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36 pages, 11303 KB

Open AccessArticle

Thermo-Mechanical Finite Element Analysis of Multi-Pass Finish Rolling of 70S-6 Welding Wire Steel: Effects of Pass Schedule, Finish Rolling Temperature, and Rolling Speed

by Lisong Zhou, Lisong Zhu, Hongqiang Liu, Cheng Ma, Li Sun, Zhengyi Jiang and Jian Han

Metals 2026, 16(1), 28; https://doi.org/10.3390/met16010028 - 26 Dec 2025

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Abstract

With the advancement of welding technology, the demand for 70S-6 welding wire steel has steadily increased in industries such as construction, automotive, pressure vessels, and line pipe manufacturing. To optimize the production process of the target material, this study utilized the finite-element software [...] Read more.

With the advancement of welding technology, the demand for 70S-6 welding wire steel has steadily increased in industries such as construction, automotive, pressure vessels, and line pipe manufacturing. To optimize the production process of the target material, this study utilized the finite-element software ABAQUS to numerically simulate the multi-pass finish rolling process of 70S-6 welding wire steel. The study investigates the effects of the key rolling parameters—pass distribution (8/10/12 passes), finish rolling temperature (860/880/900 °C), and rolling speed (0.5 Vp/1.0 Vp/1.5 Vp, here Vp denotes the reference industrial rolling speed) on the rolling force, temperature field, and equivalent stress/strain during finish rolling. The results show that the increased number of passes homogenizes deformation, reduces local stress concentration and enhances mechanical properties. Specifically, 12 passes reduce the peak rolling force from 250,972 N to 208,124 N, significantly enhancing stress and temperature uniformity across the section. Increasing the finish rolling temperature lowers the pass-averaged flow stress and attenuates rolling-force fluctuations. At 880 °C, the simulated core–surface temperature gradient is minimal (50 °C), whereas at 900 °C the gradient increases (80 °C) but the rolling-force histories exhibit a lower peak level and smaller low-frequency oscillations; thus 880 °C is preferable when through-thickness thermal uniformity is targeted, while 900 °C is more suitable when a smoother load response is required. Increasing the finish rolling speed from 0.5 Vp to 1.5 Vp reduces the peak rolling force from 233,165 N to 183,665 N and significantly damps low-frequency load oscillations. However, it concurrently intensifies stress localization at the outer-surface tracking points P3/P4, which are in direct contact with the rolls, where the local equivalent stress approaches 523 MPa, even though the overall strain distribution along the bar length becomes more uniform. Overall, the optimal processing window is identified as a 12-pass schedule, a finish rolling temperature of 880–900 °C, and a rolling speed of 1.0–1.5 Vp, which can improve both rolling quality and temperature and stress and strain uniformity. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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12 pages, 17551 KB

Open AccessArticle

Ni-Driven Martensitic Packet Refinement to Improve the Low-Temperature Impact Toughness of Simulated CGHAZ in High-Strength Steel

by Guodong Zhang, Zhongzhu Liu, Xuelin Wang, Lixia Li, Yuanyuan Li and Yanli Yang

Metals 2025, 15(12), 1382; https://doi.org/10.3390/met15121382 - 17 Dec 2025

Viewed by 185

Abstract

The effect of Ni content on the improvement of low-temperature impact toughness and microstructure refinement in a simulated coarse-grained heat-affected zone (CGHAZ) of high-strength steel was studied. The impact toughness tests revealed that as the heat input increased from 20 to 50 kJ/cm, [...] Read more.

The effect of Ni content on the improvement of low-temperature impact toughness and microstructure refinement in a simulated coarse-grained heat-affected zone (CGHAZ) of high-strength steel was studied. The impact toughness tests revealed that as the heat input increased from 20 to 50 kJ/cm, both low-nickel (L-Ni) steel and high-nickel (H-Ni) steel exhibited a rapid decline in the impact toughness of their coarse-grained heat-affected zones (CGHAZ), though the H-Ni steel consistently demonstrated significantly higher impact toughness than the L-Ni steel. Microstructural characterization showed that the microstructure of L-Ni steel gradually transitioned from lath bainite (LB) to granular bainite (GB) with increasing heat input, which accounted for its reduced impact toughness. Conversely, H-Ni steel underwent a phase transformation from lath martensite (LM) to LB with increasing heat input, showing an unexpected trend opposite to the conventional understanding of toughness enhancement. Notably, the martensitic structure obtained in H-Ni steel at 20 kJ/cm exhibited substantially higher impact energy (59.6 J) than both the LB structures of L-Ni steel (44.6 J) and those of H-Ni steel (37.8 J) observed at 20 and 50 kJ/cm heat inputs. This phenomenon is attributed to the increased Ni content significantly refining the packet of LM, thereby enhancing its resistance to brittle crack propagation. Although LB structures obtained under different conditions exhibited refined blocks, their parallel arrangement within coarse packets resulted in less effective obstruction of brittle crack propagation compared to the refined packet with interlocking arrangement. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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15 pages, 5258 KB

Open AccessArticle

Effects of Chemical Composition on Welding HAZ Softening of High-Strength Pipeline Steels

by Yu Gu, Xiao-Wei Chen, He-He Kang, Cheng-Guang Zhang, Zong-Xuan Wang and Fu-Ren Xiao

Metals 2025, 15(12), 1314; https://doi.org/10.3390/met15121314 - 28 Nov 2025

Viewed by 312

Abstract

With the increase in strength of pipeline steels manufactured by thermomechanical control process (TMCP), the softening of the welding heat-affected zone (HAZ) becomes another important factor affecting the properties of welded steel pipes and the safety of pipeline operation. In this work, based [...] Read more.

With the increase in strength of pipeline steels manufactured by thermomechanical control process (TMCP), the softening of the welding heat-affected zone (HAZ) becomes another important factor affecting the properties of welded steel pipes and the safety of pipeline operation. In this work, based on the actual welding process of steel pipes, the strength, phase transformation, and microstructure of the HAZ of six pipeline steels with different chemical compositions were studied by using a thermomechanical simulator, and the effect of chemical composition on the softening of HAZ was discussed. Results show that the strength of HAZs is significantly influenced by the peak temperature, and the softening zone mainly occurs in fine-grained HAZ (FGHAZ) when peak temperature is 900~1000 °C. Meanwhile, the degree of softening is also affected by the chemical composition of the steels. The effects of peak temperature and chemical composition of the steels on the strength of the HAZs when the peak temperature is over Ac₃ are attributed to their effect on the austenite transformation during the heating process, and then the effect on phase transformation during the cooling process and final microstructure. The strength of the HAZs is linearly related to the beginning phase temperature during the cooling process, and the strength of sub-HAZs at the same peak temperature is linearly related to the value of carbon equivalent (Ceq) of steels. Therefore, controlling the appropriate value of Ceq is necessary to improve the softening of HAZs for high-strength pipeline steels. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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20 pages, 22468 KB

Open AccessArticle

Effect of CMT Welding Heat Input on Microstructure and Mechanical Properties of Different Groove Angles for Al-6061-T6 Alloy Joint

by Guo Xian, Zhen Gao, Yunfeng Fu, Zhao Ding, Xianshu Que and Jingbang Pan

Metals 2025, 15(12), 1290; https://doi.org/10.3390/met15121290 - 25 Nov 2025

Viewed by 331

Abstract

Air suspension components are critical elements of automotive chassis and are commonly fabricated by welding 6061-T6 aluminum using 4043 filler wire with the cold metal transfer (CMT) process. Variations in vehicle architecture necessitate different groove angles and matching parameter windows. This study aims [...] Read more.

Air suspension components are critical elements of automotive chassis and are commonly fabricated by welding 6061-T6 aluminum using 4043 filler wire with the cold metal transfer (CMT) process. Variations in vehicle architecture necessitate different groove angles and matching parameter windows. This study aims to elucidate how groove angle and heat input govern weld quality to inform process optimization. Two groove angles (120° and 90°) were investigated under distinct heat-input conditions (denoted 120-H and 90-L). Characterization covered chemical composition, macroscopic morphology, porosity, microstructure, hardness, and mechanical properties. The key novelty lies in elucidating the relationship between liquation cracking and metal flow lines, which jointly govern crack propagation. Integrating evidence from porosity measurements, crack characterization, and numerical simulations indicates that the 120-H parameter set requires further optimization. Overall, the results underscore the pivotal roles of groove angle and heat input in CMT welding of 6061-T6 aluminum and provide a basis for process parameter optimization in air suspension manufacturing. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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15 pages, 11821 KB

Open AccessArticle

High-Magnification In Situ Observation of Welding Solidification

by Tamaki Ito, Shaowei Yang, Keita Marumoto, Kenji Shinozaki and Motomichi Yamamoto

Metals 2025, 15(11), 1269; https://doi.org/10.3390/met15111269 - 20 Nov 2025

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Abstract

In welding solidification, the morphology of residual liquid in the solid–liquid coexistence region affects the susceptibility to solidification cracking because this cracking is due to localized shrinkage strain in the residual liquid. Therefore, it is important to observe the residual liquid state during [...] Read more.

In welding solidification, the morphology of residual liquid in the solid–liquid coexistence region affects the susceptibility to solidification cracking because this cracking is due to localized shrinkage strain in the residual liquid. Therefore, it is important to observe the residual liquid state during solidification in detail to elucidate the occurrence of solidification cracking. In this study, a high-magnification in situ observation system was developed by combining an optical microscope and a high-speed camera. This system enables continuous, high-magnification, and high-resolution observation of welding solidification, because the objective lens of a microscope is attached to a high-speed camera. Laser welding solidification of stainless steel sheets was observed using this system and the morphology of residual liquid was visualized with higher magnification and higher definition than previous observation methods. Compared with a high-magnification image and quenched solidification microstructure, the residual state of the liquid phase during solidification could be observed in detail and dynamically. Additionally, the difference in solidification between two types of stainless sheets could be observed with high magnification in situ at one point. Finally, the combination of the observation results from this system and a high-temperature ductility curve revealed the relationship between the morphology of residual liquid and solidification cracking susceptibility. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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21 pages, 15695 KB

Open AccessArticle

Microstructure Evolution of Keyhole Repair Using Refilling Friction Stir Spot Welding of 6082 Aluminum Alloys

by Liangliang Zhang and Guijie Yue

Metals 2025, 15(9), 1029; https://doi.org/10.3390/met15091029 - 17 Sep 2025

Viewed by 524

Abstract

The keyhole defect located at the termination of the friction stir welding (FSW) seam of 6082 aluminum alloys was repaired utilizing the refilling friction stir spot technique. This study examined the impact of the plunge depths on the microstructure of the welding spot. [...] Read more.

The keyhole defect located at the termination of the friction stir welding (FSW) seam of 6082 aluminum alloys was repaired utilizing the refilling friction stir spot technique. This study examined the impact of the plunge depths on the microstructure of the welding spot. The results show that under the action of shear stress introduced by the pin, the (111)[1

\bar{1}

0] shear texture and (112)[11

\bar{1}

] Copper texture were formed. The formation of (001)[100] Cube and (001)[310] Cube_ND textures was due to the occurrence of discontinuous dynamic recrystallization. When the plunge depth of the sleeve was 1.0 mm, the volume fraction of deformed grains in the welding spot reached 45%, and the tensile strength of the welding spots was 184 MPa. When the plunge depth of the sleeve was 1.5 mm, the tensile strength of the repaired spot welding was 210 MPa, which was basically equal to the strength of the FSW seam. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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15 pages, 5165 KB

Open AccessArticle

Microstructure and Mechanical Properties of Shoulder-Assisted Heating Friction Plug Welding 6082-T6 Aluminum Alloy Using a Concave Backing Hole

by Defu Li and Xijing Wang

Metals 2025, 15(8), 838; https://doi.org/10.3390/met15080838 - 27 Jul 2025

Viewed by 653

Abstract

Shoulder-assisted heating friction plug welding (SAH-FPW) experiments were conducted to repair keyhole-like volumetric defects in 6082-T6 aluminum alloy, employing a novel concave backing hole technique on a flat backing plate. This approach yielded well-formed plug welded joints without significant macroscopic defects. Notably, the [...] Read more.

Shoulder-assisted heating friction plug welding (SAH-FPW) experiments were conducted to repair keyhole-like volumetric defects in 6082-T6 aluminum alloy, employing a novel concave backing hole technique on a flat backing plate. This approach yielded well-formed plug welded joints without significant macroscopic defects. Notably, the joints exhibited no thinning on the top surface while forming a reinforcing boss structure within the concave backing hole on the backside, resulting in a slight increase in the overall load-bearing thickness. The introduction of the concave backing hole led to distinct microstructural zones compared to joints welded without it. The resulting joint microstructure comprised five regions: the nugget zone, a recrystallized zone, a shoulder-affected zone, the thermo-mechanically affected zone, and the heat-affected zone. Significantly, this process eliminated the poorly consolidated ‘filling zone’ often associated with conventional plug repairs. The microhardness across the joints was generally slightly higher than that of the base metal (BM), with the concave backing hole technique having minimal influence on overall hardness values or their distribution. However, under identical welding parameters, joints produced using the concave backing hole consistently demonstrated higher tensile strength than those without. The joints displayed pronounced ductile fracture characteristics. A maximum ultimate tensile strength of 278.10 MPa, equivalent to 89.71% of the BM strength, was achieved with an elongation at fracture of 9.02%. Analysis of the grain structure revealed that adjacent grain misorientation angle distributions deviated from a random distribution, indicating dynamic recrystallization. The nugget zone (NZ) possessed a higher fraction of high-angle grain boundaries (HAGBs) compared to the RZ and TMAZ. These findings indicate that during the SAH-FPW process, the use of a concave backing hole ultimately enhances structural integrity and mechanical performance. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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13 pages, 2082 KB

Open AccessArticle

Laser–Arc Welding Adaptive Model of Multi-Pre-Welding Condition Based on GA-BP Neural Network

by Zesheng Wu, Zhaodong Zhang and Gang Song

Metals 2025, 15(6), 611; https://doi.org/10.3390/met15060611 - 28 May 2025

Cited by 2 | Viewed by 850

Abstract

In large welding structures, maintaining a uniform assembly condition and machined dimension in the pre-welding groove is challenging. The assembly condition and machined dimension of the pre-welding groove significantly impact the selection of the welding parameters. In this study, laser–arc hybrid welding is [...] Read more.

In large welding structures, maintaining a uniform assembly condition and machined dimension in the pre-welding groove is challenging. The assembly condition and machined dimension of the pre-welding groove significantly impact the selection of the welding parameters. In this study, laser–arc hybrid welding is used to perform butt welding on 6 mm Q345 steel in various assembly conditions, and we propose an adaptive model of the BP neural network optimized by a genetic algorithm (GA) for laser–arc welding. By employing the GA algorithm to optimize the parameters of the neural network, the relationship between the pre-welding groove parameters and welding parameters is established. The mean square error (MSE) of the GA-BP neural network is 0.75%. It is verified via experiments that the neural network can predict the welding parameters required to process a specific welding morphology under different pre-welding grooves. This model provides technical support for the development of intelligent welding systems for large and complex components. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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24 pages, 23216 KB

Open AccessArticle

Effect of Aging at Different Temperatures on Microstructure Evolution of 347H Heat-Resistant Steel-Welded Joints

by Jun Xiao, Geng Tian, Di Wang, Kuo Cao and Aimin Zhao

Metals 2025, 15(5), 518; https://doi.org/10.3390/met15050518 - 4 May 2025

Cited by 4 | Viewed by 1685

Abstract

This study used 347H heat-resistant steel as the base material and systematically investigated the microstructural evolution and second-phase precipitation in typical regions during welding and aging processes. The results showed that the weld metal consisted of austenitic dendrites and inter-dendritic ferrite in a [...] Read more.

This study used 347H heat-resistant steel as the base material and systematically investigated the microstructural evolution and second-phase precipitation in typical regions during welding and aging processes. The results showed that the weld metal consisted of austenitic dendrites and inter-dendritic ferrite in a lath-like form. In the welded samples, the HAZ (Heat-Affected Zone) and BM (Base Material) regions were composed of equiaxed crystals. The microhardness of the HAZ was lower, mainly due to the coarser grain size and fewer second-phase particles. After aging at 700 °C, the hardness of all regions of the welded joint increased significantly due to the precipitation of M₂₃C₆ and MX phases. When the aging temperature increased to above 800 °C, the stability of the M₂₃C₆ phase decreased, and the diffusion rate of Nb in the matrix accelerated, promoting the preferential growth and stable presence of the MX phase. As the MX phase competes with the M₂₃C₆ phase for carbon during its formation, its generation suppresses the further precipitation of the M₂₃C₆ phase. Under 800 °C aging conditions, the γ/δ interface exhibited high interfacial energy, and the Nb content in the ferrite was higher, which facilitated the formation of the MX phase along this interface. As the aging temperature continued to rise, the hardness of the HAZ and BM regions initially increased and then decreased. After aging at 800 °C, the hardness decreased because the M₂₃C₆ phase no longer precipitated. After aging at 900 °C, the hardness of the HAZ and BM regions significantly increased, mainly due to the large precipitation of the MX phase. The hardness of the W (Weld Zone) and FZ (Fusion Zone) regions gradually decreased with the increase in aging temperature, mainly due to the reduction of inter-dendritic ferrite content, coarsening of second-phase particles, weakening of the pinning effect, and grain growth. In the 900 °C aging samples, the MX phase particle size from largest to smallest was as follows: W > HAZ > BM. The Nb-enriched ferrite provided the chemical driving force for the precipitation of the MX phase, while the δ/γ interface provided favorable conditions for its nucleation and growth; thus, the MX phase particles were the largest in the W region. The HAZ region, due to residual stress and smaller grain boundary area, had MX phase particle size second only to the W region. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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14 pages, 8294 KB

Open AccessArticle

Study of Electrochemical Migration Behavior of Sn1.0Ag Solder

by Tianshuo Zhou, Fuye Lu, Min Shang, Yunpeng Wang and Haitao Ma

Metals 2025, 15(4), 434; https://doi.org/10.3390/met15040434 - 12 Apr 2025

Cited by 1 | Viewed by 1472

Abstract

With the enhancement of environmental protection awareness and the implementation of related regulations, lead-free soldering materials are gradually replacing the traditional leaded soldering materials in the field of electronics manufacturing. Sn–Ag soldering materials have become a research hotspot because of their good mechanical [...] Read more.

With the enhancement of environmental protection awareness and the implementation of related regulations, lead-free soldering materials are gradually replacing the traditional leaded soldering materials in the field of electronics manufacturing. Sn–Ag soldering materials have become a research hotspot because of their good mechanical properties, solderability, and thermal fatigue reliability, but their high cost limits their large-scale application. The low silver content of the Sn–Ag solder reduces the cost while maintaining an excellent performance. However, as the size of electronic components shrinks and the package density increases, the solder joint spacing decreases, the potential gradient increases, and electrochemical migration (ECM) becomes a key factor affecting the reliability of solder joints. In this study, the ECM failure process was simulated by the water droplet method, and the SEM and XPS analyses were utilized to investigate the ECM mechanism of Sn1.0Ag solder alloys, and the effects of different concentrations of NaCl solutions on their ECM were investigated. The results showed that the ECM of the Sn1.0Ag solder occurred in a 0.01 M NaCl solution, the dendritic composition was pure Sn, and the white precipitate was a mixture of Sn(OH)₂ and Sn(OH)₄. With the increase in the NaCl concentration, the corrosion resistance of the Sn1.0Ag solder alloy decreases and the ECM reaction intensifies, but with a high concentration of the NaCl solution, a large amount of precipitation hinders the migration of Sn ions, resulting in the generation of no dendrites. The present study provides new insights into the ECM behavior of a low-silver-content Sn–Ag solder system. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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22 pages, 7759 KB

Open AccessArticle

Numerical Analysis of Thermal and Flow Behaviors with Weld Microstructures During Laser Welding with Filler Wire for 2195 Al-Li Alloys

by Dejun Liu, Qihang Xv, Gan Tian, Ling Zhao, Xinzhi Yang and Maochuan Li

Metals 2025, 15(4), 348; https://doi.org/10.3390/met15040348 - 23 Mar 2025

Cited by 1 | Viewed by 1005

Abstract

This study investigates the effects of heat transfer and molten pool flow behavior on the final structure of laser filler wire welds, aiming to improve weld quality. Laser filler wire welding experiments and numerical simulations were performed on 2195 Al-Li alloy workpieces with [...] Read more.

This study investigates the effects of heat transfer and molten pool flow behavior on the final structure of laser filler wire welds, aiming to improve weld quality. Laser filler wire welding experiments and numerical simulations were performed on 2195 Al-Li alloy workpieces with varying welding parameters. Numerical simulation of the heat transfer and flow in the molten pool was carried out using the CFD method, and the moving filler wire was introduced from the computational boundary by secondary development. Simulation results indicated that reducing welding speed and increasing wire feeding rate enhanced the cooling rate of the weld. Additionally, energy absorbed by the filler wire contributed between 6% and 16% of the total energy input during the liquid bridge transition. Comparing experimental and simulation data revealed that the cooling rate significantly affected the weld’s micro-structure and hardness. Notably, the formation of the equiaxed grain zone (EQZ) was crucial for weld performance. Excessive cooling rates hindered EQZ formation, reducing flow in this critical region. These findings offer valuable insights for optimizing welding parameters to enhance weld quality and performance. Full article

(This article belongs to the Special Issue Advances in Welding and Joining of Alloys and Steel)

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