TY - GEN A1 - Nikitin, Alexander A1 - Schleuß, Leander A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin T1 - Corrosion Behavior of Brazed Zinc-Coated Structured Sheet Metal T2 - International Journal of Corrosion Y1 - 2017 U6 - https://doi.org/10.1155/2017/4768505 SN - 1687-9333 SN - 1687-9325 VL - 2017 SP - 4768505 ER - TY - GEN A1 - Ermilova, Evgeniia A1 - Nikitin, Alexander A1 - Weiß, Sabine ED - Daehn, Glenn ED - Cao, Jian ED - Kinsey, Brad ED - Tekkaya, A. Erman ED - Vivek, Anupam ED - Yoshida, Yoshinori T1 - The Local Strain Evolution for Structured Sheet Metals During Uniaxial Deformation T2 - Forming the Future : Proceedings of the 13th International Conference on the Technology of Plasticity N2 - Structured materials can be progressive alternatives to commonly used flat sheets because of their higher bending stiffness and stability compared to flat sheet metals, made of the same alloy. The application of sheet metals requires accurate information regarding their strength and deformation behavior. Such data are not commonly available and have to be measured by specific test setups and implementation of tests. The aim of this work is to obtain new knowledge about deformation mechanisms of structured sheet metals. Structured sheet metals (SSM) made of conventional deep-drawing steel DC04 were investigated by means of tensile tests. The influence of the structure type arrangement on the deformation behavior was analyzed. The evolution of local strains was analyzed by means of strain gauge measurements as well as 3D-displacement measurements with an ARAMIS highresolution camera system. Local orientation changes in different structural elements were measured using the electron backscatter diffraction technique. KW - structured sheet metals, ssm, tensile test, ARAMIS, strain gauge, EBSD, REM, electron microscopy, DC04 steel Y1 - 2021 SN - 978-3-030-75381-8 SN - 978-3-030-75380-1 SN - 978-3-030-75383-2 U6 - https://doi.org/10.1007/978-3-030-75381-8_143 SN - 2367-1696 SP - 1701 EP - 1711 PB - Springer, Cham ET - 1 ER - TY - GEN A1 - Kotlarski, Georgi A1 - Ormanova, Maria A1 - Ossenbrink, Ralf A1 - Nikitin, Alexander A1 - Doynov, Nikolay A1 - Valkov, Stefan A1 - Michailov, Vesselin T1 - Fabrication and Characterization of Wire Arc Additively Manufactured AlSi5 Structures T2 - Metals N2 - For the purpose of this research, single track details were manufactured in the shape of thin walls with a length of 100 mm and a height of 80 mm. Two welding speeds were chosen for this experiment–13.3 mm/s and 20.0 mm/s corresponding to the following heat inputs: 120 J/mm and 80 J/mm. The gas metal arc welding (GMAW) method was used for the build-up of the specimens in the cold arc pulse mode. The structure of the specimens was studied using X-ray diffraction (XRD) analysis carried out with CuKα radiation with a wavelength of 1.5406 Ǻ, optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Furthermore, the Vickers hardness of the samples was determined using a ZwickRoell DuraScan 10/20 G5 unit at a force of 1 N. A preferred crystallographic orientation towards the (200) plane was observed in all cases, however a vastly textured structure was observed with inclusions of peaks in the (111), (220), and (311) crystallographic planes. The full width at half maximum (FWHM) of samples taken from different stages of build-up was calculated indicating an increase of the dislocation density at the more advanced stages of specimen growth. Despite that an increase of the hardness was observed towards the top of both specimens. This is attributed to the change in the structure of the αAl + Si formations from an irregular one at the bottom of the specimens, towards a fibrous one at the top. The results are discussed in regard to the optimization of the build-up process during wire arc additive manufacturing (WAAM). KW - wire arc additive manufacturing KW - Al4043 KW - AlSi5 KW - heat input KW - microstructure KW - eutectic formations Y1 - 2022 SN - 2075-4701 VL - 12 IS - 11 ER - TY - GEN A1 - Kotlarski, Georgi A1 - Ormanova, Maria A1 - Nikitin, Alexander A1 - Morozova, Iuliia A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin A1 - Doynov, Nikolay A1 - Valkov, Stefan T1 - Structure Formation and Mechanical Properties of Wire Arc Additively Manufactured Al4043 (AlSi5) Components T2 - Metals N2 - In the current paper, the correlation between the physical size of additively built wire arc specimens and their structure and properties is studied. For the purpose of this work, two oval shaped specimens of different lengths were manufactured under the same technological conditions. The specimens have a length of 200 mm and 400 mm and will be referred to as L200 and L400. The microstructure of the samples was studied using X-ray diffraction analysis (XRD), optical microscopy, and scanning electron microscopy (SEM). The microhardness, yield strength (YS), and ultimate tensile strength (UTS) were determined and their correlation with the technological conditions of specimen build-up was clarified. The results of the carried out experiments indicated that the crystallographic structure of both specimens is similar. The scanning electron microscopy images show a higher concentration of irregularly shaped micro-pores formed near the edge of the αAl grains in the structure of the L400 specimen compared to the L200 one. An increase in the size of the αAl solid solution grains in the case of the L200 specimen towards its top section was noticed using optical microscopy. A slightly lower magnitude change was noticed concerning the L400 specimen. The increase in the size of the aluminum crystals was determined to be the increasing interpass temperature. Due to the much smaller thermal dissipation capacity of the smaller specimen, the interpass temperature of the same increased faster compared to the larger specimen. All of the above-mentioned factors led to a decrease in the microhardness of the specimens at higher stages of build-up. Since the specimens were deposited using similar layer deposition conditions, the resultant YS and UTS data are also highly comparable. KW - structure KW - morphology KW - hardness KW - tensile strength KW - defects formation KW - WAAM KW - AlSi5 KW - Al4043 KW - GMAW KW - cold arc pulse Y1 - 2024 U6 - https://doi.org/10.3390/met14020183 SN - 2075-4701 VL - 14 IS - 2 ER - TY - GEN A1 - Nikitin, Alexander A1 - Turabov, Dashqin A1 - Ermilova, Evgeniia A1 - Evdokimov, Anton A1 - Ossenbrink, Ralf A1 - Seidlitz, Holger T1 - Using dynamic resistance to predict electrode surface degradation in resistance spot welding of 5182 aluminum alloy T2 - Welding in the World N2 - In this study, the correlation between dynamic resistance during the first 10 ms of welding time and the electrode surface condition in resistance spot welding of 5182 aluminum alloy has been investigated. The electrode surface rapidly degrades due to contamination and morphological changes, adversely affecting the weld spot surface. The accumulation of Cu-Al intermetallic phases on the electrode surface alters its roughness, leading to variations in dynamic resistance. By analyzing this correlation, optimal electrode milling intervals were identified to extend electrode life. This work focused on detecting crater formation on the electrode surface through dynamic resistance monitoring. The results indicate that resistance measurements provide a reliable approach for evaluating electrode wear, optimizing maintenance schedules, and reducing material removal during milling. KW - resistance spot welding KW - aluminum alloy KW - electrode wear KW - dynamic resistance KW - electrode surface Y1 - 2024 U6 - https://doi.org/10.1007/s40194-024-01872-9 VL - 69 SP - 449 EP - 458 ER - TY - GEN A1 - Ormanova, Maria A1 - Kotlarski, Georgi A1 - Kaisheva, Darina A1 - Nikitin, Alexander A1 - Ossenbrink, Ralf A1 - Doynov, Nikolay A1 - Valkov, Stefan T1 - Investigation of the thermal gradients formed during the process of cooling of WAAM built Al99.7 specimen T2 - Journal of Physics: Conference Series N2 - This work presents a preliminary experiment used to determine the possibility of developing a thermal model used to predict the thermal gradients formed during the process of wire and arc additive manufacturing (WAAM). For this purpose, an Al99.7 specimen was built using gas metal arc welding (GMAW) in the cold arc pulse mode. The temperature of both the substrate and each consecutive layer was measured using thermocouples and infrared thermometers and the experimental data was used for the calibration of the developed thermal model. The obtained results can be used for the further development of the thermal model. KW - Thermal model KW - Wire arc additve manufacturing KW - Waam KW - Gas metal arc welding KW - Gmaw KW - Aluminum KW - Al99.7 Y1 - 2024 U6 - https://doi.org/10.1088/1742-6596/2710/1/012038 SN - 1742-6596 VL - 2024 IS - 2710 ER - TY - GEN A1 - Kotlarski, Georgi A1 - Ormanova, Maria A1 - Nikitin, Alexander A1 - Ossenbrink, Ralf A1 - Doynov, Nikolay A1 - Valkov, Stefan A1 - Michailov, Vesselin ED - Tsankov, Plamen ED - Maximov, Jordan ED - Aleksandrov, Anatoliy ED - Todorov, Todor ED - Peneva, Petya T1 - Structure, morphology and hardness of a WAAM built Al99.7 specimen T2 - International Scientific Conference Unitech 2023, Gabrovo : selected papers N2 - The present work discusses the possibility of wire arc additive manufacturing (WAAM) of pure aluminum specimens (Al99.7). The manufactured specimen's structure was studied using X-ray diffraction (XRD) experiments. The morphology of the specimen at different stages of build-up was studied by examining prepared mechanical properties of the specimen, and for this reason the microhardness of the specimen was studied as well. The results of the present study were discussed regarding the change of the structure of the samples with the increase of the specimen's height during the manufacturing process and its influence on the resultant microhardness. KW - WAAM KW - Al99.7 KW - Structure KW - Morphology KW - Hardness Y1 - 2023 UR - https://unitech2023.tugab.bg/images/thematic-sessions/CHEMISTRY_PHYSICS_AND_ECOLOGY/s17_p149_v1.pdf U6 - https://doi.org/10.70456/PJKY7011 SN - 1313-230X VL - 2 SP - 349 EP - 353 PB - Union of Automation & Informatics CY - Gabrovo ER - TY - GEN A1 - Köhler, Marcel A1 - Nikitin, Alexander A1 - Sonnenfeld, Peter A1 - Ossenbrink, Ralf A1 - Jüttner, Sven T1 - Wire arc additive manufacturing of aluminum foams using TiH2-Laced Welding Wires T2 - Materials N2 - Composite materials made from aluminum foam are increasingly used in aerospace and automotive industries due to their low density, high energy absorption capacity, and corrosion resistance. Additive manufacturing processes offer several advantages over conventional manufacturing methods, such as the ability to produce significantly more geometrically complex components without the need for expensive tooling. Direct Energy Deposition processes like Wire Arc Additive Manufacturing (WAAM) enable the additive production of near-net-shape components at high build rates. This paper presents a technology for producing aluminum foam structures using WAAM. This paper’s focus is on the development of welding wires that are mixed with a foaming agent (TiH2) and produce a foamed weld metal as well as their processing using MIG welding technology. KW - MIG welding KW - wire arc additive manufacturing KW - direct energy deposition KW - aluminum foam KW - titanium hydride KW - foaming agent KW - metal-cored wires KW - continuous powder extrusion KW - energy absorption Y1 - 2024 U6 - https://doi.org/10.3390/ma17133176 SN - 1996-1944 VL - 17 IS - 13 PB - MDPI AG ER - TY - GEN A1 - Turabov, Dashqin A1 - Evdokimov, Anton A1 - Nikitin, Alexander A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin T1 - Vorhersage des Elektrodenverschleißes beim Widerstandspunktschweißen von Aluminium durch dynamische Widerstandsmessung T2 - DVS Congress 2023, Große Schweißtechnische Tagung, DVS Campus ; Kurzfassungen der Vorträge der Veranstaltung in Essen vom 11. bis 14. September 2023 ; (Langfassungen der Beiträge auf USB-Karte) N2 - Das Widerstandspunktschweißen ist ein weit verbreitetes Schweißverfahren, insbesondere bei der Karosserieherstellung in der Automobilbranche. Im Hinblick auf den Leichtbau werden zunehmend Aluminiumlegierungen verwendet. Das Hauptproblem beim Widerstandspunktschweißen von Aluminiumlegierungen ist der schnelle Elektrodenverschleiß. Dadurch wird die Qualität und Effizienz des Schweißprozesses beeinträchtigt. Die Elektrodenstandmenge ist erreicht, wenn die Schweißverbindung eines der Qualitätskriterien nicht erfüllt. Um die Elektrodenstandmenge zu ermitteln, werden in der Industrie im Rahmen der Schweißnahtqualifizierung zeit- und ressourcenaufwändige Methoden, u. a. zerstörende Prüfmethoden, verwendet. In dieser Arbeit wird eine Methode zur Vorhersage des kritischen Elektrodenverschleißes beim Aluminiumschweißen durch Messung des dynamischen Widerstandes vorgeschlagen. In umfangreichen Versuchsreihen an einer automobiltypischen Al-Legierung der 5000er Gruppe wurden dynamische Widerstandsmessungen durchgeführt. Aus den Widerstandsmesswerten konnte ein Indikator ermittelt werden, welcher auf das Auftreten von Poren in Schweißverbindung und auf einen bald auftretenden kritischen Elektrodenverschleiß hinweist. Y1 - 2023 UR - https://www.dvs-ev.de/call4papers/abstract.cfm?vid=116&pid=7816 SN - 978-3-96144-230-0 VL - 389 / 2023 SP - 780 EP - 787 PB - DVS Media GmbH CY - Düsseldorf ER - TY - GEN A1 - Kotlarski, Georgi A1 - Ormanova, Maria A1 - Nikitin, Alexander A1 - Morozova, Iuliia A1 - Ossenbrink, Ralf A1 - Michailov, Vesselin A1 - Doynov, Nikolay A1 - Valkov, Stefan T1 - Microstructural and Mechanical Properties of CAP-WAAM Single-Track Al5356 Specimens of Differing Scale T2 - Materials N2 - The mass production of metallic components requires high agility in the working process conditioned by the necessity of building details of different shapes and sizes. Changing the size of the components theoretically influences the thermal dissipation capability of the same, which could lead to a change in their structure and mechanical properties. This is particularly important when aluminum alloys are concerned. For this reason, two Al5356 single-track specimens were built using the same technological conditions of layer deposition by varying only their geometrical size. In all cases, the specimens were wire and arc additively manufactured (WAAM) using a process based on gas metal arc welding (GMAW) in the cold arc pulse mode (CAP). The structure of both specimens was studied and defects along their surfaces were detected in the form of micro-pores and micro-cracks. A high concentration of undissolved Mg particles was also detected, along with some standalone Si particles. Uniformity in the build-up process was achieved, which led to the formation of nearly identical structures in the specimens. Subsequently, the resultant mechanical properties were also highly comparable. This indicates that the geometry-related variation in thermal conditions has an insignificant influence on the component’s structure and properties. KW - microstructure KW - WAAM KW - cold arc pulse (CAP) KW - AlMg5Cr KW - Al5356 KW - single-track KW - mechanical properties Y1 - 2024 U6 - https://doi.org/10.3390/machines12010072 SN - 2075-1702 VL - 12 IS - 1 ER - TY - GEN A1 - Kotlarski, Georgi A1 - Ormanova, Maria A1 - Nikitin, Alexander A1 - Parasar, Ashirwad A1 - Ossenbrink, Ralf A1 - Doynov, Nikolay A1 - Valkov, Stefan A1 - Michailov, Vesselin T1 - Wire arc deposition of specimens using a special-designed aluminum-cored wire with CNTs T2 - Journal of physics : conference series N2 - This work investigated the possibility of manufacturing components using an aluminum welding wire with an aluminum powder core reinforced with carbon nanotubes (CNTs). Appropriate technological conditions of deposition were selected for the successful manufacturing of a wall-shaped specimen. The last was built using a multi-track approach. The results indicated the presence of a large quantity of pores within the volume of the specimen with values of over 30%. Regardless of the high defect quantity within the specimen a number of successfully integrated carbon nanoparticles were detected in certain areas of the cross-section of the specimen in the form of an Al₄C₃ composite. Y1 - 2025 U6 - https://doi.org/10.1088/1742-6596/2994/1/012024 SN - 1742-6588 SN - 1742-6596 VL - 2994 IS - 1 SP - 1 EP - 6 PB - IOP Publishing CY - Bristol ER -