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Corrosion damage on wheel suspension parts has been noticed in recent years by the Swedish Motor Vehicle Inspection Company in their annual control inspection of motor cars. This type of damage, which affects relatively new cars, has not occurred on earlier models to any great extent. Since the breakdown of a wheel suspension can lead to a traffic accident, it has been considered necessary to investigate the problem. By evaluating results from the yearly inspections of motor cars, different car models could be judged with respect to extent and age of corroded vehicles. Damaged wheel suspension parts, especially spring mountings of the McPhearson type, were analysed to explain the causes of the corrosion. To promote traffic safety in Sweden the Swedish Motor Vehicle Inspection Company is responsible for the annual control inspection of motor cars. The age of the car fleet in Sweden has increased according to Fig. 1 if the situation in 1979 is compared with that in 1989.

In the sample test accounted for in this article, 650 cars of 18 different makes were inspected with respect to resistance against perforation corrosion. The method applied - that of sawing out body parts from collision-damaged cars and inspecting internal open surfaces and crevice surfaces - allows corrosion attack to be discovered at an early stage. The results show great differences in corrosion resistance between different makes of car. For some makes, severe crevice corrosion was found on three-year-old vehicles, whereas other makes included six-year-old vehicles without any severe attacks. The results also show that the makes with the best corrosion resistance had a favorable construction, combined with the use of precoated material with a certain thickness of the zinc or zinc-alloy layer and the use of anti-rust agents with good penetration properties.

The use of cyclic corrosion tests which consist of salt spraying, humidifying, and drying phases is desirable in the evaluation of the corrosion performance of automotive body panels. In this work, coupons of zinc-coated steel and of cold rolled steel were exposed to a defined cyclic corrosion test (CCT) which has shown to be suitable for simulating diverse outdoor conditions for evaluating the cosmetic corrosion of precoated steel. Micro-environment data in the gap of lapped panel specimens, such as wetness, corrosion rate of test materials, pH value, chloride content, have been obtained during the CCT test. The galvanic current flowing between a gold electrode and the test materials was measured to monitor the degree of wetness inside the crevice. The results show that the surface of the test materials never became really dry even during the dry period of the CCT cycle. Furthermore, the wetness during wet and dry periods in the crevice increased with increasing number of CCT cycle.