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Cu alloy composites
Materials Science & Engineering A 770 (2020) 138547
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Materials Science & Engineering A journal homepage: http://www.elsevier.com/locate/msea
Compaction pressure and Si content effects on compressive strengths of Al/ Si/Cu alloy composites Yuri A. Meyer a, Rodrigo S. Bonatti a, Diego Costa a, Ausdinir D. Bortolozo a, b, �rio a, b, * Wislei R. Oso a
School of Technology, University of Campinas UNICAMP, Limeira, SP, 13484-332, Brazil School of Applied Sciences / FCA, Research Group in Manufacturing Advanced Materials (CPMMA), University of Campinas, UNICAMP, Campus Limeira, 1300, Pedro Zaccaria St., Jd. Sta Luiza, 13484-350, Limeira, SP, Brazil
b
A R T I C L E I N F O
A B S T R A C T
Keywords: Recycled Al-based alloy powder Powder metallurgy (P/M) Recycling powder Compressive behavior Intermetallic T4 temper
This paper is focused on the effect of distinctive compaction pressures and Si content on the resulting mor phologies and compressive strengths (CS) of the sintered and quenched composites. The powder particles from the as-cast Al-9wt.%Si and Al-5wt.%Cu alloys constituting recycled powders are used. A mixture 1:1 wt ratio between aforementioned casting alloys is also examined. With the applied compaction pressure, the resulting microstructural array has no modified. After heat-treating, the chemical content has important role on the mechanical behavior. It is found that the CS increases with the increase of the compaction pressure. Also, when the Al–5Cu alloy powder is used, the highest CS is attained. The intermediate CS is that of the mixture composite (1:1) and the lowest is obtained when the Al–9Si sample powder is used. The specific strengths are also deter mined, which favor the composite constituted by the Al–5Cu alloy powder. This induces both the economical and environmental-friendly aspects intending to produce engineering components using as-recycled powders.
1. Introduction In the last 20 years, a number of experimental investigations considering Al-based metal matrix composite (AMMCs) with distinctive and various industrial applications have been focused [1–3]. The main reason is associated with low density, high strength, and reasonable corrosion resistance [1–3]. The nature of particles and the mechanics used to incorporate the reinforcing particle determine the microstruc tural array, and consequently, its corresponding final properties are affected [3,4]. Also, it is reasonably recognized that the size and dis tribution [5–9] and the interactions between particles and matrix significantly affect the resulting properties. Also, other metallurgical parameters applied in the stages of powder metallurgy (P/M) can affect the microstructure, and consequently, the resulting properties (e.g. compaction pressure, sintering temperature and time) are also modified [2]. In the present investigation, the AMMCs utilizing powders of two distinctive as-cast Al-based alloys (i.e. Al-5 wt.% Cu and Al-9 wt.% Si) are focused. These will constitute the recycled composites with a po tential utilization in automobile components. The selection of these two
* Corresponding author. School of Technology, University of Campinas E-mail address: [email protected] (W.R. Os� orio).
examined alloys is due to their corresponding contents in both auto mobile and aerospace industries are widely applied [10]. Al–Cu and Al–Si alloys are commonly designated as 2xxx and 3xx.x series family alloys. Also, they are applied for many decades in fuselages, wing sking, combustion engines and cylinders [10–12]. The binary Al–Cu casting alloys containing between 4% and 10 wt% Cu are widely used [10–12]. When the Al–Si casting alloys are considered, into the automobile in dustry, the majority chemical composition ranging between 5 and 7% wt.% Si is considered. Additionally, the manufacturing routes using sand molds and using another route called as investment casting is also considered. On the other hand, 7 and 9% wt. %Si contents are used when the casting route using permanent mold is considered [11,12]. It is remarkable that in this present investigation, no alternative routes commonly used in the P/M are not carried out, e.g. infiltration casting, gravity casting, vortex [13-15]. Additionally, it is remembered that no casting procedure is applied. This indicates that a reasonable electrical economy and a lower loss of material are attained. Although, it is recognized that the powder production has a high cost limiting the P/M application, the waste Al-based alloys originated from the machining, drilling, turning can be used as a recycled material. With
UNICAMP, Limeira, SP, 13484-332, Brazil.
https://doi.org/10.1016/j.msea.2019.138547 Received 22 June 2019; Received in revised form 19 September 2019; Accepted 11 October 2019 Available online 12 October 2019 0921-5093/© 2019 Elsevier B.V. All rights reserved.
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Materials Science & Engineering A 770 (2020) 138547
Fig. 1. Schematic representation of: (a) an as-cast powder (as-received) and compacted powder and the indentation marks in the Al–Cu (b) and Al–Si (c) cast ing alloys.
composite containing an “in-situ” Al2Cu intermetallic compound (IMC), which are formed during solidification (at eutectic temperature, ~548 � C) and the resulting dispersed IMC with a reasonable interfacial bonding with Al matrix [14]. Similarly, the as-cast Al–Si alloy also constitutes a eutectic mixture (lamellar morphology) formed at eutectic temperature (~577 � C). In this present investigation, the powder particles of the two distinctive binary systems, i.e. Al–Cu and Al–Si alloys, are considered. This certificates the effect of Si content on the resulting compressive strengths of the three different composites containing only powders of Al–Cu, Al–Si and a mixture 1:1 (weight ratio). For this purpose, three distinctive compaction pressures, followed by sintering and a quenching are provided.
this, it seems that the components using the P/M (compaction, sintering and eventually a quenching) can reasonably be produced. In the literature, the experimental investigations concerning to the recycled Al-based casting alloy powders in order to constitute compos ites without casting route are scarce [13,14]. It is also scarce those studies focusing on the recycled Al alloys powders using simplified compaction, sintering and quenching. Additionally, the literature has demonstrated that the complementary or additional manufacturing stages (e.g. ball mill mixing and hot pressing, and extrusion) are pro posed [13-15]. With this, additional and an increased total manufacturing cost is induced. Based on the limitations and relative cost associated with the manufacturing routes aforementioned, the novelty intrinsically pro vided in this present experimental investigation concerns to the utili zation of the powders from the as-cast Al-9 wt.% Si and Al-5 wt.% Cu alloys constituting elemental recycled powders to produce the three composites proposed. It is worth noting that the composites constituted by Al-based alloys reinforced with ceramic particles (e.g. SiC) [1–4, 12–14], which are manufactured by using the casting route are commonly investigated and reported. Additionally, the commercial Al-based alloy powders (e.g. Alumix 431 and 231 [7–9]) are also widely applied. It can clearly be perceived that the former composites contain ceramic particles as reinforcement while the latter consider strength ening elements (e.g. Mg, Zn, Cu) constituting intermetallics contributing with reinforcing mechanism. Tash and Mahmoud [14] have recently developed an Al-based
2. Experimental procedure 2.1. Materials Two distinctive Al alloys widely used in automobile and aerospace industries were considered, i.e. Al–9%Si alloy (in weight percent, wt.%) and Al-5 wt.% Cu alloy. This constitutes the reason for the selection of these kinds of the recycled powders to be used. An as-cast Al–9Si alloy commercially used by Alux company was supplied and used in the ex perimentations (www.aluxdobrasil.com.br). The chemical composition has Si content between 8.5 and 9.5 wt%, 0.8 and 1.2 wt% Fe, 0.5 and 0.7 wt% Mg, 0.4 and 0.6 wt% Cu, 0.1 and 0.2 wt% Mn 0.1 and < 0.02 wt 2
Y.A. Meyer et al.
Materials Science & Engineering A 770 (2020) 138547
Fig. 2. Typical SEM images (with SE-secondary and BSE-backscattering electrons) of the compacted þ sintered þ quenched composites produced using: (a) powder of as-cast Al–5Cu alloy, (b) Al–9Si alloy and (c) Mixture 1:1 between Al–9Si þ Al–5Cu (Al4⋅5Si-2.5Cu). Inside powder distribution particles are also depicted.
3
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Materials Science & Engineering A 770 (2020) 138547
% Sn. Another as-cast Al–5Cu (containing 0.2 wt % Fe, 0.08 wt% Zn, 0.10 wt% Si, and other <0.01 wt%) was produced in our laboratory using pure both Al (99.88 wt%) and Cu (99.93 wt%). \ Since it is aimed to constitute powder from these as-cast alloys simulating recycled powders, the cast ingots were drilled and adequate powder portions (~2 g) to constitute the samples were obtained. Finer size powders ranging between 120 and 180 μm of the Al–9Si alloy with a spheroidal morphology are used. When an as-cast Al–5Cu alloy is dril led, elongated particles ranged between 150 (�90) μm in width and 450 (�140) μm in length are obtained. When a mixture 1:1 between these two elemental alloy powders is considered, of about 50 (�5)% of each one of the aforementioned sizes and morphologies are attained, as depicted in Fig. 2. 2.2. Sample preparation and characterization Three distinctive compaction pressures (i.e. 125, 250, and 430 � 5 MPa) were adopted. This selection is based on the commonly applied loading and compaction pressure used into common industrial applications. A single acting hydraulic press was used. A VC131 (AISI D6) material die with a hardness of about 60 (�5) HRc (http://www.vi llaresmetals.com.br) was used. Cylindrical pellets of 10 mm2 with resulting areas of 78.5 (�0.5) mm2 and a height-to-diameter ratio 1.1:1 are produced (ASTM E8M/04). A muffle type furnace adopting an inert atmosphere (using ~5 L.p.m of argon flow) to provide the heat-treating was used. A heating rate of 10 � C/min and a plateau at 540 (�3) � C during 1 h are applied. This sintering time is coincident with the solution since a T4 quenching (water at ~23 � C) is carried out. The sintering temperature is based on 70 and 85% of the melting temperature [15–18] and those eutectic temperatures considering that no liquid portions are formed. In order to characterize the resulting microstructural arrays, powder sizes and morphologies and formed phases, a scanning electron micro scope, an optical microscope and a diffractometer (40 kV and 30 A, Cu Kα radiation and wavelength of 0.15406 nm) were used. A gauge length marked at ~15 (�0.5) mm and a diameter of 10 (�0.1) mm2 constitute the resulting sectional area of ~78.5 (�0.5) mm2. An electro hydraulic servo machine applying a strain rate ~2.5 � 10 4s 1 with speed cross head of 0.25 mm/min [18] was used. 3. Results and discussion 3.1. Powder morphology It is firstly elucidated that the examined powder particles of the ascast Al-5 wt.% Cu and Al-9 wt.% Si alloys are used. The resulting sam ples are compacted using distinct compaction pressures. Sequentially, the samples are sintered and water quenched. Based on this and previous reports in literature [13–16], the Al-based composites are constituted due to its eutectic morphologies are formed, i.e. Al2Cu and lamellar Si particles. From the industrial point of view, or intending a mechanical application, a sample solely compacted has no interesting. This is based on the fact that other additional manufacturing routes are commonly practiced (e.g. sintering and/or other heat-treating). Although an only compacted sample is not attractive, it is worth noting that the applied compaction pressure has no substantial effect on the resulting micro structural arrays. This mainly in terms of the chemical composition and phases formed. This means that after the compaction action, the observed as-cast phases and chemical compositions of the compacted samples are remained. Also, the compacted samples have their dendritic arrays reasonably remained. Evidently, a slightly deformed dendritic array is observed. However, this affects more substantially the resulting hardness, i.e. before the compaction action, both the as-cast Al–Cu and Al–Si alloy powder particles have average hardness values of about 82 (�5) HV, while the compacted samples have slightly increased to 95 (�5) HV. Before the compaction action, the corresponding dendritic arm
Fig. 3. Experimental results of compressive strength of the examined com posites: (a) comparison among the Al–9Si, Al–5Cu and Al-4.5Si-2.5Cu alloy composites, (b) and (c) the Al–5Cu and Al–9Si composites considering three distinct compaction pressures.
spacings are of about 30 (�5) μm, as also previously reported [17]. Fig. 1(a) shows a schematic representation of a typical compacted powder and micrographs depicting the indented sample of Al–Cu and Al–Si, as shown in Fig. 1(b) and (c), respectively. After the compaction, followed by sintering and water-quenching, the dendritic spacings seem to be slightly lower (~18 � 3 μm) than the as-cast condition, as it will forwardly be shown. Also, after the applied quenching, the main 4
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Materials Science & Engineering A 770 (2020) 138547
detected phases are remained, but a more substantial modification in the resulting microstructural array and hardness are observed [17]. The Al-5 wt.% Cu alloy powder has evidenced a hardness of about 72 � 5 HV, while a hardness ~60 (�8) HV is observed when the Al-9wt.% Si alloy powder is analyzed. This is intimately associated with incoher ent/coherent Al2Cu transformation and annealing occurred predomi nantly at Al-rich matrix, as also previously reported [17]. Considering that no substantial modifications in the phase forma tion, chemical composition and resulting microstructural array (i.e. structure inside powder particle) are not responsible for those distinctive compressive strengths obtained, as will forwardly be discussed, the morphology of the powders are examined. Typical SEM (scanning electron microscope) images of the sintered composite samples (compacted under 430 MP) using only powders of the as-cast Al–5Cu alloy are shown in Fig. 2(a). Both the secondary electrons (SE) and backscattering electrons (BSE) images are shown. Also, the powder distributions are also depicted. Predominant elongated powder particles are characterized. These are majority sized in width between 45 and 155 μm (~55%), and their length ranging be tween ~ 300 and 425 μm (~75%). This elongated powder particle seems to be intimately correlated with the resulting dendritic array and distributed Al2Cu at interdendritic regions. Fig. 2(b) and (c) show SEM images of the proposed composite using a mixture 1:1 between Al–9Si þ Al–5Cu (Al4⋅5Si-2.5Cu) and using only powders of the as-cast Al–9Si alloy, respectively. It is clearly observed that the sintered Al–9Si alloy composite has predominant particles (spheroids) sizing between ~45 and 180 μm (~55%), as shown in Fig. 2(b). It is remarked that the as-cast Al–9Si alloy powder has also provided spheroidal-like particles. Also, this seems to be intimately associated with the resulting dendritic array and Si needle-like distributed at eutectic region (interdendritic region), which provides a fracture mechanism inducing to predominant sphe roidal particles, as also previously reported [17]. When a mixture powder particle using both the Al–5Cu and Al–9Si alloys is used (constituting the composite Al-4.5Si-2.5Cu), the width and length are between 45–180 μm (~66%) and 270–360 μm (~68%), respectively, as indicated into Fig. 2(c). With these aforementioned observations, it is evidenced that the Al–Si powder has a trend to spheroid-like morphology, but the size magnification of the examined powder particles are very similar. Pre vious investigation [17] has demonstrated that the morphology and size magnification have no substantial effect on both the densification level of the compacted samples. Based on aforementioned assertions, it is remained to investigate the solute content (i.e. Cu and Si contents) and their possible variations in terms of the microstructural arrangement, the phase constitution and the distribution/morphology of the Al and Cu rich region after sintering and quenching content.
Fig. 4. Experimental relation between: (a) yield strength (YS) and ultimate compressive strength (UCS) vs. compaction pressure (CP) of the examined Al–5Cu and Al–9Si alloy powder composites.
microwave sintered-hot extruded). However, this slight comparison helps to demonstrate that the attained compressive results can be industrially adopted and they are competitive. Although other low concentrations (e.g. 1.5 in a vol%) and nature of the ceramic reinforce particles (e.g. SiC, Al2O3, or Si3N4) are used, it seems that the attained compressive results provided by using the recycled powders from the as-cast Al-based alloys can be potentially considered. Although it is reasonably recognized that the operational parameters significantly affect the resulting mechanical behavior of the AMMCs, as previously reported [1–7,13–19], the examined Al-based composites produced using as-cast powders were produced using three distinct compaction pressures. Besides, the sintering time (1 h) and temperature (540 � C) are also applied. Into the industrial sectors using P/M, this compaction pressuring range (i.e. between 100 and 600 MPa) is commonly utilized [13–16,18–22]. Fig. 3(b) and (c) shows the compressive strength results of the composites using the powder particles of the as-cast Al–5Cu and Al–9Si alloys as a function of three distinct compaction pressures, respectively. As expected, the compressive strengths (both UCS and YS) have decreased with the decrease of the compaction pressure. Although these values have decreased, the Al–5Cu alloy composite at the other two pressures exhibits their corresponding values higher than those obtained when the Al–9Si alloy composite is considered. The differences between the UCS of Al–5Cu and Al–9Si are ~1.5x up to the 250 MPa and ~1.8x when a 250 MPa of the compaction pressure is considered. It should also be mentioned that both the Al–5Cu and Al–9Si alloy composites have
3.2. Solute content and compaction pressure effects Fig. 3(a) shows the experimental curves of the compressive strengths of the examined Al–9Si, Al–5Cu and Al-4.5Si-2.5Cu alloy composites. These samples were compacted under a 430 (�4) MPa, followed by a heat-treated at 540 � C (solution heat treating). Sequentially, a T4 water quenching was carried out. It can be seen that the ultimate compressive strength (UCS) related with the Al–9Si composite sample has achieved ~268 (�8) MPa. This means that the UCS is ~1.5 times higher than the UTS result of the Al–9Si sample. Interestingly the intermediate result of the compressive behavior is that of the Al-4.5Si-2.5Cu sample (~195 � 6 MPa), while the lowest UCS is that of the Al–9Si sample composite. Also, the compressive yield strengths (YS) of the examined samples reveal similar trend when the composites with Si content are analyzed. The highest YS value is that of the Al–5Cu sample. Similar UCS results are also reported when the same order of magnitude for the strain rate was also applied [13]. Also, a similar YS result is also reported when an Al-1.5SiC (vol%) composite is investigated. Evidently that other distinct solute contents and operational parameters were applied (e.g. 5
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Materials Science & Engineering A 770 (2020) 138547
Fig. 5. (a) Resulting microstructural array of an Al-4.5Si-2.5Cu composite evidencing distinctive nature of the powders from Al–5Cu and Al–9Si (b) when compared with the elemental as-cast alloys (c).
their UCS and YS differentiating of about 2.5x under a compaction pressure of 430 MPa. Also it is decreased of about 1.6x under 250 MPa and it has decreased of about 1.4x when a 125 MPa is applied. This in dicates that the compaction pressure (CP) has a non-linear effect on the yield strength (YS) parameter, as depicted in Fig. 4(a). On the other hand, the linear trends are clearly characterized when the ultimate compressive strength (UCS) and CP for both the examined composites (Al–5Cu and Al–9Si) are considered, as depicted in Fig. 4(b). Fig. 5(a) shows a typical resulting microstructure array of a mixed powders between the Al–9Si and Al–5Cu casting alloys (1:1 wt ratio). The optical images show light (or white) region constituting of the ascast Al–5Cu alloy powders are characterized. On the other hand, the gray regions (or white and gray) correspond with the Al–9Si casting alloy powders, which is constituted by lamellar (needle-like) morphology between Al and Si rich-phases [11,13,17–23], as shown in Fig. 4(b). Similarly, the correspond Al–5Cu alloy powder has also an Al-rich region with Al2Cu [11, 17, 24] contrasted (dark region in left position in Fig. 5(b)). The resulting microstructure arrays shown in Fig. 5(b) are
considerably different from those depicted in Fig. 5(c). The former are constituted when the sintering and quenching are carried out, while the latter are those corresponding with the resulting as-casting microstruc ture arrays (or as-received powders). An as-received Al–5Cu alloy sample (i.e. as-casting sample) has distributed Al2Cu intermetallic par ticles into the interdendritic region. This constitutes an expected eutectic mixture due to the solidification route applied [11; 17, 22–24]. After 1 h of the sintering time, a solution treatment is provided. Subse quently, after quenching, a possible coarsening of Al-rich dendritic arms seems to be occurred, as observed when Fig. 5(b) and (c) are compared. Fig. 5(c) clearly reveals that both the as-cast Al–5Cu and Al–9Si alloys have their corresponding averages of the dendritic arm spacings of about 20 (�5) and 30 (�5) μm, respectively. On the other hand, after the adopted heat-treating the dendritic spacing formations are not clearly characterized. Besides, the Al–9Si alloy composite has its resulting Si particles considerably modified, as also previously reported [20,22] when a T4 treating is also carried out. Thus, the needle-like Si morphology is modified to a spheroid-like Si morphology, as demon strated at right side in Fig. 5 (b). 6
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Materials Science & Engineering A 770 (2020) 138547
Acknowledgements
Table 1 Experimental results of ultimate compressive strengths (UCS), yield strengths (YS) and calculated specific strengths (SS) and relative weights of each examined Al–9Si, Al–5Cu and Al-4.5Si-2.5Cu composites. Alloy composite
Compaction Pressure (MPa)
UCS (MPa)
YS (MPa)
SS (a) 103 x m2 s 2
Relative lightweight (b)
Al–9Si
430
180 (�8) 90 (�3) 30 (�8) 268 (�8) 138 (�3) 58 (�2) 195 (�6)
64 (�4) 45 (�2) 22 (�2) 104 (�3) 85 (�3) 39 (�1) 71 (�2)
68 (�2)
1
250 125 Al–5Cu
430 250 125
Al-4.5Si2.5Cu
430
Financial support provided by FAEPEX-UNICAMP (#2478/18), and CNPq, #304950/2017-3 and #405602/2018-9). Also Mr. Alexandre Litzberger, manufacturing manager at Alux do Brasil and Mr. Luiz Antonio Garcia due to supplying materials and valuable technical contributions. References
–
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– 89 (�2)
1.13
–
–
–
–
69 (�2)
1.06
a
The SS (specific strength) values were determined using UCS per theoretical density. These values of the Al–5Cu, Al–9Si and Al-4.5Si-2.5Cu alloys compos ites are: 3.01, 2.67 and 2.84 g x cm 3, respectively. b The relative lightweight effect is based on the their corresponding theoret ical densities.
In this condition, due to the coarsened Al-rich phase and their ductile characteristic, it contributes with absorption of the energy and the Al2Cu shows an important role on the blocking of the dislocation motion. The as-cast Al–9Si alloy, due to the compaction pressure and sintering, has certain clusters of Si (brittle) in a “pseudo-spheroid” forming a “lamellar” morphology with a ductile Al-rich matrix. Under a compressive pressure, some microcracks at interface between ductile Almatrix and Si particle can be provided, as previously reported [21]. With this, it is observed that resulting mechanical behavior is decreased, as demonstrated in the experimental compressive strength plots. Table 1 shows the compressive behavior of the examined Al-based composites. Considering the UCS results concatenated with light weight, it can be seen that the Al–5Cu is of about 13% weightier than other two composites examined. However, their corresponding specific strengths (SS) are approximately 30% higher than other two composites examined. It is also presumed that the relative cost is ranging between 8 and 10% cheaper than the Al–9Si sample. This means that an econom ical and an environmentally friendly aspects favor the Al–5Cu alloy examined. This induces to feasibility to apply the Al–5Cu alloy powders as recycled powders in order to possibly constitute automobile components. 4. Conclusions From the experimentations and analyses provided, the follow con clusions can be drawn. It is found that the increase of the compaction pressure, an increasing in the compressive strength is also attained. It is also found that the highest compressive behavior is that of the Al-5 wt.% Cu alloy powder composite. This is followed by a result from a mixture 1:1 wt ratio between the Al-5 wt.% Cu and Al-9 wt.% Si composites. The lowest compressive behavior is that of the Al-9 wt.% Si composite. When the as-cast Al-9 wt.% Si alloy powder is used, a cluster of brittle Si particles is formed and microcracks induces to a decreasing of the me chanical behavior when Si particles are involved. This indicates that the chemical content powder and the subsequent heat-treating have important roles on the resulting compressive strengths.
7
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Materials Science & Engineering A journal homepage: http://www.elsevier.com/locate/msea
Compaction pressure and Si content effects on compressive strengths of Al/ Si/Cu alloy composites Yuri A. Meyer a, Rodrigo S. Bonatti a, Diego Costa a, Ausdinir D. Bortolozo a, b, �rio a, b, * Wislei R. Oso a
School of Technology, University of Campinas UNICAMP, Limeira, SP, 13484-332, Brazil School of Applied Sciences / FCA, Research Group in Manufacturing Advanced Materials (CPMMA), University of Campinas, UNICAMP, Campus Limeira, 1300, Pedro Zaccaria St., Jd. Sta Luiza, 13484-350, Limeira, SP, Brazil
b
A R T I C L E I N F O
A B S T R A C T
Keywords: Recycled Al-based alloy powder Powder metallurgy (P/M) Recycling powder Compressive behavior Intermetallic T4 temper
This paper is focused on the effect of distinctive compaction pressures and Si content on the resulting mor phologies and compressive strengths (CS) of the sintered and quenched composites. The powder particles from the as-cast Al-9wt.%Si and Al-5wt.%Cu alloys constituting recycled powders are used. A mixture 1:1 wt ratio between aforementioned casting alloys is also examined. With the applied compaction pressure, the resulting microstructural array has no modified. After heat-treating, the chemical content has important role on the mechanical behavior. It is found that the CS increases with the increase of the compaction pressure. Also, when the Al–5Cu alloy powder is used, the highest CS is attained. The intermediate CS is that of the mixture composite (1:1) and the lowest is obtained when the Al–9Si sample powder is used. The specific strengths are also deter mined, which favor the composite constituted by the Al–5Cu alloy powder. This induces both the economical and environmental-friendly aspects intending to produce engineering components using as-recycled powders.
1. Introduction In the last 20 years, a number of experimental investigations considering Al-based metal matrix composite (AMMCs) with distinctive and various industrial applications have been focused [1–3]. The main reason is associated with low density, high strength, and reasonable corrosion resistance [1–3]. The nature of particles and the mechanics used to incorporate the reinforcing particle determine the microstruc tural array, and consequently, its corresponding final properties are affected [3,4]. Also, it is reasonably recognized that the size and dis tribution [5–9] and the interactions between particles and matrix significantly affect the resulting properties. Also, other metallurgical parameters applied in the stages of powder metallurgy (P/M) can affect the microstructure, and consequently, the resulting properties (e.g. compaction pressure, sintering temperature and time) are also modified [2]. In the present investigation, the AMMCs utilizing powders of two distinctive as-cast Al-based alloys (i.e. Al-5 wt.% Cu and Al-9 wt.% Si) are focused. These will constitute the recycled composites with a po tential utilization in automobile components. The selection of these two
* Corresponding author. School of Technology, University of Campinas E-mail address: [email protected] (W.R. Os� orio).
examined alloys is due to their corresponding contents in both auto mobile and aerospace industries are widely applied [10]. Al–Cu and Al–Si alloys are commonly designated as 2xxx and 3xx.x series family alloys. Also, they are applied for many decades in fuselages, wing sking, combustion engines and cylinders [10–12]. The binary Al–Cu casting alloys containing between 4% and 10 wt% Cu are widely used [10–12]. When the Al–Si casting alloys are considered, into the automobile in dustry, the majority chemical composition ranging between 5 and 7% wt.% Si is considered. Additionally, the manufacturing routes using sand molds and using another route called as investment casting is also considered. On the other hand, 7 and 9% wt. %Si contents are used when the casting route using permanent mold is considered [11,12]. It is remarkable that in this present investigation, no alternative routes commonly used in the P/M are not carried out, e.g. infiltration casting, gravity casting, vortex [13-15]. Additionally, it is remembered that no casting procedure is applied. This indicates that a reasonable electrical economy and a lower loss of material are attained. Although, it is recognized that the powder production has a high cost limiting the P/M application, the waste Al-based alloys originated from the machining, drilling, turning can be used as a recycled material. With
UNICAMP, Limeira, SP, 13484-332, Brazil.
https://doi.org/10.1016/j.msea.2019.138547 Received 22 June 2019; Received in revised form 19 September 2019; Accepted 11 October 2019 Available online 12 October 2019 0921-5093/© 2019 Elsevier B.V. All rights reserved.
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Fig. 1. Schematic representation of: (a) an as-cast powder (as-received) and compacted powder and the indentation marks in the Al–Cu (b) and Al–Si (c) cast ing alloys.
composite containing an “in-situ” Al2Cu intermetallic compound (IMC), which are formed during solidification (at eutectic temperature, ~548 � C) and the resulting dispersed IMC with a reasonable interfacial bonding with Al matrix [14]. Similarly, the as-cast Al–Si alloy also constitutes a eutectic mixture (lamellar morphology) formed at eutectic temperature (~577 � C). In this present investigation, the powder particles of the two distinctive binary systems, i.e. Al–Cu and Al–Si alloys, are considered. This certificates the effect of Si content on the resulting compressive strengths of the three different composites containing only powders of Al–Cu, Al–Si and a mixture 1:1 (weight ratio). For this purpose, three distinctive compaction pressures, followed by sintering and a quenching are provided.
this, it seems that the components using the P/M (compaction, sintering and eventually a quenching) can reasonably be produced. In the literature, the experimental investigations concerning to the recycled Al-based casting alloy powders in order to constitute compos ites without casting route are scarce [13,14]. It is also scarce those studies focusing on the recycled Al alloys powders using simplified compaction, sintering and quenching. Additionally, the literature has demonstrated that the complementary or additional manufacturing stages (e.g. ball mill mixing and hot pressing, and extrusion) are pro posed [13-15]. With this, additional and an increased total manufacturing cost is induced. Based on the limitations and relative cost associated with the manufacturing routes aforementioned, the novelty intrinsically pro vided in this present experimental investigation concerns to the utili zation of the powders from the as-cast Al-9 wt.% Si and Al-5 wt.% Cu alloys constituting elemental recycled powders to produce the three composites proposed. It is worth noting that the composites constituted by Al-based alloys reinforced with ceramic particles (e.g. SiC) [1–4, 12–14], which are manufactured by using the casting route are commonly investigated and reported. Additionally, the commercial Al-based alloy powders (e.g. Alumix 431 and 231 [7–9]) are also widely applied. It can clearly be perceived that the former composites contain ceramic particles as reinforcement while the latter consider strength ening elements (e.g. Mg, Zn, Cu) constituting intermetallics contributing with reinforcing mechanism. Tash and Mahmoud [14] have recently developed an Al-based
2. Experimental procedure 2.1. Materials Two distinctive Al alloys widely used in automobile and aerospace industries were considered, i.e. Al–9%Si alloy (in weight percent, wt.%) and Al-5 wt.% Cu alloy. This constitutes the reason for the selection of these kinds of the recycled powders to be used. An as-cast Al–9Si alloy commercially used by Alux company was supplied and used in the ex perimentations (www.aluxdobrasil.com.br). The chemical composition has Si content between 8.5 and 9.5 wt%, 0.8 and 1.2 wt% Fe, 0.5 and 0.7 wt% Mg, 0.4 and 0.6 wt% Cu, 0.1 and 0.2 wt% Mn 0.1 and < 0.02 wt 2
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Fig. 2. Typical SEM images (with SE-secondary and BSE-backscattering electrons) of the compacted þ sintered þ quenched composites produced using: (a) powder of as-cast Al–5Cu alloy, (b) Al–9Si alloy and (c) Mixture 1:1 between Al–9Si þ Al–5Cu (Al4⋅5Si-2.5Cu). Inside powder distribution particles are also depicted.
3
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% Sn. Another as-cast Al–5Cu (containing 0.2 wt % Fe, 0.08 wt% Zn, 0.10 wt% Si, and other <0.01 wt%) was produced in our laboratory using pure both Al (99.88 wt%) and Cu (99.93 wt%). \ Since it is aimed to constitute powder from these as-cast alloys simulating recycled powders, the cast ingots were drilled and adequate powder portions (~2 g) to constitute the samples were obtained. Finer size powders ranging between 120 and 180 μm of the Al–9Si alloy with a spheroidal morphology are used. When an as-cast Al–5Cu alloy is dril led, elongated particles ranged between 150 (�90) μm in width and 450 (�140) μm in length are obtained. When a mixture 1:1 between these two elemental alloy powders is considered, of about 50 (�5)% of each one of the aforementioned sizes and morphologies are attained, as depicted in Fig. 2. 2.2. Sample preparation and characterization Three distinctive compaction pressures (i.e. 125, 250, and 430 � 5 MPa) were adopted. This selection is based on the commonly applied loading and compaction pressure used into common industrial applications. A single acting hydraulic press was used. A VC131 (AISI D6) material die with a hardness of about 60 (�5) HRc (http://www.vi llaresmetals.com.br) was used. Cylindrical pellets of 10 mm2 with resulting areas of 78.5 (�0.5) mm2 and a height-to-diameter ratio 1.1:1 are produced (ASTM E8M/04). A muffle type furnace adopting an inert atmosphere (using ~5 L.p.m of argon flow) to provide the heat-treating was used. A heating rate of 10 � C/min and a plateau at 540 (�3) � C during 1 h are applied. This sintering time is coincident with the solution since a T4 quenching (water at ~23 � C) is carried out. The sintering temperature is based on 70 and 85% of the melting temperature [15–18] and those eutectic temperatures considering that no liquid portions are formed. In order to characterize the resulting microstructural arrays, powder sizes and morphologies and formed phases, a scanning electron micro scope, an optical microscope and a diffractometer (40 kV and 30 A, Cu Kα radiation and wavelength of 0.15406 nm) were used. A gauge length marked at ~15 (�0.5) mm and a diameter of 10 (�0.1) mm2 constitute the resulting sectional area of ~78.5 (�0.5) mm2. An electro hydraulic servo machine applying a strain rate ~2.5 � 10 4s 1 with speed cross head of 0.25 mm/min [18] was used. 3. Results and discussion 3.1. Powder morphology It is firstly elucidated that the examined powder particles of the ascast Al-5 wt.% Cu and Al-9 wt.% Si alloys are used. The resulting sam ples are compacted using distinct compaction pressures. Sequentially, the samples are sintered and water quenched. Based on this and previous reports in literature [13–16], the Al-based composites are constituted due to its eutectic morphologies are formed, i.e. Al2Cu and lamellar Si particles. From the industrial point of view, or intending a mechanical application, a sample solely compacted has no interesting. This is based on the fact that other additional manufacturing routes are commonly practiced (e.g. sintering and/or other heat-treating). Although an only compacted sample is not attractive, it is worth noting that the applied compaction pressure has no substantial effect on the resulting micro structural arrays. This mainly in terms of the chemical composition and phases formed. This means that after the compaction action, the observed as-cast phases and chemical compositions of the compacted samples are remained. Also, the compacted samples have their dendritic arrays reasonably remained. Evidently, a slightly deformed dendritic array is observed. However, this affects more substantially the resulting hardness, i.e. before the compaction action, both the as-cast Al–Cu and Al–Si alloy powder particles have average hardness values of about 82 (�5) HV, while the compacted samples have slightly increased to 95 (�5) HV. Before the compaction action, the corresponding dendritic arm
Fig. 3. Experimental results of compressive strength of the examined com posites: (a) comparison among the Al–9Si, Al–5Cu and Al-4.5Si-2.5Cu alloy composites, (b) and (c) the Al–5Cu and Al–9Si composites considering three distinct compaction pressures.
spacings are of about 30 (�5) μm, as also previously reported [17]. Fig. 1(a) shows a schematic representation of a typical compacted powder and micrographs depicting the indented sample of Al–Cu and Al–Si, as shown in Fig. 1(b) and (c), respectively. After the compaction, followed by sintering and water-quenching, the dendritic spacings seem to be slightly lower (~18 � 3 μm) than the as-cast condition, as it will forwardly be shown. Also, after the applied quenching, the main 4
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detected phases are remained, but a more substantial modification in the resulting microstructural array and hardness are observed [17]. The Al-5 wt.% Cu alloy powder has evidenced a hardness of about 72 � 5 HV, while a hardness ~60 (�8) HV is observed when the Al-9wt.% Si alloy powder is analyzed. This is intimately associated with incoher ent/coherent Al2Cu transformation and annealing occurred predomi nantly at Al-rich matrix, as also previously reported [17]. Considering that no substantial modifications in the phase forma tion, chemical composition and resulting microstructural array (i.e. structure inside powder particle) are not responsible for those distinctive compressive strengths obtained, as will forwardly be discussed, the morphology of the powders are examined. Typical SEM (scanning electron microscope) images of the sintered composite samples (compacted under 430 MP) using only powders of the as-cast Al–5Cu alloy are shown in Fig. 2(a). Both the secondary electrons (SE) and backscattering electrons (BSE) images are shown. Also, the powder distributions are also depicted. Predominant elongated powder particles are characterized. These are majority sized in width between 45 and 155 μm (~55%), and their length ranging be tween ~ 300 and 425 μm (~75%). This elongated powder particle seems to be intimately correlated with the resulting dendritic array and distributed Al2Cu at interdendritic regions. Fig. 2(b) and (c) show SEM images of the proposed composite using a mixture 1:1 between Al–9Si þ Al–5Cu (Al4⋅5Si-2.5Cu) and using only powders of the as-cast Al–9Si alloy, respectively. It is clearly observed that the sintered Al–9Si alloy composite has predominant particles (spheroids) sizing between ~45 and 180 μm (~55%), as shown in Fig. 2(b). It is remarked that the as-cast Al–9Si alloy powder has also provided spheroidal-like particles. Also, this seems to be intimately associated with the resulting dendritic array and Si needle-like distributed at eutectic region (interdendritic region), which provides a fracture mechanism inducing to predominant sphe roidal particles, as also previously reported [17]. When a mixture powder particle using both the Al–5Cu and Al–9Si alloys is used (constituting the composite Al-4.5Si-2.5Cu), the width and length are between 45–180 μm (~66%) and 270–360 μm (~68%), respectively, as indicated into Fig. 2(c). With these aforementioned observations, it is evidenced that the Al–Si powder has a trend to spheroid-like morphology, but the size magnification of the examined powder particles are very similar. Pre vious investigation [17] has demonstrated that the morphology and size magnification have no substantial effect on both the densification level of the compacted samples. Based on aforementioned assertions, it is remained to investigate the solute content (i.e. Cu and Si contents) and their possible variations in terms of the microstructural arrangement, the phase constitution and the distribution/morphology of the Al and Cu rich region after sintering and quenching content.
Fig. 4. Experimental relation between: (a) yield strength (YS) and ultimate compressive strength (UCS) vs. compaction pressure (CP) of the examined Al–5Cu and Al–9Si alloy powder composites.
microwave sintered-hot extruded). However, this slight comparison helps to demonstrate that the attained compressive results can be industrially adopted and they are competitive. Although other low concentrations (e.g. 1.5 in a vol%) and nature of the ceramic reinforce particles (e.g. SiC, Al2O3, or Si3N4) are used, it seems that the attained compressive results provided by using the recycled powders from the as-cast Al-based alloys can be potentially considered. Although it is reasonably recognized that the operational parameters significantly affect the resulting mechanical behavior of the AMMCs, as previously reported [1–7,13–19], the examined Al-based composites produced using as-cast powders were produced using three distinct compaction pressures. Besides, the sintering time (1 h) and temperature (540 � C) are also applied. Into the industrial sectors using P/M, this compaction pressuring range (i.e. between 100 and 600 MPa) is commonly utilized [13–16,18–22]. Fig. 3(b) and (c) shows the compressive strength results of the composites using the powder particles of the as-cast Al–5Cu and Al–9Si alloys as a function of three distinct compaction pressures, respectively. As expected, the compressive strengths (both UCS and YS) have decreased with the decrease of the compaction pressure. Although these values have decreased, the Al–5Cu alloy composite at the other two pressures exhibits their corresponding values higher than those obtained when the Al–9Si alloy composite is considered. The differences between the UCS of Al–5Cu and Al–9Si are ~1.5x up to the 250 MPa and ~1.8x when a 250 MPa of the compaction pressure is considered. It should also be mentioned that both the Al–5Cu and Al–9Si alloy composites have
3.2. Solute content and compaction pressure effects Fig. 3(a) shows the experimental curves of the compressive strengths of the examined Al–9Si, Al–5Cu and Al-4.5Si-2.5Cu alloy composites. These samples were compacted under a 430 (�4) MPa, followed by a heat-treated at 540 � C (solution heat treating). Sequentially, a T4 water quenching was carried out. It can be seen that the ultimate compressive strength (UCS) related with the Al–9Si composite sample has achieved ~268 (�8) MPa. This means that the UCS is ~1.5 times higher than the UTS result of the Al–9Si sample. Interestingly the intermediate result of the compressive behavior is that of the Al-4.5Si-2.5Cu sample (~195 � 6 MPa), while the lowest UCS is that of the Al–9Si sample composite. Also, the compressive yield strengths (YS) of the examined samples reveal similar trend when the composites with Si content are analyzed. The highest YS value is that of the Al–5Cu sample. Similar UCS results are also reported when the same order of magnitude for the strain rate was also applied [13]. Also, a similar YS result is also reported when an Al-1.5SiC (vol%) composite is investigated. Evidently that other distinct solute contents and operational parameters were applied (e.g. 5
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Fig. 5. (a) Resulting microstructural array of an Al-4.5Si-2.5Cu composite evidencing distinctive nature of the powders from Al–5Cu and Al–9Si (b) when compared with the elemental as-cast alloys (c).
their UCS and YS differentiating of about 2.5x under a compaction pressure of 430 MPa. Also it is decreased of about 1.6x under 250 MPa and it has decreased of about 1.4x when a 125 MPa is applied. This in dicates that the compaction pressure (CP) has a non-linear effect on the yield strength (YS) parameter, as depicted in Fig. 4(a). On the other hand, the linear trends are clearly characterized when the ultimate compressive strength (UCS) and CP for both the examined composites (Al–5Cu and Al–9Si) are considered, as depicted in Fig. 4(b). Fig. 5(a) shows a typical resulting microstructure array of a mixed powders between the Al–9Si and Al–5Cu casting alloys (1:1 wt ratio). The optical images show light (or white) region constituting of the ascast Al–5Cu alloy powders are characterized. On the other hand, the gray regions (or white and gray) correspond with the Al–9Si casting alloy powders, which is constituted by lamellar (needle-like) morphology between Al and Si rich-phases [11,13,17–23], as shown in Fig. 4(b). Similarly, the correspond Al–5Cu alloy powder has also an Al-rich region with Al2Cu [11, 17, 24] contrasted (dark region in left position in Fig. 5(b)). The resulting microstructure arrays shown in Fig. 5(b) are
considerably different from those depicted in Fig. 5(c). The former are constituted when the sintering and quenching are carried out, while the latter are those corresponding with the resulting as-casting microstruc ture arrays (or as-received powders). An as-received Al–5Cu alloy sample (i.e. as-casting sample) has distributed Al2Cu intermetallic par ticles into the interdendritic region. This constitutes an expected eutectic mixture due to the solidification route applied [11; 17, 22–24]. After 1 h of the sintering time, a solution treatment is provided. Subse quently, after quenching, a possible coarsening of Al-rich dendritic arms seems to be occurred, as observed when Fig. 5(b) and (c) are compared. Fig. 5(c) clearly reveals that both the as-cast Al–5Cu and Al–9Si alloys have their corresponding averages of the dendritic arm spacings of about 20 (�5) and 30 (�5) μm, respectively. On the other hand, after the adopted heat-treating the dendritic spacing formations are not clearly characterized. Besides, the Al–9Si alloy composite has its resulting Si particles considerably modified, as also previously reported [20,22] when a T4 treating is also carried out. Thus, the needle-like Si morphology is modified to a spheroid-like Si morphology, as demon strated at right side in Fig. 5 (b). 6
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Acknowledgements
Table 1 Experimental results of ultimate compressive strengths (UCS), yield strengths (YS) and calculated specific strengths (SS) and relative weights of each examined Al–9Si, Al–5Cu and Al-4.5Si-2.5Cu composites. Alloy composite
Compaction Pressure (MPa)
UCS (MPa)
YS (MPa)
SS (a) 103 x m2 s 2
Relative lightweight (b)
Al–9Si
430
180 (�8) 90 (�3) 30 (�8) 268 (�8) 138 (�3) 58 (�2) 195 (�6)
64 (�4) 45 (�2) 22 (�2) 104 (�3) 85 (�3) 39 (�1) 71 (�2)
68 (�2)
1
250 125 Al–5Cu
430 250 125
Al-4.5Si2.5Cu
430
Financial support provided by FAEPEX-UNICAMP (#2478/18), and CNPq, #304950/2017-3 and #405602/2018-9). Also Mr. Alexandre Litzberger, manufacturing manager at Alux do Brasil and Mr. Luiz Antonio Garcia due to supplying materials and valuable technical contributions. References
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[1] D.K. Das, P.C. Mishra, S. Singh, S. Pattanaik, Fabrication and heat treatment of ceramic-reinforced aluminium matrix composites – a review, Int. J. Mech. Mater. Eng. 9 (2014) 1–15. [2] V.V. Vani, S.K. Chak, The effect of process parameters in aluminum metal matrix composites with powder metallurgy, Manuf. Rev. 5 (2018) 1–13. [3] L. Jiang, H. Yang, J.K. Yee, X. Mo, T. Topping, E.J. Lavernia, J.M. Schoenung, Toughening of aluminum matrix nanocomposites via spatial arrays of boron carbide spherical nanoparticles, Acta Mater. 103 (2016) 128–140. [4] I.A. Ibrahim, F.A. Mohamed, E.J. Lavernia, Particulate reinforced metal matrix composites: a review, J. Mater. Sci. 26 (1991) 1137–1156. [5] D. Bouvard, Densification behaviour of mixtures of hard and soft powders under pressure, Powder Technol. 111 (2000) 231–239. [6] H.R. Hafizpour, A. Simchi, Investigation on compressibility of Al–SiC composite powders, Powder Metall. 51 (2008) 217–223. [7] H. Rudianto, S. Yang, K. Nam, Y. Kim, Mechanical properties of Al-14Si-2.5Cu0.5Mg Aluminum-Silicon P/M alloy, Rev. Adv. Mater. Sci. 28 (2011) 145–149. [8] H. Rudianto, S. Yang, Y. Kim, K. Namb, Sintering of Al-Si-Fe-Cu-Mg-SiC powder prepared by gas atomization process, J. Ceram. Process. Res. 13 (2012) 119–122. [9] H. Rudianto, G.J. Jang, S.S. Yang, Y.J. Kim, I. Dlouhy, Effect of SiC particles on sinterability of Al-Zn-Mg-Cu P/M alloy, Arch. Metall. Mater. 60 (2015) 1383–1385, https://doi.org/10.1515/amm-2015-0136. [10] E.L. Rooy, Metals Handbook, vol. 15, ASM International, Materials Park, Ohio, 1988, p. 743. [11] W.R. Os� orio, C.A. Siqueira, C.A. Santos, A. Garcia, The correlation between electrochemical corrosion resistance and mechanical strength of as-cast Al-Cu and Al-Si alloys, Int. J. Electrochem. Sci. 6 (2011) 6275–6289. [12] S.G. Shabestari, H. Moemeni, Effect of copper and solidification conditions on the microstructure and mechanical properties of Al-Si-Mg alloys, J. Mater. Process. Technol. 153 (2004) 193–198. [13] J. Zhou, J. Duszczyk, Preparation of Al-20Si-4.5Cu alloy and its composite from elemental powders, J. Mater. Sci. 34 (1999) 5067–5073. [14] B. Ogel, R. Gurbuz, Microstructural characterization and tensile properties of hot pressed Al–SiC composites prepared from pure Al and Cu powders, Mater. Sci. Eng. A301 (2001) 213–220. [15] M. Kok, Production and mechanical properties of Al2O3 particle-reinforced 2024 aluminium alloy composites, J. Mater. Process. Technol. 161 (2005) 381–387, https://doi.org/10.1016/j.jmaprotec.2004.07.068. [16] M.M. Tash, E.R.I. Mahmoud, Development of in-situ Al-Si/CuAl2 metal matrix composites: microstructure, hardness, and wear behavior, Materials 9 (2016) 442–457, https://doi.org/10.3390/ma9060442. [17] R.S. Bonatti, Y. Meyer, A.D. Bortolozo, D. Costa, W.R. Os� orio, Morphology and size effects on densification and mechanical behavior of sintered powders from Al-Si and Al-Cu casting alloys, J. Alloy. Comp. 786 (2019) 717–732. [18] R.S. Bonatti, R.R. Siqueira, G.S. Padilha, A.D. Bortolozo, W.R. Os� orio, Distinct Alp/ Sip composites affecting its densification and mechanical behavior, J. Alloy. Comp. 757 (2018) 434–447. [19] S. Tiwari, P. Rajput, S. Srivastava, Densification behaviour in the fabrication of AlFe metal matrix composite using powder metallurgy route, Int. Sch. Res. Netw. (2012) 8, https://doi.org/10.5402/2012/195654. Article ID 195654. [20] M. Penchal Reddy, F. Ubaid, R.A. Shakoor, P. Gururaj, M. Vyasaraj, A.M. A. Mohamed, M. Gupta, Effect of reinforcement concentration on the properties of hot extruded Al-Al2O3 composites synthesized through microwave sintering process, Mater. Sci. Eng. A 696 (2017) 60–69. [21] K. Ma, E.J. Lavernia, J.M. Schoenung, Particulate reinforced aluminum alloy matrix composites – a review on the effect of microconstituents, Rev. Adv. Mater. Sci. 48 (2017) 91–104. [22] W.R. Os� orio, N. Cheung, J.E. Spinelli, P.R. Goulart, A. Garcia, The effects of a eutectic modifier on microstructure and surface corrosion behavior of Al-Si hypoeutectic alloys, J. Solid State Electrochem. 11 (2007) 1421–1427. [23] M. Peres, C.A. Siqueira, A. Garcia, Macrostructural and microstructural development in Al-Si alloys directionally solidified under unsteady-state conditions, J. Alloy. Comp. 381 (2004) 168–181. [24] J.M. Quaresma, C.A. Santos, A. Garcia, Correlation between unsteady-state solidification conditions, dendrite spacings, and mechanical properties of Al-Cu alloys, Metall. Mater. Trans. A, Phys. Metall. Mater. Sci., Estados Unidos 31A (2000) 3167–3178.
– 89 (�2)
1.13
–
–
–
–
69 (�2)
1.06
a
The SS (specific strength) values were determined using UCS per theoretical density. These values of the Al–5Cu, Al–9Si and Al-4.5Si-2.5Cu alloys compos ites are: 3.01, 2.67 and 2.84 g x cm 3, respectively. b The relative lightweight effect is based on the their corresponding theoret ical densities.
In this condition, due to the coarsened Al-rich phase and their ductile characteristic, it contributes with absorption of the energy and the Al2Cu shows an important role on the blocking of the dislocation motion. The as-cast Al–9Si alloy, due to the compaction pressure and sintering, has certain clusters of Si (brittle) in a “pseudo-spheroid” forming a “lamellar” morphology with a ductile Al-rich matrix. Under a compressive pressure, some microcracks at interface between ductile Almatrix and Si particle can be provided, as previously reported [21]. With this, it is observed that resulting mechanical behavior is decreased, as demonstrated in the experimental compressive strength plots. Table 1 shows the compressive behavior of the examined Al-based composites. Considering the UCS results concatenated with light weight, it can be seen that the Al–5Cu is of about 13% weightier than other two composites examined. However, their corresponding specific strengths (SS) are approximately 30% higher than other two composites examined. It is also presumed that the relative cost is ranging between 8 and 10% cheaper than the Al–9Si sample. This means that an econom ical and an environmentally friendly aspects favor the Al–5Cu alloy examined. This induces to feasibility to apply the Al–5Cu alloy powders as recycled powders in order to possibly constitute automobile components. 4. Conclusions From the experimentations and analyses provided, the follow con clusions can be drawn. It is found that the increase of the compaction pressure, an increasing in the compressive strength is also attained. It is also found that the highest compressive behavior is that of the Al-5 wt.% Cu alloy powder composite. This is followed by a result from a mixture 1:1 wt ratio between the Al-5 wt.% Cu and Al-9 wt.% Si composites. The lowest compressive behavior is that of the Al-9 wt.% Si composite. When the as-cast Al-9 wt.% Si alloy powder is used, a cluster of brittle Si particles is formed and microcracks induces to a decreasing of the me chanical behavior when Si particles are involved. This indicates that the chemical content powder and the subsequent heat-treating have important roles on the resulting compressive strengths.
7