Experimental Investigation on Microstructure and Segregation of Ultrahigh Strength Al-Zn-Mg-Cu-Zr-Sc-Ni Alloy during Homogenization

Ultrahigh strength Al-12Zn-2.4Mg-1.1Cu-0.20Zr-0.30Sc-0.30Ni alloy billets were fabricated by spray deposition method(the Osprey process). The effect of homogenization treatment on the microstructures and tensile properties were investigated by OM, SEM and EDS. The results show that adding small amount of Sc and Zr can greatly refine the grain size of the billet, with the average grain size of 10 μm. Grain-boundary becomes coarser firstly and then thinner under different homogenizing condition and grain coarsening were observed. The solute elements content of Zn inside grains has a peak at 490 ℃ /2 h, and Cu element, which was solved into matrix, can enhance the matrix hardness obviously during homogenization. The suitable homogenizing treatment is 460～490 °C/2 h for the hot extrusion of the studied alloy; after the optimized solid solution and T6 aging, the highest ultimate tensile strength (UTS) is 858 MPa with a ductility of 4.8%.

Ultrahigh strength Al-12Zn-2.4Mg-1.1Cu-0.20Zr-0.30Sc-0.30Ni alloy billets were fabricated by spray deposition method（the Osprey process）. The effect of homogenization treatment on the microstructures and tensile properties were investigated by OM, SEM and EDS. The results show that adding small amount of Sc and Zr can greatly refine the grain size of the billet, with the average grain size of 10 μm. Grain-boundary becomes coarser firstly and then thinner under different homogenizing condition and grain coarsening were observed. The solute elements content of Zn inside grains has a peak at 490 ℃/2 h, and Cu element, which was solved into matrix, can enhance the matrix hardness obviously during homogenization. The suitable homogenizing treatment is 460-490 ℃/2 h for the hot extrusion of the studied alloy; after the optimized solid solution and T6 aging, the highest ultimate tensile strength （UTS） is 858 MPa with a ductility of 4.8%.