Effect of Sc and Zr co-microalloying on microstructure evolution and mechanical properties of 7085Al alloy

In this paper, the trace addition of Sc and Zr in 7085Al alloy significantly improved strength and ductility at room and high temperature. The Al₃(Sc, Zr) precipitates with Sc-rich core and Zr-rich shell and their size ranged from 20 to 80 nm, such special structure made Al₃(Sc, Zr) precipitates owned excellent thermal stability. Hence Al₃(Sc, Zr) precipitates can still effectively pin grain boundaries and hinder dislocation movement at high temperature. The dislocation accumulation caused by Al₃(Sc, Zr) precipitates during hot rolling promoted dynamic recrystallization. The average grain size of α-Al grains was increased with the increase of rolling reduction and the average size grains of 7085Al- 0.3Sc- 0.2Zr alloy with 90 % rolling reduction were decreased to 3.2 μm. Compared with 7085Al matrix alloy under 90 % rolling reduction, the average grains size was decreased to 70.3 %. Al₃(Sc, Zr) precipitates had good strengthening effect at both room and high temperature. The UTS, YS and elongation of 7085Al- 0.3Sc- 0.2Zr alloy at 25 °C were increased to 611.7 MPa, 523.8 MPa and 13.8 % respectively, the UTS, YS and elongation of 7085Al- 0.3Sc- 0.2Zr alloy at 300 °C were increased to 223.4 MPa, 201.2 MPa, 27.9 % respectively. The increase of mechanical properties was attributed to the synergistic strengthening effect induced by the fine grain strengthening and the Orowan bypassing strengthening mechanisms.