Dual Modification of Hypereutectic Al-Si Alloy and Spheroidization Mechanism of Primary Silicon with Eu Addition

The effects of Eu addition on the silicon phase and mechanical properties of hypereutectic Al-16Si alloys have been investigated using optical microscopy, scanning electron microscopy, electron probe microanalysis mapping, and high-angle annular dark-field scanning transmission electron microscopy. In addition, the mechanism of spheroidization of the primary silicon was studied. The addition of 0.8% Eu generated a refined spheroidal primary silicon and a fibrous eutectic silicon in the hypereutectic Al-16Si alloys. The ultimate tensile strength and elongation were increased by 16.26% and 166%, respectively. The refinement of the primary silicon was caused by a constitutional undercooling of the Eu element. The spheroidization of primary silicon can be attributed to an impurity induced twinning mechanism and a poisoning of the twin plane re-entrant due to the adsorption of Eu at the parallel twins, intersection twins and 141 degrees twin plane re-entrant.

Automated summary

The effects of Eu addition on the silicon phase and mechanical properties of hypereutectic Al-16Si alloys were investigated. The addition of Eu resulted in the refinement of the silicon phase and the formation of spheroidal primary silicon and fibrous eutectic silicon. Moreover, it significantly improved the ultimate tensile strength and elongation of the alloy. The refinement of the primary silicon was attributed to constitutional undercooling of the Eu element, while the spheroidization was caused by impurity induced twinning mechanism and poisoning of the twin plane re-entrant due to the adsorption of Eu.