Microstructure Evolution and Heat Resistance of an Al–Fe–Mg–Zr Eutectic Alloy Fabricated by Laser Powder Bed Fusion

We report a eutectic Al–Fe–Mg–Zr alloy produced by laser powder bed fusion that achieves crack-free fabrication with 99.8% relative density and an ultrafine, cellular–lamellar microstructure. Direct aging at 400 °C for 4 h delivers peak room-temperature strength (yield strength (YS) of 392.9 MPa, ultimate tensile strength (UTS) of 415.8 MPa, and elongation of 8.5%) owing to a dual mechanism: load transfer from a dense dispersion of Fe-rich intermetallics and precipitation strengthening from coherent L12–Al3Zr nanoparticles. Multiscale microstructure characterization shows that the rapidly solidified Al6Fe formed in the as-built state evolves toward thermodynamically stable Al13Fe4 during aging, while Al3Zr remains coherent. After 400 °C annealing for 100 h, coarsening of Al–Fe dispersoids increases interparticle spacing and reduces the load-transfer contribution, but the slow-coarsening, coherent Al3Zr dispersion stabilizes the microstructure and supports strength retention (YS of 309.7 MPa and UTS of 354.6 MPa). The results demonstrate a process-compatible pathway to combine high strength with thermal stability in LPBF aluminum alloys through coordinated control of intermetallic dispersoids and coherent nanoprecipitates.