Microstructure and Tensile Property of Al₃Zr/Al-Cu-Ni-V Composite Prepared by In Situ Reaction

In this work, the high-temperature stable D0₂₃-Al₃Zr was introduced to an Al-Cu-Ni-V alloy to improve the HT (350 °C) mechanical properties by the melt in situ reaction. The effect of Al₃Zr contents and T6 heat treatment on the microstructure, room temperature, and high-temperature tensile properties of the Al₃Zr/Al-6Cu-2Ni-0.5 V composites was investigated. The α-Al, Al₂Cu, Al₃Ni, Al₃CuNi, Al₇Cu₄Ni, and Al₃Zr phases were present in the as-cast composites. The amount of the fine (2-4 μm) blocky D0₂₃-Al₃Zr increases with the increased addition of K₂ZrF₆ salt. After T6 heat treatment, the dispersed fine θ′-Al₂Cu precipitates (200-300 nm) formed in the matrix. The interconnected structure of the Al₃CuNi phase was broken, became spherical and coarsened. In addition, the Al₃Zr particles had higher Cu content and changed from blocky to elliptical or spherical shapes without changing the tetragonal crystal structure after the T6 treatment. The highest HT tensile strength was observed for the as-cast composite containing 12 wt.%Al₃Zr, reaching 118 MPa, 35.48% higher than the base alloy. After the T6 treatment, the tensile strength of 9 wt.%Al₃Zr/Al-6Cu-2Ni-0.5 V composite at room and the elevated temperature reached 288.5 and 143.1 MPa, respectively. The analysis shows that the addition of K₂ZrF₆ not only introduced the high thermal stability D0₂₃-Al₃Zr, but also promoted the precipitation and refinement of the θ′-Al₂Cu after aging. The improvement of high-temperature mechanical properties of the composites is mainly attributed to the precipitation strengthening of the D0₂₃-Al₃Zr phase and the dispersion strengthening by the θ′-Al₂Cu phase that indirectly modifies by K₂ZrF₆.