Microstructure, mechanical properties and corrosion behavior of friction stir processed AA2014 alloy

In the present study, a large-area stir zone (SZ) was fabricated in AA2014 alloy using multi-pass friction stir processing (FSP) with pin overlapping. The microstructure evolution, crystallographic texture, precipitation phenomenon, and tensile behavior were studied and reported. The microstructure of the large-area SZ consists of equiaxed fine grains with a high density of high angle boundaries caused by dynamic recovery (DRV) and continuous-dynamic recrystallization (C-DRX), and the grain refining has been uniform in each overlapping pass (the grain size within 4–7 μm range). The material flow around the pin caused by the stirring action of the tool contributed to the creation of a strong Brass-{110} < 112 > and A-{110} < 111 > components in the first pass of SZ. Unlike first pass SZ, the second to fifth-pass SZ presents Copper-{112} < 111 > and Cube-{001} < 100 > components due to an increase of heat input by the shoulder to participate multiple times on each overlapping SZ. The hardness and strength of the FSP sample were found to be lowered relative to a base metal. Simultaneously, the SZ ductility increased after FSP by 155% due to the material softening and dissolution of Al2Cu precipitates in the SZ. Kocks-Mecking plots of the BM and FSP samples witnessed the Stage-III of work-hardening behavior. The fine-grain structure and precipitation phenomenon in the FSP sample resulted in better corrosion resistance than the base metal.