In this paper, HSC software was used to perform a thermodynamic analysis of A5083/ZrO
2 metal matrix composite to predict the phases which formed during the manufacturing processes (vortex method). The base matrix was purchased commercially and the zirconia particles were extracted from Egyptian zircon as a reinforcing material by alkaline fusion technique. The base material was melted in an electric furnace at 750°C, and the extracted zirconia particles were added while stirring. Thermodynamic diagrams predicted that ZrO
2 would react with the matrix to produce new phases such as MgO and Al
2O
3 in preference to the formation of MgO. Characterization of the fabricated zirconia and composites was performed by various methods; Scanning Electron Microscopy (SEM), Energy Distributed X-ray (EDS) and X-ray Diffraction (XRD). The results demonstrate successful extraction of high purity zirconia (98.85%) and fabrication of composites during stir casting. Furthermore, SEM mapping of the fabricated composite revealed the presence of MgO and Al
2O
3 consistent with thermodynamic studies.
For the last few decades, the development of materials shifted from monolithic alloy to composite materials in order to meet the global industrial needs. Conventional alloys have limits to realize a good combination of strength, stiffness, toughness and density. To overcome these shortcomings and to meet the ever-increasing demand of modern technology, composites are the most promising materials of recent interest [1] [2] [3]. The continuous developments in composite fabrications are directed to the use of composite materials in more and more diversified applications [4] [5]. Metal matrix composites (MMCs) reinforced with ceramic materials have improvements in their mechanical properties so has a high strength and modulus, as well as good high-temperature properties, when compared with corresponding base matrix alloys. MMCs are considered promising materials for automotive and aerospace applications due to their high strength to weight ratio [6] [7].
Aluminum and its alloys are the most selected matrix for MMCs. Al alloys are quite attractive and becoming potential engineering materials having excellent combination of properties such as high specific strength, high specific stiffness, electrical and thermal conductivities, low coefficient of thermal expansion and wear resistance [7] [8] [9] [10]. Aluminum-Magnesium alloys are non-heat treatable, and they drive their strength from solid solution strengthening, grain refinement, and strain hardening. Al-Mg alloys with low Mg content have better formability and are more suitable for large wrought products [11]. Al-Mg alloys reinforced with ceramic particulates have significant potential for structural applications due to their high stiffness and specific strength as well as low density. where Mg has a density (1.7 g/cm3) lower than density of Al (2.67 g/cm3), alloy of Mg-Al, used recently to produce lightweight and economical products. Also, Al-Mg alloys have been reported as a promising alloy system for investigation due to their low electrode potential, and high current capacity to be used as galvanic anode.
The addition of the reinforcement enhances the mechanical properties of Al based composite, when compared to the matrix alloy. Various forms of reinforcements are used in Al matrices such as silicon carbide, alumina, and zirconia. In the form of fibers, whiskers or particulate to enhance the overall performance of alloys [12] [13]. The process for manufacturing of MMCs generally depends on the types of reinforcement. There are different methods to fabricate MMCs; liquid-state, solid-state, semi-solid state, and in situ fabrication technique. Stir casting technique is one of the promising routes for producing large size components and high-volume production with low cost [14] [15]. On the other hand, the literature [1] [2] [4] - [9] [11] - [16] showed that the fabrication of MMCs are facing some difficulties which hider the development. The non-wetting behavior between the host matrix and particles is the most critical issue in MMCs fabrication. Attempts to overcome this have usually involved the use of chemical activations or heat treatments for the reinforcement to improve the wettability and assist the infiltration.
The use and application of MMC in many technical structures is constantly increasing, and its properties can be handcrafted by modifying their constituents, matrix and reinforcement, and fabrication method. Therefore, this current work aims to predict potential reactions that may occur during the fabrication of zirconia-reinforced A5083.
2. Thermodynamic Studies
Thermodynamic data are used to predict the types of reactions that may occur between reinforcing materials and base matrix elements during casting and solidification processes. For this purpose, the chemistry software program HSC-6 is used. HSC-6 is basically used to determine the probability of formation within a matrix, whether it is an element, an oxide, or a compound, based on the chemical analysis of the matrix. Predict the probability of ZrO2 reduction reaction to Zr metal and the stability of elements and oxides at different temperatures,
Where the base matrix for this investigated is A5083, it consists of Al and Mg as the major alloying element (5%). while, the selected reinforcement material is the prepared ZrO2 particle. Thermodynamic stability plots of A5083 systems with different ZrO2 percentages (5%, 10%, 15%, and 20%) are generated by HSC software as shown in Figure 1. These diagrams show the potential elements and compounds might be formed during casting and solidification.
This clearly indicates the potential formation of MgO and Al2O3 during fabrication and solidification temperatures. Furthermore, it was revealed that the formation potential of MgO is higher than that of Al2O3 in the temperature range from room temperature to casting temperature (650˚C - 800˚C) as shown in Figures 1(a)-(d). This behavior implies that Mg completely reacted with ZrO2 to form MgO and Zr metal. When the ZrO2 fraction is increased, Mg is not sufficient to react with this high ZrO2 fraction. After Mg was consumed, Al reacted with ZrO2 and he started to form Al2O3 and Zr metal. Figure 1(c) was chosen to illustrate the stability diagram for metals and oxides. The figure represents metals and oxides where the sum of metals (Al, Mg, Zr) equals 100% and the sum of oxides (Al2O3, MgO, ZrO2) equals 100% at each temperature. Therefore, the proportions of Al, Mg, and Zr metals at the casting temperature (750˚C) are thermodynamically assumed to be about 89.2% and 9%, respectively. Similarly, the percentages of Al2O3, MgO, and ZrO2 oxides are about 28.67% and 5%, respectively, at that temperature. This result indicates that about two-thirds of the added ZrO2 is reduced to Zr metal and its oxygen combines with Al and/or Mg to form Al2O3 and/or MgO depending on composition and temperature. It is obviously showed the formation of MgO and Al2O3 during fabrication and solidification temperatures will be occur.
To determine the dominant reaction of ZrO2 with Al or Mg, thermodynamic calculations such as enthalpy (ΔH), entropy (ΔS), and free energies (ΔG) are performed. Thermodynamic data for reaction (1) and (2) are recorded in Table 1 and Table 2 respectively. Its noted that the ΔG values are negative at zero temperature for both reaction which means can take place spontaneously and by increasing the temperature, the ΔG values decreased. At casting temperature
Thermodynamic data for equation (1)
1.5 ZrO 2 + 2Al = 1.5 Zr + Al 2 O 3 (1)
Temperature ˚C
Delta (H) kJ
Delta (S) J/K
Delta (G) kJ
0
−24.841
−21.011
−19.102
100
−26.382
−25.837
−16.741
200
−27.433
−28.360
−14.014
300
−27.944
−29.355
−11.119
400
−28.190
−29.751
−8.162
500
−28.553
−30.250
−5.166
600
−29.185
−31.018
−2.102
700
−51.254
−54.677
1.955
800
−51.568
−54.985
7.439
900
−45.907
−50.016
12.770
1000
−46.948
−50.868
17.815
Thermodynamic data for equation (2)
ZrO 2 + 2Mg = Zr + 2MgO (2)
Temperature ˚C
Delta (H) kJ
Delta (S) J/K
Delta (G) kJ
0
−102.761
−21.890
−96.781
100
−103.216
−23.330
−94.510
200
−103.509
−24.030
−92.139
300
−103.755
−24.502
−89.712
400
−104.030
−24.943
−87.239
500
−104.395
−25.446
−84.721
600
−104.905
−26.065
−82.146
700
−122.718
−45.359
−78.577
800
−123.712
−46.332
−73.991
900
−120.727
−43.722
−69.435
1000
−122.208
−44.934
−65.001
(above 700˚C), its clearly noted that ΔG value is become positive for the formation of Al2O3 and still negative for the formation of MgO. This means that, at casting temperature, MgO has formation priority and stability.
Moreover, clearly indicated that the formation potentials for MgO is higher than Al2O3 for all investigated percentages of ZrO2 in temperature range from room temperature up to casting temperatures (650˚C - 800˚C). This behavior means that Mg fully reacted with ZrO2 to form MgO and Zr metal. By increasing the percentage of ZrO2, Mg become not enough to react with that higher percentage of ZrO2. After consumable of Mg, Al began to react with ZrO2 to form Al2O3 and Zr metal.
3. Experimental Work3.1. Materials3.1.1. Al-Alloy
The selected Al-alloy for the present investigation is the commercial alloy (A5083) with the chemical composition as shown in Table 3, maintaining the Integrity of the Specifications.
3.1.2. Reinforcement Material
The selected reinforcement material for using in production of A5083 MMCs are ZrO2 particles. ZrO2 particles will be prepared from the Egyptian zircon via alkaline fusion technique. Zircon is the most abundant zirconium ore and the main source for commercial production of zirconium, its compounds and alloys. The chemical composition of zircon concentrate (ZrSiO4), separated from the Egyptian black sand heavy mineral from Egyptian Nuclear Materials Authority (ENMA) is shown in Table 4.
The chemical composition of A5083 base matrix
Element
Mn
Mg
Fe
Si
Cu
Al
%
0.46
4.22
0.23
0.35
0.09
Balance
Average chemical composition of the concentrated Egyptian zircon
Compound
ZrO2
SiO2
HFO2
Al2O3
Fe2O3
TiO2
Other
%
63.07
31.23
2.27
0.87
0.77
0.82
Balance
The production and applications of zirconia have continued to attract the interest of scientists and technologists. The dry and wet chemical methods are the main conventional ways for synthesizing ZrO2 powder. The wet chemical methods (extraction with caustic alkalis, fluorides and lime) can produce high-grade zirconia because the impurities can be separated by controlled precipitation from the solutions. Various methods of decomposition have been investigated owing to the different levels of purity required and the cost of manufacture [17] [18] [19]. All these methods have three steps in common. Firstly, zircon is decomposed or dissociated by chemical, thermal or mechanochemical means. Secondly, the products obtained are treated by solubility differentiation. Thirdly, zirconium compounds are isolated from the residual impurities. Alkali fusion of zircon concentrates presents good versatility, is simple and economic process where requires low capital and operation costs [20]. These features make alkali fusion the selected method for producing zirconia particles.
Alkali fusion technique for zircon is known as zircon opening which include the following procedure which schematically represented in Figure 2. Firstly, mixture zircon with NaOH by ratio 1:1.35 in stainless steel crucible then fused in a Muffle furnace at 650˚C ± 10˚C for 2.5 h. The opening product (frit) consists of two major compounds Na2SiO3 (water soluble) and Na2ZrO3 in addition to some impurities and unreacted zircon. Frit was water leached to remove the impurities (sodium silicate). Hydrated sodium zirconate is obtained by filtration then followed by drying at 110˚C for 12 h. The dried frit is leached in 6 M HCl at 90˚C and left overnight to produce a jelly like mixture of silica gel and zirconium oxychloride. The products of leaching are separated by water dissolution and filtration to produce pure zirconium oxychloride solution. Pure oxychloride crystals are obtained by evaporation of the zirconium oxychloride solution then washed by acetone to remove excess chlorine. To precipitate zirconium hydroxide (Zr(OH)4), the white crystals were leached with distilled water and pH was adjusted at 10 by the addition of ammonia. Next, the precipitate washed with water for several times and dried at 110˚C for 12 h followed by calcination for 1.5 h at 900˚C.
3.2. Preparation of Composite
The fabrication of MMCs was carried out by stir casting process. The base alloy
A5083 was placed in a graphite crucible inside an electrical resistance furnace. During heating, the Al alloy was melted and adjusted the casting temperature at 750˚C. After melting, the molten metal was purfacition by addition of flux. Next, the formed slag on the surface was removed carefully. This step also helped to effectively remove gases from the metal phase. The mechanical stirrer was inserted in the molten metal rotated at an impeller speed of 1200 rpm. The preheated ZrO2 particles were gradually added to the vortex. ZrO2 particles were heated to remove the gas layer from surface which enhances the fabriction of composoite. The presence of gas layer on the surface of particles ellimite the reaction between molten Al and ZrO2 which in turn decreasing the wetabbility [1] [5]. The melt was continuously stirred for seven min after the addition of ZrO2 to ensure the homogeneous distribution of the particles. Finally, the molten was poured into the permanent mold and allowed to cold in the air.
3.3. Microstructure
Scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (PHILIPS, XL 30 ESEM at 30 kV voltage) was used to characterize the microstructure of the materials. The samples were first ground on a series of SiC emery papers underwater stream, followed by polishing a series of polishing cloths with alumina suspension.
Also, X-ray diffraction analysis was performed using Philips Machine to determine the different phases of AA5083 and its composites. The XRD machine was operated at the following conditions; monochromatic Cu-K radiation with l = 0.154 nm, scanning range was 10 - 80 (2θ), and scanning step size of 0.01˚ (2θ)/Sec.
4. Results and Discussion4.1. Preparation of ZrO<sub>2</sub> Particles
The preparation of Zirconia particles starts with opening-up of zircon concentrate followed by a series of hydrometallurgical and pyrometallurgical processes. Firstly, zircon is fused with sodium hydroxide at 650˚C for 2 h then cooled in the furnace. The main reactions that take place between ZrSiO4 and NaOH during alkali fusion are as follows [20] [21] [22]:
ZrSiO 4 + 2NaOH → Na 2 ZrSiO 5 + H 2 O (3)
ZrSiO 4 + 4NaOH → Na 2 ZrO 3 + Na 2 SiO 3 + 2H 2 O (4)
ZrSiO 4 + 6NaOH → Na 2 ZrO 3 + Na 4 SiO 4 + 3H 2 O (5)
The product of fusion is named frit which, according to the Equations (3)-(5) consisting of sodium zirconate (Na2ZrO3), sodium zirconium silicate (Na2ZrSiO5) and sodium silicate (Na2SiO3, Na4SiO4) beside water vapor. Next, frit is washed with cold water for three times to remove both soluble silicates and excess caustic. Most of the water soluble Na2SiO3, Na4SiO4, and unreacted NaOH dissolve in water, whereas the insoluble Na2ZrO3 is hydrolyzed to ZrO(OH)2 as per reaction (6). By filtration the solution, the filtrate consists of the soluble substances while the residue represents both ZrO(OH)2 and Na2ZrSiO5 which are dried, then leached with HCl according to Equations (7) and (8).
Na 2 ZrO 3 + 2H 2 O → ZrO ( OH ) 2 + 2NaOH (6)
ZrO ( OH ) 2 + 2HCl → ZrOCl 2 + 2H 2 O (7)
Na 2 ZrSiO 5 + 4HCl → ZrOCl 2 + 2NaCl + H 2 SiO 3 + H 2 O (8)
The solution was left overnight to assist silica to precipitate in the form of silica gel, and zirconium oxychloride to crystallize. The freeze solution was dissolved in the water, then filtrate to remove silica. The filtrated solution was concentrated via volume reduction evaporation process to obtain ZrOCl2 crystals as shown in Figure 3(a). ZrOCl2 crystals were water leached then treated with ammonium hydroxide to precipitate zirconium hydroxide as illustrated in Equation (9).
Finally, zirconium hydroxide was washed, dried and calcined at 900˚C for 1.5 h producing zirconium dioxide (ZrO2 particles) as per Equation (10). The prepared white zirconia is shown in Figure 3(b).
SEM/EDS analysis of the prepared zirconia is shown in Figure 4. It is important to note that ZrO2 particles have irregular shape and size as shows in Figure 4(a). However, the purity of ZrO2 particles is about 98.85% where Si, Ca, and Cl are the accompanied impurities with 0.8%, 0.23%, 0.12% respectively as recorded in Table 5.
4.2. Microstructure
SEM images of typical microstructures of as-cast composites are shown in Figure 5. The microstructure of A5083 consisted of Al-Mg solid solution with a long arm spacing dendritic structure. The most important aspect of the microstructure is the distribution of the reinforcing particles. Achieving a uniform distribution of reinforcement is one such challenge which impacts directly on the properties and quality of the composite material. The produced MMCs containing 5 and 10 weight fractions of ZrO2 which are wetted and well bonding to the matrix. A representative cross section of the ZrO2 distribution in matrix is shown in Figure 5. On the other hand, the presence of the ZrO2 decreases the arm spacing as shown in Figure 5(b) and Figure 5(c). Also, Figure 5 shows that the constituents of the base matrix and the composite are homogeneously distributed.
As shown in Figure 6, the XRD analysis shows that the base alloy consists mainly of α-Al solid solution, while the composite contains the same composition and ZrO2 particles. It is evident that with increasing ZrO2 particle content, the intensity of ZrO2 peak increases and the intensity of Al peak decreases. The reducing in intensity is due to the difference in thermal expansion between the Al matrix and ZrO2 particles. On the other hand, Al2O3 and/or MgO do not appear in XRD patterns. This means that the percentage is below the detection limit of XRD.
SEM mapping demonstrates the presence of Zr, O, Mg and Al as shown in Figure 7. It is clearly noted that the particle at middle of the image refers to the ZrO2 due to that red color means Zr while green color refers to Oxygen. The presence of Oxygen surrounding the red color revealed the presence of ZrO2. Furthermore, the presence of high concentration of green color as indicated in
EDS analysis of the prepared Zirconia
Element
Zr
Hf
Si
Cl
Ca
%
95.88
2.97
0.8
0.12
0.23
the red rectangular means the Al and/or Mg reacted with Oxygen and formed new phases (Al2O3 and/or MgO).
5. Conclusions
The chemistry software HSC-6 was used to investigate the thermodynamic behavior of ZrO2-reinforced Al alloys. The study yielded the following key findings:
1) Thermodynamic analysis results predicted that ZrO2 would react with the base alloy to form new phases such as MgO and Al2O3.
2) Based on the thermodynamic stability diagram and ΔG values, the formation of MgO is the dominant reaction.
3) Succeeded in producing high-purity (98.85) zirconia by alkali fusion method.
4) Effective fabrication of Al 5083 composites reinforced with ZrO2 particles by stir casting
5) SEM mapping approved the presence of MgO and Al2O3, consistent with thermodynamic studies.
Conflicts of Interest
The author declares no conflicts of interest.
Cite this paper
Abdelkareem, A. (2022) Thermodynamic Analysis of Al Alloy Reinforced with Zirconia Particles. Open Access Library Journal, 9: e9569. https://doi.org/10.4236/oalib.1109569
ReferencesAbdizadeh, H. and Baghchesara, M.A. (2013) Investigation on Mechanical Properties and Fracture Behavior of A356 Aluminum Alloy Based ZrO2 Particle Reinforced Metal-Matrix Composites. Ceramics International, 39, 2045-2050.
https://doi.org/10.1016/j.ceramint.2012.08.057Girish, K. and Shobha, B. (2018) Synthesis and Mechanical Properties of Zirconium Nano-Reinforced with Aluminium Alloy Matrix Composites. Materials Today: Proceedings, 5, 3008-3013. https://doi.org/10.1016/j.matpr.2018.01.100Mohrez, W.A., Abdelkareem, A., Gamal, H. and Rashed, G.M. (2018) First Trial of SiC/SiC Tube Fabrication for Tungsten Monoblock Armor. Journal of Radiation Research and Applied Sciences, 11, 242-248.
https://doi.org/10.1016/j.jrras.2018.03.003Harsha, R., Kulkarni, M.V. and Babu, B.S. (2020) Study of Mechanical Properties of Aluminium/Nano-Zirconia Metal Matrix Composites. Materials Today: Proceedings, 26, 3100-3106. https://doi.org/10.1016/j.matpr.2020.02.641Rashed, G., Sadawy, M., Kandil, A., Abd Elkarim, A. and Mohrez, W. (2021) Influence of ZrO2 Particles on the Tribological Properties of AlMg5 Alloy. Journal of Petroleum and Mining Engineering, 23, 95-103.
https://doi.org/10.21608/jpme.2021.68312.1078Beyrami, B.P., Abdizadeh, H., Baharvandi, H. and Bonab, M. (2008) The Effect of Composition and Stir-Casting Parameters on the Mechanical Properties of Al/ZrO2p Nanocomposites. Proceedings of the 13th European Conference on Composite Materials, Stockholm.Alaneme, K.K. and Bodunrin, M.O. (2011) Corrosion Behavior of Alumina Reinforced Aluminium (6063) Metal Matrix Composites. Journal of Minerals and Materials Characterization and Engineering, 10, 1153-1165.
https://doi.org/10.4236/jmmce.2011.1012088Hynes, N.R.J., Sankaranarayanan, R., Tharmaraj, R., Pruncu, C.I. and Dispinar, D. (2019) A Comparative Study of the Mechanical and Tribological Behaviours of Different Aluminium Matrix-Ceramic Composites. Journal of the Brazilian Society of Mechanical Sciences and Engineering, 41, Article No. 330.
https://doi.org/10.1007/s40430-019-1831-7Abbas, A., Huang, S.J., Ballokova, B. and Sülleiová, K. (2020) Tribological Effects of Carbon Nanotubes on Magnesium Alloy AZ31 and Analyzing Aging Effects on CNTs/AZ31 Composites Fabricated by Stir Casting Process. Tribology International, 142, Article ID: 105982. https://doi.org/10.1016/j.triboint.2019.105982Ekuma, C., Osarolube, E., Chukwuocha, E.O. and Onyeaju, M.C. (2011) New Trends in Corrosion Analysis of Al-Sn Alloy Duplex System. World Journal of Condensed Matter Physics, 1, 33-36. https://doi.org/10.4236/wjcmp.2011.12006Narain, V. and Ray, S. (2020) Comparative Study of Mechanical Properties of Cast and Forged Al-3Mg-MnO2 and Al-8Mg-MnO2 Composites. Heliyon, 6, e03275.
https://doi.org/10.1016/j.heliyon.2020.e03275Panwar, N. and Chauhan, A. (2018) Fabrication Methods of Particulate Reinforced Aluminium Metal Matrix Composite—A Review. Materials Today: Proceedings, 5, 5933-5939. https://doi.org/10.1016/j.matpr.2017.12.194Marini, C.D. and Fatchurrohman, N. (2015) A Review on the Fabrication Techniques of Aluminium Matrix Nanocomposites. Jurnal Teknologi, 74, 103-109.
https://doi.org/10.11113/jt.v74.4840Srivastava, A.K., Gupta, Y., Patel, S., Tiwari, S.K. and Pandey, S. (2018) Metal Matrix Composites—A Review on Synthesis and Characterization. IOP Conference Series: Materials Science and Engineering, 691, Article No. 012077.
https://doi.org/10.1088/1757-899X/691/1/012077Suthar, J. and Patel, K. (2018) Processing Issues, Machining, and Applications of Aluminum Metal Matrix Composites. Materials and Manufacturing Processes, 33, 499-527. https://doi.org/10.1080/10426914.2017.1401713Srivyas, P.D. and Charoo, M.S. (2018) A Review on Tribological Characterization of Lubricants with Nano Additives for Automotive Applications. Tribology in Industry, 40, 594-623. https://doi.org/10.24874/ti.2018.40.04.08El-Kareem, A.A. (2019) New Extraction Technique of Zirconium and Hafnium from Zircon Mineral. Arab Journal of Nuclear Sciences and Applications, 52, 201-208. https://doi.org/10.21608/ajnsa.2019.3052.1066De Souza, S. and Terry, B. (1994) Production of Stabilized and Non-Stabilized ZrO2 by Carbothermic Reduction of ZrSiO4. Journal of Materials Science, 29, 3329-3336.
https://doi.org/10.1007/BF00356681Rizzuti, A., Leonelli, C., Corradi, A., Caponetti, E., Martino, D.C., Nasillo, G. and Saladino, M. (2009) Structural Characterization of Zirconia Nanoparticles Prepared by Microwave-Hydrothermal Synthesis. Journal of Dispersion Science and Technology, 30, 511-1516. https://doi.org/10.1080/01932690903123676Abdel-Rehim, A.M. (2005) A New Technique for Extracting Zirconium Form Egyptian Zircon Concentrate. International Journal of Mineral Processing, 76, 234-243.
https://doi.org/10.1016/j.minpro.2005.02.004Liu, J.C., Song, J., Qi, T., Zhang, C.Q. and Qu, J.K. (2016) Controlling the Formation of Na2ZrSiO5 in Alkali Fusion Process for Zirconium Oxychloride Production. Advanced Powder Technology, 27, 1-8. https://doi.org/10.1016/j.apt.2015.08.005Abdelkader, A., Daher, A. and El-Kashef, E. (2008) Novel Decomposition Method for Zircon. Journal of Alloys and Compounds, 460, 577-580.
https://doi.org/10.1016/j.jallcom.2007.06.032