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Research Papers: FORMING

Effect of Deformation and Temperature Paths in Severe Plastic Deformation Using Groove Pressing on Microstructure, Texture, and Mechanical Properties of AZ31-O

[+] Author and Article Information
Kai Soon Fong

Singapore Institute of Manufacturing Technology, 71 Nanyang Drive,
Singapore 638075
e-mail: ksfong@SIMTech.a-star.edu.sg

Danno Atsushi

Singapore Institute of Manufacturing Technology, 71 Nanyang Drive,
Singapore 638075
e-mail: Danno@SIMTech.a-star.edu.sg

Tan Ming Jen

School of Mechanical and
Aerospace Engineering,
Nanyang Technological University,
50 Nanyang Avenue,
Singapore 639798
e-mail: MMJTAN@ntu.edu.sg

Beng Wah Chua

Singapore Institute of Manufacturing Technology,
71 Nanyang Drive,
Singapore 638075
e-mail: bwchua@simtech.a-star.edu.sg

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received November 30, 2014; final manuscript received June 23, 2015; published online September 4, 2015. Assoc. Editor: Yannis Korkolis.

J. Manuf. Sci. Eng 137(5), 051004 (Sep 04, 2015) (16 pages) Paper No: MANU-14-1643; doi: 10.1115/1.4031021 History: Received November 30, 2014

Processing of wrought magnesium alloy sheet by severe plastic deformation (SPD) for improving its formability is attractive so as to encourage the wider applications of the alloy. In this study, SPD by means of groove pressing (GP) was carried out on AZ31B-O magnesium sheet at different deformation paths and temperatures in order to investigate its effects on microstructure, textures, and mechanical properties. GP using an orthogonal pressing at every cycle and at a progressively decreasing temperature was found to be effectively for manufacturing fine-grained microstructures with an average grain diameter of 1.9 μm. The final microstructures were homogenous in both the transverse direction (TD) and rolling direction (RD) and consisting of fine grains of 0.6–1 μm with a small fraction of coarser grains of 3–5 μm. The increase in yield stress (YS), ultimate tensile strength (UTS), and tensile elongation after annealing was 12%, −2.9%, and 25.6%, respectively, in the RD. A good balance between fine-grained microstructure and ductility was obtained by the pressing at a constant processing temperature of 473 K. In this pressing path, average grain diameter was 3.8 μm and the increased in YS, UTS, and tensile elongation before annealing was 21.9%, 9.1%, and 19.8%, respectively, in the RD. It was shown that the texture modification combined with fine-grained microstructure contributed to the overall improvement in ductility.

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References

Figures

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Fig. 1

Schematic diagram of a single cycle of GP

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Fig. 2

Shear strains imposed along the 45 deg incline regions of the specimen

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Fig. 3

(a) Experimental setup, (b) groove dies, and (c) straightening dies

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Fig. 4

Schematic diagrams illustrating the first two deformation cycles in DA

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Fig. 5

Schematic diagrams illustrating a single deformation cycle in DB

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Fig. 6

FE simulation showing the effective strain distribution in the specimen deformed to deformation path DA

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Fig. 7

FE simulation showing the effective strain distribution in the specimen deformed to deformation path DB

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Fig. 8

Effective strain distributions in the midsection of the specimen after each deformation pass according to DA simulation

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Fig. 9

Effective strain distributions in the midsection of the specimen after each deformation pass according to DB simulation

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Fig. 10

Effective strain distribution in cross section of specimen deformed according to deformation path DA after (a) first pass, (b) second pass, (c) third pass, and (d) fourth pass

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Fig. 11

Maximum principal stress distributions in specimen deformed to DB during the fourth pass at the (a) start and (b) end of the pass, and expanded views at the (c) start, (d) intermediate, and (e) end of the pass

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Fig. 12

Microstructures of the initial AZ31B-O sheet (a) in the RD and (b) in the TD

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Fig. 13

Microstructure evolution of specimen I after GP by DA and TA in the (a) first cycle, (b) second cycle, (c) third cycle, and (d) fourth cycle

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Fig. 14

Microstructure of specimen I at the end of four cycles of GP by DA and TA along the initial (a) TD and (b) RD

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Fig. 15

Microstructure distributions along the thickness direction (a) 30 μm–130 μm from top, (b) middle, and (c) 30 μm ∼ 130 μm from bottom surface of the specimen

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Fig. 16

Microstructure distributions across RD of specimen I at end of four cycles of GP by DA and TA at distance of (a) 1 mm, (b) 2 mm, (c) 3 mm, and (d) 4 mm observed in midthickness

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Fig. 17

Comparison of microstructures of (a) specimen I, (b) specimen II, (c) specimen III, (d) specimen IV, (e) specimen V, and (f) specimen VI

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Fig. 18

Comparison of the average grains diameter of specimen I, specimen I (annealed), and specimens II–VI

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Fig. 19

Pole figures of AZ31B-O alloy (a) prismatic, (b) basal, and (c) pyramidal

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Fig. 20

Texture evolution showing the prismatic, basal, and pyramidal pole figures of specimen I processed by DA and TA at the end of (a) first cycle, (b) second cycle, (c) third cycle, and (d) fourth cycle

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Fig. 21

Final prismatic, basal, and pyramidal pole figures of (a) specimen I, (b) specimen I (annealed), (c) specimen II, (d) specimen III, (e) specimen V, and (f) specimen VI

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Fig. 22

Hardness variations across thickness of specimen I at end of each cycle

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Fig. 23

Plot of average hardness and grain size of specimen I against total cumulative strain (simulation values) at the end of first to fourth cycle

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Fig. 24

True stress and strain curves of specimen I from first to fourth cycle, and fourth cycle (annealed) as compared to initial alloy in the (a) RD and (b) TD

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Fig. 25

True stress and strain curves comparisons for specimens I–VI at the end of their respective cycles in the (a) RD and (b) TD

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Fig. 26

Comparisons of the yield strength and UTS along the (a) RD and (b) TD

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Fig. 27

Comparisons of the elongation at break along the (a) RD and (b) TD

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