Resistance Spot-welded Joints Research Articles

Corrosion Behavior and Mechanical Property of 5182 Aluminum/DP780 Steel Resistance Spot Welding Joints

Corrosion behavior is critical to the application of lightweight aluminum/steel joints using new resistance spot welding (RSW) technology. The study investigated the corrosion mechanism and the shear strength of RSW joints comprising 1.2 mm 5182 aluminum and 1.5 mm DP780 galvanized steel. Electrochemical corrosion tests were conducted on the base materials and various positions of the welds in a 3.5% NaCl solution. This result revealed that the corrosion susceptibility of the interfacial intermetallic compound (IMC) layer was not accelerated by the aluminum nugget because of the noble corrosion potential. Subsequently, the spray acceleration test was employed to investigate the corrosion mechanism. It is noteworthy that microcracks, as well as regions enriched with silicon and oxygen at the interface front, are preferential to corrosion during salt spray exposure, instead of the IMC layer. Moreover, the shear strength of the joints decreases with the reduction in the effective joint area after the salt spray exposure of the weld joints. This research systematically explored the corrosion behavior and its relationship with the mechanical properties of Al alloy/steel RSW joints.

Artificial Neural Networks and Experimental Analysis of the Resistance Spot Welding Parameters Effect on the Welded Joint Quality of AISI 304.

The automobile industry relies primarily on spot welding operations, particularly resistance spot welding (RSW). The performance and durability of the resistance spot-welded joints are significantly impacted by the welding quality outputs, such as the shear force, nugget diameter, failure mode, and the hardness of the welded joints. In light of this, the present study sought to determine how the aforementioned welding quality outputs of 0.5 and 1 mm thick austenitic stainless steel AISI 304 were affected by RSW parameters, such as welding current, welding time, pressure, holding time, squeezing time, and pulse welding. In order to guarantee precise evaluation and experimental analysis, it is essential that they are supported by a numerical model using an intelligent model. The primary objective of this research is to develop and enhance an intelligent model employing artificial neural network (ANN) models. This model aims to provide deeper knowledge of how the RSW parameters affect the quality of optimum joint behavior. The proposed neural network (NN) models were executed using different ANN structures with various training and transfer functions based on the feedforward backpropagation approach to find the optimal model. The performance of the ANN models was evaluated in accordance with validation metrics, like the mean squared error (MSE) and correlation coefficient (R2). Assessing the experimental findings revealed the maximum shear force and nugget diameter emerged to be 8.6 kN and 5.4 mm for the case of 1-1 mm, 3.298 kN and 4.1 mm for the case of 0.5-0.5 mm, and 4.031 kN and 4.9 mm for the case of 0.5-1 mm. Based on the results of the Pareto charts generated by the Minitab program, the most important parameter for the 1-1 mm case was the welding current; for the 0.5-0.5 mm case, it was pulse welding; and for the 0.5-1 mm case, it was holding time. When looking at the hardness results, it is clear that the nugget zone is much higher than the heat-affected zone (HZ) and base metal (BM) in all three cases. The ANN models showed that the one-output shear force model gave the best prediction, relating to the highest R and the lowest MSE compared to the one-output nugget diameter model and two-output structure. However, the Levenberg-Marquardt backpropagation (Trainlm) training function with the log sigmoid transfer function recorded the best prediction results of both ANN structures.

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.

Study on precise weld diameter validations by comparing destructive testing methods in resistance spot welding

AbstractThe torsion test is rarely used for resistance spot-welded joints since they are not subjected to torsion in applications. Normal, shear, and/or peel loads are usually the main stresses. Extensive scientific investigations in the context of Kunsmann’s dissertation date back more than 50 years. These investigations are still the basis of ISO 17653 and the German guideline DVS 2916-1. Recent scientific investigations only use torsion tests, but do not describe the reason for its use. A decisive advantage of the torsion test over the other standardized destructive testing methods lies in the types of fracture modes that occur and the properties of the fracture surfaces. Torsional loading results in either interfacial or button-pulled fracture modes. No material residues occur on the fracture surfaces for ductile and advanced high-strength steels. Hence, the measurement of weld diameter is achievable with minimal constraints, resulting in reduced variability and facilitating objective assessments of spot welds. This article delineates these attributes through a comparative analysis of various destructive testing methods employing statistical approaches. Additionally, the article expounds on the design concept of the developed rig for conducting torsion tests on spot welds.

Machine learning tool for the prediction of electrode wear effect on the quality of resistance spot welds

AbstractThe quality of resistance spot welding (RSW) joints is strongly affected by the condition of the electrodes. This work develops a machine learning-based tool to automatically assess the influence of electrode wear on the quality of RSW welds. Two different experimental campaigns were performed to evaluate the effect of electrode wear on the mechanical strength of spot welds. The resulting failure load of the joints has been used to define the weld quality classes of the machine learning tool, while data from electrode displacement and electrode force sensors, embedded in the welding machine, have been processed to identify the predictors of the tool. Some machine learning algorithms have been tested. The most performing algorithm, i.e., the neural network, achieved an accuracy of 90%. This work provides important theoretical and practical contributions. First, the decreasing thermal expansion of the weld nugget as the electrode degradation advances results in a strong correlation between the difference of the maximum displacement value and the last value recorded during the welding and the relative failure load. Then, this work offers a practical decision support tool for manufacturers. In fact, the automatic detection of low-quality welds allows to reduce or eliminate unnecessary redundant welds, which are performed to compensate for the uncertainty of electrode wear. This leads to savings in time, energy, and resources for manufacturers. Finally, general recommendations for the timing of redressing or replacing the electrode are provided in the manuscript based on the company willingness to accept some non-compliant welds or not.

Behaviour of aluminium/steel hybrid RSW joints under high cycle fatigue loading

The lightweight construction of automotive car bodies is the more important to reduce the fuel consumption and costs. High-strength steels and aluminium alloys are suitable for achieving these aims. Recent car bodies contain both materials, therefore necessary to make reliable joints between them. The resistance spot welding (RSW) can be used for joining of car bodies and it is applicable for aluminium/steel hybrid joints, too. High cycle fatigue (HCF) test results can be rarely found in the literature while HCF loading basically determines the lifetime of hybrid joints. 5754-H22, 6082-T6, and DP600 base materials were used for similar and hybrid RSW joints and HCF tests were performed. Number of cycles to failure values, failure modes, furthermore brittle intermetallic compound (IMC) layers were studied and analysed. In both aluminium/steel hybrid joints, the HCF test results showed better endurance limit like concerning aluminium/aluminium similar joints, but worse than steel/steel joints. For 5754-H22 alloy the endurance limit values are 648 N, 939 N, and 1285.5 N, for similar aluminium, hybrid, and similar steel joints, respectively. For 6082-T6 alloy these values are 513 N, 625.5 N, and 1285.5 N, respectively. In case of similar joints only base material fracture happens, but hybrid joint specimens show different failure modes. Base material fracture and shearing after partial base material fracture were typical failure modes in case of 5754-H22/DP600 and 6082-T6/DP600 hybrid joints, respectively. The full and partial plugging as a failure modes appeared for hybrid joints, too. The IMC layer characteristics showed opposite results in cases of hybrid joints, both the layer thicknesses of the shared and plugged joints and the thickness differences between the inner and outer parts of the joints were different.

Improving the performance of steel aluminum resistance spot welding joints based on steel coating design

The surface coating of steel significantly impacts intermetallic compounds (IMC) distribution and the performance of steel aluminum resistance spot welding (RSW) joints. In this paper, four sheets of steel with different surface coating were individually designed for welding with aluminum alloy. The results showed that the welded steel with coating performs better than that of Bare plate, while the welded steel with galvannealed (GA) coating has better performance than galvanized (GI) coating. The joints with GA coating failed in button pullout (PF) under tensile shear tests, while others failed in an interface (IF). The reason can be that the surface alloying zinc plating helps improve the combination reaction of Fe and Al, and the Zn will undergo a ternary combination reaction with Fe and Al to form a new compound containing Zn. The presence of the Zn layer can promote the interfacial reaction between steel and aluminum, and the welded joint performance reduces the impact of oxide film, even when the coating is thicker than 10 μm.

A multi-response optimization approach to mechanical properties improvement of dissimilar resistance spot welding joints

Purpose This study aims to investigate the effects of process input parameters (welding current, welding time, electrode pressure and holding time) on the output responses (nugget diameter, peak load and indentation) that control the mechanical properties and quality of the joints in dissimilar resistance spot welding (RSW) for the third generation of advanced high-strength steel (AHSS) quenching and partitioning (Q&P980) and (SPFC780Y) high-strength steel spot welds. Design/methodology/approach Design of experiment approach with two level factors and center points was adopted. Destructive peel and shear tensile strengths were used to measure the responses. The significant factors were determined using analysis of variance implemented by Minitab 18 software. Finally, multiresponse optimization was carried out using the desirability function analysis method. Findings Holding time was the most significant factor influencing nugget diameter, whereas welding current had the greatest impact on peak load and indentation. Multiresponse optimization revealed that the optimal settings were a welding current of 12.5 KA, welding time of 18 cycles, electrode pressure of 420 Kgf and holding time of 10 cycles. These settings produced a nugget diameter of 8.0 mm, a peak load of 35.15 KN and an indentation of 22.5%, with a composite desirability function of 0.764. Originality/value This study provides an effective approach for multiple response optimization to the mechanical behavior of RSW joints, even though there have been few studies on the third generation of AHSS joints and none on the dissimilar joints of the materials used in this study.

High Cycle Fatigue Testing of Lap Shear RSW Joints from Martensitic MS1400 Steel Sheets

Resistance spot welding (RSW) is one of the most common welding methods for steel sheets, as it is mainly used to join the automotive body structure parts. Different types of ultra-high strength steels (UHSS) have become widely used in the automotive body to obtain the required demands such as lower car weight, improving crashworthiness behavior, and enhancing strength–ductility combination. Martensitic UHSS belong to the highest grades width their tensile strength above 1000 MPa. During the lifetime of the vehicle cyclic loading generally occurs, therefore the optimization of welding technology should be performed considering the fatigue resistance of the welded joints. In our research 1 mm thick standardized lap shear sheets of martensitic MS1400 steel were welded by a TECNA 8007 RSW equipment with two different welding parameter combinations. The idea was to analyze the effect of welding and pulsation parameters on joint properties under static and cyclic loading. The welding parameters have been calibrated to produce the same weld nugget size for both technological combinations. Macroscopic, hardness, and tensile-shear tests were carried out to determine the fundamental mechanical characteristics of the RSW joints. The relation between the weld nugget microstructure and mechanical properties was explored. The high cycle fatigue (HCF) tests were performed on an MTS 810.23 universal electro-hydraulic materials testing system. A statistical approach was applied during the preparation and evaluation of the investigations, which increased their reliability. Measured and analyzed data of the lap shear welded joints, prepared by different technological parameters, were compared and discussed. The parameters of the HCF experiments were calculated considering the Japanese testing method (JSME S 002-1981). In most of the samples it was observed from both welding parameter combinations that the fatigue cracks initiate and grow in curvature shape in the softened part of the heat-affected zone towards the base metals in both directions symmetrically. A slight difference was observed in the HCF resistance of the welded joints prepared by different welding parameters.

Effect of post-welding sensitisation on the degree of sensitisation of the welding zones of AISI 304 resistance spot welding joints studied by using an electrochemical minicell

ABSTRACT In resistance spot welding (RSW) joints of austenitic stainless steel (ASS), a small-scale electrochemical cell (minicell) was used for assessing individually, on each of the three welding zones, of size less than 1000 µm (fusion zone (FZ), heat affected zone (HAZ) and base metal (BM)), the combined effect of a RSW process and post-welding sensitisation on the degree of sensitisation (DOS). The results show that the three welding zones have different microstructures that make each of them respond differently to post-welding sensitisation. The DOS varies with post-welding sensitisation time in all three welding zones, but it varies at a different rate in each welding zone (the highest rate in the FZ). This variation is due to the fact that when the DOS reaches a certain level, which is observed when plotting the reactivation charge (Qr) versus the post-welding sensitisation time, a microstructural regeneration occurs.

Prediction of the fatigue curve of high-strength steel resistance spot welding joints by finite element analysis and machine learning

The process of resistance spot welding is extensively utilized in automotive assembly. Analyzing the fatigue strength of resistance spot welded (RSW) joints of thin plate high-strength steel holds significant importance in reducing production costs and enhancing vehicle safety during operation. By combining finite element analysis (FEA) and machine learning (ML), a novel method has been developed to predict fatigue curves of RSW joints with high-strength steels of different thicknesses, widths, and nugget diameters. In this study, the impact of various experimental conditions, such as the thickness and width of the sheet material, and the diameter of the nugget, on the fatigue test results, has been quantified. Moreover, the model established through this research enables accurate prediction of the F-N fatigue curves of RSW joints without the need for fatigue testing, thereby saving costs and time required for experimentation. The average error is approximately 8% of the experimental results.

Local mechanical characterization and fracture prediction modeling for resistance spot-welded joints of advanced high-strength steel

During resistance spot-welding of advanced high-strength steel (AHSS), heat-affected zones (HAZs) are formed and mechanical properties around the welding area are altered, causing a different mechanical response from that of the base metal. This study aimed to develop a finite element modeling method for welded AHSS. Hardness measurements were conducted for JSC590, JSC980, and JSC1180 steels through nano-indentation, and their local mechanical properties were identified using miniature tensile experiments. Then, the correlations between Vickers hardness, tensile strength, and strain were quantified and applied to the shifting of the altered mechanical properties at the HAZ. In the finite element method (FEM) simulations, the nugget parts and HAZ parts of the different FEM models were defined basing on the correlations identified previously. Eventually, the fracture behaviors were elucidated in combination with the modified Mohr–Coulomb (MMC) model. The simulation results indicate that the fracture strain and tensile stress of each material were predicted within a range of 3.3∼17.2 % and 1.4∼6.3 % depending on steel grades. In addition, the behaviors of crack generation and propagation obtained through the simulation were highly consistent with the experimental results. Thus, the fracture behavior of spot-welded AHSS was accurately predicted by the more convenient hardness-based method.

Clinching of High-Strength Steel Sheets with Local Preheating

Clinching is a manufacturing method of mechanically joining two or more materials without the use of heat or additional components. This process relies on high plastic deformation to create a secure bond. Clinching technology is widely used for joining materials of various grades and thicknesses. Especially in the automotive industry, clinching is an alternative to resistance spot welding. However, the load-bearing capacity of clinched joints is comparatively lower when compared to resistance spot-welded joints. This research aimed to increase the load-carrying capacity of clinched joints. To enhance the load-bearing capacity of the clinched joints, localized modification of the microstructure was carried out, primarily focusing on the neck area of the joint. The alteration of the microstructure within the clinched joint was accomplished through the application of localized heating using the resistance spot welding method. The microstructure distribution in the clinched joint region was analyzed using light and scanning electron microscopy, as well as microhardness measurements. Two material grades, micro-alloyed steel HX420LAD+Z and dual-phase ferritic–martensitic steel HCT600X+Z, were tested. Each grade underwent five groups of ten samples, which were subjected to identical experimental conditions of local heating by resistance spot welding (RSW) and clinching. The utilization of RSW on the clinched joint region resulted in an average enhancement of 17% in the load-carrying capacity for material HCT600X+Z, and an average increase of 25% for material HX420LAD+Z.

Comparison of RSW technologies on DP steels with modified instrumented Charpy impact test

In recent decades the toughness of welded structures becomes more and more important. This trend is particularly valid for the advanced high-strength steels (AHSS), which have reduced toughness comparing to the low-strength structural steels. Dynamic characteristics of the welded joints of the newly developed high-strength steel sheets required by the automotive industry have been neglected, with welding procedures being optimized on the static joint properties, mainly on the tensile-shear force. Up to the present time, testing of dynamic properties of the spot-welded joints has been performed by increased testing speed during tensile testing. The authors have developed a new dynamic testing method and designed new testing equipment for impact bending, which can give a numeric result to characterize the resistance of spot-welded joints against dynamic load. In this paper, this method will be used to evaluate resistance spot-welded joints made on DP600 and DP800 steels with three different technological parameters, comparing long-time welding, short-time welding, and two-pulse welding. The different parameters cause different weld nugget sizes, failure modes, impact energies, and force–time diagrams. All test results show that bigger weld nugget diameters cause better impact energies and impact forces, but the differences are not perfectly correlated.

Effect of paint baking on the halo ring and mechanical behavior of 30MnB5 hot-stamped steel resistance spot welding joints

The present work investigates the effect of paint baking (PB) on the resistance spot welding (RSW) joints of 30MnB5 (1.8 GPa grade) hot-stamped (HS) steel, with focus on the halo ring and fracture behavior under cross-tension loading condition. Microstructural and elemental distribution analyses reveal that severe segregation of alloying elements occurred in the fusion zone (FZ) and that a halo ring with a martensitic structure and a width of about 78 μm was formed in the as-welded joint. The PB process resulted in uniform distribution of alloying elements and recarburization in the halo ring region, thereby drastically decreasing the halo ring width to about 33 μm, which changed the fracture behavior of the joint. Therefore, the as-welded joint failed through the halo ring, while in the PB joint, the fracture propagated partly through the FZ and then redirected through the thickness direction. The PB joints exhibited superior mechanical performance to the as-welded joint, especially the energy absorption.

Study on microstructure and mechanical properties of RSW joints of 7075T-6 containing Sc

Currently, resistance spot welding (RSW) is a common welding method used in automobile and other industries, and 7000 series aluminum (Al) alloys have become a very common industrial material because of their high strength and easy machinability. Scandium (Sc) is often used for alloy strengthening; however, there are few studies on the RSW joints of aluminum alloys containing scandium. Here, 7075-T6 alloys containing a small amount of scandium were obtained to investigate the joint of resistance spot weldability. The simulation shows that the effective contact area between the aluminum sheet surface is about 19.5%, which is an important factor in nucleation. It was found that the average grain size of the nugget decreased from 51.51 ± 5.74 to 8.15 ± 1.09 μm when scandium was added from 0 to 0.4 wt%, which is mainly due to Al3Sc particles acting as a heterogeneous nucleus in the melt. The test results show that the tensile shear strength of welded joints with 0.4 wt% scandium addition is 29.2% higher than that of the joints without scandium because of grain refinement strengthening.

Effect of intermetallic compound on the corrosion behaviour of resistance spot welding joints between 5182 aluminium alloy and galvanized DP780 dual-phase steel

Interfacial intermetallic compound (IMC) layer is critical during realizing the galvanic corrosion mechanism and strength degradation of aluminium/steel resistance spot welding (RSW) joints. The effect of IMC layer on the corrosion behaviour of RSW joint between 5182 aluminium alloy and galvanized DP780 dual-phase steel was investigated by immersion corrosion method and electrochemical method. Results demonstrated localized corrosion around Fe-rich phase particles on aluminium nugget and preferential corrosion at the interface front near IMC layer. The IMC layer had the highest open circuit potential value of −0.569 V and low corrosion current density among the investigated nugget and substrates. The potential difference (0.184 V) between the cathodic IMC layer and large area of anodic aluminium nugget was responsible for the preferential initiation of localized corrosion at the interface front near the IMC layer.

EFFECTS OF HOLDING TIME ON MICROSTRUCTURE AND SHEAR STRENGTH OF RESISTANCE SPOT-WELDED JOINTS BETWEEN MILD STEEL AND ALUMINUM WITH ZINC POWDER FILLER

This study aimed to determine effects of holding time on microstructure and shear strength of resistance spot-welded joints between mild steel and aluminum with zinc powder filler. The materials used are 0.9 mm thick mild steel, 1.2 mm thick 3000 series aluminum, and 200 mesh zinc powder. Welding parameters were selected as welding time of 0.5 seconds (s), electric currents of 8000 A and 9000 A, with holding time variations of 1 s, 3 s, and 5 s. Macro and scanning electron microscope (SEM) images follow ASTM E3-01, while ASME IX was used as tensile test standards. The macro images showed that holding time affected quality of the welded joints. Applying a longer holding time was able to reduce defects on the welded joints. SEM energy-dispersive X-ray spectroscopy (SEM-EDX) analysis exhibited that the holding time of 1 s produced a lack of density in the spot-welded joint, resulting in the existence of porosity. In contrast, increasing the holding time to 5 s gives a denser spot-welded joint with no defects found. The tensile test results showed that applying electric current of 8000 A, welding time of 0.5 s, and holding time of 1 s produced the joint with the weakest shear strength of 130 N. The highest joint shear strength of 790 N is obtained with the condition: electric current of 9000 A, welding time of 0.5 s, and holding time of 5 s.

Structural transformations in resistance spot-welded joints from Nimonic 80A superalloys

Joining of Nimonic alloys components delivered as sheets by resistance spot welding process, offers numerous advantages from technical and economic point of view. Knowing the structural modifications induced by the thermal-deformational cycle represents a very important problem in order to avoid the cracks occurrence in the welded joints.In the present paper are analysed the microstructural and the hardness characteristics in the three homogenous welding areas of the nickel super alloy, strengthened by artificial aging. The short time of the welding process and the high power density of the heating source results in a reduced heat-affected zone (HAZ). The dimensional development of the crystal grains from HAZ is negligible due to the low diffusivity of the nickel-based solid solution matrix, having a face-centred cubic lattice that inhibits the quick migration of the grain limits during the welding process.

Effect of Tempering Process on Microstructure and Properties of Resistance Spot-Welded Joints of δ-TRIP Steel

In this paper, a medium-frequency inverter spot welder was used for resistance spot-welding experiments on 980 MPa grade cold-rolled δ-TRIP(Transformation-induced Plasticity) steel. The effects of the tempering process on the morphology, microstructure, element distribution, and properties of spot-welded joints were studied by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), and Electron-Probe MicroAnalysis (EPMA). The microstructure of the nugget zone obtained by single-pulse process was δ ferrite, lath martensite, and twin martensite. After adding tempering under the single-pulse process, the microstructure was δ ferrite and lath martensite. However, the morphology of the microstructure was still dendritic, which remained unchanged. The tensile shear failure of spot-welded joints under the two processes was an interface failure, and the fractures were cleavage fractures. After adding tempering, the interface fracture surface presents two kinds of fracture characteristics: the outer cracks’ growth direction was consistent with the columnar crystal growth direction, and the inner crystal cracks occurred in the nugget core and finally grew along the columnar grain boundary. Due to the significant hardness difference between δ ferrite (283 HV) and martensite (533 HV), the low-strength δ ferrite phase was the main channel of crack propagation. After adding tempering, the hardness distribution of the spot-welded joints was more uniform and the tensile shear force increased (7.4 kN→8.5 kN).