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Intermetallic particle electrochemistry plays significant role in localized corrosion and stress-corrosion cracking of aluminum alloys. This article presents specific examples from recent and on-going studies of stresscorrosion cracking in Al-Mg alloys and localized corrosion in Al-Cu alloys. The common approach in these examples is an explicit accounting of the intermetallic particle-dissolution characteristics, which is developed by measuring the electrochemical behavior of bulk analog compounds. Findings from these types of measurements combined with results from new and advanced small-length scale measurements confirm some of the established ideas about localized corrosion in aluminum alloys, but also lead to new insights that are important for a thorough understanding of corrosion damage accumulation.

Wrought Al-Ge-Si alloys were designed and produced to ensure dislocation bypass strengthening ("hard pin" precipitates) without significant precipitate cutting/shearing ("soft pin" precipitates). These unusual alloys were processed from the melt, solution heat treated and aged. Aging curves at temperatures of 120, 160, 200 and 240°C were established and the corresponding precipitate spacings, sizes, and morphologies were measured using TEM. The role of non-shearable precipitates in determining the magnitude of Bauschinger was revealed using large-strain compression/tension tests. The effect of precipitates on the Bauschinger response was stronger than that of grain boundaries, even for these dilute alloys. The Bauschinger effect increases dramatically from the under-aged to the peak aged condition and remains constant or decreases slowly through over-aging. This is consistent with reported behavior for Al-Cu alloys (maximum effect at peak aging) and for other Al alloys (increasing through over-aging) such as Al-Cu-Li, Al 6111, Al 2524, and Al 6013. The Al-Ge-Si alloy response was simulated with three microstructural models, including a novel SD (SuperDislocation) model, to reveal the origins of the Bauschinger effect in dilute precipitation-hardened / bypass alloys. The dominant mechanism is related to the elastic interaction of polarized dislocation arrays (generalized pileup or bow-out model) at precipitate obstacles. Such effects are ignored in continuum and crystal plasticity models.