that grain refinement is uniform in each overlapping pass for both cooling conditions. The IP-FSP resulted in better grain refinement than PP-FSP. Three different types of intermetallic particles (needle-shaped Fe-containing, rod-shaped Mg-containing, and very small Mg-containing grain boundary intermetallic particles) were identified in the base alloy and OL-FSP samples. The hardness was observed to be constant across the WSZ due to the uniform grain refinement, and the IP-FSP sample has better hardness and strength than the PP-FSP sample due to the better cooling effect. The elongation followed a similar trend of hardness. The electrochemical findings revealed that the IP-FSP sample has better corrosion resistance than the PP-FSP sample due to the better grain refinement and fine intermetallics.