Effect of solid solution temperature on microstructure and mechanical properties of Sc-containing 7085 alloy

Abstract

The microstructure, mechanical properties, and electrical conductivity of 7085 alloy sheet without and with Sc (0.25 wt%) at different solid solution temperatures were investigated by using OM, SEM, TEM, EBSD, XRD, and the strengthening mechanism of the alloys were analyzed. The results show that the micrometer-scale second phases in the 7085 alloy are mainly the T(AlZnMgCu) phase and the Al7Cu2Fe phase, while Al3(Sc, Zr) particle and the AlZnMgCuSc phase are also formed in the 7085-Sc alloy. The Mg, Zn, and Cu elements in the soluble second phase of both alloys are mainly dissolved as the solid solution temperature increases from 460 °C to 510 °C. The 7085-Sc alloy shows a smaller grain size, higher ultimate tensile strength (UTS, 624 MPa) and yield strength (YS, 580 MPa) after treatment of 480 °C/1 h + 120 °C/24 h. The high strength of 7085-Sc alloy could be attributed to fine-grained strengthening & dislocation strengthening of Al3(Sc, Zr) particles and the precipitation strengthening of MgZn2 phases. The optimum solid solution temperature of 7085 alloy should be controlled in the range of 470–480 °C and that of 7085-Sc alloy is higher, should be 480–490 °C.