Search Results (451)

With the rapid transition of power transmission systems toward higher capacity, longer distance, and improved efficiency, aluminum alloys from the 6xxx (Al–Mg–Si) and 8xxx (Al–Fe) series have become key structural materials for overhead conductors and power cables due to their low density, cost effectiveness, and favorable strength–conductivity balance. Compared with traditional steel-reinforced conductors, optimized aluminum alloy conductors can reduce structural weight by approximately 30–40% and installation cost by about 20–30%, while maintaining comparable current-carrying capacity. This review systematically focuses on modification methods and research progress of aluminum alloy cores for electric wires and cables. The strengthening characteristics of 6xxx alloys (heat-treatment responsiveness and precipitation strengthening) and the creep-resistance stability of 8xxx alloys are comparatively analyzed. Four core performance requirements—high electrical conductivity, mechanical strength, creep resistance, and corrosion resistance—are summarized as evaluation criteria for conductor applications. Particular emphasis is placed on three major modification strategies: (1) microalloying (e.g., Zr, Sc, rare earth elements) for precipitation and dispersoid stabilization; (2) thermomechanical process optimization for grain refinement and strength–conductivity balance; (3) composite reinforcement for high-temperature and ultra-high-strength applications. Quantitative literature data indicate that microalloying and process optimization typically achieve 15–40% strength improvement with conductivity variation within 3–5% IACS, while composite strategies may provide 30–80% strength enhancement but often at the expense of 5–20% conductivity reduction. The distinct applicability of 6xxx and 8xxx alloys under different service conditions is clarified, providing guidance for conductor material selection. Finally, future research directions—including precise composition–process integration, advanced thermomechanical control, and scalable modification technologies—are proposed to support high-performance, cost-effective, and large-scale deployment of aluminum alloy conductors. Full article

Microstructural and morphological effects of cobalt (Co), nickel (Ni), and cerium (Ce) microalloying on the SAC305 lead-free solder alloy were investigated, with emphasis on the solidification behavior under slow cooling conditions. Although the individual effects of these elements have been previously reported, their combined influence remains scarcely addressed. Thermal behavior, elemental composition, and surface integrity of the solder joints were analyzed. The addition of Co, Ni, and Ce resulted in a significant shift of the onset temperature during cooling, indicating reduced undercooling. Microalloying led to a transformation of the intermetallic layer (IML) morphology from scalloped to planar, and a 60% reduction in the number of shrinkage voids. The average β-Sn grain size decreased by 37.5%, while the eutectic area increased from 32% to 38%. The substitution of Cu atoms by Co and Ni within the Cu₆Sn₅ lattice formed thermodynamically stable (Cu,Co,Ni)₆Sn₅ phases. These findings demonstrate that the synergistic effect of Co, Ni, and Ce microadditives effectively refines the microstructure, suppresses undercooling, and enhances the overall reliability of SAC305 solder joints. Full article

A microalloyed high-carbon low-alloy steel was designed to clarify the combined effects of austenitizing temperature and deep cryogenic treatment (DCT) on microstructural evolution and mechanical performance. Specimens were austenitized at 770–900 °C, water-quenched, subjected to DCT at −196 °C, and subsequently tempered at 180 °C. Microstructural characterization by XRD, EBSD, and TEM indicates that the quenched microstructure is dominated by martensite and cementite, with retained austenite below 1% at moderate austenitizing temperatures. DCT does not fundamentally alter the martensitic morphology but promotes the transformation of retained austenite and induces substructure fragmentation, dislocation reorganization, and a more homogeneous lattice strain distribution. Concurrently, carbon redistribution during cryogenic exposure facilitates the formation of finely dispersed carbides. After tempering, partial recovery and stabilization of the martensitic substructure lead to reduced lattice distortion while maintaining a high density of effective strengthening features. Mechanical testing shows that DCT combined with appropriate austenitizing (770–790 °C) improves hardness and ultimate tensile strength with acceptable ductility, whereas excessive austenitizing at 900 °C results in severe grain coarsening and intergranular brittle fracture. The results demonstrate that optimized integration of microalloying and DCT enables a favorable strength–toughness balance in high-carbon tool steels. Full article

The study investigates the microstructure evolution in the stir zone produced by the friction stir processing (FSP) of a heat-treated microalloyed Al-Mn-Cu alloy in the area subjected to the highest temperature, strain, and strain rate. The samples were studied using electron microscopy and atom probe tomography (APT) to obtain structural and chemical information from the macro to the nano scale. FSP refines the dendritic Al-rich solid solution grains through dynamic recrystallisation in the range of a few micrometres. The primary intermetallic phases were dispersed to the particles in the 0.5–3 µm range and transformed mainly into a more stable τ₁-Al₂₉Mn₆Cu₄ phase. The fraction of dispersed particles after FSP increased due to the precipitation from the solid solution during cooling. The nanoscale quasicrystalline precipitates in the matrix, formed upon heat treatment, dissolved entirely during FSP, while the strong coarsening of the L1₂ precipitates occurred due to high temperatures in the stir zone. After FSP, the hardness of the stir zone was nearly identical for specimens in the as-cast and heat-treated conditions. Full article

Particle-reinforced aluminum matrix composite (AMC)/steel hybrid structures present considerable benefits for lightweight design and enhanced product performance. This article provides a systematic overview of research advances from 2003 to 2024 on laser welding of particle-reinforced AMCs to steel, with particular emphasis on the influence of laser welding parameters, shielding gas, and reinforcing particles on the mechanical properties of the welded joints. The mechanisms by which intermetallic compounds (IMCs) impair joint strength are thoroughly analyzed. Moreover, the effects of rare earth element additions on both mechanical properties and corrosion resistance of the joints are critically assessed, along with the coupling mechanism between rare earth elements and the reinforcement phase. Key insights from the literature reveal that regulating heat input can effectively suppress harmful interfacial reactions. Meanwhile, the synergistic incorporation of rare earth elements not only refines the grain structure and boosts mechanical strength, but also improves corrosion resistance through the formation of dense surface oxide films and grain boundary strengthening. This review underscores the innovative integration of interfacial reaction control with rare earth microalloying to achieve high-performance AMC/steel laser-welded joints—a distinct departure from prior studies that typically investigated these strategies separately. Full article

High-temperature carburization (HTC, 950–1050 °C) has emerged as a pivotal low-carbon, energy-efficient manufacturing technology for gear steels, accelerating carbon diffusion for reducing processing cycles by over 60% while achieving significant energy savings and emission reductions. However, the inherent contradiction between HTC efficiency and microstructural stability, specifically austenite grain coarsening, severely degrades mechanical properties (e.g., strength, toughness, fatigue resistance) and limits widespread application. This review systematically synthesizes recent advances in austenite grain size regulation during HTC of gear steels, focusing on the core scientific framework of “grain coarsening mechanism—regulation strategy—performance enhancement”. It elaborates on thermodynamic and kinetic mechanisms of austenite grain growth, ripening behavior of microalloying precipitates (Nb(C,N), Ti(C,N), AlN, etc.), and their synergistic grain-refining effects. Comprehensive coverage of regulatory strategies (microalloying design, pretreatment technologies, process optimization, and integrated regulation) and characterization techniques is provided, along with a quantitative correlation between grain size, microstructure, and surface performance (wear resistance, corrosion resistance, and fatigue life). Numerical simulation and predictive models (empirical, theoretical, multiphysics coupling, machine learning-based) are critically analyzed, and current challenges (temperature-grain stability trade-off, multifactor synergy understanding, industrial scalability) and future research directions (advanced microalloying systems, intelligent process optimization, cross-scale modeling, green technology integration) are proposed. This review aims to provide theoretical guidance and technical support for optimizing the HTC performance of gear steels, catering to the demands of high-power-density transmission systems in automotive, aerospace, and heavy machinery industries. Full article

Hydrogen embrittlement (HE) critically limits the application of ultra-high-strength press-hardened steels (PHS) in hydrogen-containing environments. This study investigated the effect of Nb microalloying on HE resistance of 1500 MPa-grade PHS. Even with higher hydrogen contents, steel 1500Nb exhibits better HE resistance than steel 1500. The results show that Nb addition plays effective role in grain refinement, mitigating stress concentration, and effectively postponing the initiation of intergranular cracks under hydrogen-charged conditions. Additional, hydrogen diffusivity in 1500Nb steel is lower than 1500 steel, attributed to both grain refinement effect and solute drag effect of Nb. Full article

The application of microalloying technology has significantly improved the mechanical properties, oxidation resistance, and corrosion resistance of the Sn-9Zn-xAl-series solder. The effects of Al addition on microstructural evolution and service-related performance of the solders were systematically investigated using a combination of characterization techniques, including scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), differential scanning calorimetry (DSC), tensile testing, spreading testing, thermogravimetry (TG), and potentiodynamic polarization measurements. Microstructural characterization reveals that an optimal content of Al reacts with the Sn-Zn matrix to form AlZnSn intermetallic compounds (IMCs), which effectively refines the Zn-rich precipitates and eutectic lamellar structure. Concomitantly, the formation of second-phase strengthening contributes to a significant enhancement in the tensile strength of the solder alloys. Specifically, the Sn-9Zn-0.8Al solder exhibits a tensile strength of 87 MPa, corresponding to a 37% increment compared to the base Sn-9Zn alloy, whereas the elongation is reduced to 14.1%. Moreover, the in situ-formed Al₂O₃ passive film provides effective protection for the solder matrix, inhibiting oxidation induced by oxygen atoms and corrosion caused by chlorine ions, thereby remarkably improving the oxidation and corrosion resistance of the alloy. Collectively, these findings demonstrate that Al microalloying can substantially enhance the strength, oxidation resistance, and corrosion resistance of Sn-9Zn solder; however, a trade-off between wettability and ductility needs to be carefully considered for practical applications. Full article

In this work, the effects of Nb and Mo additions on the precipitation behavior and strengthening mechanisms of three ultra-low carbon Ti-Mo-Nb steels with a predominantly ferritic microstructure were investigated under two different thermo-mechanical processing (TMP) routes. A water-quenching step after hot rolling followed by furnace cooling was found to refine the average precipitate size and increase their volume fraction, leading to a significant strength improvement. Specifically, this process increased the yield strength by approximately 110~180 MPa, reaching levels above 750 MPa, with the 22Mo-Nb steel achieving a peak ultimate tensile strength of ~790 MPa. The precipitates exhibited dispersed, interphase, and grain boundary morphologies, none of which correlated directly with the TMP route or steel composition. While variations in Mo content showed little influence on precipitate characteristics, the addition of Nb markedly promoted precipitation. The strength of these Ti-Mo-Nb ferritic steels is primarily determined by precipitation strengthening. Through optimized TMP parameters and microalloying additions, the overall precipitation strengthening contribution was elevated to the 300~400 MPa range. Full article

This work systematically investigates the influence of Mn content (0.1, 0.3, and 0.5 wt.%) on the microstructure, mechanical properties, and high-temperature stability of asymmetric extruded Mg-4.0Al-0.8Sn-0.3Ca-xMn alloys. The results demonstrate that Mn addition effectively promotes the formation of multi-scale secondary phases. Increasing the Mn content refines the average grain size from ∼2.82 µm to ∼1.89 µm and significantly modulates the recrystallization behavior of the alloy. The ATX4103-05Mn alloy (0.5 wt.% Mn) exhibits an optimal strength–ductility synergy, achieving a yield strength of 281.8 MPa and an elongation of 19.1%. Quantitative analysis reveals that this enhancement is predominantly governed by dispersion strengthening (∆σ_p∼34.1 MPa), with supplementary contributions from grain boundary and dislocation strengthening. Furthermore, the ATX4103-05Mn alloy shows superior resistance to abnormal grain growth after thermal exposure at 400 °C for 10 h, which is attributed to effective Zener pinning by the uniform distribution of short rod-shaped Al8Mn5 phases along the grain boundaries. This study elucidates the multi-scale strengthening and thermal stabilization mechanisms enabled by Mn microalloying, providing a viable pathway for developing high-performance, thermally stable magnesium alloys. Full article

Medium-entropy alloys (MEAs) with a simple phase structure and nanoprecipitates have excellent mechanical properties and considerable potential for advanced structural applications. The current study investigated the effect of boron microalloying and thermomechanical treatment on the microstructure evolution and mechanical properties of Co₄₃Cr₁₅Ni₃₀Al₅Ti₇ and (Co₄₃Cr₁₅Ni₃₀Al₅Ti₇)_99.7B_0.3 MEAs. X-ray diffraction analysis revealed a single phase of face-centered cubic (FCC) structure in all as-cast samples. After cold rolling and recrystallization annealing were completed, a clear ordered FCC (L1₂) phase was observed concurrently with the FCC matrix. In the alloy doped with 0.3 at.% B, the grain size was refined from 600 to 200 nm. TEM analysis revealed a nano-sized L1₂ phase coherently embedded in the FCC matrix. Analysis of the mechanical properties of boron-doped MEA samples revealed that cold rolling to 80% thickness followed by annealing at 900 °C for 2 h and aging at 750 °C for 4 h yielded the best mechanical performance. Among all samples, the alloy doped with 0.3 at.% boron achieved an optimal combination of mechanical properties (yield strength: 1817 MPa; ultimate tensile strength: 2313 MPa; ductility: 14.5%). Full article

To elucidate how tempering temperature influences through-thickness microstructure and strength–toughness gradients in an online direct-quenched (DQ) low-alloy medium-thick plate, a 25-mm plate was direct-quenched from 900 °C to <150 °C and tempered at 530 °C × 1.5 h or 580 °C × 1.5 h. Tensile and room-temperature Charpy V-notch impact testing and microstructure characterization were performed at the upper surface, mid-thickness, and lower surface. In the as-DQ state, the upper surface contained ferrite (F, ~60%) and granular bainite (GB, ~30%) with minor lath bainite (LB, ~10%) and a small amount of martensite/austenite (M/A). The mid-thickness and lower surface remained dominated by F + GB (mid-thickness: GB~50%, F~30%, M/A~20%; lower surface: F~85%, GB~15%); the mid-thickness showed the lowest yield strength/ultimate tensile strength (YS/UTS) of 498/675 MPa. In the as-DQ state, the room-temperature Charpy V-notch absorbed energies at the upper surface, mid-thickness, and lower surface were 223.23, 229.88, and 261.22 J, respectively, indicating a pronounced through-thickness variation (ΔE_(max–min) ≈ 38 J). After tempering at 530 °C, the upper surface and mid-thickness developed an F + tempered sorbite (TS) microstructure (upper surface: F~70%, TS~30%; mid-thickness: F~60%, TS~40%), whereas the lower surface was mainly ferrite with a small amount of spheroidized carbides/tempered cementite (SC). The mid-thickness YS/UTS increased to 619/805 MPa, and the impact energies at the upper surface and mid-thickness increased to 240.62 J and 235.56 J, respectively, resulting in a reduced through-thickness gradient. After 580 °C tempering, recovery and polygonal ferrite formation dominated; surface yield strength increased but mid-thickness yield improvement was limited. Full article

Manufacturing heavy-gauge high-strength steel plates with uniform through-thickness properties is challenging due to the limited hardenability and significant cooling rate variations inherent to heavy sections. However, the mechanism governing microstructural homogenization across such large cross-sections remains not fully understood. This study investigates the through-thickness microstructure and mechanical properties of a 60 mm thick high-Nb microalloyed Q690 steel plate processed by direct quenching (AQ) and subsequent tempering at 530 °C and 580 °C. Characterization was performed at the surface (0t), quarter-thickness (1/4t), and core (1/2t) locations. Results revealed a pronounced gradient in the as-quenched state: while the surface consisted of fine lath martensite/bainite, the core formed coarse granular bainite containing blocky martensite–austenite (M-A) constituents. This microstructural heterogeneity resulted in poor core toughness (~24 J). High-temperature tempering at 580 °C promoted the complete decomposition of these metastable M-A constituents into ferrite and fine carbides, significantly improving the core impact energy to ~49 J. However, a toughness gradient persisted compared to the quarter-thickness (>120 J), attributed to the inherited coarse matrix and the formation of grain boundary carbides. Notably, high yield strength was maintained across the thickness despite matrix recovery. This is primarily attributed to a potent anti-softening effect provided by thermally stable (Nb,Ti,Mo)C nanoprecipitates, which generate strong Orowan strengthening. These findings highlight the critical role of optimizing the trade-off between M-A decomposition and carbide evolution in promoting the microstructural and property homogenization of heavy-gauge steels. Full article

The addition of Cu or La plays an important role in microstructure and property manipulation of 4xxx series Al-Si alloys. However, the effects of Cu-La hybrid modification on the microstructure and properties of Al-5Si alloys and welding performance remain unclear. In this paper, the influence of Cu-La addition on the strength and elongation of one commercial Al-5Si alloy and the welding joint characterization are investigated. The results show that the addition of Cu-La can refine α-(Al) and Fe-rich phase and improve the fluidity. Meanwhile, the elongation can be improved by Cu-La microalloying, which is beneficial for the manufacturing filler wire. The uniform distribution of Cu in the alloy but not segregation at grain boundaries due to La addition is the key factor to adjust the mechanical properties. Moreover, the filler materials were used to conduct metal inert gas welding on 6061 alloy. It reveals that, with Cu-La addition, the weld pool width increases and porosity defect decreases significantly. This is ascribed to Cu-La co-addition enhancing wettability and fluidity, which improves the welding performance. Our results offer an effective strategy for manufacturing and optimizing welding performance of welding wires. Full article

The paper focuses on materials characterization and in vivo biocompatibility tests of Ti–6Al–7Nb–0.3REE wt.% alloys (REEs—Y, Ce, La) for use as a promising material to produce personalized medical implants and shed light on possible toxicity effects of REE alloy microdoping. All alloys were produced by the electric arc melting method and characterized by scanning electron microscopy (SEM), optical microscopy (OM), energy-dispersive X-ray spectroscopy analysis (EDX), X-ray diffraction (XRD), true density analysis, micro- and nanoindentation methods, and reducing/oxidation melting techniques. True density of alloys increased in the following order: Ti−6Al−7Nb−0.3Y (4.4563 ± 0.1075 g/cm³) < Ti−6Al−7Nb−0.3Ce (4.7255 ± 0.2853 g/cm³) < Ti−6Al−7Nb−0.3La (4.8019 ± 0.0111 g/cm³). XRD analysis indicated that Ti–6Al–7Nb–0.3Y alloy consisted of single α–Ti phase in comparison with Ti–6Al–7Nb–0.3La (α–Ti to β–Ti = 82 to 18) and Ti–6Al–7Nb–0.3Ce (α–Ti to β–Ti = 90.5 to 9.5). The single-phase Ti–6Al–7Nb–0.3Y alloy had the finest α–Ti phase crystallites (22.32 nm); the larger α–Ti crystallites in the dual-phase Ti–6Al–7Nb–0.3Ce and Ti–6Al–7Nb–0.3La (30.77 nm and 29.83 nm, respectively) suggested the presence of the β–Ti phase (23.34 nm and 25.61 nm, respectively). REE microdoping of alloys changed the lattice volume (∆V): α–Ti phase—0.269% for Ti–6Al–7Nb–0.3Y, 1.799% for Ti–6Al–7Nb–0.3Ce, 0.595% for Ti–6Al–7Nb–0.3La; and β–Ti phase—0.334% for Ti–6Al–7Nb–0.3Ce, 0.670% for Ti–6Al–7Nb–0.3La. Nanohardness (H) and elastic modulus (E) increased in the following order: Ti−6Al−7Nb−0.3La (4.01 GPa and 135 GPa, respectively) < Ti−6Al−7Nb−0.3Y (4.39 GPa and 137 GPa, respectively) < Ti−6Al−7Nb−0.3Ce (4.67 GPa and 146 GPa, respectively). In vivo tests were conducted using 46 sexually mature male Wistar rats by means of skin implantation of samples with d = 11 mm and h = 1 mm. Our research shows that Ti–6Al–7Nb–0.3La alloy (Group 2) and Ti–6Al–7Nb–0.3Ce alloy (Group 3) induced sustained hepatotoxic and nephrotoxic effects. Ti–6Al–7Nb–0.3Y alloy induced a slight local inflammatory response; however, serum biochemical analysis suggested this effect was compensated. Full article