Microstructural characterization, solidification characteristics and tensile properties of Al-15%Mg2Si-x(Gd-Sb) in-situ composite

In the present study, complex modification of primary and eutectic Mg2Si particles in Al-15%Mg2Si, composite was examined by simultaneous addition of gadolinium (Gd) and antimony (Sb). It was realized that combined addition of 1.5 wt. % Gd-Sb was efficient for modifying Mg2Si, in which coarse dendritic primary Mg2Si particles were changed into a perfect truncated octahedral morphology with a decrease in average size from 40 mu m to 12 mu m an increase in density of Mg2Si per area from 495 to 1435 particle/mm(2), and a reduction in the aspect ratio from 1.34 to 1.17. Furthermore, eutectic Mg2Si particles transformed from plate-like to fiber-like structure with an average eutectic Mg2Si cell decreasing from 132 mu m to 51.22 mu m. Thermal analysis revealed that nucleation and growth temperatures of primary Mg2Si increased with addition of Gd-Sb. However, it had an opposite effect for eutectic Mg2Si. It was proposed that refinement/modification of primary Mg2Si particles was mainly derived from formation of Mg3Sb2 compounds as heterogeneous nuclei for primary Mg2Si. Meanwhile, the preferred growth of primary Mg2Si crystals along < 100 > direction can be obviously suppressed by the absorption and poisoning of Gd and Sb. The tensile results presented that addition of 1.5 wt. % Gd-Sb to the composite enhanced the UTS and %El from 204.79 MPa and 2.65% in base condition to 242.73 MPa and 3.9% in the modified composite, respectively. This study demonstrated that combined addition of Gd-Sb can provide a better effect on the modification and tensile properties of Al-15%Mg2Si composite than addition of Gd or Sb separately.