Aluminum alloy EN AW-3003 contains a certain amount of micrometer-sized constituent particles and a large number of nanometer-sized dispersoids. The practical nobility of intermetallic particles relative to an alloy matrix was evaluated ex situ by scanning Kelvin probe force microscopy ͑SKPFM͒, and localized corrosion initiation of the alloy exposed to chloride solutions was studied in situ by integrated atomic force microscopy ͑AFM͒ and scanning electrochemical microscopy ͑SECM͒. The SKPFM results show a higher Volta potential for the constituent particles than the matrix, and a larger difference for larger particles. In some cases, the boundary region between the large constituents and the matrix exhibits a minimum Volta potential. In contrast, a small Volta potential difference was measured for the particles less than 1 m. The SECM mapping of the alloy surface in the solution provided evidence of a cathodic action of some constituent particles and a local anodic dissolution adjacent to them. Concurrent AFM and SECM images indicate that only some of the constituents are prone to initiate localized corrosion. Moreover, in situ AFM observations confirm enhanced localized dissolution in the boundary regions, verifying the cathodic character of the constituent particles and a microgalvanic effect on localized corrosion. The fine dispersoids of nanometer size seem to have no effect on the corrosion initiation.

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Scanning electrochemical microscopy ͑SECM͒ has been integrated with electrochemical atomic force microscopy ͑EC-AFM͒, and applied for in situ studies of localized corrosion of Al alloys in NaCl solution. The instrument utilizes a dual mode probe, which functions both as a normal cantilever and as an ultramicroelectrode. The I − /I 3 − redox mediator was used for mapping of local electrochemical current. Concurrent topography and electrochemical activity maps have been obtained on the same surface area with micrometer lateral resolution. Preliminary results show ongoing localized dissolution related to intermetallic particles in the Al alloys, which may occur well below the breakdown potential.

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