EFFECT OF SAMARIUM (SM) ADDITION ON THE MICROSTRUCTURE AND TENSILE PROPERTIES OF Al-20%Si CASTING ALLOY

In the present work, the effect of Sm addition (0.2, 0.4, 0.6, and 0.8 wt%) on the microstructure evolution and tensile properties of as-cast hypereutectic Al-20%Si alloy were investigated. The scanning electron microscopy, X-ray diffraction (XRD), and electron probe microanalysis with wavelength dispersive spectroscopy (WDS) were used to quantitatively characterize the samples. The results indicated that the primary Si phases were significantly refined from coarse polygonal and star-like shape to fine block with smooth edges and corners when the addition of Sm increased from 0 to 0.6%. Furthermore, eutectic Si phases were fully modified from coarse platelet-like/needle-like structure to fine fibrous structure and discrete particles with the addition of 0.6%Sm. However, the primary and eutectic Si phases became coarser when the level of rare earth Sm reached 0.8%. The analysis of XRD and WDS shows that Sm mainly exists in the form of Al2Si2Sm compounds. In addition, the tensile properties of as-cast Al-20%Si alloy with different concentrations of Sm were investigated by tensile test. It was found that the ultimate tensile strength (UTS) and elongation (EL) gradually enhanced with the increasing concentration of Sm from 0 to 0.6% due to decrease of the size and the change of morphology on Si phases. Compared with unmodified Al-20%Si alloy, the UTS and EL values of Al-20%Si alloy with 0.6%Sm were increased by 48.5 and 68.8%, respectively.