Galvanic and electrolytic activity, rusting, and staining
Galvanic (or electrolytic) corrosion results from dissimilar metals coming into contact, and the consequent flow of electrical current. An electrolytic medium—e.g. water, and especially salt water—speeds up the process. If dissimilar metals are to be used, separate them by means of a neoprene gasket or washer, by fabrics, or by the use of paints. Never place different metals touching without checking their compatibility. Ideally, make all components from the same metal.
Electrolytic corrosion requires consideration when choosing metal fixings: ensure they are compatible. Metal ground fixings may well be preferred for lumber pergolas or decks, so as to protect the lumber from rotting.