Abstract
The corrosion rates of particulate 6092-T6 Al metal-matrix composites (MMCs) reinforced with 20 vol % , SiC, and as well as monolithic 6061-T6 Al immersed in American Society for Testing and Materials (ASTM) and real seawaters were lower than those immersed in 3.15 wt % NaCl or 0.5 M solutions. Scanning electron microscopy revealed that precipitates consisting of agglomerated whiskers formed on the surfaces of the MMCs and the monolithic 6061-T6 Al after prolonged immersion in seawater environments. The precipitates were tentatively identified to be Al–Mg hydrotalcite-like compounds based on energy-dispersive X-ray analyses and X-ray diffraction experiments. The MMCs immersed in ASTM seawater exhibited localized corrosion, however, the scanning ion-selective electrode technique revealed smaller pH fluctuations near the localized corrosion regions compared to the MMCs immersed in NaCl and solutions. It was postulated that the corrosion of the Al-based materials is inhibited both by the precipitates and by the buffering effect of seawater.
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