The corrosion behavior of silicon carbide/aluminum (SiCp/ Al) metal matrix composites was studied in chloride solution by means of electrochemical techniques, scanning electron microscopy (SEM), Auger electron spectroscopy (AES), energy dispersive spectroscopy (EDS), and X-ray diffraction. The materials under investigation were powder metallurgy (PIM) processed 6061 Al reinforced with increasing amounts of SiC particles (15 to 40 vol%). Electrochemical tests such as potentiodynamic polarization were done in 0.035, 0.35, and 3.5% NaCI solutions that were open to air, aerated, or deaerated to observe overall corrosion behavior. In addition, pit morphology was observed after anodic polarization to a number of potentials. It was seen that the corrosion potentials did not vary greatly or show definite trends in relation to the amounts of SiCp reinforcement. However, the degree of corrosion increased with increasing SiCp content and the presence or absence of oxygen as well as the concentration of the NaCI solution did affect corrosion potentials. Microscopic analysis techniques were used to study the corroded samples and the extensive pitting and exfoliation of the surfaces. X-ray diffraction was used to identify the compounds on the surface of the corroded samples as well as the flakes due to exfoliation.

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The behavior of steel in chloride-free and chloride-contaminated simulated concrete solutions was studied to observe the degradation of steel as a result of addition of chlorides. One of the simulated concrete solutions was a saturated calcium hydroxide (Ca [OH] 2 ) solution while the other was a solution made up of 0.6 M potassium hydroxide (KOH) + 0.2 M sodium hydroxide (NaOH) + 0.001 M Ca(OH) 2 . Corrosion behavior of the steel was studied electrochemically, and changes in the steel surfaces were studied using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). Behavior was compared to that of reinforced concrete cylinders subjected to alternating wetting and drying in 3.5% sodium chloride (NaCl) solutions.

A fluorescent indicator (FI) can be used to monitor the underlying corrosion on metal substrates based on sensing pH changes caused by corrosion reactions. One coumarin derivative was chosen as FI and added to a coated-aluminum system. The initial state of the coating system is fluorescent under UV light and it changes to nonfluorescent at the site of corrosion. The effects of the fluorescent indicator on the fluorescent intensity and protectiveness of the coating system are discussed. Electrochemical impedance spectroscopy (EIS) was used to estimate the protectiveness of the coating and interface corrosion reactions between the metal and coating. This was correlated with the fluorescent intensity change of the coating. Based on the impedance measured by EIS, the coating failed shortly after immersing into the 3.5% sodium chloride solution. After 24h , pH-induced fluorescent quenching points began to appear. Scanning electron microscopy and energy-dispersive spectroscopy of selected specimens indicated that the quenching point was the corrosion site. Several coating thicknesses were examined, and based on these tests the optimal coating thickness was determined to be about 80μm .

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