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The etching of high purity aluminum foils in hydrochloric acid under alternating current was investigated. Pit development and characteristics of etched foils were studied taking into account the a-c amplitude, the frequency, the etching time, and the electrolyte temperature, using light micrography and scanning electron micrography. A maximum of electrical capacitance CM of etched and anodized foils is observed for certain frequency value VM; C~ and vM depend on the experimental conditions. The aluminum oxide formed on the metal etched surface exhibits minimum thickness for bath temperature near 60~ Galvanodynamic voltammetry allows the determination of a pitting current and an induction time which depends on frequency. The pit density and the calculated anodic current efficiency for metal dissolution are found to decrease markedly with increasing frequency.

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“In situ” neutron small‐angle scattering experiments during the decomposition by nucleation and growth at 133 °C of the Al‐6.8 at% Zn alloy are described. In the very small angle domain (Q < 10−2 Å−1) where X‐ray measurements are difficult, the neutron scattering shows a plateau after long ageing times. This plateau is due to an interference effect between precipitates with a not completely random spatial distribution. The scattering is quantitatively explained on the basis of hard sphere pair correlation function. It appears therefore that the only presence of scattering ring cannot characterize the spinodal decomposition as it has been sometimes assumed.