Influence of chemical modification by Y2O3 on eutectic Si characteristics and tensile properties of A356 alloy
(1. Department of Casting Technology Central Metallurgical Research and Development Institute (CMRDI), P. O. 87, Helwan, Egypt;
2. Department of Mining, Petroleum and Metallurgical Engineering, Faculty of Engineering, Cairo University, P. O. 12613, Giza, Egypt)
2. Department of Mining, Petroleum and Metallurgical Engineering, Faculty of Engineering, Cairo University, P. O. 12613, Giza, Egypt)
Abstract: The modification of A356 aluminum-silicon alloy using yttrium oxide (Y2O3) was studied. Addition levels of up to 2.5 wt.% Y2O3 were investigated. A premixed powder of Al-30wt.%Y2O3 was added to the melt at about 750 °C using vortex method. Samples were then poured in sand mold. The results showed that evident modification was obtained using the Y2O3 addition. The optimum level was 1.5 wt.%, and was corresponding to a eutectic temperature depression from 568 to 557 °C. The eutectic Si particles were refined in length from 44.8 to 8.3 μm, and modified in aspect ratio from 6.8 to 0.98. Higher additions of Y2O3 caused de-modification of the eutectic Si particles. The ductility of the modified specimens was enhanced by more than 20% compared to the unmodified ones. This was associated with a gradual transfer from cleavage to a more ductile mode of fracture.
Key words: hypoeutectic Al-Si alloys; modi？cation; yttrium oxide (Y2O3); ductility; fracture mode