Search Results (425)

SiC/Al matrix composites are prone to forming brittle Al₄C₃ phase via interfacial reactions during fabrication, which severely limits their mechanical properties and engineering applications. Microalloying is an effective method to inhibit this brittle phase, yet the interfacial mechanism of alloying elements at the atomic scale remains unclear. Centered on molecular dynamics simulation combined with experimental verification, this study systematically investigates the laws of Fe and Ni microalloying on the interface regulation and mechanical property optimization of SiC/Al composites. Simulation results show that Fe and Ni atoms tend to segregate at the SiC/Al interface, which can suppress interfacial reactions, promote dislocation nucleation and proliferation, induce new dislocation types, and achieve the synergistic improvement of strength and ductility—with Ni exhibiting a more prominent strengthening effect. Composites prepared by the pressure infiltration-hot extrusion process show no Al₄C₃ phase in phase detection. Mechanical property tests confirm that Fe and Ni microalloying can effectively enhance the comprehensive performance of the materials, among which Ni increases the strength–ductility product by 54%. This study clarifies the interfacial regulation mechanism of Fe and Ni microalloying at the atomic scale, providing theoretical guidance and experimental support for the microalloying design of SiC/Al composites. Full article

7xxx series aluminum alloys are critical structural materials in aerospace applications, but their susceptibility to hydrogen embrittlement (HE) poses significant challenges to service safety and durability. The effects of Si, Er, and Zr microalloying, combined with optimized heat treatments on the HE resistance of Al–Zn–Mg–Cu alloys, were systematically investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and mechanical testing. Three alloys—1# (AlZnMgCuZr), 2# (AlZnMgCuErZr), and 3# (AlZnMgCuSiErZr)—were subjected to single-stage or two-stage homogenization, followed by solution treatments at 470 °C/2 h and 540 °C/1 h, and peak aging at 125 °C. The hydrogen charging experiment was conducted by first applying a modified acrylic resin coating to protect the gripping sections of the specimen, followed by a tensile test. Results demonstrate that alloy 3# with Si addition exhibited the lowest RA_loss, followed by the 2# alloy, which effectively improved the alloys’ hydrogen embrittlement behavior. Compared with the solution in 470 °C/2 h, the 540 °C/1 h solution treatment enabled complete dissolution of Mg₂Si phases, promoting homogeneous precipitation and peak hardness comparable to alloy 2#. Two-stage homogenization significantly enhanced the number density and refinement of L₁₂-structured Al₃(Er,Zr) nanoprecipitates. Silicon further accelerated the precipitation kinetics, leading to more Al₃(Er,Zr) nanoprecipitates, finely dispersed T′/η′ phases, and lath-shaped GPB-II zones. The GPB-II zones effectively trapped hydrogen, thereby improving HE resistance. This work provides a viable strategy for enhancing the reliability of high-strength aluminum alloys in hydrogen-containing environments. Full article

To reduce CO₂ emissions into the environment, the automotive sector uses microalloyed structural steels coated with electrophoretic paint in various components, such as the chassis, to reduce weight and increase corrosion resistance. AHSSs are coated with electrophoretic paint (E-coat). Still, to improve adhesion, they undergo a pretreatment, such as zinc phosphate or zirconium oxide. This research will analyze the effects and behavior of these coatings during corrosion on a complex-phase (CP) 780 AHSS using different electrochemical techniques, including cyclic potentiodynamic polarization (CPP), electrochemical noise (EN), and electrochemical impedance spectroscopy (EIS). The CP 780 AHSS was immersed in a 3.5 wt. % sodium chloride solution. Results show that AHSS CP 780 presented a mixed corrosion mechanism due to the heterogeneity of the surface of the zinc phosphate and zirconium oxide pretreatments. On the other hand, the samples with an E-coat paint coating and pretreatment (Zn₃(PO₄)₂/E-coat and ZrO₂/E-coat) have the lowest current densities with values of 6.44 × 10⁻¹¹ 1.02 × 10⁻⁹ A/cm² and also do not show a tendency towards localized corrosion or negative hysteresis. Full article

This research systematically investigates the influence of multi-microalloying with Sn, Mn, Er, and Zr on the homogenized microstructure, aging behavior, and mechanical properties of a 6082 Al-Mg-Si alloy. The optimization of the homogenization treatment for the alloy was based on isochronal aging curves and conductivity measurements. The results show that the addition of Mn, Er, and Zr can precipitate thermally stable Al(Fe,Mn)Si dispersoids and Al(Er,Zr) dispersoids. The three-stage homogenization treatment resulted in the precipitation of more heat-resistant dispersoids, thereby achieving the best thermal stability. During direct artificial aging, the initial hardening rate of the Mn-containing alloy was slightly delayed, but its peak hardness was significantly increased. This is due to the dispersoids offering additional heterogeneous nucleation sites for the strengthening precipitates. Meanwhile, the Sn atoms release their trapped vacancies at the aging temperature, thereby promoting atomic diffusion. However, short-term natural aging before artificial aging accelerated the early-stage aging response of the Sn-containing alloy but resulted in a reduced peak hardness. Notably, the co-microalloying with Mn and Sn led to a higher peak hardness during direct artificial aging, while it caused a more significant hardness loss when a natural aging preceded artificial aging, revealing a distinct synergistic negative effect. The reason for the negative synergy effect might be related to the weakened ability of Sn to release vacancies after natural aging. This study clarifies the process dependence of microalloying effects, providing a theoretical basis for optimizing aluminum alloy properties through the synergistic design of composition and processing routes. Full article

The 6xxx-series Al alloys have been used for decades because of their favorable strength-to-weight ratio, corrosion resistance, and fatigue performance. However, conventional welding techniques often induce localized weakening, as thermal effects modify the microstructure and compromise structural integrity. For nearly 70 years, AA4043 welding wire has been the primary choice for joining 6xxx-series Al alloys. Nevertheless, microstructural and mechanical property mismatches between the base metal and weld region remain key factors contributing to premature failure, while welding-induced defects further increase rupture susceptibility. Microalloying has emerged as an effective strategy for enhancing both the mechanical and thermal properties of aluminum alloys. In this study, rare-earth (RE) elements La and Ce were introduced into the AA4043 system to exploit their grain refining and mechanical strengthening capabilities. In addition, the effects of Sr modification were examined and compared with La-Ce addition. This work aims to elucidate the strengthening mechanisms associated with La-Ce-Ti microalloying in AA4043 welding wire, a topic that has rarely been systematically investigated. With 0.019Ti-0.02La-0.03Ce additions, the modified wire exhibited significant performance improvements, achieving an UTS of 204 MPa and a YS of 191 MPa—representing increases of 10.3% and 18.6%, respectively. Full article

Continuous cooling transformation (CCT) diagrams for two thermo-mechanically controlled processed (TMCP) steels were produced using a modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, which accounted for the simultaneous transformation of multiple phases under non-isothermal conditions. A basin hopping algorithm was used to sequentially optimize the model parameters for each phase. Samples were prepared using a dilatometer which replicated the deformation and cooling rates experienced during TMCP. Scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) were used to identify and quantify the phases present in each steel. CCT diagrams illustrating the start and stop temperatures of each phase were constructed for both steel samples. Through inclusion of the stop temperatures of each phase transformation, the utility of the CCT diagrams were expanded. This was done by introducing the possibility of applying the Scheil additive principle with respect to the beginning and end of each phase transformation. With this modification, the CCT diagrams are now more appropriately suited to predict the phase transformations that occur on the ROT, where non-continuous cooling occurs. Full article

Aluminum alloys require improved surface performance to satisfy the demands of today’s aerospace, automotive, marine, and structural applications. This paper compares three key surface hardening methods: diffusion-assisted microalloying, thermomechanical deformation-based treatments, and composite/hybrid reinforcing procedures. Diffusion-assisted Zn/Mg enrichment allows for localized precipitation hardening but is limited by the native Al₂O₃ barrier, slow solute mobility, alloy-dependent solubility, and shallow hardened depths. In contrast, thermomechanical techniques such as shot peening, surface mechanical attrition treatment (SMAT), and laser shock peening produce ultrafine/nanocrystalline layers, high dislocation densities, and deep compressive residual stresses, allowing for predictable increases in hardness, fatigue resistance, and corrosion performance. Composite and hybrid reinforcement systems, such as SiC, B₄C, graphene, and graphite-based aluminum matrix composites (AMCs), use load transfer, Orowan looping, interfacial strengthening, and solid lubrication effects to enhance wear resistance and through-thickness strengthening. Comparative evaluations show that, while diffusion-assisted procedures are still labor-intensive and solute-sensitive, thermomechanical treatments are more industrially established and scalable. Composite and hybrid systems provide the best tribological and load-bearing performance but necessitate more sophisticated processing approaches. Recent corrosion studies show that interfacial chemistry, precipitate distribution, and galvanic coupling all have a significant impact on pitting and stress corrosion cracking (SCC). These findings highlight the importance of treating corrosion as a fundamental design variable in all surface hardening techniques. This work uses unified tables and drawings to provide a thorough examination of strengthening mechanisms, corrosion and fatigue behavior, hardening depth, alloy suitability, and industrial feasibility. Future research focuses on overcoming diffusion barriers, establishing next-generation gradient topologies and hybrid processing approaches, improving strength ductility corrosion trade-offs, and utilizing machine-learning-guided alloy design. This research presents the first comprehensive framework for selecting multifunctional aluminum surfaces in demanding aerospace, automotive, and marine applications by seeing composite reinforcements as supplements rather than strict alternatives to diffusion-assisted and thermomechanical approaches. Full article

The EU’s green transition hinges on secure access to critical raw materials; vanadium is pivotal for microalloyed steels and emerging long-duration energy storage (VRFBs). Methods: We combine a market and technology review with PESTEL and Porter-5+2 analyses, complemented by a value-chain assessment and a SWOT-to-CAME strategy for the EU. Results: Vanadium supply is highly concentrated (VTM-derived, largely in CN/RU/ZA), prices are volatile, and >85% of demand remains tied to steel; yet VRFBs could shift demand shares by 2030 if costs—dominated by electrolyte—are mitigated. EU weaknesses include lack of primary mining and refining capacity; strengths include research leadership, regulatory frameworks and circularity potential (slag/catalyst recovery, electrolyte reuse). Conclusions: A resilient EU strategy should prioritize circular supply, selective upstream partnerships, battery-grade refining hubs, and targeted instruments (strategic stocks, offtake/price-stabilization, LDES-ready regulation) to de-risk vanadium for grid storage and low-carbon infrastructure. This study also discusses supply chain concentration and price volatility, and outline circular-economy pathways and decarbonization policy levers relevant to the EU’s green energy transition. Full article

By tuning the extrusion parameters, the corrosion performances of as-extruded Mg-0.5Zn(-0.2X) alloys (X: Ca/Sr/Ag/In/Cu, denoted as Z05, Z0502-Ca, Z0502-Sr, Z0502-Ag, Z0502-In and Z0502-Cu, respectively) with similar grain sizes were investigated and compared with their as-cast counterparts. The formed Fe-Si precipitates after hot processing significantly accelerate the corrosion rates of Z05, Z0502-Ag and Z0502-In, whereas the driving force from the Fe-encapsulated MgCaSi(Fe) and MgSrSi(Fe) precipitates are not as strong in Z0502-Ca and Z0502-Sr. Impacts from Fe impurity in Z0502-Cu are masked in the fast corrosion due to the noble Mg2Cu intermetallics. Fe precipitation during hot processing is critical for micro-alloyed systems, as the changes in intermetallic/impurity distributions impact the corrosion performances profoundly. The enthalpy of formation and the potential difference are the key factors that influence the distribution of precipitate during hot processing. Full article

This review systematically synthesizes the research progress on θ-series precipitates. It traces the historical evolution of θ-series precipitate research, from the accidental discovery of age hardening in Duralumin to the atomic-scale insights enabled by advanced electron microscopy and computational methods. The precipitation sequence (supersaturated solid solution → GP zones → θ″ → θ′ → θ), transformation mechanisms, and interfacial characteristics of θ′/Al are comprehensively analyzed, with special attention to ongoing controversies such as the structure of GP zones and the pathways of θ″ → θ′ transition. Furthermore, the review discusses how alloying elements regulate θ′ stability through interfacial segregation, vacancy interactions, and co-precipitation effects. Critical unresolved challenges are highlighted, including the kinetic limitations of θ′ coarsening and the need for mechanistic studies on multi-element microalloying. This synthesis aims to provide a foundation for future research toward designing high-performance age-hardenable aluminum alloys. Full article

A microalloyed (MA) steel, combined with titanium diboride (TiB₂), was utilised to create a unique steel matrix composite (SMC), enhancing the modulus of the MA steel while also improving its strength. Through thermomechanical processing stages, including hot rolling and plane-strain compression (PSC) testing, followed by various final cooling methods, a cooling rate of 0.1 °C/s was identified as the most effective for achieving a ferrite–pearlite microstructure, which is suitable for toughness and ductility. With TiB₂ reinforcement successfully incorporated via Fe-Ti and Fe-B additions during vacuum induction melting (VIM), it was observed that the TiB₂ particles were homogeneously dispersed in both 5% and 7.5% nominal volume fraction additions, exhibiting faceted and hexagonal morphology. TiB₂ was found to exert a grain-pinning effect on recrystallised austenite at 1050 °C, as evidenced by the retention of grain orientation from hot rolling, in contrast to the MA steel deformed without the composite reinforcement. Increasing the volume fraction of TiB₂ improved the stiffness and strength of both composite alloys, verified through mechanical testing. Full article

Microalloying with Sn is a pivotal strategy for enhancing the strength and thermal stability of Al-Mg-Mn-Si alloys by enabling microstructural optimization. This study systematically investigates the influence of 0.1 wt.% Sn on an Al-4.0Mg-1.0Mn-0.2Si alloy through a comparative analysis with a Sn-free counterpart. The experimental methodology included isochronal aging and isothermal aging, room-temperature tensile testing, electrical conductivity measurements, and detailed microstructural characterization via transmission electron microscopy (TEM) and optical microscopy (OM). The results unequivocally demonstrate that Sn addition significantly enhances the alloy’s microhardness, tensile properties, and heat resistance. Specifically, the Sn-containing alloy (1#) achieved a peak hardness of 98.4 HV during a three-stage aging process, which is 14.1% higher than the 84.5 HV of the Sn-free alloy (2#). In the as-rolled state, alloy 1# exhibited ultimate tensile strength (UTS) and yield strength (YS) of 397 MPa and 344 MPa, representing increases of 20.2% and 15.7%, respectively, without compromising ductility. Microstructural analysis revealed that the enhancement is attributed to the Sn-promoted formation of finely dispersed α-AlMnSi precipitates. These precipitates effectively pin dislocations, strengthening the alloy, and simultaneously suppress recrystallization nucleation and growth, thereby elevating the recrystallization temperature and improving overall heat resistance. This work confirms that microalloying with Sn is an effective strategy for developing high-performance Al-Mg-Mn-Si alloys with superior mechanical properties and thermal stability. Full article

Although low-silicon Al-Si alloys have been extensively studied, further improvement in their mechanical performance remains a critical challenge. This study examines the synergistic effects of scandium (Sc) and zirconium (Zr) additions on the solidification behavior, microstructural evolution, and mechanical properties of Al-5Si-Cu-Mg alloys. The Sc/Zr additions refine the α-Al grains and modify the eutectic Si morphology, with the most uniform microstructure obtained at 0.5 wt.% due to the formation of coherent Al₃(Sc,Zr) dispersoids. These additions also suppress the formation of needle-like β-Al₅FeSi phases and promote the transformation to compact α-Al₁₅(Fe,Mn)₃(Si,Zr,Sc)₂ intermetallics, optimizing the solidification process. The yield strength increases with Sc/Zr content owing to grain-boundary and precipitation strengthening. However, the alloy without Sc/Zr exhibits the highest ultimate tensile strength and elongation, likely due to its finer secondary dendrite arm spacing and the absence of casting-induced cracks in this investigation. Although Sc/Zr additions of 0.25–0.5 wt.% contribute to microstructural refinement, the concurrent formation of porosity and coarse intermetallic compounds leads to a deterioration in ductility. Excessive Sc/Zr additions further coarsen grains and degrade the overall mechanical integrity. Full article

316L austenitic stainless steel is an ideal candidate for high-temperature applications. However, the relatively low strength and poor wear resistance at high temperatures significantly limit its application in high-temperature environments. In this study, we address this challenge by tracing TiB₂ microalloying austenitic steel via L-PBF (laser powder bed fusion), a micro-melting pool metallurgy method. The results show that adding 2.5 wt.% TiB₂ significantly refines the austenite grain size from ~19 μm to ~1 μm. The austenite grain size characterizes thermal stability at 300 °C and 600 °C. The fabricated TiB₂-reinforced steel shows extraordinarily high-temperature tensile strength, achieving 740 MPa and 636 MPa at 300 °C and 600 °C, respectively. The high tensile strength under high temperature is attributed to the TiB₂ phase strengthening and ultrafine austenite grain sizes. Regarding the high-temperature wear friction coefficient of 0.69 at 300 °C and 0.47 at 600 °C, the predominant wear mechanism is abrasive wear, accompanied by adhesive and oxidative wear mechanisms. The present study provides new insight for the development of L-PBF austenitic steels that combine high-temperature strength with superior wear resistance. Full article