Enhanced strength and ductility synergy in dilute aluminum alloys through cryogenic multi directional forging: synergistic effects of bimodal heterostructured grains and multi scale defects

Abstract

The cryogenic multi-directional forging (Cryo-MDF) technique enables aluminum alloys to achieve a remarkable strength-ductility synergy through unique microstructural evolution. The Cryo-MDF processed T6-6061 aluminum alloy attains a high tensile strength of 412 MPa while retaining an elongation of 10.5%, overcoming the conventional strength-ductility trade-off. Post-forging microstructural characterization reveals a bimodal heterostructured grain architecture, accompanied by nano-twins, high-density stacking faults, Lomer-Cottrell (L-C) locks, and lattice distortions. These multi-scale defect configurations synergistically enhance yield and tensile strength while preserving ductility via four key mechanisms. Nano-twin boundaries act as robust barriers to dislocation glide. High-density stacking faults restrict dislocation mobility and elevate strain-hardening rates. L-C locks stabilize tetrahedral nodes through pinning effects, forcing dislocation path deviations. Lattice distortions enhance local structural stability. This hierarchical, multi-scale coordination mechanism not only elucidates the origin of exceptional mechanical properties in Cryo-MDF alloys but also establishes a microstructure design paradigm for developing next-generation high-performance aluminum alloys.

Keywords

cryogenic multi-directional forging / gradient grain architecture / multi-scale defects / synergistic strengthening

References

[1] Rajabi F, Zarei-Hanzaki A, Eskandari M, et al.. The effects of rolling parameters on the mechanical behavior of 6061 aluminum alloy [J]. Materials Science and Engineering: A, 2013, 578: 90-95

[2] Edalati K, Bachmaier A, Beloshenko V A, et al.. Nanomaterials by severe plastic deformation: Review of historical developments and recent advances [J]. Materials Research Letters, 2022, 10(4): 163-256

[3] Toth L S, Gu C. Ultrafine-grain metals by severe plastic deformation [J]. Materials Characterization, 2014, 92: 1-14

[4] Tang C, Shi D, Zhang J. Temperature-induced variations in slip behavior of single crystal aluminum: Microstructural analysis [J]. Materials, 2024, 17(9): 2084

[5] Liu Y, Pang Q, Hu Z, et al.. Tension-compression plasticity asymmetry of γ-TiAl alloy across wide temperature ranges [J]. Journal of Alloys and Compounds, 2026, 1057: 186736

[6] Sakai T, Belyakov A, Kaibyshev R, et al.. Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions [J]. Progress in Materials Science, 2014, 60(1): 130-207

[7] Yuzbekova D, Mogucheva A, Zhemchuzhnikova D, et al.. Effect of microstructure on continuous propagation of the Portevin–Le Chatelier deformation bands [J]. International Journal of Plasticity, 2017, 96: 210-226

[8] Tu S, Ren X, He J, et al.. Stress–strain curves of metallic materials and post-necking strain hardening characterization: A review [J]. Fatigue & Fracture of Engineering Materials & Structures, 2020, 43(1): 3-19

[9] Jobba M, Mishra R K, Niewczas M. Flow stress and work-hardening behaviour of Al–Mg binary alloys [J]. International Journal of Plasticity, 2015, 65: 43-60

[10] Li S, Wang Z, Zhao X, et al.. Study on the plasticity improvement mechanism and grain refinement of AZ80 Mg alloy under cryogenic multi-directional forging [J]. Journal of Materials Research and Technology, 2024, 33: 384-397

[11] Wang D, Li S, Xin Y, et al.. Simultaneously improving the deformation tolerance and mechanical properties of AZ80 magnesium alloy through the combination of pre-cryogenic and Multi-directional forging [J]. Materials Letters, 2024, 363: 136233

[12] Alyani A, Kazeminezhad M. Annealing behavior of aluminum after low-temperature severe plastic deformation [J]. Materials Science and Engineering: A, 2021, 824: 141810

[13] Zhao Z, Yi Y, Huang S, et al.. Cryogenic deformation-induced dislocation behavior and substructural evolution in 6061 aluminum alloy [J]. Journal of Alloys and Compounds, 2025, 1041: 183781

[14] Zhang C, Liang X, Sun Y, et al.. Achieving high strength-ductility synergy in TiBw/near α-Ti composites by ultrafine grains and nanosilicides via low-temperature severe plastic deformation [J]. Journal of Materials Science & Technology, 2024, 202: 253-266

[15] Mallick P, Tewary N K, Ghosh S K, et al.. Effect of cryogenic deformation on microstructure and mechanical properties of 304 austenitic stainless steel [J]. Materials Characterization, 2017, 133: 77-86

[16] Jin M, Lee B, Yoo J, et al.. Cryogenic deformation behaviour of aluminium alloy 6061-T6 [J]. Metals and Materials International, 2024, 30(6): 1492-1504

[17] Wang D, Huang S, Yi Y, et al.. Effects of cryogenic deformation on the microstructure and mechanical properties of high-strength aluminum alloys [J]. Materials Characterization, 2022, 187: 111831

[18] Feng B, Gu B, Li S. Cryogenic deformation behavior and failure mechanism of AA7075 alloy sheets tempered at different conditions [J]. Materials Science and Engineering: A, 2022, 848: 143396

[19] Su L H, Lu C, He L Z, et al.. Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures [J]. Acta Materialia, 2012, 60(10): 4218-4228

[20] Ren Y, Huang Z, Wang Y, et al.. Friction-induced rapid amorphization in a wear-resistant (CoCrNi) ₈₈Mo₁₂ dual-phase medium-entropy alloy at cryogenic temperature [J]. Composites Part B: Engineering, 2023, 263: 110833

[21] Zhao E, Gu J, Chen C, et al.. Cryogenic austenitic stainless steels: Mechanical performance and strengthening mechanisms-a mini review [J]. Materials Today Communications, 2026, 51: 114754

[22] Dong X, Gao B, Xiao L, et al.. Heterostructured metallic structural materials: Research methods, properties, and future perspectives [J]. Advanced Functional Materials, 2024, 34(51): 2410521

[23] Fan X, Kang X, Zhang Z, et al.. Influence of cryogenic deformation and post-deform aging on microstructure and mechanical properties of Al-Cu alloy [J]. Journal of Alloys and Compounds, 2024, 1005: 175894

[24] Huang Y, Prangnell P B. The effect of cryogenic temperature and change in deformation mode on the limiting grain size in a severely deformed dilute aluminium alloy [J]. Acta Materialia, 2008, 56(7): 1619-1632

[25] Wang X, Fan X, Chen X, et al.. Cryogenic deformation behavior of 6061 aluminum alloy tube under biaxial tension condition [J]. Journal of Materials Processing Technology, 2022, 303: 117532

[26] Song C, Zhang S, Liu L, et al.. Research progress on the microstructure evolution mechanisms of Al-Mg alloys by severe plastic deformation [J]. Materials, 2024, 17(17): 4235

[27] Sameti A R. Atomistic study of compression and shear in aluminum nanofoams: Dislocation mechanisms and temperature effects [J]. Journal of Materials Science, 2026, 61(5): 3425-3444

[28] Li Y S, Tao N R, Lu K. Microstructural evolution and nanostructure formation in copper during dynamic plastic deformation at cryogenic temperatures [J]. Acta Materialia, 2008, 56(2): 230-241

[29] Kalidindi S R. Modeling the strain hardening response of low SFE FCC alloys [J]. International Journal of Plasticity, 1998, 14(12): 1265-1277

[30] Launey M E, Ritchie R O. On the fracture toughness of advanced materials [J]. Advanced Materials, 2009, 21(20): 2103-2110

[31] Guan R, Tie D. A review on grain refinement of aluminum alloys: Progresses, challenges and prospects [J]. Acta Metallurgica Sinica (English Letters), 2017, 30(5): 409-432

[32] He H, Yi Y, Huang S, et al.. Effects of deformation temperature on second-phase particles and mechanical properties of 2219 Al-Cu alloy [J]. Materials Science and Engineering: A, 2018, 712: 414-423

[33] Sarac A, Oztop M S, Dahlberg C F O, et al.. Spatial distribution of the net Burgers vector density in a deformed single crystal [J]. International Journal of Plasticity, 2016, 85: 110-129

[34] Bilby B A, Bullough R, Smith E. Continuous distributions of dislocations: A new application of the methods of non-Riemannian geometry [J]. Proceedings of the Royal Society of London Series A Mathematical and Physical Sciences, 1955, 231(1185): 263-273

[35] Yang J B, Nagai Y, Yang Z G, et al.. Quantization of the Frank–Bilby equation for misfit dislocation arrays in interfaces [J]. Acta Materialia, 2009, 57(16): 4874-4881

[36] Fei S, Aifantis K E. Using molecular dynamics to determine mechanical grain boundary energies and capture their dependence on residual Burgers vector, segregation and grain size [J]. Acta Materialia, 2020, 195: 358-370

[37] Vignal V, Ba D, Zhang H, et al.. Influence of the grain orientation spread on the pitting corrosion resistance of duplex stainless steels using electron backscatter diffraction and critical pitting temperature test at the microscale [J]. Corrosion Science, 2013, 68: 275-278

[38] Hadadzadeh A, Mokdad F, Wells M A, et al.. A new grain orientation spread approach to analyze the dynamic recrystallization behavior of a cast-homogenized Mg-Zn-Zr alloy using electron backscattered diffraction [J]. Materials Science and Engineering: A, 2018, 709: 285-289

[39] Allain-Bonasso N, Wagner F, Berbenni S, et al.. A study of the heterogeneity of plastic deformation in IF steel by EBSD [J]. Materials Science and Engineering: A, 2012, 548: 56-63

[40] Ruggles T J, Fullwood D T. Estimations of bulk geometrically necessary dislocation density using high resolution EBSD [J]. Ultramicroscopy, 2013, 133: 8-15

[41] Yi G, Collins D M, Tarleton E, et al.. Dislocation density distribution at slip band-grain boundary intersections [J]. Acta Materialia, 2020, 182: 172-183

[42] Naghdy S, Verleysen P, Petrov R, et al.. Resolving the geometrically necessary dislocation content in severely deformed aluminum by transmission Kikuchi diffraction [J]. Materials Characterization, 2018, 140: 225-232

[43] Ruggles T J, Fullwood D T, Kysar J W. Resolving geometrically necessary dislocation density onto individual dislocation types using EBSD-based continuum dislocation microscopy [J]. International Journal of Plasticity, 2016, 76: 231-243

[44] Zhang K, Liu X, Fan P, et al.. Characterization of geometrically necessary dislocation evolution during creep of P91 steel using electron backscatter diffraction [J]. Materials Characterization, 2023, 195: 112501

[45] Toth L S, Gu C F, Beausir B, et al.. Geometrically necessary dislocations favor the Taylor uniform deformation mode in ultra-fine-grained polycrystals [J]. Acta Materialia, 2016, 117: 35-42

[46] Du C, Maresca F, Geers M G D, et al.. Ferrite slip system activation investigated by uniaxial micro-tensile tests and simulations [J]. Acta Materialia, 2018, 146: 314-327

[47] Li X, Bu W, Lu K, et al.. Rugged dislocation slip energy landscape and coordinated activation of multi-slip systems enable superior strength-ductility synergy in TiVZrNbAl(Mo) lightweight multi-principal element alloys [J]. Materials Science and Engineering: A, 2025, 939: 148498

[48] Nan X, Wang H, Zhang L, et al.. Calculation of Schmid factors in magnesium: Analysis of deformation behaviors [J]. Scripta Materialia, 2012, 67(5): 443-446

[49] Qi A, Goddard W AIII, Xie K Y, et al.. Superstrength through nanotwinning [J]. Nano Letters, 2016, 16(12): 7573-7579

[50] Cheng Z, Zhou H, Lu Q, et al.. Extra strengthening and work hardening in gradient nanotwinned metals [J]. Science, 2018, 362(6414): eaau1925

[51] Huang S, Li W, Lu S, et al.. Temperature dependent stacking fault energy of FeCrCoNiMn high entropy alloy [J]. Scripta Materialia, 2015, 108: 44-47

[52] Sarma V S, Wang J, Jian W W, et al.. Role of stacking fault energy in strengthening due to cryo-deformation of FCC metals [J]. Materials Science and Engineering: A, 2010, 527(29–30): 7624-7630

[53] Tan Y, Chen Z, Su M, et al.. Lattice distortion and magnetic property of high entropy alloys at low temperatures [J]. Journal of Materials Science & Technology, 2022, 104: 236-243

[54] Wang H, He Q, Gao X, et al.. Multifunctional high entropy alloys enabled by severe lattice distortion [J]. Advanced Materials, 2024, 36(17): 2305453

[55] Yan Z, Lin Y. Lomer-Cottrell locks with multiple stair-rod dislocations in a nanostructured Al alloy processed by severe plastic deformation [J]. Materials Science and Engineering: A, 2019, 747: 177-184

[56] Wang X, Ding Y, Yu H, et al.. High strength and ductility in a novel Ni-based superalloy with γ′ and nanotwins/stacking faults architectures [J]. Materials Science and Engineering: A, 2022, 847: 143293

[57] Wang Z, Lu W, An F, et al.. High stress twinning in a compositionally complex steel of very high stacking fault energy [J]. Nature Communications, 2022, 13: 3598

[58] He B B, Hu B, Yen H W, et al.. High dislocation density–induced large ductility in deformed and partitioned steels [J]. Science, 2017, 357(6355): 1029-1032

[59] Zhang Z, Yang Z, Qian W, et al.. Achieving enhanced toughness of a nanocomposite coating by lattice distortion at the variable metallic oxide interface [J]. Materials & Design, 2022, 224: 111316

[60] du Plessis A, Yadroitsava I, Yadroitsev I. Effects of defects on mechanical properties in metal additive manufacturing: A review focusing on X-ray tomography insights [J]. Materials & Design, 2020, 187: 108385

RIGHTS & PERMISSIONS

Central South University

Just Accepted

This article has successfully passed peer review and final editorial review, and will soon enter typesetting, proofreading and other publishing processes. The currently displayed version is the accepted final manuscript. The officially published version will be updated with format, DOI and citation information upon launch. We recommend that you pay attention to subsequent journal notifications and preferentially cite the officially published version. Thank you for your support and cooperation.