Intermetallic Morphology Development in AM60 Alloy

摘要

It has been well established that entrapped Al-Mn-Fe intermetallics can act as microgalvanic cathodes in magnesium alloys. Many of these studies present evidence suggesting that these particles are Al_8(Mn,Fe)_5 or at least Al-Mn rich. However the morphology development characteristics of these particles in a magnesium alloy have not been documented before. This study investigates the morphology development of these Al-Mn-Fe phases and presents evidence to suggest that there are two types of intermetallic particles which develop in a AM60 melt. There are nearly spherical/elliptical Al_8(Mn,Fe)_5 particles which fall to the bottom of the melt and collect as sludge, and there is an Al-Mn rich phase which could also be Alg(Mn,Fe)5, but which grows over long holding times into floating intermetallic particles. These floating or suspended particles are quite different in appearance to, and have much lower Fe contents than, those seen in the sludge. They initially form as faceted particles just after alloying, and grow into complex "floral" structures after ten hours holding time. These floral structures tend to develop with more branching when the holding temperature is higher.