There is a need to develop new treatments for the corrosion protection of metals, and especially for alloys of aluminum. This work is required following concerns about the carcinogenic natures of chromates, which have traditionally been used in conversion coatings.
Our program had three main thrusts. The first emphasized the development of coating chemistries for forming new phosphate conversion coatings with the capability of providing environmentally benign and effective protective coatings for aluminum alloys.
The second was directed at investigating the use of organosilanes as coupling agents, again for the passivation of aluminum surfaces. This required the optimization of organosilane-aluminum interactions in order to strengthen adhesive bonding and corrosion resistance.
The third thrust of this research was to establish mechanisms of coating formation. The coating process is electrochemical in nature, and the integrity of a coated material in an aggressive environment depends closely on the microstructures involved within a coating and at the metal itself, where second-phase particles are generally present along with other defects. The second-phase particles may exhibit microanodic or microcathodic characteristics in working operation, but they have significant influences on the coatings and the corrosion resistance. A wide range of interfacial and materials techniques have been used in order to determine the microscopic mechanisms for the chemical processes occurring at the various interfaces.