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In this work, the corrosion susceptibility of powder coated Al6060 alloys with increasing Cu and Zn content is evaluated in a benchmark test. Although higher Cu and Zn limits would enable the industry to increase the use of end-of-life scrap and thus produce eco-friendlier aluminium profiles, such alloys are often disregarded due to concerns of corrosion, especially filiform corrosion. Our results suggest that this concern is ungrounded as long as typical quality specifications for the pre-treatment and coating process are followed and the alloy composition is kept within the limits of the European norm AW6060. Furthermore, we point out that the variation of the results due to processing at different coating production lines is larger than the difference between alloys of different Cu and Zn contents.

This work analyses the microstructural defects and the corrosion behaviour of 316L stainless steel clads deposited by laser metal deposition on wrought conventional material, which is a highly relevant system for repair applications. The different defects and microstructural features found in these systems were identified and analysed from a perspective relevant to the corrosion performance of these materials. The role of these features and defects on the corrosion process was evaluated by exposure of the samples to corrosive media and further examination of the corrosion morphology. The heat-affected zone, located on the wrought base material in close vicinity of the deposited clad, was identified to be the primary contributor to the corrosion activity of the system due to the large depletion of alloying elements in this region, which significantly decreased its pitting resistance. Alongside the heat-affected zones, relatively small (

The reliability of printed circuit boards (PCB) is at risk due to continuous miniaturization. As a result, PCBs are more susceptible to external factors such as humidity, temperature, contamination, etc., which affect their general performance, leading to failure of electronic devices. Therefore, protection of the devices against these factors is gaining greatly in importance. Plasma polymerization is used as a method to form a protective barrier by applying plasma polymer films on PCBs. However, the humidity robustness of such plasma coatings on the PCB surface is unknown. In this work, several methods were used to characterize two types of plasma-coated PCBs based on 1H,1H,2H-perfluorodecyl acrylate precursor (single-layer and stacked coatings) upon exposure to humidity, temperature, and bias voltage. Modulated-temperature differential scanning calorimetry enabled thermal analysis of the plasma coatings. Electrochemical impedance spectroscopy in combination with the gravimetric moisture vapor sorption technique were used to study the interaction of these coatings with moisture and quantify the water uptake. The results revealed an only 2% increase of the capacitance of the coatings due to water uptake. Direct-current (DC) leakage current measurements were used to study the influence of a bias voltage applied between the electrodes on the coated PCBs upon exposure to cyclic climatic conditions. Electrical DC testing revealed the protective character of the stacked coating, which did not fail under the given stress conditions, in contrast to the single-layer plasma coatings.

Aluminum alloy (AA) 3003 is widely used as fin and tube material in heat exchangers. In these heat exchangers, the tube and fin material are brazed together by means of an AA4xxx alloy. In this study, the effect of a simulated brazing step on the microstructure and corrosion behavior of a twin roll casted (TRC) AA3003 was studied. In particular, the effect of simulated brazing on the corrosion properties of the centre line segregation (CLS) of alloying elements and the interaction of the intermetallic particles with the surrounding matrix is explored. It is shown that the cross sections are significantly more active than the surface of the TRC AA3003, revealing the importance of the CLS on the corrosion behavior. Furthermore, it is shown that the number of pits and their depths decreased considerably on the exposed cross sections after simulated brazing, especially near the CLS. Scanning Kelvin probe force microscopy measurements show that after the simulated brazing step the Volta potential difference between the intermetallic particles and the matrix reduced significantly. This change in the Volta potential could be caused by the slight increase of Si content in the matrix.

The Zinc level in many 6000 Al alloys (Al-Mg-Si-type) was set to a maximum of 0.03 wt% as common industrial practice. Concentrations above 0.03 wt% can modify the alkaline etching mechanism causing the surface to go from a desired smooth look associated with a grain boundary attack (GBA), into an undesired speckled appearance due to preferential grain etching (PGE), visible after anodizing. This significantly limits the ambition of reducing the carbon footprint of Aluminum by increasing the amount of recycled material in the production process. Because Cu has been reported to counteract this negative effect of Zn, the present study is dedicated to contribute to the understanding of this interaction and is focused on Zn and Cu in peak aged AlMgSi alloys. The chemical composition of the various precipitates formed in two Al6063 alloys was studied by means of TEM and EDX, whereby Zn was found in the Q phase (AlMgSiCu) grain boundary precipitates. Two alloys, with different content of Cu and Zn were studied. The Zn/Cu ratio in the bulk was similar for both alloys, but the level of Zn in the Cu containing Q particles in the grain boundaries was different. The increased Zn concentration in Q phase precipitates is believed to decrease the potential of the precipitates with respect to the surrounding matrix. Thus, the Cu/Zn ratio in these alloys is extremely important as it defines the potential differences that in turn cause either GBA or PGE., SCOPUS: ar.j, info:eu-repo/semantics/published

Sr is known to transform the morphology of the eutectic silicon phase as well as the Fe-rich β phase in Al-Si alloys, improving their mechanical properties. However, little is known about the effect Sr has on the (local) corrosion properties of aluminium alloys. This study investigates the effect of Sr addition to a modified AA3003 heat exchanger material on the morphology of the different phases present, especially the Fe-rich phases, as well as on the (local) corrosion properties of this material. This work reports the formation of a Sr-rich phase, which slightly increases the macrohardness of the material. The Fe-rich phases are not shown to be refined/influenced by the addition of Sr Potentiodynamic polarization experiments showed an increase in pitting potential by increasing the amount of Sr in the material up to 0.4 wt.%. Nevertheless, the analysis of the corrosion morphology revealed that the Sr-containing particles did not contribute to the corrosion process despite their cathodic behaviour compared to the Al matrix as measured by Scanning Kelvin Probe Force Microscopy. This behaviour was attributed to the thicker oxide layer found on the Sr-rich particles.

This work studies the passive behavior and growth kinetics of the native oxide on additively manufactured AlSi10Mg and compares it with that of the conventional cast alloy, which presents a markedly different microstructure. With the use of a scanning Kelvin probe force microscopy (SKPFM)-based methodology, the growth kinetics of native oxide films on these alloys was examined. The microstructure of these materials had a great impact on the oxide growth and thickness, and consequently on its passive behavior. The native oxide on the additively manufactured sample presented faster growth and superior passive behavior than those of the cast alloy.

Press-hardened steels are commonly protected with hot-dip Al-Si coating. Due to the electrochemical complexity of this system, either before or after hot-stamping process, SKPFM was used to investigate the influence of the thermo-mechanical process on the electrochemical behaviour of the galvanic coupling. The hot-stamping process changed significantly the anodic/cathodic coupling of the coating/steel due to iron enrichment in the coating layer. Hence, a concurrent mechanism was thoroughly established, i.e., while the press hardening enhances the corrosion properties of the steel system (steel and metallic coating) through diffusion, at the same time it diminishes the cathodic protection of the Al-Si layer.

In this work, the effect of heat treatments on the anodizing behavior of additive manufactured AlSi10Mg material is studied. Specimens are subjected to artificial aging or stress release heat treatments, followed by galvanostatic anodizing in sulfuric acid. Optical and scanning electron microscopy are employed to study the microstructure and the oxide layer characteristics. Upon applying the heat treatments, the microstructure shows a gradual evolution from a continuous 3D silicon network toward separate coarse silicon particles in an aluminum matrix. The morphology of the silicon phase is found to be a deciding factor as it determines the fraction of silicon that is oxidized during anodizing. This in turn is found to have a direct impact on the anodizing efficiency and oxide layer uniformity. Thicker and more uniform oxide layers are obtained for the additive manufacture AlSi10Mg specimens after the silicon network is broken up due to the heat treatments.

This work analyzes the galvanostatic anodizing behavior of additive manufactured (AM) Al-Si alloys. Two main factors were studied here: 1) the influence of Si content on the anodizing behavior and on the porous structure of the anodic oxide film, and 2) the effect of pre-existing internal pores on the anodizing behavior of these materials. Three different alloys were anodized in H2SO4 electrolyte, with 7%, 10%, and 12% Si. The voltage responses of the different samples during anodizing were compared and the formed oxide was analyzed. The amount of Si in the AM Al-Si alloys was found to have a great influence on the anodizing voltage and consequently on the porous structure of the anodic oxide layer. However, the anodic oxide growth rate was nearly independent of the Si content in the samples. Moreover, the effect of internal porosity resulting from the metal additive manufacturing process on the anodizing behavior of these specimens was also analyzed. An outer anodic oxide layer decorated the pre-existing internal pores that were reached by the anodic oxide front. These internal pores were also characterized by the systematic appearance of cracks resulting from the volume expansion of anodic oxide layers advancing in opposite directions.

This work addresses the effect of deformation twinning on the dissolution corrosion behaviour of 316 L austenitic stainless steels in contact with static liquid lead-bismuth eutectic (LBE). For this purpose, plastically deformed 316 L steel specimens with distinctly different deformation twin densities were simultaneously exposed to oxygen-poor (

Additively manufactured (AM) AlSi10Mg is one of the most studied AM aluminium alloys to date. While several studies have focused on investigating its mechanical properties and corrosion performance, very little work has been dedicated to study corrosion protection mechanisms and surface treatments applicable for this material. This work presents for the first time an analysis of the mechanism of Zr electrochemical conversion on AM AlSi10Mg parts. A comparison with the conventional cast alloy was also conducted. An analysis of the specimens using SEM/EDS provided interesting insights concerning the effect of the microstructure on the deposition of the Zr conversion layer. This work demonstrates that due to the very fine microstructure and distribution of alloying elements in AM AlSi10Mg, a homogeneous deposition of the Zr conversion layer is promoted. Conversely, the cast alloy is characterized by a very heterogeneous deposition of the Zr conversion layer due to the presence of relatively large Fe-containing intermetallic particles. The influence of the conversion coating on the corrosion performance of these materials was also studied. The results show that while the conversion treatment has no impact on the corrosion resistance of the cast alloy, it greatly improves the passivity of the AM AlSi10Mg samples.

In this work, the role of the Si phase microstructure in the anodizing behavior of Al-Si alloys is studied. Experiments were conducted using an additive manufactured (AM) Al-Si10-Mg specimen and a cast alloy of approximately the same chemical composition. A systematic characterization of the anodic oxide film was conducted using a variety of surface analysis techniques. Clear evidence is provided through X-ray photoelectron spectroscopy analysis for the almost entire oxidation of Si during the anodizing of the additive manufactured specimens, which can explain the lower anodizing efficiency observed in the AM material compared to the cast alloy. Additionally, a more detailed characterization of the oxide layer revealed that a slightly thinner anodic oxide film is formed at the borders of the characteristic melting tracks resulting from the metal additive manufacturing process. Furthermore, the features observed in the voltage–time response during the anodizing of the AM specimens seem to be closely associated with the dimensions of the Al/Si cells present in the plane parallel to the direction of the oxide front growth.

Two types of self-repairing coatings for the protection of Al and its alloys are reviewed: (1) organic coatings with capsules containing repairing agent and (2) porous anodic oxide films with inhibitor solution stored in the pores of the oxide film. First, polyurethane microcapsules containing liquid surface-repairing agents were synthesized and polyurethane coating with the capsules was painted on Al alloy specimens. After mechanical damage to the coating, self-repairing occurred by the reaction of water vapor in the air with the repairing agents released from the capsules. Second, porous-type anodic oxide films were formed on Al alloys, and the pores of the anodic oxide films were filled with inhibitor solutions, followed by application of a covering polyurethane layer. Inhibitors released from the pores efficiently protected the Al alloy substrate from corrosion arising from induced mechanical damage.

When aiming for an increased and more sustainable use of metals a thorough knowledge of the corrosion phenomenon as function of the local metal microstructure is of crucial importance. In this work, we summarize the information presented in our previous publications[1-3] and present an overview of the different local (electrochemical) techniques that have been proven to be effective in studying the relation between different microstructural variables and their different electrochemical behavior. Atomic force microscopy (AFM)[1], scanning electrochemical microscopy (SECM)[2], and electrochemical scanning tunneling microscopy (EC-STM)[3] were used in combination with electron backscatter diffraction (EBSD). Consequently, correlations could be identified between the grain orientation and grain boundary characteristics, on the one hand, and the electrochemical behavior on the other hand. The grain orientation itself has an influence on the corrosion, and the orientation of the neighboring grains also seems to play a decisive role in the dissolution rate. With respect to intergranular corrosion, only coherent twin boundaries seem to be resistant.

The microcapillary cell electrochemical method is capable of evaluating hydrogen (H) uptake in steel with respect to deformation, which is induced by various mechanical methods (cold rolling, bending and punching). A clear relation between the deformation degree and the local H-content is established for dual phase (DP600) steel. The magnitude of the deformation nearby a punched edge is quantitatively determined using electron backscatter diffraction technique. A shear-affected zone is identified at the edge of the punched hole. The dedicated local electrochemical measurements confirm the presence of high concentrations of local-H in this shear affected zone, which is likely detrimental for H-embrittlement.

This study focuses on the effect of heat treatments on the microstructure and corrosion behaviour of additive manufactured AlSi10Mg specimens. Non heat treated, artificially aged and stress released specimens were studied. The microstructure showed an evolution from cellular aluminium cells surrounded by a 3D network of fibrous eutectic silicon phase to coarse separated silicon particles. The corrosion behaviour was found to change with the heat treatments. Untreated and artificially aged specimens showed superficial corrosion attacks with microcrack formation while stress released specimens showed penetrating attacks without microcrack formation. Mechanisms were proposed for the microstructure evolution and the different corrosion behaviours.

This work compares the microstructure and corrosion resistance of 316 L stainless steel samples prepared using two different additive manufacturing methods: selective laser melting (SLM), and laser metal deposition (LMD). A wrought material was used as reference. The specimens showed marked differences in their microstructure, as a result of the specific manufacturing conditions. All samples displayed similar corrosion potential and passive current density values. However, variations were seen in their potential passive range (SLM > LMD > Wrought). The wider passivity of the SLM specimen can be associated with its finer microstructure, which leads to a more stable native oxide.

Metal additive manufacturing (MAM), also known as metal 3D printing, is a rapidly growing industry based on the fabrication of complex metal parts with improved functionalities. During MAM, metal parts are produced in a layer by layer fashion using 3D computer-aided design models. The advantages of using this technology include the reduction of materials waste, high efficiency for small production runs, near net shape manufacturing, ease of change or revision of versions of a product, support of lattice structures, and rapid prototyping. Numerous metals and alloys can nowadays be processed by additive manufacturing techniques. Among them, Al-based alloys are of great interest in the automotive and aeronautic industry due to their relatively high strength and stiffness to weight ratio, good wear and corrosion resistance, and recycling potential. The special conditions associated with the MAM processes are known to produce in these materials a fine microstructure with unique directional growth features far from equilibrium. This distinctive microstructure, together with other special features and microstructural defects originating from the additive manufacturing process, is known to greatly influence the corrosion behaviour of these materials. Several works have already been conducted in this direction. However, several issues concerning the corrosion and corrosion protection of these materials are still not well understood. This work reviews the main studies to date investigating the corrosion aspects of additively manufactured aluminium alloys. It also provides a summary and outlook of relevant directions to be explored in future research.

This work evaluates the corrosion resistance of three Al-Si alloys processed by additive manufacturing (Al-Si7-Mg, Al-Si10-Mg, and Al-Si12) through a comparative analysis. It explores the influence of the silicon content on the microstructure and corrosion behavior of these alloys. An initial scanning electron microscopy analysis revealed that the silicon content in the samples affected the level of connectivity of the Si network, and this, consequently, influenced the formation of micro-cracks during corrosion. A model describing the evolution of the corrosion attacks and micro-cracks formation in the AM Al-Si alloys is proposed here.

This work presents a novel procedure to study the growth of the surface native oxide film on metals in air, based on scanning Kelvin probe force microscopy. For reactive metals such as aluminium, when the native metal oxide is damaged, fast reformation of the oxide film occurs. The methodology presented here allows this oxide film reformation to be studied in situ. By monitoring the evolution of the Volta potential with time in a scratch on the sample's surface, the characteristic behavior of the oxidation of aluminium metal could be observed. The procedure was carried out on a pure aluminium sample, but could potentially be applied in other metals, provided that the relation between the oxide film and the Volta potential is established. Keywords: SKPFM, Surface repassivation, Native oxide film

In a previous study, self-healing polyurethane coatings with microcapsules containing the high reactive liquid phase have been developed for the protection of metal from corrosion for long periods. In this study, we examine the effect of the amount of glycerol added in the microcapsule formation process on the shape of capsules and the self-healing ability of coatings with microcapsules. The capsule formation with large amounts of glycerol gave rise to clusters of capsules, while with small amounts of glycerol, the capsules were mainly independent ones. The selfhealing property of the coatings was more remarkable with decreasing the amount of glycerol in the capsule formation process.

Surface corrosion product formation is one of the important factors affecting the corrosion rate and hydrogen uptake in a H2S environment. However, it is still unclear how the base material composition will affect the corrosion products that are generated, and consequently their impact on the corrosion rate. In this paper, corrosion product formation and the impact of the Mo content of the base material on the composition of the corrosion products and hydrogen absorption in a sour environment was investigated. The corrosion layer was composed of a double layered mackinawite (FeS1−x) structure, which was enriched with molybdenum and chromium. The layers were formed via two different mechanisms, i.e., the inner layer was created via a general oxide film formation corrosion mechanism, whereas the upper layer was formed by a precipitation mechanism. The presence of this double corrosion layer had a large influence on the amount of diffusible hydrogen in the materials. This amount decreased as a function of contact time with the H2S saturated solution, while the corrosion rate of the materials shows no significant reduction. Therefore, the corrosion products are assumed to act as a physical barrier against hydrogen uptake. Mo addition caused a decrease in the maximal amount of diffusible hydrogen.

This work studies the influence of the proportional change in discharge power and the monomer feed on the morphology and the chemistry of atmospheric plasma deposited films. Atmospheric plasma coatings of allyl methacrylate were deposited using dielectric barrier discharge plasma under different conditions but always under the same ratio between the discharge power and monomer feed (W/FM). It is shown that a constant W/FM does not necessarily provide the same chemistry and the same morphology for atmospheric pressure plasma. This is explained by the higher discharge power of the plasma resulting in an increase of streamers which alter the distribution of energy among the plasma species. On the surface of the deposited coatings, globular-like features were observed, which are suggested to be formed in the volume of the discharge. The deposition rate is also influenced. providing thicker coatings, when high monomer feed/high power are used. Finally, infrared spectra showed a higher retention of the ester functionality at high power/high monomer feed.

The galvanostatic anodizing behavior of additive manufactured (AM) Al-Si10-Mg alloy was studied in H 2SO 4 electrolyte. The analysis of the voltage vs time response was complemented with a systematic characterization of the anodic oxide layer using a variety of techniques. In addition, a cast alloy of approximately the same chemical composition as that of theAMspecimens was used as a reference in this study. Significant differences were found in the voltage-time characteristics of the samples analyzed. Besides, an anisotropic anodizing behavior was observed in the additive manufactured specimens. Due to the fine silicon microstructure present in the additive manufactured samples, the anodic oxide growth was much more obstructed than for the cast alloy. Nevertheless, even though the oxide layer was generally thinner in the AM samples for the same conditions and anodizing time, a much more continuous and uniform oxide layer was found in the additive manufactured specimens compared tothe cast alloy. The porous structure was found to be greatly affected by the fine distribution of the silicon phase in the AM parts.

Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimens without capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.

In a previous study, self-healing polyurethane coatings with microcapsules containing healing agents have been developed for the protection of metal from corrosion. At the initial stage of the development of these coatings, we synthesized the microcapsules containing healing agents by adding organic solvents to inhibit the solidification of the whole capsule. In this study, the structure of the capsules formed with different solvents, such as chlorobenzene, toluene and xylene was examined. We also evaluated the self-healing ability of coatings with these capsules after damaging the coating by scratching. The amount of healing agents contained in capsules depends on the kind and the amount of solvents added. In the capsule formed with 20 or 50 wt%-chlorobenzene, there is almost no healing agent of liquid phase, while in the capsule formed with 70 wt%-chlorobenzen healing agents are contained. Toluene and xylene are more effective inhibitors than chlorobenzene. The capsule formed with 70 wt%-toluene or xylene contains much more amounts of the healing agent of liquid phase than that formed with 70 %-chlorobenzene, and the coatings with the former capsules have an appreciable self-healing ability.

A new approach for studying the effect of temperature on electrochemical processes is presented in this paper. Using an in-house developed electrode holder, experiments are performed under conditions of applied and controlled electrode temperature. This new approach provides an improved temperature control during the experimental study and, additionally, allows distinguishing both the influences of the electrolyte and electrode temperatures. The advantages of the applied electrode temperature approach are illustrated by considering porous anodizing of aluminium. In a broad temperature range the electrochemical behaviour of the aluminium electrodes, recorded during the new and the conventional way of anodizing, are compared. Differences between the anodic potential evolutions in both approaches are observed, and are explained by a heat flux to the surroundings during the experiments at uncontrolled electrode temperature. These results illustrate the advantage of applying the electrode temperature. If the influence of temperature on a process is investigated by merely varying the electrolyte temperature, the electrode temperature is only indirectly influenced and can significantly differ from the electrolyte temperature. Therefore, when evaluating the influence of temperature on an electrochemical system the electrode temperature should be considered, and preferentially also controlled. Keywords: Temperature, Electrode temperature, Aluminium, Anodizing, Porous oxide

Self-healing polymer coatings are a type of smart material aimed for advanced corrosion protection of metals. This paper presents the synthesis and characterization of two new UV-cure self-healing coatings based on acrylated polycaprolactone polyurethanes. On a macroscopic scale, the cured films all show outstanding mechanical properties, combining relatively high Young’s modulus of up to 270 MPa with a strain at break above 350%. After thermal activation the strained films recover up to 97% of their original length. Optical and electron microscopy reveals the self-healing properties of these coatings on hot dip galvanized steel with scratches and microindentations. The temperature-induced closing of such defects restores the corrosion protection and barrier properties of the coating as shown by electrochemical impedance spectroscopy and scanning vibrating electrode technique. Therefore, such coatings are a complementary option for encapsulation-based autonomous corrosion protection systems.

Introduction Many kinds of metals are used as structural material in the building or other constructions. It is important to protect the metal from corrosion, because the corrosion of the metal may cause a significant damage of the building and the constructions. One way of the corrosion protection of the metal is to cover with organic or inorganic coatings, isolating the metal substrate from water or oxygen. When some parts of the coating is removed mechanically or chemically, the corrosion of the material may occur at the damaged areas. Therefore, it is necessary to keep the paint layer protective by a periodic painting that costs much labor and expense. From the point of view of time- and money-saving, we started to develop a “self-healing coating” on the metals for corrosion protection. When the organic coating is damaged by mechanical impulsions, the coating at the damaged areas is healed automatically without painting again, heating or any other external treatments.The above concept is accomplished by the following process. Micro capsules that contain reactive liquid agents are dispersed in coatings (Fig. 1-a). The reactive liquid agent in the capsule is easy to react with water or oxygen in the air to form an organic compound with properties similar to those of the coatings. When the coating is damaged to form flaws, the capsule is also destructed (Fig. 1-b). Then, the reactive liquid agent included in the capsule flows out, and the flaw is filled with the organic compound after reacting with water or oxygen in the air (Fig. 1-c). In the present investigation, capsules that contain a prepolymer agent were dispersed in polyurethane coatings to examine the self-healing ability of the coating. The effect of glycerol on the formation of the capsule was also examined. Experimental At First, 7.7 g of tolylene-2,4-diisocyanate (TDI) and 1.3 g of glycerol were added to 18 g of cyclohexanone, and mixed by stirring with a magnetic stirrer at 600 rpm and 75 ˚C for 24 h. In the period, a prepolymer is formed in cyclohexanone by the reaction shown in Fig. 2. Then, 9.5 g of isophorone diisocyanate and 17 g of chlorobenzene were added to 11 g of the prepolymer/cyclohexanone to obtain a prepolymer solution. Micro droplets of the prepolymer solution were dropped into an aqueous solution containing 3 g of sodium dodecyl sulfate (SDS) and 0.10 – 0.50 g of glycerol. The droplet of the prepolymer solution reacts with SDS/glycerol solution at the interface between two phases to form polyurethane capsules as shown in Fig. 3, since the prepolymer solution doesn’t dissolve in the toSDS/glycerol solution, As a result of the reaction, capsules, which have a polyurethane shell and contain high reactive liquid, were obtained. The capsules collected on a filter were observed by scanning electron microscopy (SEM).The polyurethane dispersed with the microcapsules was coated on Al substrate by spreading 1.5 g of the prepolymer solution containing 10 mg of the capsules after mixing with ethylene glycol ultrasonically, and then kept at room temperature for 48 h to allow the polymerization of the prepolymer and the evaporation of ethylene glycol. Self-healing ability of the coating was evaluated by SEM after damaging the coating with a sharp blade at the pressure of 6.1 MPa. Results and Discussions Fig. 4 shows SEM images of micro capsules synthesized with a) 0.5 and b) 0.1 g of glycerol. All the capsules are spherical, and some of them are coalescent, forming clusters. Fig. 5 shows distribution of the diameter of the micro capsules synthesized with different amounts of glycerol. The most frequent diameter of capsules synthesized with 0.5 g and 0.1 g of glycerol is 4.0 and 3.2 µm, suggesting the coalescence of capsules is easier with larger amounts of glycrol. All the coatings with capsules showed self-healing after damaging with the blade, and the healing effect was more remarkable with smaller amounts of glycerol. Figure 1

Over the last decades much research has been dedicated and reported in literature on the Alternating Current electrograining (A.C. electrograining) mechanism and the parameters that change the final pitting morphology of electrograined aluminium. The reason is the increasing industrial demand every year (currently estimated to be 800,000,000 m2/year) for high quality litho-printing and super capacitors for energy storage. Both applications relay on the production of a controlled roughened surface on aluminium foil which can be achieved through A.C. electrograining. In this case pitting is used as a surface treatment for the production of a larger surface area with uniform pits.

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Press-hardened steel (PHS) is a strategic steel for the automotive industry. The application of this type of steel in the vehicle structure allows safety improvement, mass reduction and less fuel consumption. Due to its ultra-high-tensile strength, the PHS components are produced by means of hot-stamping process. Hot stamping is a thermo-mechanical process in which a steel blank is heated at austenitisation temperatures and then is transferred to a press tool, where the material is formed and quenched simultaneously. The steel substrate is often protected with metallic coatings prior to hot stamping to avoid its oxidation and decarburisation. Zinc and aluminium based systems are often used as coatings for automotive applications. However, for hot stamping, the hot-dip aluminium-silicon (Al-Si) system is the most widespread and used. This coating presents good corrosion and oxidation resistance at high temperatures. However, during hot stamping, the initial microstructure and chemical composition of the metallic coating changes completely due to diffusion. These microstructural and compositional changes take place in the austenitisation step. Hence, after hot stamping the whole coating layer becomes a complex multi-layered system in which the sublayers are enriched in either aluminium or iron/silicon. Consequently, the coating properties, including the corrosion properties, also change after hot stamping. However, little is known about the effect of the morphological and compositional changes of the Al-Si coating due to the thermo-mechanical process on its corrosion behaviour and performance. The different sublayers in the coating form different micro-galvanic-couplings, which can affect the global electrochemical behaviour of the system. Therefore, a detailed approach based on local electrochemical techniques was suggested to evaluate the role that each sublayer plays on the electrochemical behaviour. This work aimed at evaluating the effect of the hot-stamping process on the electrochemical behaviour of 22MnB5 coated with hot-dip Al-Si (10 % Si in mass fraction). The morphology-composition of the layered structure was obtained using field emission scanning electron microscopy (FE-SEM) combined with energy dispersive X-ray spectroscopy (EDS). Global corrosion properties were evaluated by open circuit potential (OCP), linear sweep voltammetry (LSV) and accelerated corrosion test. Nonetheless, the effect of each sublayer of the coating-steel system, on the electrochemical behaviour was investigated on a local scale by two complementary techniques: scanning Kelvin probe force microscopy (SKPFM) and electrochemical micro cell. The former was carried out in the samples\' cross-section and it shows high lateral resolution, while the latter was done from the top surface in a depth profile approach. Thus, it enabled the local potentiodynamic polarisation in an isolated sublayer. The results obtained during the implementation of this work highlight the high complexity of the Al-Si coating-steel system (composed of several layers), which in turn supports the need for local investigations. The morphology and composition of the coating were shown to be greatly influenced by the hot-stamping process (parameters) and this resulted in considerable variations of the local corrosion and electrochemical behaviour of the coating-steel system. O aço endurecido por prensagem (PHS- do inglês, press-hardened steel) é um aço estratégico para a indústria automotiva. A aplicação desse tipo de aço na estrutura do veículo permite melhoria da segurança, redução de massa e menor consumo de combustível. Devido à sua ultra-alta resistência à tração, os componentes de PHS são produzidos por meio do processo de estampagem a quente. A estampagem a quente é um processo termo-mecânico no qual um blanque de aço é aquecido a temperaturas de austenitização e então é transferido para uma ferramenta de prensagem, onde o material é conformado e temperado simultaneamente. O substrato de aço é frequentemente protegido com revestimentos metálicos antes da estampagem a quente para evitar sua oxidação e descarbonetação. Os sistemas baseados em zinco e alumínio são frequentemente usados como revestimentos para aplicações automotivas. No entanto, para estampagem a quente, o sistema de alumínio-silício por imersão a quente (Al-Si) é o mais difundido e utilizado. Este revestimento apresenta boa resistência à corrosão e oxidação em altas temperaturas. No entanto, durante a estampagem a quente, a composição química e microestrutural inicial do revestimento muda completamente devido à difusão. Essas mudanças microestruturais e composicionais ocorrem na etapa de austenitização. Portanto, após a estampagem a quente, toda a camada de revestimento se torna um sistema complexo de múltiplas camadas no qual as subcamadas são enriquecidas tanto em alumínio como em ferro/silício. Consequentemente, as propriedades do revestimento, incluindo as propriedades de corrosão, também mudam após a estampagem a quente. No entanto, pouco se sabe sobre o efeito das mudanças morfológicas e composicionais do revestimento de Al-Si devido ao processo termo-mecânico sobre seu comportamento e desempenho à corrosão. As diferentes subcamadas no revestimento formam diferentes acoplamentos micro-galvânicos, que podem afetar o comportamento eletroquímico global do sistema. Portanto, uma abordagem detalhada baseada em técnicas eletroquímicas locais foi sugerida para avaliar o papel que cada subcamada desempenha no comportamento eletroquímico. Este trabalho teve como objetivo avaliar o efeito do processo de estampagem a quente no comportamento eletroquímico do aço 22MnB5 revestido com Al-Si por imersão a quente (10% Si em fração de massa). A morfologia-composição da estrutura em camadas foi obtida usando microscopia eletrônica de varredura por emissão de campo (FE-SEM- do inglês, field emission-scanning electron microscopy) combinada com espectroscopia de energia dispersiva de raios X (EDS- do inglês, energy dispersive X-ray spectroscopy). As propriedades de corrosão global foram avaliadas por potencial de circuito aberto (OCP- do inglês, open circuit potential), voltametria de varredura linear (LSV- do inglês, linear sweep voltammetry) e teste de corrosão acelerada. No entanto, o efeito de cada subcamada do sistema revestimento-aço no comportamento eletroquímico foi investigado em escala local por duas técnicas complementares: microscopia de varredura de força por sonda Kelvin (SKPFM- do inglês, scanning Kelvin probe force microscopy) e microcélula eletroquímica. O primeiro foi realizado na seção transversal das amostras e apresenta alta resolução lateral; enquanto o último foi feito a partir da superfície superior em uma abordagem de perfil de profundidade. Desta forma, isso permitiu a polarização potenciodinâmica local em uma subcamada isolada. Os resultados obtidos durante a implementação deste trabalho destacam a alta complexidade do sistema de revestimento de aço Al-Si (composto por várias camadas), o que por sua vez suporta a necessidade de investigações locais. A morfologia e a composição do revestimento mostraram ser bastante influenciadas pelo processo de estampagem a quente (parâmetros) e isso resultou em variações consideráveis da corrosão local e do comportamento eletroquímico do sistema revestimento-aço.