Stress Analysis of Friction Stir Spot Welded Magnesium Alloy Sheet under Tensile-Shear Load (original) (raw)
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Residual stresses of a magnesium alloy (AZ31) welded by the friction stir welding processes
MATEC Web of Conferences, 2016
The objective of this study was to evaluate the residual stresses of FSW welding magnesium alloys (AZ31). The results show that the FSW processes lead to the formation of several distinct zones with differing mechanical properties. The residual stresses evolution have been explained by the heterogeneous modifications of the microstructure particularly a marked decrease in the grain size, a high modification of the crystallographic texture and the different anisotropic properties resulting from plasticity induced by the FSW process.
Bonfring
Friction Stir Welding (FSW) was performed on 5-mm thick plates, machined from rolled AZ31B Magnesium alloy.The microstructure and defects formation were investigated by optical microscope. The mechanical properties were determined by tensile and hardness tests. Frictional heat and plastic flow during friction stir welding create the fine recrystallized grain (Stir Zone, SZ) and the elongated and recovered grain (Thermo-Mechanical Affected Zone, TMAZ) in the weld zone. Heat affected zone (HAZ), which can be identified only by hardness test due to no difference in grain structure compared with the base metal, is formed beside the weld zone. In this study, the effect of rotational speed on microstructure , hardness and mechanical properties of Friction stir welded Mg AZ31B alloy have been investigated. Friction stir welding (FSW) is carried out at different rotational speeds of 900 rpm, 1120 rpm, 1400 rpm and 1800 rpm with High speed steel (HSS) at a constant welding speed of 40 mm/min, tilt angle of 2.50 and axial force of 5 KN. It is observed that the joint fabricated using HSS tool material at a rotational speed of 1400 rpm obtained higher mechanical properties as compared to those of 900 rpm, 1120 rpm and 1800 rpm
EFFECT OF FRICTION STIR WELDING PARAMETERS ON IMPACT STRENGTH OF THE AZ31 MAGNESIUM ALLOY JOINTS
In this experimental work, a study was done to see the effect of Friction stir welding parameters on the impact strength of the welded joints of AZ31 magnesium alloy. The AZ31 magnesium alloy was taken in form of plates with a thickness of 6mm. The plates were welded usinga tool made up of alloy steel using three different pin profiles i.e. cylindrical, tapered and threaded. The joints were welded at a three different rotational speeds keeping feed rate constant.The Impact strength of the welded joints was evaluated using Charpy test. Joints fabricated at the rotational speed of 1200 rpm with threaded pin profile showed better impact strength than the joint welded with other pin profiles. It shows as the as the rotational speed increases, a temperature of the weld increases which improves the ductility of the material which in turn improves the impact strength. More the contact surface of the pin profile more will be the impact strength. Results obtained mechanically is also verified by obtaining microstructures of base material i.e. AZ31 and nugget region obtained at 1200 rpm using threaded tool for FSW process.
Investigation of mechanical properties of friction stir spot welded light metal alloys
The use of light metals today is of great importance, for example in the automotive, aviation and aerospace industries, where energy consumption is minimized and thus the economy is being attempted. By using light metals, weight is reduced so that energy is saved. Aluminum and magnesium alloys are particularly used thanks to their lightweight. Vehicles in the automotive, aerospace and space industries are expected not only to have lightweight but also high static and dynamic strengths since they are exposed to static and dynamic cyclic loads. However, the structural components can quickly become fatigued and fail under cyclic load due to the notch factor of the joining zones. Compared to the fusion welding method, joining of material is realized mechanically below the melting point of the material in the friction stir spot welding (FSSW) method. Thus, the fatigue strength of the assembly is much higher than that of the fusion welding. In this study, Light metal alloy of magnesium AZ...
Lap Shear Test of a Magnesium Friction Spot Joint: Numeric Modeling
Tecnologia em Metalurgia Materiais e Mineração, 2013
Friction spot welding (FSpW) is one of the most recently developed solid state joining technologies. In this work, based on former publications, a computer aided draft and engineering resource is used to model a FSpW joint on AZ31 magnesium alloy sheets and subsequently submit the assembly to a typical shear test loading, using a linear elastic model, in order to conceive mechanical tests results. Finite element analysis shows that the plastic flow is concentrated on the welded zone periphery where yield strength is reached. It is supposed that "through the weld" and "circumferential pull-out" variants should be the main failure behaviors, although mechanical testing may provide other types of fracture due to metallurgical features.
Evaluation of welding parameters effects in friction stir welding of AZ31B Mg alloy
Kovove Materialy-Metallic Materials
The joining of magnesium alloys with conventional fusion welding methods often causes porosity and hot cracking defects. The use of friction stir welding, a solid-state welding technique for joining Mg alloys, solves these problems. In this study, AZ31B Mg sheets with 3 mm in thickness were joined by friction stir welding at a constant feed rate (50 mm min −1) and different tool rotational speeds (900 and 1400 rpm), and different tool tilt angles (0 • and 1.5 •) using tapered pin. Tensile strength and microhardness tests were carried out to examine the mechanical properties of the welded specimens. The microstructures of the welded zone were analyzed by obtaining optical microscopy and scanning electron microscopy images. According to the tensile test results, specimen welded at 50 mm min −1 feed rate, 900 rpm tool rotational speed, and 1.5 • tool tilt angle showed the highest welding strength value 176.03 MPa.
This study aims at researching mechanical properties of TIG welding which has been used for magnesium welding and friction stir welding; this is a new method for magnesium welding. It particularly focuses on analysing of bending fatigue test among other mechanical properties. Joints made through TIG and FSW welding for magnesium applications in automotive and aeronautical-astronautical industries are exposed to various mechanical stresses and in particular to dynamic loads when vehicles are in motion. Fracture has been observed in welding areas due to such dynamic loads. This analysis mainly concentrates on the differences between these two welding methods: TIG and FSW welding, and on determining the method with superior advantages due to the fact that TIG welding has been intensely used for magnesium welding, and friction stir welding is a new application in terms of magnesium welding.
Microstructure and tensile properties of friction stir welded AZ31B magnesium alloy
The microstructural change in AZ31B-H24 magnesium (Mg) alloy after friction stir welding (FSW) was examined. The effects of tool rotational speed and welding speed on the microstructure and tensile properties were evaluated. The grain size was observed to increase after FSW, resulting in a drop of microhardness across the welded region from about 70 HV in the base metal to about 50 HV at the center of the stir zone. The obtained Hall–Petch type relationship showed a strong grain size dependence of the hardness. The aspect ratio and fractal dimension of the grains decreased towards the center of the stir zone. The welding speed had a significant effect on the microstructure, with larger grains at a lower welding speed. The yield strength and ultimate tensile strength increased with increasing welding speed due to a lower heat input. A lower rotational speed of 500 rpm led to higher yield strength than a higher rotational speed of 1000 rpm. The friction stir welded joints were observed to fail mostly at the boundary between the weld nugget and thermomechanically affected zone at the advancing side. Fracture surfaces showed a mixture of cleavage-like and dimple-like characteristics. Crown
Increasing global demands for energy conservation and environmental protection led to the replacement of heavy components with lighter alloys. As magnesium alloys are believed to be unique candidates for lightweight applications and friction stir welding (FSW) is capable of joining magnesium alloys, in the current work, FSW joint of AZ61 Mg alloy has been fabricated. Microstructure and mechanical properties of the joints were evaluated. The elongated grains of the base metal were recrystallized in the stir zone and in transition zone during friction stir welding. The formation of finer grains in the stir zone of the joint is responsible for increase the hardness of the stir zone. The microhardness of base metal is higher than that of thermo-mechanically affected zone but lower than that of stir zone. The tensile strength of the weld was about 82% of the as-received base metal. The joint failed in ductile mode. This ductile failure of joint was due to the uniform deformation of material.
Metallurgy and mechanical performance of AZ31 magnesium alloy friction spot welds
Journal of Materials Processing Technology, 2013
Microstructural features were studied along the cross-section of AZ31 magnesium alloy friction spot welded joints made using different combinations of welding parameters. Static lap shear testing was performed to evaluate the mechanical properties of the welded joints, and the resulting fracture mechanisms and crack propagation paths were fully examined. Failure load is optimized when the welding procedure is performed with the combination of parameters that maximizes the material mixing, the size of fully metallurgical bonding and simultaneously minimizes the vertical displacement of hook region. The welds demonstrate three failure modes during lap shear testing: through the weld and non-circumferential pull-out modes, in which crack propagation crosses the recrystallized zone, and circumferential pull-out mode, around this zone.