Preparation, microstructures and mechanical properties of in-situ (TiB2 + ZrB2)/AlSi9Cu3 composites

In this paper, the preparation, microstructures and mechanical properties of in-situ (TiB2 + ZrB2)/AlSi9Cu3 composites are investigated by X-Ray diffraction (XRD), optical microscope (OM), scanning electronic microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM) and tensile testing. The composites are fabricated from Al-K2TiF6-K2ZrF6-KBF4 system via melt in-situ reaction technology. The results reveal that the morphology of TiB2 and ZrB2 particles is presented in rectangular and nearly hexagonal, and the size of 20-100 nm in the synthesized composites. In addition, the particles are agglomerated as many of Reinforced Group, which are distributed along the crystal boundary of the matrix. The silicon phase and secondary dendrite arm spacing of AlSi9Cu3 alloy are obviously changed by the introduction of in-situ particles. The morphology of the silicon phase is presented in rod-shape or needle-shape with the size of about 3-10 mu m. The particles affect the formation of dendrites and the size of the secondary dendrite arm spacing is 9.8-20 mu m, while it seems to not affect the morphology of the CuAl2 phase. Tensile testing results show that the tensile strength and elongation clearly increase with the introduction of in-situ particles. Moreover, the tensile strength and elongation reach 265 MPa and 14.8% respectively, with the best reaction time (30 min) and mass fraction of reactants (20wt.%). The mechanical stirring also significantly affected the particles dispersion in the composites. (C) 2016 Elsevier B.V. All rights reserved.