Methods of protection and decoration of aluminum profiles

Abstract

The article provides a review of scientific and technical information on methods of applying a special protective coating to aluminum profiles to increase their properties and improve the marketability of products used as decoration. The most common among them are: anodizing (anodic oxidation), painting, coloring, laser processing, chemical etching, electropolishing, etc. It is shown that almost all processing methods begin with special preparation of the profile surface: degreasing, washing, etching and lightening (deoxidation). Anodizing is an electrochemical process in which a strong porous oxide film is formed on the surface of aluminum, which provides more reliable protection of the surface compared to a natural oxide film. This process allows you to improve the appearance of the aluminum profile, increases the corrosion resistance of the profiles, gives the surface layer wear resistance, as well as thermal and electrical insulating properties, increases the adhesion strength to the surface of the paint coating product. Anodized aluminum is easy to clean and can withstand short-term exposure to temperatures at which pure aluminum melts. Anodizing technologies used to achieve the required coating color are described. Painting is the process of applying a liquid or powder organic coating to the surface of the profile, which must resist the effects of sunlight, moisture, aggressive environments, temperature changes, and physical damage. Powder coatings have practically the same performance characteristics as liquid coatings of the same material, but the cost of their application is lower. They are applied electrostatically. The ingredients of the powder are binders (resin and polymer), organic and inorganic pigments to ensure the color of the coating, additives that improve the technological properties of the powder. Most often, the process of chromating and applying a conversion coating is used for aluminum profiles that can be powder coated. The chromate layer improves the adhesion between the surface of the profile and the coating, increases the corrosion resistance of the painted profile. A thick chromate coating has good corrosion resistance, but less adhesion compared to a thinner layer. They use "yellow" and "green" chromating, which, above all, differ in composition, number of components and processing time. Technological features of applying powder coating are considered. Abrasive cleaning is used as an independent way to give a special appearance to the surface of the profile, as well as to prepare the surface before anodizing or painting. Abrasive cleaning is carried out by blowing the surface of the profile with a high-speed stream of dry metal or non-metal particles, as a rule, washed quartz sand or aluminum oxide is used. This type of treatment can be used before painting not only for cleaning, but also for obtaining a matte texture. Laser processing makes it possible to manufacture products without roughness and notches, to increase corrosion resistance, wear resistance and strengthening of aluminum profiles due to surface alloying with chromium, nickel, niobium disilicide, etc. The saturation of the surface layers of the alloy with alloying elements occurs as a result of diffusion and mass transfer in the liquid phase with possible convective or purely mechanical mixing of the melt in the zone of action of laser radiation. Chemical polishing is carried out in acid solutions. Small concentrations of heavy metals in the solution enhance the polishing effect, especially when processing alloys with a small copper content. Air mixing is used, although a mechanical method is preferred. Agitation that is too intense can lead to streaking and pitting of the profile metal. The technological process of electropolishing includes preliminary treatment (cleaning, washing) and, in fact, electropolishing. The profiles are placed in a bath through which a direct current pass, where it acts as an anode. This type of treatment is used both as an independent operation and in technological processes of surface treatment, which include anodization. Typical modes of electropolishing depend significantly on the chemical composition of aluminum and its alloys. Patent studies conducted by the authors of this work showed that despite the variety of surface treatment methods, achieving a shiny profile surface is a complex technical task, the solution of which largely depends on the chemical composition of the aluminum alloy.