ABSTRACT

The importance of and difficulty to control the melt cleanliness of Mg alloys are described. The melt uncleanliness is mainly attributed to the non-protective porous surface oxide layer, which is the reason for the inherent SHE (Safety/Health/Environment) obstacles and for the uncontrolled, deteriorated process-ability and property. The challenge is to find out the solution that should generate the protective surface oxide layer but should not damage the real process-ability and property. Moreover, the solution can be applied in the same way to all types of Mg alloys. As one possible solution to satisfy all the issues together, this paper demonstrates ECO-Mg alloys, which can be simply made by adding CaO powders into current all types of Mg alloys. The stable oxide layer on all ECO-Mg alloys can ensure no burning during process and application (Safety), non-SO2 processing and Be-free alloying (Health), and non-SF6 processing (Environment), which in turn ensure the melt cleanliness, and therefore, the improved fluidity and ductility. It is of interest that the added CaO is reduced thermodynamically to form Mg2Ca (C14) in pure Mg and Al2Ca (C15) and/or (Mg, Al)2Ca (C36) in Mg-Al alloys with α-phase of having almost no Ca solid solution in it. The CaO on the oxide layer is not the added CaO but the re-oxidized CaO from the initially reduced Ca phase.