Microstructure Evolution and Performance Improvement of Hypereutectic Al-Mg₂Si Metallic Composite with Ca or Sb

In this article, the modification effects on Al-Mg₂Si before and after heat treatment were investigated with Ca, Sb, and (Ca + Sb). In comparison with single Ca or Sb, the samples with composition modifiers (Ca + Sb) had the optimal microstructure. The sample with a molar ratio for Ca-to-Sb of 1:1 obtained relatively higher properties, for which the Brinell hardness values before and after heat treatment were remarkably increased by 31.74% and 28.93% in comparison with bare alloy. According to differential scanning calorimetry analysis (DSC), it was found that the nucleation behavior of the primary Mg₂Si phase could be significantly improved by using chemical modifiers. Some white particles were found to be embedded in the center of Mg₂Si phases, which were deduced to be Ca₅Sb₃ through X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM) analyses. Furthermore, Ca₅Sb₃ articles possess a rather low mismatch degree with Mg₂Si particles based on Phase Transformation Crystallography Lab software (PTCLab) calculation, meaning that the efficient nucleation capability of Ca₅Sb₃ for Mg₂Si particles could be estimated.