Towards restoring mechanical properties by aging only after friction screw extrusion additive manufacturing of Al–Mg–Si alloy

This study examines whether post-deposition aging alone, without solutionizing and quenching, can recover strength in AA6060 builds produced by friction screw extrusion additive manufacturing (FSEAM), a solid-state process that avoids melting-related defects. In FSEAM, the feedstock is preheated inside the printhead by a rotating threaded tool before deposition, which can generate temperatures high enough to dissolve strengthening precipitates. If cooling during deposition is sufficiently rapid, a supersaturated solid solution may be retained, enabling strength recovery by aging only. AA6060, an Al-Mg-Si alloy with a relatively low critical cooling rate, was selected to assess this concept. Builds were fabricated at deposition velocities of 100-500 mm/min. Samples produced above 200 mm/min showed no major defects, and printhead temperatures increased with deposition velocity, exceeding the alloy solvus temperature at velocities above 200 mm/min. After fabrication, samples were aged at 170 °C for 3 h and 20 h, omitting the conventional solutionizing and quenching steps of the full T6 treatment. Aging significantly increased hardness and strength, particularly in the top layers of builds processed above the solvus temperature. Hardness reached 85-88 HV, compared with about 76 HV for the T6 feedstock and 79 HV after a full T6 treatment. The ultimate tensile strength increased to approximately 230 MPa after aging-only, compared with about 211 MPa for the feedstock. These results indicate that solute supersaturation can be retained during FSEAM and exploited by post-deposition aging alone. The findings show that key elements of T6 strengthening can be partially integrated into FSEAM, reducing post-processing requirements.