Guys,
does anyone remember a topic about how to clean and treat corrosion on aircraft parts?

The methods and materials used depends on what material you’re treating!

Can you find out if you’re dealing with Steel, Aluminium, “Alclad” or any form of Magnesium Alloy?

This info should be in the “spec” of repair materials – if you have a repair manual…

Try this:
http://www.corrosionist.com/Aircraft_corrosion_protection_library.htm

Alternatively try describing the type of corrosion you can see.