In large-scale friction stir additive manufacturingAdditive manufacturing, theAluminum alloys multitrackMulti-track friction stir processingFriction stir processing (FSP) of each layer with suitable overlap is crucial. In this process, the material is subjected to multiple thermal cycles and repeated severe plastic deformation due to overlapping, leading to variations in microstructureMicrostructure and mechanical propertiesMechanical properties. To mitigate these effects and maintain uniform properties across the processing plate, heat treatmentHeat treatment is often employed for precipitation-hardenable aluminumAluminum 6061-T6. In this investigation, multi-trackMulti-track FSP of aluminumAluminum 6061-T6 alloys was performed using a raster pattern with a 50% overlap relative to the tool probe dimension. The heat treatmentHeat treatment conditions were optimized to retain the refined microstructureMicrostructure, control grain growth, and enhance the mechanical propertiesMechanical properties of the processed materials. The influence of the optimized heat treatmentHeat treatment was assessed, with predictions made regarding the mechanisms behind the microstructural evolution and the improvement in mechanical propertiesMechanical properties. These findings have significant implications for the fabrication of multi-layered, multi-trackMulti-track additive manufacturingAdditive manufacturing structures and coatings.