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

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 degrees C for 5 h. Three types of precipitates, Al20Cu2Mn3 and Al-3(Zr,Y), were formed in the heat-treated structure in the course of homogenization at 605 degrees C. The size of Al-3(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 theta''(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 degrees C. This was explained by a predominance of aging over softening, which retards the growth of dispersoids of Al20Cu2Mn3 and Al-3(Zr,Y) phases and dispersed Al8Cu4Y and (Al,Cu)(11)Y-3 particles of crystallization origin. At 210 degrees 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 degrees C and to increase the temperature of the onset of recrystallization to 350-400 degrees C. After rolling followed by annealing at 150 degrees C the alloy was shown to possess high mechanical properties: sigma(0.2) = 330-334 MPa, sigma(u) = 374 MPa, and delta = 3.6-5.5%.