All-Russian Scientific Research Institute of Aviation Materials, Moscow, Russia:

E. N. Ryabova, Engineer, e-mail: journal@viam.ru
N. I. Kolobnev, Chief Researcher
L. B. Khokhlatova, Head of a Sector
M. S. Oglodkov, Senior Researcher

We investigated the mechanical properties, tensile, impact toughness, fracture toughness, and phase composition of cold-rolled experimental-industrial plates, made of a new Al – Cu – Li alloy with Ag, Sc, Mg and Zn additives after different heat treatment. The hardening heat temperature was (530±3) ^оС, and its holding period was 15–20 minutes. The plates were stretch flattened with a permanent form change for 0.5–0.8% after quenching. The quenching treatment schedule was the same as for the industrial Al – Cu – Li alloys. The phase and microstructure analysis were made in wide time-temperature area from 120 to 170 ^оС for 10–60 hours on JEM200CX (EM 1132039–49) transmission electron microscope (according to MM 1.595-17-344–2007). The tensile properties, KCU and fracture toughness were defined in the plate-made L and L – T transverses samples. The tensile tests at the room temperature were made using Zwick Roell Z100 testing machine according to the standard GOST 1497–84. The fracture toughness tests at the room temperature were made using MTS-100 testing machine according to the standard GOST 25.506–85. Alloy`s phase composition analysis showed that T₁′, θ′ and S′ precipitations exist at almost all time-temperature aging area from 130 to 160 ^оC for 20 to 60 hours. The maximum strength was reached at 160 ^оC (σ_b≥525 МPа, σ_0.2≥480 МPа). The best combination of impact strength, fracture toughness and strength characteristics was reached at 140–150 ^оС temperature: КСU = 200 kJ/m, К_с^у = 95 МPa√m (В = 200 мм), σ_u≥490 MPа, σ_0.2≥450 МPа, which is caused by the precipitation morphology of presented T₁′(Al₂CuLi), S′ (Al₂CuMg), θ′ (Al₂Cu) phases at the same time.
The investigation was made in the framework of implementation of an 8.1 integral research area: high-strength weldable aluminum alloys and low-density aluminum-lithium alloys with high fracture toughness (“Strategic orientations of materials, treatment processes development for the period to 2030”).

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