Microstructure and mechanical properties of novel Al–Cu–Mg–Zn lightweight entropy alloys for elevated-temperature applications

In this study, the microstructural evolution and mechanical properties of five lightweight Al–Cu–Mg–Zn entropy alloys (Al85Cu5Zn5Mg5, Al74Cu10Zn8Mg8, Al93Cu4Zn1Mg1Cr1, Al84Cu10Zn3Mg2Cr1, and Al77Cu17Zn3Mg2Cr1) were investigated. The five experimental alloys revealed lightweight characteristics with density values ranging from 2.95 to 3.63 g/cm3 and multiphase features. The microstructural and phase evolutions at elevated-temperature were characterized using X-ray diffraction and optical, scanning, and transmission electron microscopy. With the increase in Cu and other element contents, the volume fraction of intermetallic compounds (ICs) increased, resulting in an improved yield strength (YS) and reduced plasticity. The GP zone and fine η' precipitates were effective strengthening sources in fcc-Al, but they were unstable at 300 °C and transformed into coarse and submicron-sized particles. The main source of strengthening in the alloy series was the well-interconnected IC network. Among the five alloys studied, Alloy 5 (Al77Cu17Zn3Mg2Cr1) exhibited the highest YS of 588 MPa at room temperature and retained the highest YS of 199 MPa at 300 °C after thermal exposure for 100 h. Combining its high strength and good thermal stability at 300 °C, Alloy 5 exhibits promising potential for elevated-temperature applications.