TY - JOUR A1 - Schempp, P. A1 - Rethmeier, Michael T1 - Understanding grain refinement in aluminium welding N2 - Grain refinement is an important opportunity to improve mechanical properties of fusion welds and the weldability (susceptibility to solidification cracking) of the base metal. In this study, grain refinement was achieved in aluminium welds through additions of grain refiner to the weld metal. Increasing grain refiner additions led to a decrease of the weld metal mean grain size (down to −86 %). The grain refinement efficiency was the highest in commercial pure Al (Alloy 1050A, Al 99.5), followed by Alloy 6082 (Al Si1MgMn) and Alloy 5083 (Al Mg4.5Mn0.7). To investigate this clear influence of alloy content on grain size, the undercooling parameters P and Q were calculated. Temperature measurements revealed that solidification parameters such as solidification growth rate or cooling rate vary significantly along the solidification front, dependent upon torch speed and alloy. On the basis of this comparison, an analytical approach was used to model the columnar to equiaxed transition (CET). Moreover, wavelength dispersive X-ray spectroscopy (WDS) and transmission electron microscopy (TEM) analyses revealed particles rich in Ti and B that are probably TiB2 particles coated by Al3Ti nucleating Al grains during solidification. Also, Ti/B contents needed in commercial filler wires to allow optimum weld metal grain refinement were calculated dependent upon base alloy and welding process. PY - 2015 DO - https://doi.org/10.1007/s40194-015-0251-2 SN - 0043-2288 SN - 1878-6669 VL - 59 IS - 6 SP - 767 EP - 784 PB - Springer CY - Oxford AN - OPUS4-34840 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schneider, André A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Mobile vacuum in pocket format, mobile local low-pressure cap for high power laser beam welding of thick materials N2 - The presented apparatus enables laser beam welding of thick materials under local reduced pressure conditions, thus improving the quality of welds and reducing the laser beam power necessary for complete penetration welding. The vacuum cap presented in this article uses a local reduced ambient pressure environment in a tight zone around the welding area and, in contrast to a conventional vacuum chamber, it is movable in the welding direction. The mobile installation is very compact and reaches pressure values of around 200 mbar. The reduced pressure in the vacuum cap is sufficient to generate 50 % higher penetration depth in comparison to welding under ambient pressure conditions. The low pressure around the keyhole reduces the vapour-plasma plume and therefore prevents a defocusing and scattering of the laser radiation. This allows to raise the amount of laser beam power entering the keyhole as well as the effective power density. KW - High power laser beam welding KW - Mobile vacuum KW - Local reduced pressure KW - Vapor plume KW - Keyhole PY - 2015 DO - https://doi.org/10.1002/latj.201500025 SN - 1613-7728 SN - 1863-9119 VL - 12 IS - 4 SP - 43 EP - 44 PB - Wiley-VCH CY - Weinheim AN - OPUS4-34583 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Kunze, R. A1 - Avilov, Vjaceslav A1 - Rethmeier, Michael T1 - Finite element modeling of an alternating current electromagnetic weld pool support in full penetration laser beam welding of thick duplex stainless steel plates N2 - An electromagnetic weld pool support system for 20 mm thick duplex stainless steel AISI 2205 was investigated numerically and compared to experiments. In our former publications, it was shown how an alternating current (AC) magnetic field below the process zone directed perpendicular to the welding direction can induce vertically directed Lorentz forces. These can counteract the gravitational forces and allow for a suppression of material drop-out for austenitic stainless steels and aluminum alloys. In this investigation, we additionally adopted a steady-state complex magnetic permeability model for the consideration of the magnetic hysteresis behavior due to the ferritic characteristics of the material. The model was calibrated against the Jiles–Atherton model. The material model was also successfully tested against an experimental configuration before welding with a 30 mm diameter cylinder of austenitic stainless steel sur-rounded by duplex stainless steel. Thereby, the effects of the Curie temperature on the magnetic characteristics in the vicinity of the later welding zone were simulated. The welding process was modeled with a three-dimensional turbulent steady-state model including heat transfer and fluid dy-namics as well as the electromagnetic field equations. Main physical effects, the thermo-capillary (Marangoni) convection at the weld pool boundaries, the natural convection due to gravity as well as latent heat of solid–liquid phase transitions at the phase boundaries were accounted for in the model. The feedback of the electromagnetic forces on the weld pool was described in terms of the electromagnetic-induced pressure. The finite element software COMSOL Multiphysics 4.2 was used in this investigation. It is shown that the gravity drop-out associated with the welding of 20 mm thick duplex stainless steel plates due to the hydrostatic pressure can be prevented by the application of AC magnetic fields between around 70 and 90 mT. The corresponding oscillation frequencies were between 1 and 10 kHz and the electromagnetic AC powers were between 1 and 2.3 kW. In the experiments, values of the electromagnetic AC power between 1.6 and 2.4 kW at os-cillation frequencies between 1.2 and 2.5 kHz were found to be optimal to avoid melt sagging or drop-out of melt in single pass full-penetration laser beam welding of 15 and 20 mm thick AISI 2205. KW - Laser KW - Numerical simulation KW - Laser beam welding KW - Electromagnetic weld pool support KW - Duplex stainless steel PY - 2016 DO - https://doi.org/10.2351/1.4943906 VL - 28 IS - 2 SP - 022404-1 EP - 022404-9 PB - AIP Publishing AN - OPUS4-35676 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gebhardt, M.O. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Solidification cracking in laser GMA hybrid welding of thick-walled parts N2 - Laser GMA hybrid welds, producing partial penetration, were conducted on stiff tubes made of S460NH. Experiments, using a design-of-experiments plan were conducted to examine the influence of the welding parameters on the occurrence of solidification cracks. Results say that cracks diminish, when high levels of arc power are applied, while their number increases with rising laser beam power. The weld velocity had no measurable impact. KW - Laser hybrid welding KW - Solidification cracking KW - Partial penetration welding KW - Tube welding KW - Thick walled parts KW - Design of experiments PY - 2014 DO - https://doi.org/10.1179/1362171813Y.0000000171 SN - 1362-1718 SN - 1743-2936 VL - 19 IS - 3 SP - 209 EP - 213 PB - Maney CY - London AN - OPUS4-30297 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Avilov, Vjaceslav A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Magnets improve quality of high-power laser beam welding N2 - Welding is one of the most critical operations for the construction of reliable metal structures in everything from ships to reactor vessels. When welds fail, often the entire structure fails, and expectations on weld quality have never been higher. Any process that uses a localized heat source, such as welding, is likely to result in some distortion. The welding process of very thick metal components is not inherently stable and is barely controllable without external forces. KW - Electromagnetic weld pool control KW - Laser beam weliding KW - Marangoni effect PY - 2014 VL - 2013-2014 SP - 30 EP - 32 AN - OPUS4-30338 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heinze, Christoph A1 - Michael, Thomas A1 - Pittner, Andreas A1 - Rethmeier, Michael T1 - Microcrack formation during gas metal arc welding of high-strength fine-grained structural steel N2 - The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc, which results in higher penetration depths and welding speed. However, microcracks occurred in the weld metal while approaching the process limits of the modified spray arc, represented by a 20-mm double layer DV-groove butt-weld. These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself. The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks. The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment. However, these microcracks do not impact the design specification for toughness in the Charpy V-notch test (absorbed energy at -40 °C for the present material is 30 J). KW - High-strength low-alloy steel KW - Welding KW - Fracture KW - Design of experiments KW - Microcracking PY - 2014 DO - https://doi.org/10.1007/s40195-013-0011-5 SN - 1006-7191 SN - 1000-9442 VL - 27 IS - 1 SP - 140 EP - 148 PB - Springer CY - Shenyang AN - OPUS4-30123 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Neubert, Sebastian A1 - Pittner, Andreas A1 - Rethmeier, Michael T1 - Numerical sensitivity analysis of TRIP-parameter K on weld residual stresses for steel S355J2+ N N2 - A combined experimental numerical approach is applied for sensitivity analysis of the transformation induced plasticity (TRIP)-parameter K on weld residual stresses for welding of structural steel of grade S355J2+N. K was determined experimentally using the Gleeble 3500 facility. A thermomechanical FE model of the real welding process was experimentally validated against temperature field and X-ray stress measurements. Within sensitivity analyses K was varied by several orders of magnitude and the influence on the calculated residual stresses is evaluated by performing corresponding FEA. The correct order of magnitude is sufficient to reproduce the residual stresses qualitatively and quantitatively. KW - TRIP - transformation induced plasticity KW - welding residual stresses KW - sensitivity analysis KW - FEA PY - 2016 DO - https://doi.org/10.1080/01495739.2015.1124641 SN - 0149-5739 VL - 2016 IS - 39/2 SP - 201 EP - 219 PB - Journal of Thermal Stresses AN - OPUS4-35880 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Rethmeier, Michael A1 - Wu, Chuan Song T1 - Sensitivity analysis of the residual stress state in friction stir welding of high strength aluminium alloy N2 - In this paper, the friction stir welding process was numerically investigated for 6 mm thick aluminum alloy AA2024-T3. The finite element software COMSOL Multiphysics was used to calculate the transient thermal field during welding and the mechanical reaction depending on different mechanical clamping conditions and hardening models subsequently. A thermal pseudo-mechanical (TPM) heat source was implemented. Softening effects of the material due to precipitation hardening dissolution caused by the frictional heat were accounted for. The transient temperature evolution measured by thermocouple elements at various locations was compared to the numerical results. A good agreement was found for the thermal field. A sensitivity study of the mechanical models showed the strong influence of the clamping conditions and the softening model. PY - 2016 DO - https://doi.org/10.3139/120.110809 SN - 0025-5300 VL - 58 IS - 1 SP - 20 EP - 26 PB - Hanser CY - München AN - OPUS4-35269 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael ED - Bakir, Nasim T1 - Numerical simulation of solidification crack formation during laser beam welding of austenitic stainless steels under external load N2 - Solidification cracking phenomena taking place under Controlled Tensile Weldability (CTW) test conditions have already been investigated both experimentally and numerically via FEA in order to get a better understanding of the mechanisms of hot crack formation during laser beam welding of austenitic steel grades. This paper develops a three dimensional finite element model employing the contact elements technique to simulate the formation and propagation of solidification cracks during laser full penetration welding of fully austenitic stainless steel 1.4376. During the experimental procedure the resulting strain and displacement directed to the laser beam in the Close vicinity of the weld pool was measured at the surface of the workpiece using a Digital Image Correlation (DIC) technique with an external diode laser as an illuminating source. Local strain fields, global loads and crack lengths predicted by the model are in good Agreement with those observed in experiments. T2 - The 3rd IIW South‐East European Welding Congress CY - Timisoara, Romania DA - 03.06.2015 KW - Solidification cracking KW - DIC technique KW - Laser beam welding KW - Contact element KW - FEA PY - 2015 SN - 978-606-554-955-5 SP - 1 EP - 6 CY - Timisoara, Romania AN - OPUS4-36519 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - El-Batahgy, A. A1 - Saiyah, A. A1 - Khafagi, S. A1 - Gumenyuk, Andrey A1 - Gook, S. A1 - Rethmeier, Michael T1 - Shielded metal arc welding of 9%Ni steel using matching ferritic filler metal N2 - Motivated by the tensile strength loss of 9%Ni steel arc welded joints made using Ni-based austenitic filler metals, the feasibility of maintaining the tensile strength using matching ferritic filler metal has been demonstrated. In comparison with shielded metal arc welded joint made using Ni-based austenitic electrode ENiCrMo-6, higher tensile strength comparable to that of the base metal was obtained using matching ferritic electrode. Besides, sufficient impact toughness energies with much lower mismatch were obtained for weld metal and heat-affected zone. Welded joint with a lower mechanical mismatching is of considerable importance for achieving acceptable combination of tensile strength and impact toughness.Abetter combination of These mechanical properties is ensured by applying a post weld heat treatment. KW - Mechanical mismatching KW - Mechanical properties KW - Microstructure KW - Austenitic welding electrode KW - Matching ferritic welding electrode PY - 2020 DO - https://doi.org/10.1080/13621718.2020.1846936 SN - 1362-1718 SP - 1 EP - 7 PB - Taylor & Francis AN - OPUS4-51835 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -