Collaborative Enhancement of Ce and Yb Addition to Microstructure and Mechanical Properties of In Situ Al6Si/5TiB2 Metal Matrix Composites

In this work, the effects of combined addition of Ce and Yb on the microstructure and mechanical properties of Al6Si/5TiB2 MMC were systematically investigated by using optical microscopy (OM), x-ray diffraction (XRD), scanning electron microscopy (SEM) configured with energy diffraction spectrum (EDS), electron probe micro-analysis (EPMA), transmission electron microscopy (TEM) and mechanical tests. The results show that the combined addition of Ce and Yb can simultaneously refine α-Al grains and modify eutectic Si as well as suppress the agglomeration of TiB2 particles to a certain extent. The ultimate tensile strength (UTS), yield strength (YS) and elongation (El) of the composites reached the maximum values of 367.5, 271.3 MPa and 6.1% when the content of Ce and Yb was 0.4 wt.%, which were 14.4, 17.1 and 38.6% higher than that the situation without Ce and Yb addition, respectively. The tensile fracture mode of Al6Si/5TiB2 MMC belongs to a typical mixed brittle–ductile fracture, but when the Ce and Yb were added, it can change part of the brittle fracture into ductile fracture.