Work Hardening Effect Research Articles

Modification of Microstructure and Properties of Cold-Sprayed AlSi10Mg+TiB2 Composite by Friction Stir Process

This study investigates the influence of friction stir processing (FSP) on the microstructure, microhardness, and tribological properties of cold-sprayed AlSi10Mg+TiB2 composite coatings on Al substrates. Due to the limitation of particle deformation during cold spraying, there were still some porosities and poorly bonded regions in the as-deposited AlSi10Mg+TiB2 composite coating, which decreased the mechanical performance. Applying FSP to the composite coating significantly reduced the porosity and improved metallurgical bonding. Further, the FSP process induced severe plastic deformation, leading to a more uniform distribution of TiB2 particles and a homogenized microstructure in the composite coating. The microhardness decreases progressively from the unaffected region through the heat-affected zone and thermomechanical-affected zone, and ultimately reaches its lowest value in the stir zone. The decreased microhardness is primarily attributed to the removal of the work-hardening effect. The FSP treatment seems to have little impact on the wear performance for both the pure AlSi10Mg and AlSi10Mg+TiB2 composite samples, as the coefficient of friction values and wear rates remain essentially unchanged after the FSP treatments.

Effect of ultrasonic shot peening on the microstructure, surface residual stress, and wear properties of Ti-6Al-4V alloy

In this study, ultrasonic shot peening (USP) was used to enhance the surface of a Ti-6Al-4V alloy. Samples treated with different amplitudes were characterized and their wear resistance was tested and analyzed. The results demonstrate that the surface morphology of the Ti-6Al-4V alloy changed significantly after USP treatment, and the surface roughness increases at first, then stabilizes as the amplitude increases. The surface grain of the material is refined due to severe plastic deformation, and the average grain size after USP treatment is 27.93% finer than the original sample. Due to the effect of fine grain strengthening and work hardening, the microhardness of the material's near-surface layer is also enhanced in varying degrees, showing a gradient decrease throughout the depth of the cross-section. Furthermore, USP produces compressive residual stress as high as −791.01 MPa in the near-surface layer. When the USP amplitude is 80% and the treatment time is 240 s, the wear resistance of Ti-6Al-4V alloy is substantially enhanced under the combined action of hardness, compressive residual stress, and surface pits, reducing wear resistance. The wear mechanism is primarily abrasive wear and oxidation wear.

Effect of ultrasonic impact on the microstructure and properties of 30% WC-Ni ceramic coatings by laser cladding

In this study, 30%WC-Ni coatings were prepared using the laser cladding process. Ultrasonic impact treatment (UIT) was performed on the surface of the coatings with different UIT time to systematically investigate the effects of UIT on the microstructure and properties. The results showed that surface plastic deformation became more pronounced as UIT time increased. The matrix phase exhibited grain refinement and lattice distortion, inducing work-hardening effects. After UIT, the coating surface displayed a dispersed distribution of numerous broken WC particles. Furthermore, UIT significantly reduced the size and number of pores in the coating, enhancing its density. These combined effects significantly improved the microhardness and wear resistance of the coatings. The surface microhardness and wear resistance increased with UIT time. After UIT with the time of 20 min, the microhardness of the coating surface is the highest, 759.4 HV0.3, and the wear resistance of this coating was also optimal, with a wear rate of 4.09×10-3 μm3·N-1·μm-1. In addition, more Cl- intrusion channels can be generated due to broken WC particles, grain refinement, and internal cracks of WC particles, which results in specimens being prone to micro electro-coupling and the formation of a corrosion mechanism for the exfoliation of WC particles after UIT. The findings can offer experimental insights and a basis for the effects of UIT process on metal-ceramic alloys.

Effect of pre-aging on mechanical reinforcement of the Cu–Fe–Nb composites

Pre-aging treatment was demonstrated to significantly enhance the mechanical properties of Cu–10Fe–1Nb (wt.%) composites. Specifically, after rolling and aging at 400 °C for 8 h, the microhardness, tensile strength, and elongation of the pre-aged samples reached 163 HV, 559 MPa, and 11.2%, respectively. The refinement of Fe-rich phases in pre-aged samples was primarily attributed to the increased shear strain between the Fe-rich phases and the matrix, which was driven by the precipitation-strengthening effect induced by pre-aging. Additionally, the matrix of the pre-aged samples suffered significant refinement as dynamic recovery and recrystallization of the matrix were suppressed during the rolling process, forming a high-density dislocation structure that greatly enhances the work-hardening effect. The main contribution to strength improvement in the Cu–10Fe–1Nb composites was identified as precipitation strengthening, refinement strengthening, and work hardening. Moreover, compared with the sample without pre-aging treatment, the refinement strengthening and work hardening effects of pre-aged samples exhibited substantial improvements, with increment of 49 MPa and 21 MPa, respectively.

Synergistic strengthening effects of precipitation and work hardening in cold-rolled Cu-0.4 wt%Cr alloy

Given the limitation of the precipitation strengthening effect in high strength and high conductivity Cu-Cr alloy, work hardening emerges as a practical and effective means to further enhance its strength. The Cu-0.4 wt%Cr alloy underwent varying degrees of cold rolling between the solution and aging treatments. The results of TEM characterization indicate that plastic deformation enhances precipitation, which occurs earlier than recrystallization in the deformed Cu-0.4 wt%Cr alloy. Thermodynamic calculations indicate that the driving force for precipitation is several orders of magnitude higher than that for recrystallization, while the nucleation barrier for precipitation is several orders of magnitude lower than that for recrystallization. Thus, the delayed recrystallization relative to precipitation theoretically allows for the coexistence of precipitates and deformed microstructures. In the peak aging state, despite the presence of numerous deformed microstructures, conductivity is almost fully restored. After aging for 1 h, the synergistic strengthening effects of precipitation and work hardening result in the yield strength and tensile strength of the sample cold rolled 64 % reaching 384.6 MPa and 422.0 MPa, respectively.

Microstructure and properties controlling of Al-xGd alloys for thermal neutron absorbing

A novel lightweight thermal neutron absorbing Al-xGd alloy (x = 2.5, 5, and 10 wt.%) with tunable mechanical properties was fabricated by induction melting followed by a rolling process and an annealing treatment. During solidification, the Al3Gd phase predominantly formed and was distributed along grain boundaries. Cold rolling crushed and redistributed the Al3Gd phase throughout the matrix. Furthermore, the large deformation imposed on the material during cold rolling enhanced the work hardening effect and promoted dynamic recrystallization. The load transfer strengthening effect was influenced by the size, volume fraction, and distribution of the second phase. The spheroidization of the second phase increased rapidly and then remained stable during 5000 h long-term aging at 400 °C. The thermal neutron absorbing performance of the Al-5Gd alloy is comparable to the 30 %B4C/Al composite evaluated by Monte Carlo simulations. Furthermore, Al-5Gd alloy exhibited higher plasticity (>20 %). This novel Al-xGd alloy is a promising candidate for future lightweight thermal-neutron-absorbing materials.

500 μm heavy micro-alloyed Cu wire for IGBT application: The study on microstructure characteristics, electrical fatigue fracture mechanism and bonding reliability

In this study, we introduced trace amounts of silver and nickel into 500 μm diameter copper wires to form micro-alloyed copper wires used in insulated gate bipolar transistors (IGBT). The addition of silver and nickel enhanced the mechanical properties of the conductors and suppressed the work hardening effect, significantly improving the power cyclic lifetime. Additionally, this study conducted chlorination and high-temperature oxidation test to compare the application characteristics of the heavy micro-alloyed copper wires with pure copper wires, through tensile and bending test, as well as electrical property comparisons. Finally, Cu50Ni (50 ppm Ni) wires were selected and nickel ceramic substrates for wire bonding to evaluate module electrical properties and bonding reliability.In the chloride test, there was no significant pitting corrosion observed in copper wire, and the micro-alloyed copper wire outperformed the pure copper wires in terms of bending lifetime and power cycling performance. In the high-temperature oxidation test, an oxide layer of cuprous oxide formed on the surface of all wires. The pure copper wire exhibited a significant increase in resistance. Notably, the micro-alloyed copper wires had better resistance to oxidation. Regarding wire bonding, the use of Cu50Ni wires and nickel ceramic substrates reduced the diffusion rate of nickel atoms from the substrate to the copper wire, forming a thinner alloy diffusion layer. This prevented electrical degradation and achieved high bonding reliability, especially under higher bonding forces. These findings confirm that micro-alloyed copper wires are suitable for high-power applications.

Deformation mechanism of dislocation slip and kinking behaviour in dynamic compression response of TiZrHfNb alloy fabricated by laser directed energy deposition

ABSTRACT In this study, the dynamic response and deformation mechanism of TiZrHfNb RHEA fabricated by laser directed energy deposition (L-DED) were researched under a dynamic compression test at a nominal strain rate of 3500 s−1. The L-DED TiZrHfNb alloy with columnar grains exhibits exceptional mechanical properties with a uniform dynamic flow stress of 1670 ± 10 MPa and a maximum plastic strain of 0.28 ± 0.03. The dislocation slipping and kinking behaviour dominate uniform plastic deformation. First, the dislocations are primarily confined within dislocation channels due to coplanar slip, and the evolution of them in dynamic compressive deformation process has undergone spacing refinement and crossing. Furthermore, the kinking behaviour induced by the lattice rotation with the T = <011> axis denotes the work hardening effect. Particularly, the second kinking behaviour effectively relieves local stress concentration and delays fracture before the formation of adiabatic shear band (ASB).

Strengthening Mg–8Li–3Al–2Zn-1Gd-0.2Zr alloy by combining hot extrusion and cold rolling

The microstructure, texture, and mechanical properties of as-extruded and cold-rolled Mg–8Li–3Al–2Zn-1Gd-0.2Zr (LAZ832-1Gd-0.2Zr) alloys were investigated with the aim of strengthening the alloy by combining hot extrusion and cold rolling. Cold rolling does not change the phase composition of as-extruded LAZ832-1Gd-0.2Zr alloy, but introduces a larger number of dislocations and twins into alloy matrix. Cold rolling leads to the weakening of the original {0001} basal and {112‾0}-{011‾0} prismatic textures in α-Mg matrix, as well as the α and γ fiber textures in β-Li matrix. But new slip systems that are favorable for cold rolling are activated, resulting in the formation of {033‾8} pyramidal and new prismatic ({112‾0}⟨101‾4⟩ and {101‾0}⟨21‾1‾10⟩) texture components. Cold rolling further strengthens LAZ832-1Gd-0.2Zr alloy on the basis of hot extrusion, mainly through work hardening effect caused by introducing a large number of dislocations into α-Mg matrix. When the rolling reduction is 45%, the yield strength and tensile strength of LAZ832-1Gd-0.2Zr alloy are increased to 269.8 ± 4.0 and 308.6 ± 4.1 MPa, respectively, and the elongation is higher than 15%.

The Influence of Aging Temperatures on the Microstructure and Stress Relaxation Resistance of Cu-Cr-Ag-Si Alloy

Copper alloys used in connectors rely significantly on stress relaxation resistance as a key property. In this study, a heavily deformed Cu-Cr-Ag-Si alloy underwent aging at varying temperatures, with a subsequent analysis of its mechanical properties and microstructure, with a particular emphasis on understanding the mechanism of improving stress relaxation resistance. As the aging temperature rose, the Cr precipitated into a Cr-Si composite element precipitated phase. Both work hardening and precipitation strengthening played vital roles in enhancing the stress relaxation resistance of the Cu-Cr-Ag-Si alloy, with the latter exerting a more pronounced impact. The notable performance enhancement observed after aging at 450 °C can be attributed to the synergistic effects of work hardening and precipitation strengthening. Following aging at 450 °C, the alloy demonstrated optimal performance, boasting a tensile strength of 495.25 MPa, an electrical conductivity of 84.2% IACS, and a level of 91.12%. These exceptional properties position the alloy as a highly suitable material for connector contacts.

Evolution of deformation structures in CrCoNiSi0.3 medium entropy alloy subjected to high-strain-rate and quasi-static compressive deformation

The objective of the present study is to fundamentally explore the evolution of deformed structures of CrCoNiSi0.3 medium entropy alloy subjected to high-speed compression deformation with true strains of 0.16, 0.33, and 0.46 (via split Hopkinson pressure bar system, strain rate of ∼6 × 103 s−1, denoted as HSR deformation), and quasi-static compression deformation with true strains of 0.20, 0.30 and 0.50 (via MTS compression system, strain rate of ∼10−3 s−1, denoted as LSR deformation). From the comparison between the results of HSR and LSR samples, it clearly indicates that the formation of deformation nanotwins is promoted under the HSR deformation and enhances the work hardening effect in the early stage of deformation; as the HSR deformation proceeds, the nanotwins effectively provide the dynamic Hall–Petch effect, leading to an increase in flow stress beyond the stress required for HCP phase transformation. The HCP phase also induces a stronger work hardening capacity at the late stage of deformation. Profuse deformation nanotwins and HCP phase promoted by HSR deformation result in a strong work hardening effect. Furthermore, the flow stress of the HSR deformed sample with a true strain of 0.46 is 1536 MPa, which is about 36% higher than that of the LSR deformed sample with the same true strain, 1102 MPa. It is clear that under the HSR deformation, the defect structures including deformation nanotwins and ultra-thin HCP platelets are much more favorably generated, greatly improving the working capacity.

Tribological behaviour of microindented 100Cr6 steel surfaces in dry contact conditions

In the present work, we studied the dry tribological behaviour of a 100Cr6 steel, the spherical surface of which was texturized with microindentation. The purpose of adopting a mechanical indentation technique on a non-planar surface was to simultaneously evaluate the effectiveness of adopting a fast, deformation-based technique for improving the contact tribological properties. Specifically, dimples were created using an automatic microhardness tester equipped with a Vickers indenter, setting a load of 0.5 N. Friction tests were performed at different speeds considering textured surfaces with two different void ratios (VRs). Textured and untextured surfaces were tested using a ball-on-disc tribometer. In addition, the effect of dimple size was evaluated by producing Vickers indented surfaces at a load of 5 N per each indentation, while keeping the VR values unchanged and testing the frictional properties of such surfaces at a fixed speed of 4.18 mm/s. Textured surfaces were deeply investigated to motivate the improvement of tribological properties. Notably, compared to the untextured samples, the microindented samples exhibited a much lower coefficient of friction (COF), with a friction reduction compared to the untextured case ranging from 45 to 65%, depending on the VR values. The adoption of large dimples allowed the reduction of the COF, already at smaller VR value but, in such a case, the presence of bulges at the edge of the dimple worsens the wear resistance of the counter surface. In addition to reducing the contact area and the capability to trap any debris in the dimples, the local measurement of strength allowed to clarify that the friction reduction is also determined by the work hardening effect produced by the microindentation texturing. Considering the significant improvements recorded in terms of COF and the high ability to indent even non-planar surfaces, the proposed approach can be considered very promising and, therefore, industrially applicable (e.g. using a specifically designed multi-indenter tool) to affect the friction behaviour of components, even locally, during both their use and their production.

Comparison of analytical and numerical methods for estimating notch strains**

AbstractIn fatigue assessments, local strains and stresses can be easily evaluated using accurate finite element analysis in a case of an individual fatigue‐critical notch or structural detail. In practical design and analysis of global models, the consideration of local notch effects using suitable estimation rules in the combination with linear elastic analysis is reasonable. Various notch rules exist but the current knowledge lacks understanding how applicable different notch rules are for estimating notch strains from elastic stresses. This work studies the Neuber′s rules for sharp and mild notches, Glinka′s equivalent strain energy density method, the correction of Neuber′s rule proposed by Sonsino for mild notches, as well as the Seeger‐Beste method. The application of different estimation rules for notch strains, applied to the elastic‐perfectly plastic steel material and to Ramberg‐Osgood material model for the aluminum material, including work hardening effect, was studied in this work by comparing the estimations with the corresponding experimental data and finite element analysis results. The Neuber′s rule for mild notches and Sonsino′s averaging method gave best correlations with the experimental data and numerical (finite element analysis) results and can be thus recommended for such analyses in compatible cases studied in this work.

L12 nanoparticle-strengthened CoNi-based superalloy with ultrahigh yield stress developed using CALPHAD method

In this study, a Co-30Ni-10Ti-2Ta-3Al (30Ni3Al) alloy with high γ′ phase dissolution temperature (1215°C), excellent mechanical properties, and low density (8.46 g/cm3) was developed based on the thermodynamic database of Co-based high-temperature alloys established by our group. Compositional design and microstructure control were achieved through the utilization of thermodynamic phase diagrams and phase fractions. It is found that the addition of 2 at.% Ta significantly improves the γ′ phase fraction and solvus while maintaining a suitable working window. However, a rafting trend of γ′ phase was observed as heat treatment for a long time at 750°C. By introducing 3 at.% Al and 30 at.% Ni into the optimized Co-10Ti-2Ta master alloy, the rafting of the γ′ phase was effectively suppressed. Benefiting from the fine, stable, high volume fraction γ′/γ microstructure, the 30Ni3Al alloy demonstrates compressive yield strengths of approximately 1487±7 MPa and 1319±13 MPa at room temperature and 600°C, respectively. The superb mechanical property at high temperatures can be attributed to the work-hardening effect resulting from the interactions of superattice stacking faults in γ′ phase.

Dynamic Mechanical Properties and Modified Material Constitutive Model for Hot Forged Ti2AlNb over Wide Ranges of Temperature and Strain Rate.

In this paper, the stress-strain curves of Ti2AlNb are established based on uniaxial impact tests over wide ranges of temperature and strain rate. The Ti2AlNb exhibited the work hardening effect but did not show an obvious yield stage during a quasi-static compression test. In the SHPB test, an obvious temperature softening effect was found, the strain rate strengthening effect was detected when the strain rate was 4000-8000 s-1, and the strain rate softening effect was detected in the range of 8000-12,000 s-1. A function describing the effect of strain rate on the strain rate strengthening parameters under various temperatures was proposed to modify the basic J-C constitutive model. The relative errors between the experimental measured value and predicted values in various experimental conditions with a modified J-C model were less than 5.0%. The results verified that the modified J-C model could accurately describe the dynamic mechanical properties of Ti2AlNb at high temperatures and strain rates. The research could help to illustrate the cutting mechanism and finite element simulation of Ti2AlNb alloy.

Enhanced crack propagation resistance after healing treatment by addition of boron in FeNi-base superalloy

The objective of the present study was to investigate whether the crack propagation resistance of boron-containing FeNi-based superalloy could be enhanced by healing treatment. The healing treatment was performed by pre-straining and subsequent heat treatment, resulting in a pronounced boron segregation zone at the interface. Formation of boron segregation zone reinforced the crack propagation path, thereby effectively enhancing the mechanical properties of FeNi-based superalloy. The tested alloys were prepared by hot-rolling followed by aging treatment, resulting in precipitation of γ′-Ni3Ti and γ''-Ni3Nb embedded in the γ matrix. After pre-straining and healing heat treatment, η-Ni3Ti phase formed at the grain boundary, leading to the formation of a boron segregation zone at the interface between the η-Ni3Ti phase and γ matrix. Both strength and ductility were improved with increasing boron content from 0 at% to 0.2 at% after healing treatment. The spontaneous segregation of boron at the precipitate-matrix interface played a role in enhancing both strength and ductility by interface strengthening. Moreover, it was revealed that a critical amount of boron segregation is required for interface strengthening. Dislocation density analysis revealed that the recovery effect was weaker in alloys with boron than in those without it, leading to a more pronounced work-hardening effect.

Tailoring properties of directed energy deposited Al-Mg alloy by balancing laser shock peening and heat treatment

Wire arc-directed energy deposition (WADED) has shown great advantages and potential in fabricating large-scale aluminum (Al) alloy components. However, WADED Al alloys typically exhibit low strength and reliability due to pore defects and lack of work hardening or precipitation strengthening. This study utilized a combination of laser shock peening (LSP) and annealing to regulate the microstructure of WADED Al-Mg4.5Mn alloy and enhance mechanical properties. The effects of LSP and annealing on phase composition, pore distribution, and microstructures at multiple scales were systematically investigated to reveal the mechanical property improving mechanism. The results demonstrated that LSP-induced plastic deformation formed a defect-free zone by closing near-surface pore defects. LSP created the hardened layer with gradient mechanical properties by inducing gradient changes in grain size, the number of low-angle grain boundaries (LAGBs), and dislocation density along the depth direction. The annealing process promoted grain coarsening and reduced excessive dislocations and LAGBs, weakening the work hardening effect caused by LSP. Furthermore, the high-density dislocations and high stored energy generated by LSP accelerated the recrystallization, facilitating growth of near-surface grains. The defect-free zone, dislocation strengthening, and LAGBs strengthening were responsible for the increase in strength, while the synergistic deformation between hardened layers and soft core facilitated maintaining excellent elongation. The strength and elongation of WADED Al alloy can be synergistically improved by balancing the effects of LSP and heat treatment.

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.

Effect of laser shock peening on stress corrosion cracking of TC4/2A14 dissimilar metal friction stir welding joints

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

Preparation of ultra-high ductility and high strength Mg-Sn-Zn-Zr alloy by differential thermal ECAP (DT-ECAP) induced heterogeneous structure

Developing high-ductility magnesium (Mg) alloys has become an imminent issue for their wide application. In this work, a new Mg-Sn-Zn-Zr alloy with ultra-high ductility (elongation, El. over 40 %) and high ultimate tensile strength (UTS, ∼309–354 MPa) was prepared by a novel differential thermal equal-channel angular pressing (DT-ECAP). Heterogeneous structures, including bimodal grain structures and inhomogeneous distribution of second phases composed of banded structure and particle free zone (PFZ), were induced by DT-ECAP process. Based on the results of electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED), the bimodal grain structure originated from incomplete dynamic recrystallization (DRX) dominated by Zener pinning, strain-induced grain boundary migration (SIBM) and the limitation of polycrystallization due to lower dislocation density. Meanwhile, the bimodal distribution of second phases was highly associated with the defect density and initial structure. More importantly, the enhanced strength of DT-ECAPed alloys can be primarily attributed to hetero-deformation induced (HDI) strengthening, grain boundary strengthening, and precipitation strengthening. Moreover, HDI hardening, texture weakening or randomizing activation of non-basal slip, high density of dislocations in sub-structures, and twining induced superior work-hardening effect, which was highly responsible for the ultra-high ductility in sixth pass (6P) alloy. The current work provides a novel DT-ECAP process for inducing heterogeneous structure and offers beneficial insight into the development of ultra-high ductility and high strength for rare-earth-free Mg alloys via a combination of HDI strengthening and hardening and other vital mechanisms.