Shielding Efficiency of Electrically Conductive Protective Coatings for Magnesium and Aluminum Surfaces

Although several proprietory finishes have been available for aluminum and magnesium protection from corrosion, the electrical properties at radio frequencies have never been sufficiently defined. In order to evaluate the relative merits of such finishes for aluminum and magnesium, a test program was established. Fixtures were designed to measure bonding impedance from dc to RF, and to evaluate shielding efficiency and insertion loss from gaskets used in joint interfaces. Marked differences in performance were observed between the radio frequency shielding obtained at radio frequencies and the bonding impedance measurements, indicating that the commonly used criterion of dc or RF bonding impedance is not sufficiently sensitive to provide good control of conductive coatings. Corrosion tests indicated several finishes would be acceptable from both the corrosion and electrical viewpoint.