Corrosion resistance is a must for light-alloy wheels

There are standard aluminium wheels and there are Fuchsfelge® wheels. When hearing this product name, every Porsche owner immediately thinks of outstanding driveability and the famous Porsche 911, with which the Fuchsfelge® became a legend as well.

Today, manufacturer OTTO FUCHS supplies various car makers with light-alloy wheels. Surfaces are produced with uni colour and twin tone paint as well as polished. The complex forged, distinctive light-alloy wheels have become an integral part of leading car makers’ premium class. Therefore, the manufacturer Otto Fuchs KG from Meinerzhagen, located in the German Sauerland, places great importance on quality assurance. In a Memmert climatic test chamber, prototypes and pilot runs are tested for corrosion resistance.

Testing for filiform corrosion resistance

Designs with twin tone surfaces (polished sections) and/or polished surfaces show an increased tendency for filiform corrosion. In a Memmert climatic testing chamber CTC, Otto Fuchs tests the quality of paint adhesion to polished aluminium surfaces in accordance with DIN ISO 4623-2 (paints and varnishes – determination of resistance to filiform corrosion) or the factory standard DBL 7381. This form of corrosion, with its typical filiform appearance, can be caused in particular by mechanical damage of the coating, e.g. a scratch. The main reason is thought to be chlorides, which are for example contained in road salt or in sea air.

Important: Long-term stability of the climatic test chamber

Once a scratch mark is applied to the surface to-be-tested, it stays in a salt fog chamber for 24 hours under defined conditions (e.g. in accordance with DIN EN ISO 9227 CASS, a different inoculation is possible) and is afterwards put in a Memmert climatic test chamber CTC for 28 days for corrosion. The temperature-humidity combination varies according to the applied standard or manufacturer. However, usually 40 °C/82 %rh or 60 °C/82 %rh is used. At the end of the test period, the corrosion creep depth of the filiform corrosion is evaluated subsequently.

Temperature may deviate by a maximum of ±1 K over the entire test period. For this reason, Holm Vogt, responsible for corrosion testing at Otto Fuchs, along with the simple menu navigation, especially appreciates the long-term stability and associated failure-free weekend operation of the climatic test chamber CTC. After all, there is hardly any quality manager who would be pleased having to repeat a test that had been running for weeks under certain circumstances.

Atmosafe wants to thank Otto Fuchs KG, in particular the head of the chemical laboratory, Holm Vogt, for the assistance in writing this article.