Mechanical Properties and Microstructural Evolution of Yb-Modified Al-20%Si Alloy

In the study, the mechanical properties and microstructural evolution of hypereutectic Al-20%Si-xYb alloys (x = 0, 0.1, 0.3, 0.5 and 0.7 wt.%) were studied. The as-prepared samples were characterized by scanning electron microscopy, optical microscope, x-ray diffraction (XRD) and electron probe microanalysis. The characterization results showed with the addition amount of Yb increasing to 0.5%, the eutectic Si structure was gradually modified from coarse needle-like/platelet-like structure into fine coral-like fibrous structure and the primary Si phases were gradually converted from coarse platelet-like/star-like/polygonal shape into fine blocky shape. In particular, according to the results of WDS and XRD analyses, the Yb-rich intermetallic phase in the Al-20%Si alloy is Al3Yb. Tensile test was carried out to study the mechanical properties of Al-20%Si-x%Yb alloys, and results showed that the elongation and ultimate tensile strength increased by 73.6% and 64.5%, respectively.