Passivation of aluminium, steel and stainless steel

In general, the passivation of aluminium, steel or stainless steel is an essential component for optimal corrosion protection. However, the passivation of metals also plays a central role for the adhesion to adjacent coatings, for friction and wear reduction and for possible electrical insulation. The demands on such coating systems have increased due to legal requirements in health and environmental protection and the demand for more sustainability, but also due to more intensive stress on materials and growing cost pressure.

At Zitt, we carry out intensive research and development work on new coating systems and, together with renowned partners from industry and in collaboration with academic institutions, we are intensely involved with the most innovative technologies in modern surface technology. In doing so, we have set ourselves the goal of not simply accepting the status quo of what is technically feasible and of constantly exploring new boundaries when it comes to innovative processes for the passivation of aluminium, steel or stainless steel.

Due to the excessive growth of the world's population and the high demands of industry, today's researchers are expected to develop new innovative and durable materials. For metals, corrosion is the biggest problem to be solved through efficient and sustainable passivation processes, so innovative corrosion protection systems and methods need to be continuously developed.

Why is there a need for innovative conversion coatings? It is about complying with legal requirements, protecting health and the environment, and reducing costs.

The need for innovative passivation of aluminium, steel or stainless steel arises from various factors and requirements: On the one hand, many conventional corrosion protection methods are banned due to environmental and health aspects.For example, in the automotive industry (but is also in other fields, like aviation, etc.) it is forbidden to use passivation methods with chromium (VI) species due to their toxicity and carcinogenic properties [1]. On the other hand, by finding new, environmentally friendly materials and methods, more effective corrosion resistance could be achieved in a more cost-effective way. For example, if a specific additive (inorganic or organic nanomaterial, organic molecule with active functional groups, hybrid, etc.) could be found which, in a conversion coating or paint system, massively increases the corrosion resistance, the thickness of the coating could be reduced, which would of course represent a significant economic advantage.^[2]

Our focus lies with the materials aluminium 2024, aluminium 7075, hot-dip and electrolytically galvanised steel as well as stainless steel. The current challenges are to ensure REACh compliance, energy saving and sustainability. Furthermore, conventional processes are unstable and not sufficiently efficient.

• Development of chromium-free conversion coatings (CCC, REACh!) based on silane, e.g. integration of high-performance nanomaterials with the aim of
  • increasing corrosion resistance
  • increasing compatibility with typical automotive and aerospace coatings
  • improving mechanical resistance (deformability, scratch resistance...)
• Development of additives for corrosion protection coating systems

• Robust and fast technology, possibility for local application/repair (spraying, brushing).
• Innovative sustainable coatings from raw material to process chemicals
  • Environmentally friendly and energy efficient
  • Low temperature processes
  • Low rinse water requirement, thus less waste water
  • Low need for inspection and repair

[1] Xingwen, Y., et al., Study of double layer rare earth metal conversion coating on aluminum alloy LY12. Corrosion Science, 2001. 43(7): p. 1283-1294.

[2] First part according to P. Velicsanyi, PhD thesis, Vienna University of Technology, 2019