In this study, nano-scale microstructural evolution in 6061-T6 alloy after laser shock processing (LSP) was studied. 6061-T6 alloy plate was subjected to multiple LSP. The LSP treated area was characterized by X-ray diffraction and the microstructure of the samples was analyzed by transmission electron microscopy. Focused Ion Beam (FIB) tools were used to prepare TEM samples in precise areas. It was found that even though aluminum had high stacking fault energy, LSP yielded to formation of ultrafine grains and deformation faults such as dislocation cells, stacking faults. The stacking fault probability (PSF) was obtained in LSP-treated alloy using X-Ray diffraction. Deformation induced stacking faults lead to the peak position shifts, broadening and asymmetry of diffraction. XRD analysis and TEM observations revealed significant densities of stacking faults in LSP-treated 6061-T6 alloy. And mechanical properties of LSP-treated alloy were also determined to understand the hardening behavior with high concentration of structural defects.

1. Ren X, Zhang Y, Zhang T, et al. Comparison of the simulation and experimental fatigue crack behaviors in the nanoseconds laser shocked aluminum alloy. Materials & Design 2011; 32(3): 1138–1143.

2. Yang C, Hodgson PD, Liu Q, et al. Geometrical effects on residual stresses in 7050-T7451 aluminum alloy rods subject to laser shock peening. Journal of Materials Processing Tech 2008; 201(1-3): 303–309.

3. Ye L, Ding K. Laser shock peening: Performance and process simulations. Cambridge: Woodhead Publishing; 2006. p. 172.

4. Lu J, Luo K, Zhang Y, et al. Grain refinement mechanism of multiple laser shock processing impacts on ANSI 304 stainless steel. Acta Materialia 2010; 58(16): 5354–5362.

5. Irizalp SG, Saklakoglu N, Yilbas BS. Characterization of microplastic deformation produced in 6061-T6 by using laser shock processing. International Journal of Advanced Manufacturing Technology 2014; 71(1-4): 109–115.

6. He T, Xiong Y, Guo Z, et al. Microstructure and hardness of laser shocked ultra-fine-grained aluminum. Journal of Materials Science & Technology 2011; 27(9): 793–796.

7. Chu JP, Rigsbee JM, Bana G, et al. Laser-shock processing effects on surface microstructure and mechanical properties of low carbon steel. Materials Science & Engineering A 1999; 260(1-2): 260–268.

8. Li Y, Zhou L, He W, et al. The strengthening mechanism of a nickel-based alloy after laser shock processing at high temperatures. Science & Technology of Advanced Materials 2013; 14(5): 1–9.

9. Ren X, Ruan L, Yuan S, et al. Dislocation polymorphism transformation of 6061-T651 aluminum alloy processed by laser shock processing: Effect of tempering at the elevated temperatures. Materials Science & Engineering 2013; 578: 96–102.

10. Sathyajith S, Kalainathan S, Swaroop S. Laser peening without coating on aluminum alloy Al- 6061-T6 using low energy Nd: YAG laser. Optics & Laser Technology 2013; 45: 389–394.

11. Gencalp Irizalp S, Saklakoglu N, Akman E, et al. Pulsed Nd: YAG laser shock processing effects on mechanical properties of 6061-T6 alloy. Optics & Laser Technology 2014; 56: 273–277.

12. Rubio-Gonzalez C, Gomez-Rosas G, Ocana JL, et al. Effect of an absorbent overlay on the residual stress field induced by laser shock processing on aluminum samples. Applied Surface Science 2006; 252(18): 6201–6205.

13. Rubio-Gonzalez C, Ocana JL, Gomez-Rosas G, et al. Effect of laser shock processing on fatigue crack growth and fracture toughness of 6061-T6 aluminum alloy. Materials Science and Engineering: A 2004; 386(1-2): 291–295.

14. Sanchez-Santana U, Rubio-Gonzalez C, Gomez Rosas G, et al. Wear and friction of 6061-T6 aluminum alloy treated by laser shock processing. Wear 2006; 260(7-8): 847–854.

15. Kalantar DH, Belak J, Bringa E, et al. High-pressure, high-strain-rate lattice response of shocked materials. Physics of Plasmas 2003; 10(5): 1569–1576.

16. Cao XJ, Pyoun YS, Murakami R. Fatigue properties of a S45C steel subjected to ultrasonic nanocrystal surface modification. Applied Surface Science 2010; 256(21): 6297–6303.

17. Zehetbauer M, Valiev RZ. Nanomaterials by severe plastic deformation. Weinheim, Berlin: Wiley-VCH; 2004. p. 1–850.

18. Chen K, Zheng C, Yuan Z, et al. Deformation microstructures of austenitic stainless steel 2Cr13Mn9Ni4 under ultrafast strain rate by laser shock processing. Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing 2013; 587: 244–249.

19. Ye Y, Feng Y, Lian Z, et al. Plastic deformation mechanism of polycrystalline copper foil shocked with femtosecond laser. Applied Surface Science 2014; 309: 240–249.

20. Yilbas BS, Arif AFM, Shuja CZ, et al. Investigation into laser shock processing. Journal of Materials Engineering and Performance 2004; 13: 47–54.

21. Saklakoglu N, Gencalp Irizalp S, Akman E, et al. Near surface modification of aluminum alloy induced by laser shock processing. Optics & Laser Technology 2014; 64: 235–241.

22. Jublot M, Texier M. Sample preparation by focused ion beam micromachining for transmission electron microscopy imaging in front-view. Micron 2014; 56: 63–67.

23. Grassian VH (editor). Nanoscience and Nanotechnology. Bridgewater, New Jersey: John Wiley & Sons, Inc., 2008. p. 461.

24. Committe AIH. Metals handbook volume 10 — Materials characterization. Fifth Printing. Novelty, Ohio: ASM Int; 1998. p. 1310.

25. Fultz B, Howe JM. Diffraction Lineshapes. In: Transmission Electron Microscopy and Diffractometry of Materials. 4th ed. Berlin Heidelberg: Springer; 2013. p. 429–462.

26. Zhou W, Jiang B, Liu Y, et al. Stacking fault probability and stcaking fault energy in CoNi alloys. Transactions of Nonferrous Metals Society of China 2001; 11(4): 555–558.

27. Noskova NI, Pavlov VA. Stacking faults in nickel solid solutions. Physics Metal and Metallography 1962; 14: 86.

28. Li B, Yan P, Sui M, et al. Transmission electron microscopy study of stacking faults and their interaction with pyramidal dislocations in deformed Mg. Acta Materialia 2010; 58(1): 173–179.

29. ] Hull D, Bacon DJ. Introduction to dislocations. 3rd ed. Oxford, United Kingdom: Pergamon Press. 1984. p. 80.

30. Ren X, Zhou W, Ren Y, et al. Dislocation evolution and properties enhancement of GH2036 by laser shock processing: Dislocation dynamics simulation and experiment. Materials Science & Engineering: A 2016; 654: 184–192.

31. Xu Z, Liu M, Jia Z, et al. Effect of cryorolling on microstructure and mechanical properties of a peak-aged AA6082 extrusion. Journal of Alloys and Compounds 2017; 695: 827–840.

32. Shin DH, Park JJ, Kim YS, et al. Constrained groove pressing and its application to grain refinement of aluminum. Materials Science & Engineering: A 2002; 328(1-2): 98–103.

33. Lu J, Luo K, Zhang Y, et al. Grain refinement of LY2 aluminum alloy induced by ultra-high plastic strain during multiple laser shock processing impacts. Acta Materialia 2010; 58(11): 3984–3994.

34. Wang J, Zhang Y, Chen J, et al. Effect of laser shock peening on the high-temperature fatigue performance of 7075 aluminum alloy. Materials Science & Engineering: A 2017; 704: 459–468.

35. Liu M, Roven HJ, Yu Y, et al. Deformation structures in 6082 aluminium alloy after severe plastic deformation by equal-channel angular pressing. Materials Science & Engineering: A 2008; 483-484: 59–63.

36. Gencalp Irizalp S, Saklakoglu N. High strength and high ductility behavior of 6061-T6 alloy after laser shock processing. Optics & Lasers in Engineering 2016; 77: 183–190.

37. Sun H, Shi Y, Zhang M, et al. Plastic strain-induced grain refinement in the nanometer scale in a Mg alloy. Acta Materialia 2007; 55(3): 975–982.

38. Lu K, Lu J. Nanostructured surface layer on metallic materials induced by surface mechanical attrition treatment. Materials Science & Engineering: A 2004; 375-377: 38–45.

39. Hurley PJ, Humphreys FJ. Modelling the recrystallization of single-phase aluminium. Acta Mater 2003; 51(13): 3779–3793.

40. Zhang X, Hu T, Rufner JF, et al. Metal/ceramic interface structures and segregation behavior in aluminum-based composites. Microscopy and Microanalysis 2015; 21(S3): 1053–1054.

41. Zhang Y, Jiang S. The mechanism of inhomogeneous grain refinement in a NiTiFe shape memory alloy subjected to single-pass equal-channel angular extrusion. Metals 2017; 7(10): 400.

42. Youssef KM, Scattergood RO, Murty KL, et al. Ultrahigh strength and high ductility of bulk nanocrystalline copper. Applied Physics Letters 2005; 87(9):1–3.

43. Chen H, Yao YL, Kysar JW. Spatially Resolved Characterization of Residual Stress Induced by Micro Scale Laser Shock Peening. Journal of Manufacturing Science and Engineering 2004; 126(2): 226–236.

44. Jeong JS, Woo W, Oh KH, et al. In situ neutron diffraction study of the microstructure and tensile deformation behavior in Al-added high manganese austenitic steels. Acta Materialia 2012; 60(5): 2290–2299.

45. Tomota Y, Tokuda H, Adachi Y, et al. Tensile behavior of TRIP-aided multi-phase steels studied by in situ neutron diffraction. Acta Materialia 2004; 52(20): 5737–5745.

46. Jeong JS, Koo YM, Jeong IK, et al. Micro-structural study of high-Mn TWIP steels using diffraction profile analysis. Materials Science & Engineering: A 2011; 530: 128–134.

47. Rafaja D, Siıma, M, Klemm V, et al. X-ray diffraction on nanocrystalline Ti1−xAlxN thin films. Journal of Alloys and Compounds 2004; 378(1-2): 107–111.

48. Nie X, He W, Zhou L, et al. Experiment investigation of laser shock peening on TC6 titanium alloy to improve high cycle fatigue performance. Materials Science & Engineering: A 2014; 594: 161–167.

49. Huang C, Hu W, Yang G, et al. The effect of stacking fault energy on equilibrium grain size and tensile properties of nanostructured copper and copper–aluminum alloys processed by equal channel angular pressing. Materials Science & Engineering: A 2012; 556: 638–647.

50. Das J. Evolution of nanostructure in α-brass upon cryorolling. Materials Science and Engineering: A 2011; 530: 675–679.

51. Roy B, Kumar NK, Nambissan PMG, et al. Evolution and interaction of twins, dislocations and stacking faults in rolled α-brass during nanostructuring at sub-zero temperature. AIP Advances 2014; 4(60): 1–8.

52. Kumar NK, Roy B, Das J. Effect of twin spacing, dislocation density and crystallite size on the strength of nanostructured α-brass. Journal of Alloys and Compounds 2015; 618: 139–145.

53. Zhu Y, Liao X, Wu X. Deformation twinning in nanocrystalline materials. Progress in Materials Science 2011; 57(1): 1–62.

54. Wert JJ, Singerman SA, Caldwell SG, et al. An X- ray diffraction study of the effect of stacking fault energy on the wear behavior of Cu-Al alloys. Wear 1983; 92(2): 213–229.

55. Talonen J, Hanninen H. Formation of shear bands and strain-induced martensite during plastic deformation of metastable austenitic stainless steels. Acta Materialia 2007; 55(18): 6108–6118.

56. Gong Y, Wen C, Wu X, et al. The influence of strain rate, deformation temperature and stacking fault energy on the mechanical properties of Cu alloys. Materials Science & Engineering: A 2013; 583: 199–204.

57. Yamanaka K, Mori M, Sato S, et al. Stacking-fault strengthening of biomedical Co–Cr–Mo alloy via multipass thermomechanical processing. Scientific Reports 2017; 7(1):1–13.

58. Lu K, Lu L, Suresh S. Strengthening materials by engineering coherent internal boundaries at the nanoscale. Science 2009; 324(5925): 349–352.

59. Jiang B, Qi X, Yang S, et al. Effect of stackingfault probability on martensitic transformation and shape memory effect in Fe-Mn-Si based alloys. Acta Materialia 1998; 46(2): 501–510.

60. Mahato B, Shee SK, Sahu T, et al. An effective stacking fault energy viewpoint on the formation of extended defects and their contribution to strain hardening in a Fe–Mn–Si–Al twinning-induced plasticity steel. Acta Materialia 2015; 86: 69–79.

61. Valiev RZ, Islamgaliev RK, Alexandrov IV. Bulk nanostructured materials from severe plastic deformation. Progress in Materials Science 2000; 45(2): 103–189.

62. Liao X, Zhao Y, Zhu Y, et al. Grain-size effect on the deformation mechanisms of nanostructured copper processed by high-pressure torsion. Journal of Applied Physics 2004; 96(1): 636–640.

63. Azushima A, Kopp R, Korhonen A, et al. Severe plastic deformation (SPD) processes for metals. CIRP Annals 2008; 57(2):716–735.

64. Lugo N, Llorca N, Cabrera JM, et al. Micro structures and mechanical properties of pure copper deformed severely by equal-channel angular pressing and high pressure torsion. Materials Science & Engineering A 2008; 477(1-2): 366–371.

65. Liao X, Zhou F, Lavernia EJ, et al. Deformation mechanism in nanocrystalline Al: Partial dislocation slip. Applied Physics Letters 2003; 83(4): 632–634.

66. Lee ML, Simmonds PJ. Tensile strained III-V self-assembled nanostructures on a (110) surface. Nano-epitaxy: Homo- and Heterogeneous Synthesis, Characterization, and Device Integration of Nano- materials 2010; 7768: 5.