Research Papers

Plastic Forming of AZ91 Alloy Using the KOBO Method

[+] Author and Article Information
Włodzimierz Bochniak

AGH—University of Science and Technology,
Faculty of Non–Ferrous Metals,
A. Mickiewicza Avenue 30,
Cracow 30–059, Poland
e-mail: bow@agh.edu.pl

Paweł Ostachowski

AGH—University of Science and Technology,
Faculty of Non–Ferrous Metals,
A. Mickiewicza Avenue 30,
Cracow 30–059, Poland
e-mail: pawel.ostachowski@agh.edu.pl

Sylwester Jagieła

AGH—University of Science and Technology,
Faculty of Non–Ferrous Metals,
A. Mickiewicza Avenue 30,
Cracow 30–059, Poland
e-mail: sylwesterjagiela@gmail.com

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received August 13, 2015; final manuscript received April 12, 2016; published online June 13, 2016. Assoc. Editor: Ashraf Bastawros.

J. Eng. Mater. Technol 138(4), 041002 (Jun 13, 2016) (6 pages) Paper No: MATS-15-1191; doi: 10.1115/1.4033465 History: Received August 13, 2015; Revised April 12, 2016

The desirability of using the KOBO extrusion process for AZ91 magnesium alloy preceding its further plastic processing has been experimentally verified. Importantly, during the conducted experiments, heat treatment (e.g., homogenization) was applied either before or after direct KOBO extrusion, which if used might have affected the properties of the alloy. The products of the cold KOBO process take the form of tapes with different cross sections. They were pressed (deep drawing), or, alternatively, subjected to conventional indirect extrusion in order to acquire the desired spatial geometry of the product. Due to the need for relatively wide strips, a variant of the KOBO extrusion with lateral outflow was used, since the press structure, providing reversibly oscillating die, strongly limited the cross sections of directly extruded products. The research procedure, involving plastic deformation with cyclic changes of the deformation path, allowed to obtain results indicating new potential properties of metallic materials crucial for their applicability.

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Fig. 1

Scheme of lateral (angular) extrusion of metal by the KOBO method ((a): 1—punch, 2—container, 3—reversibly rotating mandrel with ragging on front surface, 4—extruded ingot, 5—product/tape, 6—lock, 7—die located on container's side surface) and a part of the KOBO press with the produced tape (b)

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Fig. 2

The diagram shows the process of cutting the samples after spatial forming deep drawing (a) or conventional indirect extrusion and (b) with particular spots to be investigated marked

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Fig. 3

Structure of the billet (ingot) of AZ91 alloy (a), and of the tape with a cross section of 30 × 1 mm extruded with the KOBO method; (b) optical evidence; (c) TEM; and (d) STEM

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Fig. 4

Structures of the cut part of the product, according to schemes A–A (a), B–B (b), and C–C (c) as in Fig. 2(a)

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Fig. 5

Structures of Part A (as in Fig. 2(b)) of cell phone housing; location: button ((a) and (b))

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Fig. 6

Structures of Parts A (a) and B (b) of cell phone housing; location: corner

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Fig. 7

Typical structure of Part C (as in Fig. 2(b)); location: bottom



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