Welded Lap Joints Research Articles

完全熔透和部分熔透搭接激光焊接接头的残余应力和变形

完全熔透和部分熔透搭接激光焊接接头的残余应力和变形

Fatigue Behavior of Friction Stir Welded Lap Joints for Dissimilar AA7150-AA2524 Aluminum Alloy

The detail fatigue rating (DFR) value of friction stir welded (FSW) lap joints for dissimilar AA7150-AA2524 aluminum alloy was experimentally investigated. The metallographic analysis was carried out on by optical microscope (OM). Fatigue fractography was observed under scanning electron microscope (SEM). The results indicate that DFR value of AA7150-AA2524 FSW lap joints is 191.54MPa. There is no distinct different boundary between HAZ and BM of the upper AA7150 sheet. The grains in the upper NZ of AA7150 are coarser than those in the bottom NZ of AA2524. Fracture morphologies shows that lots of hook defects in the FSW lap joint. Fractography indicates that fatigue crack is initiated from the AA2524 bottom surface around the weld center, where weak-bonding defects can be seen. The hook defects and weak-bonding defects have obvious influence on the fatigue property of friction stir welding lap joints, which seriously reduce the fatigue strength.

Ultrasonic welding of all‐polypropylene composites

ABSTRACTIn this study, the mechanical properties of ultrasonic welded lap joints of all‐polypropylene composite (APPC) were investigated and compared to the interlaminar properties of the composite sheet itself. The process control parameter was welding time: welded samples were prepared with an ultrasonic welding machine in the 0.1–1.0 second time range. In most cases, the shear strength of the welded samples exceeded that of the unwelded APPC. Although it was found that during the ultrasonic welding process, the reinforcing tapes partially melted in the welding zone (WZ), the seam remained strong enough because the heat released and the pressure applied during the welding process further improved the consolidation of the APPC layers. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48799.

Mechanical characterization of laser-welded double-lap joints in ultra-high and low strength steels for sandwich panel applications

This study is to investigate the microstructure and the mechanical properties (hardness, strength, fatigue resistance) of laser welded double-lap joints from two different steels, ultra-high strength abrasion resistant steel (AR400) and low strength structural (S355 MC) steels. The laser welding was conducted at two different energy density 170 and 958 J/mm2 and constant power 3 kW. The morphology and the microstructure of the cross-section lap joints have examined by optical microscopy. The shear strength and the fatigue resistance of the double-lap joints were evaluated by uniaxial tensile tests and fully reversed tension–compression strain-controlled fatigue tests, respectively. Whereas the hardness of the welded lap joints of UHS steel has been decreased due to the tempered martensite formation. The microstructure of the laser welded lap joints of LS steel shows martensite formation in the fusion zone. Hence, the hardness has been significantly increased to 300 Hv. The shear strengths of the welded lap joints have significantly influenced by the laser power density. Significant improvement in the strength could be observed in the strength of the lap joints of UHS steel at energy density 958 J/mm2. Fatigue cracking along steels sheets boundaries that intersect the weld zone in the welded lap joints and the crack propagation towards the weld zone observed to be the fatigue-induced microstructural features in the lap joints welded by laser.

Improving Joint Morphologies and Tensile Strength of Al/Mg Dissimilar Alloys Friction Stir Lap Welding by Changing Zn Interlayer Thickness

The pure Zn foils with different thicknesses (0.02, 0.05, 0.1, 0.2 and 0.3 mm) were selected as interlayers to improve the quality of friction stir lap welding joint of 7075-T6 Al and AZ31B Mg dissimilar alloys. The effects of the interlayer thickness on joint formation, microstructure and tensile strength were analyzed. The results displayed that the maximum length of the boundary between stir zone (SZ) and thermo-mechanically affected zone in lower plate was obtained by the addition of the Zn interlayer with 0.05 mm thickness. The Mg–Zn intermetallic compounds (IMCs) were discontinuously distributed in the SZ, replacing the continuous Al–Mg IMCs. The size of Mg–Zn IMCs increased with the increase in the thickness of the Zn interlayer. The maximum tensile shear strength of 276 N mm−1 was obtained by the addition of 0.05 mm Zn foil, which increased by 45.6% of that of the joint without the Zn foil addition.

Effect of tool tilt angle on strength and microstructural characteristics of friction stir welded lap joints of AA2014-T6 aluminum alloy

Abstract Friction stir welding (FSW) has been extensively adopted to fabricate aluminium alloy joints by incorporating various welding parameters that include welding speed, rotational speed, diameters of shoulder and pin and tool tilt angle. FSW parameters significantly affect the weld strength. Tool tilt angle is one of the significant process parameters among the weld parameters. The present study focused on the effect of tool tilt angle on strength of friction stir lap welding of AA2014-T6 aluminium alloy. The tool tilt angle was varied between 0° and 4° with an equal increment of 1°. Other process parameters were kept constant. Macrostructure and microstructure analysis, microhardness measurement, scanning electron micrograph, transmission electron micrograph and energy dispersive spectroscopy analysis were performed to evaluate the lap shear strength of friction stir lap welded joint. Results proved that, defect-free weld joint was obtained while using a tool tilt angle of 1° to 3°. However, sound joints were welded using a tool tilt angle of 2°, which had the maximum lap shear strength of 14.42 kN and microhardness of HV 132. The joints welded using tool tilt angles of 1° and 3° yielded inferior lap shear strength due to unbalanced material flow in the weld region during FSW.

Effect of Post Weld Heat Treatment on Strength and Microstructure of Friction Stir Welded Lap Joints of AA2014-T6 Aluminum Alloy

Lap joints of AA2014 aluminum alloy produced by friction stir welding and subjected to post weld heat treatment have been studied. The shear strength and hardness of the welded joints were determined. The structure of the weld and weld-affected zone was studied. A fractographic analysis of the fracture surface of the tested samples was performed. The post weld heat treatment modes were established to enable recovery of the mechanical properties of the welded joints.

Mechanical behavior of transverse fillet welded joints of high strength steel using digital image correlation techniques

Mechanical behavior of 24 lap-welded fillet joints and 20 cruciform fillet joints made of high strength steels (HSS) under tension load is investigated by experimental study. Traditional deformation measurements for transverse fillet weld joints have many weaknesses, which can be solved by digital image correlation techniques (DIC). The strain distribution development over the specimen along the whole loading process were analyzed by using DIC measurement. Test specimens were prepared using four classifications of filler metal and two weld sizes were included in each type of transverse fillet welded specimens. The effect of parameters (e.g. weld size and mismatch ratio) on mechanical properties (e.g. failure modes, fracture angle, ultimate strength and weld ductility) of those two types transverse fillet weld were compared. Due to the softening and other metallurgical effects, cruciform type specimens are more prone to fail around fusion lines than weld metal. Generally, because of the existence of friction force, mean strength of lap-welded specimens are higher than that of cruciform type specimens. The mean ductility of lap-welded specimen is similar to that of cruciform type specimen. Two load-deformation curve features, “rise” feature and “platform” feature, were identified. Most lap-welded specimens have “rise” feature load-deformation curve while most cruciform type specimens have “platform” feature load-deformation curves. Generally, the specimens with “rise” feature load-deformation curve are more likely to suffer sudden fracture. The instantaneous and simultaneous fracture was observed at fracture surface of lap-welded specimen. Joint misalignment has significant impact on the deformation patterns of cruciform type specimens. Based on load-deformation curves of cruciform type specimens, three deformation patterns were proposed. Due to the existence of three deformation patterns, the variability of strength and ductility are much larger than lap-welded joints. Moreover, it is confirmed that EC3 and AISC Specification are conservative for all mismatched filler metals.

Evaluation of load-carrying capabilities of friction stir welded, TIG welded and riveted joints of AA2014-T6 aluminium alloy

PurposePresently, the materials used in light combat aircraft structures are aluminium alloys and composites. These structures are joined together through riveted joints. The weight of these rivets for the entire aircraft is nearly one ton. In addition to weight, the riveted connection requires a lot of tools, equipments, fixtures and manpower, which makes it an expensive and time-consuming process. Moreover, Al alloy is also welded using tungsten inert gas (TIG) welding process by proper control of process parameters. This process has limitations such as porosity, alloy segregation and hot cracking. To overcome the above limitations, an alternative technology is required. One such technology is friction stir welding (FSW), which can be successfully applied for welding of aluminium alloy in LCA structures. Therefore, this paper aims to compare the load carrying capabilities of FSW joints with TIG welded and riveted joints.Design/methodology/approachFSW joints and TIG welded joints were fabricated using optimized process parameters, followed by riveted joints using standard shop floor practice in the butt and lap joint configurations.FindingsThe load-carrying capabilities of FSW joints are superior than those of other joints. FSW joints exhibited 75 per cent higher load-carrying capability compared to the riveted joints and TIG-welded joints.Practical implicationsFrom this investigation, it is inferred that the FSW joint is suitable for the replacement of riveted joints in LCA and TIG-welded joints.Originality/valueFriction stir butt joints exhibited 75 per cent higher load-carrying capability than riveted butt joints. Friction stir welded lap joints showed 70 per cent higher load-carrying capability than the riveted lap joints. Friction stir butt joints yielded 41 per cent higher breaking load capabilities than the TIG-welded butt joints. Moreover, Friction stir lap weld joints have 57 per cent more load-carrying capabilities than the TIG-welded lap joints.

An Optimization of Welding Process Parameters :To Maximize the Ultimate Tensile Strength of Lap Welding Joint by using Orthogonal Array and Taguchi Method followed by ANOVA Techniques

An Optimization of Welding Process Parameters :To Maximize the Ultimate Tensile Strength of Lap Welding Joint by using Orthogonal Array and Taguchi Method followed by ANOVA Techniques

Investigation of humping defect formation in a lap joint at a high-speed hybrid laser-GMA welding

Abstract Productivity rise can be realized at high-speed welding, but in a practice, the constraints emanate from the tolerance welding speed limit beyond which generate humping defects and the likes. These defects are undesirable in welding as they undermined the weld bead integrity and decrease productivity. In this study, an investigation on a lap joint welding using a hybrid Laser-GMAW (L-GMAW) welding process on a carbon steel sheet was undertaken to examine the mechanisms involved in the arc behavior, the droplet transfer, and the weld pool flow dynamics in a hump defect formation at high-speed welding. A variation of the process parameters in the hybrid welding system such as the wire feed speed (WFS), the traveling speed (TS) and the oscillation of the laser beam were used as input signals. A high-speed video camera was used with different viewing positions to capture the sequence of events during the hybrid welding process. The high-speed images of the arc behavior, the weld pool flow pattern with the use of tracer particles in arriving at the root mechanisms were acquired. Based on the experimental resultant, the occurrence mechanisms of the weld defects were proposed. In this study, the key factors in the humping defect formation are the two dominant lateral flows toward the top and bottom sheets, the collision between the weld pool back- and rear-flow and the interruption of the weld pool flow channel. Also, the generation of copious spatter due to the two lateral flows and the swollen buildup towards the hump closure were responsible for the next hump initiation formation. The beam oscillation applied to wet the weld toe angle to delay the outset of the humping defect occurrence was insignificant at higher travel speed. Furthermore, the force of gravity and surface tension were the key forces in this study.

A finite element analysis on mechanical behavior of Al/Al-Mg composites for the design of tank cars under actual measuring loads

The transportation safety of tank cars carrying concentrated nitric acids under conditions of heavy loads has attracted the increasing attention. The use of Aluminum/Aluminum-Magnesium(Al/Al-Mg) alloys to form laminated composites can solve the problems associated with the low corrosion resistance and strength of tank car bodies. In this work, a finite element analysis was used to simulate the tensile tests of the Al/Al-Mg laminated composites. In particular, the stress and strain behavior of the composites under tensile loads was investigated, and the corresponding mechanical properties of the composites were determined, which was verified by the tension test results. Furthermore, the effective load time history was obtained by processing the measuring data of C70E type gondola car body on three typical general railway line. Load spectra of car body were compiled using the rain-flow count method, which was applied to do the fatigue design for 70 t Al/Al-Mg tank body. Most importantly, in conjunction with the SN curve of the base materials and the lap-welded joint, based on the tank car finite element analysis results under various load cases, the fatigue life of the 70 t Al/Al-Mg tank body was calculated based on Miner's linear accumulative damage theory. The results showed a very promising application of such composite materials to meet the safety requirements.

Polyoptimisation of the refill friction stir spot welding parameters applied in joining 7075-T6 Alclad aluminium alloy sheets used in aircraft components

In the aerospace industry, the refill friction stir spot welding (RFSSW) method is increasingly used to join thin sheets, especially those made of 2xxx and 7xxx series aluminium alloys. This paper presents the results of spot welding lap joints of 7075-T6 aluminium alloy sheets. The load capacity of joints was determined by tensile/shear tests using a universal testing machine. The effect of tool plunge depth, tool rotational speed and duration of welding on joint load capacity and failure mode was investigated. The polyoptimisation of the values of welding process parameters was carried out to ensure the highest load capacity of the joint at a minimum variance of the results obtained. The selection of the optimal parameters of the RFSSW process was carried out using an adequate mathematical model obtained on the basis of Weierstrass’ theorem. It was found that tool rotational speed had the greatest impact on the load capacity of the joints. It was possible to increase the load capacity of the joint by increasing the duration of welding but only to a limited extent. The selection of optimal welding parameters requires a compromise solution, i.e. the selection of a tool rotational speed that ensured adequate plasticisation of the material with a welding duration that ensured that an appropriate joint microstructure was obtained and assured the required load capacity of the joint. The methodology of mathematical modelling of polyoptimisation presented can be useful in optimising similar joining processes.

Microstructures and Properties of Friction Stir Welded Al-Cu Lap Joints

Friction stir welded lap joints of 5083 aluminum alloy plates with thickness of 2mm and T2 pure copper plates with thickness of 3mm were prepared, and the microstructures and properties of lap joints were investigated. The results showed that Al and Cu interdiffusion occurred at the interface of the lap joints, the grains in the stir zone of Al were refined and the microhardness increased sharply. The joint of Cu can be divided into four parts, including the nugget zone (NZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM). Using the optimum welding parameters (rotation speed of 900rpm and welding speed of 100mm/min), the lap joints were well formed. There were fewer welding defects and the average shear tensile force reached 3.155KN. Also, the ductile-brittle hybrid fracture occurred at the transitional zone of the advancing side of the Al plates. XRD results showed that intermetallic compounds (IMCS) mainly composed of Al2Cu and AlCu4 were produced in the interface of the lap joints during welding.

Evaluation on Microstructures and Mechanical Properties in Friction Stir Welded Lap Joints of Invar 42/SS 400

This study evaluated the microstructures and mechanical properties of friction stir welded lap joints. Invar 42 and SS 400 as experimental materials were selected, and friction stir welding was carried out at tool rotation speed of 200 rpm and welding speed of 100 mm/min. Applying the friction stir welding was notably effective to reduce the grain size of the stir zone, consequently, the average grain size of Invar 42 was reduced from 11.5 μm in the base material to 6.4 μm in the stir zone. Joint interface between Invar 42 and SS 400 showed a sound weld without voids and cracks, and the intermetallic compounds with Ll₂ type in lap joint interface were partially formed with size of 100 nm. Also, the hook, along the Invar 42 from SS 400, was formed at advancing side, which directly affected an increase in peel strength.

Mechanical Properties Optimization of Friction Stir Welded Lap Joints in Aluminium Alloy

This work focuses on the influence of the rotational and travel speed on the strength of AA 2024 T3 friction stir welded lap joints. Tensile tests were carried out on minispecimens extracted from different welding zones. A central composite design was applied to identify the relative importance of the variable factors’ effects and their interaction on yield/ultimate strength and elongation for both the heat affected-zone (HAZ) and nugget zone. Surface methods and gradient algorithms were used to optimize the yield strength of the joints. Shear and microhardness tests were executed to achieve a more complete mechanical characterization.

Fatigue properties of AL/AL-MG alloy laminated materials for the applications to railway tank cars

In this study, Al/Al-Mg alloy laminated plates were developed, and such composite materials are applied in a 70 t tank car for transporting concentrated nitric acids. The fatigue tests of the base materials and the lap-welded joint of the Al/Al-Mg alloy laminated plate were conducted, and the stress-cycle (S-N) curve with a survival rate of 97.7% was obtained. The fatigue failure mode was analyzed, and its fracture mechanism of the laminated plates was determined. Furthmore, the mechanical behavior of Al/Al-Mg alloy laminated plate was investigated using the finite element analysis (FEA). Based on the load spectrum of 100 t tank car described in the Association of American Railroads (AAR) standard, in conjunction with the S-N curve of the base materials and the lap-welded joints, the fatigue life of the 70 t tank body was calculated based on the Miner’s linear accumulative damage theory. The results showed that the 70 t tank car constructed with such materials can meet the safety requirements of operating for 2.5 million km.

Improving mechanical properties of composite/metal friction stir lap welding joints via a taper-screwed pin with triple facets

Material flow rates at the horizontal and vertical directions were markedly increased by a taper-screwed pin with triple facets. A stationary shoulder could prevent plasticized materials overflowing out of the weld and make them backflow into the nugget zone, achieving good surface integrity. The short carbon fiber-reinforced poly-ether-ether-ketone and the AA2060-T8 were tightly joined, and the carbon fibers were dispersedly distributed at the nugget zone, which attributed to the effective load transfer effects and then improved the joint strength. The tensile shear strength reached 18 MPa. The combination of the stationary shoulder tool system and plunging the taper-screwed pin with triple facets into the composite was feasible and effective to improving mechanical properties of composite/metal friction stir lap welding joints.

Global and Cluster-wise Regression Models for Total Bead Area as Welding Quality

Abstract In recent years, the automated welding system is used in high volume production industries for efficient and precise welding works. It can be applied for not only a simple machine, but also production of a single part. Therefore, a new algorithm that estimates the optimal welding parameters on a given bead geometry and accomplishes the desired mechanical properties of the weldment in order to make the automatic GMA (Gas Metal Arc) welding process, desirable. The developed algorithm could use for a wide range of material thicknesses, and be applicable for all welding positions. In addition, the models must be available in the form of mathematical equations, which can program to the robot, and give a high degree of confidence in predicting the bead dimensions. In this study, two regression models employing global regression analysis and cluster-wise regression analysis are proposed to be applicable for prediction of optimal welding parameters on the total bead area. For development of the proposed regression models, an attempt has been employed for finding the optimal welding parameters. A full factorial design is adopted to investigate welding parameters effect on total bead area in lap-joint welding. as a function of key output parameters in the automated GMA welding process was utilized. Not only the fitting of these models were checked and compared by using a variance test (ANOVA), but also the prediction of total bead area using the developed regression models was carried out the basis of the additional experiments. The fitness and variance test of the regression model is performed by using experimental data and ANOVA. The prediction of total bead area was carried out via regression model. Experimental results showed that the fitting on the experimental data of the cluster-wise regression model with the RMS value of 0.0026 is better than the developed global regression model for determining total bead area.

Fatigue Properties of Arc Welded Lap Joints of Joggled Steel Sheets

Fatigue Properties of Arc Welded Lap Joints of Joggled Steel Sheets