Magnesium alloys are well known for their high specific strength.
There is growing interest in the alloys as structural materials in the
automotive, aerospace and electronic industries. However, the
corrosion performance of most magnesium alloys is not satisfactory
for some practical applications. The Cooperative Research Centre for
Cast Metals Manufacturing (CAST) has been investigating the corrosion
behaviour of magnesium and its alloys since 1995. This paper
presents some of the major achievements in this area recently made
by CAST. The following issues are addressed: Negative Difference
Effect (NDE), role of alloying elements, effect of microstructure and
galvanic corrosion. It was found that: (a) the NDE is a common
phenomenon for all alloys investigated; (b) alloying with aluminium
and zirconium can stabilise the matrix phase of magnesium alloys in
corrosion; (c) in the aluminium containing alloys the β phase appears
to have a beneficial effect on the corrosion resistance especially where
a fine grain size is produced, but in some cases, its presence in an
alloy accelerates the corrosion of the alloy; (d) galvanic corrosion of
magnesium alloys strongly depends on the cathode material and the
manner by which the galvanic couples are exposed to the
environment.

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SOURCE; G.Song. “Investigation on Corrosion of Magnesium and its Alloys”. Journal of Corrosion Science and Engineering. Vol. 6 Paper C104.