xAl3Zr/Al-5Cu-0.6Mn-0.15Ti composites were fabricated via an in situ reaction method, and the influence of Al3Zr content on the microstructure and mechanical properties in both as-cast and T6-treated conditions was systematically investigated. The results reveal that the D023-Al3Zr content increases in proportion to the K2ZrF6 addition level. Following T6 heat treatment, finely dispersed θ′-Al2Cu precipitates were formed within the matrix, and the α-Al + θ-Al2Cu eutectic network dissolved. The blocky Al3Zr particles underwent spheroidization and could continuously exert a grain boundary pinning effect to suppress grain coarsening. After T6 heat treatment, the 4.5 wt.% Al3Zr composite exhibited average ultimate tensile strengths of 324.44 MPa at room temperature and 123.38 MPa at 350 °C, corresponding to improvements of 8.56% and 23.31%, respectively, relative to the unreinforced base alloy. Following thermal exposure at 350 °C for 24 h, the composite exhibited less pronounced coarsening of the θ′-Al2Cu precipitates compared with the base alloy, while the Al3Zr particles retained their morphological and dimensional stability. Consequently, the reductions in both tensile strength and hardness were smaller than those observed for the base alloy. Analysis indicates that Al3Zr particles significantly refine the α-Al grains and enhance the alloy’s thermal stability. The superior property retention is attributed primarily to the high thermal stability of the Al3Zr particles, which preserve their dispersion-strengthening contribution at 350 °C, with the reduced θ′ coarsening as a contributing factor. The overall strengthening of the composite arises from the combined and largely independent contributions of Al3Zr particle strengthening and θ′-Al2Cu precipitation strengthening.
Zhang et al. (Fri,) studied this question.