Search

This study investigated quantitatively the thermomechanical degradation of polyetherimide (PEI) due to Friction-based Injection Clinching Joining (F-ICJ) and the effects on the mechanical strength of hybrid joints with aluminum. PEI samples extracted from process-affected regions of the joints were characterized in terms of their molecular weight distribution (MWD) and glass transition temperature (Tg), while mechanical strength of the joints was evaluated by cross tensile testing. PEI samples produced by the most severe joining condition showed decrease of 37 % of number-average molecular weight (Mn) and 17 % of weight-average molecular weight (Mw), while polydispersity index (Mw/Mn) increased 33 % as compared with as-received polymer. The chain scission distribution function (CSDF) indicated non-random multiple scissions as the main degradation mechanism of PEI due to F-ICJ. From the dependence of Tgwith Mnthe parameters of the Fox-Flory equation for PEI were obtained. A fractional factorial design of experiments was adopted to analyze the influence of the process parameters on the polymer degradation, based on Tgvalues. High level of PEI degradation and microstructural defects caused by high energy inputs have combined negative effect on the ultimate cross tensile force and displacement of joints. In general, these results can contribute to the knowledge of thermomechanical degradation of PEI and help with the optimization of F-ICJ.

ABSTRACTThe purpose of the present study was to fulfil the knowledge gap concerning residual stresses evaluation of friction stir welded GL E36 shipbuilding steel. Plates of 6 mm thickness were welded using two different welding speeds (1 and 3 mm s−1) at a constant rotational speed of 500 rev min−1. This led to different thermal cycles and the objective is to analyse the resulting microstructures and residual stress states. Therefore, in this work, residual stresses were evaluated by X-ray diffraction; metallography and microhardness testing were performed to support these measurements. Results showed that welds produced with different heat inputs have distinguishable residual stress distributions. Increases in the welding speed led to higher residual stress and microhardness in the stir zone.

The purpose of the present study was to fulfil the knowledge gap concerning residual stresses evaluation of friction stir welded GL E36 shipbuilding steel. Plates of 6?mm thickness were welded using two different welding speeds (1 and 3?mm?s-1) at a constant rotational speed of 500?rev?min-1. This led to different thermal cycles and the objective is to analyse the resulting microstructures and residual stress states. Therefore, in this work, residual stresses were evaluated by X-ray diffraction; metallography and microhardness testing were performed to support these measurements. Results showed that welds produced with different heat inputs have distinguishable residual stress distributions. Increases in the welding speed led to higher residual stress and microhardness in the stir zone.

ABSTRACTIn the present study, dissimilar welds of an Al–Mg–Mn alloy and a Zn-coated high-strength low-alloy steel were welded by refill friction stir spot welding. The maximum shear load recorded was approximately 7.8 kN, obtained from the weld produced with a 1600 rev min−1tool rotational speed. Microstructural analyses showed the formation of a solid–liquid structure of an Al solid solution in Mg–Al-rich Zn liquid, which gives rise to the formation of Zn-rich Al region and microfissuring in some regions during welding. Exposure of steel surface to Mg–Al-rich Zn liquid led to the formation of Fe2Al5and Fe4Al13intermetallics. The presence of defective Zn-rich Al regions and Fe–Al intermetallics at the faying surface affects the weld strength.

ABSTRACTIn recent years, interest has been increasing in application of Nickel alloys in the oil industry. For subsea engineering, the possibility to weld high-strength materials in an effective manner is essential. Friction Stir Welding (FSW) is alternative to join several materials retaining their properties or even improving them. This fact is relevant for Corrosion-Resistant Alloys (CRA) used in deep-water exploitation of hydrocarbons. Publications up to now have focused on FSW of Inconel® series as alloy 600, 625, and 718. To provide a solid basis for development, this review discusses the crucial points for FSW. The tool materials are described, as well as the joint microstructure and properties achieved. Furthermore, the basics of the corrosion resistance and the early corrosion studies of FSW joints are presented. It is concluded that FSW is a promising process for Ni alloys, but depends on upcoming research regarding tool technology and corrosion investigations.

In recent years, interest has been increasing in application of Nickel alloys in the oil industry. For subsea engineering, the possibility to weld high-strength materials in an effective manner is essential. Friction Stir Welding (FSW) is alternative to join several materials retaining their properties or even improving them. This fact is relevant for Corrosion-Resistant Alloys (CRA) used in deep-water exploitation of hydrocarbons. Publications up to now have focused on FSW of Inconel® series as alloy 600, 625, and 718. To provide a solid basis for development, this review discusses the crucial points for FSW. The tool materials are described, as well as the joint microstructure and properties achieved. Furthermore, the basics of the corrosion resistance and the early corrosion studies of FSW joints are presented. It is concluded that FSW is a promising process for Ni alloys, but depends on upcoming research regarding tool technology and corrosion investigations.

In the present study, dissimilar welds of an Al–Mg–Mn alloy and a Zn-coated high-strength low-alloy steel were welded by refill friction stir spot welding. The maximum shear load recorded was approximately 7.8 kN, obtained from the weld produced with a 1600 rev min−1tool rotational speed. Microstructural analyses showed the formation of a solid–liquid structure of an Al solid solution in Mg–Al-rich Zn liquid, which gives rise to the formation of Zn-rich Al region and microfissuring in some regions during welding. Exposure of steel surface to Mg–Al-rich Zn liquid led to the formation of Fe2Al5and Fe4Al13intermetallics. The presence of defective Zn-rich Al regions and Fe–Al intermetallics at the faying surface affects the weld strength.

AA2198–T851 sheets were welded by bobbin tool friction stir welding using a rotational speed of 800 rpm and welding speed of 42 mm min−1. The microstructure and precipitates within the joint were characterised by transmission electron microscopy. The global and local mechanical behaviour was determined using a digital image correlation system. Specific attention was given to the relationship between the local microstructure and properties across the joint, which govern the global strength and ductility of the welds. A lower global elongation of the joint is caused by the premature strain localisation in the softened zone.

AA2198–T851 sheets were welded by bobbin tool friction stir welding using a rotational speed of 800 rpm and welding speed of 42 mm min−1. The microstructure and precipitates within the joint were characterised by transmission electron microscopy. The global and local mechanical behaviour was determined using a digital image correlation system. Specific attention was given to the relationship between the local microstructure and properties across the joint, which govern the global strength and ductility of the welds. A lower global elongation of the joint is caused by the premature strain localisation in the softened zone.

This study presents an approach to model the shear layer in bobbin tool friction stir welding. The proposed CFD model treats the material in the weld zone as a highly viscous non-Newtonian shear thinning liquid. A customised parametric solver is used to solve the highly non-linear Navier–Stokes equations. The contact state between tool and workpiece is determined by coupling the torque within the CFD model to a thermal pseudomechanical model. An existing analytic shear layer model is calibrated using artificial neural networks trained with the predictions of the CFD model. Validation experiments have been carried out using 4 mm thick sheets of AA 2024. The results show that the predicted torque and the shear layer shape are accurate. The combination of numerical and analytical modelling can reduce the computational effort significantly. It allows use of the calibrated analytic model inside an iterative process optimisation procedure.

AbstractThis study presents an approach to model the shear layer in bobbin tool friction stir welding. The proposed CFD model treats the material in the weld zone as a highly viscous non-Newtonian shear thinning liquid. A customised parametric solver is used to solve the highly non-linear Navier–Stokes equations. The contact state between tool and workpiece is determined by coupling the torque within the CFD model to a thermal pseudomechanical model. An existing analytic shear layer model is calibrated using artificial neural networks trained with the predictions of the CFD model. Validation experiments have been carried out using 4 mm thick sheets of AA 2024. The results show that the predicted torque and the shear layer shape are accurate. The combination of numerical and analytical modelling can reduce the computational effort significantly. It allows use of the calibrated analytic model inside an iterative process optimisation procedure.

Die steigenden Forderungen nach Umweltverträglichkeit, Kosteneinsparung, und hochleistungsfähigen Endprodukten hat Wissenschaftler und Ingenieure veranlasst neue Materialien und Technologien zu entwickeln. Daraus resultierten beispielsweise die PolymerMetall Hybridstrukturen. Diese werden insbesondere in Transport und moderner Bauindustrie angewandt. Geeignete herkömmliche Fügeverfahren dafür Kleben und mechanische Fügeverfahren sind üblicherweise entweder teuer, weisen limitierte Festigkeit und Anwendbarkeit auf oder sind nicht umweltfreundlich. Die im Rahmen dieser Arbeit behandelte neue Reibnieten FricRiveting Methode für PolymerMetall Mischverbindungen wurde hierfür als alternative, zuverlässige, umweltfreundliche, und potenziell kostengünstige Punktverbindungstechnik entwickelt, beschrieben und nachgewiesen. In der einfachsten Variante des Reibnietens dringt eine in Rotation versetzte zylinderförmige metallische Niete in die Oberfläche eines oder mehrerer KunststoffGrundwerkstoffe ein. Aufgrund der hohen Rotation bzw. des hohen Axialdruckes wird Reibungswärme erzeugt. Mit Erreichen einer vorprogrammierten Zeit erhöht sich die Prozesstemperatur signifikant. Dadurch wird die Spitze der Niete plastifiziert; in diesem Moment wird die Rotation verzögert und der Axialdruck in die Fügepartner erhöht. Als Folge verformt sich die Nietenpitze entsprechend des Druckverhältnisses. Nach der Abkühlungsphase wird die verformte Nietspitze formschlüssig im Kunststoff verankert. Die in dieser Arbeit vorgeschlagenen Theorien, und Mechanismen wurden bei Verbindungen von Polyetherimid PEI und Aluminium 2024T351 AlCuMg Legierung nachgewiesen. Punkt und Überlappverbindungen mit hohem FestigkeitsWirkungsgrad unter Raumtemperatur der Zugfestigkeit Wirkungsgrad betrug bis zu ca. 97  der Nietfestigkeit und der ScherzugfestigkeitWirkungsgrad betrug bis zu ca. 70  der Kunststofffestigkeit wurden reibgenietet. Zum Schluss wurden die Gefügeänderung und mikrostrukturellen Eigenschaften dieser reibgenieteten Verbindungen beschrieben. Die im Laufe dieser Arbeit entstandenen wissenschaftlichen bzw. technischen Ergebnisse beweisen die Durchführbarkeit des Reibnietens. Als Ergebnis dieser Arbeit kann das Reibnieten als potenzielle zuverlässige, einfache, kostengünstige, und umweltfreundliche Fügetechnik für PolymerMetall Verbindungen vorgeschlagen werden.

Friction weldability of Mg based alloys has been worldwide discussed. Within this context the aim of this study was to investigate rotational friction welding of an Aluminum‐Rare Earth based high creep resistance Mg alloy AE42HP from the viewpoint of thermo cycle‐microstructure‐performance relationships to evaluate the potential use of FW in joining modern Mg‐alloys.

Das Rührreibschweißen (Friction Stir Welding (FSW)) stellt einen innovativen Schweißprozess zum Fügen von Leichtmetallen insbesondere von Aluminiumlegierungen dar. Die Herstellung von Aluminiumverbindungen mit konventionellen Schmelzschweißverfahren erfüllt nicht immer und nicht bei jeder Legierung die von der Industrie gestellten Qualitätsanforderungen. Das Rührreibschweißen stellt eine Alternative zu den Schmelzschweißverfahren dar. Die entstehenden Schweißnähte weisen gute mechanische Eigenschaften auf, das Verfahren ist robust und seine Reproduzierbarkeit sehr gut. Im Rahmen dieser Arbeit wird der Einsatz des Rührreibschweißens zum Fügen von Aluminium- und Magnesiumlegierungen erläutert. Dabei werden artgleiche und artungleiche Verbindungen und deren mechanische Eigenschaften beschrieben. Das Rührreibschweißen von Stahl mit seinen besonderen Anforderungen an das Schweißwerkzeug wird ebenfalls vorgestellt.

This study forms part of a joint three year project between the GKSS‐Forschungszentrum and Airbus Deutschland titled “Effect of material flow patterns on the properties of friction stir welds in aluminium alloys for aircraft structures” ‐EMFASIS. The global aim of our research project is to identify how process and geometric parameters such as weld tool geometry influence the weld energy and subsequent joint properties of four friction stir welded aerospace grade aluminium alloys. The current study reports on the visualisation and displacement of a Ti powder marker material dispersed within the weld zone and investigated with the aid of X‐ray computer microtomography (μCT) and dedicated metallographic techniques.

In the present study the microstructure and properties of a dissimilar friction stir weld between the magnesium alloy AZ31 and the aluminium alloy 6040 have been investigated. The intermetallic leads to a loss of strength and ductility of the join. In this study optical and scanning electron microscopy as well as energy dispersive spectroscopy (EDS) have been used to analyse the join interface as well as workpiece residues bonded to the joining tool. Dynamic recrystallisation was observed in the stir zone resulting in a substantial reduction in grain size particularly for the Al base material.