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Superplastic behaviour of AZ91 magnesium alloy processed by high– pressure torsion

Superplastic behaviour of AZ91 magnesium alloy processed by high– pressure torsion
Superplastic behaviour of AZ91 magnesium alloy processed by high– pressure torsion
An investigation has been conducted on the tensile properties of a fine–grained AZ91 magnesium alloy processed at room temperature by high pressure torsion (HPT). Tensile testing was carried out at 423 K, 473 K and 573 K using strain rates from 1×10–1 s–1 to 1×10–4 s–1 for samples processed in HPT for N = 1, 3, 5 and 10 turns. After testing was completed, the microstructures were investigated by scanning electron microscopy and energy dispersive spectroscopy. The alloy processed at room temperature in HPT exhibited excellent superplastic behaviour with elongations higher than elongations reported previously for fine–grained AZ91 alloy produced by other severe plastic deformation processes, e.g. HPT, ECAP and EX–ECAP. A maximum elongation of 1308 % was achieved at a testing temperature of 573 K using a strain rate of 1×10–4 s–1, which is the highest value of elongation reported to date in this alloy. Excellent high–strain rate superplasticity (HSRSP) was achieved with maximum elongations of 590 % and 860 % at temperatures of 473 K and 573 K, respectively, using a strain rate of 1×10–2 s–1. The alloy exhibited low–temperature superplasticity (LTSP) with maximum elongations of 660 % and 760 % at a temperature of 423 K and using strain rates of 1×10–3 s–1 and 1×10–4 s–1, respectively. Grain–boundary sliding (GBS) was identified as the deformation mechanism during HSRSP, and the glide–dislocation creep accommodated by GBS dominated during LTSP. Grain–boundary sliding accommodated with diffusion creep was the deformation mechanism at high test temperature and slow strain rates. An enhanced thermal stability of the microstructure consisting of fine equiaxed grains during deformation at elevated temperature was attributed to the extremely fine grains produced in HPT at room temperature, a high volume fraction of nano ?–particles, and the formation of ?–phase filaments.
az91, magnesium alloy, high pressure torsion, microstructure, superplasticity
0921-5093
1-11
Al–Zubaydi, Ahmed S.J.
d59e9818-6c38-4a94-9c5a-e40f9b875862
Zhilyaev, Alexander P.
d053e518-1976-4633-8953-e8f34b9b7c44
Wang, Shuncai
8a390e2d-6552-4c7c-a88f-25bf9d6986a6
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Al–Zubaydi, Ahmed S.J.
d59e9818-6c38-4a94-9c5a-e40f9b875862
Zhilyaev, Alexander P.
d053e518-1976-4633-8953-e8f34b9b7c44
Wang, Shuncai
8a390e2d-6552-4c7c-a88f-25bf9d6986a6
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17

Al–Zubaydi, Ahmed S.J., Zhilyaev, Alexander P., Wang, Shuncai and Reed, P.A.S. (2015) Superplastic behaviour of AZ91 magnesium alloy processed by high– pressure torsion. Materials Science and Engineering: A, 637, 1-11. (doi:10.1016/j.msea.2015.04.004).

Record type: Article

Abstract

An investigation has been conducted on the tensile properties of a fine–grained AZ91 magnesium alloy processed at room temperature by high pressure torsion (HPT). Tensile testing was carried out at 423 K, 473 K and 573 K using strain rates from 1×10–1 s–1 to 1×10–4 s–1 for samples processed in HPT for N = 1, 3, 5 and 10 turns. After testing was completed, the microstructures were investigated by scanning electron microscopy and energy dispersive spectroscopy. The alloy processed at room temperature in HPT exhibited excellent superplastic behaviour with elongations higher than elongations reported previously for fine–grained AZ91 alloy produced by other severe plastic deformation processes, e.g. HPT, ECAP and EX–ECAP. A maximum elongation of 1308 % was achieved at a testing temperature of 573 K using a strain rate of 1×10–4 s–1, which is the highest value of elongation reported to date in this alloy. Excellent high–strain rate superplasticity (HSRSP) was achieved with maximum elongations of 590 % and 860 % at temperatures of 473 K and 573 K, respectively, using a strain rate of 1×10–2 s–1. The alloy exhibited low–temperature superplasticity (LTSP) with maximum elongations of 660 % and 760 % at a temperature of 423 K and using strain rates of 1×10–3 s–1 and 1×10–4 s–1, respectively. Grain–boundary sliding (GBS) was identified as the deformation mechanism during HSRSP, and the glide–dislocation creep accommodated by GBS dominated during LTSP. Grain–boundary sliding accommodated with diffusion creep was the deformation mechanism at high test temperature and slow strain rates. An enhanced thermal stability of the microstructure consisting of fine equiaxed grains during deformation at elevated temperature was attributed to the extremely fine grains produced in HPT at room temperature, a high volume fraction of nano ?–particles, and the formation of ?–phase filaments.

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Submitted date: 10 February 2015
Accepted/In Press date: 6 April 2015
e-pub ahead of print date: 13 April 2015
Published date: 18 June 2015
Keywords: az91, magnesium alloy, high pressure torsion, microstructure, superplasticity
Organisations: Engineering Mats & Surface Engineerg Gp

Identifiers

Local EPrints ID: 376371
URI: http://eprints.soton.ac.uk/id/eprint/376371
ISSN: 0921-5093
PURE UUID: 88bc14e1-17b2-4fb0-bb66-287570d26f4e
ORCID for P.A.S. Reed: ORCID iD orcid.org/0000-0002-2258-0347

Catalogue record

Date deposited: 27 Apr 2015 11:00
Last modified: 26 Nov 2019 02:03

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