NaCl-induced atmospheric corrosion of two MgAl alloys in semi-solid cast and diecast states - Influence of microstructure and CO2

The atmospheric corrosion of MgAl alloys AM50 and AZ91 was studied in the laboratory at constant (95.0%) relative humidity and 22\ub0C, in the presence and absence of 400 ppm CO2. NaCl was added prior to exposure. The materials were in semi-solid cast (SSC) and pressure diecast (DC) states. Crystalline corrosion products were identified by X-ray diffraction (XRD). Alloy microstructure and corrosion morphology were characterized by scanning electron microscopy (SEM). Corrosion was more localized in CO2-free environment compared with air with 400 ppm CO2. The different corrosion behavior of the materials is discussed in terms of differences in the microstructure, especially the area fraction and distribution of β-phase. The surface film formed in the absence of NaCl was investigated by X-ray photoelectron spectroscopy (XPS)