10 April 2026, Volume 18 Issue 4

    

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Light Alloy Forming
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  Influence of Extrusion Rate on Evolution of LPSO Phase and Dynamic Recrystallization of Mg-Gd-Y-Zn-Zr Alloys

  DU Zelong, ZHANG Zhirou, GUO Enyu, WANG Tongmin

  Journal of Netshape Forming Engineering. 2026, 18(4): 1-10. https://doi.org/10.3969/j.issn.1674-6457.2026.04.001

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  Aiming at the challenge of poor formability in high-strength magnesium alloys, the work aims to optimize the microstructure and mechanical properties of Mg-Gd-Y-Zn-Zr alloys by modulating the extrusion rate, so as to provide a new theoretical basis for the thermomechanical processing of high-ductility magnesium alloys. Hot extrusion experiments were conducted at 480 ℃ and 0.1 mm/s and 1 mm/s. The microstructural evolution, second-phase distribution, dynamic recrystallization behavior, and texture characteristics of the extruded samples were examined by optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Room-temperature tensile tests were performed to evaluate the mechanical properties. After extrusion, the microstructure consisted of elongated deformed grains and dynamically recrystallized grains. The second phases were distributed in an elongated morphology along grain boundaries, while lamellar LPSO phases were dynamically precipitated within the grains. The degree of their bending deformation significantly increased with the increase of extrusion rate. With the increase of extrusion rate, the volume fraction of dynamic recrystallization increased, leading to a significant decrease in alloy strength, while the elongation was only improved slightly. In conclusion, although increasing the extrusion rate can improve plasticity to a certain extent, it will cause a significant reduction in strength, which is not conducive to the comprehensive mechanical properties of the alloy. The strength and plasticity matching of the alloy is regulated by the extrusion rate which influences the degree of dynamic recrystallization and texture characteristics. Therefore, it is a key technological path to reasonably choose an appropriate extrusion rate for optimizing the strength-plasticity balance of magnesium alloys.
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  Cryogenic Mechanical Properties and Machine Learning Prediction Model of Ti6554 Titanium Alloy

  LIU Chuankun, QU Zhoude, WU Chuan

  Journal of Netshape Forming Engineering. 2026, 18(4): 11-23. https://doi.org/10.3969/j.issn.1674-6457.2026.04.002

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  The work aims to study the mechanical behavior and microstructural evolution of Ti-6554 titanium alloy subject to cryogenic conditions, elucidating the underlying mechanisms governing temperature-dependent property variations. Load-displacement curves were captured via a liquid nitrogen-integrated tensile testing apparatus, while temperature-dependent mechanisms governing mechanical properties were probed through comprehensive analysis of true stress-strain curves, fractographic observations, work hardening rate quantification, and electron backscatter diffraction (EBSD) characterization. Based on these findings, a Support Vector Regression optimized by Particle Swarm Algorithm (PSO-SVR) and an Error Back-Propagation neural network model (EBP) were formulated. Experimental outcomes revealed that progressive temperature reduction induced significant flow stress elevation of Ti-6554 titanium alloy, where twin-dislocation interactions were found to enhance yield strength yet diminish elongation. Crucially, a fracture mode transition from ductile to ductile-brittle mixed failure was documented across the 0 ℃ to -180 ℃ regime. Model validation demonstrated optimal R² values of 0.94 and 0.98 for PSO-SVR and EBP respectively, with corresponding mean RMSE of 11.12 MPa and 4.01 MPa, and mean MAE of 9.024 MPa and 2.067 MPa, conclusively establishing the superior predictive capability of the EBP framework. Cryogenic temperatures substantially enhance both the yield strength and ultimate tensile strength of the material. This strengthening is fundamentally attributed to increased interatomic bonding forces, which elevates the lattice friction resistance that dislocation slip must overcome, coupled with the diminished thermal activation energy available for dislocations to surmount obstacles. However, this strengthening is accompanied by degradation in plasticity, manifested as reduced elongation. As the tensile temperature decreases from 0 ℃ to -180 ℃, the alloy's dominant fracture mechanism shifts from ductile fracture to a ductile-brittle mixed fracture. The developed EBP neural network prediction model demonstrates significantly superior predictive accuracy compared to the PSO-SVR model.
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  Forming Process and Optimization of Straight-wall Ribbed Irregular Al-Mg-Zn Alloy Wire Clamps

  HU Ning, ZHANG Zhimin, REN Xianwei, LI Zhiyong

  Journal of Netshape Forming Engineering. 2026, 18(4): 24-32. https://doi.org/10.3969/j.issn.1674-6457.2026.04.003

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  To solve the problems of severe flash and low material utilization in the current production of a straight-wall ribbed irregular aluminum alloy wire clamp via open-die forging, the work aims to design a forming die with a closed cavity structure and optimize the geometric parameters of the pre-forged part matching the finishing die cavity, achieving precision die forging of the wire clamp. Finite element simulations were carried out in Deform-3D for two forming processes. By optimizing the shape and dimensions of the pre-forged part, the appropriate die structure and pre-forged part geometry were determined. Orthogonal experiments were further conducted to investigate the effects of forming temperature and strain rate on forming load and strain distribution, and the suitable forming process parameters for the aluminum alloy wire clamp were obtained. Finally, the feasibility of the forming scheme was verified through experimental trials. Simulation analysis determined the appropriate shape and dimensions of the pre-forged part and the forming die for the straight-wall ribbed irregular aluminum alloy wire clamp. Orthogonal experiment optimization yielded the optimal forming process parameters for the wire clamp as follows: forming temperature of 450 ℃ and extrusion speed of 1 mm/s, which successfully resolved the issues of excessive flash and insufficient filling of the highest straight wall during forming. Compared with the final formed part obtained from the open-die forging pre-forged part, the closed-die forging process achieved a 31.39% increase in material utilization, a 69.9% reduction in flash area, and a 56.73% decrease in forming load. The finite element simulation optimization results indicate that compared with the open-die forging process, the straight-wall ribbed irregular aluminum alloy wire clamp prepared by the closed-die forging process exhibits higher material utilization, smaller machining allowance area, fuller filling, and lower forming load. The wire clamp is successfully formed on a 1 600 t press, and its dimensions meet practical production requirements.
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  Effect of High-temperature Oxidation Treatment on the Corrosion Resistance of Mg-Nd Alloys

  XIA Shouxin, YUE Siyu, WANG Li, LONG Jiabao, WANG Qinghang

  Journal of Netshape Forming Engineering. 2026, 18(4): 33-44. https://doi.org/10.3969/j.issn.1674-6457.2026.04.004

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  The work aims to investigate the corrosion behavior and corrosion resistance of as-cast Mg-xNd alloys (x=1.1%, 5.5% and 9.9%) and high-temperature oxidized Mg-xNd alloys in a 3.5 wt.% NaCl solution. The corrosion resistance of alloy samples was compared and analyzed with hydrogen evolution method and electrochemical method. The phase composition of alloy samples was obtained by X-ray diffractometer. The microscopic morphology characteristics of alloy samples before and after corrosion were observed by scanning electron microscopy. The corrosion depth of alloy samples after removal of corrosion products was analyzed by laser confocal microscopy. Under both the as-cast condition and the high-temperature oxidation treatment conditions, the corrosion rate of alloy samples increased with the increasing content of Nd element. Especially in the high-Nd content as-cast alloy, the Mg₁₂Nd phase and the magnesium matrix suffered severe galvanic corrosion, significantly reducing the corrosion resistance of alloy samples. However, the sample surface after high-temperature oxidation formed a dense Nd₂O₃/MgO composite protective film, which further isolated the chloride ions from eroding the magnesium matrix and effectively improved the corrosion resistance of alloys. Among them, the corrosion resistance of the Mg-1.1% Nd alloy in the high-temperature oxidation state was the most outstanding. The corrosion resistance of alloy samples is the result of the combined effects of Nd element content, phase composition, heat treatment state and oxide film structure. Although the increase in Nd element content leads to an increase in the corrosion rate of alloys, through high-temperature oxidation treatment, a dense Nd₂O₃/MgO composite protective film can be formed with the Nd element, thereby partially counteracting its promoting effect on corrosion and achieving an improvement in corrosion resistance.
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  Effect of HFC-134a Concentration on High-temperature Oxidation Behaviour of Mg-8Gd-4Y Alloy

  ZHAO Xinyi, XIAO Yao, QIN Hong, SUN Yang, LI Tianqing

  Journal of Netshape Forming Engineering. 2026, 18(4): 45-55. https://doi.org/10.3969/j.issn.1674-6457.2026.04.005

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  The work aims to systematically investigate the effect of HFC-134a concentration on the high-temperature oxidation behavior of magnesium alloys to elucidate the flame-retardant mechanism of HFC-134a/CO₂ mixed gases, determine the optimal concentration range of HFC-134a for developing effective protective atmospheres for magnesium alloys. The Mg-8Gd-4Y alloy was selected as the experimental material. Isothermal oxidation experiments were conducted under varying temperature and HFC-134a concentrations. The composition and microstructure of the resulting oxide layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thermodynamic calculations were performed to analyze the formation mechanism of protective oxide layers. Results demonstrated that increasing HFC-134a concentration promoted the transformation of oxide layers from MgO to a composite structure containing MgF₂ and rare-earth oxides. At 600 ℃ (solid-state oxidation), discontinuous rare-earth oxide layers dominated by Y₂O₃ were observed. In contrast, at 700 ℃ (liquid-state oxidation), continuous rare-earth oxide layers with increased Gd₂O₃ content were formed. The findings indicate that while higher HFC-134a concentrations enhance the protective properties of oxide layers, concentrations exceeding 10% lead to deteriorated surface quality of castings. Therefore, a 10% HFC-134a/CO₂ mixed gas is recommended as the optimal protective atmosphere for magnesium alloy processing.
Additive Manufacturing
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  Research Status in Aluminum Alloy Additive Manufacturing from a Patent Analytics Perspective

  WANG Xiaoli, JING Huaiyu

  Journal of Netshape Forming Engineering. 2026, 18(4): 56-68. https://doi.org/10.3969/j.issn.1674-6457.2026.04.006

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  The work systematically analyzes global patent data related to aluminum alloy additive manufacturing since 2011, with a focus on patent application trends, geographical distribution, key technical subcategories, major applicants, and core patents, to comprehensively map the intellectual property landscape and provide references for further research. The findings reveal that the technology lifecycle of aluminum alloy additive manufacturing has progressed through emergence, growth, and maturity stages. Geographically, China, the United States, and the EPO dominate patent filings. Regarding patent flows among major patent offices, the United States, France, and Japan dominate in patent outflows, while the EPO, the United States, and China rank as the top three recipients of patent inflows. Key technical clusters include alloys based on aluminium, additive manufacturing of workpieces or articles from metallic powder, metallic powder and its treatment, e.g. to facilitate working or to improve properties, manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering, apparatus specially adapted therefor. Among top applicants, France’s Constellium leads with 118 patents, followed by Central South University (53 patents) and Shanghai JiaoTong University (42 patents). Among major applicants, Chinese applicants predominantly concentrate their filings domestically, while foreign applicants maintain significant patent portfolios in non-home countries. Additionally, among the top 5 most cited patents, three originate from the United States and two from China.
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  Hot Deformation Behavior and Hot Workability of Mg/Al Bimetals Prepared by Cold Spray Additive Manufacturing

  ZHANG Qixu, LIU Sitong, LONG Jinchuan, LIN Yongcheng, DENG Lei, HAN Xu

  Journal of Netshape Forming Engineering. 2026, 18(4): 69-78. https://doi.org/10.3969/j.issn.1674-6457.2026.04.007

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  The work aims to explore flow behavior and process window during hot deformation of Mg/Al bimetals prepared by cold spray additive manufacturing. Firstly, Mg/Al bimetal specimens were fabricated by cold spray. Subsequently, hot-compression tests were conducted at temperatures from 523 K to 673 K, strain rates from 0.001 s^-1 to 1 s^-1 and a maximum true strain of 50%. By analyzing the flow curve characteristics of the Mg/Al bimetal, an Arrhenius-type high-temperature constitutive model based on the Zener-Hollomon parameter was established and the activation energy for hot deformation under various conditions was calculated and displayed as a 3D activation-energy map. In addition, a 3D processing map was constructed with a modified dynamic material model combined with the Murty instability criterion. Superimposing the activation-energy map and the processing map yielded an activation-energy-processing map that delineated flow-instability regimes and safe deformation domains. The flow curves exhibited pronounced dynamic-recrystallization softening with the increasing strain and were highly sensitive to temperature and strain rate. The flow stress decreased as temperature rose and strain rate dropped. The established high-temperature constitutive model is capable of precisely predicting the flow stress of bimetals under different deformation conditions. The optimal process window obtained based on the activation energy-processing map is a temperature range of T=530 K to 570 K and a strain rate of $\dot{\varepsilon}$=0.001-0.006 s^-1.
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  Evolution of Microstructure and Defects of High-strength Steels Fabricated by Plasma Arc Deposition

  GUO Zhenghua, LU An, ZHAO Mingjie, OUYANG Xianghai, TU Junyang, JIANG Lihong

  Journal of Netshape Forming Engineering. 2026, 18(4): 79-89. https://doi.org/10.3969/j.issn.1674-6457.2026.04.008

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  The work aims to optimize the forming quality of 300M steel manufactured by plasma arc additive manufacturing. Taking 300M steel as the research object, a combination of experiment and finite element simulation was used to investigate the dynamic evolution of the temperature field during the cooling process of the deposited layer on the influence law of the microstructure and defects of plasma deposited 300M steel. The results showed that the thickness of the equiaxed grain region of the deposited layer was mainly related to the amount of powder fed per unit length, which increased with the increase of the amount of powder fed per unit length, and there was no significant relationship with the plasma arc current. However, the monotonous linear relationship between the percentage of equiaxed grains in the sedimentary layer and the amount of powder delivered per unit length was not presented. To investigate the influence law of process parameters on the evolution mechanism of equiaxed grains in the deposited layer, a columnar grains-equiaxed grains transformation prediction model was established, and the prediction error was 4%. In addition, it was found from the micro-defect analysis that the porosity decreased with the increase of the bulk energy density. The optimized process parameters based on volumetric energy density were a welding current of 150 A, a scanning speed of 0.06 m/min, and a powder feed rate of 9 g/min, and the porosity under the optimized process parameters decreased to 0.37%. During the additive manufacturing process, the smaller the temperature gradient and the greater the solidification rate, the more conducive it is to the formation of equiaxed grains. Volumetric energy density has a significant influence on porosity. Increasing volumetric energy density can effectively reduce porosity.
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  CMT Arc Additive Manufacturing Process of Gradient Transition High-strength Wear-resistant Layer

  WU Jiaxin, WANG Jinfeng, GUO Yi, LI Wenjuan, WEI Jiaan

  Journal of Netshape Forming Engineering. 2026, 18(4): 90-98. https://doi.org/10.3969/j.issn.1674-6457.2026.04.009

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  The work aims to study the formation of a gradient transition high-strength wear-resistant layer on the surface of high-strength die steel by CMT arc additive manufacturing, so as to obtain a composite cladding layer to improve the surface hardness and wear resistance and prolong the service life of the die. Based on CMT arc additive manufacturing technology, a composite cladding layer with hardness gradient transition was designed by selecting appropriate welding materials. With the general H13 die steel as the substrate, FK1000 welding wires were used as the intermediate transition layer, and YD322 welding wires were used as the high-strength wear-resistant layer for layer-by-layer cladding to achieve the purpose of gradient transition of hardness and toughness. The microstructure and mechanical properties of the composites after cladding were studied. The results showed that the macroscopic forming of the cladding samples was good and there were no obvious metallurgical defects. The high-strength wear-resistant layer was mainly composed of fine lath martensite and retained austenite. The transition layer was mainly bainite and ferrite, and the tempering structure appeared in the secondary heating zone and the heat-affected zone. The hardness of the composite cladding layer from the substrate to the transition layer to the high-strength wear-resistant layer was gradient, and the hardness increased step by step. The hardness of the composite increased from 248HV of the substrate to 581HV of the wear-resistant layer, and the hardness increased by 135%. The impact toughness decreased slightly from 12 J of the substrate to 9.3 J of the composite sample. And the fracture mode was cleavage fracture. The wear mass of the wear-resistant layer was 1.3 mg, and the wear coefficient was 0.365. Compared with the substrate, the wear mass was reduced by 69.7%, and the average wear coefficient was reduced from 0.43 to 0.365.
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  Dimensional Characteristics and Mechanical Properties of Support-free Arc Additive Manufactured Cr13Ni5Mo Stainless Steel

  CHENG Chuanshi, QIN Yanping, CHEN Weidong, XU Ning, MA Taide, CAI Xin

  Journal of Netshape Forming Engineering. 2026, 18(4): 99-107. https://doi.org/10.3969/j.issn.1674-6457.2026.04.010

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  For arc additive manufacturing based on large non-overturnable components, directly applying conventional arc additive forming processes is prone to issues such as flow, humping, and insufficient strength. Therefore, the work aims to study the forming process of support-free arc additive manufacturing. The arc cold metal transfer technology was used to additively manufacture Cr13Ni5Mo stainless steel on a vertical substrate. A mathematical model of arc additive manufacturing process parameters and forming morphology was established. The impact of wire feed speed, welding speed, and torch deflection angle on the cross-sectional dimensions of a single weld bead was investigated. Based on the quadratic regression fitting equation, the optimal process parameters were selected to form a single-layer multi-bead specimen, and the mechanical properties of the specimen were tested. The specimen was prepared completely according to specifications, and the tensile mechanical properties of the support-free arc additive manufactured Cr13Ni5Mo stainless steel were tested with a universal tensile testing machine. The mathematical model prediction was consistent with the actual results. Based on the ANOVA results, the F-values for the regression models of weld width, weld reinforcement height, and reinforcement deviation were 18.64, 9.78, and 8.99, respectively. Using a significance level of α=0.01 and referencing the F-distribution table with degrees of freedom f_R, f_Q, the critical value F_0.99 (f_R, f_Q)=4.94 was determined. Since all computed F-values exceeded this critical value, the statistical significance level for each model surpassed 99%. The wire feed speed had the most significant impact on weld width, the welding speed had a significant impact on reinforcement, and the torch deflection angle had the greatest impact on the amount of reinforcement offset. The tensile mechanical property test results showed that the average transverse tensile strength was 1 017.3 MPa, with an elongation of 13.7%, and the average longitudinal tensile strength was 1 067.5 MPa, with an elongation of 15.6%. The support-free arc additive manufacturing forming process based on Cr13Ni5Mo stainless steel in this work not only controls defects such as flow and humping but also contributes to excellent mechanical properties, providing a reference for subsequent in-situ additive manufacturing of large components.
Advanced Joining Technology
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  Design of PAW-GTAW Hybrid Welding Platform and Exploration of Hybrid Welding Process

  WANG Hao, SONG Zhenghao, DING Tongming, LI Tianqing, BAO Jian, CHEN Changxin

  Journal of Netshape Forming Engineering. 2026, 18(4): 108-116. https://doi.org/10.3969/j.issn.1674-6457.2026.04.011

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  The work aims to study the PAW-GTAW hybrid welding process, achieve a synergistic effect of “1+1>2”, and obtain higher-quality and more efficient hybrid welded joints. A self-designed PAW-GTAW hybrid welding platform was constructed for experimentation. Firstly, by capturing the changes of each process arc before and after coupling and measuring the arc voltage and current signals, the static characteristics of the arc before and after coupling were further analyzed, thereby preliminarily exploring the mechanism of the PAW-GTAW hybrid welding process. Secondly, quantitative comparisons of weld penetration depth and bead width before and after coupling were conducted to elucidate the mechanism by which the coupled arc improved surface formation. The coupled arc significantly enhanced the stability of the plasma arc voltage while reducing the average PAW voltage after coupling, with minimal changes observed in the GTAW arc. The hybrid weld exhibited a synergistic penetration effect of "PAW penetration depth +GTAW penetration depth < PAW-GTAW hybrid welding penetration depth", and the bead width increased by 0.99 mm compared with single PAW welding. The PAW-GTAW hybrid welding process demonstrates a “1+1>2” advantage in welding speed and penetration depth. The coupled arc notably improves weld surface formation, indicating that the hybrid process not only increases arc energy density but also optimizes the thermal-mechanical distribution in the molten pool and the flow of molten metal.
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  Microstructural and Performance Analysis of 304 Stainless Steel Narrow Gap Oscillating TIG Welded Joints

  GAO Hui, QU Jiajun, ZHANG Dongsheng, CHENG Jincai

  Journal of Netshape Forming Engineering. 2026, 18(4): 117-125. https://doi.org/10.3969/j.issn.1674-6457.2026.04.012

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  The work aims to investigate the applicability of narrow-gap oscillating TIG welding technology for stainless steel pipes and the microstructural and mechanical property distribution patterns of narrow-gap single-pass multi-layer welded joints in 304 stainless steel U-groove pipes using 316L welding wires. Narrow-gap oscillating TIG welding technology was employed to weld 304 stainless steel. The microstructural distribution of the welded joints was observed with an optical microscope. Additionally, tensile experiment, impact experiment, microhardness experiment, and electrochemical corrosion experiment were conducted on the welded joints using equipment such as a tensile testing machine, Vickers hardness tester, and impact testing machine, followed by analysis. The results showed that a high-quality welded joint with a thickness of 20 mm was obtained, featuring an aesthetically pleasing weld bead formation, no weld porosity, and no incomplete fusion on the side walls. The weld microstructure consists of directional austenite with a small amount of discontinuous skeletal ferrite dispersed in the matrix. Its morphological characteristics are mainly determined by the inhibitory effect of Ni and Mo in the welding wire on ferrite formation, as well as the phase transformation and microstructure evolution during multilayer welding. The weld heat-affected zone (HAZ) exhibited a microstructural gradient: near the fusion line, the austenite grains were significantly coarsened, while in the distant regions, the grains were refined to the base metal state. The weld microstructure was significantly directional, while the HAZ was weakly directional, primarily consisting of equiaxed grains. The hardness of the joint decreased in the following order: weld center, heat-affected zone, and base metal. The average tensile strength of the weld was 563 MPa, the average elongation after fracture was 31.2%, and the average impact toughness of the HAZ was 407 J/cm², which was higher than that of the weld zone and the fusion line region. The corrosion resistance and stability of the weld zone were superior to those of the HAZ and the base metal. Narrow-gap oscillating TIG welding technology is suitable for stainless steel welding, and the welded joint performance of 304 stainless steel paired with 316L welding wire is excellent.
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  Effect on Different Groove Forms on Microstructure and Properties of 10CrNi3MoV Steel Joints Welded by Laser-MAG Hybrid Welding

  MA Lulu, FAN Qiaofang, LONG Fei, ZHANG Fuqiang, SHI Xiaohui, PU Juan, SUN Yubo, XU Xiangping

  Journal of Netshape Forming Engineering. 2026, 18(4): 126-135. https://doi.org/10.3969/j.issn.1674-6457.2026.04.013

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  The work aims to conduct welding experiments on 10 mm thick 10CrNi3MoV steel by Laser-MAG hybrid welding to analyze the effect of different groove forms on the forming quality, microstructure and mechanical properties of welded joints, and explore the feasibility of laser-MAG hybrid welding for 10 mm thick 10CrNi3MoV steel. Laser-MAG hybrid welding experiments were carried out on 10 mm thick 10CrNi3MoV steel with Y grooves and I grooves, respectively. The microstructure, microhardness and mechanical properties of the joints with the two groove forms were compared. The macroscopic forming of welded joints obtained by Y groove two-pass welding and I groove one-pass welding is better. The weld center of the welded joint is mainly composed of intragranular acicular ferrite, proeutectoid ferrite and a small amount of granular bainite. The heat affected zone is composed of lath martensite and a small amount of granular bainite. The maximum microhardness values of the welded joints obtained by the two groove forms appear in the coarse grain zone of the heat affected zone. The hardness of the weld zone obtained by the Y groove is slightly larger than that of the I groove, and the minimum hardness is located in the softening zone of the heat affected zone. The value is about 230HV10. The average tensile strength of the welded joints obtained by the Y groove and the I groove are 782 MPa and 735 MPa, respectively, and the tensile fracture is at the base metal. The -20 ℃ impact toughness of the weld center obtained by the I groove is greater than that of the Y groove, but the impact toughness of the fusion line and the fusion line +2 mm is less than that of the Y groove. The joint contains no cracks after 180° positive bending and back bending tests, which meets the use requirements. The electrochemical testing on the joint with the I groove shows that the corrosion resistance of the weld seam is better than that of the base metal and heat affected zone.
Iron and Steel Forming
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  Martensitic Transformation Behavior and Ultra-high Toughness Mechanism of M_f Point Quenching Isothermal in the Medium Carbon Steel Containing Si-Al

  HU Feng, WANG Tongliang, WANG Kun, QIU Baowen

  Journal of Netshape Forming Engineering. 2026, 18(4): 136-146. https://doi.org/10.3969/j.issn.1674-6457.2026.04.014

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  In response to the bottleneck problem of difficult synergistic improvement of high strength and ultra-high toughness in traditional medium carbon steel, the work aims to take the medium carbon steel containing Si-Al as the object, to systematically compare the traditional quenching and tempering (QT) with the new M_f point quenching isothermal (QI) process, and reveal the effect mechanism of M_f point (200 ℃) isothermal phase transformation behavior on material strength and toughness, so as to develop structural steels that combine high strength and ultra-high toughness by adjusting the isothermal time to optimize the carbon distribution effect and retained austenite stability. The microstructure was observed through OM and SEM, the width of lath and the morphology of retained austenite were analyzed by TEM, the carbon content of retained austenite was calculated by XRD, and the mechanical properties were evaluated by tensile and impact tests. The microstructure under QT process consisted of tempered martensite and ε-carbides. However, the QI process formed a lamellar structure of isothermal martensite/high carbon retained austenite (1.46%) through carbon partition effect, the volume fraction of retained austenite was stabilized at 5.5%, and the average width of isothermal martensite lath was reduced to (216±95) nm (42.7% finer than QT). The impact absorption energy of QI200-32 reached >130 J, which was 2.7 times that of QT200-32, while a tensile strength of 1 436 MPa was maintained, achieving a synergistic improvement of high strength and ultra-high toughness. The study breaks through the inversion limit of strength and toughness of the traditional QT process, and the M_f point quenching isothermal process regulates the dual phase structure (martensite and retained austenite) through the transformation mechanism dominated by carbon distribution. The ultra-high toughness is attributed to the refinement of isothermal martensite lath, which significantly improves the dislocation blocking effect, and the high carbon retained austenite film absorbs plastic deformation work, deflects and passivates cracks through the TRIP effect. This study provides a new approach for the development of high-strength and ultra-high toughness medium carbon steel. By regulating the isothermal phase transformation behavior of M_f point quenching and optimizing the layer structure and carbon distribution design, the fracture resistance of the material can be significantly improved.
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  High Temperature Microstructure Stability of CLAM Steel Strengthened by Deformation Heat Treatment

  WANG Chenghao, ZHAO Fei, XU Fahong, XIONG Suiping, YANG Ming

  Journal of Netshape Forming Engineering. 2026, 18(4): 147-154. https://doi.org/10.3969/j.issn.1674-6457.2026.04.015

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  The work aims to clarify the changes in mechanical properties of low activation martensitic (CLAM) steel strengthened by deformation heat treatment during high-temperature long-term service, and to study the microstructure evolution mechanism of CLAM steel strengthened by deformation heat treatment during high-temperature long-term thermal exposure. High-temperature long-term heat exposure tests were conducted on materials with a muffle furnace at different temperature (600 ℃, 650 ℃) and duration (1 100 h, 2 100 h). The microstructure of CLAM steel before and after thermal exposure was characterized and analyzed by OM, XRD, SEM, and TEM, and the changes in hardness were analyzed with a microhardness tester. As a result, with the extension of heat exposure duration and the increase of temperature, the deformation heat treatment strengthened CLAM steel showed a slight increase in grain size, an increase in precipitation phase size, a decrease in dislocation density, and other microstructural evolution laws,, accompanied by a decrease in hardness. Taking the 650 ℃-2 100 h heat exposure with the largest change amplitude as an example, the size of the M₂₃C₆ phase in CLAM steel increased by 65.8 nm, the size of the MX phase increased by 9.29 nm, the dislocation density decreased by 17.2%, and the hardness value decreased by 7.05%. However, as the CLAM steel after deformation heat treatment played a pinning role by precipitating excessive fine MX phases, the lath structure and some dislocations were well retained during the high temperature heat exposure process, which slowed down the decline rate of hardness and achieved a certain strengthening effect. In conclusion, the microstructure of CLAM steel strengthened by deformation heat treatment undergoes a certain degree of degradation during long-term high-temperature thermal exposure. However, the stability of the microstructure of the material under high-temperature thermal exposure is improved by the precipitation strengthening effect enhanced by deformation heat treatment.
Superalloy Forming
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  Hot Deformation Behavior and Microstructure Evolution of As-cast Ni-Cr-Co-based Superalloy

  SHA Lei, ZHONG Kangdi, WANG Bingbing, MA Pingdong

  Journal of Netshape Forming Engineering. 2026, 18(4): 155-166. https://doi.org/10.3969/j.issn.1674-6457.2026.04.016

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  The work aims to investigate the hot deformation behavior and microstructure evolution of an as-cast precipitation-strengthened Ni-Cr-Co-based superalloy under varying thermomechanical parameters, elucidate dynamic recrystallization (DRX) nucleation mechanisms, and provide theoretical support for optimizing the cogging process and microstructure control of as-cast superalloy. Hot compression tests were performed on a Gleeble-3800 thermomechanical simulator within temperature ranges of 1 030-1 150 ℃, strain rates of 0.01-10 s^-1, and true strains of 0.16-0.92. The flow stress characteristics under varying deformation parameters were analyzed. Electron backscatter diffraction (EBSD), backscattered electron (BSE) imaging, and transmission electron microscopy (TEM) were utilized to investigate the effects of different deformation temperature and strain levels on the microstructure morphology and evolution with a focus on DRX nucleation mechanisms. The results showed that the flow stress of as-cast Ni-Cr-Co based superalloy increased with the decrease of temperature or the increase of strain rate, and the stress-strain curves exhibited typical DRX characteristics. DRX grain size and volume fraction increased with the increase of deformation temperature. At lower temperature (1 030 ℃), DRX grains were distributed in agglomerated clusters, and the degree of recrystallization progressed slowly with the increase of strain. At higher temperature (1 150 ℃), the coarsened DRX grains were distributed in a "necklace" shape along the grain boundary and formed a homogeneous structure under high strain. At 1 060 ℃, discontinuous dynamic recrystallization ( DDRX ) and continuous dynamic recrystallization (CDRX) coexisted, with particle-stimulated nucleation (PSN) induced by γ′ phase pinning dislocations and grain boundary bulging dominating as primary nucleation mechanisms, while CDRX served as an auxiliary mechanism. At 1 150 ℃, DDRX through grain boundary bulging became the predominant mechanism, and the overall contribution of CDRX decreased. By studying the hot deformation flow behavior, microstructure evolution and DRX mechanism of an as-cast Ni-Cr-Co-based superalloy with different deformation parameters, the influence of deformation parameters and γ' precipitates on the microstructure and nucleation mechanism of hot deformation is obtained, which can be used to optimize the process parameters and microstructure control of Ni-Cr-Co-based superalloy ingots.
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  Rolling Forming Process of Thin-walled V-shaped Sealing Rings of Superalloys

  WANG Tao, LIU Jing, LI Lanyun, ZHU Zheyi

  Journal of Netshape Forming Engineering. 2026, 18(4): 167-177. https://doi.org/10.3969/j.issn.1674-6457.2026.04.017

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  The work aims to study the stress-strain law of thin-walled superalloys during the rolling forming of V-shaped sealing rings to address the issues of wrinkling in the forming process. A 3D elastoplastic finite element model for multi-pass rolling forming of sealing rings was established using ABAQUS software. The influence of die structure on the deformation characteristics of V-shaped superalloy sealing rings during rolling forming was systematically analyzed. Additionally, the effects of process parameters (roller diameter, mandrel rotational speed, and roller feed rate) on wrinkling, wall thickness, and outer diameter of the sealing rings were investigated via a single-factor approach. The wrinkling defect in sealing ring rolling forming was fundamentally attributed to circumferential buckling of the blank ends due to insufficient die constraints. Adding stiffening ribs to both ends of the mandrel significantly enhanced forming stability and effectively mitigated wrinkling. Roller diameter increase reduced the wall thickness thinning rate but had negligible impact on outer diameter. Mandrel rotational speed increase initially intensified then suppressed wall thickness thinning, while outer diameter remained stable. Roller feed rate increase exacerbated wall thinning and expanded outer diameter. Based on the above findings, rolling experiments are conducted using optimized process parameters (roller diameter 60 mm, mandrel rotational speed 6.3 rad/s, roller feed rate 2.1 mm/r), outer diameter deviations are within 1%, cross-sectional wall thickness deviations remain below 10%. This validates the precision forming capability of V-shaped superalloy sealing rings.
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  Effect of Assembly Modes on the Directional Solidification Process of Single-crystal Guide Vanes

  YANG Zhenyu, CHEN Hao, HU Songsong, ZHENG Sujie, LUO Kailun, LUO Yushi, DAI Shenglong

  Journal of Netshape Forming Engineering. 2026, 18(4): 178-185. https://doi.org/10.3969/j.issn.1674-6457.2026.04.018

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  The work aims to investigate the effect of two assembly modes (vertical vane body and inclined vane body) on the directional solidification process of single-crystal guide vanes, thereby providing technical and theoretical support for optimizing the directional solidification process and industrial production of single-crystal guide vanes. ProCAST + CAFE numerical simulation was employed to simulate the evolution of temperature field, undercooling, and grain structure during directional solidification for vertical vane body and inclined vane body at 40°. The inclined-assembly guide vanes were fabricated with the seed crystal embedding method and then subject to microstructural observation and crystal orientation determination via Electron Backscatter Diffraction (EBSD). Under the vertical assembly mode, the solid-liquid interface evolved from an initial near-planar shape to a concave shape in the upper-middle part of the vane body as the solidification progressed, accompanied by an increase in the width of the mushy zone. A high undercooling zone formed at the edge of the lower platform, leading to the generation of stray grains. Severe shrinkage porosity was also observed in the upper edge of the platform and the middle part of the vane body. In contrast, for the 40° inclined assembly mode, the solid-liquid interface maintained a wavy near-planar shape throughout the solidification process, with a narrow and stable mushy zone. The overall undercooling of the vane was reduced, and no stray grains were formed. Combined with the seed crystal embedding method, single crystals with <001> orientation were successfully obtained. Only a small amount of shrinkage porosity was detected in the platform, while the vane body exhibited minimal shrinkage porosity. Compared with the vertical vane assembly mode, the 40° inclined vane assembly mode effectively suppresses the formation of stray grains and shrinkage porosity. It is therefore recommended as the preferred assembly scheme for improving the manufacturing quality of single-crystal guide vanes.
Copper Alloy Forming
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  Effect of Pulsed Electric Current on the Distribution of Pb Impurities in Oxygen-free Copper

  XIONG Jiao, LI Kun, YANG Xiangjie

  Journal of Netshape Forming Engineering. 2026, 18(4): 186-195. https://doi.org/10.3969/j.issn.1674-6457.2026.04.019

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  The work aims to systematically investigate the purification effect of pulsed electric current (PEC), an auxiliary physical field technology, on Pb impurities in an oxygen-free copper melt, to reveal the migration behavior and underlying mechanism of Pb and to develop an efficient and green purification process. With oxygen-free copper containing 1 wt.% Pb as the research object, the melt prepared in a high-frequency induction furnace was treated with PEC at varying parameters (electrode insertion depth, pulsed current intensity and frequency). The microstructure, size, area fraction and spatial distribution of Pb impurities in the treated samples were systematically characterized and quantitatively analyzed through optical microscopy (OM), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectrometry. The PEC effectively drived Pb impurities to overcome central segregation, achieving directional migration towards the anode and the bottom of the melt, thereby forming purified zones in the central and cathode areas. Parameter optimization experiments revealed that the optimal purification efficiency was achieved with an electrode insertion depth as 1/4 of the depth of the graphite crucible, a pulsed current of 150 A, and a frequency of 1 500 Hz, resulting in a maximum Pb removal rate of 58.75% in the central region. The underlying mechanism was primarily attributed to the combined driving forces of electromigration (electron wind force) and the reduction in electrochemical free energy induced by the current density gradient. However, when the current or frequency exceeded critical thresholds, the intense Joule heating effect induced disordered convection within the melt, consequently reducing the purification efficiency. Pulsed electric current technology can effectively achieve directional migration and selective purification of Pb impurities in oxygen-free copper melts. The impurity migration is driven synergistically by electromigration force and current density gradient force, with an optimal processing window existing. This research clarifies the key process parameters and mechanism of this technology, providing a theoretical basis and practical guidance for the green preparation of high-performance oxygen-free copper.
Advanced Manufacturing Technology and Equipment
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  Multi-station Forming Process Analysis and Die Design of a Multi-step Double-pass Connecting Joint

  FANG Jie, TONG Zeqi, HU Kaiming, WU Jianjun, CAI Yafang

  Journal of Netshape Forming Engineering. 2026, 18(4): 196-205. https://doi.org/10.3969/j.issn.1674-6457.2026.04.020

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  The work aims to select a multi-step double-pass connecting joint as the research object to address the issues of incomplete forming, insufficient punching, and low dimensional accuracy in the hot forging process. Numerical simulation experiments were conducted with the finite element method. The multi-station hot forging process was simulated with Deform-3D software to investigate the metal flow behavior and temperature evolution of the forging. The analysis focused on the filling integrity of the forging, the peak variation trend of forming load, the distribution uniformity of equivalent stress and strain, as well as the cross-sectional temperature difference of the forging. In addition, die design and trial production were carried out for the multi-station scheme. The simulation results showed that, in the multi-station forming process, the surface node distribution of the forging was uniform, metal flow was normal, and no folding or other defects occurred, with no underfilling inside the die. The forming load increased steadily without abrupt changes in stress or strain, and the temperature difference remained within a reasonable range. The final forging met the specified external dimensional requirements. In the trial production, the forgings exhibited good formability, complete die filling, clear punching, and dimensional accuracy within tolerance. For the multi-step double-pass connecting joint, the multi-station forming process effectively avoids forging defects. The feasibility and reliability of applying the multi-station hot forging process to the multi-step double-pass connecting joint are verified through both simulation and experimental results, providing a reference for the precision forging of similar complex structural components.
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  Defect Segmentation and Detection Method for Injection Molding Products Based on SAM2-U-Net and Semi-supervised Learning

  YANG Hongyu, ZHU Xudong, SONG Shuai, ZHANG Sichang, YANG Weimin

  Journal of Netshape Forming Engineering. 2026, 18(4): 206-212. https://doi.org/10.3969/j.issn.1674-6457.2026.04.021

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  To enhance the accuracy and robustness of deep learning methods in the detection of injection molding products while reducing their dependence on high-quality labeled data, the work aims to construct a defect detection method that integrates general visual knowledge with task-specific features. Specifically, the Segment Anything Model 2 (SAM2) was utilized to transfer visual priors learned from large-scale natural image datasets. Adapter modules were introduced to enable efficient parameter fine-tuning, allowing the model to capture the distinctive characteristics of injection molding defects. At the same time, the U-Net decoding structure was employed to achieve high-precision semantic segmentation of defect regions. A semi-supervised auxiliary training strategy was adopted, introducing non-defective samples to enhance the model's generalization ability. Compared with mainstream segmentation methods, the proposed defect detection method significantly improved segmentation performance. The mIoU increased by 7.13%, Recall by 7.87%, Pixel Accuracy (PA) by 0.67% and mPrecision by 4.83%. Under the condition of scarce defect samples, the proposed defect detection model combining SAM2 and U-Net, along with a semi-supervised auxiliary training strategy, significantly improves the performance of injection molding product defect detection, reduces reliance on high-quality annotated data, and demonstrates promising application value in the plastics industry.
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  Research on Flow Stress Model Based on Strain Evolution

  YUAN Jindong, MA Junqiang, CUI Xuexi, JIANG Sheng

  Journal of Netshape Forming Engineering. 2026, 18(4): 213-220. https://doi.org/10.3969/j.issn.1674-6457.2026.04.022

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  The work aims to study the strain hardening index evolution law, stress-strain relationship and plastic flow characteristics of aluminum alloys such as 2024 and 7A09, and to explore the flow stress model suitable for these materials, so as to provide better material model selection for these materials in part design, precision manufacturing and accurate finite element calculation. The evolution history of strain hardening indexes during the test was obtained by combining the single tension test with the theoretical formula of stress and strain, and the relationship between strain hardening indexes and strain variables was obtained. The stress-strain curves of 2024 and 7A09 aluminum alloys were established to verify the validity of the Hollomon-n flow stress model. By analyzing the test data, it was found that the n values of 2024 and 7A09 aluminum alloys were not fixed, but showed a nonlinear decreasing trend with the increase of strain. The n values decreased rapidly at small strain and slowly at large strain, and finally tended to be stable. Based on this, the Hollomon n flow stress model with variable n values could better describe the stress-strain relationship of the two aluminum alloys, and the error e_Hollomon-n average values of the two aluminum alloys were lower than 5.4%, indicating that the flow stress model had high prediction accuracy. The n values of 2024 and 7A09 aluminum alloys are not constant in the deformation process, and the relationship between the n values and the dependent variables is in accordance with the power function. Hollomon-n flow stress model with variable n values can describe the stress-strain relationship of these two aluminum alloys well.
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  Auto-pouring Design for Vacuum Furnaces Based on the Constant-flow Tilting and Gating Horizontal Motion Compensation Model

  ZHENG Hang, YU Shiya, HAO Xin, LIU Guohuai, LIU Xu, WANG Ye, YI Chushan, WANG Zhaodong

  Journal of Netshape Forming Engineering. 2026, 18(4): 221-227. https://doi.org/10.3969/j.issn.1674-6457.2026.04.023

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  In order to avoid the poor pouring stability, uncontrollable fluid flow behavior, low pouring accuracy and other shortcomings of the traditional manual control in the pouring process, the work aims to improve the vacuum pouring equipment, establish a mathematical model and develop a PLC program to optimize the quality of castings. According to actual working conditions, mathematical modeling was conducted on the tilting process of the crucible during vacuum pouring. Based on the instantaneous relationship between the crucible tilting angular velocity and the pouring velocity of the superalloy melt, a horizontal movement compensation model for the pouring cup under constant flow rate was established. The model was compiled in MATLAB and the corresponding VC++ programs and PLC programs were finally developed. The calculated auto-pouring curve was then input into the vacuum pouring equipment. The auto-pouring curve obtained by calculation according to the input of actual parameters could compensate the transverse displacement caused by the positional shift of the liquid metal generated in the falling process thought the movement of pouring platform, ensuring the melt entering into the pouring cup completely. The application of the crucible tilting and pouring platform horizontal displacement compensation model developed in this work can effectively ensure the stability of the pouring process of nickel-based superalloy during precision casting.