Ally for corrosion-free alloy

Lightweight solutions are in high demand in many industries. In the aerospace, automotive and construction industry often aluminum alloys are chosen to do the job. Their low density and high strength to weight ratio renders them a valuable material. Although some aluminum alloys exhibit good corrosion resistance on exposure to the environment, the majority requires protection against corrosion.

However, established methods of surface treatment, including chromating and phosphating, are increasingly reaching their limitations and are seen more and more critically, owing to their environmental impact. In Europe, the use of substances containing chromium (VI) is being banned in an increasing number of applications, through such provisions as the second RoHS Directive (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment), which came into force in 2013. The US, Japan, China, and South Korea have adopted similar regulations.

Hence, alternative methods for protecting metal surfaces against corrosion are urgently needed. Evonik’s specialists have developed, under the Dynasylan® SIVO brand name, a series of binders that have proved their worth in a wide range of materials and application methods.

When it comes to combining environmental friendliness with uncompromising performance in metal treatment, Dynasylan® SIVO 160 is the solution of choice. It is particularly suitable for protecting materials like aluminum, magnesium, and zinc-galvanized iron or steel against corrosion. In contrast to many other solutions employed in this area, this binder contains neither heavy metals nor fluorides.

In automotive metal pretreatment Dynasylan® SIVO 160 has proven effective for corrosion protection and imparting alkali resistance. In construction and industrial applications, it provides excellent corrosion protection to aluminum and galvanized steel. Due to its polymeric nature, it is highly reactive, which makes it a popular primer for low temperature powder coatings.

Water-borne silane systems like Dynasylan® SIVO 160 are fully hydrolyzed and contain reactive silanol groups that are stabilized: This ensures a shelf life of at least one year. They are easily diluted in water, non-flammable and release only minimal amounts of volatile organic compounds (VOC) during curing. It is a defined product with constant product quality and performance.

Silane based water-borne sol–gel systems are usually applied as a thin layer in the nanometer range. A film thickness of just 100 to 200 nanometers is all that is needed to protect aluminum from further corrosion. As the silanol groups react not only with the metal substrate but also with each other during condensation, a dense two- and three-dimensional network is created that protects against water and chloride. For use in exterior applications, the system can be formulated with additional additives and stabilizers. Thanks to the high reactivity of the organofunctional silanol groups, curing can take place at temperatures as low as 60°C. The cured coating layer can protect without top coat against corrosion, whilst simultaneously acting as an adhesion promoter when any subsequent coating is applied.

Dynasylan®-based corrosion-control coatings have been tried and tested over many years—in Basel’s Picasso Center, for example, and London’s “Gherkin” office tower, as well as in protective paints on innumerable bridges and ships all over the world. In all these areas Dynasylan® SIVO offers unparalleled performance and a double benefit for the environment: directly, by releasing fewer volatile organic compounds, and also by increasing the service life of structures and installations as a result of its corrosion-inhibiting action. This prevents waste and represents a genuine contribution to sustainability.