Effect of Cr on the Microstructure and Mechanical Properties of the Al-Cu-Y-Zr Alloy

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The present investigation aimed at the determination of Cr addition on microstructure, phase composition, and mechanical properties of the Al-Cu-Y-Zr alloy. Quasi-binary alloys of the ternary Al-Cu-Y system with atomic rotation of Cu/Y = 4/1 have a narrow solidification range with high solidus temperature. The addition of 0.3% Cr in the Al-5.1Cu-1.7Y-0.3Zr alloy provides a formation of a novel quaternary Al81–85Cu7–10Y3–4Cr5 phase. L12-Al3(Zr,Y) phase spherical particles with a diameter of 50 nm were nucleated during solution treatment at 600 °C. Al7Cr precipitates were not found in the microstructure. The main strengthening effect of 32.4 MPa and 29.1 MPa was achieved from L12 and θ’(Al2Cu) precipitates, respectively, in accordance with the calculation. The calculated hardness of 61.5HV based on the calculated σy is consistent with the experimental value of hardness. Al3Zr and Al7Cr phases should be in equilibrium with (Al) in accordance with the calculated polythermal section. However, transmission electron microscopy investigation demonstrates the Al3(Zr,Y) precipitates only. As a result, the dissolved Cr atom provides a slightly higher hardness in the rolled and annealed AlCuYZrCr alloy. A suitable combination of strength and ductility was observed both after rolling and after rolling with subsequent annealing at 150 °C for 3 h—the alloy exhibited a yield strength of 308–315 MPa, an ultimate tensile strength of 323–335 MPa, and an elongation to failure of 2.0–3.3%.