Synergistic Effects of the Combined Addition of (Ce+Yb) on the Microstructure and Mechanical Properties of Al–Si–Mg–Cu–Cr Casting Alloy

In this study, Al-6Si-0.6Mg-0.6Cu-0.2Cr alloys were prepared with the combined addition of (Ce+Yb) using the traditional ingot metallurgy method. The synergistic effects of (Ce+Yb) modification on the microstructure, including α-Al dendrites and eutectic Si phases, as well as the mechanical properties of Al-6Si-0.6Mg-0.6Cu-0.2Cr cast alloys were systematically investigated using differential scanning calorimetry (DSC), optical microscopy (OM), scanning electron microscopy (SEM), energy diffraction spectrum (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and mechanical tests. The results showed that the combined addition of (Ce+Yb) refined the α-Al grains and modified eutectic Si phases, with the combined addition of 0.6 wt% (Ce+Yb) exhibiting the best impacts on them. The Al11Ce3 and Al3Yb intermetallics were also obtained from the modification. Moreover, the Al11Ce3 and Al3Yb intermetallics functioned as strengthening precipitates and the eutectic Si phases were further spheroidized in the alloy during heat-treatment processing with the combined addition of (Ce+Yb). Coupled with heat treatment, the alloy with 0.6 wt% (Ce+Yb) exhibited enhanced mechanical properties with microhardness, ultimate tensile strength, yield strength and elongation of 89.4%, 114.1%, 183.9% and 208.0%, respectively, which were higher than those of the alloy without (Ce+Yb) modification and heat treatment. Notably, when the alloy was modified with the combined addition of (Ce+Yb), its strength significantly improved, whereas the elongation was not reduced and inversely was increased.