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The current Friction Stir Welding (FSW) based solid-state defect repairing method is an ideal repair technology for high-strength aluminum alloy. However, due to the limitation of pin length and the existence of shoulder, the stirring pin cannot penetrate deep into the root of defects and is difficult to extend in the width direction, which poses great challenges for components with large defects, such as one-dimensional, two-dimensional and volume defects. To overcome these limitations, this study successfully achieved effective repair of various forms of defects using the solid-state Friction Rolling Repair (FRR) technology through multi-layer multi-bead deposition. The microstructure and mechanical properties of the repaired ZL114A cast aluminum alloy joints were investigated. The results demonstrate well-bonded repaired boundaries, significant grain refinement at the junction between the repaired area and boundary, and ultimate tensile strength exceeding 80 % of base material strength. The average grain size of the repaired area can reach a minimum of 2.82 μm. The grain refinement degree of the side joint of the surface defect repair sample is higher than that of the bottom joint, and the corner joint of the bottom surface shows the highest proportion of recrystallized grains. Fracture locations were consistently within the interior of the repair zone in tensile specimens, indicating superior properties at side joints compared to those within the interior. The research proves that FRR has the ability to repair a variety of typical defects, including one-dimensional, two-dimensional and volume defects, in the process of processing and service, which lays a foundation for the industrial application of FRR.

In response to the shortcomings of traditional Gas Tungsten Arc Welding (GTAW), such as low penetration, slow welding speed, and low production efficiency, an Ultra-High-Frequency Adjustable Multi-Pulse Gas Tungsten Arc Welding (UFMP-GTAW) process is proposed. This process more effectively concentrates the temperature distribution of the welding arc. To characterize the arc morphology and its dynamic changes, high-speed photography captured ten images of the UFMP-GTAW welding arc within one cycle. The arc image processing algorithm proposed in the paper was used to study the arc's variation characteristics over one cycle. This algorithm includes binarization, arc segmentation, and edge detection to obtain arc morphology parameters. The arc symmetry algorithm is used to symmetrize the arc images for Abel inversion, resulting in the emission coefficient distribution. Further calculations provide the temperature distribution, electrical conductivity distribution, and current density distribution of the arc. Analysis reveals that changes in arc temperature, electrical conductivity, and current density lag behind changes in current. The temperature of the arc spreads from the central axis to the surrounding arc space. When high-frequency current variations occur, the heat input generated by the current increase takes time to transfer to the entire arc space. Conversely, if the current suddenly decreases, the heat input rapidly diminishes. However, because heat transfer takes time, the arc space remains relatively stable for a short period, making the ultra-high-frequency arc form more stable.

• The cooling rate increased by 11.7 times, and the high-temperature residence time decreased by more than 50 % through instant water cooling. • Fine grains could be obtained by preheating and water-cooling-assisted FRAM, and the average grain size was approximately 3.77±1.03 µm. • The distribution and variation characteristics of microstructure under different thermal cycle conditions were investigated. • The relationship between the microstructure and mechanical properties was established. Friction rolling additive manufacturing (FRAM) is a solid-state additive manufacturing technology that plasticizes the feed and deposits a material using frictional heat generated by the tool head. The thermal efficiency of FRAM, which depends only on friction to generate heat, is low, and the thermal-accumulation effect of the deposition process must be addressed. An FRAM heat-balance-control method that combines plasma-arc preheating and instant water cooling (PC-FRAM) is devised in this study, and a temperature field featuring rapidly increasing and decreasing temperature is constructed around the tool head. Additionally, 2195-T87 Al-Li alloy is used as the feed material, and the effects of heating and cooling rates on the microstructure and mechanical properties are investigated. The results show that water cooling significantly improves heat accumulation during the deposition process. The cooling rate increases by 11.7 times, and the high-temperature residence time decreases by more than 50 %. The grain size of the PC-FRAM sample is the smallest, i.e., 3.77±1.03 µm, its dislocation density is the highest, and the number density of precipitates is the highest, the size of precipitates is the smallest, which shows the best precipitation-strengthening effect. The hardness test results are consistent with the precipitation distribution. The ultimate tensile strength, yield strength and elongation of the PC-FRAM samples are the highest (351±15.6 MPa, 251.3 ± 15.8 MPa and 16.25 %±1.25 %, respectively) among the samples investigated. The preheating and water-cooling-assisted deposition simultaneously increases the tensile strength and elongation of the deposited samples. The combination of preheating and instant cooling improves the deposition efficiency of FRAM and weakens the thermal-softening effect. [Display omitted] [ABSTRACT FROM AUTHOR]

By adjusting the inter-wire arc (IWA) posture, the skew-coupling arc (SCA) is proposed to address the polar effect in the cross arc, enabling decoupling control of heat, force, and mass transfer. Despite the advancement, the arc stabilization mechanism in the SCA remains poorly understood, hindering its application as a heat source in welding or additive manufacturing. To elucidate this mechanism, various influencing factors such as power supply characteristics, shielding gas composition, IWA posture, and plasma main arc (PMA) were analyzed. An electrical signal and high-speed camera synchronous acquisition system was utilized to analyze current-voltage waveforms and arc shapes. The results indicate that the arc stability of the SCA can be enhanced by ensuring specific external conditions. Constant voltage power supply enhances the self-regulating effect of the IWA, maintaining the IWA and the PMA in a hybrid state at all times. Introducing an oxidizing gas to the shielding gas can effectively suppress cathode spot climbing and stabilize the IWA. The vertical spacing between wires directly impacts the PMA deflection, while the wire horizontal angle has a lesser effect. The heat-regulating effect of the PMA column boosts the arc length regulation by the IWA. The current and the ion gas flow rate in the PMA minimally influence the SCA stability. These findings can provide a solid foundation for further applications of the SCA as heat source.

This study introduces a novel vector gas regulated plasma arc welding technique incorporating four auxiliary gas channels integrated within the water-cooled nozzle. Four different forms plasma arcs were generated by introducing four, three, two or none gas streams through the auxiliary channels respectively. Experimental and simulation methods were used to compare arc pressure, arc temperature characteristics for different arc types respectively. It was found that auxiliary gases can adjust the arc pressure and temperature field distribution on workpiece. In comparison to conventional plasma arc welding, the novel PAW can enhance the plasma arc penetration and adjust the thermal and force distribution. It offers increased welding efficiency and adaptability to diverse conditions, has a significant application potential in plasma arc welding technology.

Friction-rolling additive manufacturing (FRAM) is a solid-phase additive manufacturing technology that relies on the insertion of a high-speed rotating toolhead into a previous layer to generate heat for deposit formation. Press depth is a key parameter of FRAM, and insufficient press depth may result in defects that affect the mechanical properties of the deposited material. In this study, the effect of press depth on heat generation and defect formation in materials was revealed for the first time using the Coupled Eulerian-Lagrangian method. The results showed that at a small press depth, the temperature and stress of the material on both sides of the interface are low, and the plastic deformation produced by the toolhead does not affect the interface; thus, two types of bonding defects: voids and tunnels, appear easily at the interface position. With an increase in the press depth, material flow along the travelling direction and the toolhead direction was enhanced, and the temperature, stress, and plastic deformation at the interface gradually increased, resulting in the disappearance of the defects, and the order of disappearance was related to the morphology of the toolhead. When the press depth was 1.90 mm, the materials on both sides of the bonding interface reached 70 % of the melting point, resulting in an almost defect-free interface. The simulation results were consistent with the experimental results. This study provides a better understanding of the defects formation during FRAM and provides guidance for regulating the defects in the future.

Directed energy deposition (DED) represents a pivotal advancement in intelligent manufacturing, facilitating efficient near-net shape metal part production, particularly suited for aerospace and defense applications demanding high precision. Arc-based DED relies on meticulous process and trajectory planning, where AI-driven manufacturing systems optimize paths and parameters to surmount intricate physical phenomena like material melting and heat transfer. AI methodologies such as deep learning and big data analytics offer promising solutions. The exclusive process planning software for DED-Arc (EPPS−DED) broadens the technology's application domains. This paper comprehensively outlines core algorithms pertinent to EPPS-DED and essential process strategies for meticulous process planning, providing insights for software development and part quality enhancement. Key topics covered include 3D model slicing, path planning, printing efficiency, and scanning order for 2D contours with diverse geometries, alongside strategies for inclined structures and lattices. Moreover, it discusses the latest AI applications in process planning. The paper concludes with current progress and future outlooks aimed at refining the accuracy and performance of DED-fabricated components.

The hot roll bending patchwork components of B1500HS uncoated ultra-high strength steel processed at industrial scale were welded with filler wire. The microstructure, grain orientation, mechanical properties and fracture behavior of the joint were investigated. The results showed that the weld metal (WM) was mainly composed of lath martensite and lower bainite (LB). Various microstructure appeared in different positions of the HAZ, among which martensite-austenite (M-A) constituents in the incompletely quenched zone and tempered martensite (TM) in the tempered zone were the key factors determining the performance of the joint. The welded joint exhibited complex structure and anisotropic mechanical response due to the decarburization and rolling texture of the original base material (BM). In the tempered zone, lath merge and boundaries disappear lead to the annihilation of dislocations, carbide precipitation leads to reduction of mobile dislocations, and recrystallization and recovery eliminate work hardening. The reduction of the effect of dislocation strengthening results in the formation of a softening belt at 6 mm from the center of the weld, with a minimum hardness of 266 HV. The tensile strength of the joint in the rolling direction (RD) was 983 MPa, and the fracture occurred in the softening belt. Both brittle and ductile fracture features were observed. The reason why the fracture occurs in the high temperature tempered zone instead of the incompletely quenched zone was the difference in the effect of “constraint strengthening”. Fracture occurred through delamination cracking along the “weak interface” owing to precipitated high-hardness cementite particles and the unfavorably oriented ferrite cleavage planes.

Graphical Abstract

Joint homogenization during transition metal carbides ceramic bonding has attracted much attention as a technique to increase the service temperature and relieve the residual stress for various high-temperature applications. In this work, homogeneous joints of ZrC0.85ceramic were obtained by diffusion bonding using single Nb and multiple Ti/Nb/Ti as the interlayer. The effect of interlayer composition, bonding temperature and holding time on the microstructure of the joints was investigated. The effect of Nb and Ti on the composition homogeneity and the formation of Kirkendall voids in the ZrC0.85joints was also discussed. When using single Nb as the interlayer, the homogenization of the joints can be achieved at a bonding temperature of ∼1500 °C and holding for 1 h and no Kirkendall voids were observed when further increasing the bonding temperature to 1600 °C because of the good mutual solubility of NbCxand ZrCxand the relative moderate diffusion rate of Nb. However, severe Kirkendall effects were observed at a higher temperature of 1700 °C, which would deteriorate the high-temperature performance of the joints. The adoption of Ti/Nb/Ti further minished the diffusion rate difference of the interfacial elements through the formation of TiCxphase. As a result, only a few Kirkendall voids were formed at 1700 °C. Nano-hardness of the resultant homogeneous joints was comparable to that of the ZrC0.85ceramic due to their similar composition. This study shows that active diffusion bonding based on interlayer design for homogeneous joints could pave a new way to join transition metal carbides.

Theoretically, the cross coupled arc (CCA) welding process holds the potential for decoupling heat and mass transfer during welding, allowing for independent control. However, conventional CCA processes typically utilize low-frequency alternating current (AC) as input heat sources for the bypass arc, which can lead to oscillation of the main arc due to changes in polarity of the bypass arc. This arc oscillation can result in uneven heat distribution among arcs, consequently affecting the decoupling effect on heat and mass transfer. When applied in additive manufacturing, it may cause issues such as uncontrollable droplet placement and reduced molding accuracy. To reduce the main arc oscillation, this study presents a designed and developed CCA welding heat source using a high-frequency AC square wave with an output frequency up to 20 kHz for input of bypass arc. Through analyses and experimental verification, it has been demonstrated that increasing the variable polarity frequency effectively suppresses the main arc oscillation, achieves control over the melting rate of the filled welding wire within the CCA, and enables decoupled heat transfer between the workpieces' input energy. Furthermore, after suppressing main arc oscillation, it operates with high-frequency vibrations at small amplitudes expected to induce stirring effects on molten pools, promoting dendrite fragmentation and weld grain refinement, which has important potential application and research value.

Variable polarity plasma arc welding (VPPAW) is a highly efficient method for joining aluminum and magnesium alloys, primarily because of the automatic removal of oxide layers through cathode spots. Additionally, the high energy density generated by a variable polarity plasma arc creates a keyhole within the weld pool, enabling single-pass welding of medium-thick plates with minimal deformation and residual stress. Understanding the keyhole behaviors, arc physics, and control methodologies are essential to optimize and improve the stability of this welding process. This survey paper offers an overview of the development of the VPPAW process and its recent developments of detecting, modeling, and controlling. It shows that the potential applications of hybrid processes derived from VPPAW have expanded. Advanced process detection techniques, particularly the utilization of X-ray-based vision systems for the in-situobservation of molten metal flow, have significantly contributed to the understanding of VPPAW. Moreover, studies investigating VPPAW across different welding positions have enhanced the adaptability of this welding method. Accurate numerical models and intelligent deep learning methodologies have been crucial in unveiling the underlying mechanisms and facilitating the predictive analysis of welding quality.

A photocatalytic three-component sulfonyl peroxidation of alkenes with N-sulfonyl ketimines and tert-butyl hydroperoxide is reported. The reaction takes place via the photoinduced EnT process, which allows the efficient synthesis of a variety of β-peroxyl sulfones under mild reaction conditions in the absence of a transition metal catalyst. The downstream derivatizations of the peroxides were also performed. Furthermore, the utility of this protocol was manifested by the synthesis of 11β-HSD1 inhibitor and the antiprostate cancer drug bicalutamide.

At present, the in-situ forging devices do not have the ability to flexibly adjust impacting forces over a wide frequency range and cannot be easily integrated, which restricts its application on DED-arc (directed energy deposition-arc) technology for additive manufacturing. A novel method and system of in-situ micro-impacting assisted DED-arc based on a compact high-dynamic linear actuator was proposed, developed and verified in arc deposition of 5B06 aluminum alloy. The terminal impacting head could be sufficiently close to the molten pool to enforce the obtaining of flat surface of the deposited layer. The results show that the in-situ micro-impacting could produce accumulating rapid micro-deformation and thus induce a gradient microstructure. DDRX (discontinuous dynamic recrystallization) and CDRX (continuous dynamic recrystallization) hybrid dynamic recrystallization behavior was observed. The microhardness of impacted samples was increased by 9.5 % and 8.0 % in vertical and horizontal direction, respectively. The process of rapid micro-deformation contributes to the retaining of the in-situ work-hardening effect at high temperatures, which made the proposed in-situ impacting method a preferred option for DED-arc additive manufacturing.

The sintering technology of iron and steel enterprises in China has reached a certain level. However, due to serious resource and environmental issues, how to achieve the greening of the sintering process, the intelligence of the equipment, the high quality of the products and the acceleration of the digital transformation based on intelligent decision-making and control are still key issues to be solved by the iron and steel industry. Based on the historical data of massive sintering production, this study establishes a big data platform for the whole sintering process to realise the reasonable storage and effective organisation of massive data. A sinter quality cascade prediction system, including the sinter bed permeability prediction model, burning through point (BTP) prediction model and sinter quality prediction model and a detailed software structure design are given for the application of the system. The development and application of the system are beneficial for realising the important development goals of low pollution, high yield and high quality in sinter production.

ABSTRACTIn the data collection of a multi-sensor system, there are problems with large errors, conflicts, and redundancy. To solve the above problem, a multi-sensor data fusion algorithm based on anomaly data preprocessing and adaptive weighted estimation is proposed. To improve the reliability of the algorithm, first, for a single sensor measurement signal sequence, a consistency preprocessing using the off-centre distance method is performed, and the weighting factor of each measurement data is calculated. Then, the measurement signal sequence is weighted and fused; Secondly, in response to the uneven distribution of measurement errors among multiple sensors in different directions, an adaptive weighted data fusion method based on the principle of optimal weight allocation is proposed. The proposed method was compared with the adaptive weighting method and arithmetic mean method. The simulation results showed that the total mean square error of the data fusion results obtained using the proposed algorithm is smaller. The proposed algorithm can effectively improve the accuracy of data measurement, reduce redundancy, and improve the stability of data measurement.

As a key part of solid-state friction rolling additive Manufacturing (FRAM), the toolhead is used to generate heat and deformation through friction with the feed material to form a deposit, and its geometric size directly affects the formation of the FRAM plastic zone; however, to date, no in-depth studies have been conducted. In this study, the effects of toolhead diameters (25, 50, and 100 mm) on the temperature history, material flow, and mechanical properties of the deposited samples are investigated via thermocouple measurements, optical microscopy, and mechanical property tests. The results indicate that, with the increase in toolhead diameter from 25 mm to 100 mm, the area of the interaction zone between toolhead and strip increases from 138 mm2to 274 mm2, peak temperature increases from 522.3 °C to 559.8 °C, the material flow distance in the plastic zone increases from 7.03 mm to 16.6 mm, and the deposition height decreases from 2.4 mm to 1.2 mm. Regardless of the chosen toolhead size, defect-free and high-performance deposited materials can be obtained by optimizing the process parameters. The mechanical properties of deposited 6061 via a 100-mm toolhead are optimal, and the microhardness, tensile strength, and elongation of the deposited material are 66 HV, 234.7 MP, and 28.3 %, respectively. This study provides a basis for the selection and optimization of toolhead size in the FRAM process.

In present study, 50 μm thick Ti/Cu pure metal ultra-thin foils are successfully lap-welded by a nanosecond fiber laser. The joints with adjustable depths are obtained by controlling the laser energy input precisely. The microstructure and mechanical properties of Ti/Cu joints with different depths are well analyzed, respectively. In the joint with smaller penetration depth of 10 μm, thin band-like Ti/Cu intermetallic compounds (IMCs) are formed, while in the joint with a larger penetration depth of 40 μm, thicker band-like Ti/Cu IMCs and sizable bright dendritic Ti2Cu phases are formed, since more Cu element are involved in the chemical reaction in the joint with penetration depth increasing. The tensile test results show that the weld with 10 μm penetration depth has the best tensile strength up to 240 MPa, which is mainly due to less IMCs and low heat input in the weld. In addition, the fracture mode of the joint is classified into two models, including brittle quasi-cleavage fracture on the Ti side fusion zone (FZ) and ductile fracture on the Cu heat affected zone (HAZ), respectively, depending on the penetration depth above or below 30 μm.

The keyhole welding process in Variable Polarity Plasma Arc Welding enhances weld quality significantly, yet it introduces pool instability. Dynamic stability is pursued by investigating molten metal flowing within keyholes and their characteristics. Weld pool flow patterns are obtained via particle tracking, while instability characteristics are captured employing a high-speed camera. Analysing directional molten metal flow unveils Convergence and Separation Points in weld pool flow. The latter's displacement induces weld pool instability, resulting in an increase in keyhole area and a reduction in the pinch angle. The keyhole area signifies pool instability, while the rear wall angle reflects the welding state. These findings provide a theoretical basis for weld control and advance vision-based intelligent manufacturing welding techniques.

This article presents a hybrid full-bridge for high efficiency in a wide output voltage range, especially for pulsed output current applications. For the conventional phase-shift full-bridge dc–dc converter, the hard switching and circulating current lower the efficiency in the wide output conversion ratio. To improve the efficiency of the dc–dc power supply for the pulsed output current, a hybrid dc–dc converter is proposed. On the primary side, two full bridges are integrated by sharing a bridge leg. The circuit on the secondary side is a hybrid rectifier stage. For the pulsed output current with a constant load resistor, a single full bridge works in a low output current. For the large output current, the hybrid two full bridges work together. The circulating current in the hybrid working mode is reduced by a blocking capacitor. The converter is controlled by phase shift and duty cycle control. All the switches work in zero-voltage switching. A prototype is built to verify the performance and control strategy of the converter.

ABSTRACTIn the long process of iron and steel, the sintering process has the largest amount of flue gas emissions, many types of pollutants and high concentrations. The source control of SO2and NOx in sintering flue gas through digital technology has become a new emission reduction technology. In this study, the BP neural network model (BP-NN) is optimized by using the particle swarm algorithm (PSO) to form the PSO-BPNN model, which effectively improves the characteristics of BP-NN with slow convergence speed and easily falls into local minima, and improves the learning ability and generalization. The test results show that the PSO-BP-NN algorithm not only has fast convergence speed and high prediction accuracy, but also has smaller training and inspection errors. In addition, this model combines process theory and feature engineering selection of parameters, which effectively improves the accuracy of the model and the interpretability of the results based on the linkage of process knowledge, and has certain analytical significance for the source management and post-treatment of sintered flue gas.

The keyhole welding process in Variable Polarity Plasma Arc Welding enhances weld quality significantly, yet it introduces pool instability. Dynamic stability is pursued by investigating molten metal flowing within keyholes and their characteristics. Weld pool flow patterns are obtained via particle tracking, while instability characteristics are captured employing a high-speed camera. Analysing directional molten metal flow unveils Convergence and Separation Points in weld pool flow. The latter’s displacement induces weld pool instability, resulting in an increase in keyhole area and a reduction in the pinch angle. The keyhole area signifies pool instability, while the rear wall angle reflects the welding state. These findings provide a theoretical basis for weld control and advance vision-based intelligent manufacturing welding techniques.

In the long process of iron and steel, the sintering process has the largest amount of flue gas emissions, many types of pollutants and high concentrations. The source control of SO2and NOx in sintering flue gas through digital technology has become a new emission reduction technology. In this study, the BP neural network model (BP-NN) is optimized by using the particle swarm algorithm (PSO) to form the PSO-BPNN model, which effectively improves the characteristics of BP-NN with slow convergence speed and easily falls into local minima, and improves the learning ability and generalization. The test results show that the PSO-BP-NN algorithm not only has fast convergence speed and high prediction accuracy, but also has smaller training and inspection errors. In addition, this model combines process theory and feature engineering selection of parameters, which effectively improves the accuracy of the model and the interpretability of the results based on the linkage of process knowledge, and has certain analytical significance for the source management and post-treatment of sintered flue gas.

Al-Zn-Mg-Cu alloys are widely used in aerospace structures because of their excellent performances. To improve the poor mechanical performance of the Al-Zn-Mg-Cu arc additive manufactured deposit, heat treatments were used for the enhancement of mechanical performances. The microstructure of the deposits was improved after heat treatment due to the decomposition of intermetallic compounds. Meanwhile, the solid solution of alloying elements and the phase transformation led to two strengthening mechanisms: solid solution strengthening and the precipitation strengthening. The performance enhancement of the deposits was most significant under the T6 heat treatment. The horizontal and vertical strength increased to 513 and 504 MPa, respectively, and the hardness increased to 205 HV with more uniformly distribution in the vertical direction.

Al-Zn-Mg-Cu alloys are widely used in aerospace structures because of their excellent performances. To improve the poor mechanical performance of the Al-Zn-Mg-Cu arc additive manufactured deposit, heat treatments were used for the enhancement of mechanical performances. The microstructure of the deposits was improved after heat treatment due to the decomposition of intermetallic compounds. Meanwhile, the solid solution of alloying elements and the phase transformation led to two strengthening mechanisms: solid solution strengthening and the precipitation strengthening. The performance enhancement of the deposits was most significant under the T6 heat treatment. The horizontal and vertical strength increased to 513 and 504 MPa, respectively, and the hardness increased to 205 HV with more uniformly distribution in the vertical direction.

ABSTRACTThe sulphide capacities of CaO-SiO2-Al2O3-MgO-TiO2-FetO slags with high titanium and FetO were measured by gas-slag equilibration technique to reveal the effect of slag composition and temperature on the sulphide capacities of slags. The results showed that sulphide capacities enhanced with the increase of temperature, basicity, FetO, and MgO contents, TiO2content increased first and then decreased in the range of 10 wt-% to 20 wt-%; the influence became negligible as the TiO2content exceeded 25 wt-%. MgO significantly increased the sulphide capacities of slag in the range of 6 wt-% to 8 wt-%, continued to increase the MgO content, and the increasing trend of Log CSbecame slowly; FetO content increased from 3 wt-% to 9 wt-%, sulphide capacities increased slowly, increased dramatically in the range of 9 wt-% to 15 wt-%. Meanwhile, comparing the optical basicity models found Zhang and Tsao’s models are close to the experimentally determined values.

The sulphide capacities of CaO-SiO2-Al2O3-MgO-TiO2-FetO slags with high titanium and FetO were measured by gas-slag equilibration technique to reveal the effect of slag composition and temperature on the sulphide capacities of slags. The results showed that sulphide capacities enhanced with the increase of temperature, basicity, FetO, and MgO contents, TiO2content increased first and then decreased in the range of 10 wt-% to 20 wt-%; the influence became negligible as the TiO2content exceeded 25 wt-%. MgO significantly increased the sulphide capacities of slag in the range of 6 wt-% to 8 wt-%, continued to increase the MgO content, and the increasing trend of Log CSbecame slowly; FetO content increased from 3 wt-% to 9 wt-%, sulphide capacities increased slowly, increased dramatically in the range of 9 wt-% to 15 wt-%. Meanwhile, comparing the optical basicity models found Zhang and Tsao’s models are close to the experimentally determined values.

This study investigates the underlying causes of Variable Polarity Plasma Arc Welding (VPPAW) spatial positional instability and its adverse impact on weld seam quality. Microstructural analysis reveals that the primary cause of poor transverse mechanical properties is the asymmetric distribution of grains. Through the study of heat and mass transfer in the molten pool, it was found that the asymmetric flow of molten metal under the influence of gravity is the main factor leading to uneven temperature distribution and asymmetric grain distribution in the weld pool. A novel approach based on a predefined temperature field is proposed to regulate the weld pool's stability and welding quality. The implementation of the predefined temperature field effectively improves VPPAW weld pool flow, leading to enhanced temperature distribution and grain size and distribution. These findings provide a theoretical foundation and valuable engineering recommendations for achieving high-quality spatial position welding in VPPAW.

The dissimilar AZ31B/AZ61 Mg alloy joints were fabricated by pulse current-assisted friction stir welding (PCaFSW). The maximum tensile strength and elongation were 314.28 MPa and 13.66%, respectively. A micro interlocking structure was formed and the grain refinement effect was enhanced by the PCaFSW process, which was improved relative to that in the conventional FSW. The enhanced strength and plasticity with increasing pulse current were attributable to the grain refinement, weakening of texture strength, formation of nano-scale precipitates and increase of short dislocation lines. The fracture mode was transformed from a brittle fracture mode to a combined fracture mode of brittle and ductile fractures.

The dissimilar AZ31B/AZ61 Mg alloy joints were fabricated by pulse current-assisted friction stir welding (PCaFSW). The maximum tensile strength and elongation were 314.28 MPa and 13.66%, respectively. A micro interlocking structure was formed and the grain refinement effect was enhanced by the PCaFSW process, which was improved relative to that in the conventional FSW. The enhanced strength and plasticity with increasing pulse current were attributable to the grain refinement, weakening of texture strength, formation of nano-scale precipitates and increase of short dislocation lines. The fracture mode was transformed from a brittle fracture mode to a combined fracture mode of brittle and ductile fractures.

Background: Frailty is a state of cumulative degeneration of bodily functions that is consistently associated with poor outcomes in older people following illness. Combined stroke intervention and frailty may yield additive and synergistic effects adults with stroke. Objective: To evaluate the safety and efficacy of endovascular therapy (EVT) in frail patients. Methods: We conducted a systematic review of the relationship between debilitation and acute ischemic stroke (AIS) after EVT. Until August 2022, researchers have searched three databases (Pubmed, EMBASE and Cochrane). Random-effects meta-analysis, combined ratio (OR) and 95% confidence interval (95%CI) were used to assess efficacy values. The I2statistic was used to assess heterogeneity. Comprehensive meta-analysis software was used for meta-analysis. Results: We ultimately included eight studies including 3662 non-overlapping participants. Four studies used the Clinical Frailty Scale (CFS), two studies used the Hospital Frailty Risk Score (HFRS), a study used frailty index and a study used the comprehensive geriatric assessment (CGA). Frailty prevalence: 35%; 95% CI, 0.27–0.43; low quality evidence, downgraded due to heterogeneity, bias. Random effects showed that poor functional outcome (5 studies, OR 1.956, 95% CI 1.256–3.048) and mortality (9 studies, OR 2.320, 95% CI 1.680–3.205) was significantly associated with frailty. In adjusted analyses, poor functional outcome (4 studies, ORadj1.189, 95% CI 1.043–1.357), and mortality (3 studies, ORadj1.036, 95% CI 1.008–1.065) were significantly associated with frailty. Conclusion: Pre-stroke frailty is an important predictor of poor prognosis assessed by EVT and can be added to the classical predictors of stroke outcome. Routine assessment of pre-stroke frailty can help patients to make decisions about the efficacy of their choice of EVT.

A solid-state and continuous groove repair technology was proposed for aluminium alloy based on friction rolling additive manufacturing (FRAM). The feasibility of FRAM was explored by repairing three types of prefabricated groove damages in aluminium alloy plates. A well-repaired joint for trapezoidal groove was obtained when the press-in depth of the tool head was 2 mm. The press-in depth was the key factor to complete filling of the groove damage. Effective grain refinement of the repair centre and the significant refinement area are observed, which leads to the hardness of these two areas reaching 99% and 102% of the substrate, respectively. The material migration behaviour of the filling material during the process was clarified.

A solid-state and continuous groove repair technology was proposed for aluminium alloy based on friction rolling additive manufacturing (FRAM). The feasibility of FRAM was explored by repairing three types of prefabricated groove damages in aluminium alloy plates. A well-repaired joint for trapezoidal groove was obtained when the press-in depth of the tool head was 2 mm. The press-in depth was the key factor to complete filling of the groove damage. Effective grain refinement of the repair centre and the significant refinement area are observed, which leads to the hardness of these two areas reaching 99% and 102% of the substrate, respectively. The material migration behaviour of the filling material during the process was clarified.

To overcome the strength–ductility trade-off dilemma, the microstructure of Al–Zn–Mg–Cu alloy was controlled by adding TiN nanoparticles and heat treatment successively. Al–Zn–Mg–Cu alloy deposition with both high strength and high elongation was achieved. The tensile strength, elongation, and microhardness were increased by 122.3%, 173.9%, 86.1%, and 82.5%, respectively. The columnar grains were completely transformed into equiaxed grains with the addition of TiN particles and the grain size was reduced by 92.9%. The elongation increase was mainly because of the grain refinement, and the distribution fluctuation of the properties decreased. After T6 heat treatment, the elongation remained high because the grain size changed negligibly. Precipitation strengthening is the main mechanism for the improved tensile strength and hardness.

Vertical material flow and microstructure evolution were investigated by the material tracing technology during friction stir lap welding of 6061-T6 aluminium alloys from a new perspective: various angles of keyhole obtained by emergency stop technique. First, lamellar grains were transformed into equiaxed subgrains, and texture was transitioned from {110}//shear direction fibre texture to strong components when materials flowed from the advancing side to the leading side. Then subgrains grew into recrystallised grains at the retreating side. After that the downward material flow at the trailing side induced plastic deformation, resulting in many subgrains with strong texture components. Finally, grains grew up and retained with strong components in the stir zone.

To overcome the strength–ductility trade-off dilemma, the microstructure of Al–Zn–Mg–Cu alloy was controlled by adding TiN nanoparticles and heat treatment successively. Al–Zn–Mg–Cu alloy deposition with both high strength and high elongation was achieved. The tensile strength, elongation, and microhardness were increased by 122.3%, 173.9%, 86.1%, and 82.5%, respectively. The columnar grains were completely transformed into equiaxed grains with the addition of TiN particles and the grain size was reduced by 92.9%. The elongation increase was mainly because of the grain refinement, and the distribution fluctuation of the properties decreased. After T6 heat treatment, the elongation remained high because the grain size changed negligibly. Precipitation strengthening is the main mechanism for the improved tensile strength and hardness.

Vertical material flow and microstructure evolution were investigated by the material tracing technology during friction stir lap welding of 6061-T6 aluminium alloys from a new perspective: various angles of keyhole obtained by emergency stop technique. First, lamellar grains were transformed into equiaxed subgrains, and texture was transitioned from {110}//shear direction fibre texture to strong components when materials flowed from the advancing side to the leading side. Then subgrains grew into recrystallised grains at the retreating side. After that the downward material flow at the trailing side induced plastic deformation, resulting in many subgrains with strong texture components. Finally, grains grew up and retained with strong components in the stir zone.

The flow and slip rate of material in friction stir welding mainly determined the weld quality, flow rate depended not only on the shape of pin and welding parameters but also on slip, and an instantaneous centre of speed was generated by rotating speed and welding speed. The relative speed of contact interface is generally an important factor in material flow. The material experienced different viscous slips when rotating around the pin, which disengaged pin at a larger slip and adhered to pin at a smaller slip, resulting in large differences in two sides. The first derivative of the dividing line at the boundary of SZ was extracted to investigate material flow.

The flow and slip rate of material in friction stir welding mainly determined the weld quality, flow rate depended not only on the shape of pin and welding parameters but also on slip, and an instantaneous centre of speed was generated by rotating speed and welding speed. The relative speed of contact interface is generally an important factor in material flow. The material experienced different viscous slips when rotating around the pin, which disengaged pin at a larger slip and adhered to pin at a smaller slip, resulting in large differences in two sides. The first derivative of the dividing line at the boundary of SZ was extracted to investigate material flow.

Mg alloys have been extensively used in lightweight manufacturing owing to excellent mechanical properties. However, liquation cracking occurred during welding of dissimilar Mg alloys, significantly deteriorating mechanical properties. The temperature-stress distribution and generation law of liquation cracking in circular-patch welding of dissimilar Mg alloys were investigated by a combination of numerical simulation and experimental work. The peak temperature in the partially melted zone 0–2.5 mm from the outside of the weld exceeded 710 K (eutectic temperature of AZ91), which is prone to eutectic liquation. The radial tensile stress exerted on the partially melted zone during the cooling process. The peak value of radial tensile stress in the last stage of solidification of eutectic liquid phase reached about 24.4 MPa. Heat treatment before welding was used to dissolve the intermetallic compounds γ(Mg17Al12) to prevent liquation cracking.

Adding heterogeneous nucleation refiners is an effective route to obtain fine grained microstructure. To investigate effect of silicon carbide (SiC) particles on mechanical properties of Al–Mg alloy, metallic matrix composites (MMCs) were fabricated by an innovative powder and wire cold metal transfer (CMT) process with enhanced mechanical properties. Microstructure evolution, grain orientation and mechanical properties of CMT processed MMCs reinforced by SiC particles at different concentrations were discussed. The mechanical properties of Al–Mg alloy reached the highest tensile strength of 325.6 ± 16 MPa by addition of SiC particles with a volume fraction of 8% and an average grain diameter of 49.1 μm. This research provided a novel, time-saving, low-cost approach to fabricate Al–Mg composites and expands application of Al–Mg alloy.

ABSTRACTStable powder injecting into a weld pool in gas metal arc welding (GMAW) process cannot be guaranteed by a regular by-pass-feed method due to the strong repelling from the shielding gas. A novel trial of co-axial through-the-arc powder injecting is thus proposed to study its effect on the bead formation, microstructure, and surface hardness of aluminium-alloy welds. The weld depth and bead width could be both increased. Cellular grains grow on most of the surface of TiC particles, some of which even grow into columnar grains and dendrites. Effective grain refinement of the melted zone (MZ) is observed. The surface hardness of the cross section is significantly increased. These positive results would be beneficial for arc welding and additive manufacturing processes.

Stable powder injecting into a weld pool in gas metal arc welding (GMAW) process cannot be guaranteed by a regular by-pass-feed method due to the strong repelling from the shielding gas. A novel trial of co-axial through-the-arc powder injecting is thus proposed to study its effect on the bead formation, microstructure, and surface hardness of aluminium-alloy welds. The weld depth and bead width could be both increased. Cellular grains grow on most of the surface of TiC particles, some of which even grow into columnar grains and dendrites. Effective grain refinement of the melted zone (MZ) is observed. The surface hardness of the cross section is significantly increased. These positive results would be beneficial for arc welding and additive manufacturing processes.

Al–Zn–Mg–Cu alloys are widely used in large-scale structural components of the aerospace industry, but research on wire and arc additive manufacturing (WAAM) of Al–Zn–Mg–Cu alloys is lacking. This research focused on grain refining of Al–Zn–Mg–Cu alloys by adding TiN particles during WAAM. The WAAM component was filled with equiaxed grains and the grain orientation became more random because the coarse columnar grains were eliminated. The average grain size was reduced from a value of 459 μm to a value of 104 μm. Heterogeneous nucleation by TiN particles was the main grain refining mechanism, and the TiN particles located along the grain boundaries also helped prevent grain growth. The horizontal and vertical elongations were increased by 160% and 98%, respectively, because of grain refinement; whereas the horizontal tensile strength was increased by 38.1%. The enhanced mechanical properties were mainly attributable to grain refinement and weakening of the texture strength.

High-strength Al–Zn–Mg–Cu aluminum alloys are widely used in large-scale aerospace parts. However, high crack sensitivity limits their development during additive manufacturing. The mechanism of crack formation in Al–Zn–Mg–Cu alloy parts manufactured by wire-arc additive manufacturing was studied through a combination of thermal stress simulations and microstructure analyses. Increasing number of deposition layers gradually expanded the partial melting zone, leading to heat accumulation. In addition, the equivalent stress at both sides was considerably higher than that at the center of the parts, and the equivalent stress at the bottom was the highest, which gradually decreased with increasing distance from the bottom. However, in the initial stage of the deposition, the area of the partial melting zone in the bottom was small; the crack sensitivity was low (no cracks were found). With further deposition, liquation cracks occurred 40–60 mm from the bottom and were initiated at sufficient stress and temperature. The increase in the deposition height increased the stress and crack propagation to form a macro crack.