dc.description.abstract |
Electroplated cadmium coatings are widely used in the aerospace industry to provide
corrosion protection for components such as fasteners, which are manufactured from
high strength steels. Due to environmental and safety concerns with regard to the use of
cadmium, there is a requirement to investigate suitable replacements. Any alternate
coating, in addition to effective corrosion protection, must not have deleterious effects
on the steel substrate. Hydrogen is known to be absorbed during electroplating and there
are concerns that this could cause hydrogen embrittlement of high strength steel
fasteners. This study has investigated the effect of zinc-cobalt electroplating on the
embrittlement of high strength steels used for aerospace applications, due to promising
corrosion properties.
i
Permeation measurements have been used to measure the hydrogen uptake during
electroplating, and slow strain rate testing performed to establish the effect of hydrogen
on the embrittlement of the steel substrate. The influences of bath composition,
temperature and pH have been studied, plus the addition of other iron group elements to
the plating bath to minimise the risk of embrittlement. Hydrogen that has passed into the
metal substrate has been located by a decorative mapping technique that also showed
the high concentration present in the electroplated coatings. Corrosion tests have been
executed to assess the performance of the electroplated coatings that have been tested.
The factors that affect the ernbrittlement of zinc-cobalt electroplated high strength steels
and the methods, including modulated multi-layer coatings and baking, that could be
used for its control are described.
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