Shot noise analysis on corrosion behavior of zinc alloy (ZnAl4Cu1) under dry-wet cycles

The corrosion behaviors of zinc alloy (ZnAl4Cu1) in 3.5% (mass fraction) NaCl, 7.3% (mass fraction) Na2SO4 and simulated acid rain solutions were investigated using electrochemical measurements. The potential noise during dry-wet cycle was monitored and analyzed by fast Fourier transform (FFT), fast wavelet transform (FWT), shot noise theory and stochastic theory. Cumulative probability curves of event frequency fn indicate that the corrosion events in the dry cycles are greater than those in the wet cycles. Uniform corrosion was observed in the NaCl solution compared with more localized corrosion in the Na2SO4 solution, which is evidenced by FWT and SEM. Conditional events generation rate r(t) for diffusion controlled reactions decreases with increasing the time. r(t) values for uniform corrosion and diffusion controlled process are the largest in the wet cycle in 3.5% NaCl solution. The values of r(t) for pitting corrosion in Na2SO4 solution are observed to become large during spraying periods, and r(t) for pitting corrosion has the largest value in the Na2SO4 solution. The intergranular corrosion of zinc is serious in simulated acid rain solution.