mold metal reactions of magnesium alloy az91E using sf6 and 3m novec 612 as protective gasses in investment casting technology

Abstract

In this article, the intensity of mold metal reactions between ceramic shell and magnesium alloy AZ91E is studied. The two possible protective gasses used for melt protection are studied SF6 (sulphur hexafluoride) and 3M NOVEC 612. The scanning electron microscopy (SEM) with X-ray spectroscopy (EDS) were used for the analyses of the mold-metal reaction products on the interface between the magnesium alloy and the ceramic shell. Penetration of AZ91E into the ceramic shell was observed, thickness of mold-metal reaction products layer ranged from 0 μm to 80 μm. The intensity of mold metal reaction is much higher on the outer surface than on the inner surface of the casting. The thicker layer of the fine zircon particles as the first layer of ceramic shell seems to lower the mold metal reactions intensity to minimum. While using SF6, the penetration of AZ91E into ceramic shell was observed, the corroded layer consists of Al-enriched phase with higher content of oxygen. The use of 3M NOVEC 612 as the protective gas led to formation of continuous MgO layer between the ceramic shell and the magnesium alloy, thickness of this layer was up to 60 μm depending on the ceramic shell composition in the close surrounding area.