Scratching the Surface on Corrosion Testing of Automotive Coatings
Exposure to road salts, UV radiation, heat, moisture and chipping from kicked-up road debris can quickly degrade an automotive coating system. To continually improve coating performance, companies seek to mimic and accelerate real-life exposure conditions in the laboratory.
Recent years have seen a marked improvement in automotive coatings technology, and laboratory testing has played a key role.
A common test involves the purposeful damage of the coating layer to determine a property referred to as rust creep, a quantitative measure of how far the corrosion travels along the substrate/coating interface to either side of a mechanically-induced scratch during exposure to a corrosive environment—typically a neutral salt spray or cycle corrosion test. Rust creep results are used to determine whether a coating process meets the automotive manufacturer’s stringent requirements.
The scribing process can be performed on standardized flat test panels, or on the actual automotive component, if size and geometry permit. Some test specifications call for a single linear scribe, whereas others specify an intersecting set of two scribes, such as seen in Figure 1.