Evolution of Entrainment Defects Formed in Mg-Y Alloy Castings

Entrainment of the oxidized surface of a light alloy melt can result in the entrapment of a doubled-over surface oxide film containing a small quantity of the local atmosphere, forming an entrainment defect (also known as a double oxide film defect) in the final casting, which decreases the reproducibility of the casting. Most previous investigations into these defects were carried out on aluminum alloys, while research into these defects in Mg alloys has been relatively limited. The work reported herein aimed to characterize the behavior of entrainment defects formed in a Mg-Y alloy, under a cover gas of SF₆/CO₂. The entrainment defects were observed using scanning electron microscopy (SEM) and focused ion beam milling (FIB). A sandwich-like structure that likely corresponds to a deactivated entrainment defect, which has not been reported by previous publications, was discovered.