Role of hybrid tool pin profile on enhancing welding speed and mechanical properties of AA2219-T6 friction stir welds

The friction stir welds of thick precipitation-hardenable aluminum alloys suffer from reduced joint strength due to dissolution/coarsening of the strengthening precipitates. The article portray hybrid pin profiled tool that enables sound welds at speeds 7-times faster than a conventional tool (a conical threaded tool), without pin breakage. The conical threaded and triangular cross-section in the upper and lower pin half-lengths of the hybrid tool facilitate material flow in a downward direction and shear deformation at a faster rate, respectively. The paper brings out the process mechanism responsible for the enhanced welding speed and mechanical properties obtainable with the hybrid tool through a case of 13-mm thick aluminum alloy AA2219-T6. The hybrid tool facilitates a 28% improvement in weld strength by reducing TMAZ softening, as evidenced by the microhardness and mechanical properties and supported by microstructural investigation and fractography

Comprehensive Weldability Criterion for Magnetic Pulse Welding of Dissimilar Materials

Despite its exceptional ability to join dissimilar materials and environmental friendliness, several challenges must be addressed in magnetic pulse welding (MPW). The conventional weldability criterion (i.e., minimum impact velocity) is analytically calculated as a function of material properties without considering the geometry of electromagnetic coil, electrical and physical parameters, making the minimum impact velocity a necessary but not sufficient condition for a sound MPW joint. A new weldability criterion, namely effective impact velocity, is proposed, which overcomes the conventional weldability criterion’s limitations. The effective impact velocity can be inversely modelled to identify shop-floor relevant process parameters and it eliminates the need to fabricate several coils in the process and product proving stages. The proposed approach is demonstrated by a case study on tubular welding of Aluminium and SS304. The weld’s soundness produced with computed process parameters was corroborated by experimental observations on lap shear tests, hardness measurements, optical and scanning electron microscopy, and surface energy dispersive spectroscopy mapping. This investigation is expected to pave the way for developing the process window for MPW of several material combinations, with high cost and time savings. © 2022 by the authors

Dissimilar Friction Stir Welds in AA2219-AA5083 Aluminium Alloys: Effect of Process Parameters on Material Inter-Mixing, Defect Formation, and Mechanical Properties

Dissimilar friction stir welds of aluminium alloys AA5083 and AA2219 were investigated in a view to get defect free welds by varying process parameters. An attempt has been made to develop a mathematical model to predict sound welds. Design of experiments with three parameters and five levels were used to optimize the effectiveness of process parameters. Analysis of variance and response surface methodology were used to determine the significance and optimal level for each parameter to minimize % area of volumetric defect. The experimental and predicted values of % area of volumetric defect were in good agreement. The effects of process parameters and tool-offset on the extent of intermixing of materials and to minimize % area of volumetric defects were analyzed in detail by employing different methods such as macrostructural analysis and electron probe micro analysis. The defect free dissimilar weldments were characterized for transverse tensile properties. The observed tensile strength values were correlated with reference to the extent of intermixing of materials in the stir/nugget zone. Established mathematical models have depicted a good prediction of relationship between the investigated FSW process parameters and the % area of defect of the welds. It is understood that the mixing pattern in nugget zone and further joint strength are primarily affected by the tool offset and welding parameters

Process parameters-weld bead geometry interactions and their influence on mechanical properties: A case of dissimilar aluminium alloy electron beam welds

Prediction of weld bead geometry is always an interesting and challenging research topic as it involves understanding of complex multi input and multi output system. The weld bead geometry has a profound impact on the load bearing capability of a weld joint, which in-turn decides the performance in real time service conditions. The present study introduces a novel approach of detecting a relationship between weld bead geometry and mechanical properties (e.g. tensile load) for the purpose of catering the best the process could offer. The significance of the proposed approach is demonstrated by a case of dissimilar aluminium alloy (AA2219 and AA5083) electron beam welds. A mathematical model of tensile braking load as a function of geometrical attributes of weld bead geometry is presented. The results of investigation suggests the effective thickness of weld - a geometric parameter of weld bead has the most significant influence on tensile breaking load of dissimilar weld joint. The observations on bead geometry and the mechanical properties (microhardness, ultimate tensile load and face bend angle) are correlated with detailed metallurgical analysis. The fusion zone of dissimilar electron beam weld has finer grain size with a moderate evaporation and segregation of alloying elements magnesium and copper respectively. The mechanical properties of weld joint are controlled by optimum bead geometry and HAZ softening in weaker AA5083 Al alloy

Electron Beam Welding and Friction Stir Welding of Dissimilar Aluminium Alloys (AA2219 and AA5083)

Certain critical and high performance applications require distinct attributes in the either sides of the weld, e.g. load bearing capability in one side and corrosion resistance in the other. In order to meet these requirements, such systems are designed with a high strength aluminium alloy and a medium strength aluminium alloy with good corrosion resistance. However, in some stringent scenario, the weldment need to be used in as-welded condition as one of the alloys may be non-heat treatable (e.g. AA5083) and further machining of the weld is not possible because of inevitable reasons. On the other hand, another alloy may be heat treatable (e.g. AA2219) which may impose a limitation on use of filler wire as it may reduce the resulting mechanical properties of the weld joint. The development in welding technologies such as friction stir welding (FSW) and electron beam welding (EBW) have made it possible to weld aforementioned dissimilar materials that are otherwise difficult to weld with conventional arc welding processes. FSW (solid state) and EBW (fusion) processes are considered in this study as both the processes are autogenous welding processes result in minimum possible heat input, better joint quality and mechanical properties among the respective category of welding processes. Many more investigations are required to exploit the best of the aforementioned developments. The thesis presents such an effort and primarily focuses on establishment of friction stir and electron beam welding technology for dissimilar aluminium alloys AA2219 and AA5083, considering two different thicknesses, by developing a detailed understanding on the effect of process parameters on material intermixing in weld/nugget zone, defect formation, mechanical properties, and tensile failure location. The problem definition of the investigation in this thesis reads as “An experimental investigation through parametric study, tool and process development, and mechanical and microstructural characterization with a direction to produce high performance low- and high- thick section weld joints in dissimilar aluminium alloys (AA2219 and AA5083) using election beam welding and friction stir welding”. The work innovatively brings out a hybrid tool pin profile for welding thick section aluminum alloys, which has improved joint strength even at welding speeds seven times more than that is generally possible with conventional tool. The thesis also presents new models that can predict relation between weld bead geometry and weld strength in EBW and the prediction of defects in FSW. The outcome of this research is envisaged to provide a better insight into metallurgical understanding and its correlation with mechanical properties of EBW and FSW joints of dissimilar aluminium alloys. The research work reported in this thesis establishes An industry friendly comprehensive technology for welding of low- and high- thick dissimilar aluminum alloys (AA2219 and AA5083), both by fusion and solid state welding processes has been developed over a wide range of workable welding parameters. In low-thick welds produced, either by EBW or FSW, very good joint strengths are achievable and the failure location of tensile specimen is always located in HAZ or fusion line AA5083 alloy depending upon the type welding process employed. However, at a higher thickness of weld joint, the friction stir welding scores better in terms of joint strengths, %elongation and quality, with a failure location located in TMAZ of AA2219 alloy. The electron beam welding produces dissimilar weld joint with relatively lower tensile properties and quality with failure location at PMZ of AA2219 alloy

Process parameters-weld bead geometry interactions and their influence on mechanical properties: A case of dissimilar aluminium alloy electron beam welds

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Unveiling Liquation and Segregation Induced Failure Mechanism in Thick Dissimilar Aluminum Alloy Electron-Beam Welds

This study presents new findings on the underlying failure mechanism of thick dissimilar electron-beam (EB) welds through a study on the AA 2219-AA 5083 pair. Contrary to the prior studies on EB welding of thin Al alloys, where liquation in the grain boundaries (GBs) in the partially melted zone (PMZ) was not observed, the present investigation for thick EB welds reports both liquation and increased segregation of Cu in the PMZ. The work is thus directed towards understanding the unusual observation in the PMZ of thick EB weld through investigation of the microstructural variation across the various regions of the produced weld. The microstructural results are correlated with the mechanical properties of the weld, i.e., hardness variation and tensile response. Results of this investigation suggest that unlike the convention that EB welding produces sound dissimilar Al welds, the weld performance for thick EB Al welds is affected by the heat input, the associated cooling rates, and most importantly by the base material thickness. Extensive liquation and Cu segregation induced failure in the PMZ on the AA 2219 side of the dissimilar weld. The underlying failure mechanism is explained through a heat-transfer analysis. Beyond a certain plate thickness, the heat transfer changes from two to three-dimensional. As a result, retarded cooling promotes liquation and Cu segregation in thick EB welds. © 2022 by the authors. Licensee MDPI, Basel, Switzerland