To protect components from corrosion, processes such as hot-dip galvanizing, spray galvanizing, electrogalvanizing, zinc flakes, etc. are usually used today. Another process has attracted increasing attention in recent years due to the upgrading of process engineering. Zinc thermal diffusion (ZTD) has many advantages over conventional corrosion protection processes and is suitable for coating various materials such as unalloyed steel, stainless steel, copper, cast iron, sintered metals and titanium as well as titanium alloys. Ebbinghaus Verbund holds a patent for the ZTD process in combination with inductive heating and has successfully tested zinc thermal diffusion with a wide variety of materials in its technical center in Solingen.
There are many reasons for coating using the zinc thermal diffusion process. For example, hydrogen embrittlement is excluded in the ZTD process, which is particularly important for safety-relevant and tempered components that are often exposed to high dynamic loads. The hardness of ZTD coatings (300 to 500 HV) is, for example, higher than that of zinc flake, hot-dip galvanizing and some electroplated zinc coatings and therefore leads to a high level of wear resistance. This is an advantage for materials that are exposed to high mechanical loads. It also gives materials such as cast iron or copper a harder, more wear-resistant surface and also improves corrosion resistance.
ZTD coatings have a rough surface that can be controlled by the process and therefore offers good adhesion for other, subsequent coatings - top coats. The ZTD can therefore serve as an adhesion promoter for special top coats. If the ZTD is used for screw connections, for example, the rougher surface can counteract loosening of the screws, especially if they are exposed to vibrations.
The "relatively" low process temperature of 350 to 400°C in the ZTD process compared to hot-dip galvanizing ensures that properties are not affected by previous tempering processes. In addition, zinc coatings produced by ZTD adapt very well to the contours of complex components.
Several of the advantages mentioned here often play a role in the decision to use the ZTD process. One example: for safety-relevant applications, tempered springs must be free of hydrogen in order to avoid hydrogen embrittlement. At the same time, their mechanical properties must not be affected or reversed by the galvanizing process after the tempering process. As a technical spring has a complex shape, the galvanizing process must also ensure that the zinc layer adapts evenly to the contours of the component. Neither electrogalvanizing nor hot-dip galvanizing are suitable here, as they cannot cover all requirements at the same time. ZTD offers an alternative here, as all the desired properties for tempered springs are guaranteed by this process: there is no hydrogen embrittlement, the mechanical properties remain unaffected and no reworking is necessary due to uneven zinc layers, which would lead to higher costs in production.
