Search Results (2,078)

Dual beam laser welding of UNS S32750 superduplex stainless steel was performed to investigate the effect of beam-power distribution on microstructure and mechanical properties. Plates with a thickness of 3 mm were welded at a constant total power and travel speed using leading and lagging power splits of 50:50, 80:20, and 65:35. The heat affected zone width was metallographically estimated at approximately 100 µm for all conditions, consistent with comparable gross thermal exposure under constant nominal linear energy input (P_total/v). A slight modification to the power distribution altered the solidification texture and austenite morphology. The 50:50 configuration produced a refined ferritic matrix with a continuous network of grain boundaries, Widmanstätten, and intragranular acicular austenite. The 80:20 condition increased ferrite path continuity, while the 65:35 split produced an intermediate morphology. Vickers hardness reached a maximum for the 80:20 split (HAZ: 345 HV; weld metal: 349 HV). Ultimate tensile strength remained statistically constant between 908 MPa and 914 MPa, whereas elongation decreased from 28% at 50:50 to 24% at 80:20 and 23% at 65:35. All welds exhibited ductile fracture with microvoid coalescence, and electrochemical performance was comparable, with critical pitting temperature values between 78 °C and 91 °C. Beam power distribution primarily affects solidification morphology and enables control of the hardness-to-ductility balance, with a 50:50 split providing the most favorable combination of properties. Full article

In the present work, eleven self-shielded flux-cored wires with nickel (Ni) contents ranging from 1.42 wt.% to 4.02 wt.% were designed for the semi-automatic welding of X80 pipeline steel. The effects of Ni on the microstructural evolution and mechanical properties of the weld metal were investigated. The results indicate that when the Ni content is below 2.06 wt.%, the microstructures of both the solidification zone and the inter-pass reheating zone are dominated by coarse granular bainite and martensite/austenite (M/A) constituents. As the Ni content increases from 2.06 wt.% to 3.73 wt.%, the microstructure transforms to fine lath bainite with M/A constituents characterized by low content, small size, and uniform distribution. When the Ni content reaches 3.73 wt.%, the microstructure becomes almost fully bainite. Furthermore, with increasing the Ni content, both the yield strength and tensile strength of the weld metal increase from ~600 MPa to ~700 MPa and from ~660 MPa to ~730 MPa, respectively. However, the impact energy at −20 °C of the weld metal initially increases and then decreases, reaching a peak of ~110 J with the lowest degree of dispersion at a Ni content of approximately 3.73 wt.%. When the Ni content exceeds 3.73 wt.%, the ductility decreases slightly. Further analyses indicate that the synergistic effects of Ni in refining the microstructure and reducing the activity coefficient and solubility of nitrogen (N) jointly contribute to the impact toughness of the weld metal. Full article

Dissimilar 7075-T6 and 6061-T6 aluminum alloy joints were fabricated using pulsed metal inert gas (P-MIG) welding with ER5356 filler wire. The effects of welding current (224 A, 234 A, and 244 A) on macro-morphology, microstructure, mechanical properties, and corrosion behavior were systematically investigated. As welding current increased, the top and bottom reinforcements first increased and then decreased, reaching maximum values at 234 A, while the front weld width exhibited the opposite trend. The weld zone consisted of equiaxed and dendritic grains, with partial remelting of AlFeMnSi intermetallic compounds observed in the heat-affected zones. The microhardness and tensile strength of the joints followed a similar trend of first decreasing and then increasing with welding current, achieving a maximum tensile strength of 203.9 MPa at 244 A, corresponding to 89.5% of the 6061-T6 base metal strength. Corrosion resistance varied across regions depending on the evaluation method. In intergranular corrosion tests, the 7075-HAZ showed the highest susceptibility due to grain boundary segregation of Mg and Zn. In electrochemical tests, the WZ exhibited the poorest corrosion resistance. For the 7075-HAZ, optimal corrosion resistance was achieved at 234 A, attributed to a stable passive film and uniform precipitate distribution. These findings provide valuable guidance for optimizing P-MIG welding parameters for dissimilar 7075/6061 aluminum alloy joints. Full article

The objective of this study was to systematically investigate the effect of welding speed on the microstructure, mechanical properties, and corrosion behavior of 7075-T6 aluminum alloy similar joints. Pulsed metal inert gas (P-MIG) welding with ER5356 filler wire was employed as the methodology to fabricate the joints, with welding speed as the sole variable parameter (450, 500, 550, and 600 mm/min) while maintaining constant welding current and voltage. The key results showed that increasing welding speed refined the dendritic structure in the weld zone (WZ) and promoted a more uniform distribution of precipitates. The tensile strength first increased and then decreased, reaching a maximum of 257.7 MPa at 550 mm/min, with a corresponding elongation of 8.1%. The microhardness of the WZ increased from 91 HV_0.1 (450 mm/min) to 107.4 HV_0.1 (600 mm/min). Corrosion resistance, assessed via intergranular corrosion tests and electrochemical analysis, varied significantly with welding speed; optimal performance was obtained at 450 mm/min, while the poorest occurred at 550 mm/min due to variations in precipitate distribution and passive film stability. The conclusion is that an optimal welding speed of 550 mm/min achieves the best balance between mechanical strength and ductility by refining the microstructure, while the corrosion resistance is primarily governed by the electrochemical activity of grain boundary precipitates induced by the welding thermal cycle. Full article

To investigate the mechanism by which metal bellows affects the dynamic behavior of the mechanical seal system under high pressure and strong vibration conditions in the turbopump, a multi-degree-of-freedom finite element dynamic model is established based on ANSYS Workbench (2024 R2), using a stator-welded metal bellows as the sealing assembly system. The effects of sealing medium pressure and installation offset angle on the dynamic natural characteristics of the bellows assembly are considered. Furthermore, the influence of different operating parameters under radial and axial excitation on the dynamic response of stationary ring and bellows, as well as the amplitude–frequency characteristics of the bellows assembly, are investigated using the base-excitation method. The results indicate that the first three natural frequencies dominate the dynamic response of the assembly and are prone to resonance within the operating frequency range of turbopumps. Radial excitation induces significant high-frequency vibration of the stationary ring, with radial amplitudes exceeding 110 μm, while axial vibration is primarily absorbed by the bellows. Increasing the sealing medium pressure effectively enhances structural stiffness and reduces resonance amplitude, whereas installation misalignment leads to additional resonance points and deteriorates dynamic stability. These findings provide useful guidance for avoiding resonance, improving vibration stability, and optimizing the structural design of mechanical seal bellows assemblies in high-parameter engineering applications. Full article

Welding is one of the key joining routes for expanding the engineering applications of dissimilar magnesium alloys. However, after experiencing rapid non-equilibrium heating and cooling cycles, the heat-affected zone (HAZ) of a welded joint tends to undergo grain coarsening as well as dissolution or agglomeration of precipitates, and therefore becomes the region most susceptible to failure. In this study, 3 mm thick sheets machined from AZ61A and AZ80A magnesium alloy hollow sections were joined by metal inert gas welding (MIG). Different ranges of welding heat input were obtained by combining multiple sets of welding parameters, in order to further tailor the HAZ of dissimilar magnesium alloy joints and achieve sound weld quality. The results showed that the joint exhibited the best overall mechanical performance at 523 J·mm⁻¹, with an ultimate tensile strength, yield strength, and elongation of 292 MPa, 172 MPa, and 5.4%, respectively. All fractures occurred in the HAZ on the AZ61A side. Under this condition, the second phases in the HAZ were more finely and uniformly dispersed, with a volume fraction of 3.19%, an average size of 2.51 μm, and a minimum average grain size of 23.65 μm. Full article

Hot extrusion tools operate under severe thermal and mechanical conditions, which significantly limit their service life. During operation, the punch and die absorb large amounts of heat from the hot billet while being subjected to high pressures and intense friction, leading to severe abrasive wear and progressive hardness reduction. In practice, the punch generally exhibits a shorter service life than the die. The present study proposes a technological solution for reconditioning worn extrusion punches using vibration-assisted welding (VAW). A wear-resistant layer was deposited by MIG welding using DUR 600 filler material, while mechanical vibrations were introduced through a vibrating welding table. The applied vibration regime consisted of a frequency of 50 Hz–108 Hz and acceleration components of a_x = 30–60 m/s² and a_z = 35–70 m/s². The experimental investigations included macroscopic analysis, hardness and microhardness measurements, microstructural observations, and SEM-EDS line scanning analysis of the dilution zone between the cladding material and the base metal. The results suggest that vibration-assisted welding may influence the microstructural characteristics, hardness distribution, and dilution behavior of the cladded layer. The vibrated specimens exhibited higher hardness values in the range of 702 to 908 HV5–10. Under the investigated conditions, the process did not require additional hardening treatment, and only a stress-relief annealing stage was applied. The proposed VAW approach appears to be a promising option for the reconditioning of hot extrusion tools; however, further investigations are required to validate its performance under industrial conditions. Full article

This study investigates the influence of specific heat input and weld configuration on heat affected zone hardness and residual stress of S960MC high strength steel welds. In total, five types of weld samples were manufactured by Tungsten Inert Gas (TIG) autogenous welding and Metal Active Gas (MAG) butt welding to simulate the effect of increasing heat input and constraining the relative motion of welded parts during the heating and cooling phase. The obtained results show that the highest axial tensile residual stresses with magnitude above 900 MPa, combined with a hardness drop in a range from 13 up to 18%, occur mostly in the sub-critical heat affected zone, making it the critical zone of the weld. Increasing the heat input during welding does not have a simple correlation with generating more residual stresses and the trends obtained on the surface are different from results evaluated at a depth of 0.2 mm. Restraining the relative part motion during the welding affects mostly the tangential residual stresses, causing an increase in their tensile magnitude localized in the middle of the heat-affected zone while almost no influence on the axial residual stress component was recorded. Full article

Aiming at the urgent heat dissipation demands of high-power, high-integration electronic devices, Cu/Al composite heat sinks combine the high thermal conductivity of copper and the lightweight advantage of aluminum, becoming a mainstream solution for advanced thermal management systems. The significant physicochemical differences between Cu and Al, however, make high-quality joining a technical bottleneck. In this study, flux-free ultrasonic brazing with a Zn-based filler metal was used to join 6061 aluminum alloy and industrial pure copper. Gradient heat treatment (55–300 °C) was subsequently applied to systematically investigate its effect on the microstructure, microhardness, and thermal properties of the joints. The results show that the as-brazed joint exhibited excellent bonding (97.3% bonding rate) and shear strength (95.24 MPa). The weld seam consisted of Zn solid solution, Cu solid solution, and Al-Cu-Zn ternary compounds. Heat treatment did not induce new phases but led to the coarsening of Zn-Al-Cu compounds and aggregation of the eutectic structure, reducing grain boundaries. Consequently, the microhardness at the weld center varied non-monotonically, and the thermal conductivity of the joint showed an overall increasing trend with rising heat treatment temperature. This enhancement is attributed to reduced phonon scattering at diminished grain boundaries. This study clarifies the heat treatment–microstructure–thermal properties relationship, providing important guidance for the thermal performance optimization of Cu/Al composite heat sinks. Full article

For large-scale manufacturing of profile-intensive vehicle bodies, a suitable joining process for hollow profile–sheet metal joints is required. These joints pose challenges related to minimizing plastic deformation while ensuring low, localized heat input to preserve the properties of high-strength steels. Conventional resistance spot welding often leads to profile deformation due to concentrated force and heat input and the lack of mechanical backing. For this reason, CD-welding tests on sandwich structures consisting of hollow profile-sheet metal with a wire mesh interlayer used as natural projections are conducted. This enables multiple small welds with localized heat input and welding times below 10 ms. This study investigates the influence of the weld parameters electrode force and charging energy, and illustrates that as the electrode force increases, plastic deformation increases up to the point of failure above 24 kN. In this regard, support structures and inserts made of copper and plastic, as well as novel welding electrodes with lateral profile contacts, are being investigated. Joint quality is evaluated based on setdown, electrical resistance, shear strength, and plastic deformation of hollow profiles. The highest shear tensile forces of up to 47 kN were achieved using 60 projections and an inner copper support structure. Full article

Duplex stainless steel (DSS) blends impressive mechanical and chemical characteristics to withstand aggressive environments. Its fabrication by Gas Metal Arc Welding-Additive Manufacturing is an emerging research topic. However, its sensitive grain structure and alloy composition are prone to deterioration by repeated thermal shocks. Whether optimal weld parameters can resolve these challenges without additional costs from special fillers, gases, or mechanisms is a valid question. In this study, how different wire feed speeds, travel speeds, and weld voltages, chosen from a set of preliminary beads, translate into wall dimensions, phase formation and distribution, morphological transformation, and elemental segregation is investigated. The unique DSS microstructures were characterised using scanning electron microscopy and energy-dispersive spectroscopy to reveal differences in microstructural evolution and ferrite-austenite (α-γ) structure. The deposited walls exhibited satisfactory geometric quality with negligible distortions. However, the height suppression was noticeable at the deposition energy (DE) of 755 J/mm. Metallographic analysis revealed low γ phase formation (<30%) at low DE (230 J/mm) and excessive γ formation (>70%) in the high DE wall (755 J/mm). The parameters WFS:TS = 15, TS = 35 cm/min, WFS = 525 cm/min, and V = 20.804 volts suppressed the elemental segregation while maintaining a suitable phase balance without post-processing. Full article

Integrated die-cast components reduce machining/assembly steps and improve mechanical dynamic characteristics, eliminating joint loosening/fracture risks after long-term use. However, the highly variable geometries and random spatial distributions of burrs, flash, parting lines, and risers in castings invalidate pre-programmed or teach-in robotic grinding methods. This paper reviews recent progress and future trends in robotic grinding, analyzing four core aspects: force control stability/adaptability (e.g., adaptive impedance control can reduce average force-tracking error to 0.38 N), trajectory planning/path generation (e.g., error-driven compensation can lower contour error by 34.2–55.1%), process parameter optimization, and challenges of sensing latency/quality evaluation (e.g., deep learning models achieve 97.64% accuracy in identifying abrasive belt wear states). The key enabling technologies are summarized, including active/passive compliant force control, model-/data-driven adaptive trajectory planning, intelligent process parameter optimization integrating physical mechanisms and data-driven approaches, and multi-modal state monitoring with online quality assessment. Representative applications (metal castings, aero-engine blades, thin-walled components, weld seams) are presented, and prospective research directions are proposed. This paper provides a comprehensive reference for theoretical research and engineering practice in this field. Full article

Ensuring the integrity of weld seams in pipeline components is critical for the safe and reliable transportation of oil and natural gas. This paper presents a systematic failure investigation of a cracked weld in a reducer located at a natural gas transmission station in Western China, aiming to identify the failure mechanism and assess its implications for pipeline safety management. A comprehensive analysis was conducted using macroscopic examination, chemical composition analysis, mechanical property testing, metallographic observation, and microscopic fracture characterization. The results reveal that the heat-affected zone (HAZ) exhibited abnormally high hardness (up to 588 HV0.1), indicating insufficient toughness that made it susceptible to cracking. The base metal showed a high carbon equivalent (CEV), placing it in the “difficult-to-weld” category and increasing its sensitivity to improper welding thermal cycles. On-site investigation further identified significant deficiencies in welding process control, including inadequate preheating, improper interpass temperature management, and insufficient post-weld heat treatment (PWHT). These deficiencies allowed welding residual stresses to persist and failed to mitigate the hardened HAZ microstructure. The combination of poor material weldability and inadequate on-site welding practices ultimately led to brittle fracture under service conditions. This failure highlights a critical vulnerability in pipeline transportation infrastructure and underscores the necessity of strict adherence to qualified welding procedures for high-carbon-equivalent steels. The findings provide practical guidance for enhancing welding quality control and ensuring the long-term operational safety of natural gas pipeline systems. Full article

This review summarizes the base materials, joining methods, filler materials, and principal technical challenges in endoscope joining fabrication, and proposes practical strategies to improve joint reliability under clinical constraints. We conducted a comprehensive search in multiple databases, including Web of Science, Google Scholar, patent databases, Scopus databases, and Medline (via PubMed), for articles on the joining for precision endoscope fabrication, covering the period from 1950 to 2026. We employed the combinations of keywords, “endoscopy”, “minimally invasive surgery”, “welding”, “joining”, “sealing”, “soldering”, “bonding”, and “brazing”. Approximately 500 references were retrieved. After excluding duplicates and irrelevant studies, 158 publications met the inclusion criteria. Data on base materials, joining, processes, filler materials, and technical issues related to sterilization, corrosion, and microstructural evolution were extracted and analyzed. Endoscopes are multi-material systems, involving metallic biomaterials (stainless steels (SSs), titanium alloys, nickel-based alloys, etc.), optical functional materials (glass, sapphire, quartz, etc.), engineering plastics, ceramics, composite materials, and coatings. Joining, sealing, and functional integration have been achieved via adhesive bonding, laser soldering, laser brazing, wave soldering, reflow soldering, fusion welding, and other joining techniques. The main challenges include how to reliably join highly mismatched dissimilar materials, how to fabricate low-residual-stress joints, and how to increase the long-term resistance to sterilization-induced degradation and thermal aging over repeated 100–200 °C thermal cycles. Conventional joining techniques struggle to balance mechanical integrity, joint hermeticity, and long-term stability under such harsh cyclic conditions. The resulting joints may suffer surface yellowing, interfacial debonding, microcracking, delamination, or progressive property degradation during service. We propose the following three strategies to achieve reliable, low-residual-stress, and sterilization-resistant joining of dissimilar materials for endoscopes: (1) A synergistic design that combines thin-film engineering (including evaporation, sputtering, and electroplating) with silver anti-oxidation layers is proposed to reduce residual stresses and to enhance the joint hermeticity. (2) To develop principles for the selection of multi-joining processes to achieve the multi-material integration and functional assembly of dissimilar material components. (3) To develop the laser-based joining methods (fusion, brazing, or braze-welding) for precision control of heat input, bonding quality, and the least damage to the heat-sensitive components. Full article