Impact of Manufacturing Pauses on Residual Stress in Additive Friction Stir Deposition

This study investigates the effects of manufacturing pauses on the mechanical properties and residual stress evolution in additive friction stir deposition (AFSD) of aluminum alloy 7075 (AA7075). Single‑wall builds were produced using closed‑loop temperature control with pauses of 15 and 100 hours introduced midway through deposition. Some samples were reheated to 120 °C before restarting deposition, while others resumed without preheating to examine the influence of thermal history on stress development.

Residual stresses were characterized using neutron diffraction to measure lattice strains throughout the deposited material and the base plate beneath the deposit. These measurements were compared with stresses reconstructed from contour measurements of a stress‑relieved surface from the central cross‑section of the builds. Mechanical properties were evaluated through tensile testing and microhardness mapping.

Both neutron diffraction and contour measurements revealed tensile residual stress concentrations near the base plate in all builds. Paused builds showed variations in stress distribution depending on restart conditions: warm restarts produced elevated tensile stresses in layers deposited before the pause, while cold restarts generated sharper stress gradients near the pause interface. These results indicate that both manufacturing pauses and re-heating of the material before continuing deposition alter the residual stress evolution in AA7075 builds.