1,721,383 research outputs found
Design of the friction stir welding tool using the continuum based FEM model
No full textIn friction stir welding (FSW), the welding tool geometry plays a fundamental role in obtaining desirable microstructures in the weld and
the heat-affected zones, and consequently improving strength and fatigue resistance of the joint. In this paper, a FSW process with varying pin geometries (cylindrical and conical) and advancing speeds is numerically modeled, and a thermo-mechanically coupled, rigid-viscoplastic, fully 3D FEM analysis able to predict the process variables as well as the material flow pattern and the grain size in the welded joints is performed. The obtained results allow finding optimal tool geometry and advancing speed for improving nugget integrity of aluminum alloys
Influence of material characteristics on plastomechanics of the fsw process for T-joints
No full textThe potential of friction stir welding (FSW) has thoroughly been investigated by several authors, however their focus has primarily been on butt joints. T-joints are of paramount interest for transportation industries especially due to their capacity to straighten panels. Welding of T-joints is very challenging due to thin walls, poor location of the rib–web interface and the requirements for corner-fillets. This paper investigates FSW of T-joints of two popular aluminum alloys, i.e. 2024-T4 and 6082-T6, and the role played by the material characteristics on joining. First, an experimental study is carried out with specially designed fixture to determine the effect of process conditions. Then, the joints are metallurgically and mechanically evaluated. Finally using a numerical model of the process previously developed by the authors, the thermal and plastic flow fields for the two alloys are calculated and compared. It is found that the material dependent thermal and plastic fields affect the state of TMAZ, HAZ and nugget-region in the joint and that the low-strength high-work hardening alloy 6082 provides a much better joint integrity than the higher-strength low-hardening 2024 primarily due to the greater penetration of the plastic zone in the former
CDRX modelling in friction stir welding of AA7075-T6 aluminum alloy: analytical approaches
No full textFriction stir welding (FSW) is an energy efficient and environmentally "friendly" (no fumes, noise, or sparks) welding process, during which the workpiece are welded together in a solid-state joining, process at a temperature below the melting point of the workpiece material under a combination of extruding and forging. Significant microstructural evolution takes place during FSW: in particular continuous dynamic recrystallization (CDRX) phenomena result in a highly refined grain structure in the weld nugget and strongly affect the final joint resistance. In the paper two different analytical models aimed to the determination of the average grain size due to continuous dynamic recrystallization phenomena in FSW processes of AA7075-T6 aluminum alloys have been implemented in a 3D FEM model and numerical analyses of the welding processes have been performed to verify their effectivenes
Mechanical and metallurgical effects of in process cooling during friction stir welding of AA7075-T6 butt joints
No full textThis paper presents the results of a combined experimental and numerical investigation focused on the effects of an in process water cooling treatment aimed at improving the final quality of friction stir welded butt joints in terms of mechanical resistance and metallurgy of the processed material. Micro and macro observations, together with the evolution of an already developed finite element tool, have
been used to analyze specimens obtained under different process conditions. Water cooling was found to enhance joint strength, reducing the material softening usually observed in the thermo-mechanically affected zone area, with no detrimental effect on nugget integrity
In-process heat treatments to improve FS-welded butt joints
No full textFriction-stir welding (FSW) is a relatively new but already well known solid-state welding process whose main advantage with respect to fusion welding processes is the possibility to successfully weld light alloys, traditionally considered difficult to weld or unweldable. Despite the good mechanical performances that can be obtained, there exists the possibility to further improve the joints' effectiveness through post-welding heat treatments that are however time and cost-expensive and, therefore, not best suited for industrial applications. In the present paper, the authors report the results of an experimental campaign, developed on FSW of AA7075-T6 aluminum alloy, aimed to investigate the possibility to enhance the joint performances through in process heat treatments. Welded joints were developed under three different conditions, namely, free air, forced air, and with water flowing on the surface of the joint itself. The influence of the external refrigerants was investigated at the varying of the specific thermal contribution conferred to the joint. Both mechanical and metallurgical investigations were developed on the welded joints highlighting both improvements of mechanical performances of the joints and reductions in the softening of the material when external refrigerants are used. © 2008 Springer-Verlag London Limited
Dual phase titanium alloy hot forging process design: experiments and numerical modeling
Get PDFTitanium alloys are considered desirable materials when both good mechanical properties and weight reduction are required at the same time. This class of materials is widely used in those fields (aeronautics, aerospace) in which common steels and light-weight materials, e.g., aluminum alloys, are not able to satisfy all operative service conditions. During the last decade, forging of titanium alloys has attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a near net shaped part with minimal need for machining. In this paper, a numerical model of the forging sequences for a Ti-6Al-4V titanium alloy aerospace component is presented. The model was tested and validated against experimental forgings. The model is then applied to predict loads final microstructure and defects of an aeronautical component. In addition to metal flow and die stresses, microstructural transformations (α and β phases) are considered for the determination of proper process parameters. It is found that transformation from α/β to β phase during forging and reverse transformations in post-forge cooling needs to be considered in the computational model for reasonable prediction of forging loads and product properties
On the material flow in fsw of T-joints: influence of geometrical and tecnological parameters
No full textInfluence of geometrical ratios in forgeability of complex shapes during hot forging of Ti-6Al-4V titanium alloy
No full textAbstractTitanium alloys are considered desirable materials when both mechanical properties and weight reduction are requested at the same time. This class of materials is widely used in application fields, like aeronautical, in which common steels and light-weight materials, like aluminum alloys, are not able to satisfy all operative service conditions. Most of manufacturing processes of titanium alloy components are based on machining operations, which allow obtaining very accurate final shapes but, at the same time, are affected by several disadvantage like material waste and general production costs. During the last decade, the forging processes for titanium alloys have attracted greater attention from both industrial and scientific/academic researchers because of their potential in providing a net shaped part with minimal need for machining. In this paper, a numerical analysis of the forging process design for an Ti-6Al-4V titanium alloy aerospace component is presented that focuses on the role of material evolution during thermomechanical processing. This component geometry is characterized by thin webs and ribs, and sharp corner and fillet radii. The numerical model was tested and validated by means of comparison with real experimental forgings in order to verify the quality in the prediction of material flow and microstructure evolution. Moreover, the analysis of forgeability of the same component with more critical geometrical ratios is considered in order to test the capability of code to support the forging sequence design in the case of a complex shape component
Material Flow in FSW of AA7075 - T6 butt joint: numerical simulations and experimental verifications
No full textFriction stir welding (FSW) has reached a large interest in the scientific community and in the recent years also in the industrial environment, owing to the advantages of such solid state welding process with respect to the classic ones. Advanced finite element method tools are needed in order to develop an effective engineering of the processes; quantitative results can be acquired from numerical simulations once the basic information such as the material flow is certain. A 3D Lagrangian implicit coupled rigid viscoplastic model has already been developed by the authors to simulate FSW of butt joints. In the present paper the material flow in the FSW of AA7075–T6 butt joints is investigated on the varying of the most relevant technological and geometrical parameters with numerical simulations and experiments. In particular to investigate the metal flow a wide campaign of experimental tests and observations has been developed utilising a thin foil of copper as marker
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