Characterization of Residual Strain in Additive Friction Stir Deposition Aluminum 7075

Additive Friction Stir Deposition (AFSD) is a solid-state metal additive manufacturing process in which a consumable rod plastically deforms as it is deposited through a rotating tool. The frictional layer-by-layer nature of AFSD imposes a highly complex thermo-mechanical history upon the deposited material, generating residual stress. Previous residual stress characterization in AFSD has focused on the principal deposition directions but lacks full strain and stress tensor information. This study characterizes stress and strain tensors within an AFSD Aluminum 7075 sample via neutron diffraction, conducted at 57 sample locations in 36 orientations within the steady-state region of the deposit and baseplate. The stresses within the principal deposition directions align with previously reported results, transitioning from tensile to compressive approaching the baseplate. The strain magnitude is greatest in the final deposited layers and reduced in the lower deposited regions. The strain tensor orientation is out of plane at the top of the deposit and transitions to in plane in lower layers, indicating a significant shear deformation gradient. These observations highlight the need to consider the shear component of residual stress to fully describe the complex residual strain and stress state within AFSD material.