Non-SF6 and Beryllium-Free ECO-Mg Alloys with Improved Recyclability

It is well known that Mg alloy, due to its nature of poor oxidation and burning resistance, should be processed under protective gases and contain a toxic element, Beryllium (Be) with also poor recyclability. The generally used protective gas is SF₆ of extremely higher global warming potential or a toxic gas of SO₂ with rotten smell. This paper will discuss the nature of the surface oxide layer of Mg alloys to explain why conventional Mg alloys have no resistance of ignition and oxidize and burn so easily. As one of potential environmentally friendly Mg alloys with improved recyclability, ECO-Mg alloys will be addresses to form the thin and stable surface oxide layer.

ECO-Mg alloys are expected to reduce or eliminate SF₆ and SO₂ protective gases; eliminate Be addition; and improve melt cleanliness. Special attention is also paid to the improved melt cleanliness of ECO-Mg alloys not only for improved mechanical properties and enhanced castability and formability but also for improved recyclability.

The main point of ECO-Mg alloys in terms of microstructure is that incorporated CaO is reduced 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 CaO powder incorporated to make ECO-Mg alloys but the re-oxidized CaO from initially reduced Al₂Ca.