Mechanical and microstructural behavior of friction stir powder additive manufactured ceria-stabilized zirconia and polymer-derived ceramic reinforced AA7075 composites

Fusion-based additive manufacturing of Al-based composites faces challenges such as oxidation, hot cracking, metallurgical incompatibility, and brittle intermetallic formation due to liquid-solid phase transformations. Solid-state friction stir-based AM processes, on the other hand, minimize these issues but are limited by the availability of suitable feedstock forms, especially for manufacturing composites. Recently developed friction stir powder additive manufacturing (FSPAM) is an emerging solid-state additive manufacturing process that reduces solidification-related issues and overcomes feedstock limitations by using readily available powders, allowing easy preparation of composite feedstocks through powder mixing. This study investigates ceria-stabilized zirconia and polymer-derived ceramic-reinforced AA7075 composites manufactured using the FSPAM process. Microstructure confirmed a uniform, defect-free deposition having fine grains of size 6.4 ± 2.9μm and 58 % high-angle grain boundaries, indicating significant grain refinement due to dynamic recrystallization. The reinforcement particles refined the microstructure through the Zener pinning effect, while η and S precipitates (∼45 nm size) enhanced mechanical strength by inhibiting grain coarsening. The composite exhibited a yield strength of 223 ± 7 MPa, an ultimate tensile strength of 393 ± 3 MPa, and a microhardness of 125 ± 9 HV, closely matching AA7075-T4 alloys. However, elongation was limited to 5.5 ± 0.4 %, possibly due to localized agglomeration of reinforced particles. These findings highlight FSPAM as a promising process in solid-state AM of Al-based composites for high-strength and high-temperature applications, though further research is needed to address geometric constraints for broader industrial adoption.