F. Andreatta

Electrochemical characterisation of aluminium AA7075-T6 and solution heat treated AA7075 using a micro-capillary cell

Localised corrosion of 7xxx aluminium alloys initiates at cathodic intermetallics containing Cu and Fe due to a strong galvanic coupling with the matrix. In order to study this galvanic coupling, the electrochemical behaviour of AA7075-T6 and solution heat treated AA7075 has been investigated by means of complementary techniques: micro-capillary cell, scanning Kelvin probe force microscopy (SKPFM) and scanning electron microscopy (SEM). Characterisation with the micro-capillary cell showed that the intermetallics cause a more cathodic breakdown potential in the solution heat treated AA7075 compared with the AA7075-T6. This is associated with a higher Volta potential difference between the intermetallics and the matrix in the solution heat treated AA7075, indicating a stronger galvanic coupling for this temper. From these results, it is concluded that the breakdown potential of areas containing the intermetallics is related to the Volta potential difference between the intermetallics and the matrix.

Effect of solution heat treatment on galvanic coupling between intermetallics and matrix in AA7075-T6

Abstract Susceptibility to localised corrosion is strongly affected by heat treatments performed on Al–Zn–Cu–Mg alloys. In order to study how galvanic coupling between intermetallics and matrix is affected by solution heat treatment, AA7075-T6 and solution heat treated AA7075 have been characterised by means of scanning electron microscopy and scanning Kelvin probe force microscopy. Solution heat treatment strongly increased the Volta potential difference between the intermetallics and the surrounding matrix showing a strong increase in galvanic coupling. This is explained by Zn and Mg enrichment of the matrix caused by dissolution of strengthening particles during solution heat treatment.

Atomic layer deposition: state-of-the-art and research/industrial perspectives

Abstract Interest on nanometric conformal coatings is currently growing across a wide range of applications, from electronic components to corrosion protection, chemical barriers or even wear decrease. Currently, atomic layer deposition (ALD) is one of the most promising nanometric deposition technologies: it offers the possibility to obtain conformal coatings even on very complex tridimensional substrates, with a strict thickness tolerance. During an ALD cycle, only one molecular layer is deposited on the substrate surface, enabling the theoretical possibility to tailor the composition of the deposit up to molecular resolution. In the first part of this review, a brief history of ALD is presented to better understand the evolution of the technique during the past five decades; in the second part, a short description of the main ALD techniques is given, considering their main advantages and drawbacks. In the third part, a short review about ALD applications is presented, and in the fourth part the most useful and used instruments for the analysis and characterization of ALD are listed; some results are discussed and particular emphasis on the corrosion protection of different metallic alloys of common industrial interest is given.