Evaluation technology of corrosion behavior for automotive steel sheet.

Abstract

An appropriate evaluation technology of corrosion is essential for the development of precoated steels for automotive use. There are various test methods: field surveys, monitor car tests, proving ground tests, vehicle exposure tests, under- and on-vehicle tests, the Volvo test and laboratory tests. They are briefly explained.A cyclic corrosion test (CCT) which simulates and accelerates the field situations is usually carried out in the laboratory. For the design of a CCT, micro-climate in vehicles, corrosion mechanism and environmental tactors must be clear. The environmental factors taken into account for CCT are salt, temperature, humidity, wet/dry ratio and cyclic frequency. In addition, water immersion, ultraviolet rays and air pollutants are of importance in their own ways.A perforation test is conducted with hem flange models or lapped panels in the CCT. Cosmetic evaluation consists of paint adhesion, wet adhesion in water and paint degradation by ultraviolet ray.When a corrosion test is carried out in the CCT, it is recommended to test cold rolled steel and certain zinc coated steel, the behaviors of which in the field are well-known, together with other specimens. The lifespan of these specimens could be estimated in comparison with such steels.