Rational interlayer cooling time management emerges as a critical yet underexplored parameter for controlling microstructural evolution and mechanical performance in wire-arc additive manufacturing (WAAM) of rare-earth magnesium alloys. The present work systematically investigates, through integrated experiment and simulation, how varying cooling intervals (45–180 s) affect grain morphology, phase precipitation, and tensile properties in CMT-WAAM fabricated Mg-Gd-Y-Zn-Zr components. Repetitive thermal cycling during deposition induces solid-state transformations, notably promoting the formation of long-period stacking ordered (18R-LPSO) phases. The phases volume fractions were determined by quantitative metallography, reach a maximum of 1.43 % at a cooling time of 120 s and a minimum of 0.41 % at 45 s. Microstructural characterization reveals a characteristic bimodal grain structure comprising alternating coarse (15–35 µm) and fine (5–12 µm) equiaxed grains, with average sizes ranging from 11.32 ± 5.35 µm (180 s) to 15.62 ± 6.94 µm (45 s). Mechanical testing demonstrates strength-ductility trade-off: samples with 90 s cooling duration exhibit peak ultimate tensile strength (259.7 ± 12.7 MPa) and yield strength (224.3 ± 2.5 MPa), while 120s-cooled samples display superior elongation (8.5 ± 0.54 %) but reduced strength. These findings establish interlayer cooling time as an effective microstructural engineering tool for tailoring mechanical properties in WAAM-processed Mg-RE alloy systems through controlled thermal management.

The wire-arc directed energy deposition (WA-DED) of Mg-RE alloys is often limited by microstructural heterogeneity and unclear heat-treatment responses. In this study, the microstructural evolution and strengthening mechanisms of a WA-DED Mg-9Gd-4Y-2Zn-0.5Zr alloy during solution and aging treatments were investigated. The as-built alloy exhibited a heterogeneous α-Mg matrix containing γ′ precipitates, divorced (Mg,Zn)₃(Gd,Y) eutectic phases, and (Gd,Y)H₂ particles. Solution treatment at 450–500°C preserved the bimodal grain structure, while grain growth followed a normal grain-growth law with an apparent activation energy of ∼374.8 kJ mol⁻¹. Under sub-solvus solution treatment, the 14H-LPSO phase mainly formed through the solid-state transformation of eutectic lamellae, whereas prolonged treatment at 500°C promoted both eutectic-to-LPSO transformation and supersaturation-driven LPSO. After solution treatment at 480°C for 1 h followed by aging at 200°C for 72 h, the alloy achieved an optimized combination of strength and ductility, with yield strength, ultimate tensile strength, and elongation values of 261 MPa, 368 MPa, and 5.02%, respectively. The enhanced strength was mainly attributed to refined α-Mg grains and dense β′ precipitates.

Wire arc additive manufacturing (WAAM) provides a viable route for fabricating large-scale rare-earth (RE) magnesium-alloy components. In WAAM, the cold metal transfer (CMT) mode strongly affects arc behavior, droplet transfer, and heat-input distribution. In this study, Mg–9Gd–4Y–1Zn–0.5Zr (wt%) alloy specimens were fabricated using four CMT-derived modes, namely, CMT, CMT Pulse (CMT-P), CMT Advanced (CMT-ADV), and CMT Pulse Advanced (CMT-PADV), and their effects on arc behavior, bead geometry, microstructure, and mechanical properties were systematically investigated. Stable deposition was achieved under all four modes, but clear differences were observed in average heat input and the within-cycle distribution of arc energy and droplet transfer. CMT exhibited relatively gentle arc action and stable short-circuit transfer, CMT-P showed the strongest arc spreading capability, and CMT-ADV and CMT-PADV displayed more pronounced expansion–contraction modulation characteristics. Polarity switching in CMT-ADV and CMT-PADV reduced the difference in eutectic-phase fraction between the fine- and coarse-grained regions. The as-deposited microstructures under all four modes were dominated by equiaxed grains and comprised similar phase constituents, predominantly including the α-Mg matrix and RE-rich secondary phases such as the (Mg,Zn)3(Gd,Y) eutectic and blocky RE-rich cubic phases. CMT, CMT-P, CMT-ADV, and CMT-PADV had average grain sizes of 22.14 ± 8.04, 17.41 ± 7.10, 16.08 ± 6.46, and 17.30 ± 7.21 μm, respectively. CMT-ADV specimens exhibited the highest tensile strength (264 ± 5 MPa), whereas CMT-PADV specimens showed the highest elongation (6.37 ± 0.52%) and weakest anisotropy. These results provide guidance for the process-mode selection and performance optimization in WAAM for RE magnesium alloys.

This study systematically investigates the effects of hot drawing speed (1.5 m/min to 3.5 m/min) on the microstructure and mechanical properties of Mg-9.5Gd-3.5Y-1Zn-0.3Zr alloy wires. Results show that a higher drawing speed intensifies the thermo-mechanical coupling effect, which uniformly fragments and disperses the long-period stacking ordered (LPSO) phase throughout the matrix. This process further refines dynamic recrystallized grains, reducing the average matrix grain size from 13.11 to 6.26 μm in the final 1.4-mm-diameter wire. Moreover, the increased speed shortens the high-temperature exposure time, keeping the wire temperature below the dissolution point of Mg5(Gd,Y)(Mg5RE) and thereby suppressing its solid solution. Consequently, the Mg5RE phase remains as a high-density dispersion in the matrix. These microstructural improvements lead to a significant increase in ultimate tensile strength (from 428 to 536 MPa) and yield strength (from 401 to 514 MPa). The strengthening mechanisms are attributed to: (1) improved distribution and aspect ratio of the LPSO phase, which inhibits grain coarsening; and (2) a strong pinning effect induced by the uniformly dispersed Mg5RE precipitates, which stabilizes the fine-grained structure and promotes the formation of high-density dislocation substructures, resulting in synergistic strengthening.

Ti6Al4V alloy, with its high strength, excellent corrosion resistance, and good biocompatibility, is increasingly being used in the field of dental implants. Selective Laser Melting (SLM) technology provides an efficient manufacturing method for producing Ti6Al4V alloy medical implants. However, the effects of different process parameters on the corrosion behavior of Ti6Al4V alloy formed by SLM in simulated artificial saliva are not yet fully understood. This study investigated the effects of different laser powers and scanning speeds on the corrosion performance of SLM-formed Ti6Al4V alloy. Simulated artificial saliva was used as the electrolyte, and analyses were conducted using metallographic microscopy, scanning electron microscopy (SEM), x-ray diffraction (XRD), electrochemical testing, immersion experiments, and x-ray photoelectron spectroscopy (XPS). For SLM-formed Ti6Al4V alloy under different laser power and scanning speed conditions, metallographic microscope observations indicated that the sample surface defects were minimal under the process parameters of 180W laser power and 1000 mm/s scanning speed. SEM observations revealed that the microstructures of the samples under different process parameters all contained α/α′ phase and β phase. XRD analysis indicated that the microstructure of the sample formed under the process parameters of 180W/1400 mm/s had the highest content of β phase and the lowest content of α/α′ phase. Corrosion morphology observations showed that the corrosion mode of Ti6Al4V formed by SLM under different process parameters in simulated artificial saliva was pitting corrosion. XPS detection results indicate that samples with a higher content of β phase in their microstructure have a higher content of stable TiO2 in their passivation film, resulting in a more stable and dense passivation film with better corrosion resistance. Electrochemical test results indicate that samples formed at 180 W and 1000 mm/s exhibit the best corrosion resistance compared to other process parameters.

This work investigates the grain orientation evolution, second phase, and their influence on the mechanical properties of Mg-8.5Gd-4Y-2Zn-0.3Zr alloy wires during multi-pass hot drawing. A Phi 6 mm extruded Mg-8.5Gd-4Y-2Zn-0.3Zr alloy rod was processed into a Phi 1.45 mm wire via multi-pass hot drawing at 450 degrees C. During the drawing process, the intergranular 18R-LPSO phase transformed from a block-shaped morphology to fragmented strip-shaped morphology. The average grain size decreased slightly from 7.83 mu m to 7.44 mu m. Initially weak <0001>//ED anomalous texture and strong <01-10>//ED texture gradually transformed the strong <01-10>// DD basal texture. The final Phi 1.45 mm wire exhibited a tensile strength of 495 MPa, yield strength of 447 MPa, and elongation of 2.41 %, demonstrating significant strength enhancement compared to the initial state. Calculations revealed that grain boundary strengthening, dislocation strengthening, and 18R-LPSO phase strengthening contributed collectively to yield strength. The 18R-LPSO phase strengthening identified as the dominant mechanism.

This study examines hot isostatic pressing (HIP) effects on a selective laser melting (SLM)-produced Ti-48Al-2Cr2Nb alloy. Post-HIP, the as-built alpha 2/gamma lamellar structure transitions to a gamma-dominant duplex microstructure via stress-induced dynamic recrystallization (DRX) (exploiting gamma-phase's low stacking fault energy) and alpha 2-phase suppression. HIP-driven grain refinement and gamma-enrichment improve plasticity (elastic yield onset) and reduce peak stress. Deformation shifts from dislocation hardening to dynamic softening through recrystallization/recovery equilibrium. HIP synergizes defect elimination (crack closure) with microstructure optimization (gamma-phase control, grain refinement), balancing ductility and strength. The phase energetics (alpha 2/gamma) and dislocation dynamics under thermomechanical coupling guide additive manufacturing strategies, establishing HIP as a vital post-process for high-temperature TiAl alloys requiring microstructural precision and performance stability.

Achieving a synergistic balance between strength and service-related thermophysical properties remains a significant challenge in structural material. This study addresses this issue by employing cooperative heat treatment strategies to optimise Inconel-copper bimetallic structures fabricated via Directed Energy Deposition-Arc (DED-Arc). Phase diagram calculations guided the design of these heat treatments. Comparative analyses revealed that the solution plus aging treatment (STA2#) achieved a balance between high strength and ductility with a tensile strength of 342.4 MPa and an elongation of 22.2%, while maintaining excellent thermal conductivity. Digital image correlation revealed localised deformation in the C18150 region, and the improved mechanical properties were attributed to grain boundary and precipitation strengthening. The thermophysical properties were significantly improved by the designed cooperative heat treatment, with the thermal conductivity of the STA2# bimetallic ranging from 41.16 to 56.08 W/(mk) over a temperature range of 30 to 310 degrees C, approximately 13% improvement than the as-fabricated sample. This improvement in thermal conductivity resulted from the decomposition of the supersaturated solid solution. This study provides a promising heat treatment strategy for advancing Inconel-copper bimetallic in next-generation rocket engine potential application.

In this study, the Mg-8.5Gd-4Y-2Zn-0.5Zr alloy was fabricated using Gas Tungsten Arc Welding-Wire Arc Additive Manufacturing (GTAW-WAAM). The results show that the as-deposited microstructure mainly consists of the alpha-Mg phase, skeletal-like (3-(Mg, Zn)3(Gd, Y) phase, and RE-rich phase, with equiaxed grains having an average size of 24.6 mu m. After solution treatment at 480 degrees C x 1 h, the (3 phase partially dissolves and transforms into a continuous network, while 18R-LPSO are distributed at the grain boundaries; however, the (3-(Mg, Zn)3(Gd, Y) phase does not fully transform. Subsequent aging at 200 degrees Cx 60 h leads to the precipitation of (3 ' nano-precipitates, thereby improving the mechanical properties. Finally, in the transverse direction (TD), the solution+aging sample exhibits an ultimate tensile strength (UTS) of 366 + 4.2 MPa, a yield strength (YS) of 296 + 3.4 MPa, and an elongation (EL) of 6.77 + 0.2 %.

In this study, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) titanium alloy samples are fabricated via arc-wire directed energy deposition (AW-DED) and laser powder bed fusion (L-PBF). The variant-selection (VS) mechanism of the a grain boundary (aGB) and the intragranular microstructure are characterized via electron backscatter diffraction, and the related formation mechanisms are discussed. The continuous aGB maintained Burgers orientation relationships with one of the adjacent lamellas in the AW-DED sample and the adjacent acicular a' laths in the l-PBF sample as much as possible, respectively. For the intragranular microstructure, the VS of the colony and basket-weave microstructures maintained a common {11 (2) over bar0} pole with one of their adjacent microstructures in the AW-DED sample. The VS of the acicular a' lath in the intragranular region is maintained as the common {0001} pole and {11 (2) over bar0} pole section as much as possible with the adjacent acicular a' lath. Type-2 (60 degrees/[11 (2) over bar0]) boundaries dominated the colony microstructure and the basket-weave microstructure because of their low cooling rate in the AW-DED sample. By contrast, type-4 (63.26 degrees/[(10) over bar5 5 (3) over bar]) boundaries are composed of the acicular a' lath owing to their high cooling rate in the l-PBF sample during deposition.

The Ti48Al2Cr2Nb alloy formed by selective laser melting (SLM) was simulated by first-principles. The crystal phase relationship and interface bonding mechanism between the basic phases alpha 2-Ti3Al and gamma-TiAl in the alloy were simulated, and the interface stability of the Ti48Al2Cr2Nb alloy structure was explored. The results show that the Ti center-ST model in the gamma-TiAl(111)/alpha 2-Ti3Al(0001) interface model has the largest interfacial bonding work, the smallest interfacial energy and the strongest interfacial stability. The Cr and Nb elements are doped in the alpha 2-Ti3Al(0001)/gamma-TiAl(111) interface system, the bonding work and segregation enthalpy of the interface under the four doping systems were compared. It was found that the interface model doped with Cr and Nb was beneficial to improve the bonding strength of the interface and was beneficial to the stability of the interface.

Segregation affects the solute content within the grains, as well as the content and distribution of the secondary phases at grain boundaries, leading to structural and property inhomogeneity. It also influences the microstructure evolution during the remelting and post-heating in directed energy deposition-arc (DED-Arc), ultimately impacting product performance in both as-built and heat-treated states. In this study, a 2219 aluminum alloy wall was fabricated using DED-Arc. Numerical simulation was employed to calculate the temperature field of the additive manufacturing process and solidification parameters. The segregation behavior and microstructure characteristics were analyzed. Both macrosegregation and microsegregation were observed in the as-built wall. Within a single layer, the Cu content is higher at the top where the metal solidifies last, than at the bottom where it solidifies first. The microsegregation is more severe in the first few layers due to the higher cooling rate. As the DED-Arc process progresses, eutectics enriched in the interlayer form a reticular network due to remelting, while a finer grain size is achieved through Cu enrichment and Al3Zr nucleants. As the layer-by-layer deposition process continues, the as-built wall alternates between coarse-grained unmelted intralayers, coarse-grained partially remelted intralayers with network-distributed eutectics, fine-grained remelted interlayers with network-distributed eutectics and fine-grained newly deposited interlayers.

Wire-arc directed energy deposition (WA-DED) has emerged as a transformative technology for producing large-scale metal components owing to its capacity for cost-effective fabrication and suitable deposition rates. Recently, the focus has shifted to the WA-DED of magnesium alloys, which are promising lightweight structural materials in the aerospace transportation and military industries. This article systematically reviews recent advancements in magnesium alloys fabricated using WA-DED. It discusses aspects such as forming quality, internal defects, microstructural evolution, and mechanical properties. Prevalent internal defects such as pores and cracks in WA-DED magnesium alloys are identified and characterized. Additionally, strategies for enhancing the manufacturing quality are elucidated. Furthermore, this article comprehensively explores the underlying mechanisms of the interplay among process parameters, internal defects, and microstructural heterogeneity. The main objective is to provide insights into and strategies for defect elimination, microstructural homogenization, and property enhancement. Finally, some perspectives are proposed for further progress in the application of WA-DED magnesium alloy components for superior performance.

Significance Large-scale, integrated, lightweight, and high-precision structures are becoming crucial trends in the development of aerospace equipment. Laser directed energy deposition (LDED) technology, with its high forming efficiency, flexible material feeding methods, and extensive freedom in shaping, proves to be highly suitable for the evolving trends in aerospace equipment development. It has gained significant traction in sectors such as launch vehicles, manned spacecraft, and rocket engines, positioning the aerospace industry as a key driver in the development and application of LDED technology. However, the current progress in LDED additive manufacturing technology is not adequately aligned with industry needs. This misalignment leads to underutilization of its technical advantages, vague directions for technological development, and limited application scenarios and fields. To expedite the technology s industrialization and intelligent evolution, and to achieve large-scale, systematic applications, it is essential to review and document the current research and application advancements of LDED for large-scale metal components in aerospace. This involves examining material research, process development, and application progress, and identifying future directions for LDED technology. Progress In recent years, significant breakthroughs have been made in the LDED process for aluminum alloys, titanium alloys, nickel-based superalloys, and their composites. The introduction of rare earth elements, such as Sc and Zr, for microalloying modifications and the addition of nanoparticles address challenges such as hot cracking, excessive defects, and the limitations of a single strengthening mechanism that leads to insufficient performance in aluminum alloys. This advancement enables the preparation of various high-density and high -performance aluminum alloy materials, including Al-Mn-Sc, TiB2/Al-Mg-Sc-Zr, and 6061-RAM2. Additionally, the development of a range of titanium alloys and their composites suitable for the LDED process, such as Ti-Cu, Ti -O - Fe, and TiB/TC4, eliminates coarse columnar crystal structures in favor of uniform and fine equiaxed crystal structures. This development is expected to address the longstanding challenge of performance anisotropy in additive manufacturing titanium alloys. Issues such as the suppression of solidification and liquation cracks, microstructure refinement, uniformity improvement, and performance enhancement in nickel-based/nickel-iron-based superalloys, including IN 718, IN 625, and HR-1, have been resolved. These solutions lead to a significant performance improvement in the prepared materials, with the IN 718 and IN 625 superalloys achieving performance levels comparable to forged materials of the same grade.This paper first summarizes the current research status of LDED technology applied to three primary structural materials in aerospace equipment. Currently, the LDED process for metal materials faces challenges such as hard-to-manage defects, uneven microstructures, insufficient strength and toughness, low manufacturing efficiency, and poor surface quality. In response, researchers domestically and internationally have developed various new high -performance, high-efficiency, and high-precision LDED processes aimed at enhancing performance, deposition efficiency, and manufacturing accuracy. By employing external fields such as acoustic, deformation, and magnetic fields to assist LDED, significant strides have been made in eliminating defects, refining microstructures, and improving performance. The development of laser processing heads with high deposition rates, multi-channel deposition equipment, and processes have boosted deposition efficiency. Additionally, the creation of high-precision powder feeding nozzles and additive-subtractive hybrid manufacturing equipment and processes has enhanced the quality of deposited surfaces. Notably, the Fraunhofer Institute for Laser Technology s development of three-dimensional EHLA technology has achieved manufacturing accuracy of up to 100 mu m and a deposition efficiency of up to 532 cm3/h, setting a benchmark for the future direction of LDED technology. As LDED processes for aluminum alloys, titanium alloys, nickel-based superalloys, and their composites mature and stabilize, alongside the development of new, high -performance, high-efficiency, and high-precision processes, LDED technology has realized significant applications in aerospace. This includes use in critical areas, such as launch vehicles and manned spacecraft s main load- bearing components, as well as in the manufacturing of copper alloy/superalloy heterogeneous alloy combustion chambers and integrated nozzles for rocket engines. The aerospace industry s demand for lightweight, integrated, high-temperature-resistant, and high-precision equipment has propelled the development and industrial application of LDED technology. Conclusions and Prospects This paper first summarizes the current research status of LDED technology applied to three primary structural materials in aerospace equipment: aluminum alloy, titanium alloy, nickel -based superalloy, and their composites. Building on this foundation, it organizes the development directions and research progress of LDED processes. It then delves into the manufacturing challenges, research, and application advancements of three typical aerospace equipment structures: the main loadbearing structure, the integrated structure of heterogeneous alloy, and the integrated structure with integrated flow channels. Lastly, the paper forecasts the development trajectory of materials, processes, and equipment for LDED additive manufacturing technology, highlighting the following strategic directions: the promotion of dedicated high-performance alloy materials design and development, tailored to the unique non -equilibrium physical metallurgy characteristics of the LDED process; the acceleration of high -precision LDED process, equipment, and software research and development, including the high -precision formation of large complex structures; the advancement of additive and subtractive hybrid manufacturing technology research; and the hastening of low-cost LDED manufacturing technology development.

Directed Energy Deposition-Arc (DED-Arc) was utilized to fabricate Inconel-copper bimetallic structures, with the aim of improving manufacturing modes and reducing costs for rocket engine thrust chambers. In this paper, bimetallic Inconel superalloy (GH4169) and copper alloy (C18150) structures were deposited using different deposition strategies. The formation mechanisms of grain-size gradients and heterogeneous interfacial microstructural evolution were comprehensive investigated and further discussed. Both strategies produced high-quality bimetallic samples with tensile strength exceeding 260.2 MPa. Fractures occurred within the C18150 metal rather than at the interface, indicating successful interface strengthening of the bimetallic samples. Gradual gradients in grain size distribution and nano-hardness were observed across the interface. The crystal structures of C18150 were unaffected by GH4169, and no new phases were generated in the interfacial region. The crystallographic orientation relationship between Ni and Cu was determined to be [011]Cu//[011]Ni and (111)Cu//(111)Ni, and interfaces were strengthened by grain boundary and dislocation strengthening through. This work demonstrates an approach for fabricating large, high-performance bimetallic structures with tailored grain-size gradients and heterogeneous microstructures, suitable for rocket engine thrust chamber applications.

Interface stability homogeneity control remains a challenging problem in large-scale laser-melting-deposited titanium (LLMDT) alloy components for aerospace applications. In this study, the homogeneity of the interface stability of LLMDT components after post heat treatment was investigated. Recrystallized grains nucleated and grew in the equiaxed and columnar grain regions in the LLMDT part, whereas they did not form in the interface region because the recrystallization driving force in the interface region was lower than that in the LLMDT part. The microstructures of the LLMDT components showed coarsened α lamellae, and their width varied from 1.65 μm to 2.18 μm. The α lamellae did not completely coarsen during post heat treatment (950 °C/1 h/air cooling+550 °C/4 h/air cooling) because of the low coarsening driving force. For the LLMDT components, the ultimate tensile strength (UTS) and yield strength (YS) were slightly different in different regions owing to the slight difference in the width of the α lamellae. The elongation (EL) of the LLMDT components exhibited no difference, and there was nearly zero anisotropic ductility. The highest fluctuation ratios of the UTS, YS, and EL were 3.11%, 3.8%, and 7.18%, respectively. The tensile properties of the LLMDT components showed no difference in the different regions, indicating interface stability homogeneity.

The static coarsening behavior of laser powder directed energy deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy and its effects on the alloy's tensile properties were investigated. The static coarsening kinetics of the crab-like primary α (αP) and secondary α (αs) were satisfied by the Lifshitz–Slyozov–Wagner relationships. For the coarsening of the crab-like αP, the coarsening efficiency (n) was satisfied at 0.25–0.35 for 910 °C, whereas it was satisfied at 0.45–0.50 for 950 and 990 °C. For the coarsening of the αs, the n was satisfied at 0.45–0.50 for 950 °Cand 990 °C. Compared to the as-built sample, the samples heat-treated at 910 °C/2 h/air cooled and 950 °C/2 h/air cooled exhibited good yield strength (930–1005.5 MPa), the highest elongation (14.5%–16.6%), and the lowest anisotropic ductility (0.6%) among all samples. The crab-like αP and αs increased the crack growth resistance and decreased the fracture difference in two different directions in the samples.

In this study, the static globularization and static coarsening behavior of arc wire directed energy deposited (AWDEDed) Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloy and their affected on tensile properties were studied. The asdeposited sample and the 550-AC (550 degrees C/4h/air cooling) sample showed columnar prior-beta grains, while the microstructure showed the continuous alpha GB grew up through the colony microstructure and the basket-weave microstructure. The driving force in the alpha/beta interface was enough for static globularization and static coarsening, which formed crack-like primary alpha (crab-like alpha P), alpha G (globularized alpha), and the alpha s (secondary alpha) during 970AA (970 degrees C/2h/air cooling+550 degrees C/4h/air cooling) or 990-AA (990 degrees C/2h/air cooling+550 degrees C/4h/air cooling). The microstructure evolution and formation mechanism of the crab-like alpha P, the alpha G, and the alpha s were discussed. The formation of the alpha G was mainly via grain boundary splitting, and the formation of the crab-like alpha P was mainly via terminal migration with different interchanged interfaces. The ultrafine lamellae alpha nucleated with the sympathetic mechanism grew until lost burgers orientation relationships with adjacent grain boundaries and formed alpha S. The 550-AC sample showed the highest yield strength (YS, 905 MPa) and the highest anisotropic ductility (Delta EL, 7.9) than those in the 970-AA sample and the 990-AA ample. It was because the crab-like alpha P, the alpha G, and the alpha s decreased the fracture resistance in the 970-AA sample and the 990-AA sample.

Wire arc additive manufacturing (WAAM) offers significant advantages in rapid manufacturing of complex integral parts. In this study, Mg-Gd-Y-Zn-Zr alloy deposited walls were fabricated by cold metal transfer (CMT) based WAAM. The interface bonding relationship between the additive zone and the substrate was studied, as well as the effect of the microstructure of the additive zone on the mechanical properties. The precipitated phase Mg24Y5 mainly distributed at the grain boundary was found in the additive zone of deposited walls, nano-scale contact interface and diffusion bonding interface were formed between beta-Mg24Y5 and alpha-Mg (OR: [001]beta-Mg24Y5// [10 1 0]alpha-Mg), and a portion of the 18 R-LPSO phase to 14H-LPSO phase transition occurred in the substrate zone. In each layer of deposited metal, the bottom zone had a higher cooling rate than the top zone, which led to the supersaturation of rare earth elements. The precipitated phases between different deposition layers showed a decreasing trend from the bottom zone to the top zone due to the complex multiple thermal cycles in the additive manufacturing process. Compared with the cast Mg-Gd-Y-Zn-Zr alloy, the mechanical properties (UTS, YS and EL) of the Mg-Gd-Y-Zn-Zr alloy fabricated by WAAM were significantly increased. The ultimate tensile strength of the deposited walls along the travel direction was 227.27 MPa, and the elongation was 8.08 %.

Magnesium rare-earth (Mg-RE) alloys have great potential in lightweight applications because of the high specific strength. Wire-arc directed energy deposition (WA-DED) exhibits great prospects for the fabrication of largescale monolithic structural components with high manufacturing flexibility. In this work, a single-pass multilayer Mg-10Gd-3Y-1Zn-0.5Zr (wt%, GWZ1031K) deposit was prepared via WA-DED. Electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are conducted to systematically explore the microstructural evolution during the WA-DED process and the subsequent heat treatment. The GWZ1031K alloy deposit fabricated by WA-DED exhibits uniform equiaxed grain structure whose average grain size is 22.3 +/- 5.6 mu m. The (Mg,Zn)(3)(Gd,Y) phase and RE segregation can be observed along the alpha-Mg grain boundaries (GBs). A number of needle-like gamma'/gamma '' phases embedded in the alpha-Mg grain interior (GI). In addition, there is a small number of fine RE-rich cubic phase and (Gd,Y)(2)O-3 particles. The deposit shows significantly enhanced ductility and slightly improved strength after solution treated at 500 degrees C for 12 h. After the solution treatment, the intergranular (Mg,Zn)(3)(Gd,Y) eutectics dissolve into the matrix and long period stacking ordered (LPSO) phases precipitate from the GBs into the GI, contributing to the enhancement in ductility. Besides, the LPSO phase along with the existing RE-rich cubic phase, (Gd,Y)(2)O-3 and Zr particles at GBs also play a role in hindering grain growth. The high-density nanoscale beta' phases appear in the GI after aging treated at 200 degrees C for 24 h, resulting in the remarkable precipitation strengthening. In comparison with the solution-treated GWZ1031K deposit, the aging-treated exhibits a prominently improved ultimate tensile strength of 337 +/- 7 MPa in the building direction (BD) and 331 +/- 5 MPa in the travelling direction (TD). It is envisaged that the WADED manufacturing method will provide a simple and effective route to fabricate large-scale Mg-RE alloy components for various applications.