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Parameters controlling the milling process applied to the production of AI-Cu-Mg-Si alloys (2214) by mechanical
alloying
X. Yan, N. Bois, G. Cizeron
To cite this version:
X. Yan, N. Bois, G. Cizeron. Parameters controlling the milling process applied to the production of AI-Cu-Mg-Si alloys (2214) by mechanical alloying. Journal de Physique III, EDP Sciences, 1994, 4 (10), pp.1913-1928. �10.1051/jp3:1994247�. �jpa-00249232�
Cla~sillcation Phv.uc.s Ab~iiJ.acts
8 20E 8 20G 8 20J
Parameters controlling the milling process applied to the
production of Al,Cu,Mg,Si alloys (2214) by mechanical
alloying
X. X. Yan, N. Bois and G. Cizeron
Laboratoire de Structure de~ Matdriaux Mdtalliques, Bitiment 465, Universitd Paris Sud, Centre d'or~ay, 91405 Orsay Cedex, France
(Receii.e<J 4 June 1993, iei,ised 4 July J994. accepted 7 July J994)
Rdsumd. Dans cette Etude ont dtd analysdes )es influences respectives de divers param6tres (temp~ de broyage t~, vitesse de rotation de l'axe de l'attriteur w et rapport R masse des billes/masse des poudres) sur le processus de mdcanosynthbse appliqud h do poudres mdlangdes
en vue d'obtenir des alliage~ Al -Cu-Mg-Si (type 2214). II en a dtd ddduit que le parambtre essentiel dtait w. En outre, par microscopic et par diffraction X, les conditions optimales de broyage ant dtd
ddtermindes, ainsi que le~ caractdristiques essentielles de la poudre rdsultant du processus d'attritiun. L'aptitude au frittage des comprimds rdalisd~ h partir de poudres traitdes par voie mdcanique a dgalement dtd dtudide par dilatomdtrie et comparde h cello de la poudre initiale. Une relation permettant de relier la diminution de la taille des particules d'aluminium aux param6tres
d'attntion a dtd dtablie.
Abstract. In this study are analysed the respective influence of various parameters (processing
time t~. speed of rotation
w of the attritor axis and ratio R : the ball to powder masses) on the mechanical alloying process applied to mixed powders in order to obtain Al-Cu-Mg-Si alloys (2214 type). It was deduced that the most effective parameter is w. Furthermore the optimum proce~~ing conditions were determined as well as the main characteristics of the powder resulting
from the milling proce~s u~ing microscopy and X-ray diffraction. The sintering ability of samples pressed from
« MA » powders was also studied thanks to dilatometric tests and compared with that of initial powder mixtures. A relationship between the size reduction of Al particles and the milling
parameters is establi~hed.
1. Introduction.
The possibilities for Mechanical Alloying (MA) powders are promising, especially in the field of light metal alloys [1, 2]. Various structural applications, in the marine and defence fields, have been reported both in USA and in UK.
First in 1966 exploratory research on mechanical alloying began with the objective of
obtaining a homogeneous and fine dispersion of oxide particles in nickel-base superalloys [3-
5]. Following the nickel- and iron-base oxide dispersion strengthened (CDS) alloys was the
development of MA aluminium-base alloys [6-8].
Three main CDS aluminium-base alloys (Al-Mg, Al-Li and Al-Cu) have been produced by
MA [9-18]. During milling, an equilibrium particle size distribution is established. This submicron grain size is stabilized by dispersing very fine and stable dispersoids (oxides and/or carbides) and this contributes to new properties.
In the case of Al-4 Mg alloys, the mechanically alloyed materials have a better corrosion resistance and an improved strength compared to the corresponding ones in cast alloys (5 000
or 7 000 series).
The Al-Li alloys made by MA also have attractive mechanical properties. It has been
demonstrated that the fatigue resistance of the MA Al-Li alloys is higher than that of alloys obtained by ingot metallurgy or by powder metallurgy of similar tensile strength I, 12, 15].
A mechanically alloyed Al-Cu-Mg-C-O alloy (IN-9021) has been well-characterized [7, 8, 14, 16, 17]. The results showed that MA IN-9021 leads to a good combination of tensile
strength, fatigue strength, toughness and corrosion resistance [14]. In all the above studies, only few detail was given about the preparation of these alloys through MA.
Today, several aluminium-base MA alloys are commercially produced by MA, such as Inco
MAP AL 9052, Inco MAP AL 9021 and Inco MAP AL 905XL [2, 14].
Considerable research has been done on the improvement in mechanical properties, but work by Benjamin et al. [19] showed that the mechanical alloying process is not restricted to producing complex oxide dispersion-strengthened (CDS) alloys. It also can be used for
producing powders with controlled and extremely fine microstructure. In addition to the
strengthening due to finely dispersed dispersoids, a significant part of the strengthening in
these alloys is linked to the fine grain size and high dislocation density resulting from the
severe cold working suffered by the powders [8, 19]. From this angle, the preparation of an Al-
Cu alloy powder with a very fine microstructure and a good homogeneity by mechanical attrition was investigated in this study.
More recently a separate field of research has investigated MA as an amorphization process [20, 21]. It is known that in binary alloys from transition metal amorphized by MA, the
essential factors are the fast diffusion behaviour of one metal in the other, and the existence of
a negative heat of mixing in the amorphous alloy [22].
From thermodynamic and kinetics viewpoints, it is important to clarify which systems can
be amorphized by MA [23]. More recently, a study has been done in order to predict the
possibility of amorphization for binary TM-TM (TM
= Transition Metal) systems by MA.
Other important research has been done to know the influence of milling conditions on the
amorphization processing in TM-TM systems. This led to the first crystal-amorphous phase dynamical equilibrium diagram [24, 25]. But, recent research showed the lack of amorphous phases in aluminium-copper alloys the only meta~table phases formed by MA in the Al-Cu system have a distordered body-centered cubic (bcc) structure [26]. Data related to the motions of milling system in an attritor and the efficiency of various physical parameters in MA process
have also been reported [27, 29].
This paper is only concerned with the influence of milling parameters on the morphology
and the conventional sintering characteristics of the resulting powders. Three parameters are
considered the rotational speed of the attritor axis w, the processing time t~ and the ratio R of the mass of zirconia balls to the mass of powder. Each of these parameters were optimized by studying the corresponding effect on the milling process while keeping the other values
constant. The MA powders were characterized by optical microscopy, scanning electron
microscopy, X-ray diffraction and dilatometry.
We have applied mechanical alloying process in order to obtain a finer structure and to increase the homogeneity of the composition of the studied quatemary alloy.
2. Experimental procedure.
2, MATERIAL. The powder used in this investigation was a mixture, designated as 210BP
(SPMS POUDMET), with atomized aluminium, copper, magnesium, silicon particles for a
density of 1.40 (in a tapped state). Table I gives its composition and jarticle size.
Table I. Composition and,qranulometric anal»sis of the starting pow>den (201 BP).
Composition wt fb
Al Cu Mg Si (Fe Zn Mn) impurities
balance 4.4 0.54 0.42 0.06 0.005
~ 0.002 Granulometric analysis
10 fb
~ 107 ~Lm, 50 fb
~ 53 ~Lm
2.2 HIGH-ENERGY BALL MILLING TECHNIQUE.
Equipment. In this study, a Wieneroto high-energy attrition mill was used. Agitation was provided by the shearing action of four impeller arms fixed on the attritor shaft, tuming inside a
cylindrical water cooled tank. The mill contained zirconia balls of 3 mm in diameter and the
rotational speed could be ajusted from loo to 300r.p,m. (the zirconia does not induce
pollution). The 201BP powder was milled with an acetone addition in order to prevent oxidation and act as a process control agent. After milling the removal of acetone adsorbed on the MA powder was carried out in a Heidolph rotary-evaporation system at 80 °C under partial
vacuum.
Principle [30]. During the mechanical alloying process, the impeller arms agitate the balls
very strongly, the impact/rolling of these balls refines the internal structure of the powders and also produces a uniform distribution of dispersoids throughout the matrix. The powder particles are repeatedly flattened, fractured and rewelded, this leading to a steady state.
2.3 CHARACTERIZATION TECHNIQUES.
Compaction. Compacts were pressed without any binder under 400N.mm~~ for the following studies : X-ray diffraction measurements and dilatometric tests.
Microscopic e-raminations. The morphology and microstructure of the MA powders have been observed by optical microscopy and scanning electron microscopy (SEM). The samples
were polished and etched with Keller's reagent [2 ml HF (48 fb 3 ml HCI (conc.) 5 ml HNO~ (conc.) 190 ml water].
X-ray diffraction analysis. A Siemens D501 X-ray diffractometer with CUK~ radiation (A = 0.1540 nm ) was used to identify the phases present in the as-milled powder and after
heat treatment. From the X-ray line broadening measurements on Al(220), Al(311) and
Al(222) peaks, mean crystallite size of the MA powder was calculated using Scherrer's formula (t #£
~'~ ~ ), where A is the X-ray wavelength, o the diffraction angle and
Bcos o
B the full width at half height of the «j component profile. The separation of the
K~ doublet was performed using the Rachinger correction [31]. The scanning speed was
0.5 °min~ ' or 0.05 °min~ ' (2 o).
Nonisotheimal dilatomen.y. Dilatometric analysis was carried out with an ADAMEL Dilatometer DI ?4 in a protective atmosphere of purified nitrogen with a heating rate of 300 °C.h~ ' Dilatometric method has been used for the analysis of structural changes on
heating in compacts of the starting and the milled powder as well.
3. Experimental results.
3. STARTING POWDER. The initial 201 BP powder is shown in figure I. The Al particles
have an irregular shape and a non-uniform size. The maximum size is 200 ~Lm in length and 100~Lm in width; the smaller size is approximately 4~Lm in diameter. A dendritic
microstructure is present within the Al particles. Cu particles are reddish and have a spherical shape, their average diameter is about 10 ~Lm. Si particles are grey with a size of 5 to 7 ~Lm. Mg
particles are not resolvable by microscopy because of the same coloration as Al under
microscopy. X-ray diffraction pattern of the 201BP powder before milling is shown in
figure ?. The peaks of Al and Cu are observed, but other elements are not detected, probably
because of their small quantity. Three peaks, Al(220), Al(3 II and Al(22? ), were recorded with a slow scanning ;peed of 0.05 °C.min~ and an amplification in intensity for the
determination of the Al crystallite size (t~j). After elimination of the a~ component, t~j was calculated from the Scherrer's formula : t~j = 62 nm. Dilatometric measurement of the
thermal behaviour was done in order to reveal the structural changes in pressed compacts. The result is given in figure ~a. Fir~t, an expansion is observed in the range of o
=
270,490 °C (II) this phenomenon was also observed in the case of a pure Al compact without any
additional element~; be~ides, this phenomenon is irreversible. Figure 3b show~ three
successive cycles on the same sample. The previous anomaly results from the removal of water
vapour and organic compounds. Then, the normal thermal expansion is ob~erved between
490 °C and 520 °C ((II). In fact, the ~lope of the curve in this interval is lower than the one in the interval (9
=
?0-270 °C this might corre~pond to a weak shrinkage in the solid state.
The other observation in the same interval (III) is a very limited diffusion of Cu into the Al
matrix. Thi~ fact was confirmed by studying a powder mixture with a higher content of
Cu(Al ~ 10 at.fb Cu). At about 520 °c, the accelerated diffusion of Cu within the Al particles leads to the formation of an eutectic phase therefore an abrupt expansion is observed at 520- 540 °C due to the enhanced diffusion of Cu in Al grain boundaries. Above 545 °C, a liquid- phase sintering and some creep develop under the force applied by the pushrod. During cooling, solidification of the liquid phase is not very marked (535-505 °C). In the range of 440- 400 °C, the rejection of Cu atoms results in the formation of Aljcu compound.
3.2 INFLUENCE oF THE R, w AND i~ PARAMETERS DURING MtLLI~G. Three serie~ of
experiments were conducted. Each of the three parameters was examined. Table II indicates the chosen values.
Table II. Condition (>f'tfie milling pioce.is for the three series of e~ipeiiments.
lst set of tests 2nd set 3rd set
R
= 8, lo, 12
w = loo, 200, 300 r-p-m- t~ =
20, 30, 50 hours
£
= 200 r-p-m- R
=
12 R
=
12
t~ = 20 h t~ =
40 h w = 250 r-p-m-
a
- fi'
Al
~~
5pm~~ ~j~
@$'_w
%~
'~i
iopm,
Fig, I. (a) Optical and (b) (cl SEM micrographs on 201 BP initial powder. The different constituents
were identified by local microanalysis in SEM.
P o(2OO) a(ill) a Al
§
o CM
, a(222) °(220)
al311)
«)
j
i; I ;
> yj. ÷' f
~ .'( .~i. 8
z ? ".__
~
fl
w
~~~~
( al 82.S la ~S.S °
So So lo
- 2e(degree)
hi a
Fig. 2. X-ray diffraction pattern from the initial powder.
~
iV ~~
3
Ml I
~
2~~
1
m
#
w w
~ i
# , l~~
tO
$~
j
, lCYCLE
100 300 500 loo 300 SOD
T£»,£KITVK£(°cJ
(al (b)
Fig. 3. Dilatometric curves recorded at a rate of 300 °C/h (powder in the initial ~tate). (a) Single cycle.
(b) Three succe~sive cycle~.
3.2, Moipholo~q_v. In the st set of tests, R was varied from 8 to lo and to 12. Figures 4a, b show the resulting particles after milling in the ca~e of R
#
8 and 12. The increase in
R results in a size reduction. In figure 5a is plotted the mean particle size, measured in width,
+
80~m
Fig. 4. Optical micrographs showing the MA powder milled with the following conditions:
w =
200 r-p-m-, i~ =
20 h (a) R
= 8, (b) R 12.
o
I
~
~ .
#
w
«
©
~.~
o . ~
~ ~
, u_~
8 lo 12 loo 200 300 20 30 40 50
R W(rpm) t (h)
jai 16 (Cl
Fig- 5. Effect of the three process parameters, R, w and t, on particle size during milling
(~l'~ :
~
2°° T-P-m-
t 20 h ; R 8, lo, 12. (b) R 12 t 40 h; w
= loo, 200, 300 r-p-m- (c) R 12
w 250 r-p-m- t 20, 30, 50 h.
as a function of R. From this curve, it is observed that particle size fragmentation is much more important with R
=
lo- When R
=
12, the size of the fragments is approximately equivalent to
that of powders processed for R
=
lo. So their mean size is 25 ~Lm.
in the 2nd and 3rd sets, the morphological change of the powder particles is similar to the
one in the lst case. The average size decreases with increasing the rotation speed and/or the
milling time (see Figs. 5b and 5c). It can also be noticed that the increase in the rotation speed
from loo to 300 r-p-m- i~ very efficient in a rapid reduction in size. During the period from 30 to 50 h, the mean particle size decreases slightly while the fine particles are uniformly flake- shaped after 20 h milling.
3.2.2. X-jay studies. Figure 6 shows the X-ray diffraction pattern from a pressed compact of the powders milled with R
= 12, w
=
250 r-p-m- and t~ = 20 h. As compared with the diffraction pattern of the starting powder, the peaks from Cu have disappeared.
~ u u Al
z
~ u
~ D
« D
«
«
~
,
o~ ' ,
« / ,'
« '
~ ,,
ii ,,
,,," '"...,,__ ,,'
li
£ 79 78 655
SO 40 30
- 29 <degree>
(hi jai
Fig. 6. X-ray diffraction scan for the powder milled with R
= 12, w
= 250 r-p-m- and t 20 h.
When the powders are milled with acetone in the water cooled attritor, the particles are cold worked, fragmented and microstresses are produced [3 Ii. Therefore, the line broadening of the milled powder is due to fine size and to nonuniform strain as well. In the present work, the minimum crystallite size of Al particles was e~timated using the Scherrer's equation [31].
Variation of the Al crystallite size with increasing each of three parameters (R, w and t~) is given in figure 7. Only a small decrease in the Al crystallite size is observed when the ball to powder mass ration (R is 8 (1st series of experiments). The rate of reduction in crystallite
size is more pronounced when increasing the speed of rotation (w). The crystallite size decreases ~lowly after a milling time of 20 h in the 3rd set of tests it appears that this value is stabilized with a longer milling time (t~ 50 h).
3.2.3 Dilutometiic analj,sis. Figure 8 shows the dilatometric curves recorded during
heating on samples milled in various conditions. For comparison, the dilatometric curve recorded from a sample pres~ed with the starting powder is also shown in the figure 8 (curve down). The increase in each variable (R, cu and t~) leads to a decrease in the thermal expansion
~ ~~
~
w
~~
lQ
~
ii " ° °
.
~
~
~o
~
~ D
~l
« o
8 lo 12 loo 200 300 20 30 40 SO
R WlrPm) t (h)
(al 16) (Cl
Fig. 7. Effect of the three procew parameter~, R, w and t, on Al cry~tallite ~ize for
(a) w 200 r-p-m- 20 h R 8, lo, 12. (b>R 12, t 40 h w loo, 200, 300 r-p-m
(c) R
= 12, w
=
250 r-p-m- ; t 20. 30, 50 h.
j~)
°*j III j"
~ 490
~?~ 430
'
270
i~~ ~~~i i i~~~' I° i~l I°
~
120
50
~ ' ' '' i,
,
' ' ',
~ ,
' ' ill
, ,
# ' ' , ' ' ,
"
~z
'
,
ill
~ ' ' ' ~ ' ' , '
v v
~
R ' w t
th)
ioo loo boo loo loo boo ioo loo boo
iimPiuii#vii°ci
(a( j>j ICI
Fig. 8. Effect oi the milling parameters on the dilatometric curve~: jai Influence of R
(w = 200 r-p-m-, t 20 h)- (b) Influence oi w (R 12, 40 h)- (c) Influence of t (R
= 12.
w =
250 r p-m-1-
coefficient of the pres~ed compact~. Figure 8a corresponds to the first serie~ of tests where R is varied (8
~ R ~12 while keeping
w =
200 r-p-m-, t~ = 20 h. A slight contraction is observed at approximately 120 °C (11) as to outline this, we drawn dotted lines parallel to the
