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%.
Aluminum alloys alloyed with rare earth and transition metal are promising materials for electric energy transportation due to their high properties of strength, thermal stability, and electrical conductivity. The features of strengthening, their mechanical properties and electrical conductivity of Al–0.2Y–0.2Sc–0.3Er alloy after cold rolling have been established. The alloy as a cast structure is presented by aluminum solid solution (Al) and dispersed eutectics with τ2 (Al75-76Er11-17Y7-14) phase upon complete dissolution of scandium in (Al), and a content of yttrium and erbium at the level of 0.2–0.3 % each. Cold rolling the ingot accelerates strengthening upon annealing at 270 and 300 °C, reducing the time of achieving peak hardness. The maximum strengthening due to precipitation of L12 dispersoid of Al3(Sc,Y,Er) phase with the average particle size up to 10 nm is achieved after 7 h of annealing at 300 °C after cold rolling. This shows the prevailing heterogeneous mechanism of nucleation due to defects accumulated during cold rolling which stimulates strengthening. The eutectic particles are located mainly along the boundaries, elongated in the rolling direction. Irrespective of the mode of sheet fabrication, the alloy demonstrates high thermal stability up to 400 °C. During annealing of the sheets to 450 °C, their non-recrystallized structure is retained. Ingot annealing at t = 300 °C in 7 h and cold rolling with subsequent annealing under the same conditions provide a high level of mechanical properties and electrical conductivity: σ0.2 = 194 MPa, σu = 210 MPa, δ = 12.1 % and IACS – 60,1 %. The alloy has demonstrated high yield stress up to 100 h of annealing at t = 300 °C.
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