The microstructure diversity in different areas of the ring-route Al 6061-T6 additive zone by friction stir additive manufacturing.

Friction stir additive manufacturing technology has emerged as an efficient solid-state process option that provides superior connectivity for lightweight structural material with equiaxed microstructures and outstanding mechanical properties. In this paper, a multilayer ring-shaped build made from 6061-T6 aluminum alloy using friction stir additive manufacturing (FSAM) was characterized. The rotating torque exerted on the friction tool by the surrounding material was measured as it moves to the middle and the end of the ring. Additionally, the correlation between the microstructure and the rotating torque was investigated. The results revealed a significant decrease in rotating torque when the stir tool returned to its original position in the additive zone, leading to a reduction in grain size within the additive zone. Underneath the bottom of the stir zone, there was an overlapping interface filled with deformed grains. Along the horizontal direction, the highest hardness existed in the base material region, while the lowest value appeared in the mixed area of the thermal–mechanical affected zone and heat-affected zone. The hardness value of the stir zone was found to be intermediate between the base material region and the mixed area of the thermal–mechanical affected zone and heat-affected zone. The highest and lowest hardness values along the tool-axial direction were observed at the top of the stir zone and the overlapping interface below it. [ABSTRACT FROM AUTHOR]