CORROSION AND CORROSION INHIBITION OF ALUMINA PARTICULATE ALUMINUM-ALLOYS METAL-MATRIX COMPOSITES IN NEUTRAL CHLORIDE SOLUTIONS

A study of the corrosion behaviour and corrosion inhibition of AA 6061 and AA 2014 metal matrix composites (MMCs) reinforced with alumina pa rticles, during exposures to 0.1 M NaCl solution is reported. Many tun gsten and molybdenum-containing inorganic salts were tested as corrosi on inhibitors, but only ammonium tetrathiotungstate afforded good inhi biting properties, particularly towards the AA 2014-based MMC. The cor rosion behaviour of the composites in uninhibited or inhibited solutio ns was compared by different techniques to that exhibited by the corre sponding matrices. The techniques adopted included weight loss measure ments, electron probe microanalysis (EPMA), scanning electron microsco py (SEM), linear polarization resistance measurements, polarization cu rve recordings and current noise analysis. The analysis of the current fluctuations showed that different patterns of the time records were obtained during pit initiation, stable pitting and general corrosion. The power spectrum density plots exhibited f(-alpha) trends, with alph a values around 20 dB decade(-1) when corrosion was mainly localized i n pits, while values tending to zero were measured when general corros ion became dominant.