In this study, grain refining effect of AI-1.5C master alloy was examined on an AZ63B magnesium alloy, and therefining mechanism was studied through investigating the role of C and Fe in this process. The results show thataddition of AI-1.5C master alloy leads to significant decrease of the mean grain size from about 270 μm to 50 μmat the center of the AZ63 alloy ingot. Grain refinement by carbon addition is mainly due to the heterogeneitynucleation on the AI-, C-, O-, Fe- and Mn-rich particles, but not constitutional undercooling caused by the carbonsolute element. Fe plays an important role in the formation of the nucleating particles, but not acts as an inhibitingelement.
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