No abstract is provided for this article.
7xxx aluminium alloys (Al-Zn-Mg-Cu) are susceptible to localised corrosion like pitting, intergranular and exfoliation corrosion. Their susceptibility is strongly affected by heat treatments. In order to study localised corrosion in 7xxx alloys, solution heat treated and overaged (T76) tempers of AA7075 were characterised using complementary techniques like SEM-EDS, scanning confocal laser microscopy, OCP and potentiodynamic polarisation measurements, scanning Kelvin probe force microscopy and micro-capillary cell. The samples that underwent potentiodynamic polarisation showed localised attack at the intermetallics and intergranular and exfoliation corrosion. The SKPFM investigation proved that the attack at the intermetallics was caused by strong potential differences between intermetallics and matrix. Moreover, the SW60 temper showed higher potential differences between intermetallics and matrix than the T76 temper. The investigation with the micro-capillary cell showed the higher potential differences between intermetallics and matrix in the SW60 temper caused a shift in the negative direction of the local breakdown potentials for areas containing a few intermetallics. It is concluded that the heat treatment of AA7075 affects the localised corrosion at the intermetallics.
No abstract is provided for this article.
Polycrystalline thin films have been grown on gold substrates by electrodeposition, leading to different film compositions. In particular, our conditions allow growing smooth and shiny surface films in a thickness range of nanometers to micrometers. In this article, electroplated layers were analysed by InfraRed Spectroscopic ellipsometry. The dielectric functions have been obtained from ellipsometry analyses using the Drude and Tauc-Lorentz models. We attributed the scattering distribution of the mobility with the carrier concentration to the presence of grain boundaries in the films. The energy bandgap appears to be constant whatever the carrier concentration. This result can be interpreted by bandgap shrinkage that occurs simultaneously with bandgap widening. These results were supported by additional Hall Effect Measurements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
The use of a rotating ring disc electrode (RRDE) is introduced in this paper to study the formation of chromate–phosphate layers on rolled aluminium surfaces. A RRDE was developed containing an Al disc, which was converted with a chromate phosphate film, and a carbon ring, where the Cr6+ reduction rate was measured in situ. The principle of the method is that Cr6+ is transported from the bulk of the solution towards the disc and the ring electrode. At the disc electrode, a fraction of Cr6+ is consumed during the conversion of the Al disc electrode. This leads to a decrease in ring current, which is directly related to the amount of Cr6+ being reduced at the disc electrode. For proper operation of the RDDE system, an electrode with optimised geometrical characteristics is used. In order to be sure that the measured current on the ring is in relation with the Cr6+ reduction rate occurring at the aluminium disc, a number of requirements need to be fulfilled. After showing that the RDDE system is indeed able to monitor in situ the Cr6+ content during conversion, the amount of Cr6+ reduced at the disc electrode is calculated from the recorded ring current time curves. The method allows (i) to follow the growth of a conversion layer quantitatively in situ and (ii) to study the influence of important process parameters such as fluoride content, chromate content of the conversion bath and influence of mass transport.
