Corrosion of Aircraft Al and Al-Zn Ion Plated Steel Fasteners

摘要

The effect of coating material, coating thickness and coating conditions on the corrosion resistance of aluminum and aluminum-zinc coatings with different zinc contents was studied. Corrosion tests were performed on assemblies of Al and Al-Zn coated high strength steel bolts fastened into aluminum alloy blocks. It is found that the addition of Zn to Al coatings greatly improves their sacrificial corrosion protection with respect to steel and provides cathodic protection for the aluminum alloys. The galvanic currents and galvanic potentials of the coupled Al and Al-Zn ion plated fasteners to three aluminum alloys were measured. The average galvanic current densities were calculated and the minimum amount of Zn content in Al coatings to ensure anodic polarity of the coatings and consequently cathodic protection for the alloys is found. The addition of Zn reduces the average coefficient of friction and increases the wear life of aluminum coatings.