Plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte containing nanosized sepiolite fibers was carried out on magnesium alloy AZ31. The mineral fibers were loaded with different corrosion inhibitors and incorporated in situ during the PEO treatment. The composition and microstructure of the PEO coatings were investigated by SEM. It was shown that the fibers are located on the surface as well as inside the “weak spots” of the coating, i.e., pores and discharge channels. The fixation of the particles is caused by sintering due to the heat developed during the PEO treatment. Investigations using electrochemical impedance spectroscopy and linear sweep voltammetry in 0.01 M NaCl solution confirmed an improvement of the corrosion protection. The use of the inhibitors shifts the critical pitting potential in the anodic direction. Regarding efficiency, cerium-loaded sepiolite showed the best behavior by shifting the pitting potential by +0.9 V.

One of the key urban air quality issues is pollution by nitrogen oxides (NOx). To reduce NOx, facade cladding could be provided with photocatalytic properties by incorporating titanium dioxide nanoparticles. For this purpose, a modified phosphoric acid anodizing process (MPAA) was developed for the facade alloy EN AW-5005, in which highly ordered anodized structures with a low degree of arborization and tortuosity were produced. Pore widths between 70 nm and 150 nm and layer thicknesses of about 2–3 μm were obtained. The subsequent impregnation was carried out by dip coating from water-based systems. Depending on the dip-coating parameters and the suspension used, the pores can be filled up to 60% with the TiO2 nanoparticles. Photocatalytic tests according to ISO 22197-1 certify a high photocatalytic activity was obtained with rPCE values > 8 and with rPCE > 2, achieving “photocatalytically active for air purification”. Tests on the corrosion resistance of the anodized coatings with a commercially available aluminum and facade cleaner confirm a protective effect of the anodized coatings when compared with nonanodized aluminum material, as well as with compacted anodized layers.

AC‐induced corrosion is a big threat even for cathodically protected pipelines nowadays. While this phenomenon was intensively investigated in the last decades, the corrosion mechanisms due to AC interference remain unclear. In the present work, investigations on the surface processes on cathodically protected mild steel during AC polarization have been performed. They utilized high‐speed potential measurements that have demonstrated the influence of the polarization parameters on the resulting alternating voltage. The corrosion product layer was characterized with scanning electron microscopy, electron probe microanalysis, and Raman spectroscopy, which clearly show the effect of the parameters of the applied alternating current on the surface under different cathodic protection (CP) conditions. It was demonstrated that the properties of the formed corrosion product layer, meaning the layer thickness, amount of oxygen, and so on, is not only dependent on the AC polarization parameters but also on the CP potential itself.

Wear resistant ceramic coatings were generated on novel commercially pure titanium grade 4+ alloys by the plasma electrolytic oxidation technique (PEO) in an aluminate and zirconia containing electrolyte. The coatings were obtained adopting a full regular two-level factorial design of experiments (DoE) varying the PEO process parameters current density, repetition rate and duty cycle. The generated coatings were characterized with respect to its wear resistance and mechanical properties by reciprocal ball-on-flat tests and nanoindentation measurements. Thickness, morphology and phase formation of the PEO coatings was analyzed by scanning electron microscopy (SEM/EDS) and X-ray diffraction. XRD results indicate the formation of crystalline aluminium titanate (TiAl2O5) as well as t-ZrO2 and alumina leading to an increase in hardness and wear resistance of the PEO coatings. Evaluation of the DoE's parameter interaction shows that the main effects for generating wear resistant coatings are current density and repetition rate. In particular, the formation of mechanically stable and adhesive corundum and zirconia containing coatings with increasing current density and frequency turned out to be responsible for the improvement of the tribological properties. Overall, the PEO processing significantly improves the wear resistance of the CP titanium base alloy.

Friction stir welding (FSW) is a solid‐state joining method that is suitable for joining dissimilar materials such as aluminum and steel due to its comparatively low process temperatures. Such hybrid joints are of great interest in view of lightweight construction efforts in various industrial sectors such as transportation. As the combination of different metals in hybrid structures may cause corrosion problems in the welding area because of the formation of a galvanic couple, the corrosion properties are investigated. This work also deals with the influence of additionally transmitted power ultrasound during friction stir welding on the joint properties of AA6061/DP600. Light microscopic analysis and radiographic results show differences in the amount and size of steel particles in the near‐surface area of the joints depending on the used ultrasound power. Although the aluminum alloy and the dual‐phase steel exhibit a Volta potential difference of about 0.8 V in scanning Kelvin probe (SKP) measurements, the measured corrosion current densities on different positions of the AA6061/DP600 joints in 0.5 m sodium chloride solution are only low and no enhanced Galvanic corrosion is observed. A distinct influence of the power ultrasound on the corrosion properties is not given.

This issue from the topic series “Corrosion” contains articles published by Trans Tech Publications in the 2017 - 2018 years. The volume “Corrosion. Protection of Structural Metals and Alloys (2017-2018)” presents readers with a wide range of research results and engineering solutions in providing the anti-corrosion protection of structural metals, alloys, and engineering objects. We hope this collection will be useful and interesting to a broad audience of researchers and engineers from various modern manufacturing areas.

This issue from the topic series “Corrosion” contains articles published by Trans Tech Publications in the 2019 - 2020 years. The volume “Corrosion. Protection of Structural Metals and Alloys (2019-2020)” is the second book on this topic and presents readers with a wide range of research results and engineering solutions in providing anti-corrosion protection of structural metals, alloys, and engineering objects. This collection will be valuable and exciting to a broad audience of researchers and engineers from various modern manufacturing areas.

Corrosion is an important issue in many industrial fields. Among others, coatings are by far the most important technology for corrosion protection of metallic surfaces. The special issue "Advanced Coatings for Corrosion Protection" has been launched as a means to present recent developments on any type of advanced coatings for corrosion protection. Fifteen contributions have been collected on metallic, inorganic, polymeric and nanoparticle enhanced coatings providing corrosion protection as well as partly other functionalities.

As consistent lightweight construction nowadays becomes more and more important in smart production processes, the demand for joints of dissimilar materials increases steadily due to their variety of advantages in engineering. Friction stir welding (FSW) is an innovative pressure welding technique, which offers the ability to realize such dissimilar joints while achieving high tensile strengths. Furthermore, it has been proved that ultrasound enhanced friction stir welding (USE-FSW) has an additional positive effect on the joint strength of these compounds due to the additional introduction of mechanical energy into the joining zone through influencing the formation of brittle intermetallic phase (IMP) and particle allocation in the weld nugget. In this paper, the influence of power ultrasound introduction via USE-FSW on hybrid joints of industrially die-cast aluminum alloy EN AC-48000 (AlSi12CuNiMg) and magnesium alloy AZ91 (MgAl9Zn1) has been investigated. Besides mechanical testing, light microscopic and scanning electron microscopic investigations (SEM) as well as differential scanning calorimetry have been conducted. Furthermore, corrosion behavior of the base material and X-ray radiographic images of FSW and USE-FSW joints have been examined. Additionally, the influence of different ultrasound powers and changes in the introduction side on the tensile strength and microstructure of the joints has been investigated.

The innovative joining process of friction stir welding (FSW) offers a wide range of advantages for welding similar as well as dissimilar materials. Even for the field of poorly weldable material combinations like aluminum to steel with their strongly differing physical properties the method of FSW proved its capability for realizing dissimilar joints with tensile strengths up to more than 80 % of the aluminum base material. Trying to improve this value and other properties of the joints several approaches for hybrid friction stir welding processes were tested in the scientific community, whereas the ultrasound enhancement of FSW (USE-FSW) looked as one of the most promising reaching good results. To gain a deeper knowledge of the influence of the ultrasound on the friction stir welds different investigations were carried out in this paper. Therefore the method of USE-FSW was applied on two dissimilar aluminum/steel-joints with varying carbon content of the steel in this work. The material combinations AA6061/SAE1006 and AA6061/SAE1045 were welded successfully with and without additional power ultrasound. Afterwards a comparison between FSW-and USE-FSW-joints was carried out regarding the microstructure of the nugget and interface (IF) by light-microscopy as well as scanning electron microscopy. Furthermore the mechanical properties were characterized in a first step.

The wall thickness of microprocess apparatuses is not comparable to those of stirred vessels used in chemical industries. Already changes of the composition of corrosion resistant alloys in the range of the specification may cause severe deviations of the corrosion rate. Ideally, for micro process apparatuses, completely suppression of corrosion should be accomplished. Therefore, tantalum is the material of choice due to its superior corrosion resistance. It is demonstrated that microchannels possessing a small cross section but large length could be homogeneous coated with tantalum by means of a CVD process without any defects. Corrosion tests in 70% sulfuric acid proved that no loss of weight or corrosion occurred.

Plasma electrolytic layers on AZ31 provide an efficient corrosion protection. However, the process‐related pores and holes are weak points in view of risk of corrosion. The incorporation of a small amount of nano‐sized inhibitor‐loaded zeolite particles leads to a significant improvement of the corrosion resistance. The study shows that the inhibitor‐loaded particles can be incorporated directly during plasmaelectrolytic oxidation in a one‐step‐process. The risk of pitting corrosion decreases in comparison with inhibitor free anodized layers and the cerium inhibitor was found to deposit directly inside pits.

As an innovative hybrid joining process ultrasound enhanced friction stir welding (USE-FSW) was successfully applied on Al/Mg-joints and offers a beneficial impact on the resulting microstructure and mechanical properties. Whereas in conventional FSW of Al to Mg continuous band-shaped intermetallic layers of Al3Mg2 and Mg17Al12 are always present, the formation of these layers can be influenced positively by the ultrasound energy that is transferred into the stirred zone in USE-FSW. In this case, the intermetallic phases are spread over the complete nugget zone. Consequently, the tensile strength increases about 25% and the fatigue strength rises by up to 3.5 times. Based on this USE-FSW was investigated with regard to possible advantages for Al/steel-hybrid-joints. Preliminary investigations have shown significant differences in the microstructure of ultrasound enhanced and non-ultrasound enhanced EN AW-6061/DC04-joints. While conventional FSW led to hooks and larger particles of steel in the aluminum, USE-FSW-joints show remarkably smaller and more homogenous distributed steel particles in the nugget. Beside mechanical investigations, non-destructive examinations and corrosion tests were carried out.

In this work, the joining of aluminum to steel was conducted by ultrasound enhanced friction stir welding (USE-FSW). The power ultrasound was introduced into one of the metal sheets by an ultrasonic roll seam module synchronously to the FSW-process. The effect of the ultrasound on the resulting welds, their microstructure and their corrosion properties was investigated by light and scanning electron microscopy and corrosion investigations. The USE-FSW-joints showed less and smaller steel particles in the nugget zone as well as a thinner continuous intermetallic phase of FeAl3 at the interface. The nondestructive testing method of computed laminography proved the observations made by optic microscopy due to non-porous joints for both techniques. Corrosion investigations showed only low corrosion current densities and no enhanced galvanic corrosion for the EN AW-6061/DC04-hybrid joints in sodium chloride solution.

Bioleaching and biocorrosion are based on similar biochemical processes. Microbe-surface interaction, biofilm formation and concomitant extracellular polymeric substance (EPS) production gained increasing interest in the past decades. Nowadays it is generally accepted that biofilm formation and an accompanying formation of manganese oxides by manganese oxidizing bacteria such as Leptothrix spp. account for one type of pitting corrosion of stainless steel (SS). However, little is known about biofilm formation, EPS composition of manganese oxidizing microorganisms and their influence on microbiologically influenced corrosion. Consequently, we studied biofilm formation of Leptothrixdiscophora, the biooxidation of manganese in biofilms on floating filters as well as biofilm formation on stainless steel and the involved corrosion processes. Cells were visualized by epifluorescence (EFM) or confocal laser scanning –microscopy (CLSM). Additionally, the influence of biofilm formation and biooxidation of manganese by L. discophora on the open circuit potential (OCP) and pitting potential (Epit) of stainless steel was measured using a 3 electrode setup. L. discophora grew well in biofilms on floating filters and on SS coupons and incorporated in both conditions Mn2+ in the form of MnO2 from the bulk phase into the biofilm. OCP measurements of actively manganese-oxidizing biofilms on stainless steel showed a significant ennoblement of ≥200 mV.

Fusion welding of dissimilar metals is in the most cases difficult or even impossible as a result of different melting points and the development of undesirable brittle intermetallic phases. This often leads to joint strengths considerable below the tensile strength of the base materials. By using Friction Stir Welding (FSW) it is possible to reduce the development of the intermetallic phases of Al/Mg-joints significantly but not to avoid them completely. Hence a hybrid welding system at the WKK of the University of Kaiserslautern was developed called “Ultrasound Supported Friction Stir Welding (US-FSW)” with the aim to shatter the brittle interlayer lines and to scatter fragments in the welding area during the FSW process. Pre-investigations have shown that for Al/Mg-US-FSW-joints the strength can be increased up to 30% in comparison to conventional FSW. Moreover for the reliable detection of nonconformities in the weld during a post-process inspection by suitable non-destructive testing (NDT) methods is necessary. Also there is a strong need for better process monitoring and control by in-process NDT methods. Furthermore the corrosion behavior of the basic materials and hybrid-joints was investigated by electrochemical methods indicating an increased corrosion of the Mg alloy in the area of the Al/Mg-butt weld.

Coating systems used for oxidation protection of high-strength steel alloys all have certain disadvantages concerning e.g. further processing of the steel parts. Therefore, our aim is the development of a new, nanoparticle-based system obtained by the sol-gel process which improves the oxidation resistance of boron-manganese steel alloys (22MnB5) during press-hardening and which may stay on the steel parts during further processing.Coatings obtained from three sols containing lithium aluminum silicate and potassium aluminum silicate showed the best performance against oxidation. The structural properties of the materials were characterized using different methods like XRD and DTA. Comparison of the oxidation rate constants (K-P '') of samples coated with selected sols and treated at different temperatures with the bare material and steel coated with Usibor (R) as reference coating proved the ability of the coatings to protect against oxidation at temperatures up to 800 degrees C. The absence of any secondary intermetallic phases and layer residues during laser beam welding proves the suitability of nano-particulate coatings for further industrial processing.

Titanium alloys combine outstanding specific mechanical properties with corrosion resistance and biocompatibility. Addition of lanthanum to (a +beta)-titanium alloys like Ti6A14V leads to improved machinability due to formation of short breaking chips and thus, the possibility of automated manufacturing. These alloys consist of a titanium matrix and metallic lanthanum particles located on the grain boundaries. Free-machining alloys based on Ti6A14V have been developed by replacing vanadium with an iron-molybdenum pre-alloy to lower the material costs, by adding lanthanum to improve machinability and copper and silicon to improve particle distribution. Two alloys, Ti6Al2Fe1Mo0. 9La0. 5Cu and Ti6Al2Fe1Mo0. 9La0.-5CuO. 3Si, have been investigated. Both alloys contain precipitates of lanthanum as well as Cu4 La intermetallic phase besides the (alpha-beta)-matrix. The focus of this work lies on the characterisation of the local corrosion properties by atomic force microscopic methods, like Scanning Kelvin Probe Force Microscopy (SKPFM) and in-situ Atomic Force Microscopy (EC-AFM) in a fluid cell to understand the underlying corrosion mechanisms. Integral testing methods like potentiodynamic polarization and electrical impedance spectroscopy (EIS) are also conducted. The alloys have been exposed to different corrosive media. The results show that the precipitates undergo selective dissolution in time intervals of a few minutes up to several hours depending on the electrolyte.