KM Corrosion Resistant Coating for Magnesium ZE41A-T6

Magnesium has the highest specific strength (strength-to-weight ratio) of any metal. However, magnesium is exceptionally susceptible to corrosion, severely limiting its usefulness. Even with standard Dow coatings (e.g., Dow 1, 7, 9, 17, etc.), magnesium begins corroding in less than 24 hours in an ASTM B117-95 Neutral Salt Spray test. Inovati's Kinetic Metallization (KM) aluminum coated magnesium (ZE41A-T6) lasted 192 hours in a standard Neutral Salt Spray test, more than eight times longer than industry standard Dow coated magnesium. This makes KM aluminum coatings on magnesium an excellent choice for marine applications, or anywhere else magnesium could not previously be used due to corrosion. For basic information on KM technology, please navigate to our technology section.

Experimental Procedure
Corrosion protection performance tests were done on Mg ZE41A-T6 coated with a KM coating. The coating was scratched in the corner of the specimen using a sharp scriber, to produce damage in the aluminum coating. This scriber was applied with sufficient force for the scratch to penetrate the coating to the Mg substrate.

A cast magnesium ZE41A-T6 plate 150mm x 100mm x 6mm in size was used as a substrate, with a nominal coating thickness of 0.003" (75 microns). The central section of the substrate was masked prior to coating to leave a 25 mm strip around the edges, as can be seen in the diagram. The specimen was then powder-coated with a high quality resin to cover the back, sides, and edges, leaving a window of Commercially Pure (CP) aluminum AA 1100 coating in the center.


Cross-sectional view of aluminum on magnesium (90X mag)

Test Procedure
The Neutral Salt Spray (NSS) test was operated in accordance with ASTM B117-95 with the specimen placed at an angle of 6 degrees from normal. The specimen was examined daily, except for weekends, and photographs taken as corrosion developed.

Conclusions
Salt fog tests on standard Dow type (MIL-M-3171C) corrosion resistant coatings result in extensive deterioration in less than 24 hours. In contrast, Inovati's KM aluminum coating lasted 192 hours before noticeable corrosion occurred. This corrosion was in a small localized area, and no corrosion was observed at the scribe mark in the coating.