The cathodic dissolution of Al, Al2Cu, and Al alloys

The cathodic dissolution of aluminum has been investigated for 99.99% Al, synthetic Al2Cu, and three Al-Cu-Mg alloys: AA2024, AA7050, and AA2214 offering a range of over two orders of magnitude in hydrogen reduction activity. Atomic emission spectroelectrochemistry (AESEC) was used to directly measure the dissolution rate of the alloy components as a function of the cathodic current during potential sweep and potential step experiments. It was found that for all samples, regardless of the cathodic current density, the stoichiometric ratio of OH produced to Al dissolved varied between 1.4 and 1.8. This value is interpreted in terms of a simple model in which hydroxide generation, Al(OH)3 formation/dissolution, and Al(OH)4- diffusion are kinetically coupled together. The selective dissolution of Mg and Cu is also measured and discussed.