Investigating size and proximity effects in Al-Au micro-galvanic corrosion

The influence of Al-Au intermetallic particle size and distribution in an Al-Au micro-galvanic corrosion system was investigated by coupling post-corrosion scanning electron microscopy imaging with computer vision analysis. Au-Al specimens were fabricated by electron beam evaporation and thermal annealing, resulting in Al 2 Au intermetallic particles with a moderate size range embedded in an Al film. The samples were immersed in a 0.6 M NaCl solution, leading to galvanic corrosion of the Al matrix. Analysis of the corroded samples showed that corrosion progressed via micro-galvanic cell formation, with the likelihood of galvanic attack tied directly to both the size of the particles and the proximity of neighboring particles. This led to the identification of a ‘safe’ zone where particles less than ~0.02 μm 2 in projected area and farther than ~0.2 μm from a nearest neighbor were unlikely to induce galvanic corrosion. Finite element simulations showed that this behavior corresponds to the anode electrochemical potential and total cathodic current. • The influence of particle size and nearest neighbor proximity on galvanic corrosion was investigated in a Au-Al system. • It is shown that there exists a ‘safe’ region where sufficiently small and widely spaced particles were not susceptible to galvanic corrosion attack. • The likelihood of galvanic corrosion attack is linked to the potential on the anode and total cathodic current.