Accelerated corrosion of zinc alloys exposed to ultraviolet light

The present study demonstrated that alloying had an effect on the photo corrosion rates of zinc coated steel. The corrosion rates of 99·9%Zn, galvanise (>99Zn), galfan (95Zn–5Al), galvanneal (90Zn–10Fe) and galvalume (43Zn–55Al–1·5Si–0·5Fe) were all compared by immersion in flowing fresh water for four months. One set of samples was exposed to ultraviolet (UV) fluorescent lamps, while the second set was up stream and illuminated only by the natural day–night lighting. The field test demonstrated that the UV light exposure increased the corrosion rates of all the zinc alloys tested. Laboratory experiments with photoelectrochemistry showed that alloying changed both the flat band potential and the photospectrum. The flat band potential is the potential where the photocurrent goes to zero. The samples with the more negative flat band potentials also had the higher corrosion rates. This correlation between the flat band potential and the corrosion rate provides a possibility for designing corrosion resistant alloys.