D. Nickel

Effect of additive and current mode on surface morphology of palladium films from a non-aqueous deep eutectic solution (DES)

Electrodeposition of palladium from a non-aqueous electrolyte solution [choline chloride/urea/palladium(II)chloride] has been carried out by direct and pulse current electroplating. In this study, the influence of an organic additive (nicotinic acid amide), current mode (direct current or pulse current deposition) and hydrodynamic on the surface morphology of electroplated palladium films was investigated. In order to determine the surface morphology and thickness of the electrodeposited palladium layers, a scanning electron microscope and an energy dispersive X-ray fluorescence spectroscope were used. In addition, the cell voltage during the different electrodeposition experiments was recorded and analysed. The experimental results showed that the surface morphology of the palladium deposits could be remarkably affected either by addition of the additive or by applying pulse current. Pulse plating and the selected inhibitor mutually interfere with each other, causing changes in the microstructure of the palladium deposits (e.g. smoothening or forming of micro-cracks). It was possible to optimise the palladium deposit quality by applying pulse current or by addition of the appropriate inhibitor.

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.

Microstructural evolution in the bonding zones of co-extruded aluminium/titanium

In the present study, the interfacial microstructure of dissimilar Al/Ti joints formed by a co-extrusion process has been investigated. The material combinations used for the experiments were commercially pure aluminium and titanium, respectively, in the alloys EN AW-6082 and TiAl6V4. X-ray diffraction, energy-dispersive X-ray spectroscopy, electron microscopy and electron backscatter diffraction revealed titanium aluminide formation in the interface, the development of deformation bands in the sleeve material, and the occurrence of grain size refinement and twinning in the core material. The results are discussed with respect to the concept of a hard core–soft sleeve co-extrusion comprising plastic deformation to promote solid-state diffusion. The study shows the phase distribution and the microstructural evolution in the bonding zone with the aim to improve the quality of the bonding by adequately adjusting the process parameters.

Electrochemical Properties of AL-6060 Alloy After Industrial-Scale ECAP

The equal-channel angular pressing (ECAP), as the most famous method of severe plastic deformation, has the potential for upscaling from the laboratory to industrial scale. Thus, it is important to examine the practice-relevant properties of large billets deformed by this process. Mechanical properties and corrosion resistance significantly affect the service life of the structural components. The mechanical properties of Al-6060 alloy after industrial-scale ECAP (the cross-sectional sizes of the billets were 50 × 50 mm2) were analyzed by P. Frint. In the present work, we investigate the effect of one pass of the in-dustrial-scale ECAP on the electrochemical properties of Al-6060 alloy by means of potentiodynamic polarization tests in a 0.1 M NaCl solution. The corroded surfaces were analyzed by means of optical microscopy and scanning-electron microscopy. In order to characterize the homogeneity of the corrosion behavior of the ECAP-processed material, all analyses were taken in different zones perpendicular to the extrusion axis. The results indicate that one pass of ECAP does not deteriorate the electrochemical behavior of Al-6060 alloy.

Controlled grain size distribution and refinement of an EN AW-6082 aluminium alloy: Dedicated to Prof. Bernhard Wielage on the occasion of his 65thbirthday

Abstract An EN AW-6082 aluminium alloy was subjected to incremental deformation by a new process named gradation rolling. The process has been used to generate a grain size distribution in a rod-shaped billet. A grain size gradient ranging from coarse-grained in the billet core to ultrafine-grained at the surface of the billet can be obtained. The grain size distribution has been confirmed by electron backscatter diffraction showing the grain refinement related to the true strain. The fibre texture of the base material has been transformed to a rolling texture in the surface region. This results in strain-hardening and grain-boundary strengthening in the surface region (130 HV0.5) as compared to the unchanged core material (110 HV0.5).

Anodisation of Aluminium Alloys by Micro-Capillary Technique as a Tool for Reliable, Cost-Efficient, and Quick Process Parameter Determination

Anodisation is essential for improving surface properties of aluminium alloys and composites regarding wear and corrosion behaviour. Optimisation of the anodising process depends on microstructural constituents contained in aluminium alloys and represents a key task, consisting of the control of process parameters and electrolyte formulation. We applied the micro-capillary technique known from corrosion studies and modified it to form anodic aluminium oxide films on high-strength aluminium alloys in comparison to pure aluminium in sulphuric acid. A glass capillary with an opening of 800 μm in diameter was utilized. Corresponding electrochemical measurements during potentiodynamic and potentiostatic anodisation revealed anodic current responses similar to conventional anodisation. The measurement of film thickness was adapted to the thin anodised spots using ellipsometry and energy dispersive X-ray analysis. Cross sections prepared by focused ion beam milling confirm the thickness results and show the behaviour of intermetallic phases depending on the anodising potential. Consequently, micro-capillary anodising proved to be an effective tool for developing appropriate anodisation conditions for aluminium alloys and composites because it allows quick variation of electrolyte composition by applying low electrolyte volumes and rapid film formation due to short process durations at small areas and more flexible variation of process parameters due to the used set-up.

Anodic Oxidation of AMCs: Influence of Process Parameters on Coating Formation

Aluminium matrix composites (AMCs) consisting of high-strength, age-hardenable aluminium alloys and homogeneously dispersed hard particles open up new possibilities in designing light-weight material based security related structures. The susceptibility of the matrix alloy to selective corrosion can be reduced significantly by anodic oxidation. A powder-metallurgical processed alloy AlCu4MgMn with hard particles and a commercial wrought alloy for reference were used for the investigations.In order to control the microstructure of anodic aluminium oxide (AAO) formed on AMCs, it is necessary to understand the formation mechanism and the influencing parameters. Therefore in a first run, the anodizing behaviour of matrix alloy was separated from the behaviour of hard particles. The AAO coatings show small growth rates on the matrix and the reference alloy accompanied by a complex pore structure which differs from the ordered vertical pore structure on pure aluminium. Depending on the type and the size as well as the anodizing parameters, the particles are either incorporated into the AAO coating unchanged or partly resp. completely oxidized. The AAO microstructure changes significantly in dependence of the anodizing parameters. It is shown that a technically relevant coating thickness can be achieved on AMCs by choosing appropriate process parameters.

Phosphorus Distribution in Electrodeposited Ni-P-Diamond Composites Influencing Structure and Mechanical Properties

The properties of Ni-P composite coatings are related to the microstructure evolution by co-deposition of phosphorus, particle incorporation and subsequent annealing. This study focuses primarily on the effect of phosphorus content in the electrolyte on the incorporation of sub-micron diamond particles in order to understand the complex influence of Ni/Ni3P crystallization and particle embedment on Martens hardness.