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| {111}/{111} Near Singular Boundaries in a Dynamically
Recrystallized Al-Zn-Mg-Cu Alloy Compressed at Elevated Temperature |
LIU Guanghui 1,
WANG Weiguo 1,2, Gregory S Rohrer 3, CHEN Song 1,2,
LIN Yan 1,2, TONG Fang 1, FENG Xiaozheng 1,
ZHOU Bangxin 4
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1 Institute of Grain Boundary Engineering, Fujian
University of Technology, Fuzhou 350118, China
2 School of Materials Science and Technology, Fujian
University of Technology, Fuzhou 350118, China
3 Department of Material Science and Engineering,
Carnegie Mellon University, Pittsburgh, PA15213-3890, USA
4 Institute of Materials, Shanghai University,
Shanghai 200072, China
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Abstract Increasing the fraction of {111}/{111} near-singular
boundaries ({111}/{111}-NSBs) has been reported as a primary solution to
intergranular corrosion failure in Al–Zn–Mg–Cu alloys. The authors’ previous
work demonstrates that continuous static recrystallization resulting from a
specific prestrain and annealing is conducive to the formation of
{111}/{111}-NSBs in Al–Zn–Mg–Cu alloys. Therefore, the development of such
boundaries in the alloys during dynamic recrystallization (DRX), particularly
during discontinuous DRX (DDRX) and continuous DRX(CDRX) at elevated
temperatures, should be elucidated. In the present work, an Al–Zn–Mg–Cu alloy
containing 7.79% Zn, 1.53% Mg, and 1.68% Cu (mass fractions) was selected as the
experimental material. A hot-rolled plate of the alloy was subjected to a
two-stage solution treatment at 470oC for 12 h and 520℃ for 6 h
followed by cold rolling and recrystallization annealing. Three parallel
samples cut from the recrystallized plate were compressed at 450oC,
480oC, and 520oC at a strain rate of 0.001 s–1 to a true strain of 1.20. The samples were water quenched immediately after the
compression. Electron backscatter diffraction and grain boundary
inter-connection measurement based on five-parameter analysis were performed to
examine the microstructures and grain boundary character distributions of the
compressed samples. The results indicate that the microstructures of the
samples were uneven, exhibiting fine- and coarse-grained regions. Low-angle grain
boundaries are dominant in the fine-grained regions, whereas high-angle grain boundaries
are dominant in the coarse-grained regions. The fraction of {111}/{111}-NSBs increases
with the compression temperature in fine- and coarse-grained regions. In the
sample compressed at 520oC, the{111}/{111}-NSBs from the low-angle grain
boundaries constitute 8.77% of all grain boundaries, while those from the high-angle
grain boundaries constitute 4.53%. The stress–strain curves and the
microstructures of the sample compressed at 450oC to a true strain of
0.36 show that primary DRX occurs at strains from 0.05 to 0.7. Furthermore, the
coarse-grained microstructures and high-angle grain boundaries develop during
the stage involving steady-state flow. When the strain increases from 0.70 to
1.20, secondary DRX—including DDRX and CDRX—occurs in some regions, leading to dramatic grain
refinement and a sharp increase in flow stress. In this stage, CDRX intensifies
with increasing compression temperature, and {111}/{111}-NSBs in the low-angle grain
boundaries increase rapidly.
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Received: 17 April 2023
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