Determination of Lower-Bound Ductility for AZ31 Magnesium Alloy by Use of the Bulge Specimens

[+] Author and Article Information
Rimma Lapovok

Department of Materials Engineering, Monash University, VIC 3800 Australia

Peter D. Hodgson

Centre for Material and Fibre Innovation, Deakin University, Geelong, VIC 3217 Australia

J. Eng. Mater. Technol 129(3), 407-413 (Dec 08, 2006) (7 pages) doi:10.1115/1.2744400 History: Received April 13, 2006; Revised December 08, 2006

Despite the high demand for industrial applications of magnesium, the forming technology for wrought magnesium alloys is not fully developed due to the limited ductility and high sensitivity to the processing parameters. The processing window for magnesium alloys could be significantly widened if the lower-bound ductility (LBD) for a range of stresses, temperature, and strain rates was known. LBD is the critical strain at the moment of fracture as a function of stress state and temperature. Measurements of LBD are normally performed by testing in a hyperbaric chamber, which is highly specialized, complex, and rare equipment. In this paper an alternative approach to determine LBD is demonstrated using wrought magnesium alloy AZ31 as an example. A series of compression tests of bulge specimens combined with finite element simulation of the tests were performed. The LBD diagram was then deduced by backward calculation.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Set for compression test of bulge specimens: (a) compression dies; (b) compression specimens Barrel-0, Barrel-1, and Barrel-2 (from the right to left); and (c) equipment setting with microscope during the compression

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Figure 2

Cracks initiation and development with extend of compression for bulge samples (Barrel-0 and Barrel-1)

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Figure 3

Engineering strain in compression test at the time of crack initiation on free surface

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Figure 4

The flow stress curves at 250°C and 400°C at strain rates - 0.03s−1, 0.3s−1, and 3.0s−1

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Figure 5

FE simulation of geometry of samples with “tracked” points shown where the history of all variables is recorded (from Q-Form software)

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Figure 10

Example of forged and machined magnesium wheel from Ref. 17

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Figure 11

FE simulation of three blows forging of magnesium wheel using QForm (13)

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Figure 6

Main stress (a) and equivalent strain (b) histories for three different sample geometries (upsetting performed at 400°C and strain rate 3s−1)

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Figure 7

Coefficients of LBD function (Eq. 4) and intensity of damage accumulation (Eq. 1) (a) coefficient “a”; (b) coefficient “b”; and (c) coefficient “ao”

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Figure 8

Graphical representation of LBD diagram: (a) for different temperatures at the strain rate equal to 0.3s−1; and (b) for different strain rates at the temperature of 200°C

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Figure 9

Damage accumulated at the free surface of different bulge samples up to the level of crack initiation at the strain rate of 0.03s−1: (a) at the temperature of 400°C; and (b) at the temperature of 200°C



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