Novel Cast and Wrought Al-3Zn-3Mg-3Cu-Zr-Y(Er) Alloys with Improved Heat Resistance

The main weaknesses of commercial high-strength Al-Zn-Mg-Cu-based alloys are the low casting properties, corrosion and heat resistance. Al-Zn-Mg-Cu-based alloys with Zn/Mg ratio equal to 1 combine good strength, corrosion and heat resistance. Al alloys with atomic ratio Cu/Y(Er) equal to 4 have a narrow solidification range and high solidus temperature. Two basic principles were taken into consideration to develop novel heat-resistant Al-Zn-Mg-Cu-based alloys with improved casting properties: 1—mass ratio of Zn/Mg = 1, and 2—atomic ratio of Cu/Y(Er) = 4. The microstructure, phase transformation and tensile properties of the novel cast and wrought Al–3Zn–3Mg–3Cu–0.2Zr–Y(Er) alloys were investigated. The structure and phase composition were investigated via thermodynamic calculation, optical and scanning electron microscopy and X-ray diffraction methods. A two-step solution treatment with higher temperature in the second step provides a microstructure with better elongation, making possible to increase the hot rolling temperature of the Y or Er-containing alloys. The yield strength (YS) of the alloys decreased insignificantly from 270 to 290 MPa at room temperature to 225 to 260 MPa at 200 °C after casting, solution treatment, water quenching and aging. A better combination of the YS = 291–345 MPa and elongation (El.) (11–14.8%) was achieved in the Al3Zn3Mg3CuY and Al3Zn3Mg3CuEr alloys after solution treatment, rolling, recrystallization annealing, water quenching and aging compared with the Al3Zn3Mg3Cu alloy with YS = 245–340 MPa and El. = 6.8–12.5%.