Tailoring in-situ TiB2 particulates in aluminum matrix composites

TiB2 particulates were produced in-situ in aluminum matrices through chemical reactions of K2TiF6 and KBF4 salts with aluminum melts. The formation and growth of the in-situ diboride particulates are studied in the presence of different alloying elements, Mg, Zr, Ti and Si respectively, modifying the reaction chemistry. Microstructural analyses revealed alloying elements playing a significant role on the formation and growth of the in-situ particulates. The addition of 5 w.t. pct. in-situ TiB2 particulates, for example, resulted in a 14% increase in ultimate tensile strength for an as-cast Al-Sialloy. The strengthening effect is attributed to both the direct strengthening of TiB2 particulates as a reinforcement and their effects on modifying eutectic Si in the castings. The morphology and dispersion of the in-situ reinforcing particulates are discussed in terms of reaction chemistry, the heterogeneous nucleation of alpha aluminum grains and the modification of Si in eutectic Al-Si phase.