Electrochemical and Mechanical Properties Studies of Flexible Mg-rich Primers

Abstract

The coating systems for military aircraft must protect the aluminum skin and frame, and associated fastening and joining from corrosion in a variety of aggressive environments. Excessive grinding is often needed to remove the corrosion products at the cracks formed around the seams and fasteners on the aircraft resulting from poor system flexibility of coatings, which causes high maintenance cost and damages the integrity of the aircraft's body. Thus the U.S. Air Force wants to develop an advanced performance coating system with a primer that can provide superior flexibility and good corrosion protection. Currently commercialized magnesium-rich corrosion protection primers were initially developed from some epoxy-amine coating systems, the most common polymer system for aircraft primer use. But the primers were developed under the old specification, which cannot meet the "ideal" goals of the Air Force. Thus, as a carefully selected alternate, polysulfide modified polymers, which have lowest gas permeability, outstanding oil resistance and UV resistance, and especially great flexibility, are being examined as candidate materials. In this research, a number of accelerated laboratory testing methods were applied to measure the electrochemical and mechanical properties of the modified Mg-rich primers which are based on polysulfide modified polymer as binder. Electrochemical measurement results and visual inspections show that the Mg-rich flexible primer has better or equal corrosion protection performance versus a standard epoxy-based Mg-rich primer with the same PVC. The flexibility of the newly formulated Mg-rich primer was also indicated by the results of a variety of empirical testings and instrumental characterizations. Meanwhile, the weathering impact introduced by the laboratory accelerated exposure cannot compromise the superiority of the flexible Mg-rich primers. Based on the results found, future work will be focused on creating a new formulate method or making some modification of the sulfur-containing polymer's structure to achieve a really low VOC.