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Department of Materials EngineeringThe University of British Columbia
Overview
Starting Material: AZ80
Mechanical Response
SummaryTwo double twinning sequences have been found in AZ80 tested in compression at 77K. In contrast only primary twins have been found in room temperature deformed AZ80. The {1012}-{1012} and {1012}-{1011} double twins twin first on {1012} planes followed by re-twinning inside the primary twins on {1012} and {1011} planes respectively. The two double twin types differ considerably in morphology. The methodology used here is able to unambiguously identify the twinning sequence (e.g. tension twin first, compression twin second). This is not possible when only boundary misorientation is used to define the double twins.
Double twinning in AZ80 Magnesium alloyJ. Jain, J. X. Zou, C. W. Sinclair and W. J.
Poole
Calculated Pole Figure
Green: experimentalBlue: calculated
RD
TD
=50 µm; Copy of Default Map; Step=0.1 µm; Grid1459x1544
10 µm
Calculated Pole Figure
Composition (all in wt%) of AZ80
Al Zn Mn Bal.8 0.5 0.2 Mg
0.00 0.05 0.10 0.15 0.20 0.250
100
200
300
400
500
600
700
293K
77K
Tru
e st
ress
(M
Pa)
True strain
13mm
10mm9.45mm
Optical micrograph and (0001) EBSD pole figure of solution-treated AZ80. The average initial grain size of the material is 32µm.
Uniaxial compression tests performed on solution treated samples at 77K (liquid nitrogen) and 293K.
EBSD & TEM Observations
•Results:
• Many double twins are only observed for samples deformed at 77K.
• No double twins were observed for samples deformed at 293K.
• Confirmation of double twinning by TEM (dark field image shown in inset left)
M T1
T2
The prevalence of deformation twinning relative to slip can be modified both through alloying and deformation temperature. We have used temperature in this study to examine the changes in both mechanical properties and microstructure in an Mg-Al-Zn alloy. One focus of this work has been to clearly identify the detailed microstructure development with deformation. Here we report specific observations of uncommon double twinning events observed when deformation occurs at low-temperature.
50 μm
T = 300K, = 0.08
Compression Direction
Details of Observed Double Twins:: {1012}-{1012} Double Tensile Twin
{0001}
Start from matrix (M) test all possible axis-angle pairs corresponding to known twins. Sequence that best fits is shown in pole figure – this is double tensile twinning
0.5 m
[1120] [1120]ZM = [1 2 1 1]
ZT1 = [1 1 0 0]
ZT2 = [0 0 0 1]
Matrix
Primary Twin
Secondary Twin
TEM observations confirm EBSD determined sequence of double tensile twinning observed in samples deformed at 77K
Majority of twins exhibit this form of twinning in TEM
: {1012}-{1011} double tensile-compression twin
As above, sequence and type of twinning was confirmed by iteratively computing orientation of twins relative to experiments from axis angle pairs.
Note: in tension-compression (TC) case the secondary twin appears to fill the primary twin. In double tensile twinning (TT) secondary twins are fine – related to common rotation axis in TC compared to separate rotations axes in TT
25 µm 25 µm
M
T1
T2
TD
RDM
T1
T2
Green: experimentalBlue: calculated
=50 µm; Copy of Default Map; Step=0.2 µm; Grid929x672
10 µm
T2
Matrix
TD
RD
{0001}T1
RD
TD
T2
T1
Matrix
[1010]
[1010]
[1103]
[0113]
[0113]
[1103]
[0110]
[0110]
[1010]
[1010]
[1100]
[1100]
[1120]
[1120]
[1120]
[0002]
[0002]
[1120]
Matrix primary twin
[1210]
Primary secondary twin
[1120]
Rotation axis
T = 77K, = 0.08
Compression Direction
1 m
