Interfacial precipitation of the in-situ TiB2-reinforced Al–Zn–Mg–Cu–Zr composite

Abstract

The interfacial precipitation of reinforced particles has a critical influence on particle-reinforced aluminum-matrix composites. In this study, TiB2 interfacial precipitation of 6 wt% TiB2/Al–10Zn–2.3 Mg–2Cu–0.12Zr composite was studied. The results demonstrate that the TiB2 surface has a considerable impact on precipitation during different states of the composite preparation process (including heat treatments). The TiB2 surface acted as a nucleation site for D023–Al3Zr and was wrapped with the T phase during solidification; a good orientation relationship existed between TiB2 and D023–Al3Zr: (0 00 1)TiB2//(1‾ 03‾)D023–Al3Zr, (1 01‾ 0)TiB2//(1 05‾)D023–Al3Zr, and [1 21‾ 0]TiB2//[0 1 0]D023–Al3Zr. After homogenization or solution, the TiB2 wall hindering solute atoms diffused into the matrix, particularly for Mg and Cu, causing the T phase to dissolve incompletely, and the residual T phase on the TiB2 surface transformed to the S phase layer at a longer holding time. Additionally, the hindering effect of the TiB2 walls results in the enhancement of the local high solute atom concentration and provides a high precipitation driving force. Therefore, the interfacial phase, Mg(Cu2-XZnX), preferentially precipitated at the D023–Al3Zr and S phase interface during peak aging. In this process, the periodic misfit dislocations of the interface facilitate the diffusion of solute atoms and reduce the nucleation energy barrier, promoting interfacial precipitation. Eventually, the interfacial precipitates layer relieved the local stress concentration but consumed the solute atoms, which was considered to be beneficial to plasticity at the cost of strength weakening to achieve excellent comprehensive mechanical properties.