MAGNESIUM RICH PRIMERS AND RELATED DEVELOPMENTS FOR THE REPLACEMENT OF CHROMIUM CONTAING AEROSPACE PRIMERS

This paper reports the current development status of magnesium rich primer (MgRP) as a replacement for chromated primers used in aerospace.  The current MgRP formula was optimized as part of a Cr-free coating system for the corrosion protection of aircraft and has been observed to match and even exceed the performance of chromated primers in accelerated neutral salt spray testing. This result was achieved after modification of earlier prototype MgRP formulas to ensure consistent performance in accelerated corrosion testing. Adjustments in the formula were directed at controlling the activity of the metallic magnesium in the primer.  In a parallel development, the same technology used to modify the MgRP formula was also incorporated into a nonmetallic primer formulation which has been optimized for corrosion inhibition.  The ability of this nonmetallic primer to inhibit corrosion of aerospace aluminum alloys implies that the modifications to the MgRP formula have resulted in a secondary inhibition mechanism for the MgRP in addition to the primary galvanic protection mechanism.