Spatially optimized dual-scale precipitates via additive friction stir deposition achieve strength-ductility synergy in Al-Fe-Cr-Ti alloys

Heat resistance Al-Fe-Cr-Ti alloys achieve exceptional thermal stability, yet suffer from severe brittleness due to coarse intermetallic phases and processing defects. This study systematically investigates how processing routes-spray forming (SF), hot extrusion (EX), and additive friction stir deposition (AFSD)-tailor dual-scale microstructures and mechanical properties from room temperature to 400 °C. SF produces extensive porosity (4.91%) and dual-scale phases (Al 3 Ti and Al 13 (Fe, Cr) 4 ), yielding 6.5% elongation (EL). EX eliminates porosity and refines dual-scale phases, achieving 11.2% EL, but particle-decorated grain boundaries persist. AFSD converts grain-boundary-segregated micron-scale Al 3 Ti and Al 13 (Fe, Cr) 4 into a uniformly dispersed population by severe shear-induced fragmentation, refining their size to 1.18 and 0.8 μm, respectively. Concurrently, nanoscale Al 3 Ti and Al 13 (Fe, Cr) 4 and Al 13 (Fe, Cr, Ti) 4 (51 nm) formed, establishing a dual-scale precipitate structure. This yields synergy-185.7 MPa yield strength (YS) with 32.1% elongation (EL) at the room temperature, representing a 187% ductility enhancement relative to the EX while maintaining comparable strength. Compared to the EX, AFSD demonstrates superior high-temperature strength retention with YS values 26.4% and 25.0% higher at 350 °C and 400 °C, respectively. In addition to the dual-scale precipitate structure, the mechanical properties derive from: (i) eliminating grain boundary embrittlement, transforming fracture from intergranular quasi-cleavage to intergranular ductile mode; (ii) enhanced work hardening via uniform dislocation distribution; (iii) texture weakening enabling multi-slip activation; and (iv) threshold stress strengthening through fine interparticle spacing. The study establishes that in the Al-Fe-Cr-Ti alloy, spatial distribution of strengthening phases-rather than absolute magnitude-is critical for strength-ductility synergy.