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Materials Science and Engineering A 527 (2010) 5582–5591
Contents lists available at ScienceDirect
Materials Science and Engineering A
journal homepage:www.elsevier.com/locate/msea
ExperimentalandmodelinginvestigationonSiCp distributioninpowder
metallurgyprocessedSiCp/2024Alcomposites
Z.Y. Liu, Q.Z. Wang, B.L. Xiao∗, Z.Y. Ma, Y. Liu
ShenyangNationalLaboratoryforMaterialsScience, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China
article info abstract
Article history: SiCp/2024Alcompositeswerefabricatedthroughthepowdermetallurgy(PM)technique.Themixingpro-
Received15March2010 cesswasmodiedbyusingahighballtochargeratio(BCR),whichresultedinimprovedhomogeneityof
Accepted4May2010 theSiCp distribution,aswellasenhancedtensilestrengthsoftheas-pressedcomposites.Asmallparticle
size ratio of aluminumtoSiCp (PSR)andextrusionalsoimprovedtheuniformityoftheSiCp distribution.
Theimprovementsbythethreeapproacheswerequantitativelyanalyzedusingacriticalvolumefraction
Keywords: model. The model demonstrates that a small PSR and a large deformation ratio of aluminum particles
Analytical modeling weretwoessentialfactors of improving the homogeneity of the SiC . A homogeneity analysis using the
Metal-matrixcomposites p
Powdermetallurgy Dirichlet Tessellation method provided an additional explanation for the model.
Reinforcementdistribution Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
1. Introduction a critical volume fraction model based on the as-extruded SiC /Al
p
composites. However, the above models could only be suited for
SiCparticulate(SiC )reinforcedAlmatrixcompositesarepow- oneprocess,eitherthehot-pressprocessortheextrusionprocess.
p
erful candidates in the automobile and aerospace industries [1–5]. Furthermore,thecritical volume fraction on the deformation of Al
Control of the SiC distribution in the Al matrix is an important powders during mixing process was seldom discussed. Therefore,
p
technique, since clustering degrades the tensile properties of the acritical volume fraction model considering the deformation of Al
composites [6–15]. In powder metallurgy (PM) SiC /Al compos- powderandPSRduringdifferentprocessesishighlydesirable.
p
ites, SiCp agglomeration or necklace structure might be produced In this article, the effects of modied mixing processes with a
in the case of a large volume fraction of SiCp or a large parti- high ball to charge ratio, extrusion and PSR, respectively on the
cle size ratio (PSR) of Al to SiC [13–17]. Enhancing the mixing homogeneityofSiC distribution were investigated. A critical vol-
p p
process [18–21], properly selection of the PSR [13–17] and per- ume fraction model was proposed to quantitatively evaluate the
forming a post-fabrication deformation such as extrusion [22] are homogeneity of the distribution. Furthermore, the reinforcement
the most common methods of improving the homogeneity dis- distributionassociatedwiththePSR,mixingprocessandextrusion
tribution. However, the principles which are responsible for the werealsoanalyzedbytheDirichletTessellationmethod[12,23].
improvementhavenotbeenwellunderstood.
In order to guide the fabrication and secondary processing of
the composites, it is necessary to build a criterion for evaluating 2. Experimentalprocedure
the homogeneity of the reinforcement distribution. Some critical
volume fraction models of reinforcement [14,16] have been built 2.1. Materials and mixing process
todescribetheinuencesofthePSRandthevolumefraction(Vf)on
the homogeneity of the reinforcement distribution. If the volume Theas-received 2024Al and -SiC powders were spherical and
fraction of the reinforcement exceeded the critical volume frac- polygonalshaped,respectively.2024Alhadanominalcomposition
tion, a non-homogeneousdistributionofthereinforcementwould of Al–4.5%Cu–1.5%Mg (wt.%). In order to investigate the effects of
appear. Bhanu Prasad et al. [16] set up a clustering probability the ball to charge ratio (BCR), extrusion and the PSR on the homo-
mapof the reinforcement for the as-pressed or as-sintered com- geneityofSiCp andmechanicalpropertiesofthecomposites,three
posites in view of geometrical location. Slipenyuk et al. [14] set up groupsofsampleswerefabricated(Table1).
Intherstgroupofsamples,thecompositepowdersweremixed
for 12h. For comparison, the powders mixed for 1, 4 and 8h were
also withdrawn. For convenience, the powders or the composites
∗ Correspondingauthor.Tel.:+862483978630;fax:+862423971749. underBCRof1:1and10:1werelabeledasBCR1andBCR10,respec-
E-mail address: blxiao@imr.ac.cn (B.L. Xiao). tively. In the second group of samples, the experiment aimed at
0921-5093/$–seefrontmatter.Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.msea.2010.05.006
Z.Y. Liu et al. / Materials Science and Engineering A 527 (2010) 5582–5591 5583
Table1
Materials and process parameters used in mixing.
Experiment D (m)a D (m)a SiC vol.% Ball to charge ratio (BCR) Mixingtime(h)
SiC Al
Group1 3.5 13 15 1:1 12
15, 20 10:1
Group2 7 29 5, 10, 15, 20 1:1 8
Group3 3.5 3, 5, 7, 13, 29 15 1:1 8
a D andD arediametersofSiCandAlpowders,respectively.
SiC Al
investigating the effect of extrusion on the critical volume frac- theSiCp werefreelydistributedattheperipheryoftheAlparticles.
tionandhomogeneityoftheSiC distributioninthecomposites.In However,fortheBCR10powders,thecompositepowdersdisplayed
p
order to investigate the PSR effect on the distribution of the SiC , an irregular morphology, indicating that they underwent severe
p
in the third group of samples, 15vol.% SiCp/2024Al powders were deformationduringmixing.
preparedbyxingthesizeoftheSiC andchangingthesizeoftheAl Fig.2showstheevolutionofthemorphologyoftheBCR10com-
p
powders. For all samples, the SiC powders were dried in a furnace posite powders mixed for 1, 4, 8 and 12h. For the 1h sample, the
at 423K for 5h and then mixed with the Al powders in a bi-axis Alparticlesremainedinspheroidalshape,andtheSiC werefound
p
rotary mixer with a rotation speed of 50rpm. No process control mainly among the spheroidal Al particles. After being mixed for 4
agentwasadded. and8h,theAlparticlesweretransformedfromspheroidalshapeto
akyshape.Inaddition,manySiCparticleswereenclosedbetween
2.2. Fabrication of composite theakyparticleswhentheywereaggregatedintolamellarstruc-
turesthroughcoldwelding(Fig.2(b)and(c)).Thewidthofasingle
Theas-mixedpowderswerecoldpressedinadie,degassedand akeinthelamellarparticles, measured using the linear intercept
then hot-pressed in vacuum under a pressure of 80MPa. The as- method,wasabout3–5m.Whenmixedfor12h,almostallofthe
pressed composites in the rst group were solutionized at 768K SiC particles were enclosed into the lamellar particles. The pow-
for 1h, water quenched and then naturally aged for 96h. The as- dersturnednearlyequiaxial,implyingthatabalancebetweencold
pressed billets in the second and third groups were hot extruded welding and fracture was built. The evolution of the morphology
into rods at 723K at an extrusion ratio of 9:1. The extruded rods indicates that the low energy mixing using high BCR behaved a
were heat treated with the same procedure as the samples in the similar process as the high energy ball mill [18–21].
rst group.
3.2. Microstructure of SiC /2024Al composites
p
2.3. Microstructure and mechanical properties
Fig. 3 shows the optical micrographs of the as-pressed 15vol.%
Morphologies of the as-mixed powders were observed by scan and20vol.%SiCp/2024Alcompositesintherstgroupofsamples.
electron microscopy (SEM, SSX-550). The SiC distribution in the The SiC in the BCR1 composite with concentration of 15vol.%
p p
as-mixed powders, the as-pressed and as-extruded composites showed obvious necklace structure. Similar observations were
wereobservedbyopticalmicroscopy(OM,Axiovert200MAT).Den- found in previous studies [15–16]. For the BCR10 composite with
sityofeachofthecompositeswasmeasuredusingtheArchimedean concentrationof15vol.%,astreamline-likedistributionofSiC was
p
principle. Room temperature tensile tests were performed at a observedandtheSiCp weremorehomogeneous(Fig.3(b)).Itindi-
strainrateof0.001s1 onanAG-100kNGtester.Tensilespecimens cates that a large BCR could improve the uniformity of the SiC
with a gauge diameter of 5mm and gauge length of 20mm were distribution.Howeverclustersappearedinthe20vol.%SiC /2024Al
p
machinedfromtheheattreatedsamples. evenwithahighBCRof10:1(Fig.3(c)).
Fig. 4 shows the microstructure of the second group of com-
3. Results posites. Similar to the observations of the BCR1 samples in the
rst group, the SiC were found at the periphery of the Al parti-
p
3.1. Microstructure of SiC /2024Al composite powders cles in the as-pressedcomposites.Forthecompositeswithvolume
p
fractions of 5 and 10vol.%, the SiC were relatively homogeneous
p
Themorphologyofthecompositepowdersmixedfor12hwith (Fig. 4(a) and (b)). However, clusters appeared at higher volume
different BCRs in the rst group of samples are shown in Fig. 1. fractions of 15 and 20vol.%, due to the inadequate specic surface
For the BCR1 powders, the Al particles remained spheroidal and area of the Al particles (Fig. 4(c) and (d)). Compared with that in
Fig. 1. SEM images of composite powders (group 1) mixed at ball to charge ratio of (a) 1:1 and (b) 10:1.
5584 Z.Y. Liu et al. / Materials Science and Engineering A 527 (2010) 5582–5591
Fig. 2. Optical micrographs of composite (group 1) powders mixed at 10:1 ball to charge ratio for (a) 1h, (b) 4h (c) 8h, and (d) 12h. Dashed line in (c) referred to interfaces
andstreamlinedirectionofSiCdistributionincold-weldedlamellarstructure.
Fig. 3. Microstructure of various composites in group 1: (a) 1:1 BCR, 15vol.% SiC; (b) 10:1 BCR, 15vol.% SiC; (c) 10:1 BCR, 20vol.% SiC.
Z.Y. Liu et al. / Materials Science and Engineering A 527 (2010) 5582–5591 5585
Fig. 4. Microstructure of as-pressed SiCp/2024Al composites (group 2) with SiC volume fraction of (a) 5%, (b) 10%, (c) 15%, and (d) 20%.
Fig. 5. Microstructure of as-extruded SiCp/2024Al composites (group 2) with particle volume fraction of (a) 5%, (b) 10%, (c) 15%, and (d) 20%. The extrusion direction is
horizontal.
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