Steering and suspension 28 www.aftermarketonline.net APRIL 2025 Keeping parts protected with corrosion control Steering and suspension parts manufacturer Meyle considers whether zinc flake coatings are the anti-corrosion solution mechanics could be looking for Corrosion and control arms is a topic that, above all, owners of VW Golf 7 vehicles often find themselves confronted with. The reason for this being the special design of the rear, lower control arm. Not only does the spring sit in the rear axle suspension, but the whole control arm is open at the top. This means that dirt and water can get to the spring’s seat at all times and water can enter through cracks in the finish. As a result, the drainage holes get clogged up, preventing the water from draining away fully. In addition, if the finish is damaged by the impact of stones, the material underneath can rust so badly over time that the spring penetrates the control arm. In a case like this, the safety of the vehicle is no longer guaranteed and continued use of the vehicle is not advisable. So why are control arms so susceptible to corrosion? The spring-carrying control arm is highly susceptible as it is exposed to various external influences. These include mechanical stress — an accumulation of sand and dirt at the spring seat leads to a higher degree of wear of the protective layer and thereby premature wear and tear. In addition, direct contact with the road surface damages the coating, allowing moisture to find its way in. Water penetration under the paint layer then causes infiltration and detachment, which in extreme cases can lead to spring breakage. These problems are regular causes of complaint by testing institutions such as TÜV and often lead to the rejection of rusted control arms. Good protection against corrosion is vital for spare parts, which are exposed to severe environmental stress. The distinction is made here between passive and active corrosion protection. Passive corrosion protection is achieved through a coating, such as conventional paint. This forms a barrier between the metal and the environment. But only as long as the coating remains undamaged. With active corrosion protection, on the other hand, chemical processes come into play which minimise corrosion. A well-known procedure is the cathodic protective effect, whereby the metal itself is protected against corrosion and no additional barrier, such as paint, for example, is used. However, it is important to mention that not every material is suitable for active corrosion protection! Not all coatings are alike. In addition to the standard galvanic coating procedure, there are also so-called zinc flake coatings available today. In this process, zinc particles in the form of flakes are used, which adhere to the metal surface thanks to special bonding agents. This means that it is active protection! Zinc flakes act as pigments or layers that not only passively protect the steel beneath by acting as a barrier, but also actively, as the zinc oxidises preferentially, thereby protecting the steel from corrosion. Zinc flake coatings also have a high temperature resistance, which creates a resistant and robust protective layer. As a result, control arms with this coating can withstand a high level of mechanical stress. Incidentally, corrosion resistance is tested in so-called ‘salt spray chambers’. To summarise, zinc flake coatings offer effective protection against corrosion and significantly lengthen the service life of control arms.
RkJQdWJsaXNoZXIy MjQ0NzM=