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Research Papers

Sheet Orientation Effects on the Hot Formability Limits of Lightweight Alloys

[+] Author and Article Information
Fadi Abu-Farha

 Mechanical Engineering, Penn State Erie, 5101 Jordan Road, 246 REDC Building, Erie, PA 16563fka10@psu.edu

Louis G. Hector

 General Motors R&D Center, General Motors, 30500 Mound Road, Warren, MI 48090louis.hector@gm.com

J. Manuf. Sci. Eng 133(6), 061005 (Nov 28, 2011) (8 pages) doi:10.1115/1.4004850 History: Received March 20, 2011; Revised August 04, 2011; Published November 28, 2011; Online November 28, 2011

The formability curves of AZ31B magnesium and 5083 aluminum alloy sheets were constructed using the pneumatic stretching test at two different sets of forming conditions. The test best resembles the conditions encountered in actual hydro/pneumatic forming operations, such as the superplastic forming (SPF) and quick plastic forming (QPF) techniques. Sheet samples were deformed at (400 °C and 1 × 10−3 s−1 ) and (450 °C and 5 × 10−3 s−1 ), by free pneumatic bulging into a set of progressive elliptical die inserts. The material in each of the formed domes was forced to undergo biaxial stretching at a specific strain ratio, which is simply controlled by the geometry (aspect ratio) of the selected die insert. Material deformation was quantified using circle grid analysis (CGA), and the recorded planar strains were used to construct the forming limit curves of the two alloys. The aforementioned was carried out with the sheet oriented either along or across the direction of major strains in order to establish the relationship between the material’s rolling direction and the corresponding limiting strains. Great disparities in limiting strains were found in the two orientations for both alloys; hence, a “composite FLD” is introduced as an improved means for characterizing material formability limits.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 2

Computer controlled pressure regulating instrumentation

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Figure 3

Four elliptical die inserts with different aspect ratios (k: minor/major axis)

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Figure 4

Micrographs of the (a) AA5083 and (b) Mg AZ31B after pre-annealing at 450 °C for 5 min

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Figure 5

An example of a square blank with an electrochemically etched circular grid (φ = 2.54 mm) oriented along the sheet’s rolling direction (shown here is AA5083 sheet sample)

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Figure 6

Pressure-time profiles for forming AZ31B magnesium alloy sheets through the four elliptical die inserts at 400 °C and 1 × 10−3 s−1

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Figure 7

A plot of the temperature curves for both the furnace and an AA5083 blank during the heating phase (immediately after inserting the blank into the furnace)

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Figure 8

An illustration of the relationship between the major/minor strains developed at the apex of a formed ellipsoidal dome and the corresponding die insert geometry

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Figure 9

A set of Mg AZ31B ellipsoidal domes pneumatically formed at 400 °C and 1 × 10−3 s−1 in the (a) 0 deg orientation and (b) 90 deg orientation

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Figure 1

(a) An overall view of the elevated temperature pneumatic forming setup (b) A detailed isometric section-view of the forming die assembly

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Figure 12

Summary of the results obtained for the AA5083 sheet at 450 °C and 5 × 10−3 s−1 . (a) FLCs in the 0 deg orientation, (b) FLCs in the 90 deg orientation, and (c) a “composite FLD” showing the FLCs for both orientations.

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Figure 10

Summary of the results obtained for the Mg AZ31B sheet at 400 °C and 1 × 10−3 s−1 . (a) FLCs in the 0 deg orientation, (b) FLCs in the 90 deg orientation, and (c) a “composite FLD” showing the FLCs for both orientations.

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Figure 11

Summary of the results obtained for the Mg AZ31B sheet at 450 °C and 5 × 10−3 s−1 . (a) FLCs in the 0 deg orientation, (b) FLCs in the 90 deg orientation, and (c) a “composite FLD” showing the FLCs for both orientations.

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