Effect of Mn on the Phase Composition and Properties of Al–Cu–Y–Zr Alloy

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%.