پوشش های آلومینیمی : شرح و سنجش

Aluminum Coatings: Description and Testing 
پوشش های آلومینیمی : شرح و سنجش

ABSTRACT

Pure aluminum, the 3xxx, 5xxx, and most 6xxx series alloys, are sufficiently resistant to be used in industrial atmospheres and waters without any protective coatings. Coatings are recommended for the higher strength 6xxx alloys, such as alloy 6013, and for all 2xxx and 7xxx alloys. The thickness of the natural oxide passive film can be increased by a factor of 10 by prefilming in hot water and by a factor of 1000 or more by anodizing in sulfuric acid. Different options for mechanical and chemical surface preparation are available depending on choice of coating, appearance, and/or performance. Weak organic acids and their derivatives form insoluble salts and rely on the adsorption of the hydrophobic anions to provide a thin barrier layer. Chelating inhibitors create a thin tenacious passive layer (up to 20 nm). Aluminum alloys are protected by more active metals or by cathodic protection. Corrosion can be prevented or reduced by cladding. Some joint-sealing compounds that contain suitable soluble inhibitors are particularly recommended. Aluminum can be protected by electroless or conventional plating. Aluminum and aluminum alloys in the active state act as a sacrificial anode in the form of plate or as a powder coating. Conversion layers can be created through physical vapor deposition, cathodic magnetron sputtering, high-energy ion beams, and laser ablation. Electrochemical anodization, plasma ablation, and chromate conversion coatings are frequently considered. There are thermoplastic coatings and converted coatings that are applied during or after processing and include principally three types of paints: epoxy, polyurethane, and moisture coatings. Corrosion monitoring is currently carried out by electrochemical impedance spectroscopy methods and electrochemical noise measurements.