Understanding and Controlling Corrosion of Aircraft Structures











What finishes provide the best corrosion performance in exterior applications?

Obtaining good corrosion performance is dependant on a variety of variables.  Selecting the right finish can be as important as selecting the right stainless steel. Conversely, finish selection can make it necessary to use a more or less corrosion resistant stainless steel if corrosion free performance is desired.  When a stainless steel has a pickled, electro-polished, or a mirror-like polished and buffed finish, it will generally provide the best corrosion resistance.

Light gauge sheet and strip with 2D, 2B, or BA (2R) mill finishes also provide very good corrosion performance.  These finishes can be used as-is or patterns may be pressed into them. These patterns can include common coined and embossed finishes that look like fabric (cambric, linen), diamonds, and many other shapes.  They can also simulate polishing and abrasive blasting.  The performance of the patterned finishes varies with the finish pattern and its orientation.  Some patterns are more easily washed clean by rain or manual cleaning and these will provide better performance than those which retain surface deposits.  Vertical rather than horizontal finish orientation also encourages rain cleaning.  These finishes vary in appearance from dull to mirror-like.
Is a rougher polished surface finish more likely to corrode?

Research has shown a direct correlation between the roughness of mechanically abraded or polished surface finishes and the likelihood of corrosion. Smoother surface finishes typically retain less dirt and debris, and provide better corrosion performance than rougher finishes. For that reason, European Standard EN 10088 recommends a surface roughness of Ra 0.5 microns (20 micro-inches) or less for polished finishes used in environments with high levels of particulate, corrosive pollution, and/or salt exposure and in applications where regular maintenance is unlikely. Similar guidelines should be followed for finishes produced by means other than polishing.
Does the surface finish grain orientation have any influence on corrosion performance?

If a finish has an obvious directional grain, design or profile and it is oriented horizontally, the surface will collect more dirt and require more frequent cleaning.  This is primarily a concern in exterior applications or dirty interior environments.  A vertical grain orientation is more easily washed by rain and collects less dirt.