ABSTRACT
The cathodic plasma polymerization employed in SAIE for corrosion protection of aluminum alloys is a 1-min deposition process, during which the temperature of the substrate alloy rises approximately 2-3C. Minimization of this rise in temperature was found to be an important factor in yielding a good corrosion protection system in the case of aluminum alloys because the temperature rise causes the change of alloy components near the top surface yielding poor corrosion protection. The effectiveness of plasma polymerization coating depends on the preparation (interface engineering) of the surface onto which a plasma polymer deposits. In the interface engineering, gas plasma such as plasmas of oxygen, argon, and so forth are also used in the pretreatment (cleaning) of the chemically prepared surface prior to the deposition of a plasma polymer. In the case of corrosion protection of steel, plasma treatment to remove oxides was found to be very effective as described in Chapter 33. The optimal combination of these chemical and/or lowpressure plasma processes constitutes the system approach to low-pressure plasma interface engineering
Using the aluminum sheet substrate as the cathode of a direct current (DC) glow discharge, cathodic plasma polymerization is carried out. Dealing with metal surfaces, cathodic plasma polymerization is the most practical means to provide the best corrosion protection (see Chapter 13). A primer is applied on the surface of the plasma polymer. The thickness of the plasma polymer is roughly 50 nm on average and that of the primer layer is about 30,000 nm (30 mm). Primers used included E-coat (electrolytic deposition of paint) and spray primers, but no top coat was applied in the study of corrosion protection.
