Corrosivity of HFC125 as shielding gas for magnesium melt under high temperature

Abstract

HFC 125 is a potential substitutive to SF6 in terms of its protective effectiveness, reduced GWP and cost. In the present study, corrosivity of HFC 125 containing nitrogen atmosphere to the medium-carbon steel of C45E4 was examined by systematic experiments under the temperatures and HFC 125 concentrations commonly used in Mg die-casting practice. For comparison, the corrosivity of SV6, containing nitrogen atmosphere was examined in the identical conditions, followed by X-ray diffraction and X-ray fluorescence characterization of the corrosion products. The results show that the HFC125 containing nitrogen atmosphere was less corrosive to C45E4 than SF6 containing one in long-playing corrosion under identical conditions. Oxidation was the major cause of the corrosion to C45E4 and HFC 125 or SF6 was of secondary contribution. HFC 125 or its decomposition was deduced to corrode C45E4 to produce fluorides; SF6 or its decomposition was deduced to react with C45E4 to produce sulfides. © 2011 The Japan Institute of Metals.