Zinc-nickel: tried and tested surface – versatile solution

Zinc-nickel is a well-proven process in the field of surface finishing – and also the answer to a variety of new surface requirements. Current revisions of standards such as the VW standard TL 244 show the trend as well as emerging processes, such as the pliable coating flexcor.

The use of zinc-nickel surface finishing has given the currently widely used material mix in vehicle construction a new degree of freedom, as the coating of steel parts with zinc-nickel enables them to be directly connected with aluminium parts. State-of-the-art combustion engines require other surface concepts for the engine compartment. Here too, zinc-nickel opens up new possibilities due to its resistance to temperatures of up to 200°C. Even in terms of wear protection and robustness, zinc-nickel sets standards and guarantees both quality and durability for components subject to high stress, e.g. for applications in the suspension, braking and locking systems. The electrolytically precipitated alloy coating of zinc with an approximate nickel percentage of 12-15% offers the highest possible protection against corrosion, partly due to the special crystalline structure of the surface. More than 720 hours’ resistance to red rust (neutral salt spray test in accordance with the DIN ISO 9227 standard) can be withstood without any problems, even with low layer thicknesses of 10 µm.

Thanks to these positive characteristics, the reason is obvious as to why the versatile process has remained highly competitive on the broad market of functional surfaces for almost 30 years. Holzapfel has been a pioneer in the field of zinc-nickel surfaces since 1983 and always used its leading edge in terms of know-how to set standards for zinc-nickel applications, for example with the reliable Transcor zinc-nickel surface solution. Transcor meets the standards without the customary additional sealing and thereby offers significant advantages when it comes to stringent requirements to fit sizes or sealing surfaces.

Flexcor offers an especially interesting zinc-nickel solution: by using a special electrolyte in combination with a narrowly defined bath control, the crystalline structure and grain sizes of the precipitation are specifically changed. A formable zinc-nickel alloy surface results, which allows an entirely new value stream design. First coat it – then bend it! That helps to save resources in transportation and logistics, but also saves handling costs. Here again with or without sealing, depending on requirements. Thus it is an important surface finishing solution, e.g. for piping systems in hydraulics or the automotive industry as well as for other components that need to be coated and formed.

The zinc-nickel surfaces produced by the Holzapfel Group comply with all commonly applied standards Automobile standards. The recently published revision of the VW standard TL 244 (edition 2010-12) shows that this versatile process is also an important topic in this field. Among other things, the new standard again raises the documentation requirements for the surface morphology (coating structure) and surface roughness but also regarding the resistance to salt spraying. Furthermore, the standard extends the checking of corrosion resistance of sealed surfaces by combining it with complex tests under varying climatic conditions.

One particularly interesting point is the fact that in the revised standard, the pliable zinc-nickel surface has been included under Ofl-r647 as an independent safety class for the first time. That is yet another indication of the growing importance of this option.

Thus it is especially worthwhile these days to be up-to-date with regard to zinc-nickel surface finishing solutions. Following the current zinc-nickel hype, the Holzapfel Group too has been prompt to react: in order to satisfy the constantly growing demand for zinc-nickel coatings (especially for drum goods), two more newly converted systems designed for sophisticated surface finishing are now available – 24 hours a day, 7 days a week.

The Holzapfel Group innovation team sees additional potential in the application of special sour precipitating zinc-nickel electrolytes But more on that topic in one of the future issues of galvano news.