Showing papers on "Spot welding published in 2016"
TL;DR: In this paper, an innovative pathway was developed to obtain liquid metal embrittlement-free welds which is able to extend the weldable current range of the steels. But this pathway is limited by the high electrical resistivity of twinning induced plasticity steels, which makes their resistance spot welding difficult and limits their weldability.
97 citations
TL;DR: In this paper, the microstructure, composition, fractogragh and fracture mode of Al/steel joints were analyzed with electron probe microanalysis (EPMA), scanning electron microscope (SEM) and X-ray diffraction (XRD).
87 citations
TL;DR: In this paper, the effects of zinc layer on microstructure and mechanical behavior of resistance spot welds of aluminum to galvanized (GS-Al joint) and low carbon steel (PS-Al Joint) were explored.
87 citations
TL;DR: In this paper, a series of welds were produced at various processing parameters in friction spot welded of AA6061-T6 to investigate hook formation and mechanical properties, and two different types of hook defect were identified based on the locations, which were closely associated to the plunge depth.
84 citations
TL;DR: In this article, an improved representation of both electrical contact resistance and thermal contact resistance (TCR) in Al to zinc-coated steel RSW process is presented, which can be used to guide future welding schedule development or electrode geometry design for the RSW of Al to steel.
68 citations
TL;DR: In this paper, the first study on welding of Cu-based shape memory alloys was presented, where the superelastic wires used in the investigation had a nominal composition of Cu−17Al−11.4Mn (at%).
64 citations
TL;DR: In this article, a review on resistance spot welding of magnesium alloys is presented, with emphasis on the relationship between microstructure, properties, and performance, under quasi-static and dynamic loading conditions.
Abstract: This paper presents a review on resistance spot welding of magnesium alloys, with emphasis on the relationship between microstructure, properties, and performance, under quasi-static and dynamic loading conditions. It also compares the resistance spot welding of magnesium-to-aluminum alloys and the various techniques used to suppress the formation of brittle intermetallic compounds. Resistance spot welding of magnesium-to-steel, weld bonding, the effects of process parameters on joint quality, and the main metallurgical defects in resistance spot welding of magnesium alloys are also deliberated. Studies have shown that the pre-existence of coarse second phase particles in the base metal, the addition of particles, such as titanium powder, and welding under the influence of electromagnetic stirring effect can promote columnar-to-equiaxed transition, microstructure refinement, and improvement in mechanical properties of magnesium alloys resistance spot welds. For magnesium-to-aluminum alloys spot welds, the use of interlayers, such as pure nickel, gold-coated nickel foil, and zinc-coated steel, was found to suppress the formation of brittle intermetallic compounds and thus significantly improve the joint strength.
64 citations
TL;DR: In this paper, the acoustic patterns of resistance spot welding in a servo-based electrode actuation system were analyzed using time and frequency domain representations, and the welding processes can be significantly put into classes for their behaviour (weld formation) based on acoustic emissions.
Abstract: Acoustic emission reveals certain characteristic in resistance spot welding process as it exists due to the variation of electromagnetic ties between atomic bounds. So, the objective of this study is to analyse the acoustic patterns of resistance spot welding in a servo-based electrode actuation system. Time and frequency domains’ representations are interchangeably applied to analyse such matters as those behaviours are captured via electronics means. More than one type of weldable materials (carbon steels and stainless steels) is purposely used to analyse the dissimilarity conditions as well as the individual material’s welding processes. The interpreted waveform shows that the welding processes can be significantly put into classes for their behaviour (weld formation) based on acoustic emissions. A best weld formation will have perfect acoustic pattern, while a better one will have more than one main lobe in frequency domain. Moreover, a dissimilar weld formation will have inter-transient spike waveform, while an expulsion welding process will have a rapid drop of signal in acoustic pattern. All these observations have been revealing dissimilar characteristic of welding processes to certain degrees when the fusion process is concerned in resistance spot welding.
59 citations
TL;DR: In this paper, a study of the fatigue life was carried out on specimens welded with the above mentioned optimized process parameters, and the results showed that for a relatively low load, corresponding to 10% of the maximum supported by the joint, the number of cycles surpasses 1.
59 citations
TL;DR: Refill friction stir spot welding (RFSSW) was applied to weld 2024-T4 aluminum alloy and effects of welding parameters on the fracture mechanisms of RFSSW tensile-shear specimens were investigated as mentioned in this paper.
Abstract: Refill friction stir spot welding (RFSSW) was applied to weld 2024-T4 aluminum alloy and effects of welding parameters on the fracture mechanisms of RFSSW tensile-shear specimens were investigated. Fracture modes are mainly determined by the bonding strengths of the lap interface and the stir zone (SZ)/thermomechanically affected zone (TMAZ) interface, which are largely influenced by heat input and sleeve plunge depth. Reasonable heat input leads to shear-plug fracture mode, which owns better mechanical properties in general. When sleeve does not penetrate into the lower plate, hook is flat and bonding ligament is continuous, shear fracture mode happens. Increased heat input improves diffusion bonding effect of the SZ/TMAZ interface but decreases hardness in SZ, which also results into shear fracture mode. Big sleeve plunge depth and downward bending hook lead to plug fracture mode. Fracture positions and fracture morphologies agree with the corresponding fracture mechanisms.
57 citations
28 Apr 2016
TL;DR: In this paper, the effect of A5052 surface states on the welding joining mechanism and mechanical properties was investigated, and the results showed that the melted PET melted and formed bubbles near the joining interface and cooled, forming hollows.
Abstract: In this research, polyethylene terephthalate (PET), as a high-density thermoplastic sheet, and Aluminum A5052, as a metal with seven distinct surface roughnesses, were joined by friction spot welding (FSW). The effect of A5052’s various surface states on the welding joining mechanism and mechanical properties were investigated. Friction spot welding was successfully applied for the dissimilar joining of PET thermoplastics and aluminum alloy A5052. During FSW, the PET near the joining interface softened, partially melted and adhered to the A5052 joining surface. The melted PET evaporated to form bubbles near the joining interface and cooled, forming hollows. The bubbles have two opposite effects: its presence at the joining interface prevent PET from contacting with A5052, while bubbles or hollows are crack origins that induce crack paths which degrade the joining strength. On the other hand, the bubbles’ flow pushed the softened PET into irregularities on the roughened surface to form mechanical interlocking, which significantly improved the strength. The tensile-shear failure load for an as-received surface (0.31 μ m Ra) specimen was about 0.4–0.8 kN while that for the treated surface (>0.31 μ m Ra) specimen was about 4.8–5.2 kN.
TL;DR: In this article, the authors analyzed the force and torque developing during friction stir spot welding (FSSW) of thermoplastic sheets varying the main process parameters, including the dwell time, tool plunge rate and rotational speed.
Abstract: The present investigation analyses the force and torque developing during friction stir spot welding (FSSW) of thermoplastic sheets varying the main process parameters. In addition, measurements of the tool temperature and those of the material close to the welding region were carried out to better understand the variation of the forces during FSSW and quality of the joints. Experimental tests involving an instrumented drilling machine were performed on polycarbonate sheets. The study involved the variation of dwell time, tool plunge rate and rotational speed. Mechanical characterization and dimensional analysis of the joints were performed in order to assess the influence of the process parameters on the joint quality under considered processing conditions. According to the achieved results, using low values of the plunging speed has beneficial effects on both the process (reduction in the force and torque) and the mechanical behaviour of the joints. Increasing the tool rotational speed results in reduced processing forces and higher material mixing and temperature. The dwell time has a negligible effect on developing forces while it highly influences the material temperature, dimension of the welded region and consequently the mechanical behaviour of the joint.
TL;DR: In this paper, a novel resistance element welding technology was applied to join 6061 Al alloy and uncoated 22MnMoB boron steel, and a technological hole was drilled in the Al sheet into which a Q235 steel rivet was inserted, and resistance spot welding was carried out at the rivet.
Abstract: A novel resistance element welding technology was applied to join 6061 Al alloy and uncoated 22MnMoB boron steel. To conduct the resistance element welding process, a technological hole was drilled in the Al sheet into which a Q235 steel rivet was inserted. Resistance spot welding was carried out at the rivet. The mechanical properties, fracture morphology, nugget formation process, dynamic resistance, microstructure, and hardness distribution of the resistance element welding were investigated. Traditional resistance spot weld joints were also prepared for comparison. Resistance spot welding could barely join Al 6061 and boron steel, and had a maximum tensile shear force of less than 1000 N. Novel resistance element welding could join the metals reliably with a maximum tensile shear force of over 7000 N and a relatively high toughness. Nugget formed at the interface of rivet and steel acted as loading position, and IMC interlayer connected rivet and aluminum.
TL;DR: In this paper, a case-study overlap joint using aluminum alloy AA2024-T3 and carbon-fiber-reinforced poly(phenylene sulfide) (CF-PPS) was produced.
Abstract: The employment of various materials (such as lightweight metal alloys and composites) with distinct physicochemical properties in the automotive and aerospace industries has opened a new field of research into the joining of dissimilar materials. Several alternative methods have recently been developed for joining metal-composite multi-material structures. Friction spot joining (FSpJ) is an innovative technique within welding-based joining technologies suitable for metal-composite structures. This work aims to address and overview different aspects of FSpJ. Case-study overlap joints using aluminum alloy AA2024-T3 and carbon-fiber-re-inforced poly(phenylene sulfide) (CF-PPS) were produced. Peak temperatures of up to 474 °C were recorded during the process. Such temperatures are well below thermal decomposition of PPS, and extensive thermal degradation of PPS was not detected by thermal analysis in this work. Microstructure analysis was performed showing usual metallurgical phenomena (recovery and dynamic re-crystallization) taking place with friction-based aluminum joining. Microstructural changes caused an alteration to the local mechanical properties as confirmed by microhardness and nanohardness measurements. Moreover, microstructural analysis of the composite part revealed the formation of a small number of volumetric defects such as pores and fiber-matrix debonding. Bonding mechanisms at the interface were studied into details by microscopy analysis and X-ray photoelectron spectroscopy. The influence of various aluminum surface pre-treatments on the bonding mechanisms and mechanical performance of single-lap shear joints was studied. In addition, fatigue life of the joints was investigated using an exponential model to obtain S-N curves. Finally, the quasi-static strength of the friction spot joints was compared with the state-of-the-art adhesive bonding. Friction spot joints showed 50 % stronger joints than adhesively bonded joints, indicating the potential of the technique to be used for joining lightweight metals to composite materials.
TL;DR: Three welding parameters including the welding time, the welding current, and the welding pressure were identified as the main effective parameters on the weld nugget dimensions including the weldnugget diameter and height using full factorial design of experiments.
Abstract: Resistance spot welding (RSW) is a highly used joining procedure in automotive industry. In RSW, after a number of welds the welding electrode starts to wear and its diameter changes. This causes the weld nugget diameter abnormal variations and consequently reduces the weld strength. Therefore the tip of the electrode should be dressed in RSW. Selecting the optimum time for the welding electrode tip dressing operations is very important. In this research three welding parameters including the welding time, the welding current, and the welding pressure were identified as the main effective parameters on the weld nugget dimensions including the weld nugget diameter and height using full factorial design of experiments. Then using hybrid combination of the artificial neural networks and multi-objective genetic algorithm, the optimized values of the aforementioned parameters were specified. Finally experiments were fulfilled to estimate the admissible number of the weld spots which should be done before the electrode tip dressing operation.
TL;DR: The early stages of formation of intermetallic compounds (IMC) have been investigated in dissimilar aluminum to steel welds, manufactured by high power ultrasonic spot welding (USW).
Abstract: The early stages of formation of intermetallic compounds (IMC) have been investigated in dissimilar aluminum to steel welds, manufactured by high power (2.5 kW) ultrasonic spot welding (USW). To better understand the influence of alloy composition, welds were produced between a low-carbon steel (DC04) and two different aluminum alloys (6111 and 7055). The joint strengths were measured in lap shear tests and the formation and growth behavior of IMCs at the weld interface were characterized by electron microscopy, for welding times from 0.2 to 2.4 seconds. With the material combinations studied, the η (Fe2Al5) intermetallic phase was found to form first, very rapidly in the initial stage of welding, with a discontinuous island morphology. Continuous layers of η and then θ (FeAl3) phase were subsequently seen to develop on extending the welding time to greater than 0.7 second. The IMC layer formed in the DC04-AA7055 combination grew thicker than for the DC04-AA6111 welds, despite both weld sets having near identical thermal histories. Zinc was also found to be dissolved in the IMC phases when welding with the AA7055 alloy. After post-weld aging of the aluminum alloy, fracture in the lap shear tests always occurred along the joint interface; however, the DC04-AA6111 welds had higher fracture energy than the DC04-AA7055 combination.
TL;DR: In this paper, a new approach to refill keyholes using the friction spot welding (FSpW) technology was developed Keyholes with a diameter of 75mm in aluminum alloy 6061-T6 rolled sheets were filled with a cylindrical plug of the same material Afterwards, the FSpW process joins the plug to the surrounding workpiece resulting in a sealed keyhole Microstructural analysis and mechanical testing of keyhole closures have been performed.
TL;DR: In this paper, Al-Si coated and galvannealed (GA) hot stamping steels were resistance spot welded, and the welding current, properties and mechanical performance of the joints produced were compared.
TL;DR: In this article, a tensile shear fatigue tests were conducted to evaluate fatigue strength and to determine the fatigue fracture mechanism, where plug type fracture occurred at high load levels, shear fracture through the nugget at medium load levels and through thickness fatigue crack propagation in the alloy at low load levels.
Abstract: Aluminium alloy sheets were joined to stainless steel ones by a resistance spot welding method using Al–Mg alloy interlayer. The interlayer exhibits a lower melting point than the Al alloy. Consequently, melted interlayer with a lower temperature filled the gap between the two sheets and resulted in effective joining. Subsequently, tensile shear fatigue tests had been conducted to evaluate fatigue strength and to determine the fatigue fracture mechanism. Resistance spot welding dissimilar welds exhibited higher fatigue strengths than friction stir spot welded dissimilar ones. Fatigue fracture modes were dependent on the load levels, where plug type fracture occurred at high load levels, shear fracture through the nugget at medium load levels and through thickness fatigue crack propagation in the Al sheet at low load levels. The fracture mode transition was attributed to the geometrical rotation around the nugget.
TL;DR: In this article, a metallo-thermo-mechanically coupled model was developed to model the temperature-dependent mechanical deformation and microstructural evolution during the ultrasonic spot welding process.
TL;DR: In this article, the deformation mechanisms of high power ultrasonic spot welding were examined using electron backscatter diffraction (EBSD) and an ultra-fine grain structure was observed in a thin band of flat weld interface within a short welding time of 0.10 s.
TL;DR: In this article, the relative motion of the sonotrode, aluminum specimens, and anvil in USW was investigated using an in-situ velocity measurement technique, Photonic Doppler Velocimetry (PDV).
01 Jun 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the feasibility of joining a low rare earth containing ZEK100 Mg alloy to 5754 Al alloy via solid-state ultrasonic spot welding (USW), and evaluate the interface microstructure, tensile lap shear strength, and fatigue life.
Abstract: The aim of this study was to examine the feasibility of joining a low rare-earth containing ZEK100 Mg alloy to 5754 Al alloy via solid-state ultrasonic spot welding (USW), and evaluate the interface microstructure, tensile lap shear strength, and fatigue life. A diffusion layer consisting of eutectic structure of α-Mg and Al12Mg17 intermetallic compound was observed to form at the interface during USW, and its thickness increased with increasing welding energy. The tensile lap shear strength first increased, reached a peak value and then decreased with increasing welding energy. The optimal average strength of ZEK100-Al5754 dissimilar joints arrived at ~78% of ZEK100-ZEK100 similar joints and ~55% of Al5754-Al5754 similar joints. The tensile lap shear test samples failed in an interfacial mode with partial cohesive failure through the interface diffusion layer and partial failure through Mg alloy, with Mg alloy sticking on the Al side. Fatigue life of samples welded at a welding energy of 500 J was longer than that at 1000 J at higher cyclic loading levels, and it became equivalent at lower cyclic loading levels. The bi-linear behavior of S-N curves corresponded well to the change in the failure characteristics. At higher cyclic loading levels interfacial failure prevailed, while the formation of transverse-through-thickness (TTT) crack at the nugget edge occurred at lower cyclic loading levels.
TL;DR: In this paper, the formation of Al-Mg intermetallic compounds was successfully prevented and strong Al/Mg resistance spot welded joints were achieved by inserting a Sn-coated steel interlayer between the two base metals before welding.
01 Mar 2016
TL;DR: In this paper, the influence of different welding parameters on the sensitivity to liquid metal embrittlement is investigated by means of spot welding in a high temperature tensile testing machine, regardless of the welding process.
Abstract: Automotive industry strives to reduce vehicle weight and therefore fuel consumption and carbon dioxide emissions. Especially in the auto body, material light weight construction is practiced, but the occupant safety must be ensured. These requirements demand high-strength steels with good forming and crash characteristics. Such an approach is the use of high- manganese-content TWIP steels, which achieve strengths of around 1,000 MPa and fracture strains of more than 60%. Welding surface-refined TWIP steels reduces their elongation at break and produces cracks due to the contact with liquid metal and the subsequent liquid metal embrittlement (LME). The results of resistance spot welds of mixed joints of high-manganese- content steel in combination with micro-alloyed ferritic steel and hot tensile tests are presented. The influence of different welding parameters on the sensitivity to liquid metal embrittlement is investigated by means of spot welding. In a high temperature tensile testing machine, the influence of different parameters is determined regardless of the welding process. Defined strains just below or above the yield point, and at 25% of elongation at break, show the correlation between the applied strain and liquid metal crack initiation. Due to the possibility to carry out tensile tests on a wide range of temperatures, dependencies of different temperatures of the zinc coating to the steel can be identified. Furthermore, the attack time of the zinc on the base material is investigated by defined heating periods.
TL;DR: In this paper, the microstructure, hardness and lap shear tensile strength of the joints were studied and the results showed that, with increasing the welding energy, the lap-shear tensil strength had an increasing trend and the hardness of aluminum metals decreased.
TL;DR: In this article, the role of welding parameters and tool profile on expelled flash properties of spot welds of 1.6mm thick AA2219-O alloy was carried out, and the result showed that tool profile greatly influences the volume and morphology of expelled flash.
TL;DR: In this article, an information acquisition and evaluation method based on the online monitoring of the weld quality of spot welded titanium alloys is proposed, and the characteristic information of the acquired signal is extracted to achieve the reliable quality assessment of the welding process.
TL;DR: In this paper, the effects of electrode tip morphology on RSW quality of DP590 dual-phase steel was analyzed using finite element (FE) model to predict the nugget shape and size, whose reliability is verified by experimental observation.
Abstract: Electrode pitting (EP) and electrode tip diameter enlargement (ETDE) are the two major representations of electrode wear, which lead to the change of electrode tip morphology and have significant impacts on the resistance spot welding (RSW) quality. In order to analyze the effects of electrode tip morphology on RSW quality of DP590 dual-phase steel, the RSW finite element (FE) model is developed to predict the nugget shape and size, whose reliability is verified by experimental observation. Tensile-shear tests are carried out to illustrate the failure behaviors. Three nugget shapes and two failure modes are obtained from different conditions of electrode tip morphology. The results show that EP morphologies produce incomplete fusion at the center of the workpieces’ faying surface, while ETDE morphologies reduce the nugget sizes. Both obvious EP and ETDE morphologies resulted in a decline of lap shear fracture load (LSFL).
TL;DR: In this article, the microstructure evolution was examined by optical microscopy, scanning electron microscopy and electron backscattered diffraction technique, and the microhardness distribution and tensile-shear load bearing capacity were measured.