The effect of Mn on particles morphology and property of 5 wt% TiB2/Al-4.5Cu-0.4Mn alloys

•TiB2 particles have the ability to improve the tensile properties of Al-Cu-Mn alloys by 20.7%.•TiB2 morphology underwent quasi-spherical, polyhedron, chamfered hexagonal prism, plate-like hexagonal prism, four stages.•Mn effectively inhibits the diffusion of Ti and B atoms, so the Ti and B atoms were not able to diffuse over long distances.•Mn was preferentially adsorbed on the TiB2 {0001} planes, followed by the {101̅0} planes, and finally the {101̅1} planes. In-situ 5 wt% TiB2/Al-4.5Cu-0.4Mn composites were successfully prepared via the salt-metal reactions, which were assisted by improved mechanical stirring. The morphologies of the TiB2 particles in the matrix of Al-4.5Cu-0.4Mn were investigated using field emission scanning electron microscopy (FESEM). The results indicated that TiB2 particles were mainly present in the morphology of small plate-like hexagonal prisms, with size ranging from 0 to 1.4 µm and thicknesses of 0–0.8 µm. The growth mechanism of the TiB2 and the influence of the Mn on that mechanism were also discussed based on fundamental crystal growth theories. It was found that the Mn affected the growth of the TiB2 from the following two aspects: (1) The TiB2 particles were relatively small overall, due to the fact that the Mn could inhibit the diffusion of Ti and B atoms; (2) The Mn was preferentially adsorbed on {0001}, {101̅0} and {101̅1}, which tended to effectively inhibit the growth of those faces. A lower-energy state of the TiB2 particles with plate-like hexagonal prism morphology was retained in the Al-4.5Cu-0.4Mn alloy. Furthermore, the effects of the TiB2 particles on the tensile strength and elongation of the Al-4.5Cu-0.4Mn alloy were examined.