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Research Papers

The Effect of Pulse Electric Current on the Mechanical Properties and Fracture Behaviors of Aluminum Alloy AA5754

[+] Author and Article Information
Kunmin Zhao

School of Automotive Engineering,
Dalian University of Technology,
Dalian 116024, China;
Institute of Industrial and Equipment Technology,
Hefei University of Technology,
Hefei 230601, China
e-mail: kmzhao@dlut.edu.cn

Rong Fan

School of Automotive Engineering,
Dalian University of Technology,
Dalian 116024, China
e-mail: fanrong@mail.dlut.edu.cn

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 27, 2015; final manuscript received May 2, 2016; published online July 8, 2016. Assoc. Editor: Marwan K. Khraisheh.

J. Eng. Mater. Technol 138(4), 041009 (Jul 08, 2016) (7 pages) Paper No: MATS-15-1272; doi: 10.1115/1.4033635 History: Received October 27, 2015; Revised May 02, 2016

The influences of pulse electric currents at energy density levels of 0.105 J/mm3 and 0.150 J/mm3 on AA5754's flow stress and elongation are investigated. Different combinations of current density and pulse duration are carried out for each energy density. The non-Joule heating effects in electrically assisted forming (EAF) are revealed since the temperatures generated by the electric currents of the same energy density are identical. It is observed that a pulse current helps reduce AA5754's flow stress and increase its elongation. At the same level of energy density, as the current density increases, the instant drop of stress increases as well as the elongation, although the maximum flow stress remains almost unchanged. A theoretical model is proposed that can predict the stress drop during electrically assisted forming. The fracture surfaces of AA5754 subject to pulse currents are observed and analyzed. The dimples of fracture continue to decrease until they completely disappear as the density of pulse current increases. The suppression of voids nucleation and growth by a pulse current leads to the increase of total elongation.

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Figures

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Fig. 1

Setup of electrically assisted tensile tests

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Fig. 2

Temperature distribution in the specimen under an electric current

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Fig. 3

Temperature evolution of AA5754 subject to different pulse currents

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Fig. 4

True stress–strain curve of AA5754 subject to pulse currents of 0.5 s duration at energy densities of 0.105 and 0.150 J/mm3

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Fig. 5

Instant stress drop at the initial pulse of different electric currents

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Fig. 6

Evolution of instant stress drop of AA5754 subject to pulse currents of 0.5 s duration at energy densities of 0.105 and 0.150 J/mm3

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Fig. 7

The influence of current density on maximum flow stress and total elongation

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Fig. 8

The stress–strain curves of AA5754 under oven heating

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Fig. 9

The stress–strain curves of AA5754 subject to continuous electric currents

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Fig. 10

Fractured AA5754 specimens subject to continuous electric currents

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Fig. 11

Fractured AA5754 specimens under different pulse currents

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Fig. 12

Micrograph of the fracture surfaces under different pulse currents

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