Strength-ductility Trade-off Dilemma Research Articles

Evading the strength-ductility trade-off dilemma in high-entropy alloy by lamellar structure

Constructing lamellar structures in high-entropy alloys (HEAs) is an effective strategy for addressing the inherent trade-off between strength and ductility. However, conventional processing methods often struggle to achieve precise control over the microstructures and mechanical properties of the lamellar structures. Here, we employ laser remelting technology to successfully fabricate a lamellar structure within an HEA. The lamellar HEA shows an excellent yield strength of ∼547 MPa with a large uniform elongation of ∼41 %. Such enhanced strength-plasticity synergy is mainly attributed to the hetero-deformation of lamellar structures.

Phase reversion mediated the dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium-entropy alloy

An ultra-high strain rate (104 s-1) dynamic plastic deformation treatment at liquid nitrogen temperature (LNT-DPD) followed by annealing is carried out to obtain dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium entropy alloy (MEA). Such extreme loading conditions resulted in extensive phase transformation in this MEA. Subsequent annealing at 650°C for 1 h further induced reverse phase transformation and partial recrystallization, forming a complex heterogeneous microstructure characterized by nested trimodal grain sizes and partitioned dislocation density. A superior yield strength of ∼800MPa and a good ductility of ∼40% were simultaneously achieved in this heterogeneous alloy. In order to reveal the effects of grain size and dislocation density distributions on the mechanical property improvements, the underlying deformation mechanisms were systematically discussed. High density of geometrically necessary dislocations (GNDs) would be induced in complex heterogeneous structures during tensile deformation due to strain gradients or partitioning between different regions, which would lead to additional strengthening and work hardening. These results provide a novel approach to overcome the strength-ductility trade-off dilemma for FCC-structured MEAs.

Optimization in strength-ductility synergy of extruded Mg-3Sn-2Al-1Zn-0.6Y-0.6Nd alloy via novel FPE processes

Three novel FPE processes were proposed by integrating the advantages of conventional extrusion and ECAE, optimizing the strength-ductility synergy of extruded Mg-3Sn-2Al-1Zn-0.6Y-0.6Nd alloy. The deformation mechanism, evolution of texture and variation of the tensile properties of the alloy were investigated. Findings indicate that the alloys fabricated by the FPE processes exhibit a finer and more uniform microstructure with the lowest dislocation density, undergoing the most complete DRX. The FPE process breaks the strength-ductility tradeoff dilemma of the magnesium alloys, achieving a synergistic enhancement of both strength and ductility. The FPE-105 process was determined to be the best process for strengthening the alloy, with a 24.4% (340MPa) increase in UTS compared to the FE-10 sample, along with an impressive doubling of the ductility (18.6%). The excellent mechanical properties provided by the FPE-105 process are primarily stem from the uniform and fine grain distribution and texture modification. The successful application of the three FPE processes to the fabrication of extruded magnesium alloys demonstrates that the series of novel extrusion processes can be further optimized to create magnesium alloys with excellent strength-ductility.

Atomic-scale insights into the effect of layer thickness ratio on the tensile properties of heterostructured nano-aluminum

Gradient-structured alloys with lamellar microstructures show extraordinary potential in breaking the strength-ductility trade-off dilemma. When partial grain size exceeds the Hall-Petch limit, the deformation mechanism is not fully understood. In this study, the competing relationship between grain boundary (GB) softening and hetero-deformation-induced (HDI) strengthening in laminated nano-grained aluminum was investigated under uniaxial tensile loading. In the soft domains, the high activity of grain boundaries results in pronounced GB softening. However, when the volume fraction of the soft layer exceeds 50 %, the flow stress surpasses the predicted values of the rule of mixtures (ROM), demonstrating a significant HDI strengthening. A detailed analysis of microstructural evolution is conducted, including strain gradients, GB migration, and dislocation distribution. The effects of mechanical incompatibility between soft and hard layers on the distribution of plastic strain and overall material strength are elucidated in gradient structures. The study provides critical theoretical insights into the design and development of high-performance gradient nanocrystalline aluminum alloys, particularly in applications where a balance between strength and ductility is of paramount importance.

Coarsening of alloy carbides during a cyclic heat treatment for grain refinement in ultrahigh-strength steels

Strength–ductility trade-off dilemma is acute in materials science, especially for ultrahigh-strength steels. The improvement of toughness requires careful tuning of grains and precipitates. Thermal cyclic treatment and annealing before quenching are two effective ways of microstructural refinement for steels. However, a combination of the two methods has never been studied. Complex alloy carbides form in the process of annealing, but their effects on grain refinement in the subsequent quenching are unclear. Here, a systematic comparison of microstructure and mechanical properties is established between a thermal cyclic treatment with annealing (CHT) and traditional quench-temper treatment (QT). The results indicate that the CHT treatment leads to the coarsening of alloy carbides and subgrains, and the decrease in strength and toughness.

Fabricating a pure titanium foil with excellent strength-ductility combination via bimodal grain structure coupling with deformation twins

Preparation of pure titanium foil by cold rolling deformation often confronts the strength-ductility trade-off dilemma, how to obtain an excellent strength-ductility combination remains a great challenge. In the present work, we have prepared a pure titanium foil with a bimodal grain (BG) structure consisting of coarse grain (CG) and ultrafine grain (UFG), coupling with high-density deformation twins (DT) via a cryogenic-temperature rolling (CTR) and partial recrystallization annealing (PRA) process. Notably, a high strength-ductility synergy with YS of ∼483 MPa, UTS of ∼517 MPa and elongation of ∼21 % is achieved. The high strength is mainly caused by pronounced fine grain strengthening from the UFG region and twin boundary strengthening from strong interactions between DT and dislocations activated in the CG region. The GND caused by the hetero-deformation between CG and UFG, along with the activation of pyramidal <c+a> dislocation via DT in the CG region endows the pure titanium foil with excellent ductility.

Eliminating metallurgical defects and achieving strength-ductility combination in selective laser melted martensitic stainless steel through high-pressure annealing

Due to high difficulty in fabricating and processing high-strength metals, additive manufacturing has been considered to have broad prospects compared to the traditional casting means. However, unavoidable metallurgical defects and strength–ductility trade-off dilemma have become Achilles' heels for their practical applications. In this work, one high-pressure annealing (HPA) strategy was introduced to process the selective laser melted (SLM) martensitic stainless steel. The microstructures and mechanical properties of as-built, high temperature annealing and HPA and as-rolled SLM samples were systematically investigated. It was found that the HPA treatment makes the stainless steel achieve the significant yield strength of 1828 MPa and the comparable plastic strain of 36.2% compared to other samples. The pores and laminar structures from the SLM process were eliminated by HPA. What is more, the HPA treatment results in uniform carbide precipitation, grain refinement and nanoscale heterogeneous structure comprising a series of coarse and fine grains. The physical mechanism for nanoscale heterogeneous structure induced by HPA was discussed from the perspective of the cooperative effect of temperature and pressure. Additionally, the strengthening contributions from grain refinement, carbide precipitation, dislocation hardening, heterogeneous structure and pore closure were quantitatively determined. The current study not only reveals the comprehensive effect of temperature and pressure on microstructure and mechanical properties, but also establishes HPA as an effective method to evade the strength-ductility trade-off in alloys fabricated by additive manufacturing.

Enhanced strength–ductility synergy in Ti55531 titanium alloys through gradient microstructural design strategy

The strength-ductility trade-off dilemma still exists for titanium alloys, which is a challenging and pressing issue within the realm of microstructure design and property control. In the present work, a typical axial gradient microstructure was prepared in Ti55531 titanium alloy through a composite strengthening process involving rapid electropulsing treatment (EPT) combined with step-quench treatment (SQT). The results show that a significant improvement of 450 MPa (54 %) and 6.3 % (100 %) for the strength and ductility are obtained respectively for gradient microstructure by EPT + SQT (GMES) compared to that gradient microstructure prepared by EPT (GME) only. This indicates that the enhanced strength-ductility synergy observed in GMES is attributed to the characteristic Twinning induced Plasticity (TWIP) mechanism employed in this novel design of gradient microstructure. Furthermore, a detailed analysis and discussion are provided on the physical deformation mechanism and crack initiation behaviour of the gradient microstructure, providing valuable insights for the design of high-strength, high-ductility metals such as beta titanium alloys, advanced steels, and multi-phase alloys.

Overcoming the strength-ductility trade-off dilemma in austenitic lightweight steel via stepwise controllable intragranular dual nanoprecipitation

The strength-ductility trade-off is an inevitable scenario in precipitation-hardened austenitic lightweight steels. The reduction in ductility is due to the shearing of κ′-carbides by dislocations, resulting in limited work hardening capability. Conversely, non-shearable B2 particles can effectively improve the work hardening rate. However, these B2 particles tend to precipitate along grain boundaries and coarsen due to their incompatibility with the austenite matrix, resulting in negligible strengthening effect or even brittleness. We propose a stepwise controllable dual nanoprecipitation strategy to overcome the strength-ductility trade-off. To implement this strategy, we develop a manufacturing process that includes a high-temperature annealing treatment and a three-step aging process (700 °C/15min + 900 °C/15min + 450 °C/1 h). The higher annealing temperature increases the supersaturation of solute atoms in the austenite matrix, which improves the chemical driving force for the precipitation of intragranular B2 particles during aging at 900 °C. Additionally, the coarsened κ′-carbides (30–35 nm) formed during aging at 700 °C provide heterogeneous nucleation sites for the formation of intragranular B2 particles. Further aging at 450 °C promotes the precipitation of nano-sized κ′-carbides (5 nm) within the austenite matrix. The dual nanoparticles provide a significant precipitation strengthening contribution of 400 MPa without sacrificing ductility. The multiple deformation mechanisms of nanoscale “planar slip and Orowan bowing” provide an efficient source of work hardening capability. The present work aims to overcome the strength-ductility trade-off in austenitic lightweight steels by tailoring the precipitation process, which may provide insight into producing high-performance lightweight steels.

Investigation of a novel laser powder bed fusion nickel-based superalloy with hf, Y addition: Melt characteristic, microstructure and mechanical properties

In order to resolve the inherent strength-ductility trade-off dilemma observed in precipitation-strengthened nickel-based superalloys with high Al and Ti content, a composition modification strategy was devised. This study explored a novel laser powder bed fusion (LPBF) René104 alloy by incorporating Hf and Y (HfY-René104), examining its melt characteristics, microstructures, and mechanical properties. The experimental results demonstrate that the addition of Hf and Y effectively improves the molten pool structure of the as-built, alters grain orientation, diminishes grain aspect ratio, promotes the formation of cellular structures, AlY phases, stacking faults (SFs), and Lomer-Cottrell (L-C) locks at macro, meso, and micro scales, respectively. The primary contributors to yield strength are grain boundary strengthening and dislocation strengthening. Moreover, a dynamic Hall-Petch effect associated with cellular structures, SFs, and L-C locks ultimately results in remarkable strength (yield strength of 823 MPa, ultimate tensile strength of 1158 MPa) and enhanced ductility (elongation of 24.6 %) of HfY-René104 alloy.

Designing the heterogeneous microstructure via a direct warm rolling process to synergistically enhance the strength-ductility in a medium Mn steel

This work introduced a facile method for fabricating heterostructures in a medium Mn steel via a direct warm rolling process. The heavy warm rolling promoted the transformation of metastable austenite (∼12.2 vol%) into hard domain α’ martensite, which formed a heterogeneous microstructure with the untransformed γ (soft domain). After 600 °C re-annealing, the hard domain α’ re-reversed to α + γ, and the heterostructure disappeared. Compared to the homogeneous structure, the heterostructure exhibited the synergistic enhancement of strength-ductility (yield strength (YS): 782 → 1113 MPa; ultimate tensile strength (UTS): 1099 → 1304 MPa; total elongation (TEL): 20.8 % → 21.7 %). Quantitative analysis showed that the heterogeneous deformation induced (HDI) strengthening (∼261 MPa) was the primary contributor to the increased ΔYS (782 → 1113 MPa) value, rather than the traditional strengthening mechanisms. Transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effect were the main deformation mechanisms of both homogeneous/heterogeneous structures. However, compared to the homogeneous microstructure, the heterogeneous structure possessed the more pronounced TRIP and HDI hardening effects as well as L-C locks, the cooperative effect of these three factors further improved the strain hardening ability to break through the strength-ductility trade-off dilemma.

Superior mechanical properties of additively manufactured FV520B matrix composites by microstructure tailoring

The additively manufactured martensitic stainless steel (SS) parts often manifest the strength-ductility trade-off dilemma, which severely limits their practicality. In this study, the TiC-reinforced FV520B metal matrix composites (MMCs) were deposited via laser powder bed fusion (LPBF), and the as-built MMCs exhibited a superior strength-ductility synergy (ultimate tensile strength of 1,389±29 MPa, and fracture elongation of 30.1±0.6 %) when compared to their matrix alloy. This strength-ductility synergy can be attributed to a high-density of well-dispersed TiC nanoparticles, in-situ grain boundary engineering induced by TiC particles, fully austenite structure, and progressive transformation-induced plasticity effect. Furthermore, the microstructure, and mechanical properties of the MMCs annealed at 400–700 °C were compared. As the annealing temperature increases, the matrix progressively transforms from a fully austenite structure to a fully martensite structure, enabling substantial enhancements in tensile strength and work hardening capabilities. Notably, a high number density of the Cu-rich precipitates (CRPs) can be observed in the high-temperature annealed specimen, which can yield considerable strengthening through the Orowan looping mechanism. This work paves a pathway to fabricate structural materials with unique microstructures and excellent mechanical properties for practical engineering applications.

Strengthening complex concentrated alloy without ductility loss by 3D printed high-density coherent nanoparticles

Metallic 3D printing enables fast fabrication of net-shaped components for broad engineering applications, yet it restrains the use of most mechanical processing methods for strengthening alloys, e.g. forging, rolling, etc. Here, we proposed a new strategy for enhancing the strength of 3D printed complex concentrated alloys without losing ductility. This strategy relies on the rapid cooling of 3D printing to achieve a supersaturation state that is beyond conventional casting. Then, spinodal decomposition via aging is exploited to introduce high-density coherent nanoparticles for strengthening. The proposed strategy is demonstrated in a 3D printed Cu-based complex concentrated alloy. The rapid solidification during printing strongly inhibits elemental diffusion, leading to a high supersaturation state. High-density nanoparticles with coherent interface and size of ∼7 nm are introduced into the 3D printed samples through spinodal decomposition via simple aging treatment. The strength of the 3D printed alloy is increased by 30 % after aging with no ductility loss, leading to a strength-ductility combination superior to other Cu alloys. This strategy is readily applicable to other spinodal alloys fabricated by 3D printing for circumventing the strength-ductility trade-off dilemma.

Excellent strength-ductility synergy properties of Mg–Sn–Zn–Zr alloy mediated by a novel differential thermal ECAP (DT-ECAP)

The application of structural magnesium (Mg) alloys in engineering industry is usually impeded by the challenge of strength-ductility synergy. In this study, a considerable ductility (elongation, ∼27–33 %) and high ultimate tensile strength (UTS, ∼340–370 MPa) Mg–Sn–Zn–Zr alloy was developed by a combination of aging, extrusion and novel differential thermal equal-channel angular pressing (DT-ECAP) process. Both dislocation slip and (double) cross-slip are primary deformation mechanisms of the alloy. Furthermore, jogs or kinks induced by the interaction between high density of dislocations were also observed in the alloy before and after tensile test, indicating good deformability. More importantly, based on the two-beam bright-filed TEM under three g conditions, multiple slip systems containing pyramidal <c + a>, prismatic and basal <a> dislocations were activated to accommodate both c-axis and a-axis strains of the alloy, leading to superior work-hardening effect and thus superb ductility. On the other hand, the DT-ECAP process was in favor of grain refinement and ultrafine second phases with ∼54–63 nm. Therefore, the principal strengthening mechanisms of the DT-ECAPed alloys were grain boundary strengthening, precipitation strengthening and dislocation strengthening. The contributions of the three strengthening mechanisms to TYSs of second pass (2P) and forth pass (4P) alloys are ∼77 MPa and ∼66 MPa, ∼30 MPa and ∼27 MPa, ∼34 MPa and ∼27 MPa, respectively. The current work develops a novel DT-ECAP process for preparing a new Mg–Sn–Zn–Zr alloy with strength-ductility synergy and provides a strategy to break the strength-ductility tradeoff dilemma of rare-earth-free Mg alloy.

Microstructure and enhanced strength and ductility of Ti-Zr-O alloys prepared by a laser powder bed fusion process

Non-toxic and biocompatible Ti-Zr-O alloys with excellent comprehensive properties of strength and ductility were prepared from Ti-ZrO2 powder mixtures by a laser powder bed fusion (LPBF) process. The substitutional Zr atoms and interstitial O atoms, formed by decomposition of ZrO2 during laser irradiation, were dissolved into crystal lattice of Ti, resulting in significant increases in lattice constant c and axial ratio c/a. The Ti-Zr-O alloys were characterized by fine needle-like microstructure with weakened texture compared to pure Ti. The needle-like microstructure may be generated through the growth of α-nuclei according to the Burgers orientation relationship during β→α phase transformation, and the reduction of crystallographic anisotropy in the Ti-Zr-O alloys is due to the formation of α grains with multiple variants. The LPBFed Ti-Zr-O alloys exhibited significantly enhanced strength and maintained good ductility, overcoming the strength-ductility trade-off dilemma. For example, the yield strength and ultimate tensile strength (UTS) of the Ti-1.48Zr-0.66 O alloy reached 1014 MPa and 1073 MPa, respectively, and its elongation at fracture remained at 17 %. The strength enhancement is due to the solid solution strengthening of O and Zr and grain refinement strengthening, of which the solid solution strengthening of interstitial O atoms is the most dominant contributor to the improvement in strength of the LPBFed Ti-Zr-O alloys. The good ductility is mainly attributed to the activation of pyramidal slips due to reduced critical resolved shear stress (CRSS) ratios between pyramidal and prismatic planes, especially dislocation slips along <c + a> directions on the pyramidal planes due to the fine-grained microstructure. The activation of multiple slip systems, including prismatic and pyramidal slips, contributes to the improved ductility of the LPBFed Ti-Zr-O alloys.

Exceptional ductility through interface-constrained grain growth for the ultrafine-scale Ni/Ni-W layered composites

Enhancing the strength of metallic laminates through decreasing the constituent layer thickness from micrometer to nanometer scale is usually accompanied by the degradation of ductility because plastic instability characterized by fatal shear bands inevitably occurs in the early stage of deformation. To overcome the strength-ductility trade-off dilemma, we designed a kind of metallic layered composites (LCs) consisting of nano-grained Ni (grain size: 21–37 nm) and ultrafine nano-grained Ni-W (grain size: 8 nm) constituent layers with layer thickness ranging from microns to tens of nanometers. We found that the strength and ductility of Ni/Ni-W LCs can be simultaneously enhanced by decreasing the layer thickness. Interface-constrained grain growth in the Ni layers with an initial layer thickness of less than 1 μm enhances strain hardening ability. Thus, strain delocalization characterized by the formation of rectangular strain zones instead of crossed micro shear bands appears in the LCs. Based on the above mechanism, we obtained the optimum ratio of the layer thickness to the grain size for the nano-grained Ni layers as about 15:1, which corresponds to Ni0.25/Ni-W0.025 LCs with the highest tensile strength (1.9 GPa) and elongation to failure (5.5 %). These findings may provide a new path for the design principle of metallic LCs with multi-level microstructural and geometrical scales.

Evading the strength-ductility trade-off dilemma in AA2024 alloy by short-term natural re-aging after T351 temper

In this research, the influence of short-term natural re-aging after T351 temper on the microstructural evolution and mechanical behavior of AA2024 aluminum alloy was investigated. Grain growth occurred in the microstructures of the natural re-aged sample and a large number of Al7Cu2Fe particles were located inside the alpha grains. At the re-aging time of 1440 min, the peaks of XRD were shifted strongly to the right due to the formation of θ′′, S″, θ′, and S′. The results revealed that the precipitation rate was high in the AA2024 alloy during natural aging. With increasing the re-aging time, texture parameters remained almost unchanged. The hardness increased slowly within the first 60 min, then enhanced rapidly between 60 and 2880 min, and finally became stable at around 139 HV between 2880 and 11520 min. When the natural re-aging time increased from 240 to 2880 min, the strengthening trended speed up, viz, the yield strength increased from 226.6 to 357.3 MPa, and the ultimate tensile strength enhanced from 452.2 to 535.5 MPa. Compared to the as-received sample (T351 temper), the ultimate tensile strength of the re-aged sheet improved from 455.5 to 535.5 MPa, the ductility remained unchanged, and the hardness increased from 128.8 to 138.2 HV, which was owing to the acceleration of the precipitation caused by the presence of high-content Al7Cu2Fe particles in the interior of the alpha-aluminum grains in the natural re-aged sample. It was found that the Portevin-Le Chatelier instability of AA2024 alloy was effectively postponed after natural re-aging. With increasing the natural re-aging time, the strain hardening rate of the AA2024 sheet increased. The strengthening of the natural re-aged sample for 1440 and 2880 min was a result of a synergistic effect of precipitation hardening due to the formation of θ′′, S″, θ′, and S′ phases, elimination of Portevin Le-Chatelier instability, and highly efficient load transfer from alpha-aluminum to Al7Cu2Fe. Finally, to use the A2024 alloy produced by natural re-aging for 1440 or 2880 min, two methods were proposed.

Balanced strength and ductility by asymmetric gradient nanostructure in AZ91 Mg alloy

High-strength Mg alloys have historically suffered from a challenge in achieving good ductility. Here, we report an asymmetric gradient nanostructure design prepared by ultrasonic severe surface rolling (USSR) at room temperature. Unlike conventional gradient-nanostructured materials that employ a hard-soft-hard sandwich structure, this new design incorporates a combined gradient distribution of grain microstructure and nanoprecipitates throughout the entire sample along the thickness direction. The nanoprecipitates are identified as the β-Mg17Al12 phase and are primarily generated through In-situ precipitation promoted by the USSR-induced high-density dislocations and temperature increment. Benefiting from this unique microstructure, an outstanding strength-ductility synergy is achieved, with a yield strength of 372.8 MPa, an ultimate tensile strength of 453.3 MPa, and an elongation of 11.5%. The enhanced strength can be attributed to several mechanisms, including grain boundary strengthening, dislocation strengthening, precipitation strengthening, twin strengthening, and hetero-deformation induced (HDI) strengthening. The HDI hardening and activation of multiple deformation modes also contribute to good ductility. This work provides a promising and effective method for overcoming the longstanding strength-ductility trade-off dilemma in Mg alloys.

Making ultra-high strengthening and toughening efficiency in hybrid reinforcing of aluminum laminated composites via dispersion engineering

To overcome the strength-ductility trade-off dilemma, herein we propose a hybrid in-situ/ex-situ reinforced aluminum matrix composite to achieve a uniform dispersion of reinforcements and strong reinforcement-matrix interfacial bonding. To exploit the pros of inter/intra granular dispersion of reinforcements, nano- Al3BC particles have been in-situ synthesized into ultrafine-grained (UFG) Al grain interior reinforced by carbon nanotubes (CNTs) via an elemental powder mixture, mechanical activation and subsequent annealing process. The in-situ nano-scaled Al3BC were uniformly distributed inside the elongated ultrafine Al grains, enabling stronger dislocation pinning and retention, providing stronger effective stress which consequently helps to enhance strength and strain hardening. The as-fabricated (Al3BC, CNT)/UFG Al exhibits simultaneous enhancement in strength (394 MPa) and total elongation (19.7 %) compared with its counterpart without the nano-Al3BC, suggesting the promising strengthening effects of in-situ/ex-situ reinforcing benefitting from the uniform dispersion and the strong semi-coherent interface with the matrix.

Microstructural mechanisms imparting high strength-ductility synergy in heterogeneous structured as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy

The dual-phase AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) presents a promising solution to the strength-ductility trade-off dilemma, making it a highly desirable option for structural materials with vast potential applications. However, the relationship between the mechanical properties and the unique as-cast heterostructures needs to be further revealed. Here, we conducted in-situ tensile experiments of the as-cast EHEA to unveil the mesoscopic/microscopic microstructural mechanisms of strength-ductility synergy via investigating the dynamic real-time plastic deformation behaviors and crystallographic information evolution, as well as characterizing the deformed microstructures via transmission electron microscopy. The results indicate that the sequential dominant heterogeneous deformation induced hardening resulting from the incompatible plastic deformation between different types of heterogeneous microstructures is the primary source of its remarkable strength-ductility synergy. Moreover, the unique elongated lamellar microstructures of the as-cast EHEA offer numerous phase boundaries, and the growth twins in the face-centered cubic (FCC) phase generate abundant twin boundaries, all of which contribute to boundary strengthening and further enhance the strength and ductility of the as-cast EHEA. Furthermore, abundant cross-slip and dislocation substructures in the FCC phase provide strain hardening for as-cast EHEA, while body-centered cubic phase contributes to the high strength through precipitation hardening. Consequently, the heterostructure induced multiple strengthening mechanisms are responsible for the high strength-ductility synergy in the as-cast EHEA. The present work provides a new perspective to explain the strength-ductility synergy of similar heterogeneous structured alloys.