Fastening Strategies to Prevent Galvanic Corrosion

Abstract

In marine applications aluminum structures are commonly fastened together with stainless steel fasteners. This combination of dissimilar metals causes galvanic corrosion currents which degrade the aluminum structure. The purpose of this research is to develop fastening strategies that will reduce the degradation of the aluminum structure. The impetus for this research is specifically to increase reliability and availability of equipment installed on Navy range craft which operate in the support of training and test and evaluation (T&E) events. Direct fastener substitution would cause the least impact to the overall design of a system reducing alteration costs. Therefore, in this research different types of fasteners were tested to determine their effect on corrosion in the aluminum structure. Fastener types: 316 stainless steel (control), Titanium (Ti-6Al-4V), 316 stainless steel PVD coated with TiN, 316 stainless steel PVD coated with CrN, and 316 stainless steel coated with a Sol Gel. The efficacy of each fastener type was determined by several tests. Samples representing a bolted join in an aluminum structure were assembles using each type of fastener and deployed in a marine environment, after exposure weight loss data was collected. The fasteners were also subjected to cathodic potentiodynamic polarization to determine the kinetics of oxygen reduction and hydrogen evolution on the bare 316 SS, coated 316 SS, and bare Ti-6Al-4V. The cathodic polarization data of the fasteners were compared to that of the anodic polarization data of AA6061-T6. The potentiodynamic polarization data was used to gain an understanding of the galvanic corrosion mechanisms between the fasteners and AA 6061-T6. The results from the polarization experiments were compared to the actual corrosion damage of galvanic couples in the field. Acknowledgements: This material is based on research sponsored by the USAFA and University of Hawaii under agreement number FA7000-18-2-0004. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon.