Search Results (43)

Mg-Al-Ca alloys are attractive low-cost wrought Mg alloys. However, the distinct roles of Al and Ca in regulating deformation-processed microstructures and mechanical properties remain unclear. In this work, Mg–6Al–0.5Ca, Mg–9Al–0.5Ca, and Mg–9Al–1.3Ca (wt. %) alloys were extruded at 250 °C and 300 °C to clarify the composition-dependent microstructure evolution and strengthening mechanisms. Increasing the Al content from 6 to 9 wt. % markedly promoted the formation of fine Mg₁₇Al₁₂ (f-Mg₁₇Al₁₂) and coarse Mg₁₇Al₁₂ particles, whereas increasing the Ca content from 0.5 to 1.3 wt. % promoted the formation of coarse Al₂Ca particles while reducing the density of f-Mg₁₇Al₁₂. Quantitative analysis revealed that f-Mg₁₇Al₁₂ particles refined dynamically recrystallized grains by promoting recrystallization nucleation and pinning grain boundaries while also contributing to Orowan strengthening. The Mg–9Al–0.5Ca alloy exhibited the best strength–ductility balance, with a yield strength of 338 ± 4 MPa, ultimate tensile strength of 396 ± 5 MPa, and elongation of 8.7 ± 1.6% after extrusion at 250 °C. Strengthening calculations indicated that grain-boundary strengthening was the dominant strengthening contribution, while the strength advantage of Mg–9Al–0.5Ca originated from the dual role of f-Mg₁₇Al₁₂ in grain refinement and dislocation obstruction. These findings provide a practical strategy for designing high-strength non-rare-earth Mg–Al–Ca extrusion alloys. Full article

This article deals with the substitution of a pin-type rubber extruder by alternative screw concepts based on circumferential and axial flight offsets. Alternative screw concepts were investigated using simulative and experimental methods. This revealed the opportunities and risks of the simulations and the suitability of pinless concepts for rubber extrusion. Good functionality of the simulations is shown for an SBR rubber mixture, except for thermal properties. For the SBR mixture used, pinless designs can achieve comparable material and thermal homogeneity to conventional pin extruders while achieving up to 10% higher throughputs. Therefore, this study shows that these alternative designs can increase the cost-effectiveness of rubber extrusion and be designed using simulative methods. Full article

The thermal dissipation performance of the radiator is crucial for the stable operation of power electronic devices. Due to excellent thermal performance, copper pin-type heat sink substrates are widely adopted. However, the cold extrusion process for heat sink substrates suffers from low material utilization and high forming loads. To improve material utilization and reduce cold extrusion forming load, four blank shapes (rectangular, trapezoidal, trapezoidal cap, and stepped) were designed using finite-element simulation to investigate the effects of blank shape and placement method with orientation relative to the die cavity on forming quality. Further dimensional optimization was conducted to determine the optimal configuration. The results show that the stepped blank with front orientation exhibits the optimal forming performance, featuring the lowest forming load and the most sufficient pin-fin filling. Compared with back orientation, front orientation achieves higher and more uniform material flow velocity, and significantly reduces forming load. Through dimension optimization, the 7 mm-thick stepped blank is determined as the optimal solution, with the forming load reduced to 15,000 kN (a 35.3% decrease compared to the initial 7.5 mm stepped blank), and both the substrate thickness and pin-fin height meet the design requirements (4.5 mm and 6.5 mm). Experiments verify the feasibility of the optimized scheme, providing technical support for the low-cost, high-quality mass production of copper pin-type heat sink substrates. Full article

Additive manufacturing (AM) is a significant contributor to Industry 4.0. However, one considerable challenge is usually encountered by AM due to the bed size limitations of 3D printers, which prevent them from being adopted. An appropriate post-joining technique should be employed to address this issue properly. This study investigates the influence of key friction stir butt welding (FSBW) factors (FSBWFs), such as tool rotational speed (TRS), tool traverse speed (TTS), and pin profile (PP), on the weldability of 3D-printed PLA–Chromium (PC) composites (3PPCC). A filament containing 10% by weight of chromium reinforced in PLA was used to prepare samples. The material extrusion additive manufacturing process (MEX) was employed to prepare the 3D-printed PCC. A Taguchi-based design of experiments (DOE) (L9 orthogonal array) was employed to systematically assess weld hardness (WH), weld temperature (WT), weld strength (WS), and weld efficiency. As far as the 3D-printed samples were concerned, two distinct infill patterns (linear and tri-hexagonal) were also examined to evaluate their effect on joint performance; however, all other 3D printing factors were kept constant. Experimentally validated findings revealed that weld efficiency varied significantly with PP and infill pattern, with the square PP and tri-hexagonal infill pattern yielding the highest weld efficiency, i.e., 108%, with the corresponding highest WS of 30 MPa. The conical PP resulted in reduced WS. Hardness analysis demonstrated that tri-hexagonal infill patterns exhibited superior hardness retention, i.e., 46.1%, as compared to that of linear infill patterns, i.e., 34%. The highest WTs observed with conical PP were 132 °C and 118 °C for both linear and tri-hexagonal infill patterns, which were far below the melting point of PLA. The lowest WT was evaluated to be 65 °C with a tri-hexagonal infill, which is approximately equal to the glass transition temperature of PLA. Microscopic analysis using a coordinate measuring machine (CMM) indicated that optimal weld zones featured minimal void formation, directly contributing to improved weld performance. In addition, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also performed on four deliberately selected samples to examine the microstructural features and elemental distribution in the weld zones, providing deeper insight into the correlation between morphology, chemical composition, and weld performance. Full article

During the extrusion of novel nickel-based powder superalloy bars, the die is subjected to elevated temperatures, high pressures, and severe friction, which readily lead to abrasive wear and thermal-fatigue damage. These failures deteriorate the quality of the extruded products and significantly shorten the service life of the die. Frequent repair and replacement of the tooling ultimately increase the overall manufacturing cost. This study investigates the friction and wear behavior of H13 and 5CrNiMo hot-work tool steels under extreme transient high-temperature conditions by combining finite element simulation with tribological testing. The temperature and stress distributions of the billet and key tooling components during extrusion were analyzed using DEFORM-3D. In addition, pin-on-disk friction and wear tests were conducted at 1000 °C to examine the friction coefficient, wear morphology, and subsurface grain structural evolution under various loading conditions. The results show that the extrusion die and die holder experience the highest loads and most severe wear during the extrusion process. For 5CrNiMo tool steel, the wear mechanism under low loads is dominated by mild abrasive wear and oxidative wear, whereas increasing the load causes a transition toward adhesive wear and severe oxidative wear. In contrast, H13 tool steel exhibits a transition from abrasive wear to severe oxidative wear. In 5CrNiMo steel, friction-induced recrystallization, grain refinement, and softening lead to the formation of a mechanically mixed layer, which, together with a stable third-body layer, markedly reduces and stabilizes the friction coefficient. H13 steel, however, undergoes surface strain localization and spalling, resulting in persistent fluctuations in the friction coefficient. The toughness and adhesion of the oxide film govern the differences in wear mechanisms between the two steels. Owing to its higher Cr, V, and Mo contents, H13 forms a dense but highly brittle oxide scale dominated by Cr and Fe oxides at 1000 °C. This oxide layer readily cracks and delaminates under frictional shear and thermal cycling. The repeated spalling exposes the fresh surface to further oxidation, accompanied by recurrent adhesion–delamination cycles. Consequently, the subsurface undergoes alternating intense shear and transient load variations, leading to localized dislocation accumulation and cracking, which suppresses the progression of continuous recrystallization. Full article

A hot extrusion deformation test of sintered Cu-10wt%Mo composite was carried out under deformation conditions, with deformation temperatures ranging from 800 °C to 950 °C, and extrusion ratios ranging from 2.9 to 10.5. The hot extrusion process eliminated the original interfaces between copper powder particles in sintered Cu-10wt%Mo composite. While the copper phase experienced dynamic recrystallization, the molybdenum particles effectively pinned the boundaries and inhibited subsequent grain growth. As the extrusion ratio increased, the composite material’s tensile strength, elongation, and thermal conductivity first increased and then decreased. With the rise in hot extrusion deformation temperature, the composite material’s tensile strength, elongation, and thermal conductivity gradually increased, but stabilized after reaching 900 °C. Deformation during hot extrusion is confined to the copper phase, which undergoes dynamic recrystallization (DRX), with no significant deformation occurring in the molybdenum phase. The molybdenum phase promotes an increased local strain rate in the copper phase, resulting in the formation of a certain number of twin grains. Full article

Lepidopterans produce two distinct types of sperm: nucleated eupyrene sperm for fertilization and anucleate apyrene sperm for auxiliary functions. However, the mechanisms underlying sperm dimorphism in fall armyworm Spodoptera frugiperda remain poorly understood. Serine–Arginine Protein Kinases (SRPKs) are a class of kinases that catalyze the phosphorylation of SR proteins, but recent studies have shown that SRPK is critical for chromatin remodeling of sperm in mammals. Whether SRPK is involved in lepidopteran spermatogenesis is completely unknown. Here, we describe the entire process of elongation and maturation of both eupyrene and apyrene sperm bundles in S. frugiperda. The eupyrene sperm bundles elongated from the 3-day-old 6th-instar larvae, transiently forming a bowling-pin shape prior to cytoplasmic extrusion and finally maturing into structures with a fan-shaped head and slender tail after eclosion. In contrast, apyrene sperm bundles originated at 2-day-old pupae, where they underwent immediate nuclear extrusion and elongated into bundles that later coiled into a mature, spindle-shaped spool conformation in male adults. Larval knockdown of Serine–Arginine Protein Kinase 3 (SRPK3) significantly reduced apyrene sperm ratio and induced precocious maturation of eupyrene sperm, accompanied by acrosomal malformations. Furthermore, we observed a marked downregulation of cytoskeletal genes—including α-tubulin and cofilin—in non-testicular tissues and β-actin in testicular tissues. In contrast, the expression of dynamin and Lasp was upregulated in the testis and non-testicular tissues, respectively. Our results indicate that SRPK3 regulates both apyrene sperm differentiation and eupyrene sperm maturation by modulating the expression of cytoskeletal components, which provides new clues for lepidopteran spermatogenesis. Full article

Particle-based 3D printing shows great potential in high-performance composite fabrication due to high raw material utilization and flexible material compatibility. However, constrained by conventional extrusion system structures, critical issues (non-uniform melt conveying, insufficient mixing efficacy, poor extrusion stability, etc.) remain. To address these, this study proposes a novel separate-type pin screw integrating solid–liquid separation (from split screws) and high-efficiency mixing (from pin screws) to improve CF/PLA composite extrusion efficiency and mixing homogeneity in particle-based 3D printing. Three-dimensional modeling, static strength/stiffness analysis, and POLYFLOW-based numerical simulation of particle melt conveying/mixing in the screw channel were conducted to analyze structural parameter effects on pressure field, shear rate, and mixing. Experiments assessed printer extrusion rate (different screws) and printed specimen mechanical properties. The simulation and experiment confirmed the optimized screw has better pressure distribution and mixing at 20 rpm, with optimal pin parameters: diameter 2 mm, height 1.6 mm, radial angle 60°, and axial spacing 10 mm. This work offers theoretical/structural support for particle-based 3D printing extrusion system optimization. Full article

This study investigates the influence of graphene nanoplatelets (GNPs) and the formation of nanosized Al₄C₃ on the tribological performance of hot extruded aluminum-based nanocomposites. Al/GNP nanocomposites with varying GNP contents (0, 0.1, 0.5, and 1.1 wt.%) were fabricated through powder metallurgy, including ball milling, compaction, and hot extrusion at 500 °C, which was designed to facilitate the formation of nanosized carbides during the extrusion process. The effect of GNPs and nanosized carbides on the tribological properties of the composites was evaluated using dry friction pin-on-disk tests to assess wear resistance and the coefficient of friction (COF). Microstructural analyses using scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed the uniform distribution of GNPs and the formation of nanosized Al₄C₃ in the samples. Incorporating 0.1 wt.% GNPs resulted in the lowest wear mass loss (1.40 mg) while maintaining a stable COF (0.52), attributed to enhanced lubrication and load transfer. Although a higher GNP content (1.1 wt.%) resulted in increased wear due to agglomeration, the nanocomposite still demonstrated superior wear resistance compared to the unreinforced aluminum matrix. These findings underscore the potential of combining nanotechnology with precise processing techniques to enhance the wear and friction properties of aluminum-based composites. Full article

Additive manufacturing has a strong potential to produce sound metal–polymer joints using controlled polymer deposition on a metallic substrate. In this way, this study aimed to explore the morphological and mechanical properties of metal–polymer joints produced through material-extrusion-based AM using a pin-based macro-mechanical interlocking mechanism. Joints were fabricated with polylactic acid deposited onto a heated aluminium alloy substrate to form the connection. The optimisation process was focused on improving the printing parameters and pin geometries to reduce voids and enhance joint integrity. The results indicate that optimised samples exhibit superior mechanical resistance, achieving a maximum load improvement with an overall strength increase of 368.97% compared to non-optimised joints. A combined pin geometry (50% cylindrical, 50% conical) was found to be the most effective. Morphological analysis confirmed uniform polymer deposition, ensuring reliable joint performance. These findings underscore the critical role of geometric optimisation in enhancing the strength and durability of metal–polymer joints in AM applications. Full article

In this study, we investigated the mechanical and tribological properties of the layer-by-layer structure of additively manufactured implant-grade Polyether Ether Ketone (PEEK) through the Material Extrusion (ME) process as a potential substitute for artificial joints. The effective elasticity modulus of the anisotropic 3D-printed PEEK was determined to be 2.505 GPa along the vertical and horizontal build orientations. The lubricated friction and wear performance were assessed using a pin-on-disk test under various loads, including 14, 30, 50, and 70 N, with a sliding speed of 50 mm/s over a total distance of 1 km at 37 °C. The contact parameters between the hemispherical steel pin and 3D-printed PEEK disks, involving contact pressures over the circle of contact, were observed to increase as the load increased. The results indicated that the wear coefficient exhibited a rise from $1.418{ \times 10}^{-5}$ to $2.089{ \times 10}^{-1}$ as the applied loads increased, signaling a shift from mild to severe wear regimes. Fetal Bovine Serum (FBS) as a lubricant exhibited a mixed mechanism, ascertained through the Stribeck curve, as well as a minimum fluid film thickness of 1.346 nm under an isoviscous–elastic regime, as calculated by the maximum load. Moreover, the mechanism governing wear during sliding, influenced by both normal axial and shear loads, primarily involved adhesion. Full article

The direct ink writing (DIW) process, used for creating components with functionally graded materials, holds significant promise for advancement in various advanced fields. However, challenges persist in achieving complex gradient variations in small-sized parts. In this study, we have developed a customized pin shape for an active screw mixer using a combination of quadratic B-Spline, the response surface method, and global optimization. This tailored pin design was implemented in a two-material extrusion-based printing system. The primary objective is to facilitate the transformation of material components with shorter transition distances, overcoming size constraints and enhancing both printing flexibility and resolution. Moreover, we characterized the transition delay time for material component changes and the mixing uniformity of the extruded material by constructing a finite element simulation model based on computational fluid dynamics. Additionally, we employed a particle tracking method to obtain the Lyapunov exponent and Poincaré map of the mixing process. We employed these metrics to represent and compare the degree of chaotic mixing and dispersive mixing ability with two other structurally similar mixers. It was found that the optimized pin-type mixer can reduce the transition delay distance by approximately 30% compared to similar structures. Finally, comparative experiments were carried out to verify the printing performance of the optimized pin-type active mixer and the accuracy of the finite element model. Full article

This study explores the potential of novel boron nitride (BN) microplatelet composites with combined thermal conduction and electrical insulation properties. These composites are manufactured through Fusion Deposition Modeling (FDM), and their application for thermal management in electronic devices is demonstrated. The primary focus of this work is, therefore, the investigation of the thermoplastic composite properties to show the 3D printing of lightweight polymeric heat sinks with remarkable thermal performance. By comparing various microfillers, including BN and MgO particles, their effects on material properties and alignment within the polymer matrix during filament fabrication and FDM processing are analyzed. The characterization includes the evaluation of morphology, thermal conductivity, and mechanical and electrical properties. Particularly, a composite with 32 wt% of BN microplatelets shows an in-plane thermal conductivity of 1.97 W m⁻¹ K⁻¹, offering electrical insulation and excellent printability. To assess practical applications, lightweight pin fin heat sinks using these composites are designed and 3D printed. Their thermal performance is evaluated via thermography under different heating conditions. The findings are very promising for an efficient and cost-effective fabrication of thermal devices, which can be obtained through extrusion-based Additive Manufacturing (AM), such as FDM, and exploited as enhanced thermal management solutions in electronic devices. Full article

Bobbin tool friction stir welding (BT-FSW), or self-reacting tool friction stir welding (SR-FSW), refers to a solid-state welding process which that uses two opposing rotating shoulders (top and lower of the workpiece) connected with a fully penetrated pin. In fact, the bottom shoulder in the BT-FSW design replaced the backing plate used in the conventional tool friction stir welding (CT-FSW) to promote symmetrical solid-state joints. Compared to CT-FSW, the BT-FSW process has many advantages over the use of a conventional tool such as the welded structure is symmetric in thickness, low distortion of weld joint can be obtained, the elimination of root for welds, a backing plate is not required, and high force is not required for fixing the weld plates and possibility welding a closed or a hollow section (U and H shapes). The welding parameters of BT-FSW, such as tool pin profile, rotational speed, welding speed, and axial force, have a considerable effect on the microstructure and the mechanical properties of the resulting assembly. In the current study, two extrusions of aluminum alloy 6061-T6 with 8 mm were joined by the BT-FSW technique with a tool pin with threads and eight different welding parameters (tool rotation speed and welding speed). The maximum value of tensile strength was achieved using optimum welding conditions of a tool rotation speed of 850 rpm/min and a welding speed of 650 mm/min. The study also investigated the joint efficiency of the friction stir welded joint, defects at the weld zone, and fatigue life of BT-FSW samples at the optimized level. Full article

Mg-3Sn-1Mn-xLa alloy bars were prepared using backward extrusion, and the effects of the La content on the microstructures and mechanical properties of the alloy were systematically studied using an optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile tests. The results of this research show that the Mg₂Sn phases were mainly formed at the α-Mg grain boundaries and within the grains in the Mg-3Sn-1Mn alloy. After adding a certain amount of La, the plate-shaped MgSnLa compounds consisting of Mg₁₇La₂, Mg₂Sn, and La₅Sn₃ gradually disappeared in the α-Mg matrix and grain boundaries. With an increase in La content, the Mg₂Sn phase in the crystal was gradually refined and spheroidized. When the content of La reached 1.5%, the tensile strength of the alloy reached 300 Mpa and the elongation reached 12.6%, i.e., 25% and 85% increases, respectively, compared to the Mg-3Sn-1Mn alloy. The plate-shaped compound of Mg-3Sn-1Mn-1.5La had an average length of 3000 ± 50 nm, while the width was 350 ± 10 nm. Meanwhile, the extruded alloy’s grain size was significantly refined, and there were many small cleavage steps and dimples in the fracture surface of the alloy. When the La content reached 2%, the alloy performance showed a downward trend due to the coarsening of the grains. The formed plate-shaped MgSnLa compounds and Mg₂Sn phases were consistent with the α-Mg matrix. They effectively pinned the dislocations and grain boundaries, which is the main reason for strengthening the mechanical properties of extrusion alloys. Full article