Design and characterization of lightweight Al-Cu-Mg-Zn eutectic multi-principal element alloys with exceptional strength retention at elevated temperatures

Multi-principal element alloys (MPEAs) offer potential for superior elevated-temperature properties, yet the high-temperature behavior of lightweight Al-based MPEAs remains largely unexplored. Furthermore, these alloys often exhibit room-temperature brittleness due to excessive intermetallic formation. This study addresses these challenges by employing a eutectic design strategy to develop lightweight Al-Cu-Mg-Zn MPEAs. Five alloys (A1–A5: Al50Cu5Mg20Zn25, Al55Cu5Mg20Zn20, Al70Cu5Mg15Zn10, Al70Cu5Mg10Zn15, and Al82Cu3Mg5Zn10) were designed using thermodynamic modeling, produced by casting, and characterized from room temperature to 400 °C. Microstructures evolved systematically from σ-phase-dominated (A1, A2) to α-phase-dominated (A3–A5), with intermetallic fraction decreasing from 63% to 17%. Room-temperature yield strengths ranged from 382 to 680 MPa; alloy A4 achieved the highest strength (680 MPa, 5.6% strain), while alloy A5 offered the best strength-ductility combination (417 MPa, 13.7% strain). At elevated temperatures, σ-phase-rich alloys A1 and A2 exhibited anomalous strengthening at 200 °C and superior strength retention at 400 °C, whereas α-phase-dominated alloys showed progressive thermal softening. Benchmarking against conventional cast aluminum alloys confirmed that all five alloys retain superior or comparable strength at both 200 °C and 400 °C. These results validate the eutectic design approach for developing lightweight MPEAs with tunable mechanical properties and promising elevated-temperature capability.