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Thermal Stability of
Cryomilled Al-Mg-Er Powder

TRANSFORMATION ET APPLICATIONS // TRANSFORMATION AND APPLICATIONS

45

STABILITÉ THERMIQUE
(Stabilité ThermiqueDES POUDRES BROYÉES CRYOGÉNIQUEMENT
des
Poudres Broyées
THERMAL STABILITY OF CRYOMILLED Al-Mg-Er POWDERS
Cryogéniquement)
Bamidele Akinrinlola1, Carl Blais2, Raynald Gauvin1 et Mathieu Brochu1
1Mining

2Département

Experimental Results

Introduction
Creating bulk nanostructured materials via powder
metallurgy

routes

nanostructured
consolidation

and Materials Engineering Department, McGill University, Montreal QC H3A 2B2
génie des mines,métallurgie et matériaux, Université Laval, Québec City QC G1V 0A6

requires

powders

that

conditions.

thermally
can

withstand

Addition

of

(b)

(a)

stable

Al (SS)
Si (standard)

(c)

the

lanthanide

elements, such as Sc and Er, can retard recrystallization in
deformed microstructures typically by the formation of
this study two compositions of Al-Mg-Er alloys are
investigated to observe the effect of Er addition on the

A

Element

0.1 Er
0.5 Er

B

(c)

Mg

Er

Ti

Fe

Ni

Tl

Si

Al

0.1 Er

5.006 0.095 0.308 0.268 0.154 0.096 0.058

rem.

0.5 Er

4.505 0.447 0.013 0.052 0.017 0.000 0.051

rem.

C

(b)

(a)

0.00

Heat (W/g)

(b)

Table 1. ICP results for 30 hr milled powders (wt%)

thermal stability of nanostructured Al-Mg powders.

0.25

(a)

Figure 1. (a) Schematic of cryomilling setup and TEM images of the
(b) 0.1 wt.% Er and (c) 0.5 wt.% Er powders milled for 30 hrs in liquid
Nitrogen (-196°C), with inset SAED patterns.

trialuminide Al3(Sc,Er) L12 nanoscale precipitates [1, 2]. In

D

Figure 2. XRD spectra of (a) annealed atomized Al powder,
(b) milled 0.1 wt.% Er powder, and (c) milled 0.5 wt.% Er powder.

(b)

(a)

(c)

Al (131)
Al (200)

Al (131)

E

-0.25

EXO

Al (200)

Al3Er (200)
Al3Er (220)

-0.50

[112]

-0.75

0

100

200

300

400

500

Figure 5. TEM images of 0.5 wt.% Er powder at 450°C
showing (a) the nanocrystalline regions (with inset SAED
pattern) and (b) the onset of abnormal grain growth.

Figure 4. TEM images of 0.1 wt.% Er powder at 180°C showing (a) areas of abnormal
grain growth with (b) SAED pattern of the area, and (c) the indexed SAED pattern.

600

Figure 3. Linear DSC scans of as milled powders (5K/min)
Table 2. XRD and TEM results for 0.1 wt.% Er powder
Powder
condition

Mg in SS
(at%)

Grain size,
nm

Microstrain,
%

Correlation
Coefficient, R2

TEM (GN),
nm

TEM (GA),
nm

milled

5.26

22

0.094

0.9168

16 ± 1

105

180°C – 1hr

2.08

27

0.104

0.9648

32 ± 3

232

290°C – 1hr

2.87

36

0.073

0.9548

32 ± 4

601

500°C – 1hr

2.11

51

0.092

0.8823

45 ± 5

Monolayers of Mg at the grain boundary

Temperature (C)

4

(a)

0.1 Er
0.5 Er

3.5
3
2.5
2
1.5

844

1
Complete monolayer of Mg atoms
≈ 19 at% Mg

0.5
0

0

Mg in SS
(at%)

Grain size,
nm

Microstrain,
%

Correlation
Coefficient, R2

TEM (GN),
nm

TEM (GA),
nm

milled

4.87

19

0.105

0.929

17 ± 0

47

250°C – 1hr

1.55

24

--

0.9612

18 ± 1

62

400°C – 1hr

2.36

28

--

0.9904

18 ± 1

51

550°C – 1hr

2.08

46

0.064

0.8911

50 ± 3

234

Boundary mobility, γMb (m2·s-1)

Powder
condition

400

600

Temperature, °C
1E-17

Table 3. XRD and TEM results for 0.5 wt.% Er powder

200

(b)

1E-18
0.1 Er, n = 1 - 2
0.1 Er, n = 2 - 3

1E-19

0.1 Er, n >= 3
0.5 Er, n = 1 - 2

1E-20

1E-21

Bamidele Akinrinlola
Raynald Gauvin
Mathieu Brochu
Département de génie
des mines et des matériaux,
Université McGill

0.5 Er, n = 2 - 3

1

1.5

2

2.5

Carl Blais
Département génie des mines,
métallurgie et matériaux,
Université Laval

3

Inverse Temperature, 1000/T (K-1)

Figure 6. (a) Mg segregation at the grain boundary in annealed powders
and (b) the corresponding boundary mobility.

Conclusions

Dilute additions of Er improves the thermal stability of the Al-Mg-Er powders. Abnormal grain growth is observed in the 0.1 wt.% Er powder at temperatures as low as 180°C. However, nanocrystallinity is maintained in the 0.5
wt.% Er powder up to 400°C, after which abnormal grain growth occurs. Onset of abnormal grain growth seems to coincide with changes in Mg segregation at the grain boundary which affects the grain boundary mobility;
higher Er content in the 0.5 wt.% Er alloy reduces the overall boundary motilities. Al3Er precipitates are observed, but only in areas with abnormal grain growth.
References
[1] Ferry et al, Continuous and Discontinuous grain coarsening in a fine-grained particle-containing Al-Sc alloy, Acta Materialia 53 (2005), 1097-1109; [2] Wen et al, The effect of Er on the microstructure and mechanical properties of Al-Mg-Mn-Zr alloy, Materials Science and Engineering A 516 (2009), 42 - 49

Journée des étudiants – REGAL nanostructured materials via powder metallurgy routes requires
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