Morphology evolution of primary Mg2Si in Ca-modified Al–Mg2Si alloy with various contents of Mg/Si

Abstract

The combined influence of Mg/Si and Ca contents on the crystallization of primary Mg₂Si in Al–Mg₂Si alloy is investigated. Embryo formation of primary Mg₂Si can be restricted by the addition of Ca while the restricted effect is weakened by increasing the content of Mg/Si, and content of Ca for over-modification is increased with the increased Mg/Si content. Growth of primary Mg₂Si is encouraged with the increasing content of Mg/Si, while the addition of Ca can restrict the growth rate directionally in Ca-modified Al–Mg₂Si alloy, which leads to the morphology evolution of primary Mg₂Si. The serious inhibition effect on the whole crystallization process of primary Mg₂Si caused by increasing the content of Ca is the main reason for the occurrence of over-modification. Dice-like primary Mg₂Si is prepared successfully in the over-modified alloy for the first time. The tip-growth process of the dice-like primary Mg₂Si is revealed, which is completed by 2-D nucleation growth. The study provides a novel method to control the morphology and particle size of primary Mg₂Si, which can further help understand the crystallization process of the crystal.