Effect of Zr content on microstructure and mechanical properties of lightweight Al2NbTi3V2Zrx high entropy alloy

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Lightweight Al2NbTi3V2Zrx (x = 1.0, 0.8, 0.6, 0.4, 0.2, 0) high entropy alloys are produced by mechanical milling and vacuum hot pressing. The microstructure, phase evolution and mechanical properties of the alloys are analyzed. The microstructure of the alloys with x = 1.0, 0.8, 0.6 consists of BCC solid solution matrix and two intermetallics (i.e., α and β), and then β phase disappears in Al2NbTi3V2Zr0.4 alloy. Further decreasing Zr content to below 0.2, α phase vanishes and γ and δ intermetallics emerge in Al2NbTi3V2Zr0.2 and Al2NbTi3V2 alloys. The Al2NbTi3V2Zrx alloys cannot obtain a single phase structure by decreasing Zr content with current fabrication process, which is likely because that the mixing entropy of the HEA system is not large enough to prohibit the formation of the secondary phases at hot pressing temperature of 1250 °C. All the bulks possess low density ranging from 4.93 to 5.21 g/cm3. Hardness of the Al2NbTi3V2Zrx alloys decreases from 781 HV to 697 HV and then increases to 814 HV with the decrease of Zr from x = 1 to 0. This varying tendency is closely related with the content of secondary intermetallic phases. The compressive test shows the Al2NbTi3V2Zr0.4 alloy has a yield strength of 1742 MPa, fracture strength of 2420 MPa, compressive strain of 38.2 %, which is probably related to its simplest microstructure. The comprehensive mechanical property of Al2NbTi3V2Zr0.4 alloy is superior to the majority of other HEAs and Ti64 alloy.