j mater res technol. 2013;2(3):250–254

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Original article

Fabrication and characterization of A359/Al2O3 metal matrix composite using electromagnetic stir casting method

Abhishek Kumar ∗, Shyam Lal, Sudhir Kumar

Noida Institute of Engineering and Technology, Greater Noida, Uttar Pradesh, India

article info abstract

Article history: A composite material is a material consisting of two or more physically and chemically dis- Received 4 January 2013 tinct phases. The composite has superior characteristics than those individual components. Accepted 7 March 2013 Usually the reinforcing component is distributed in the continuous or matrix component. Available online 3 August 2013 When the matrix is a metal, the composite is termed a metal matrix composite (MMC). In MMCs, the reinforcement usually takes the form of particles, whiskers, short fibers, or Keywords: continuous fibers. An MMC is a composite material with at least two constituent parts, one Aluminum alloy being a metal. The other material may be a different metal or another material, such as A359 a ceramic or organic compound. Recently, aluminum and its alloy based cast MMCs have

Al2O3 gained lot of popularity in all the emerging fields of engineering and technology owing to Metal matrix composites their superior strength, lower creep rate, better fatigue resistance, lower coefficients of ther- mal expansion as compared to monolithic materials. The desired properties of the cast MMCs are influenced by the solidification behavior of the cast MMCs. The present paper aimed to investigate the best possible predicted results and to carry out the experimental set up of electromagnetic stir casting process in composite materials. The present paper also shows significant effect of the mechanical properties such as hardness and tensile strength,

and analyzes the microstructure of A359/Al2O3. © 2013 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. Este é um artigo Open Access sob a licença de CC BY-NC-ND

consisting the matrix as the major phase in which the 1. Introduction reinforcement is added, called the reinforcement phase. Metal matrix composite (MMC) is an engineered combina- A composite material called as materials system which tion of metal (matrix) and hard particle/ceramic (reinforce- comprises two or more micro/macro matter having different ment) to get tailored properties. Composites are developed composition and insoluble in each other. In composites each with great success by the use of fiber reinforcement in metal- material retains its original properties, but when composited lic materials (ASM Metals Hand Book, 2008). MMCs are either (combined), superior properties of materials are obtained in use or in prototyping for the space shuttle, commercial air- which could not have been obtained separately. Compos- liners, electronic substrates, bicycles, automobiles, and in a ite materials are combinations of two or more materials variety of other applications [1,2].

∗ Corresponding author. E-mail: [email protected] (A. Kumar). 2238-7854 © 2013 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. Este é um artigo Open Access sob a licença de CC BY-NC-ND http://dx.doi.org/10.1016/j.jmrt.2013.03.015 j mater res technol. 2013;2(3):250–254 251

Table 1 – Chemical composition (A359) [8]. Elements Si Cu Mg Mn Fe Zn Ti Al

Percentage (%) 8.5–9.5 0.2 0.5–0.7 0.10 0.20 0.10 0.20 Remaining

MMCs in general consist of at least two components, Table2–Thermophysical properties of reinforcement namely matrix and the reinforcement. The matrix is usu- particle and A359. ally an alloy, and the reinforcement is usually a ceramic. The Properties Al O particulates A359 aim involved in designing MMC materials is to combine the 2 3 desirable attributes of metals and ceramics. The earliest work Density (g/cm3) 3.2 2.66 Average particle size (mesh) 400 – involving Al2O3 as reinforcement for composite materials con- cerned the use of tiny filamentary crystals of the order of 50 ␮m Thermal conductivity (W/m, 0 K) 100 152.0 Specific gravity (g/cm3) 3.7 2.68 long and a few microns in diameter, which could be grown Liquidus temperature (0 ◦C) 2072 600 from the vapor phase and had great strength and stiffness [1]. In general electromagnetic stir casting of MMC involves producing a melt of selected matrix material followed by the introduction of reinforcement material into the melt and dis- persion of reinforcing material during the process. The stirring velocity increases linearly with increasing stirring current and reducing the frequency enhances the turbulent mixing in the melt [3]. Electromagnetic stirring forms a vortex where the reinforcing particles are introduced to the side of vor- tex. The vortex will drag the reinforcement particles into the melt [4]. A vortex created by mechanical force of stirring pro- cess continuously dispersed the particulates in the melt [5]. The processing–microstructure–mechanical properties of alu- minum based MMC materials synthesized using stir casting route were investigated by Jokhio et al. [6]. They had used alu- minum alloy matrix with addition of Cu–Zn–Mg metals and reinforced with Al O using simple foundry melting alloying 2 3 Fig. 1 – Experimental setup. and casting route. Electromagnetic stirring improved hardness and refined microstructure of hypoeutectic Al–Si alloy 356 [7]. Literature survey did not reveal any systematic study of prop- erties with electromagnetic stirring along with microstructure graphite crucible to measure the temperature variation of the and mechanical properties of A359 alloy with aluminum oxide molten metal. Experiments carried out for a wide range of par- reinforcement. In the present work attempts are made to char- ticle weight percentage varying from 2% to 8% in steps of 2%. acterize the A359 alloy by processing it with electromagnetic Finally, the mechanical properties A359–Al2O3 composites are stir casting process. The MMC produced with this approach compared with the unreinforced A359 matrix alloy. The micro was evaluated in terms of microstructural observation and structural characteristics and hardness of the composites are mechanical testing such as hardness and tensile testing. evaluated.

3. Results and discussion 2. Experimentation Keeping in view of various limitations reported in literature The aluminum alloy A359 is an alloy of aluminum used review the present research work aimed to develop alu- as the matrix metal in the experiments for the fabrica- minum alloy MMC by using the electromagnetic stir casting tion of the composites that has been reinforced with 2 wt.%, method. The alloy properties were investigated using the elec-

4 wt.%, 6 wt.%, 8 wt.% of Al2O3 of average 30 ␮m size. The tromagnetic stir casting method. The mechanical properties chemical composition of the matrix material (A359) and the including hardness and tensile strength were investigated thermophysical properties of Al2O3 and A359 are given in because literature reveals very little information on develop- Tables 1 and 2 [8]. The composite was fabricated by the elec- ments of 3XX series of aluminum alloy matrix reinforced with tromagnetic stir casting technique. The melting was carried “Al2O3” particles using electromagnetic stir casting method. in a muffle furnace in a range of 730 ± 20 ◦C. A schematic view Hashim [4] conducted research on A359 aluminum alloy of the electromagnetic stir casting set up is shown in Fig. 1. as a matrix material and silicon carbide was added as rein- The melt has electromagnetically stirred by using a 3-phase forcement particles using modified stir casting method. He induction motor after addition of the pre-heated aluminum observed that cast MMC is produced by melting the matrix oxide particles (about 800 ◦C). The processing of the composite materials; then the molten metal is stirred to form a vor- is carried out at a temperature of 750 ◦C with a stirring speed tex and the reinforcement particles are introduced through of 300 rpm. One K-type thermocouple has inserted into the the side of vortex formed. However, he did not investigate 252 j mater res technol. 2013;2(3):250–254

Table 3 – Hardness of the MMCs at different wt.% of Al2O3.

Material A359 A359/Al2O3 A359/Al2O3 A359/Al2O3 A359/Al2O3 2.0 wt.% 4.0 wt.% 6.0 wt.% 8.0 wt.%

Hardness (HRC) 46 51.5 58.4 66.7 72.8 the effect of “Al O ” particles in A359 aluminum alloy using 2 3 Table4–Tensile strength for some aluminum alloy electromagnetic stir casting method. Literature reveals that based MMC produced by casting technique. high “Al2O3” particles in matrix require the higher melting, Researchers Cast MMC system Tensile alloying treatments temperature is also required for homoge- strength in MPa nizing the alloy chemistry. The similar effect of the processing parameters and causes of porosity in stir cast aluminum com- Present study A359/Al2O3/2p 108.7 posites were found by a number of other investigators [9–11]. A359/Al2O3/4p 120.6 A359/Al O /6p 133.8 The approach of producing MMC by mechanical stir casting 2 3 A359/Al2O3/8p 148.7 has disadvantage, mainly rising in completely liquid state the Hashim [4] A359/SiC/10p 150 mechanical stirring mixes the particles into melt but when Samuel et al. [14] A359/SiC/10p 115 the stirring stopped the particles returns to the surface. How- Parayetal.[15] A359/SiC/10p 105 ever in this research in electromagnetic stirring process the Shivkumar et al. [16] A359/SiC/5p 95.7 material rotates continuously by the electromagnetic field till Kook [11] Al–Cu2024/Al2O3/10p 112 solidification. So the MMC slurry in semisolid state at a tem- Azim et al. [17] 2024 Cu–Mg/Al2O3/10p 132 Surappa and Rohatgi [18] Al–Si/Al O /4p 118 perature within the solidification range of alloy matrix helps 2 3 to incorporate reinforcement particles into the alloy matrix. The homogeneous distribution and uniform settling of rein- homogeneously. The important aim of microstructural obser- forcement particles can be obtained through electromagnetic vation in case of reinforced samples investigated in present stir casting process. Hashim et al. [12] reported that during study was to quantify particle distribution in homogeneities. stir casting large porosity produced due to gases entrapment in melting. 3.3. Tensile properties of the as cast MMCs

The tensile behavior of all the prepared samples of composites 3.1. Hardness is determined to examine the tensile properties. The speci- mens were loaded hydraulically in the computerized universal Hardness is one of the important mechanical properties in testing machine. The loads at which the specimen has reached case of composite material as the hardness of matrix metal the yield point and broken were noted down. The tensile test is very low, which limits its wide application. The hardness specimens before tensile testing are shown in Fig. 2. The exper- of matrix metal enhances due to reinforcement of ceramic imental result shows that the tensile strength of the as cast particles with it. Hardness test has conducted on each speci- MMCs produced is somewhat higher than that of the non- men using a load of 60 kgf and a steel ball of diameter 2.5 mm reinforced A359 alloy. as indenter. Diameter of impression made by indenter is pre- It can be noted that the addition of aluminum oxide par- dicted by Rockwell hardness test. The corresponding values ticles improved the tensile strength of the composites. It is of hardness (HRC) were calculated. The results indicated in apparent that an increase in the weight percentage of alu- Table 3 show the increasing trend of hardness with increase minum oxide particle results in an increase in the tensile in weight percentage of Al O particles. 2 3 strength. The tensile strength of A359 in non-reinforced con- The experimental data show the hardness value increases dition is 103.7 N/mm2, and this value increases to a maximum as we increased the weight percentage of Al2O3 particles dur- 2 of 148.7 N/mm for A359/Al2O3/8 wt.% which is about 45% ing casting. The maximum hardness value obtained at 8 wt. % improvement on that of the non-reinforced matrix mate- of Al O (i.e., about 58% higher than the matrix metal). 2 3 rial. The result reveals that the presence of hard reinforced

particles such as Al2O3 in the matrix metal reduces the per- 3.2. Microstructural analysis centage of elongation during tensile testing as the brittleness of the metal increases. Comparing mechanical properties of Samples of as cast MMCs for microstructural examination present investigation with the previous work conducted by were prepared by grinding through different sizes of grit other investigators using stir casting method from (Table 4) papers. Then the samples were etched with the etchant i.e., [4,11,14–18] giving superior responses to strength increases up

Keller’s reagent (2.5 mL nitric acid, 1.5 mL HCl, 1.0 mL HF, to 148.7 MPa with addition of 8% “Al2O3” particles reinforced 95.0 mL water) [13]. The etched samples were dried and then in aluminum matrix. It observed that the tensile strength the microstructure was observed by using Metallurgical Micro- increases due to the presence of “Al2O3” particles which act scope. The microstructure of the as cast A359/Al2O3 MMCs is to refine the grain size of aluminum casting composites by shown in Fig. 2(a–d) at different weight fraction of Al2O3 at nucleating small grains and hence increase in amount of grain 400× magnification. It can be seen that the composite mate- boundary during the solidification process. The decrease in rials made by the investigated processing technique had a tensile strength and ductility with increase the volume frac- cast microstructure of the matrix with particle distributed tion of “Al2O3” particles up to 15% in as cast condition has j mater res technol. 2013;2(3):250–254 253

Fig. 2 – Microstructural analysis. (a) A359 + 2% Al2O3; (b) A359 + 4% Al2O3; (c) A359 + 6% Al2O3; and (d) A359 + 8% Al2O3.

been observed in aluminum alloy matrix. This is due to the increase in porosity in stir cast aluminum matrix [9–11]. Conflicts of interest

The authors declare no conflicts of interest. 4. Conclusion

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