Abstract
Advanced lightweight systems are being developed using alloys, composites, polymers, and ceramics. Lightweight magnesium (Mg) alloys and ceramics can be integrated to obtain properties not achievable with other combinations of materials. In systems of dissimilar materials, however, crevice and/or galvanic corrosion problems can be problematic if the dissimilar materials are in intimate contact. The focus of this study is corrosion of Mg alloy UNS M11311 resulting from the coupling with monolithic silicon carbide (SiC). The SiC used in this study was of high electrical resistivity and hence galvanic action was not expected. Couples of Mg alloy UNS M11311 and SiC were exposed in a multitude of natural atmospheric environments (i.e., arid, rainforest, severe marine, and volcanic) and in accelerated corrosion tests. Outdoor exposure results showed that the corrosion on Mg alloy UNS M11311 was much less in the crevice at the interface with SiC compared to corrosion outside of the crevice. Polarization experiments and corrosion potential measurements of the crevice and surrounding regions indicated that the crevice region was cathodically protected by corrosion activity outside of the crevice. The corrosion potential inside of the crevice was more positive to regions outside of the crevice. Hydrogen evolution inside of the crevice and generation of excess OH- attenuated the migration of Cl- into the crevice, as confirmed by energy dispersive-X-ray analysis (EDXA).
