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Nanocoating Protecting Die Cast Parts from Corrosion

Editor: MA Alexander Stark

Due to the Europe-wide ban on surfaces containing chromium VI, the zinc die caster Föhl has developed a nanocoating as an alternative to galvanic processes.

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The zinc die-cast base plate for an automotive roof antenna was passivated by a 2 µm thick Föhlan coating.
The zinc die-cast base plate for an automotive roof antenna was passivated by a 2 µm thick Föhlan coating.
(Source: Föhl)

Under the brand name Föhlan, the german Adolf Föhl GmbH offers a nanocoating, which is used as a thin-film passivation of zinc die cast parts to protect them from abrasion and corrosion. The high-tech process developed in-house is already applied in the coating of components of the automotive industry.

Prompted by the general, Europe-wide ban on chromium-VI-containing surfaces, Föhlan was designed as an alternative to galvanic processes. After several years of development, the new technology now offers very good corrosion protection as well as economic and ecological advantages. The new method offers an impressive savings potential in the double-digit percentage range and high corrosion resistance with a layer thickness of only approx. 2 μm. In contrast to electroplating, an even layer thickness distribution is given and protection in cavities is guaranteed. At the same time, Föhlan conserves resources on several levels: With a smaller number of process steps and a coating time of only a few minutes, the passivation machines work effectively and directly at the foundry of Föhl. In addition to saving time and simultaneously increasing the number of units, this also results in lower freight costs and less transport-related damage.

Resource-Conserving Procedure

As a so-called green technology, Föhlan is more energy-efficient than conventional coating processes for zinc parts. The chemical-physical process does not require etching in pre-treatment, avoids any wastewater problems and does not require any approval procedures, nor do any accident ordinances apply. Since the activation is based on alkaline liquids instead of acid, passivation is based on CR3 and the nanoparticles used consist of inorganic SiO2 and an organic polymer-like substance which is 100 % biodegradable, non-flammable and non-corrosive. The passivation layer, which only has a layer thickness of between 0.2 μm and 0.8 μm, acts as a bonding agent for the nano layer. To seal the surfaces, the nanoparticles are sucked in by osmotic effects and stored in capillaries. Nanocoating is possible with a layer of only 0.5 μm to 1.0 μm. Föhlan has a total layer thickness of only 1 μm to 2 μm, while a galvanic CR3 coating of approx. 10 μm is applied.

High-Quality Corrosion Protection

The new surface treatment is particularly attractive due to its corrosion resistance and because it provides the same or better corrosion protection than conventional processes. External laboratory tests verify a corrosion resistance of up to 640 h in the salt spray test according to DIN EN ISO 9227-NSS. In addition, it was possible to demonstrate better tribological properties and higher abrasion resistance than with galvanic coatings.

Original by Dorothee Quitter/ Translation by Alexander Stark

This article was first published by konstruktionspraxis.

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