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In water based solutions, electrodeposition of Pd and Pd alloys is complicated due to hydrogen embrittlement. This can be avoided by using non-aqueous solutions like deep eutectic solvents ...

Organo-functional silane coupling agents are widely used to promote adhesion in between inorganic and organic materials. Amino-functional silanes can improve bonding with polyamide. Aiming on a mechanically performant aluminum-polyamide joints, the effect of six amino silanes of different chemical structure, namely number and type of amine groups and alkyl spacers lengths, on the joint strength is investigated by means of lap-shear testing. Higher shear strengths are found along with a more pronounced capability of the amine group to form hydrogen bonds with polyamide. The results show that an additional amine group within the organo-functional group can increase joint strength, whereas long alkyl spacers reduce the observed joint strength. It is shown that high lap-shear strengths, in maximum about 15 MPa for N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are achieved and that the high reproducibility can be assured when using right processing routines.

In this study, the electrodeposition of palladium alloys was investigated in a choline chloride/urea based deep eutectic solvent containing sulfosalicylic acid dihydrate as organic additive and Pd(II) + Ag(I), Pd(II) + Pt (II), or Pd(II) + Pt (II) + Ag(I) as metal components. The electrochemical behavior of the electrolytes was characterised by cyclic voltammetry. The electrodeposition processes require nucleation overpotential. Energy-dispersive X-ray data indicated that the layer thickness and composition of the produced Pd–Ag, Pd–Pt, and Pd–Pt–Ag films could be varied by changing the deposition mode. Additions of Ag(I) to the Pd and Pd–Pt electrolytes enhanced the overall metal deposition rate. Scanning electron micrographs of the electrodeposits showed that in general, the Pd alloys deposited by pulse current were nodular and relatively compact, whereas the films deposited by potentiostatic deposition were less dense and covered with dendrite-like and sharp-edged crystallites. Data collected from X-ray diffraction (XRD) experiments proved the existence of metallic alloys.

Plasma electrolytic oxidation (PEO) is a common means for the surface modification of light metals. However, PEO of magnesium substrates in dilute electrolytes generally leads to the formation of coatings consisting of unfavorable MgO magnesium oxide. By incorporation of electrolyte components, the phase constitution of the oxide coatings can be modified. Coatings consisting exclusively of MgAl2O4 magnesium-aluminum spinel are produced by PEO in an electrolyte containing hydroxide, aluminate, and phosphate anions. The hardness of the coatings is 3.5 GPa on Martens scale on average. Compared to the bare substrate, the coatings reduce the corrosion current density in dilute sodium chloride solution by approx. one order of magnitude and slightly shift the corrosion potential toward more noble values.

In recent years, the growing environmental awareness has led to the development of energy-efficient products, for example by the replacement of steel as construction material by aluminium to save weight and thus increase the energy-efficiency of mobile systems. However, to address the energy-efficiency of a product holistically, the energy consumption of the production process also has to be considered. For the anodic oxidation process of the AlMgSi1 aluminium alloy, the influence of the sulphuric acid concentration, the glycolic acid concentration, the electrolyte temperature and current density on coating thickness, hardness, ductility and wear resistance (scratch test), as well as on the consumption of electrical energy and process costs for the oxide coating formation are investigated using a design of experiments (DOE). An analysis of variance (ANOVA) is conducted to assess the significance of the parameters for the coating and process properties. For the considered range of the process parameters a significant enhancement of thickness, hardness and wear resistance of the coatings alters also energy consumption during anodic oxidation and process costs, which are assessed by material flow cost accounting (MFCA). Keywords: Anodic oxidation, Aluminium, Energy efficiency, Hardness, Ductility

With the progress in materials science and production technology and the establishment of light-weight design in many fields of the industry, the application of light metals no longer requires only mechanical strength, but also a significant protection of the material against wear and corrosion. Hard and wear-resistant oxide coatings on aluminium are produced by plasma electrolytic oxidation (PEO). During PEO, a conversion of the aluminium substrate to a ceramic oxide takes place. While the role of strength-giving alloying elements like Cu, Mg/Si, Zn, and Zn/Cu on the PEO process has selectively been subject of investigation in the past, the significance of the alloy composition for the service properties of the coatings is still unknown. Therefore, the performance of PEO coatings produced on the widely used commercial high-strength alloys AlCu4Mg1 (EN AW-2024), AlMgSi1 (EN AW-6082), and AlZn5.5MgCu (EN AW-7075) is examined with regard to their behaviour in the rubber-wheel test according to ASTM G65 and the current density-potential behaviour of the substrates with undamaged and worn coatings in dilute NaCl solution. To give a reference to the unalloyed material the testings were carried out also on Al 99.5 (EN AW-1050) which was treated in an adjusted PEO process. Although differences in the conversion of intermetallic phases during PEO and the phase composition of the coatings on the various substrates are determined, the service properties are hardly depending on the alloying elements of the investigated aluminium materials. The wear rates in the rubber-wheel test are low for all the alloyed samples. The current density-potential curves show a decrease of the corrosion current density by approximately one order of magnitude compared to the bare substrate. Eventually, previous wear of the coatings does not deteriorate the corrosion behaviour. PEO layers on technically pure aluminum can resist the testing regimes if they are prepared in an electrolyte with an elevated silicate content and without additional hydroxide ions, during a longer process time.

The anodic oxidation process is an established means for the improvement of the wear and corrosion resistance of high-strength aluminum alloys. For high-strength aluminum-copper alloys of the 2000 series, both the current efficiency of the anodic oxidation process and the hardness of the oxide coatings are significantly reduced in comparison to unalloyed substrates. With regard to this challenge, recent investigations have indicated a beneficial effect of nitric acid addition to the commonly used sulphuric acid electrolytes both in terms of coating properties and process efficiency. The present work investigates the anodic oxidation of the AlCu4Mg1 alloy in a sulphuric acid electrolyte with additions of nitric acid as well as oxalic acid as a reference in a full-factorial design of experiments (DOE). The effect of the electrolyte composition on process efficiency, coating thickness and hardness is established by using response functions. A mechanism for the participation of the nitric acid additive during the oxide formation is proposed. The statistical significance of the results is assessed by an analysis of variance (ANOVA). Eventually, scratch testing is applied in order to evaluate the failure mechanisms and the abrasion resistance of the obtained conversion coatings.

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.

Self-tapping aluminium screws are an innovative joining technology for the assembly of lightweight components in industrial scale. It has been established in the past that porous anodic oxide coatings in many cases reduce the fatigue strength of specimens without notches. In the present work, the fatigue behaviour of notched specimens, i.e. self-tapping screws made from aluminium alloys EN AW-6056, 6082 (both in a conventional state and in a fine-grained state produced by equal channel angular pressing – ECAP) and 7068 with and without oxide coatings is examined. The coatings are produced by hard anodising and are necessary for the thread-forming process during assembly. While the coatings do not affect the static tensile strength, they reduce the fatigue strength for the specimens of the 6056 and the 6082 alloy. For the 7068 alloy a slight increase in fatigue strength is discovered on a low load horizon. The scatter of endured fatigue cycles until fracture of specimens is generally reduced by the anodic oxide coatings.

The application of Al/Mg compound materials for lightweight structures is limited by their corrosion susceptibility. The primary corrosion attack takes place at the Mg component. This may partly be caused by galvanic corrosion and partly by the insufficient formation of a natural passive layer on magnesium. Therefore, oxide coatings were produced on the co-extruded Al/Mg compounds by simultaneous plasma electrolytic oxidation (PEO). A silicate-alkaline and a silicate-phosphate-alkaline electrolyte were used for the coincident production of coatings with a thickness of several 10 microns on both the aluminum and the magnesium component. The inherent flaws of the coating (pores, cavities) allow for the infiltration with an epoxy-based sealant. The electrochemical behavior of the magnesium component covered with the oxide coatings with and without sealing was compared with reference to the unmodified surface. The surface modification (PEO w/wo sealing) significantly decreases the corrosion susceptibility of the Mg component, and thus of the compound.

Anodizing with closed electrolytic free jet enables the resource-efficient, local conversion and surface structuring of the high-strength alloy EN AW-7075 T6 aiming at the local improvement of the tribological behavior of functional surface areas. The objective of the present work was to confine the current distribution on the specimen's surface and to achieve a stronger localization of the coating oxide layer. For this purpose, the processing parameters working distance, voltage and process duration were varied systematically. Based on the refractive index of the porous oxide and laser scanning microscope imaging of the interference lines, the maximum thicknesses of the anodized spots were calculated. Moreover, the coating microstructure was investigated by scanning electron microscopy and the surface topography was measured with a stylus profiler. The results show that the reduction of the working distance to 100 μm enables a significantly improved localization of the coating growth at substantially lowered process voltages. Thus, the energy-efficient production of localized, wear-resistant oxide spots for tribological applications with local functionalization of surfaces through anodization by closed electrolytic free jet is proven.

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.

The physical and electrochemical characteristics such as density, viscosity, electrical conductivity and cyclic voltammetry of three different non-aqueous palladium electrolytes were analysed. The cyclic voltammetry behaviour showed typical reduction and oxidation peaks corresponding to the deposition and stripping of palladium in the electrolytes employed. The electrodeposition of palladium films from choline chloride/ethylene glycol (ChCl-EG), choline chloride/urea (ChCl-urea) and 1-butyl-3-methylimidazolium chloride-tetrafluoroborate (BMIM-Cl-BF4) solutions was demonstrated. Compact deposits were obtained with galvanostatic electrolysis. The scanning electron micrographs of the deposits revealed predominantly nodular Pd particles.

Three different methods to prepare 1,4-diazidobuta-1,3-dienes are presented: nucleophilic substitution of electron-poor dichlorinated substrates, nucleophilic addition of hydrazoic acid at an electron-deficient diallene, and a sequence of prototropic isomerizations of propargyl sulfones followed by nucleophilic additions. In all cases, isolation and assignment of the diastereomeric products was possible, and some sequential reactions, such as reduction or 1,3-dipolar cycloaddition of the azido groups, were performed.