Corrosion and Protection of Magnesium Alloys: An Overview of Research Undertaken by CAST

Corrosion behavior of magnesium alloys and protection techniques

“…Having realized that the hydrogen evolution is closely associated with the Song et al (1997b) to estimate the corrosion rate of Mg. After further illustration of the theory and analysis of possible errors inherent to this method (Song, 2005b(Song, , 2006Song et al, 2001), it has also been widely used on many Mg alloys (Song, 2005a;Song and St John, 2002;Hallopeau et al, 1999;Bonora et al, 2000;Eliezer et al, 2000;Mathieu et al, 2000).…”

Corrosion behavior and prevention strategies for magnesium (Mg) alloys

“…A piece of direct evidence is that the corrosion within the matrix phase stops upon reaching the β phase in an AZ Mg alloy (Song, 2005a ). The same barrier effect from the secondary phase of a non-aluminum containing alloy has also been found in a Mg-RE-Zr alloy (Song and St John, 2002 ).…”

“…For example, in the Zr-containing alloy MEZ, the central areas of many grains remain uncorroded while the grain boundaries had been severely corroded which is converse to the corrosion morphology of Al-containing Mg alloys. It was found (Song and St John, 2002 ;Song, 2005a ) that the distribution of Zr in the grain is not uniform. The grain centre is rich in Zr which may stabilize Mg through forming a more protective Zr-containing surface fi lm.…”

“…In the matrix, which is a solid solution, its solute has an important infl uence on its corrosion behavior. For an Al-containing Mg alloy, the matrix phase is a Mg-Al single phase which becomes less active as the Al content increases Song, 2005a ). More importantly, the difference in solid solution concentration can result in differences in corrosion potential and anodic/cathodic activity .…”

“…Therefore, the difference in electrochemical activity and corrosion resistance can be signifi cant even within the same grain of a Mg-Al alloy. Experimental evidence for the differences between the grain center and boundary comes from the corrosion morphology of an AZ91E alloy (Song, 2005a ). The corrosion occurred in the interior areas of α grains and the grain boundary areas were much less corroded.…”