Dissimilar Resistance Spot Welds Research Articles

A novel dissimilar resistance spot welding of Ti6Al4V alloy and 316L stainless steel via copper as interlayer by using optimal electrodes

A novel dissimilar resistance spot welding of Ti6Al4V alloy and 316L stainless steel was performed via copper as interlayer by using optimal electrodes. A significant improvement in nugget morphology being of less defects was achieved with increasing the copper interlayer thickness from 50 μm to 400 μm. Thinner interfacial reaction layers at both the nugget/titanium interface and the nugget/stainless steel interface and finer equiaxed dendritic grained structure at the inner nugget were formed with copper interlayer thickness of 300 μm compared with those without interlayer. The formation of TiCu and Ti2Cu was facilitated with the incorporation of Cu into the nugget, which effectively inhibited the formation of the brittle Ti–Fe intermetallic compounds including Fe2Ti. The nugget in the welded joint with copper interlayer in 300 μm thickness exhibited a far lower microhardness than that of the interlayer-free welded joint, and the average microhardness reduced to 604 HV in the inner nugget, which was about 36% lower than that of the interlayer-free welded joint. The tensile shear load of the welded joint exhibited an increased tendency with increasing interlayer thicknesses from 50 μm to 300 μm, and the maximum tensile shear load of 6.3 kN was obtained with the interlayer thickness of 300 μm, which was ∼97% higher than that of the interlayer-free welded joint. The welded joint with copper interlayer exhibited hybrid ductile and fragile fractured characteristics. The work would provide a facile and cost-effective method to achieve a reliable welded joint of Ti alloy and stainless steel.

Fracture mechanisms of Al-steel resistance spot welds: The role of intermetallic compound phases

This study explores the mechanical and metallographic characteristics of Al-Steel dissimilar resistance spot welds (RSW), with a particular focus on the intermetallic compound (IMC) phases and their impact on fracture mechanisms. Detailed metallographic analyses and novel miniature lap shear tests with in-situ Digital Image Correlation techniques were conducted to observe the crack propagation behavior. The findings revealed that the IMC phases significantly influence the crack path and fracture mechanisms, leading to variations in fracture energy. Specifically, three distinct IMC phases were identified at the weld interface, each exhibiting unique structural and mechanical properties, with corresponding fracture energies of approximately 0.03 kJ/m2, 1.1 kJ/m2, and 7.5 kJ/m2. These variations highlight the critical role of the IMC phase in determining the fracture behavior of the weld. The study further supported the development and validation of a finite element (FE) model, incorporating a Cohesive Zone Model to simulate debonding behavior and the Hosford-Mean fracture criterion to predict ductile fracture in the Al fusion zone, thereby successfully linking local material characteristics to mechanical properties.

Characterization of Microstructure–Mechanical Properties Relationship in Dissimilar Resistance Spot Welding of the Advanced High-Strength Steel DP590 Steel to the Interstitial-Free Steel DC 06: EBSD Study

Characterization of Microstructure–Mechanical Properties Relationship in Dissimilar Resistance Spot Welding of the Advanced High-Strength Steel DP590 Steel to the Interstitial-Free Steel DC 06: EBSD Study

Failure of dissimilar QP980/DP600 advanced high strength steels resistance spot welds

This study investigates the microstructure, failure characteristics, and mechanical properties of dissimilar resistance spot welds between QP980 quenching and partitioning steel and DP600 dual phase steel. The dissimilar spot welds exhibited a heterogeneous microstructure, with a fusion zone predominantly composed of martensite, significantly overmatching both base materials. A fully martensitic structure with grain size gradient was observed in the upper-critical heat affected zone (UCHAZ) on both sides of the dissimilar joint. In the sub-critical heat affected zone (SCHAZ), no significant phase transformation occurred on both sides. However, at high welding currents, a slight tempering of pre-existing martensite was detected on the QP980 side resulting in a minor hardness drop in this zone. There was a critical welding current at which the failure mode was changed from interfacial mode to pullout mode. The dissimilar QP/DP joint showed a lower tendency to fail via interfacial failure mode compared to similar QP/QP and DP/DP joints, attributed to a higher fusion zone hardness overmatching factor and greater nugget rotation. Pullout failure of dissimilar QP/DP combination was assessed in detail through interrupted tensile shear test. It was found that failure at stronger QP980 side occurred by ductile cracking mechanism initiated from the notch tip, while failure at softer DP600 side occurred by through-thickness localized necking. The former was found to be the prior failure mechanism controlling the load bearing capacity of the dissimilar joint. The mechanical properties of dissimilar QP/DP joints were discussed in terms of peak load and energy absorption, and then were compared to those of similar DP/DP and QP/QP joints in the light of weld microstructure and failure mechanisms.

Mechanical behavior investigation for quenching and partitioning steel dissimilar resistance spot welds

Resistance spot welding is still the most common joining process for autobody structure assembly. It has many advantages and is simple to use, but the main challenge is controlling the process parameters that affect mechanical properties and weld quality. Advanced high-strength steels were developed to meet the demands of automakers such as lighter and stronger autobody. Quenching and partitioning (Q&P 980) steel is a third-generation advanced high strength steel with a combination of high strength and high ductility. In this study, effect of resistance spot welding parameters on the mechanical performance of dissimilar combination of Q&P980 steel and SPFC780Y high strength steel was investigated. Welding current, welding time, electrode pressure and holding time were chosen as the most important process parameters influencing the weld quality. A comprehensive investigation was conducted on geometrical attributes such as nugget size, fusion zone width, fusion zone area, electrode indentation and heat affected zone area and their correlations with peak load (Pmax), failure energy, fracture energy, and elongation at peak load (Lmax). In contrast the failure modes and fracture behavior were studied using scanning electron microscopy. It was observed that using high levels of welding current and welding time while maintaining low levels of electrode pressure and holding time result in a maximum peak load, energy absorption and maximum (Lmax) with pullout failure mode (PF) and this was demonstrated for large nugget size to a critical limit. The methods and findings of this research can be used as a basis for further research and development in the field of dissimilar resistance spot welding.

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.

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.

Fatigue behavior of three-sheet aluminum-steel dissimilar resistance spot welds for automotive applications

Responding to the increasing demand of multi-material solutions for structural lightweighting in automotive industry, resistance spot welding (RSW) of two sheets, e.g. aluminum to aluminum, or aluminum to steel, has been successfully developed and implemented in production using novel multi-ring domed (MRD) electrodes and multiple solidification weld schedules. In this study, we report, for the first time, the successful RSW of three sheets, i.e. 1.2 mm thick AA6022 to 0.65 mm thick high strength low alloy (HSLA) steel and 1.4 mm thick CR780T steel sheets. The resultant RSWs formed a thin layer of intermetallic compound between the aluminum-steel interface and a much smaller but completely melted weld nugget between the two steels, achieving an acceptable joint strength com-pared to RSWs of 1.2 mm thick AA6022 to itself and 1.2 mm thick AA6022 to 2.0 mm thick HSLA. Fatigue test results show that the three-sheet RSWs reached comparable fatigue behavior to that of 1.2 mm AA6022 to 2.0 mm HSLA. Using the structural stress analysis, all the fatigue data fall onto one master curve indicating that the aluminum-steel weld nugget diameter dominates the fatigue life.

A New Perspective of Post-Weld Baking Effect on Al-Steel Resistance Spot Weld Properties through Machine Learning and Finite Element Modeling

The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistance spot welds (RSWs) has been determined by machine learning (ML) and finite element modeling (FEM) in this study. A deep neural network (DNN) model was constructed to associate the spot weld performance with the joint attributes, stacking materials, and other conditions, using a comprehensive experimental dataset. The DNN model positively identified that the post-weld baking reduces the joint performance, and the extent of degradation depends on the thickness of stacking materials. A three-dimensional finite element (FE) model was then used to investigate the root cause and the mechanism of the baking effect. It revealed that the formation of high thermal stresses during baking, from the mismatch of thermal expansion between steel and Al alloy, causes damage and cracking of the brittle intermetallic compound (IMC) formed at the interface of the weld nugget during welding. This in turn reduces the joint performance by promoting undesirable interfacial fracture when the welds were subjected to externally applied loads. The FEM model further revealed that increase in structural stiffness, because of increase in steel sheet thickness, reduces the thermal stresses at the interface caused by the thermal expansion mismatch and consequently lessens the detrimental effect of post-weld baking on the joint performance.

Tensile and fatigue behavior of novel dissimilar resistance spot welds of AA5754 to steels: interplay of intermetallic layer, weld nugget diameter and notch root angle

AA5754 sheet was resistance spot welded (RSW) to high-strength low-alloy (HSLA) steel sheet and low carbon steel (LCS) sheet respectively using multi-ring domed (MRD) electrodes and multiple solidification weld schedules. The confluence of the intermetallic compound layer, weld nugget diameter, and notch root angle are delineated. The results demonstrated that elevated Mn content (0.634%) in the HSLA steel promoted the formation of a thinner and more uniform IMC layer in AA5754-HSLA stack-ups when compared to the LCS, comprised of a lower Mn content (0.130%), in the AA5754-LCS stack-ups. Diluting the alloy content by changing the HSLA sheet to LCS sheet in AA5754-steel RSWs softened the aluminum weld nugget. Fatigue results demonstrated that fatigue life in Al-steel spot welds is greater when compared to the aluminum sheet joined to itself in the tensile shear configuration. Fatigue life was greater for the positive polarity AA5754-HSLA steel RSWs than for the AA5754-LCS. While weld nugget diameter dominates weld fatigue life, manipulation of the weld notch root angle enables additional fatigue life control. To enhance fatigue life, a large notch root angle is beneficial.

Enhancement of Mechanical Properties in Dissimilar Resistance Spot Welds between Galvannealed Dual Phase and Al–Si Coated Press Hardening Steels

Enhancement of Mechanical Properties in Dissimilar Resistance Spot Welds between Galvannealed Dual Phase and Al–Si Coated Press Hardening Steels

Microstructure and tensile-shear behavior of dissimilar resistance spot welds between 2304 duplex stainless steel and Inconel 718 superalloy

Dissimilar joints between duplex stainless steels and nickel-based superalloys are of high significance in some industries. In this research, 2304 duplex stainless steel and Inconel 718 superalloy were welded by the resistance spot welding technique. The studies showed that the fusion zone microstructure was composed of a dendritic structure related to the grains of nickel-based solid solution ( γ-phase) and γ′ islands. The heat-affected zone microstructure of 2304 duplex stainless steel includes the austenite phase with a slight volume fraction and the ferrite phase with a high volume fraction. The austenite phase was formed with two morphologies of Widmanstätten and grain boundary allotriomorphs. The heat-affected zone microstructure of Inconel 718 superalloy also contained γ phase (nickel-based solid solution), annealing twins, and some precipitates. The results of the tensile-shear test revealed that tensile-shear strength (i.e. peak load) and fracture energy were increased by increasing the welding current from 1 to 2 kA and the welding time from 1 to 2 s. However, they were reduced by increasing the welding current from 2 to 4 kA and the welding time from 2 to 4 s. This was caused by the surface splash between the electrodes and the sheets. In the above-mentioned range, an increase in the welding current and time may also intensify the surface splash. It was also found that when the welding time was constant (i.e. 2 s), the spot weld obtained at the welding current of 1 kA failed by interfacial fracture mode. All spot welds obtained at the welding currents of 2, 3, and 4 kA failed by pull-out fracture mode. On the other hand, all spot welds associated with the welding times of 1, 2, 3, and 4 s failed by PF mode when the welding current was constant (i.e. 3 kA).

Spinodal liquid phase separation enabling dissimilar resistance spot welding of immiscible iron and copper alloy system

The heat un-balance and the immiscibility of the Cu and Fe alloy system are the key challenges during Cu/Fe resistance spot welding. Utilising electrodes of different geometries enabled the formation of a mixed Cu–Fe fusion zone. It is identified that despite the immiscibility of Cu and Fe in the solid-state, metastable liquid phase separation enables a metallurgical joining between Cu and Fe. The liquid phase spinodal decomposition led to the formation of an ultra-fine interconnected network of Cu-rich and Fe-rich phases in the fusion zone. The higher hardness of the fusion zone compared to the base metals, the susceptibility to solidification cracking, and the electrode indentation in the Cu sheet govern the mechanical properties of the Cu/Fe resistance spot welds.

Particle simulation of nugget formation process during steel/aluminum alloy dissimilar resistance spot welding and thickness estimation of intermetallic compounds

A steel/aluminum alloy dissimilar resistance spot welding process was simulated by a three-dimensional smoothed particle hydrodynamics method. Furthermore, the time-dependent increase in the intermetallic compound thickness at the joint interface was estimated using the obtained numerical data of temperature history. As a result, the steel sheet started to melt from the center of the sheet in the thickness direction. The convection in the molten aluminum alloy caused by the electromagnetic force promoted the heat transfer at the solid-liquid interface because the temperature gradient becomes steeper. Moreover, the maximum thickness of the intermetallic compound was estimated to be approximately 1 µm. These results support the validity of the computational model developed in this study for simulating the nugget formation process during dissimilar resistance spot welding and estimating the intermetallic compound thickness.

Dissimilar resistance spot welding process on AISI 304 and AISI 202 by investigation metals

The point of the exploration review was to examine of divergent obstruction spot welding (RSW) process on austenitic tempered steel (304 grade) and austenitic hardened steel (AISI 202 grade) is concentrated tentatively. According to a process by using 304 stainless steel is smart choice for your cost effective in comparison to other materials, due to its durability, ease of fabrication and cleaning, corrosion resistance to oxidation. The impact of cycle boundaries, for example, welding current, welding time, welding pressure and electrode force on elastic shear strength of obstruction spot welded joints are explored with reaction surface approach (RSM). Taguchi method of design experiments was applied. This research work presents the high strength and high corrosive applicants use 304 instead of 202 are used as applications such as kitchen sinks, railway bogeys, automobile trim, chemical containers. The combination of AISI 304 and AISI 202 joined together to give the accompanying outcomes is not done before with this combination and composition, this is the Novelty of this research To achieve corrosion resistance using low grade carbon steel experimental test where taken for samples such as hardness test, tensile shear strength test and morphological characteristics on scanning electron microscope (SEM) where analysed.

Effect of specimen configuration and notch root angle on fatigue behavior of novel dissimilar resistance spot welds of AA5754 to HSLA steel

Facing stringent requirements for fuel economy and regulations for greenhouse gas emissions, structural lightweighting using multi-material solutions has become commonplace in the automotive industry. When joining dissimilar materials such as aluminum to steel by resistance spot welding (RSW), a thin layer of brittle intermetallic compound forms at the aluminum-steel interface and dominates mechanical behavior of the joint. In this contribution, RSW of 1.1 mm thick AA5754 sheet to 2.0 mm thick high-strength low-alloy (HSLA) steel sheet was performed using multi-ring domed (MRD) electrodes and multiple solidification weld schedules to achieve acceptable static joint strength. Load-controlled fatigue tests were conducted and the results show that the fatigue life is longer in the AA5754 to HSLA steel spot welds than that of the 1.1 mm thick AA5754 joined to itself (aluminum-aluminum). Structural stress analysis revealed that all fatigue life data points from both the lap shear and coach peel configurations fall onto a single master curve indicating that the weld nugget diameter is the controlling parameter for fatigue life. Finite element simulation considering material inhomogeneity in the weld further confirms that a large notch root angle at the weld nugget is beneficial to yield longer fatigue life as less maximum principal strain occurs in the aluminum sheet in the AA5754-HSLA steel spot welds.

Finite element modeling of deformation and fracture of advanced high strength steels dissimilar spot welds

A finite element model is built for the prediction of deformation and fracture behavior of Usibor1500/DP600 dissimilar resistance spot welds. The model relies on image-based discretization of the weld zones, metallurgical modeling of their respective yield and hardening behavior coupled to a modified ductile damage model and a cohesive zone model at the faying surface. The model allows quantitative prediction of load bearing capacity, damage location and failure type when compared to experimental tests. It was evaluated in 24 configurations of varying weld size, sheet thickness distribution and loading type (cross tension and tensile shear). These outputs give a deeper understanding of the key parameters influencing the overall behavior of the welds and the directions for improvement. The model shows strong potential for the design of optimized heterogeneous assemblies favoring button pullout failure types and allowing to reduce the weight of the body in white in the automotive industry.

Investigation of Dissimilar Resistance Spot Welding Process of AISI 304 and AISI 1060 Steels with TLBO-ANFIS and Sensitivity Analysis

In this work, the process of dissimilar resistance spot welding (RSW) for AISI 304 and AISI 1060 steel sheets is experimentally investigated. The effects of the main process parameters such as welding current, electrode force, welding cycle, and cooling cycle on the tensile-shear strength (TSS) of dissimilar RSW joints are studied. To this aim, using a central composite experimental design based on response surface methodology (RSM), the experimental tests were performed. Furthermore, from the test results, an adaptive neuro-fuzzy inference system (ANFIS) was developed to model and estimate the TSS. The optimal parameters of the ANFIS system were obtained using a teaching-learning-based optimization (TLBO) algorithm. In order to model the process behavior, the results of experiments were used for the training (70% of the data) and testing (30% of the data) of the adaptive inference system. The accuracy of the obtained model was investigated via different plots and statistical criteria including root mean square error, correlation coefficient, and mean absolute percentage error. The findings show that the ANFIS network successfully predicts the TSS. In addition, the network error in estimating the TSS in the training and test section is equal to 0.08% and 5.87%, respectively. After modeling with TLBO-ANFIS, the effect of each input parameter on TSS of the dissimilar joints is quantitatively measured using the Sobol sensitivity analysis method. The results show that increasing in welding current and welding cycle leads to an increase in the TSS of joints. It is concluded that TSS decreases with increases in the electrode force and cooling cycle.

Particle simulation of nugget formation process during steel/aluminum alloy dissimilar resistance spot welding and thickness estimation of intermetallic compounds

Particle simulation of nugget formation process during steel/aluminum alloy dissimilar resistance spot welding and thickness estimation of intermetallic compounds

Dissimilar resistance spot welding of mild steel and stainless steel metal sheets for optimum weld nugget size

Different grades of steels are regularly used for various structural applications and it is always a difficult task to produce dissimilar welded joints. An attempt is made to weld thin sheets of mild steel (MS) and stainless steel (SS) materials by spot welding process by varying the different process parameters such as welding current, sheet thickness and different combinations of mild steel and stainless steel like MS with SS, MS with MS and SS with SS. The electrode is used as a copper and chromium alloy of 6 mm diameter. The experiment is designed as per the Taguchi L9 orthogonal approach by varying the three factors at three levels. The optimization of chosen factors and obtained weld nugget diameters as response values are performed to testify the statistical significance of the model terms by using R-square, analysis of variance (ANOVA), t and F tests, and desirability function. The outcomes will be useful in choosing the exact combinations of process parameters to achieve the desired quality spot-welded joints for automotive applications.