Corrosion on aluminum alloy

Sia Marshall <sia.marshall [at] btinternet__com> writest

>I am planning a practical research project to try and find a
>suitable chemical technique for removing corrosion from aluminium
>alloy (navigation objects).  ...

I would suggest that, before starting whatever treatment, you
perform an analysis to identify the type of alloy, as well as its
structure.  There are hundreds of them, as you can imagine from the
different uses of 'aluminium', from airplanes to kitchenware A
single look at the web will give you an idea about it, for instance:

    <URL:http://en.wikipedia.org/wiki/Aluminium_alloy>

You cannot choose a chemical to 'clean' (clean what? which is the
surface state?) if you don't know such details, as a medical doctor
cannot apply a 'general' treatment without knowing the particular
condition of the ill person.

In principle aluminium and its alloys are cleaned (etched!) using
acidic or alkaline solutions and there are many books giving recipes
for this. They will work more or less uniformly on pure aluminium,
but can be extremely dangerous if applied on alloys, because of the
presence of alloying elements, which will form a pile with the
matrix and lead to localized corrosion, producing pitting (holes
more or less deep, depending on the element and exposure time).

Concerning marine application, the most used alloys are from types
3XXX, 5XXX and 6XXX, containing, among others, manganese, magnesium
and magnesium + silicon, respectively. Depending on these elements
and specially how they are distributed in the matrix, the effect of
the etching agent will be completely different, you have to pay
attention to it. Once you know the type of alloy and define more
precisely what you want to clean, I can suggest you pertinent
solutions to test.

Virginia Costa
Conservation Scientist


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                  Conservation DistList Instance 23:17
                 Distributed: Sunday, November 15, 2009
                       Message Id: cdl-23-17-009
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