Resistance Spot Welding Of Steel Research Articles

Resistance Spot Welding of Stainless Steel and Titanium Plates with a Supercooled Liquid of Zr55Al10Ni5Cu30 Metallic Glass Ribbons

Resistance Spot Welding of Stainless Steel and Titanium Plates with a Supercooled Liquid of Zr55Al10Ni5Cu30 Metallic Glass Ribbons

Understanding the mechanisms behind ultrasonic vibration in resistance spot welding of aluminum and steel

An ultrasonic-assisted resistance spot welding process, which can improve the quality of aluminum/steel spot-welded joints, has been developed. However, the mechanism of the thermal-electrical-mechanical behavior caused by the ultrasonic longitudinal vibration to welding process has not been clarified. In this study, the role and impact mechanisms of ultrasonic longitudinal vibration during the welding process to form joints were confirmed by combining the microstructural characterization of the formed joints with the signal analysis of the process, as well as the analysis of the independent finite element numerical calculation results. Additionally, the interface metallurgical reaction behavior, welding defects, fracture behavior, and joint strength characteristics of ultrasonic-assisted aluminum/steel resistance spot welding joints were comprehensively analyzed, and the results indicated that the sizes of the aluminum/steel nuggets decreased. It could be attributed to the competition among multiple ultrasonic effects. Specifically, ultrasonic vibration decreased the contact resistance between the aluminum/steel sheets, whereas the acoustic cavitation and acoustic streaming effects increased the electrical conductivity of molten steel and thermal conductivity of molten aluminum, respectively. Moreover, ultrasonic vibration promoted the radial creep of molten and near-molten aluminum, which expanded in the effective bonding area between the two workpieces. Furthermore, ultrasonic vibration effectively reduced the thickness of the intermetallic compound layer (<3.0 µm), concurrently inhibited the formation of interfacial welding defects. Finally, the peak tensile-shear load of aluminum/steel joints is significantly increased under multiple ultrasonic optimization mechanisms.

Enhancing load-bearing capacity of martensitic stainless steel resistance spot welds: Microstructural vs. geometrical approaches

The load-bearing capacity of resistance spot welds is determined by a combination of weld geometrical attributes, such as the size of the weld nugget (WN), and weld metallurgical features. When resistance spot welds are made on martensitic stainless steels (MSSs), their load-bearing capacity is reduced due to the formation of a brittle martensitic microstructure within the WN. In this study, we investigated two distinct approaches to enhance the mechanical properties of AISI420 MSS spot welds. The results indicated that manipulating the WN size did not effectively produce strong welds in both tensile-shear (TS) and cross-tension (CT) tests. Therefore, we focused on examining the impact of the weld microstructure by employing two different interlayers: low carbon steel (LCS) and pure nickel. The analysis using electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA), along with equilibrium and non-equilibrium phase diagrams, revealed that the microstructure of the WN with low carbon steel interlayer of various thicknesses exhibited similarities with spot welds made without an interlayer, and the solidification mode was still δ-ferrite. This microstructure primarily consisted of martensite (M) and likely residual delta ferrite (δ) phases, resulting in no significant improvements in mechanical properties. In contrast, the utilization of the nickel interlayer led to remarkable enhancements in mechanical properties. This improvement can be attributed to a shift in the solidification mode from primary delta (δ) to austenite (γ) within an optimal interlayer thickness. This transition facilitated the development of a predominantly austenitic (γ) microstructure, contributing to the formation of an exceptionally tough microstructure within the weld nugget. Consequently, the load-bearing capacity was significantly improved.

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.

Bibliometric and systematic analysis on electric resistance spot welding of 22MnB5 steel

Bibliometric and systematic analysis on electric resistance spot welding of 22MnB5 steel

An experimental methodology to characterize load-based fracture models of third generation advanced high strength steel resistance spot welds

An experimental methodology to characterize load-based fracture models of third generation advanced high strength steel resistance spot welds

Transitioning solidification mode via electroplated Ni coatings in martensitic stainless steel resistance spot welds: new insights into fabricating tough microstructure

The present study addresses the enhancement of fracture toughness of martensitic stainless steel (MSS) spot welds by utilizing through electroplating of Ni on MSS sheets. The equilibrium and non-equilibrium solidification modelling showed that by Ni coating with 50 μm thick on 1.5 mm thick MSSs, the solidification mode changes from δ-ferrite to γ-austenite, leading to a weld nugget (WN) dominated by austenite grains. Moreover, electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) showed that the other phases (martensite, δ-ferrite) appeared in band areas of WN owing to incomplete mixing of MSS and the Ni-coating. The tough microstructure in the Ni-coated MSS spot welds provided superior mechanical properties compared to non-coated welds, both in cross-tension (CT) and tensile-shear (TS) tests. Notably, the TS and CT strengths of the Ni-coated MSS spot welds showed a remarkable increase of 57% and 127%, respectively, in comparison to the conventional bare MSS spot welds. Furthermore, in terms of failure energy, the Ni-coated MSS spot welds demonstrated a substantial enhancement of 296% in TS and 520% in CT, when compared to their non-coated counterparts. This research study showcased the effectiveness of Ni electroplating as an industrial method for improving the spot weldability of MSSs.

Optimisation and study of a welding process for aluminium and galvanised steel based on resistance welding

In this study, taking six-series aluminium alloy and DC06 galvanised steel resistance spot welding as the object of study, the impacts of the electrode cap shape and process parameters on the joint welding performance were analysed, and the electrode cap was optimised. The optimised process parameters involved the use of spherical asymmetric electrodes and a pre-welding preheating step for zinc extrusion treatment, followed by a double pulse for welding. The optimal parameters resulted in an aluminium/steel spot welding head average pull shear failure load of 2858.7 N and aluminium/aluminium spot welding head failure force of 2436 N, reaching 117.3% of its original value. The minimum force value (2253.4 N) was greater than 92.5%, and the failure section was all from the aluminium side in parent material button failure, achieving good final results.

Numerical modeling of liquid metal embrittlement initiation during resistance spot welding of third generation advanced high strength steel – Effect of welding schedule and electrode alignment

Third generation (GEN3) advanced high-strength steels are increasingly used to reduce vehicle body structure weight for improved fuel economy. Zinc-induced liquid metal embrittlement (LME) has become a prevalent challenge when these steels are welded by resistance spot welding (RSW). In the literature, various numerical models have been developed to study LME during RSW of GEN3 steels. Those models tend to have a limited utility in predicting how various factors such as RSW parameters affect LME cracking. In this study, a novel LME calculation method has been developed by integrating an electro-thermo-mechanical finite element model of RSW process with an LME ratio for crack initiation established from hot tensile testing data. The onset of different types of LME cracking is tracked throughout the weld region over the entire course of RSW including the final cooling stage after electrode retraction. The model is validated using an existing set of literature data that involves different welding schedules, electrode geometries and electrode misalignments. The local temperature and stress conditions during RSW are calculated and used to understand how different welding parameters affect the severity of LME cracking. It is found that electrode misalignment exacerbates crack initiation on outer surfaces of the spot weld due to the tensile stress arisen from the off-centered squeeze force as well as the reduced surface cooling to electrodes. Initiation of cracks between the steel sheets, taking place mainly after electrode retraction, is not significantly affected by the welding schedule and the electrode tip diameter.

Effect of coating type on electrode degradation and its life in resistance spot welding of a low carbon steel

In this study, the degradation occurring on the surface of the electrodes used in resistance spot welding of hot dip galvanized and galvannealed low carbon steels are examined and the life of the electrodes are tested. Several characterization studies are carried out on the surface and cross-sections of CuCrZr-based electrodes, following the life tests that are carried out according to SEP 1220 standard, and it is observed that a more convex degradation surface is formed on the electrode surface used in the welding of galvannealed steel compared to the galvanized one. This geometry indicates that the induced current is more stable. Depending on the increase in the number of spots, coating type and the amount of convexity, it is determined that the phases formed on the electrode surface also differ. Although the coating type has no significant effect on the welding strength value and no significant difference is observed in the maximum current values, a longer life is determined in the electrode used for the welding of galvannealed steel. It has been identified that the dominant mechanism affecting electrode life is the coating type, which is directly related to electrode degradation.

Solute Enrichment in the Fusion Zone during Resistance Spot Welding of a Third Generation Advanced High Strength Steel

Resistance spot welding is a critical joining technique in automobile assembly. The load carrying properties of spot welds are generally accepted to correlate with weld diameter, which increases with increasing weld current or duration. The formation of a softened layer, or weld halo, surrounding the fusion zone in a spot-welded third generation (Gen3) advanced high strength steel (AHSS) was recently reported in the literature. To optimize weld performance by schedule design, it is necessary to understand the halo formation characteristics and potential impacts. Accordingly, welding of a Gen3 AHSS was performed using weld times between 130 – 1300 ms. Microhardness mapping characterized weld microhardness and the evolution of the halo during welding. Electron probe microanalysis and timeof-flight secondary ion mass spectrometry enabled measurement of solute distributions through the weld halo, while scanning electron microscopy was used for microstructural characterization. The solidified structure was examined using light-optical microscopy, and with the microhardness and compositional data, used to infer the mechanism by which the halo forms during welding. It was found that the halo develops due to solute rejection from a cellular solidification front that advances towards the center of the fusion zone while weld current is applied. Extended weld times increase the size of the weld halo and the solute content of the inner fusion zone. The decrease in weld halo microhardness and the increase in inner fusion zone microhardness is largely explained by the changes in local carbon content associated with halo formation.

Competing fracture modes in Al-steel resistance spot welded structures: Experimental evaluation and numerical prediction

Multi-material design has been increasingly used in the automotive industry for structural lightweighting. A novel resistance spot welding technique has been developed to join aluminium to steel with acceptable joint strength. However, aluminium to steel resistance spot welds can fail in either interfacial (IF) or pull-out (PO) fracture modes. In the present study, coupon-level tensile shear and coach peel samples are tested under quasi-static condition, and component-level T-joint structures are tested under impact load. Experimental results show that in the IF fracture mode, weld failure occurs due to the facture of the intermetallic layer, while in the PO fracture mode, weld failure occurs due to a combination of different mechanisms including through-thickness tearing of the weld nugget and possibly partial fracture of the intermetallic layer. In the finite element analysis, two force-based fracture criteria are implemented via mesh-independent connector element considering a general loading condition, and whichever fracture potential reaches unity first determines the fracture mode. The proposed method is validated by experiments and has the following features: firstly, it can capture the behaviour of fracture mode transitioning from IF to PO as weld diameter increases; secondly, it can simulate the maximum load and deformation at fracture; thirdly, it can indicate the global response and absorbed energy in impact analysis with reasonable accuracy. Furthermore, a distinct advantage of the model is that it is free of non-physical calibration. The parameters in the model are obtained from geometric and material properties of the weld directly. The developed method shows desirable performance and is potentially suitable for applications in large-scale automotive structural analysis and design.

Improving the mechanical performance of press-hardened steel resistance spot welds via in-situ grain refinement

Improving the mechanical performance of press-hardened steel resistance spot welds via in-situ grain refinement

Effect of paint baking on the fusion boundary softening and fracture behavior of Q&P 980 steel resistance spot welds

During automotive assembly, vehicles undergo low-temperature heat treatment (paint baking) to harden the paint. Although paint baking occurs at a relatively low temperature, it can remarkably affect the weld's mechanical and fracture behavior. This work studies how paint baking improving the strength and fracture behavior of Q&P 980 spot welds exhibiting a halo ring; a low carbon enriched zone in the weld nugget. The mechanical behavior of the paint-baked welds reveals an increase in cross-tensile strength and absorbed energy when baked at 180 °C for 27 min. Microstructural observation showed that the martensite present in the as-welded conditions started to decompose into tempered martensite with ε-carbide in the martensitic matrix. Gleeble thermo-mechanical simulations of the upper-critical heat-affected zone (UCHAZ) were produced to understand the mechanical and fracture micro-and macro-mechanisms, before and after the paint baking process, by widening the regions of UCHAZ. The transmission electron microscopic analysis of the Gleeble simulated sample reveals the segregation of C, Mn, Al, and Cr along the prior austenitic grain boundary which will change the nature of bonding at these boundaries. Nevertheless, paint baking treatment helps to redistribute the segregated elements from the grain boundary to the grain interior and to eliminate the solidified liquation formed at the grain boundaries during welding. The transformation of martensite to decomposed martensite, elimination of solidified liquation due to the enhanced atomic mobility and growth of surrounding grains, and the redistribution of C, Mn, Al, and Cr from the grain boundary to interior regions of grains, are the main reasons for the improvement of mechanical properties and fracture behavior of the spot welds.

Liquid metal embrittlement in Zn-coated steel resistance spot welding: Critical electrode-contact and nugget growth for stress development and cracking

Liquid metal embrittlement (LME) crack is a severe defect which can affect the joint integrity of Zn-coated advanced high-strength steel resistance spot welds (RSW). The tensile stress that causes LME cracking is a consequence of thermal contact at the electrode-sheet interface during welding. Currently, there is no systematic study to identify the critical stages of LME occurrence during welding with understanding the tensile stress development. This research aims to address this gap by combining in-situ observation, ex-situ verification, and finite element modeling to identify the critical stages in LME cracking. The study reveals that the large LME cracks form only after a critical welding time (tcrit) of 250 ms, when the growth of the weld nugget exceeds that of the electrode-sheet contact and electrode tip-face diameter. As tcrit was attained, the LME responsible thermal gradient increased from 2000 °C/mm to 4000 °C/mm, consequently tensile stress increased from 200 MPa to 300 MPa, resulting in large LME crack. A mechanistic model explaining the effect of nugget growth rate and electrode-contact growth on thermal gradient, stress development and LME cracking was then proposed and verified through cross-comparison of crack observations. This research provides valuable insights into the critical stages of LME cracking during RSW of Zn-coated steel and suggests enhancing the growth rate of electrode-contact as a solution to mitigate this issue without altering the nugget growth rate.

Control of the Martensitic Transformation During Resistance Spot Welding of High Strength S700MC Steel

Control of the Martensitic Transformation During Resistance Spot Welding of High Strength S700MC Steel

Study on Microstructure and Mechanical Properties of a New Type of Low Ni Duplex Stainless Steel Resistance Spot Welding

Study on Microstructure and Mechanical Properties of a New Type of Low Ni Duplex Stainless Steel Resistance Spot Welding

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.

Organic mechanochromic luminescence‐based visualization of fatigue damage and life prediction of aluminum to steel resistance spot welds

AbstractDissimilar material joined structures are increasingly used in the automotive industry to reduce weight in the vehicle body structure for better fuel economy. Therefore, it is necessary to reveal the fatigue damage and develop the fatigue life prediction method of dissimilar material joined structures. Unlike conventional detection methods, mechanoresponsive luminogen‐based method can directly visualize stress distribution and fatigue crack growth. An organic mechanochromic luminescence material (TPE‐4N) is therefore used to detect the fatigue damage of coach peel Al‐steel resistance spot welds. The fatigue crack initiation and propagation are detected as visible green fluorescence under ultraviolet excitation. The results show that the fluorescence intensity increases linearly in the early stage of fatigue cycles while grows much faster in the specimen with lower fatigue life. A new fatigue life prediction method has been developed based on the response of fluorescence intensity.

Investigation of the failure mechanism of dissimilar resistance spot welding of steels

Austenitic and duplex stainless steels are majorly preferred for heat exchangers and chemical containers. This research work investigated the failure mechanism of dissimilar welded joints of AISI 347 and DSS 2205. The welded specimens were investigated using tensile shear tests, cross-tension tests, coach peel tests and microhardness tests. The specimen absorbed a maximum tensile shear load of 18 kN during the tensile shear test, and the failure mode was button pull-out with brittle fracture. The test sample absorbed a load of 15.1 kN during the cross-tension test, and the failure mode was button pull-out with brittle fracture. During the coach peel test, the sample absorbed a maximum load of 4 kN and ductile fracture was observed at the vicinity of the nugget. The failure mode in the coach peel test was of button pull-out type. The microhardness test recorded a maximum hardness of 312.8 HV, which is 78.74 and 7.1% higher than the base metal hardness values of AISI 347 and AISI 2205, respectively. The specimen failed under pull-out failure mode in all the tests, and hence, the weld zone was intact in all specimen arrangements and loading conditions.