Weld Zone Research Articles

Application of gray relational analysis for optimizing stud welding parameters of IF 7114 steel for the automotive industry

In this study, the application of stud welding to IF 7114 steel sheets in the automotive industry using stainless steel and copper-plated steel studs with different diameters and welding voltages was investigated. The aim is to optimize welding parameters and investigate their effects on the mechanical properties of the weld zone. Taguchi optimization and gray relational analysis were used to identify the best welding parameters for tensile strength and torque resistance. Results showed that the highest tensile strength and torque resistance were achieved with a stainless steel M8 stud diameter and 150 V welding voltage, while the lowest values were observed with copper-plated steel M5 studs and 180 V voltage. Additionally, stainless steel studs consistently outperformed copper-plated steel in both tensile strength and torque resistance. The study concludes that stainless steel studs, particularly with an M8 diameter at 180 V, offer the most favorable welding performance.

Electrochemical Analysis on Intergranular Corrosion of Austenitic Stainless Steel Weld in Molten Nitrate Salt

An investigation of intergranular corrosion (IGC) sensitization in molten nitrate salts of austenitic stainless steel welds of AISI 304, AISI 304H, and AISI321 produced by GTAW with ER 308L and ER 347 fillers was performed. The degree of sensitization (DOS) to IGC was assessed using a double loop electrochemical potentiokinetic reactivation and pitting potential. It was found that DOS levels in weld zones were quite low, not exceeding 15%, while those in HAZs were up to 60% after exposure at 600 °C for 300 h. The low DOS levels were due to low carbide precipitation. However, another cause of DOS was the delta-ferrite to sigma transformation in weld zones. Linear sweep voltammetry was used to quantify the sigma phase.

Multi-pass weld influence on metallurgical, tensile, impact toughness and fatigue crack growth behavior of gas tungsten arc welded Ti-6Al-4V joints

A comparative study on the influence of changing the number of weld passes on the metallurgical and mechanical properties of Ti-6Al-4 V alloy was carried out. Two welded joints involving 3-pass and 4-pass welding procedure were fabricated for 7 mm thick Ti-6Al-4 V plates using gas tungsten arc welding (GTAW) process. A compatible solid filler of Ti-6Al-4 V was used to weld these plates. A significant variation in the microstructure and the microhardness of the upper part of the fusion zones of these welds was observed. Equiaxed microstructure possessed by the base metal resulted into relatively better transverse tensile strength, ductility, and impact toughness than the 3-pass and the 4-pass weld. Widmanstätten and martensite-α′ microstructure associated with the fusion zone of the 3-pass weld resulted into a larger fraction of high angle grain boundaries (HAGBs) which accounted for higher resistance to fatigue crack propagation in this weld. Fusion zone of the 4-pass weld possessed lamellar and basketweave microstructure which had a lower fraction of HAGBs and, hence exhibited relatively lower resistance to fatigue crack propagation as compared to the 3-pass weld. However, equiaxed microstructure of the base metal could not offer much resistance to fatigue crack propagation, which resulted into relatively poor fatigue performance of the base metal. These fatigue studies indicate that both the weld joints exhibited better fatigue crack resistance than the base metal. This study established that 7 mm thick Ti-6Al-4 V joint welded using 3-pass welding procedure resulted into superior mechanical properties than those obtained by using 4-pass welding procedure.

Microstructural and mechanical investigation of dissimilar U-groove weld of IN 718/ASS 304L employing ERNiCr-3 filler

This study investigates the dissimilar welding of Inconel 718 (IN 718) and austenitic stainless steel 304L (ASS 304L) using Gas Tungsten Arc Welding (GTAW) with Ni-based filler ERNiCr-3. IN 718 is valued for its high-temperature stability, oxidation, and corrosion resistance, while ASS 304L offers excellent ductility, formability, and corrosion resistance. The objective is to evaluate the impact of ERNiCr-3 on the weld’s metallurgical and mechanical attributes. The materials, prepared with U-groove edges, were optimized for manual multi-pass welding. Microstructural analysis revealed an austenitic matrix with dispersed Ti(CN) and NbC precipitates, enhancing strength through dispersion-strengthening mechanisms, with no solidification cracking due to Nb presence. FESEM/EDS and colour mapping identified elemental migration and stable carbide formation at the weld interfaces. Mechanical testing revealed uniform hardness within the weld zone and tensile resistance of 510 MPa, underscoring the robustness of ERNiCr-3 weld metal. These results indicate that ERNiCr-3 is highly effective for producing superior quality dissimilar welds amidst IN 718/ASS 304L, making it suitable for applications in elevated-temperature and mechanically demanding environments.

Microstructure, mechanical properties, and corrosion resistance of dissimilar weld joints between SS304 and Inconel 600 welded using gas tungsten arc welding

The microstructure, mechanical characteristics, and corrosion resistance of dissimilar gas tungsten arc welding (GTAW) joints of 304 stainless steel (SS304) to Inconel 600 (IN600) with Inconel 600, using ERNiCr-3 and ERSS308 filler metals were investigated. The welding process was executed at a current of 110 Amps under argon shielding gas, and all fabricated welds successfully joined SS304 to Inconel 600 without visible cracks or porosity at the weld metal interface. Microstructural analysis with optical and scanning electron microscopy revealed a mix of columnar and equiaxed dendritic structures in the weld zone for all samples. An unmixed zone was noted at the interface on the SS304 side when welded with Inconel 600 and ERNiCr-3, attributed to the differing melting points and chemical compositions of these fillers compared to SS304. The presence of Nb and Ti in the ERNiCr-3 filler facilitated the formation of TiC and NbC carbides in the welded metal structure, resulting in higher hardness compared to other specimens. Mechanically, the ERNiCr-3 welded sample exhibited superior hardness, with the highest microhardness values recorded in the ERNiCr-3 weld metal (197–207 HV) and higher values on the SS304 side (176–194 HV) compared to the IN600 side (164–176 HV). Corrosion tests, including Tafel and Electrochemical Impedance Spectroscopy, indicated that the ERNiCr-3 weld metal had better corrosion resistance than the IN600 weld metal. Due to the differences in chemical compositions of the base metals SS304 and IN600, it is necessary to consider an appropriate filler for welding these materials. ERNiCr-3 demonstrated increased hardness due to the formation of TiC and NbC carbides, along with enhanced corrosion resistance. These properties make it a promising material for industrial applications that require durability, strength, and resistance to corrosion, particularly in high-temperature or corrosive environments.

Disclosing Connection Links between Microstructure and Mechanical Performance in Pulsating Current Gas Tungsten Arc Welding of Hastelloy B-2 Superalloy

In this study, welding a Ni-Mo-based superalloy (Hastelloy B-2) was examined in order to characterize the microstructure and mechanical performance of joints along with assessing the effects of current intensity on the microstructure and mechanical responses of different weld zones. The gas tungsten arc welding (GTAW) process was used to weld the samples using ERNiCrMo-2 filler metal. The pulsed current GTAW process was used to weld the superalloy sheets of thickness of 1 mm with background current (Ib) of 20 A and 40 A and peak current (Ip) of 80 A and 60 A. Tensile and Vickers microhardness tests were conducted to evaluate the effect of pulsed current on mechanical properties of the welds along with chemistry and microstructure characterizations. Finally, the fracture surfaces after the tensile test were studied using SEM fractography analysis. The results indicated that increasing Ib and decreasing Ip led to low heat input and high cooling rate resulting in a high thermal gradient. This caused microstructure transition from the columnar dendrites to the coaxial ones in the weld zone; molten metal convection in the fusion zone led to fine grains in the weld zone during welding time. Moreover, a significant decrease in the amount of molybdenum carbides at the interdendritic regions of the weld metal was observed under these conditions. The tensile strength of the weld metal was higher than that of the base metal resulting in the fracture of all welds from the base metal. Additionally, the microhardness results indicated a significant increase for the weld metal compared to both heat-affected zone (HAZ) and base metal. The higher mechanical properties of the weld metal is attributed to the increase in background current and decrease in peak current leading to a fine grain microstructure. Fractography following the tensile test showed a completely ductile fracture.

Achieving microstructural homogeneity in the stir zone across thick AA6061 welds using self-reacting bobbin tool friction stir welding

This study focuses into strategizing the usage of self-reacting bobbin tool friction stir welding (SRBT-FSW) to obtain consistent microstructural homogeneity along the thickness of AA6061 aluminium alloy (AA) thick plates during welding. The SRBT-FSW technology, distinguished by its dual-shoulder design, represents a significant step forward in FSW by eliminating the requirement for a backing anvil and promoting balanced heat distribution. This study seeks to address the issues of maintaining uniform microstructural characteristics throughout the weld zone, which is crucial for the mechanical performance and durability of welded joints in structural applications. The experimental study entails the systematic welding of AA6061 plates of 6 mm thickness using a self-reacting bobbin tool under a fixed processing condition. Electron backscatter diffraction (EBSD) was used to characterize the grain structure and phase distribution over the weld. Mechanical parameters like as tensile strength and hardness were determined to establish correlations between microstructure and mechanical performance. The results demonstrated that SRBT-FSW significantly enhances microstructural homogeneity across the weld zone, leading to improved mechanical properties. In the Bottom Zone (BZ), a refined grain structure with an average grain size (AGS) of 3.53 µm and a random or weak texture was observed, contributing to enhanced hardness and mechanical performance, with an ultimate tensile strength (UTS) of 220 MPa. In contrast, the Top Zone (TZ) exhibited a coarser AGS of 4.33 µm with a pronounced {111} crystallographic texture, resulting in a slightly lower UTS of 205 MPa. The Middle Zone (MZ), influenced by the greater heat input from both the TZ and BZ, showed an intermediate AGS of 3.99 µm, predominantly oriented along the {101} plane, and achieved a UTS of 194 MPa, with a slight reduction in ductility. This study highlights the potential of self-reacting bobbin tool friction stir welding as a reliable method for making high-quality, homogeneous welds in thick aluminium plates and paving way for their wider application in the aerospace, automotive, and shipbuilding industries, where homogeneous microstructural qualities are of significant importance.

Enhancement on mechanical properties via phase separation induced by Cu-added high-entropy alloy fillers in metastable ferrous medium-entropy alloy welds

This study evaluated the weldability of metastable ferrous medium-entropy alloys using high-entropy alloy fillers with various Cu contents and elucidated the strengthening mechanisms at room and cryogenic temperatures by focusing on the formation of a Cu-rich phase (FCC2) in the weld metal (WM). The WM with higher Cu content exhibited more dual face-centered cubic (FCC) phases with dendrite-shaped compositional heterogeneity due to phase separation driven by higher mixing enthalpy. The FCC2 induced greater lattice distortion, resulting in higher nano-hardness and stronger solid-solution hardening. In addition, the increased presence of FCC2 in the WM promoted grain refinement and the formation of additional grain boundaries within individual grains. After cryogenic deformation, the base metal and heat-affected zone in transverse welds underwent martensitic transformation from metastable FCC (transformation-induced plasticity), while the diluted WMs exhibited twinning-induced plasticity because of their higher stacking fault energy (SFE) compared to the base metal. The combination of these deformation mechanisms enhanced the cryogenic tensile properties without compromising ductility. Furthermore, the cryogenic tensile properties of weld with higher Cu content were further improved due to the increased formation of deformation twins in the WM. The consumption of solute Cu to form more Cu-rich FCC2 resulted in compositional variations in the matrix (FCC1), leading to a further reduction in the SFE of FCC1 and the activation of additional twin formation. Additionally, FCC2 with a relatively higher SFE refined secondary twins as well as contributed to further dislocation accumulation. This study suggests that the formation of Cu-rich phase in the WM can enhance mechanical properties at both room and cryogenic temperatures and provides a valuable approach for the future development of welding materials to improve the mechanical properties of FCC-based welded structures.

A Primary Study on the Applicability of Gel-Type Filler Materials to Root Pass Welds of the Thick Plate

Welding generally uses filler material to create deposited weld metal. Filler materials play a significant role in welding by providing the material needed to fill and form the joint. Existing filler materials are limited in the workspace and welding position and need help responding flexibly to welds of complex shapes. This study conducted primary research to develop a gel-type filler material with adhesion and flexibility that can cope with limited workspace and location. We attempted to provide a new approach to welding by mixing metal powder and binder to create a gel-type filler material. Root pass welding of thick plates was performed using a laser heat source. The bead appearance and cross-section of the weld zone were observed according to the type and composition of the metal powder, the binder content, and the method of synthesizing the metal powder. The physical characteristics of the weld were analyzed through observation of the hardness and microstructure of the weld.

Interpretation of mechanical properties gradient in laser-welded joints: Experiments and grain morphology-dependent crystal plasticity modeling

The grain size and morphology of laser welds show a gradient distribution, leading to variations in mechanical properties. This study proposes a microscopic crystal plasticity constitutive (CPC) model to examine the effect of ER4047 welding wire on the mechanical properties of laser-welded aluminum alloy joints. A finite element model updating strategy was used to fully invert the morphological mechanical parameters, marking a significant advancement. This study combines mesoscale electron backscatter diffraction (EBSD) observations with macroscopic uniaxial tensile tests to obtain crystal plasticity finite element analysis and strain field data from digital image correlation. The mechanical property gradient of the welded joints was systematically analyzed from a crystal perspective. The CPC parameters were inverted for different grain sizes and morphologies. The study found that using ER4047 welding wire significantly enhanced the mechanical properties of the welded joints, especially in the welding zone. As grain size increased, the yield strength of the material decreased, while the hardening modulus increased. Additionally, the cast characteristics of columnar crystal morphology reduced both yield strength and hardening modulus.

Optimizing weld strength and microstructure in CP-titanium and 304 stainless steel friction welds with chromium interlayer

This study investigates the effect of a Cr-interlayer on the hardness and friction-welded joint strength between CP-titanium and 304 stainless steel. Rotary friction welding, with its adjustable parameters such as upset pressure, is the preferred method for this dissimilar joint. Due to the difference between these two base metals, a metallic interlayer like chromium, is crucial for controlling the formation of intermetallic compounds (IMCs). Welding was conducted at three different upset pressures, both with and without the Cr-interlayer. Tensile and microhardness tests were performed, complemented by phase analysis and microstructural characterization using XRD and SEM. Our findings reveal that employing a chromium layer and higher upset pressures enhances strength while reducing the presence of brittle IMCs in the welds. At the CP-titanium side, dynamic recrystallization occurs due to increased heat generation at the interface and strain occurred by materials flow, facilitating IMC formation, especially evident at 250 MPa upset pressure. Interestingly, relatively higher strength at 150 MPa is attributed to the absence of IMCs. Conversely, higher strength results at 350 MPa due to from the flow of softened material, effectively purging IMCs from the weld zone. Notably, both β-titanium and chromium-based IMCs form in the presence of the chromium interlayer, resulting in decreased joint hardness and increased overall ductility. In conclusion, our study's findings contribute to bridging the gap between theoretical strength and practical application, significantly advancing joint performance.

Mechanical performance of dissimilar Al6082 aluminum and AZ91 magnesium alloy joints produced by friction stir welding

Abstract The current research work aims to produce a defect free joint of Al6082 aluminum and AZ91 magnesium alloy sheets by friction stir welding (FSW) at various tool rotational and travel speeds with an objective to obtain the best combination of welding parameters to produce quality joint. The weld joint that was produced at the combination of 1400 rpm tool rotational speed and 30 mm min−1 feed exhibited defect free stir zone. Microstructural studies carried out in the weld joint demonstrated mechanical mixing of base materials from both the alloys in the stir zone. The mixing of Al6082 and AZ91 alloys was clearly appeared in the weld zone. It can be observed that the x-ray diffraction studies clearly demonstrated the development of intermetallics in the weld region. Higher hardness was observed for the joints that can be ascertained to the presence of more mixed regions in the stir zone that contains hard and brittle intermetallics. From the tensile test data, lower strength (175.71 ± 4.24 MPa) was observed for the weld joint compared with Al6082 (242. 6 ± 11.4 MPa) and AZ91 (205.27 ± 6.39 MPa) base materials. Furthermore, the ductility of the weld joint was measured as marginally higher than the AZ91 Mg alloy and lower than the Al6082 alloy. It can be concluded that the defect free weld joints of Al6082-AZ91 alloys can be successfully produced by FSW for structural applications targeted for dry environment.

Characterization of physical metallurgy of quenching and partitioning steel in pulsed resistance spot welding: A simulation-aided study

This study mainly focuses on the microstructure evolution of QP980 steel during resistance spot welding and its influence on the mechanical performance of resistance spot welds which is a critical influencing factor on the quality of body-in-white at the service condition. It is observed that the thermomechanically engineered microstructure of QP980 steel changes to form metastable phases such as martensite in the fusion zone and the heat affected zone due to rapid cooling induced by the thermal cycle of the welding. A finite element modeling of the welding process was used to predict the weldment heat distribution, thermal history and microstructure evolution in different welding zones. The modeled thermal history of the weldments shows that the peak temperature in the four-pulse resistance spot welding is delayed because of pulsed welding conditions and holding times between the welding pulses. This heat management approach in pulsed welding prevents void formation. The modeled thermal history and rapid heating, and cooling conditions are discussed here to predict the microstructure evolution and transformation in the fusion and reheated zones. The modeled results were helpful in the prediction of the microstructure at different weld zones. Then the strategic links between the microstructure and mechanical performance of the welded alloy are discussed thoroughly. The microhardness profile of the weld is discussed from a microstructural point of view to disclose the physical metallurgy of the welds. Softening phenomena were not observed in the sub-critical heat affected zone.

Study of the effect of SMAW welding speed on the microstructure and crystal stability of X70 steel using X-ray diffraction

This study investigates the impact of manual electric arc welding (SMAW) speed on the microstructure of X70 steel. Welding was performed at two distinct speeds: S1 = 20 mm/min and S2 = 35 mm/min, at the COSIDER BISKRA workshop in Algeria. X-ray diffraction (XRD) analysis was conducted on the welded zones to examine crystal orientation, size, dislocation density, and structural stability across different welding areas, including the base metal (MB), heat-affected zones (HAZ1 and HAZ2), and weld zones (WZ1 and WZ2). The XRD results revealed that key crystal peaks, such as {110} and {200}, retained their positions at both welding speeds, though variations in {110} peak intensity were noted. The lower welding speed (S1) resulted in a higher heat input, which enhanced crystal stability, increased crystal size, and reduced dislocation density. On the other hand, the higher speed (S2) produced lower heat input, leading to smaller crystal sizes, increased residual stresses, and a greater number of defects due to rapid cooling. These findings underscore the critical influence of welding speed on heat input, cooling rates, and their consequent effects on microstructure. The study highlights the importance of optimizing welding parameters to balance microstructural integrity, mechanical performance, and production efficiency.

FEM-driven machine learning approach for characterizing stress magnitude, peak temperature and weld zone deformation in ultrasonic welding of metallic multilayers: application to battery cells

Abstract This study investigates the innovative application of machine learning (ML) models to predict critical parameters—stress magnitude (SM), peak temperature (PT), and plastic strain (PS)—in ultrasonic welding of metallic multilayers. Extensive numerical simulations were employed to develop and evaluate three ML models: Radial Basis Function (RBF), Random Forest (RF), and Kernel Ridge Regression (KRR). According to the results, the KRR model demonstrated superior performance, achieving the lowest RMSE and highest R 2 values of 0.068 (R 2 = 0.941) for SM, 0.075 (R 2 = 0.929) for PT, and 0.071 (R 2 = 0.946) for PS, with fewer data samples required. KRR also exhibited low squared bias and variance values, ranging from 1 × 10 − 4 − 3.2 × 10 − 4 for bias and 2.2 × 10 − 4 − 3.6 × 10 − 4 for variance, indicating its precision in predicting the output targets. Moreover, the systematic categorization of input features, including material properties, geometrical factors, and welding parameters, highlighted their significant influence on predictive accuracy, particularly the crucial role of welding parameters at higher output values. Finally, a case study on ultrasonic welding of copper multilayers underscores the model’s effectiveness in unraveling complex relationships, providing a robust tool for optimizing and advancing ultrasonic welding processes.

Microstructure and mechanical properties of thin-walled TA1 titanium pipes fabricated by high-frequency induction welding

High frequency induction welding (HFIW) was effectively employed for the high-speed fabrication of thin-walled TA1 titanium pipes (TWTPs) with a nominal wall thickness of ∼0.6 mm. The microstructure and mechanical properties of TWTPs manufactured under varying welding parameters were investigated. The weld zone (WZ) exhibits a waist shape measuring ∼622 μm in width, and the width of the heat-affected zone (HAZ) spans between 763 and 864 μm. Both the WZ and HAZ are composed of a mixture of coarse serrated α grains with fine acicular and twins, while the BM retains equiaxed grains. This unique microstructure was resulted from the thermal cycling during HFIW, contributing to a notable increase in microhardness within the WZ compared to both the HAZ and the BM. Optimal manufacturing conditions were identified at a welding power of 14.4 kW, a welding speed of 60 m/min, an opening angle of 6°, and a squeeze displacement of 0.2 mm, yielding the TWIP with a tensile strength of ∼307 MPa and tensile elongation of ∼27%. Tensile fracture analysis revealed that failure predominantly occurred within the BM, underlining a ductile fracture mode characterized by pronounced dimple formations. The enhanced mechanical performance of the weld joints can be attributed to the heterogenous microstructure in the WZ, where the presence of large serrated α-grains enhances ductility, and the fine martensite and twins contribute to the high strength.

Effect of water quenching into strength, hardness and microstructure of the welded AA 6061 plates

Purpose The purpose of this study is to find the effect of heat treatment on the mechanical proeprties of aluminum. Aluminum exhibits a good response to heat treatment, especially quenching, according to the mechanical property improvement. The presence and orientation of secondary phases (Al-Fe-Mn-Si) are greatly affected by the quenching process. Design/methodology/approach The present work deals with the effect of water quenching on the mechanical properties of welded AA 6061 plates which were joined by using metal inert gas (MIG) welding, tungsten inert gas welding and friction stir welding (FSW). Three tests like tensile, bending and hardness were considered. The microstructural variation was analyzed by optical microscopy and elemental mapping through field emission scanning electron microscope. Findings A significant enhancement in the tensile strength and hardness was achieved on postquenched specimens. This improvement in mechanical properties is caused by the distribution of fine alloying elements throughout the metal solution rather than precipitation at the grain boundaries. In comparison to the “untreated specimens,” an improvement of 76.7%, 25.32% and 56.81% in the tensile strength of quenched TIGW, MIGW and FSW specimens, respectively, was observed. Originality/value The quenching process has increased the strength of the MIG welded joint over the base metal. The MIG welded joint has a larger flexural modulus than the other two welded plates, according to the results of the bending test. Furthermore, a uniform distribution of hardness was observed in postquenched welded specimens. It was found that welded zone was harder than heat-affected zone. Out of all the specimens, the base metal zone has the lowest hardness.

Novel approach for in-line process monitoring during ultrasonic metal welding of dissimilar wire/terminal joints based on the thermoelectric effect

AbstractUltrasonic metal welding (USMW) is a manufacturing technique widely employed in the automotive and aerospace industries due to its efficiency in joining similar as well as dissimilar metals. Despite its prevalence, the lack of effective in-line process monitoring methods has resulted in high scrap rates, product recalls due to unrecognized scrap or financial losses due to pseudo-scrap, limiting its application in more sensitive industries. This paper presents a novel thermoelectric effect-based method for in-line process monitoring of USMW processes. This approach utilizes the thermoelectric properties, that manifest at the junctions of dissimilar metals during welding to accurately measure the temperature of the weld zone without the need of additional thermocouples, pyrometers or infrared cameras. An experimental setup was developed to validate the thermoelectric-based temperature measurement methodology. Key to this approach is the detection of thermoelectric voltage developed due to thermo diffusion when dissimilar materials are joined. The experiments showed a strong correlation between the thermoelectric voltage and the mechanical strength of the welds, suggesting that this parameter can effectively predict the quality of the weld. In the trials, a series of welded samples was created under controlled conditions to measure the generated thermoelectric voltage and correlate it with ultimate tensile strength tests. The data were analyzed using Spearman’s correlation coefficients to determine the correlation of the thermoelectric signals and joint strength. Results indicate that the thermoelectric voltage measurements correlate highly with the joint strength, with a Spearman’s correlation coefficient of over 0.94, thereby providing a promising predictive metric for assessing weld quality.

Process optimization of refill friction spot stir of AA6061-T6 aluminum alloy for thick plate

To investigate the process parameters of refillable friction stir spot welding for AA6061-T6 aluminum alloy with a 3 mm plate thickness, and to extend the applicability of this technology, experiments were conducted using custom-made tools under varying rotational and penetration speeds. This study aimed to produce well-formed welds and analyze the metallurgical structure, tensile shear strength, and microhardness of the welded joints. The experiments were performed at rotational speeds of 1000, 1200, 1400, and 1600 rpm and penetration speeds of 20, 30, 40, and 50 mm/min. These conditions were found to facilitate effective refillable friction stir spot welding. The results indicated that at lower rotational speeds, the joints failed at the interface, while at higher speeds, failure occurred through the plug. Optimal tensile shear strength was achieved at a rotational speed of 1400 rpm and a penetration speed of 30 mm/min, with a peak force of 9.27 kN and a joint surface fracture mode. Microstructural examination revealed a significant refinement of grains in the weld zone compared to the base metal. Microhardness measurements showed a concentric ring pattern on the upper surface with higher hardness at the center, decreasing toward the edges. The cross-sectional hardness demonstrated a vertical gradient, being higher at the top and decreasing toward the bottom. Notably, the welded area exhibited signs of annealing with a reduced hardness compared to the base metal, where the maximum value was recorded as HV79.

Numerical simulation and modeling of the trielectrode-coupled corrosion mechanism at the laser-welded interface of N80 steel

Laser welding, a prevalent technique in automotive structure manufacturing, can introduce compositional disparities and stresses within the weld zone, exacerbating corrosion complexity at the weld interface. This paper develops a triple galvanic corrosion model for N80 steel welds under stress conditions, leveraging the COMSOL software for simulations. The findings demonstrate that, within the elastic stress range, an elevation in stress intensifies the overall electrode surface potential, ultimately transitioning into plastic stress and fostering a more negative potential. This, in turn, amplifies the cathode-anode potential difference, rendering the material more susceptible to corrosion. The deeper the depression between the weld zone and the heat-affected zone, the higher this potential difference becomes, exacerbating the corrosion risk. Under stress, the corrosion rate markedly surpasses that observed in unstressed conditions. During the 160 day corrosion period, the weld seam and heat affected zone undergo a transition from plastic strain to elastic strain, while the base metal zone experiences both plastic strain and elastic strain simultaneously. This dynamic strain evolution leads to temporal variations in the stress-induced cathode-anode potential differences. In comparison to stress-free corrosion scenarios, the impact of stress on the cathode-anode potential difference initially intensifies, yet this effect tapers off over time.