In-situ dispersed La oxides of Al6061 composites by mechanical alloying

Accepted Manuscript In-situ dispersed La oxides of Al6061 composites by mechanical alloying Chun-Liang Chen, Chen-Han Lin PII:

S0925-8388(18)33759-9

DOI:

10.1016/j.jallcom.2018.10.093

Reference:

JALCOM 47911

To appear in:

Journal of Alloys and Compounds

Received Date: 3 August 2018 Revised Date:

6 October 2018

Accepted Date: 8 October 2018

Please cite this article as: C.-L. Chen, C.-H. Lin, In-situ dispersed La oxides of Al6061 composites by mechanical alloying, Journal of Alloys and Compounds (2018), doi: https://doi.org/10.1016/ j.jallcom.2018.10.093. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT In-situ dispersed La oxides of Al6061 composites by mechanical alloying

RI PT

Chun-Liang Chen* and Chen-Han Lin

SC

Department of Materials Science and Engineering, National Dong Hwa University,

EP

TE D

M AN U

Hualien 97401, Taiwan

*Corresponding author

AC C

Postal address:

No. 1, Sec. 2, Da Hsueh Rd., Shoufeng, Hualien 97401, Taiwan E-mail: [email protected] Tel: +886-3-8903205 Fax: +886-3-8900172

1

ACCEPTED MANUSCRIPT Abstract Aluminum-based metal matrix composites (MMCs) are useful materials for structural

RI PT

applications due to their high strength to weight ratio. In this study, the addition of the rare earth element La to the Al6061 alloys as in-situ La oxide dispersoids fabricated

SC

by mechanical alloying was investigated. The result shows that an increase of La content can change the morphology of synthesized powders and has significant

M AN U

influence on microstructure uniformity, hardness, densification, and ductility of the materials. The results also show that the complex La-Al-Si-O oxides and needle-like

AC C

EP

sintering processes.

TE D

AlFeSi intermetallic compounds were formed during ball milling and subsequent

Keywords: mechanical alloying; Al6061; composite; intermetallic compounds

2

ACCEPTED MANUSCRIPT 1. INTRODUCTION Al6061 is a precipitation hardening of aluminum alloy, which exhibits high

RI PT

strength-to-weight ratio, good corrosion resistance, and excellent formability. Therefore, it is widely used in structural applications such as automotive, aircraft,

SC

military and marine industries [1-3]. In the past decades, Al6061 alloys reinforced with ceramic oxides, carbides or nitrides have been developed and possess attractive

M AN U

characteristics such as high specific modulus, good fatigue performance, and excellent wear resistance [4-9]. Mechanical alloying is one of the most promising

TE D

methods for synthesizing aluminum metal matrix composites to obtain nanostructured matrix with uniform distribution of ceramic reinforcement particulates [10-12]. In our

EP

earlier work [12], Al6061 reinforced with Y2O3 and TiC particles, fabricated by mechanical alloying, has been studied. It has been proposed that the presence of

AC C

reinforcement particles plays an important role in formation of intermetallic compounds and mechanical behaviour of materials [12]. The results suggested that the use of nano-Y2O3 particles generated a uniform microstructure with the finely dispersed oxide particles and also acted as nucleation sites to facilitate formation of Al-Si-Y-O based oxide particles [12]. In this work, the addition of the rare earth

3

ACCEPTED MANUSCRIPT element La in the Al6061 alloys has been further investigated. The rare earth elements have a high affinity with oxygen and most likely form in-situ oxides during

RI PT

mechanical alloying, which have good lattice coherence with the matrix, providing a significant improvement of mechanical properties at elevated temperature due to

SC

interaction of dislocations and inhibition of grain growth [13-15]. It has been reported that La is an effective grain refinement additive during the casting process and La can

M AN U

improve the welding properties of Al–Mg–Si aluminum alloy [16,17]. In addition, the presence of La element in AA6201 aluminum alloys can result in improvement in

TE D

thermal-resistant properties and electrical conductivity [18]. Therefore, the focus of the present work is to develop a new Al6061 composite dispersed with in-situ La

EP

oxides by mechanical alloying. It is important to evaluate and understand how the addition of the different amounts of La content influences the synthesis and

AC C

characteristics of the Al6061 alloys.

2. EXPERIMENTAL PROCEDURE The material used in the present study is Al6061 as the composite matrix with a particle size of 44–62 µm. The rare earth element La was introduced in the Al6061 matrix as in-situ formed La oxides fabricated by mechanical alloying. The La 4

ACCEPTED MANUSCRIPT powders have a purity of at least 99.9% with a particle size in 45 µm. In this study, the three different amounts of La contents were introduced into the Al6061 alloys and named as Al6061-0.5La, Al6061-1.2La and Al6061-2La (in weight percentage), see

RI PT

Table 1. Mechanical alloying was carried out using a planetary ball mill (Retsch PM 100) operated at 350 rpm under an argon atmosphere. Milling experiments were performed using a hardened stainless steel medium with a ball-to-powder ratio of 10:1

SC

for different milling times of 4 h, 8 h, 16 h, and 24 h. The mechanically alloyed powders were consolidated into green compacts with a pressure of 350 MPa and then

M AN U

were further sintered in a mixed hydrogen-argon atmosphere at 600°C for 2 h. Powder evolution of the Al6061 model alloys were examined using an X’PERT PRO X-ray diffractometer (XRD) with CuKα radiation. The crystallite size and lattice strain was

Br =

0.9λ + η tan θ t cosθ

TE D

estimated using Scherrer’s formula as follows [19].

EP

where Br is the total broadening due to crystal refining and lattice strains; λ is the X-ray wave length; t is the crystallite size, θ is the Bragg angle and η is the strain

AC C

in the material. Microstructural characterization and a further analysis of the complex dispersed oxides and phase identification were performed on a Hitachi-4700 scanning electron microscope (SEM) and a FEI Tecnai F20 G2 field emission gun transmission electron microscope (TEM). Vickers hardness measurements were performed at room temperature using a load of 1 kg for 15 s. Nanoindentation tests

5

ACCEPTED MANUSCRIPT (MTS Nanoindenter XP) were conducted to obtain the elastic modulus and hardness

3. RESULTS

SC

3.1 Characterization of Al6061-La powders

RI PT

using the continuous stiffness measurement (CSM) method.

SEM

M AN U

Fig. 1 shows the morphologies of Al6061 powders with 0.5 wt.% La as a function of milling time after 4 h, 8 h, 16 h and 24 h. At the early stage of milling, up to 4 h, see

TE D

Fig. 1a, the synthesized powders are partially refined and the morphologies of the particles are spherical and disk-like shapes. The alloyed powders can be further

EP

deformed and completely become disk-like shapes after 8 h and 16 h of milling, see Figs. 1b and 1c. It implies that as the milling time increased, ductile Al6061 particles

AC C

started to flatten and formed a laminated structure due to the high impact collision of the balls. During this stage of milling, it is believed that a cold welding process is dominant, which produces a change in the morphology of particles. At the final stage of milling, up to 24 h, see Fig. 1d, the milled powders have been refined and a considerable change in morphology of powders from a disk shape to equiaxial or

6

ACCEPTED MANUSCRIPT smaller flake-like shapes was observed. It reveals that a long milling duration results in excessive work hardening and an increment of fracture of aluminum powders.

morphology of synthesized material powders.

RI PT

Fracturing of brittle aluminum powders in the final stage controls the refinement and

SC

On the other hand, Fig. 2 shows the morphologies of Al6061 powders with a high amount of La (2 wt.%) as a function of milling time after 4 h, 8 h, 16 h and 24 h.

M AN U

After 4 h of milling, see Fig. 2a, the morphology of the powers has already become a disk-like shape. The synthesized particles can be further flattened into a thinner

TE D

disk-like shape with the increase in the milling time up to 16 h, see Figs. 2b and 2c. The results imply that the addition of a high level of La can act as a milling lubricant

EP

to prevent excessive cold welding and also to avoid agglomeration of the powders. Thus, the milling efficiency can be improved and accelerated the synthesis rates. In

AC C

this case, a large plastic deformation was generated at the early stage of milling and induced a drastic change of the morphology of powders from a rounded to disk-like shape. As the milling time increased up to 24 h, see Fig. 2d, the powders with a disk shape are further refined as the process of repeated fracturing and cold-welding was achieved.

7

ACCEPTED MANUSCRIPT XRD Fig. 3 shows XRD spectra of the Al6061 powders with different amounts of La as a function of milling time. The strong peaks of aluminum were clearly detected and

RI PT

corresponded to the (111), (200), (221) and (311) reflections. Furthermore, the XRD patterns exhibit the line broadening and a decrease in the diffraction intensity of the

SC

Al peaks as a function of milling time, which is caused by grain refinement and

M AN U

internal lattice strain. The enlarge image of the Al (111) diffraction peak in Fig. 3a also demonstrates that the peak is shifted towards lower diffraction angle as a function of milling time, which indicates that the formation of a solid solution of La in Al6061

powder.

TE D

matrix during mechanical alloying and the expansion in lattice parameter of the

EP

Fig. 4 shows the variation of crystallite size and lattice strain of the different model

AC C

alloys as a function of milling time. A similar trend was observed for all the model alloys, indicating the initial sudden drop of crystallite size up to 4 h of milling. Subsequently, the crystallite size shows only a steady-state value with further increase in milling time, which is the result of the balance between cold welding and fracturing. Fig. 4 also illustrates the lattice strain is significantly increased up to 4 h of milling, suggesting a large amount of defects such as dislocations, vacancies and stacking 8

ACCEPTED MANUSCRIPT faults was generated by severe plastic deformation at the early stage of milling.

RI PT

3.2 Microstructure evolution SEM observation

SC

Fig. 5a shows the microstructure of the Al6061-0.5La model alloy prepared by sintering of the powder milled for 24 h. A number of particles appeared as bright

M AN U

spots uniformly distributed in the Al6061 matrix were observed and contain a large amount of La, Al, Si and O. It is believed that the initial addition of La particles can

TE D

interact with the Al6061 matrix during mechanical alloying and form complex in-situ La oxide dispersoids. The phase identification and crystal structure of the small

EP

La-rich oxide will be further investigated and discussed in the TEM section. The SEM micrograph also shows the large dark particles having a high level of Mg and Si,

AC C

which might correspond to a formation of Mg2Si intermetallic compounds. As the La content increased to 1.2 wt.% La, a large bright particle containing La, Al and Si elements was observed in the microstructure of the model alloy, see Fig. 5b. The small bright spots are also represented as complex in-situ La oxide dispersoids. The microstructure of the model alloy with a high level of La content (2 wt.%) can be seen

9

ACCEPTED MANUSCRIPT in Fig. 5c. A large number of the agglomerated La-rich particles were revealed and non-uniformly distributed in the microstructure. The results suggest that a high

RI PT

concentration of La plays an important role in affecting the size, distribution and formation of La-rich particles.

SC

TEM investigation

Phase formation and crystal structure of the Al6061-1.2La alloy sample prepared by

M AN U

sintering of the powder milled for 24 h was further investigated by TEM. The TEM bright field image, see Fig. 6, revealed the microstructure consisted of the larger

TE D

rounded particles and the needle-like precipitates embedded in Al6061 matrix. At the position “A”, the coarse particle of about 300 nm was observed and contains a high

EP

level of Al, Si, La and O elements. The complex Al-Si-La-O oxide particle was further investigated to determine the crystal structure according to the selected area

AC C

diffraction (SAD) pattern. The oxide particle has been indexed as the La2(Al,Si)2O7 monoclinic structure with a=13.191Å, b=8.793Å, c=5.410Å, β=92.06°, along the zone axis of [0 0 1]. The observed large particle can be seen in the SEM investigation where small bright particles of La-rich oxides are distributed uniformly in the Al6061 matrix, see Fig. 5.

10

ACCEPTED MANUSCRIPT The results indicate that the rare earth element La has a high affinity with oxygen and most likely obtain in-situ fine lanthanum oxides such as La2O3 during mechanical

RI PT

alloying. Thus, the nano-size of in-situ La oxide dispersoids can further solid-state react with the constituent elements Al, Si, Fe, Mg in the Al6061 matrix and then

SC

formed the complex oxide phase of La2(Al,Si)2O7. It has been also reported that LaAlO3 can be synthesized through a solid-state reaction between La2O3 and

M AN U

transition alumina by a planetary ball milling at room temperature [20] In addition, a number of particles of needle-like phase consisting of Al, Fe, and Si

TE D

elements were observed in the Al6061 matrix, see the arrows in Fig. 6, suggesting the possible presence of β-AlFeSi phase. As closely observed by high-resolution TEM,

EP

the needle-like phase exhibited 20 nm diameters and about 70 nm lengths, as shown in Fig. 7a. According to the SAD, the needle-like shape of the iron-rich intermetallic

AC C

compound has been identified as the β-Al5FeSi phase and has a monoclinic structure with a=5.792Å, b=12.273Å, c=4.313Å, β=98.93°, along the zone axis of [-1-2 2]. α-Al(MnFe)Si and β-AlFeSi AlFeSi intermetallic compounds are typically found in the microstructure of the Al6061 composites. The presence of the needle-like β-AlFeSi phase is highly detrimental to the ductility and extrudability of Al [22]. It

11

ACCEPTED MANUSCRIPT has been proposed that the addition of small amount of La (0.1~0.2 wt.%) in aluminum alloys can result in transformation between the needle-like β-AlFeSi and

RI PT

the rounded �-AlFeSi phase [17,21]. Furthermore, in this study, the addition of La can also result in the formation of La containing intermetallic phases such as

SC

AlFeSiLa and AlCuLa confirmed by EDX as shown in Fig. 7b. It implies that the presence of AlFeSi and AlCu intermetallic phases can further interact with La and

M AN U

formed complex compounds during ball milling. Hosseinifar and Malakov [23] also proposed that La addition can lead to the formation of the La(Al,Si)2 phase.

TE D

XRD

Fig. 8 shows the XRD spectra of the sintered Al6061 model alloys and indicates that

EP

La-containing phases (LaSi2 and La2Si2O7) have been found in all the model alloys. The results correspond well with TEM investigation, identifying the formation of the

AC C

complex oxide phase of La2(Al,Si)2O7. Additionally, the small peaks corresponding to the Mg2Si and AlFeSi phases were found in the model alloy. The result is in agreement with SEM/TEM analyses that demonstrate the large dark particles of Mg-rich phase and the needle-like β-AlFeSi phase as shown in Fig. 5 and Fig. 7.

12

ACCEPTED MANUSCRIPT 3.3 Hardness and Nanoindentation The Vickers hardness of the different model alloys at various milling times are

RI PT

presented in Fig. 9. It can be seen clearly that the hardness increases significantly with the increasing milling time in the low La-containing samples (Al6061-0.5La and

SC

Al6061-1.2La). The hardness increased about 3.6 times from the initial to final stages of milling and a maximum hardness value of 88.5 HV was achieved after 24 h of

M AN U

milling in the Al6061-0.5La alloy. However, it was found that the high La content (2 wt.%) leads to only a slight increase of hardness with increasing milling time and

TE D

exhibits a lower hardness value of 55.9 HV for 24 h of milling. The results can be associated with the change of powder morphologies during mechanical alloying and

EP

the microstructural homogeneity and phase formation after sintering. In the model alloys with a low La, the morphology of the synthesized powders can be extremely

AC C

refined after 24 h of milling and tends to become equiaxial or smaller flake-like shapes. Furthermore, the low La containing alloys exhibit a homogeneous and dense microstructure with the fine La-rich oxide particles uniformly dispersed in the matrix; see Fig. 5. The presence of the fine dispersed oxide particles can act as pinning points

13

ACCEPTED MANUSCRIPT to inhibit dislocation movement and grain growth. Consequently, the hardness was significantly increased.

RI PT

On the other hand, a high level of La in the Al6061 alloy can promote the change of powder morphologies from a spherical to disk-like shape during mechanical alloying,

SC

which results in low densification of materials due to a large friction between powders and die wall during compaction process. The high La content alloy also demonstrates

M AN U

the formation of a large agglomerated particle and non-uniform microstructure. Nanoindentation was further used to determine the indentation hardness and elastic

TE D

modulus of the model alloys. The average indentation hardness of the Al6061-0.5La and Al6061-1.2La alloys samples is 1.25 GPa. The hardness value is much higher

EP

than that of the high La content alloy (0.87 GPa). This corresponds well with the results obtained from the Vickers hardness, see Fig. 9. In addition, it can be seen

AC C

clearly that the alloys with the low La contents also possess a higher elastic modulus (~85GPa) than that of the Al6061-2La sample (~53GPa). Load–displacement curves for three model alloys are shown in Fig. 11. It indicates that the all curves of each sample are consistent with each other. The sample with the high La content exhibits the effect of creep displacement, which could be attributed to the densification,

14

ACCEPTED MANUSCRIPT microstructure and interaction between the La-oxide dispersoids and the matrix of

RI PT

composites.

4. CONCLUSIONS

SC

In the present work, Al6061-based composites doped with rare earth element La by mechanical alloying were investigated. The in-situ La oxide dispersoids can be

M AN U

generated during processing, which play an important role in influencing the formation of intermetallic compounds, microstructural change and mechanical

TE D

behaviour of the Al6061 composites. The results show that the addition of a high level of La can change the morphology of milled powders and act as a milling lubricant to

EP

prevent excessive cold welding and agglomeration of the powders. Furthermore, a complex crystal structure of La2(Al,Si)2O7 phase oxide particles was found in the

AC C

microstructure, suggesting the solid-state reaction between the in-situ La oxides and the alloying elements in Al6061 matrix during ball milling. The addition of La can also result in the formation of La containing intermetallic phases. The results of Vickers hardness and nanoindentation show that the model alloys with low La contents exhibited relatively high hardness and elastic modulus. It can be associated

15

ACCEPTED MANUSCRIPT with a homogeneous and dense microstructure with the fine La-rich oxide particles uniformly dispersed in the matrix. These in-situ oxide dispersoids can act as pinning

RI PT

points to inhibit dislocation movement and grain growth.

SC

Acknowledgements

The authors would like to gratefully acknowledge financial support from Ministry of

M AN U

Science and Technology (MOST) Taiwan under the grant MOST 106-2221-E-259 -015-MY2. The authors would also like to thank Prof. Jian-Yih Wang, National Dong

References

TE D

Hwa University, for Al6061 material support.

EP

[1] Y.Q. Liu, H.T. Cong, W. Wang, C.H. Sun, H.M Cheng, AlN nanoparticle

AC C

reinforced nanocrystalline Al matrix composites: fabrication and mechanical properties, Mater. Sci. Eng. A 505 (2009) 151–156. https://doi.org/10.1016/j.msea.2008.12.045 [2] Z.Y. Ma, Y.L. Li, Y. Liang, F. Zheng, J. Bi, S.C. Tjong, Nanometric Si3N4 particulate-reinforced aluminum composite, Mater. Sci. Eng. A 219 (1996) 229–231. https://doi.org/10.1016/S0921-5093(96)10444-5 [3] M. Gupta, M.K. Surappa, S. Qin, Effect of interfacial characteristics on the

16

ACCEPTED MANUSCRIPT failure-mechanism mode of a SiC reinforced A1 based metal-matrix composite, J. Mater. Process. Technol. 67 (1997) 94–99. https://doi.org/10.1016/S0924-0136(96)02825-7

RI PT

[4] M. Rahimian, N. Parvin, N. Ehsani, Investigation of particle size and amount of alumina on microstructure and mechanical properties of Al matrix composite made by powder metallurgy, Mater. Sci. Eng. A 527 (2010) 1031–1038.

SC

https://doi.org/10.1016/j.msea.2009.09.034

[5] H. Ahamed, V. Senthilkumar, Hybrid Aluminium Metal Matrix Composites and

M AN U

Reinforcement Materials: A Review, Materials and Design 37 (2012) 182–192. DOI: 10.15680/IJIRSET.2016.0504224

[6] N. Nemati, R. Khosroshahi, M. Emamy, A. Zolriasatein, Investigation of microstructure, hardness and wear properties of Al–4.5 wt.% Cu–TiC nanocomposites

TE D

produced by mechanical milling, Materials and Design 32 (2011) 3718–3729. https://doi.org/10.1016/j.matdes.2011.03.056

EP

[7] J.B. Fogagnolo, M.H. Robert, J.M. Torralba, Mechanically alloyed AlN particle-reinforced Al-6061 matrix composites: Powder processing, consolidation and

AC C

mechanical strength and hardness of the as-extruded materials, Mater. Sci. Eng. A 426 (2006) 229–231. https://doi.org/10.1016/j.msea.2006.03.074 [8] N. Zhao, P. Nash, X. Yang, The effect of mechanical alloying on SiC distribution and the properties of 6061 aluminum composite, J. Mater. Process. Technol. 170 (2005) 586–592. https://doi.org/10.1016/j.jmatprotec.2005.06.037 [9] P. Krizik1, M. Balog, I. Matko, P. Svec Sr, M. Cavojsky and F. Simancik, The effect of a particle–matrix interface on the Young’s modulus of Al–SiC composites, J. 17

ACCEPTED MANUSCRIPT Compos. Mater. (2015) 1-10. https://doi.org/10.1177/0021998315571028 [10] Z. Zhang, T. Topping, Y. Li, R. Vogt, Y. Zhou, C. Haines, J. Paras, D. Kapoor, J.M. Schoenung and E.J. Lavernia, Mechanical behavior of ultrafine-grained Al

RI PT

composites reinforced with B4C nanoparticles, Scripta Materialia 65 (2011) 652–655. https://doi.org/10.1016/j.scriptamat.2011.06.037

[11] Y. Li, Z. Zhang, R. Vogt, J.M. Schoenung, E.J. Lavernia, Boundaries and

https://doi.org/10.1016/j.actamat.2011.08.005

SC

interfaces in ultrafine grain composites, Acta Materialia 59 (2011) 7206–7218.

M AN U

[12] C.-L. Chen and C.-H. Lin, Effect of Y2O3 and TiC Reinforcement Particles on Intermetallic Formation and Hardness of Al6061 Composites via Mechanical Alloying and Sintering. Metallurgical and Materials Transactions A 46 (2015) 3687-3695. https://doi.org/10.1007/s11661-015-2957-6

TE D

[13] N. Parvin, R. Assadifard, P. Safarzadeh, S. Sheibani, P. Marashi, Mater. Sci. Eng. A. 492 (2008) 134–140. https://doi.org/10.1016/j.msea.2008.05.004

EP

[14] Y. Wu, G.Y. Kim, A.M. Russell, Effects of mechanical alloying on an Al6061– CNT composite fabricated by semi-solid powder processing, Mater. Sci. Eng. A. 538

AC C

(2012) 164– 172. https://doi.org/10.1016/j.msea.2012.01.025 [15] H. Ahamed, V. Senthilkumar, Role of nano-size reinforcement and milling on the synthesis of nano-crystalline aluminium alloy composites by mechanical alloying, Journal of Alloys and Compounds. 505 (2010) 772–782. https://doi.org/10.1016/j.jallcom.2010.06.139 [16] S. Wang, H. Zhou, Y. Kang, The influence of rare earth elements on microstructures and properties of 6061 aluminum alloy vacuum brazed 18

ACCEPTED MANUSCRIPT joints, J. Alloys Compd. 352 (2003) 79–83. https://doi.org/10.1016/S0925-8388(02)01117-9 [17] M. Hosseinifar, D.V. Malakhov, Effect of Ce and La on microstructure and

(2008) 7157. https://doi.org/10.1007/s10853-008-3022-2

RI PT

properties of a 6xxx series type aluminum alloy, Journal of Materials Science. 43

[18] W. Yuan, Z. Liang, C. Zhang, L. Wei, Effects of La addition on the mechanical

SC

properties and thermal-resistant properties of Al–Mg–Si–Zr alloys based on AA 6201,

M AN U

Materials and Design. 34 (2012) 788–792. doi:10.1016/j.matdes.2011.07.003 [19] C. Suryanarayana and M.G. Norton: X-Ray Diffraction: A Practical Approach, Plenum Press, New York, 1998.

TE D

[20] Q. Zhang, F. Saito, Mechanochemical Synthesis of Lanthanum Aluminate by Grinding Lanthanum Oxide with Transition Alumina, J. Am. Ceram. Soc. 83 (2000)

EP

439–441. https://doi.org/10.1111/j.1151-2916.2000.tb01215.x

AC C

[21] A.K. Gupta, D.J. Lloyd, S.A. Court, Precipitation hardening processes in an Al– 0.40% Mg–1.3% Si–0.25% Fe aluminum alloy, Mater. Sci. Eng. A. 301 (2001) 140– 146. https://doi.org/10.1016/S0921-5093(00)01814-1 [22] N.C.W. Kuijpers, F.J. Vermolen, C. Vuik, P.T.G. Koenis, K.E. Nilsen, S.V.D. Zwaag, The dependence of the b-AlFeSi to a-Al (Fe Mn) Si transformation kinetics in Al–Mg–Si alloys on the alloying elements. Mater Sci Eng A 394 (2005) 9–19. 19

ACCEPTED MANUSCRIPT https://doi.org/10.1016/j.msea.2004.09.073 [23] M. Hosseinifar and D.V. Malakhov, The sequence of intermetallics formation

RI PT

during the solidification of an Al-Mg-Si alloy containing La, Metallurgical and Materials Transactions A. 42 (2011) 825–833.

SC

https://doi.org/10.1007/s11661-010-0453-6

M AN U

Table Caption

Table 1 Metals content of three model alloys (wt.%)

TE D

Figure Captions

Fig. 1. The morphology of the Al6061-0.5La powders as a function of milling time

EP

for (a) 4 h, (b) 8 h, (c) 16 h and (d) 24 h.

AC C

Fig. 2. The morphology of the Al6061-2La powders as a function of milling time for (a) 4 h, (b) 8 h, (c) 16 h and (d) 24 h. Fig. 3. XRD spectra of the Al6061 powders with different amounts of La milled for different milling durations: 0 h, 4 h, 8 h, 16 h and 24 h. Fig. 4. Crystallite size and lattice distortion of the model alloy powders as a function of milling time (a) Al6061-0.5La, (b) Al6061-1.2La and (c) Al6061-2La. 20

ACCEPTED MANUSCRIPT Fig. 5. SEM images of the sintered model alloys (a) Al6061-0.5La, (b) Al6061-1.2La and (c) Al6061-2La.

RI PT

Fig. 6. TEM image of the La-Al-Si-O oxide formed in the Al6061-1.2La sample. Fig. 7. TEM images of (a) the needle-like AlFeSi intermetallic phase and (b) the

SC

AlFeSiLa phase formed in the Al6061-1.2La alloy. Fig. 8. XRD spectra of the sintered Al6061 model alloys.

M AN U

Fig. 9. Variation of Vickers hardness of the Al6061 model alloys as a function of milling time.

TE D

Fig. 10. Nanoindentation measurements of the Al6061 model alloys (a) indentation hardness and (b) elastic modulus.

EP

Fig. 11. Load–displacement curves of (a) Al6061-0.5La, (b) Al6061-1.2La and (c)

AC C

Al6061-2La model alloys.

21

ACCEPTED MANUSCRIPT Table 1 Metals content of three model alloys (wt.%) Model alloys Mg Si Fe Cu Al6061-0.5La 0.8-1.2 0.65 0.45 0.15

Cr 0.1

Al Bal.

La 0.5

0.8-1.2

0.65

0.45

0.15

0.1

Bal.

1.2

Al6061-2La

0.8-1.2

0.65

0.45

0.15

0.1

Bal.

2.0

AC C

EP

TE D

M AN U

SC

RI PT

Al6061-1.2La

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT RESEARCH HIGHLIGHTS In-situ La oxide dispersoids are formed during ball milling.




Addition of La can change the morphology of milled powders.




Fine La-Al-Si-O oxides and needle-like AlFeSi phases are found.




Low La content alloys have a dense and uniform microstructure.




High hardness and modulus are obtained at low La content alloys.

AC C

EP

TE D

M AN U

SC

RI PT