Structure and Properties of Al–Cu–Yb Alloy with Iron and Silicon Impurities

The effect of iron and silicon impurities on the phase composition and properties of the Al–4.3Cu–2.2Yb quasi-binary alloy has been determined. In the microstructure of the cast alloy, in addition to the aluminum solid solution and dispersed eutectic ((Al) + Al₈Cu₄Yb), in which about 1% of iron is dissolved, the Al₃Yb/(Al,Cu)₁₇Yb₂ and Al₈₀Yb₅Cu₆Si₈ phases are identified, which are not found in an alloy of a similar composition without impurities. After homogenization annealing at a temperature of 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 the deformed sheets significantly decreases after 0.5 h and changes slightly up to 6 h of annealing at temperatures of 150–210°C. After annealing at 180°C for 3 h, a substructure with a subgrain size of 200–400 nm is formed in the alloy structure. The softening after annealing of the rolled sheets at temperatures up to 250°C occurs owing to the recovery and polygonization processes and above 300°C owing to recrystallization. After annealing for 1 h at 300°C, the recrystallized grain size is 7 μm. The grain size increases to 16 µm after annealing for 1 h at 550°C. The Al–4.3Cu–2.2Yb alloy with impurities has a conditional yield strength of 205–273 MPa, a tensile strength of 215–302 MPa, and a relative elongation of 2.3–5.6% in the rolled alloy after annealing. 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.