G. Alisch

Anodizing – A Key for Surface Treatment of Aluminium

This article describes the flexibility and the potentials of the most important finish for aluminium-based materials. After a suggestion for the classification of anodizing processes, the historical development of the electrolytic anodic oxidation (EAO) and the plasma-electrolytic anodic oxidation (PAO) are presented. In the following section the focus is given on selected topics concerning the process parameters, the microstructure including the layer composition and properties. The variability of the anodizing process parameters and the used materials provide this variety of application. Furthermore, both differences and similarities of the EAO and PAO processes are shown. The conclusion of this review emphasizes that there is still some need for further research especially in the interaction of the process, the formed microstructure and the resulted properties determining the final application. Hence new possibilities for this surface treatment will be open.

Corrosion characteristics of an ultrafine-grained Al-Mg-Si alloy (AA6082)

The corrosion behaviour of the aluminium alloy, AA6082, processed by equal-channel angular pressing (ECAP) after different passes (route E, room temperature) was studied in comparison to the coarse-grained counterpart. The results of the electrochemical investigations (cyclovoltammetry; electrochemical impedance spectroscopy, EIS) are presented in correlation with the microstructure before and after the corrosion examinations. Both, chemical (precipitations, phases) and physical (dislocations, high-angle grain boundaries, grain size, low-angle grain boundaries) inhomogeneities characterize the microstructure of this commercially used Al-Mg-Si alloy. Results indicate an improved resistance against pitting of the ECAP material expressed by a reduced pitting density of up to 50 % and lower pit depths. EIS measurements and microstructural examinations (scanning electron microscopy, transmission electron microscopy, 3D topography measurement) confirm that ECAP modifies the number, size and distribution of these inhomogeneities, which leads to a more favourable corrosion behaviour.

Fracture Behaviour of an Electron Beam Weld

This paper deals with cracks in an electron beam welded joint made of severely different materials. The motivation is to improve the design and reliability of an electron beam welded worm wheel, which may contain large cracks due to hot cracking. Material properties of the weld zones were determined by minitensile specimens. The fracture behaviour of the weld was investigated with CTSand SENB-specimen. So far, estimates of the threshold va lues for the fatigue crack growth can be presented. Further experimental and numerical investigations are pla nned.