Structure and properties of AL–Cu–Yb alloy with iron and silicon impurities

Abstract

   The effect of iron and silicon impurities on the phase composition and properties of the Al–4.3Cu–2.2Yb quasi-binary alloy was determined. In addition to the aluminum solid solution and dispersed eutectic ((Al) + Al8Cu4Yb) containing about 1 % of dissolved iron, Al3 Yb/(Al,Cu)17Yb2 and Al80Yb5Cu6 Si8 phases were identified in the cast alloy microstructure (the latter was not found in an alloy of a similar composition but without impurities). After homogenization annealing at t = 590 °C for 3 h, the structure is represented by compact fragmented and coagulated intermetallic compounds 1–2 μm in size, and a solid solution (Al) with a maximum copper content of 2.1 %. The hardness of deformed sheets significantly decreases after 30 min of annealing, and then changes slightly in the following 5.5 h of annealing at t = 150÷210 °C. After annealing at 180 °C (τ = 3 h), a substructure with a subgrain size of 200–400 nm is formed in the alloy structure. Rolled sheet softening occurs due to recovery and polygonization processes after annealing at temperatures up to 250 °C, and due to recrystallization after annealing at temperature above 300 °C. After annealing at 300 °C (τ = 1 h), the recrystallized grain size is 7 μm. The grain increases to 16 μm after annealing at t = 550 °C (τ = 1 h). The alloy under study has a high level of mechanical properties (conditional yield limit is 205–273 MPa, tensile strength is 215–302 MPa, relative elongation is 2.3–5.6 %) in the annealed state after rolling. Iron and silicon impurities do not lead to the formation of coarse lamellar intermetallic phases and do not reduce the ductility of the investigated alloy.