Tensile Shear Failure Load Research Articles

Formation mechanisms and mechanical properties in aluminum cables and copper terminals ultrasonic welded joint

To fabricate highly reliable Al cables/Cu terminals components and elucidate the microstructure evolution of the joint during ultrasonic welding, ultrasonically welded structures of 50 mm2 Al cables and 2 mm-thick copper terminals were conducted at welding energies from 1200 J to 2800 J and an amplitude of 54.6 μm in this paper. As the welding energy increased, the degree of plastic deformation of the Al wires gradually increased, the microstructure of the Cu side remained basically unchanged, and the effective contact area of the Cu/Al interface was gradually enlarged, enhancing the coherence between the Al wires, and the Cu-Al interfacial structure changed from an unbonded area to continuous mechanical interlocking. Parallelly, the Al grains transformed from fine serrated to equiaxed and lamellar crystals driven by geometric dynamic recrystallization (GDRX), continuous dynamic recrystallization (CDRX), and dynamic recovery (DRV), forming distinct shear textures of B/B̅{111}<110>, Rt Goss{110}<110>, Rt Cube{001}<110> and the recrystallization texture F{111}<112>, and the content of shear textures increased from 2.9% to 17.4%. In addition, the tensile shear failure load of the joint reached 2962 N, which met the requirements of cable installations in the field of new energy vehicles (>1650 N). Fracture analysis showed the fracture location transitioned from the Cu-Al interface to the Al-Al interface with an increase in welding energy from 1600 to 2400 J. This work has theoretical guidance for the continuous promotion of vehicle light-weighting.

A comparative study on resistance spot and laser beam spot welding of ultra-high strength steel for automotive applications

In this study, the effect of resistance spot welding (RSW) and laser beam spot welding (LBSW) processes on evolution of microstructure, load endurance capabilities, heat affected zone (HAZ) softening, and corrosion resistance of ultra-high-strength (UHSS) steel joints welded in lap joint design is investigated. The UHSS sheets of dual phase 1000 grade (UHSDP1000) having 1.20 mm thickness were joined using the RSW and LBSW parameters optimized by response surface methodology (RSM). The microstructural features of welding regions of RSW and LBSW joints were studied using optical microscopy (OM). The load endurance capabilities of RSW and LBSW joints were assessed using the tensile shear failure load (TSFL) and cross-tensile failure load (CTFL) tests. The ruptured surfaces of TSFL and CTFL tested samples were examined utilizing scanning electron microscopy (SEM). The microhardness distribution of divergent regions of RSW and LBSW joints was evaluated and imputed to the TSFL and CTFL failure of joints. The corrosion resistance of RSW and LBSW joints was analyzed using potentiodynamic corrosion and immersion corrosion tests. The RSW joints showed 183% and 62.79% greater TSFL and CTFL endurance capabilities than LBSW joints. The TSFL and CTFL endurance capabilities of LBSW joints are inferior to RSW joints due to the smaller load bearing area. It causes the stress concentration in FZ and HAZ of LBSW joints. The RSW joints and LBSW joints disclosed TSFL and CTFL failure in button pull out rupture mode with tearing of HAZ. The failure of RSW and LBSW joints in HAZ is due to the softening caused by martensitic tempering and coarsening of grains. The LBSW joints disclosed inferior resistance to corrosion than RSW joints due to the higher martensite content which contributes to greater fraction of favorable pitting sites and decreased corrosion resistance.

Microstructure and mechanical properties of Al-Zn-Mg-Cu alloy joints welded by ultrasonic spot welding with soft specification

The high-strength lightweight Al-Zn-Mg-Cu alloy sheets were welded using ultrasonic spot welding with soft specification. The peak tensile shear failure load reached 7.3 kN, which satisfies the requirements of AWS D17.2 for spot-welded specimens. This is due to the fact that the material undergoes sufficient plastic deformation during the welding process with soft specification, thereby improving metallurgical bonding. Moreover, the dynamic recrystallization resulting from plastic deformation makes the grain size of the interface significantly refined. The grains with a size of 10 μm in the base metal are transformed into recrystallized grains with a size of 2 μm at most, which is in favor of improving the mechanical properties of the joint. Finally, even under soft specification conditions, excessive welding time can lead to macroscopic damage to the joint, initiation of cracks, and destruction of the grain boundary structure.

The Influence of Tool Geometry on the Mechanical Properties and the Microstructure of AA6061-T6 Aluminum Alloy Friction Stir Spot Welding.

In this work, the influence of the tool geometry on friction stir spot welding (FSSW) was studied on sheets made of AA6061-T6 aluminum alloy. Four different AISI H13 tools with simple cylindrical and conical pin profiles and 12 mm and 16 mm shoulder diameters were used to perform the FSSW joints. Sheets of 1.8 mm thickness were used during the experimental work to prepare the lap-shear specimens. The FSSW joints were performed at room temperature. For each joining condition, four specimens were carried out. Three specimens were used to find the value of the average tensile shear failure load (TSFL), while the fourth one was used to examine the micro-Vickers hardness profile and to observe the microstructure of the cross-section of the FSSW joints. The investigation concluded that higher mechanical properties corresponding to the finer microstructure were obtained by the conical pin profile and the higher shoulder diameter compared with the specimens performed using the cylindrical pin tool and lower shoulder diameter due to the higher strain hardening and the higher frictional heat generation, respectively.

Corrosion studies on friction stir spot welded dissimilar AZ31-C27200 Cu joints

In this investigation, corrosion studies were conducted on dissimilar friction stir spot welded AZ31 Mg-C27200 Cu joints using pitting corrosion tests. Mechanical characteristics of the joints were also evaluated. By conducting tensile testing, the tensile shear failure load value of AZ31 Mg-C27200 Cu joints were 62.36% of the value of similar AZ31 Mg – AZ31 Mg joints and 51.9% of the values of C27200 Cu– C27200 Cu joints, respectively. The joint interface hardness of the dissimilar combination such as AZ31 Mg– C27200 Cu joints were 22.03 % and 35.84% greater than the interface hardness values of similar AZ31 Mg–AZ31 Mg and C27200 Cu–C27200 Cu joints, respectively. Bend tests revealed that similar joints broke with interfacial tear and the dissimilar joints broke with nugget pullout. By conducting pitting corrosion tests on the joints, potentiodynamic polarization curves were developed. The corroded samples were subjected to microstructural evaluation using scanning electron microscopy. The variations in corrosion pit density were also identified.

Improved strength of Al-Zn-Mg-Cu alloy USW joints by synchronously applying electropulsing current

The tensile lap shear failure load of Al-Zn-Mg-Cu alloy ultrasonic spot welding joints (2.89 kN) by synchronously applying electropulsing current is significantly improved compared to the traditional joints (0.39 kN). This can be ascribed to the enhancement of interfacial plastic deformation induced by the dissolution of η' phase, which is the combined effect of electropulsing current and ultrasonic vibration.

Effects of Tool Plunging Path on the Welded Joint Properties of Pinless Friction Stir Spot Welding

Four tool plunging paths including a one-time plunging path and three step-by-step plunging paths were designed to study the effects of the tool plunging path on the welded joint properties of pinless friction stir spot welding (PFSSW). The appearance, cross-sectional microstructure, welding temperature, microhardness, and tensile shear failure load of the PFSSW of thin copper sheets under different tool plunging paths were explored. Furthermore, the fracture modes of welded joints under different tool plunging paths were analyzed. Studies showed that path 1 (plunge total depth at one time) produced the largest range of stirring zone, but the grains in the stirring zone were larger and the width of the thermal-mechanical affected zone was smaller. Path 1 obtained the highest peak temperature during the welding process, and path 3 (plunge 1/3 total depth + plunge 2/3 total depth) gained the lowest peak temperature. The greater the initial plunging amount of the tool, the faster the temperature rise rate in the welding stage. The tensile shear failure loads for path 1, path 2 (plunge 1/2 total depth + plunge 1/2 total depth), path 3, and path 4 (plunge 2/3 total depth + plunge 1/3 total depth) were 8.65 kN, 8.15 kN, 8.25 kN, and 8.85 kN, respectively. The tensile shear failure load of path 4 was 2.3% higher than that of path 1. The fracture modes of welded joints under different tool plunging paths were all nugget pullout fractures. The fracture morphology indicated that the fracture type was ductile fracture. The step-by-step plunging path proposed in this work extends the traditional PFSSW process. The findings of this study can provide a reference for the selection and design of tool plunging paths for PFSSW.

Effect of tool geometry on hook formation and mechanical properties of refill friction stir spot welding in alclad 2A12-T42 aluminium alloy

Three sleeve structures (conventional sleeve, threaded sleeve, grooved sleeve) were used for refill friction stir spot welding (RFSSW) of 2A12-T42 aluminium alloy to investigate the effect of sleeve geometry on hook formation and mechanical properties of the joints. The high-pressure area generated during the plunge stage was responsible for the hook formation. Threads and grooves sleeves not only enhanced the mixing effect but inhibited the hook formation by breaking up the alclad layer or promoting the downward material flow, respectively. The welds using a grooved sleeve had the lowest hook height and highest tensile-shear failure load. As the hook height decreased, the upward tendency of crack propagation was suppressed, which confined the propagation paths within the regions of higher hardness.

Friction stir lap joining techniques effects on microstructure and tensile properties of high-strength automotive steel top hat sections

Dual Phase (DP) steel, a type of Advanced High Strength Steel (AHSS) with a thickness of 1.7 mm, is used to fabricate single-hat components that are then joined to the base plate using two friction stir welding processes: friction stir lap welding (FSLW) and friction stir spot lap welding (FSSLW). It is difficult to join this assembly using fusion welding techniques. The welding variables for the FSLW process, tool rotation speed (TRS), tool traverse speed (TTS), and plunge depth (PD), were optimized using the design of an experiments-based response surface method by experimentally measured tensile shear failure load (TFL) of top hat assembly. For the FSSLW process, the welding variable TTS was replaced by dwell time (DT). Peak temperature, microstructure at different zones, microhardness mapping, and energy absorption capacity of both processes were evaluated under optimal welding conditions. For both processes, the stir zone and the heat-affected zone had the highest and lowest microhardness, which can be correlated with the level of martensite tempering, martensite lath spacing, polygonal ferrite volume, and precipitated carbides. Under optimum welding conditions, the TSL and energy absorption of FSLW joints were 14 kN and 170 J, respectively, which is 20% and 47 higher than the TSL and energy absorption of FSSLW joints.

Mechanical properties and failure analysis of refill friction stir spot-welded 5052/2A12 joints

The mechanical properties and failure process of 2 mm-thick 5052 Al and 6 mm-thick 2A12 Al fabricated by refill friction stir spot-welding were investigated. The hooks were bent respectively downwards and upwards at plunge depths smaller and larger than the upper plate thickness. The joint area of the lap interface and bearing thickness of the upper plate were related to the hook direction. The tensile shear failure load was affected by structural characteristics and hardness of the joints. Stress concentration occurred in the hook and strain expanded with the hook during fracture. There were two fracture modes: shear fracture and shear plug fracture, where both cracks passed through the hook and fracture morphology of the hook was less plastic.

Evaluation of shear force and fractography of friction stir spot welded joints of AA 6082-T6 alloy

This experimental work investigates the tensile behavior of friction stir spot welded joints from 3 mm thick aluminum alloy AA6082-T6 sheets. Taguchi L9 Orthogonal array was used for process parameters - Tool rotational speed (TRS), Dwell time (DT) and Shoulder diameter (SD) with consideration of three levels. Friction Stir Spot Welding (FSSW) was performed on vertical milling machine. Tensile shear test was conducted on Universal testing machine (UTM) to find out the tensile shear failure load (TSFL). The optimal combinations of parameters were at tool rotational speed of 2,000 rpm, dwell time of 15 seconds and tool shoulder diameter of 16 mm. Tool rotational speed had a substantial effect on tensile shear strength of FSSW joint. Scanning Electron Microscopy (SEM) tests revealed that the changes in microstructure in different zones of FSSW joint were observed. Tensile shear specimen was analyzed using SEM to observe the behavior of fracture surfaces. Significant ductility in the fracture surface was an evident in the fractography. In this article, attention is focused on the influence of joining parameters on the mechanical behavior of the friction stir spot weld under the tensile shear load condition. Keywords: Fractography; friction stir spot welding (FSSW); heat affected zone (HAZ); scanning electron microscopy (SEM); thermo-mechanically affected zone (TMAZ).

Effect of adhesive ductility and joint configuration on the tensile-shear behaviors of friction stir spot weld bonding joints

ABSTRACT This paper introduced a hybrid joining system including friction stir spot welding (FSSW) and adhesive bonding, named friction stir spot weld bonding (FSSWB). In order to avoid adhesive layer carbonization, FSSWB was processed by flow-in method. The aim of this study was to evaluate the effect of adhesive ductility and joint configuration on the tensile-shear performances of AA6061 aluminum alloy. Two types of adhesives were considered: brittle epoxy (AV138) and ductile epoxy (Araldite 2015). Besides, hybrid joints involve three types of joint configurations (AV138, Araldite 2015 and dual adhesive). A finite element (FE) model of hybrid joints failure process was established based on the extended finite element method (XFEM) and cohesive zone model (CZM). The tensile-shear failure load (TSFL) prediction values and joint failure process were in good agreement with the experiments. Compared to FSSW, the TSFL values for the three types of hybrid joint increased by 166.5%, 294.8% and 173.8% respectively. In addition, the stresses at the hook tip of the three hybrid joints were decreased by 85.56%, 79.31% and 83.67%. From the study, it was found that the use of ductile adhesives at two sides of joint was more helpful to increase the load-bearing capacity of FSSWB joints.

Tensile-Shear Mechanical Behaviors of Friction Stir Spot Weld and Adhesive Hybrid Joint: Experimental and Numerical Study

In this work, the tensile-shear mechanical behaviors of friction stir spot weld and adhesive hybrid joint were performed from both numerical and experimental viewpoints. Weld through (WT) and flow in (FI) processes were studied in this research. The focus was to evaluate joint defects, tensile-shear failure load (TSFL), failure energy, failure mode and stress distribution of the joint. In FI joints, keyhole and hook defects appeared in the weld zone and the areas of material removed from the base metal were filled with adhesive. In the WT joints, the adhesive layer close to the weld zone was carbonized due to the welding heat. Meanwhile, under the rotating movement of welding tool, the adhesive impurities entered the stirring zone (SZ) and heat affected zone (HAZ) of the weld, which decreased mechanical performances of WT joints. Compared to the friction stir spot welding (FSSW) joint, the TSFL value, stiffness and failure energy of FI joint were increased by 2.7, 1.1 and 8.14 times, respectively. In order to study the stress distribution of the joints, a finite element (FE) model, which considered the weld structure and mechanical properties of weld regions, was implemented. Moreover, the adhesive layer was simplified by the cohesive zone model (CZM). FE results show that the FI process effectively decreases the stress concentration of the weld edge from 243.09 to 15.5 MPa, under the 2 kN tensile load. The weld can block the adhesive crack propagation, and the adhesive optimized the stress distribution of FI joints through a synergistic effect. So, the use of FI process for aluminum alloy connection is strongly recommended, especially in crucial structure areas.

Tribiological investigation and optimization of friction stir spot welding of dissimilar metals by LSSM-ANN method

In manufacturing firms, welding technology plays a supreme role in joining purposes. The joining of dissimilar metals is complex in several conventional type welding. Friction stir spot welding (FSSW) is a solid-state welding technique and it is a derivative of conventional friction stir welding (FSW) to join the metals. The recent demands of advanced engineering materials such as aluminum alloys and stainless steel in the automobile sectors are forced to facilitate this research work, at the same time, the joining of such materials is quite complex because of its different welding characteristics. The main contribution of this work is to optimize and predict the microhardness and tensile failure properties of dissimilar metals by hybrid lightning search algorithm-simplex method (LSA-SM) and ANN algorithm. The dissimilarly joined metals namely, duplex stainless steel 32760 and aluminum 7075-T6 are utilized in this work and the experimentation is performed for six different test runs. Besides, the predicted values from the proposed algorithm are compared with the existing support vector machine (SVM) method. The predicted values of 314 Hv microhardness and 4967 N tensile shear failure load are optimized by the ANN-LSA-SM method at 1900 rpm. From the test results, it shows that the proposed model is efficient to predict the mechanical properties of the dissimilar welded materials than the experimental and SVM method.

Statistical and Metallurgical Analysis of Dissimilar Friction Stir Spot Welded Aluminum/Copper Metals

In this paper, friction stir spot welding of 2-mm-thick AA 1060 Al to T2 Cu is conducted. The effects of dwell time, tool rotational speed and shoulder plunge depth on tensile shear failure load (TSFL) are investigated. A quadratic regression model is proposed to fit the relationship between TSFL of the joint and the welding process parameters. The analysis-of-variance results show that the rotational speed is the most significant factor affecting the TSFL. Joint fabricated at the low rotational speed is weak-bonded by discontinuous intermetallic layers due to the insufficient heat input. Increasing the rotational speed can improve the TSFL by promoting intermetallics formation at the interface, while an excessive increase in rotational speed results in formation of microcrack at the interface, which seriously compromises the tensile property of the joint. Shoulder plunge depth, tool rotational speed and dwell time of 0.1 mm, 2371 r/min and 4.96 s, respectively, were identified as the optimal combination of welding process parameters. Results of microstructure characterization show that the joint produced at the optimized process parameters is well metallurgically bonded by a 1.9-μm-thick laminated intermetallics layer which comprises CuAl and CuAl2 sublayers. Result of fracture path reveals that the fracture firstly extends along the interfacial CuAl2 layer by a brittle mode and then propagates through the aluminum matrix in the stir zone by a ductile mode.

Experimental investigations on interfacial characterization and mechanical performance of ultrasonic spot welded Al/brass joints

The dissimilar joining of aluminum (AA 1100) to brass (UNS C27000) in the electric power industry is highly required to transmit the electricity efficiently. However, it's hard to join these materials using fusion welding process because of the broad differences in their physical, mechanical and chemical properties, and the evaporation of zinc constituent during the welding process. Thus, it is directed the researchers to find a new technique to tackle this problem. It seems that ultrasonic metal welding (USMW) is one such promising method that is developed nowadays. In this study, lap joints of AA 1100 aluminum alloy and UNS C27000 copper alloy have been produced using USMW and the effects of process parameters on the mechanical strength and interface microstructure have also investigated. The tensile shear failure load firstly increases with the rise of weld time up to 0.55 s of weld time followed by a rapid decrement in the value due to excessive plastic deformation in the weld zone. It is confirmed from the energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction analysis (XRD) results that USWed aluminum to brass produces intermetallic compounds (IMC), and its thickness is getting wider with the increase in weld time. A composite eutectic structure of Al and Al2Cu is the first compound formed in the middle of the weld zone.

Ultrasonic spot welding of Al/Mg alloys: A state-of-the-art review

Lightweight materials like aluminum (Al) and magnesium (Mg) alloys are extensively used in automotive industries. The welding between these dissimilar alloys is inevitably essential to produce high-quality and reliable joints. High power ultrasonic metal welding (USMW) technology, which mimics the properties of solid-state bonding, offers a potential solution in welding of these difficult-to-weld materials. The superior characteristics of this welding process, such as low heat input, less weld time, and high production efficiency, reduce the tendency to form brittle intermetallic compounds (IMCs) and enhance the joint strength of Al/Mg dissimilar joints. The current study is focused on obtaining favorable performance measures during the USMW of dissimilar Al/Mg alloys through controlling the dominant input factors. The tensile shear (TS) and T-peel (TP) failure load firstly increased up to a specific limit and decreased further with the rise in weld energy. The compared fatigue strength results of Al/Mg dissimilar joints with other bonding techniques provides an insight into the fatigue failure mechanism. The mechanism behind the weld formation is discussed based on the fracture surface and interface morphologies, microstructure evolution, and IMC formation along the weld interface. At higher weld energy, the elevated interfacial temperature promoted the formation of Mg17Al12, Al3Mg2 IMCs and accelerated the elemental diffusion at the weld interface. Mechanical interlocking and dynamic recrystallization at the periphery of the weld interface due to severe shear deformation results in refining the grain structure. However, this detrimental interfacial reaction can be reduced by introducing a coating on the Mg surface. Thus, the process engineers can now adopt this technique to get best combinations of input parameters in USMW problems, and there is no need to depend on the manufacturer’s handbook.

Process parameter optimization and performance comparison of AISI 430 and AISI 1018 in resistance spot welding process

Resistance spot welding (RSW) process plays an important role in the sheet metal fabrication process, in which metal joining is obtained by heat developed through electric resistance against the current flow in the metals contact area. In this work, the impact of weld time, squeeze time, weld current and hold time on weld strength of 1.2 mm thickness ferritic stainless steel (AISI 430) and low carbon mild steel (AISI 1018) sheets by using RSW process were investigated and compared. The Design of experiment (DoE) was used to formulate the number of experiments with variations in input conditions. Welding of similar metals of AISI 430 and AISI 1018 was done according to the number of experiments obtained using DoE. The welded samples were subjected to tensile shear failure load and micro-hardness testing. The output responses were analyzed through Response surface methodology (RSM) to find the optimum control parameters to achieve higher weld strength.

Dissimilar joining of Al/SS sheets with interlayers by ultrasonic spot Welding: Microstructure and mechanical properties

Ultrasonic spot welding (USW) has received a great deal of attention by the automobile manufacturer to build lightweight structural components. However, the versatility of using this process is still limited due to the substantial instabilities in weld quality. These fluctuations are mainly due to the lack of scientific understanding of this process and poor control of intermetallic compound formation. Therefore, this study is focused on the improving of the joint strength and its quality by ultrasonic welding of Al3003 and SS304 sheets with molybdenum (Mo) and zinc (Zn) powder as interlayers. The results revealed that the optimum thickness for Mo and Zn interlayers are found to be 0.11 mm and 0.15 mm, respectively. In comparison, Al3003/SS304 joints with Zn interlayer exhibits the maximum tensile shear failure load about 626.44 N at 1.5 s of weld time, which is better than those of the joints produced with Mo interlayer. The microstructural morphologies at the weld interface reveal the different characteristics like mechanical interlocking at the outside zone of the sonotrode knurl indentation, wavy type region under the sonotrode knurl, and swirling like diffusion zone inside the sonotrode knurl.

Microstructural evolution and mechanical properties of refill friction stir spot welded alclad 2A12-T4 aluminum alloy

Refill friction stir spot welding (RFSSW) was applied to join the 2A12-T4 aluminum alloy successfully, and effects of the tool rotational speed on weld formation, microstructure evolution and mechanical properties of the RFSSW joint were investigated in detail. There existed macrostructure characteristics of bonding ligament and hook associated to the plasticized metal flow in the joint. The microstructure of the joint exhibited variations in the grain size, precipitates distribution and substructure in the width direction. A softened region existed in all the RFSSW joints and its formation could be attributed to the coarsening and dissolution of the S precipitates. Liquation cracks associated to the localized melting of S were observed in the stir zone of the joint produced at the highest rotational speed. The tensile-shear properties of the RFSSW joints were dependent on the hook geometry, distribution of the bonding ligament and hardness of the stir zone. With increasing the rotational speed from 900 to 1300mm, the hook height increased, the bonding ligament at the weld periphery got more dispersed and the hardness of the stir zone decreased. The optimized RFSSW joint was obtained when the rotational speed was 1300rpm, and the corresponding tensile-shear failure load was 10,030N. Two different fracture modes, i.e. the shear fracture mode and shear-plug fracture mode, were identified in the tensile-shear tests.