Effect of Mn on the Phase Composition and Properties of Al–Cu–Y–Zr Alloy
С. М. Амер, R. Yu. Barkov, А. В. Поздняков
Abstract
Abstract— The effect of manganese on the microstructure, phase composition, and mechanical properties of the heat-strengthened deformed Al–5.5Cu–2.0Y–0.3Zr alloy has been studied in this work. The structure of the cast alloy was shown to contain a quaternary phase enriched in copper, manganese, and yttrium with a Cu/Mn/Y ratio of 4/2/1, which corresponds to the chemical compound Al25Cu4Mn2Y. The maximum strengthening of the ingot was achieved by aging after quenching at 210°C for 5 h. Three types of precipitates, Al20Cu2Mn3 and Al3(Zr,Y), were formed in the heat-treated structure in the course of homogenization at 605°C. The size of Al3(Zr,Y) particles was 30–50 nm. The Al20Cu2Mn3 phase had a longitudinal size of 200–250 nm and a transverse size of 150–200 nm. The disc-shaped precipitates of the θ''(Al2Cu) metastable phase with a diameter of 80–200 nm and a thickness of about 5 nm formed upon aging. After rolling and annealing for 1 and 2 h, the hardness was maximum at 150°C. This was explained by a predominance of aging over softening, which retards the growth of dispersoids of Al20Cu2Mn3 and Al3(Zr,Y) phases and dispersed Al8Cu4Y and (Al,Cu)11Y3 particles of crystallization origin. At 210°C, the softening of deformed alloy prevails over the effect of aging and as a result, the hardness decreases slightly. The addition of manganese makes it possible to retain a significantly high hardness in the studied alloy at annealing temperatures up to 550°С and to increase the temperature of the onset of recrystallization to 350–400°С. After rolling followed by annealing at 150°C the alloy was shown to possess high mechanical properties: σ0.2 = 330–334 MPa, σu = 374 MPa, and δ = 3.6–5.5%.