Search Results (32)

Direct fusion welding of aluminum (Al) to magnesium (Mg) results in the formation of brittle intermetallic compounds (IMCs) that significantly restrict the application of these joints in structural applications. In this study, cold spray, a promising solid-state coating deposition technology, was employed to introduce a nickel (Ni) interlayer to facilitate joining of Al to Mg sheets by means of resistance spot welding (RSW). The ability of cold spraying to deposit metallic powder on the substrate without melting proves beneficial in mitigating the formation of the Al-Mg IMCs. The Ni-coated coupons were subsequently welded via resistance spot welding at optimized parameters: 27 kA for 15 cycles in two pulses with a 5-cycle inter-pulse delay. Scanning electron microscopy confirmed metallurgical bonding between the Al, Mg, and Ni coatings in the fusion zone. It is shown that the bonding between the three elements inhibits the formation of deleterious IMCs. Tensile shear testing showed joint strength exceeding 4.2 kN, highlighting the potential of the proposed cold spray RSW approach for dissimilar joining in structural applications. Full article

The use of weld bond (WB) joints in automotive manufacturing is gaining popularity for joining similar and dissimilar materials. This study investigated the effect of Sikaflex-252 (Sika Australia Pty Ltd, Perth, Australia) adhesive in DP600 similar steel joints and DP600 and AISI 316 stainless steel dissimilar steel joints. An increase in welding current from 7 kA to 10 kA increased the weld diameter and tensile shear strength in the RSW joints and the WB joints. WB joints had bigger weld diameters of 5.39 mm and 4.84 mm, higher tensile shear strengths of 12.3 kN and 6.85 kN, and higher energy absorption before failure of 32.6 J and 24.6 J at 10 kA compared to joints at 7 kA for similar and dissimilar joints, respectively. The use of adhesive increased heat generation at 10 kA welding current, due to the increase in dynamic resistance. At 7 kA welding current, the adhesive could not produce sufficient heat for spot weld development. The use of adhesive narrowed the weldability lobe in dissimilar RSW and WB joints and showed changes in failure mode. In similar RSW joints and WB joints, weldability lobe changes were not observed, and RSW and WB joints had the same fracture mode for the same welding current. WB welds have reduced stress distribution across the weld nugget compared to RSW welds because of the bigger weld diameter of 5.39 mm and lesser sheet bending of 1.13 mm. WB joint failure comprises the adhesive failure at the start and later the spot weld failure, while RSW joint failure is purely due to spot weld failure. Full article

Over the past decade, friction stir spot welding (FSSW) has gained increasing attention, making it a competitor to conventional welding methods such as resistance welding, rivets, and screws. This type of welding is environmentally friendly because it does not require welding tools and is solid-state welding. This study attempts to demonstrate the importance of pin geometry on temperature distribution and joint quality by using threaded and non-threaded pins for similar and dissimilar alloys. To this end, thermal analysis of the welded joints was conducted using real-time monitoring from a thermal camera and an infrared thermometer, in addition to finite element method (FEM) simulations. The thermal analysis showed that the generated temperatures were higher in dissimilar alloys (Al-Cu) than in similar ones (Al-Al), reaching about 350 °C. In addition, dissimilar alloys show more pronounced FSSW stages through extended periods for each plunging, dwelling, and drawing-out time. The FEM simulation results are consistent with those obtained from thermal imaging cameras and infrared thermometers. The dwelling time was influential, as the higher it was, the more heat was generated, which could be close to the melting point, especially in aluminum alloys. This study provides an in-depth experimental and numerical investigation of temperature distribution throughout the welding cycle, utilizing different pin geometries for both similar and dissimilar non-ferrous alloy joints, offering valuable insights for advanced industrial welding applications. Full article

Resistance spot welding (RSW) is now the primary joining process used in the automobile and aerospace sectors. Mechanical parts, when put into service, often undergo cyclic stress. As a result, avoiding fatigue failure should be the top priority when designing these parts. Given that spot welds are a type of localised joining that results in intrinsic circumferential notches, they increase the likelihood of stress concentrations and subsequent fatigue failures of the structure. Most of the fatigue failures in automotive parts originate around a spot weld. To that end, this study seeks to examine the mechanical properties and fatigue behaviour RSW joints made of titanium (Ti) grade 2 alloy and AISI 304 austenitic stainless steel (ASS) with equal and unequal thicknesses of 0.5 and 1 mm. Based on the mechanical properties and fatigue life results, the maximum tensile shear strength and fatigue life for the RSW titanium joint were 613 MPa and 7.37 × 10⁵ cycles for the 0.5–0.5 mm case, 374.7 MPa and 1.39 × 10⁶ cycles for the 1–1 mm case, and 333.5 MPa and 7.69 × 10⁵ cycles for the 1–0.5 mm case, respectively. The maximum shear strength and fatigue life of ASS welded joints were 526.8 MPa and 4.56 × 10⁶ cycles for the 1–1 mm case, 515.2 MPa and 3.35 × 10⁶ cycles for the 0.5–0.5 mm case, and 369.5 MPa and 7.39 × 10⁵ cycles for the 1–0.5 mm case, respectively. The assessment of the shear strength and fatigue life of the dissimilar joints revealed that the maximum shear strength and fatigue life recorded were 183.9 MPa and 6.47 × 10⁵ cycles for the 1 mm Ti–0.5 mm ASS case, 115 MPa and 3.7 × 10⁵ cycles for the 1 mm Ti–1 mm ASS case, 156 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–0.5 mm ASS case, and 129 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–1 mm ASS case. The fatigue life of titanium and stainless steel welded joints is significantly affected by the thickness, particularly at maximum applied stress (0.9% UTS), meaning that similar thicknesses achieve a greater fatigue life than unequal thicknesses. Conversely, the fatigue life of the dissimilar joint reached the greatest extent when an unequal thickness combination was used. The ductile failure of similar Ti and ASS welded joints was demonstrated by the scanning electron microscopy (SEM) examination of fatigue-fractured surfaces under the high-cycle fatigue (HCF) regime, in contrast to the brittle failure noticed in the low-cycle fatigue (LCF) regime. Brittle failure was confirmed by the SEM fatigue of dissimilar joint fractured surfaces due to interfacial failure. The Ti and ASS fractured surfaces presented river-like cleavage facets. On the Ti side, tiny elongated dimples suggest ductile failure before fracture. The topography results showed that the roughness topography parameters of similar and dissimilar fractured specimens made from Ti grade 2 and AISI 304 for the HCF regime were lower than those of the fractured specimens with LCF. The current study is expected to have practical benefits for the aerospace and automotive industries, particularly the manufacturing of body components with an improved strength-to-weight ratio. Full article

In response to the growing demand for fuel economy and the imperative to reduce greenhouse gas emissions, the automotive industry has embraced structural lightweighting through multi-material solutions. This poses challenges in joining dissimilar lightweight metals, such as aluminum alloys to steels. The effects of the diameter of a weld nugget have been well documented, particularly in relation to its effects on the tensile strength, tensile fracture modes and fatigue behavior. For tensile shear specimens, various methods have been developed over the years to predict fracture modes by deriving the critical nugget diameter. However, these methods have proved inadequate for coach peel specimens, where a noteworthy observation is the occurrence of pull-out fracture modes with smaller weld nugget diameters than the critical diameter. In the present study, aluminum alloy sheets and steel sheets were resistance spot welded, achieving a deliberately reduced weld nugget diameter to induce an interfacial fracture mode in the tensile testing of coach peel specimens. Intriguingly, it was noted that fatigue fracture modes in the same coach peel specimens transitioned from pull-out to interfacial with decreasing applied loads, challenging conventional expectations. Furthermore, finite element analysis was performed, and the findings indicated that the fracture modes of the coach peel specimens were influenced not only by the diameter of the weld nugget but also by local stress states, specifically the stress triaxiality at the tips of the spot weld notches. Full article

Resistance spot-welded joints are crucial parts in contemporary manufacturing technology due to their ubiquitous use in the automobile industry. The necessity of improving manufacturing efficiency and quality at an affordable cost requires deep knowledge of the resistance spot welding (RSW) process and the development of artificial neural network (ANN)- and machine learning (ML)-based modelling techniques, apt for providing essential tools for design, planning, and incorporation in the welding process. Tensile shear force and nugget diameter are the most crucial outputs for evaluating the quality of a resistance spot-welded specimen. This study uses ML and ANN models to predict shear force and nugget diameter responses to RSW parameters. The RSW analysis was executed on similar and dissimilar AISI 304 and grade 2 titanium alloy joints with equal and unequal thicknesses. The input parameters included welding current, pressure, welding duration, squeezing time, holding time, pulse welding, and sheet thickness. Linear regression, Decision tree, Support vector machine (SVM), Random forest (RF), Gradient-boosting, CatBoost, K-Nearest Neighbour (KNN), Ridge, Lasso, and ElasticNet machine learning algorithms, along with two different structures of Multilayer Perceptron, were utilized for studying the impact of the RSW parameters on the shear force and nugget diameter. Different validation metrics were applied to assess each model’s quality. Two equations were developed to determine the shear force and nugget diameter based on the investigation parameters. The current research also presents a prediction of the Relative Importance (RI) of RSW factors. Shear force and nugget diameter predictions were examined using SHapley (SHAP) Additive Explanations for the first time in the RSW field. Trainbr as the training function and Logsig as the transfer function delivered the best ANN model for predicting shear force in a one-output structure. Trainrp with Tansig made the most accurate predictions for nugget diameter in a one-output structure and for shear force and diameter in a two-output structure. Depending on validation metrics, the Random forest model outperformed the other ML algorithms in predicting shear force or nugget diameter in a one-output model, while the Decision tree model gave the best prediction using a two-output structure. Linear regression made the worst ML predictions for shear force, while ElasticNet made the worst nugget diameter forecasts in a one-output model. However, in two-output models, Lasso made the worst predictions. Full article

Performance and functionality are two key factors in designing advanced components. One promising approach in manufacturing design is the fabrication of multi-material structures by joining dissimilar materials. Steels, known for their outstanding properties and cost-effective production, are widely used across several industries. However, their high density presents challenges when designing lightweight components. A solution lies in combining steels with lightweight, non-ferrous alloys to develop cost-effective multi-material parts. However, joining different materials is generally complex due to their different properties, making it sometimes challenging or even unfeasible. Resistance element welding (REW) offers a high-performance alternative to traditional methods, such as resistance spot welding, with a high potential in mass production industries like automotive manufacturing. This article comprehensively reviews the latest research on REW for dissimilar joining of steels and non-ferrous alloys. It focuses on the microstructural and mechanical properties of joints, innovations in the REW process, the influence of process parameters on joint quality, as well as simulation and numerical studies. In addition, REW is compared with traditional joining methods. Full article

Aluminum–steel joints are increasingly used in the automotive industry to meet the requirements for energy saving and emission reduction. Among various joining technologies, self-pierce riveting (SPR) and resistance spot welding (RSW) are two well-established technologies for fabricating dissimilar joints with stable and high mechanical performance. However, corrosion will occur in these joints inevitably due to different electrochemical properties, which can degrade the surface quality and the mechanical performance, such as strength. This paper presents a method of understanding the corrosion mechanisms in joining aluminum and steel. For this understanding, a hybrid method combining experimental observations, mechanical properties identification, and analytical approaches was used to assess the evolution of the impact of corrosion on the joining performance, such as traction separation curves. The study was conducted on common combinations used in the vehicles, e.g., a 1.2 mm thickness aluminum alloy (AA 6022) and 2.0 mm thickness hot deep galvanized steel (HDG HSLA 340) joined by SPR and RSW. After the fabrication of these joints, accelerated cyclic corrosion tests of up to 104 cycles were performed, which reproduced the environmental conditions to which a vehicle was exposed. By investigating the microstructural evolution within the joints, the corrosion mechanisms of SPR and RSW joints were revealed, including the initiation and propagation. Moreover, the intrinsic impact of the corrosion on the mechanical performance, including the strength, axial stiffness, and crashworthiness, was analyzed by performing a lap-shear test. It showed that as corrosion proceeds, the fracture modes and mechanical performance are affected significantly. Full article

In this paper, the influence of interlayer on titanium/steel dissimilar metal resistance spot welding is reviewed from the aspects of macroscopic characteristics, microstructure and interface bonding properties of the joint. Previous studies have demonstrated that TiC, FeTi and Fe₂Ti intermetallic compounds with high brittleness are formed in the joint during titanium/steel welding, which reduces the strength of the welded joint. Researchers proposed different interlayer materials, including Cu, Ni, Nb, Ta, 60%Ni-Cu alloy and BAg45CuZn. Firstly, adding an interlayer can weaken the diffusion of Fe and Ti. Secondly, the interlayer elements can combine with Fe or Ti to form solid solutions or intermetallic compounds with lower brittleness than Fe–Ti compounds. Finally, Cu, Ni, Ag, etc. with excellent ductility can effectively decrease the generation of internal stress, which reduces the formation of defects to improve the strength of the joint. Full article

The resistance spot welding (RSW) process is still widely used to weld panels and bodies, particularly in the automotive, railroad, and aerospace industries. The purpose of this research is to examine how RSW factors such as welding current, welding pressure, welding time, holding time, squeezing time, and pulse welding affect the shear force, micro-hardness, and failure mode of spot welded titanium sheets (grade 2). Resistance spot welded joints of titanium sheets with similar and dissimilar thicknesses of 1–1 mm, 0.5–0.5 mm, and 1–0.5 mm were evaluated. The experimental conditions were arranged using the design of experiments (DOE). Moreover, artificial neural network (ANN) models were used. Different training and transfer functions were tested using the feed-forward backpropagation approach to find the optimal ANN model. According to the experimental results, the maximum shear force was 5.106, 4.234, and 4.421 kN for the 1–1, 0.5–0.5, and 1–0.5 mm cases, respectively. The hardness measurements showed noticeable improvement for the welded joints compared to the base metal. The findings revealed that the 0.5–0.5 mm case gives the highest nugget and heat-affected zone (HAZ) hardness compared to other cases. Moreover, different failure modes like pull-out nugget, interfacial, and partial failure between the pull-out nugget and interfacial failure were noticed. The ANN outcomes based on the mean squared error (MSE) and coefficient of determination (R²) as validation metrics demonstrated that using the Levenberg–Marquardt (Trainlm) training function with the log sigmoid transfer function (Logsig) gives the best prediction, where R² and MSE values were 0.98433 and 0.01821, respectively. Full article

This research focuses on analyzing the microstructural and mechanical characteristics of SS 347 and DSS 2205 stainless steel dissimilar welds. This is achieved by altering the weld parameters, welding current and heating cycle at three different levels each. In total, nine experimental trials were conducted and the welded sheets were applied to macrograph studies and a tensile shear test for analyzing the nugget quality and mechanical strength. The welded specimens were placed for observation under a scanning electron microscope (SEM) to observe the microstructure of the weldments. Specimen 9 was subjected to a microhardness test. The macrograph study revealed that the nugget size grows proportionally to the rise in the welding current and heating cycle. When the current exceeds 7.5 kA, the size of the nugget exceeds the threshold value of 4√t, where ‘t’ is the sheet metal thickness. The tensile shear test results clearly indicate that as the nugget size grows, the tensile force also rises. Sample 9 possesses a maximum tensile force of 18 kN and the mode of failure observed is influenced by the welding current and heating cycles. The failure mode of sample 9 was pulled out and the microhardness was maximum at the fusion zone with 320 HV. Full article

Friction stir spot welding (FSSW) is a technique employed to join materials in the solid state. It was first employed by the companies Mazda and Kawasaki as a novel sub-technique of friction stir welding to alternate the spot resistance welding. FSSW successively joined both similar and dissimilar metals. Tool rotational speed and dwell time are the most effective FSSW process parameters. This study investigated the role of the rotational speed of the tool and the dwell time in determining the FSSW joints’ strength using AA6061-T6 aluminum alloy sheets with a thickness of 1.8 mm as a work piece material. A classic milling machine was employed to carry out the welding process. Four different values of the rotational speed of tools with two dwell time values were taken to fabricate the FSSW joints. Four joints were made for each FSSW process condition. Three joints were averaged to determine the tensile–shear fracture load. The other specimen was employed to examine the micro-Vickers hardness and the microstructure. The investigation reported an increase in the joint strength within a certain range of tool rotational speeds and dwell time values corresponding to grain refinement in the weld zone. The variation in mechanical properties was attributed to the corresponding frictional heat generation and material flow during the welding process. Strain hardening and dynamic recrystallization determined the weld nugget hardness. Lower mechanical properties were observed with the excessive heat generation and flow of material with very high speeds and dwell time values. Full article

Joint strength was measured as a mechanical property of spot-welded joints of casting and wrought aluminum alloys. It was confirmed that the joints of casting alloys, wrought alloys and combinations of casting and wrought alloys exhibited different joint strengths. In addition, hardness measurements and microstructural observations of the melting zone revealed that the melt properties affected the joint strength of spot-welded joints. Full article

In this study, weldability and mechanical properties of resistance spot weld bonding were investigated when adhesives with different properties were used. The results show that weldability is improved in resistance spot weld bonding when the adhesive is discharged from the weld zone by using a multi-stage current application technique. In terms of mechanical properties, weld-bonded joints using high-strength adhesives showed improved strength because both the weld and the adhesive are subjected to loads. On the other hand, when a low-strength adhesive is used, the adhesive and the weld fail separately, and the CTS is not improved. In addition, in the resistance spot weld bonding of Fe-Al, the IMC formation area is expanded, and the CTS is improved by using a 3-stage current application. Full article

In this study, a dissimilar material joining of high-strength steel sheet and aluminum alloy using die- and punch-shaped electrodes was investigated. First, when resistance spot welding was performed using die- and punch-shaped electrodes, it is shown that the joint underwent large plastic deformation and that the deformation state changed as the current value was varied. Next, the IMC condition under the appropriate current condition revealed that relatively thin IMCs of 2 μm or less were distributed across the entire joining interface. Finally, the cross-tension strength of the joints was significantly improved compared to conditions using conventional R-type electrodes. Full article