Mechanical Behavior of Alloy AA6111 Processed by Severe Plastic Deformation: Modeling and Experiment

[+] Author and Article Information
Yuri Estrin

ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering,  Monash University, Clayton, VIC. 3800, Australia; CSIRO Division of Manufacturing and Materials Technology, Clayton, VIC. 3168, Australia

KiHo Rhee1

Department of Materials Engineering, CAST CRC, Monash University, Vic. 3800, Australiakihorhee@posco.com

Rimma Lapovok, Peter F. Thomson

Department of Materials Engineering, CAST CRC, Monash University, Vic. 3800, Australia


Corresponding author. Currently working as a researcher at POSCO, Wire Rod Research Group, Technical Research Laboratories, POSCO, 1, Goedong-dong, Nam-gu, Pohang, Gyeongbuk, 790-785 South Korea.

J. Eng. Mater. Technol 129(3), 380-389 (Feb 15, 2007) (10 pages) doi:10.1115/1.2744396 History: Received January 30, 2006; Revised February 15, 2007

An established dislocation density related, one-internal variable model was used, with some modifications, as a basis for modeling the mechanical response of aluminum alloy AA6111. In addition to conventional rolling, equal channel angular pressing (ECAP) was used to produce a wide range of grain sizes, down to the submicrometer scale. The samples were heat treated before and after both processes to optimize tensile ductility. Implementation of the model to uniaxial tensile response of the conventionally rolled and the ECAP processed materials confirmed its good predictive capability. The model was further used to formulate simple relations between true uniform strain and the constitutive parameters that allow reliable prediction of the uniform elongation.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Schematic illustrations showing: (a) details of ECAP sample which consists of stacked AA6111 sheet specimens; and (b) details of the ECAP die geometry

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Figure 2

Schematic diagram of strain hardening coefficient Θ versus reduced stress σ*=σ−σY showing a linear dependence and the definition of ΘII and σs*. The dashed line represents the Considère condition for necking.

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Figure 3

Schematic diagram of Θσ* versus σ* corresponding to the hybrid model that includes the effect of geometric obstacles to dislocation glide (such as grain boundaries or second-phase particles). The upper parabola is obtained from the lower one by a parallel shift along the ordinate axis. After Ref. 10.

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Figure 4

Schematic illustration of Θ versus σ* diagram of a typical AA6111 sample showing deviations from linear behavior and defining ΘII as well as σs1* and σs2*

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Figure 5

Schematic illustration of a Θσ* versus σ* diagram of a typical AA6111 sample showing a deviation from a parabolic form (solid line) and defining parameters used in the “two parabola” approach

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Figure 6

The dependence of yield strength on the grain size for samples heat treated at different annealing temperatures (Hall–Petch diagram)

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Figure 7

The relation between uniform elongation and grain size of samples heat treated at different annealing temperatures (full symbols: ECAP; open symbols: rolling)

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Figure 8

The stress-strain curve of commercial sheet and in-house processed sheet (AQ process, one and four passes of ECAE) annealed at 410°C and 540°C

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Figure 9

The stress-strain curves of UFG samples subjected to various numbers of ECAP passes and heat treatments

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Figure 10

A comparison of experimental and calculated plots for the strain hardening versus stress dependence ((a) and (d)); the corresponding inverted parabolic form ((b) and (e)); and the stress-strain curve ((c) and (f)) of samples produced at annealing temperatures of 250°C ((a), (b), and (c)); and 540°C ((d), (e), and (f))

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Figure 11

The relation between the reduced saturation stress and the inverse of the grain size for samples annealed at 250–275°C

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Figure 12

Correlation between the experimental and the calculated true uniform strain (full symbols: calculated from Eq. 15; open symbols: as determined from the calculated stress-strain curves (“two-parabola” description) using the Considère condition)

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Figure 13

Comparison of experimental and predicted true uniform strains presented as a function of the grain size in samples that have been subjected to different annealing temperatures: (a) 250–275°C; (b)410°C; (c)500°C; and (d)540°C. Note the logarithmic scale of the abscissa in (a).




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