Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 37 THE EFFECT OF PROCESS PARAMETERS ON MECHANICAL AND WEAR PROPERTIES OF ALUMINIUM- FIRED CLAY COMPOSITES Agbeleye A.A. * , Hassan S.B., Esezobor D.E., Balogun S.A., Agunsoye J.O. Metallurgical and Materials Engineering Department, University of Lagos, Lagos, Nigeria * Corresponding author. Tel.:+2348023165293, aagbeleye@unilag.edu.ng ABSTRACT In this paper, the mechanical and tribological behaviours of as cast and rolled samples of Aluminium AA1070/fired clay (Al-Clay) composites were studied. The composites were developed through stir casting route with 0-20 wt.% clay particles of grain sizes250, 177 and 150 µm. The samples were cold rolled to final reduction of 20 and 35%.Hardness, tensile, impact and wear tests were performed on the developed composite samples and their microstructure were examined to determine the phases present in the composite. The results showed improvement in the mechanical and wear properties of Al-Clay composites with increase in wt.% clay addition. Increase in percent reduction also showed a reasonable increase in the mechanical and wear properties of the rolled samples. The results obtained clearly shows that Al-clay composite can be produced by stir casting and possess superior properties to the Aluminium AA1070 in terms of wear properties, impact energy, tensile strength as well as hardness. Keywords: sliding wear, surface analysis, sliding friction, hardness, three-body abrasion 1.0 INTRODUCTION The increasing demand for the use of lightweight materials with high specific strength in industries such as aerospace and automotive industries has led to the development and use of Aluminum based composite. The Metal Matrix Composite (MMCs) is slowly replacing the general light metal alloys such as aluminum alloy in different industrial applications where strength, low energy and mass savings are of utmost importance in criteria (Allison and Cole, 1993).The use of aluminum in industrial application has been a common practice over the years. Aluminum is the most abundant metal in the earth’s crust and the third most abundant element we have after oxygen and silicon. The chief source of Aluminum is bauxite and aluminum is soft, durable, lightweight, ductile and malleable which makes it suitable for machining operations and various industrial applications. Aluminum alloy are alloys in which aluminum is the predominant metal. Aluminum 1000 series which is the metal matrix to be used for this project is essentially pure aluminum with a minimum 99% aluminum content by weight Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 38 and can also be work hardened. Its high ductility increases its machinability makes it suitable to be used in wires, ships, airplanes, marine, packaging etc. One of the main drawbacks of this material system is that they exhibit poor tribological properties, hence leading to the development of new material with higher wear resistance and better tribological properties, without compromising the strength to weight ratio. (Sinclair and Gregson, 1997). Clay minerals continue to be widely utilized in the production of traditional ceramics and other products due to their ubiquity and low cost combined with properties that include plasticity during forming, rigidity after drying, and durability after firing (Ries, 1927). For much of the twentieth century, the ceramics industry centered on the utilization of clays and other silicate minerals. Clay contains majorly reinforcing materials such as Al2O3 and SiO2 with trace presence of other materials (Esezobor et al., 2014) making it a potential candidate for the production of metal matrix composite for wear applications in friction related environments. This research focuses on the use of AluminumAA1070 reinforced with 150µm, 177µm and 250µm of fired clay particle sizes to produce composites with composition of 0-25wt. %.The effect of cold rolling on Aluminium AA1070/fired clay (Al-Clay)composite samples were also examined. The mechanical and wear tests will be done according to ASTM E8/ESM-13 and ASTM G-99-05 specifications respectively. 2.0 METHODS AluminumAA1070, billet from Aluminum rolling Mill, Otta, Ogun State, Nigeria was then melted and reinforced with 150µm, 177µm and 250µm of fired clay particle sizes to produce 300mm length and 18mm diameter cylindrical rod composites samples with composition of 0-20wt. % using the stir casting technique (figure 1). The composite samples were subjected to cold rolling operation with final reduction of 20 and 35%.The tensile and Brinell hardness tests of samples were conducted using respectively hydraulic universal testing machine UH-X/FX Series machine and Wolpert Testor 930 Universal Hardness Tester. Impact Test was carried out on an Avery Charpy impact-testing machine with a capacity of 298.28Nm and striking velocity of 5.03m/s. The wear characteristics of Al-clay in dry sliding conditions were subjected to a series of pin-on-disc wear tests. Cylindrical pins of 15mm diameter were made from the Al-Clay. The action of a constant load 6N on 60 grit Emory paper at a sliding speed of 1.05m/s was investigated. Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 39 Mechanical (tensile, hardness and impact) and wear tests on the composites samples were carried out according to ASTM E8/ESM-13 and ASTM G-99-05 specifications respectively. Figure 1: Graphical representation of Stir Casting process Metallographic examinations were carried out using CETI 0703552 Metallurgical Research Optical Microscope. The samples were grinded on different grit size papers sequentially by 60, 220, 320,400, 800 and 1200. After grinding the samples were mechanically polished by alumina paste and then pre etched by 1Molar NaOH, then etched by Weck’s reagent for 20 seconds to obtain a better view. 3.0 RESULTS AND DISCUSSION 3.1 Mechanical Properties The results of the analysis of the aluminium alloy and the clay are presented in Table-1 and Table-2 respectively. Electric resistance furnace Electric motor (@800 rpm) Reinforcement (Clay) feeder (@ 10-20g/min) Heating wires Graphite crucible Steel rod Graphite stirrer Molten metal Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 40 Table 1: Optical Emission Spectrometric analysis of Aluminium AA1070 Table-2: Atomic Absorption Spectroscopy (AAS) analysis of clay sample The summary of the Brinell hardness number, ultimate tensile strength (UTS), and impact energy as a function of the percentage weight addition of clay particles is presented in Figures 2, 3 and 4 respectively. The Brinell hardness values of the Al-clay composite as presented in Figure 2 show that increase in the percentage of clay particle addition was accompanied with corresponding increase in the hardness values and it reached a maximum values of 26.4 HB at 20 wt.% fired clay with 250µm particle size, which is an increase of about 28% as compare to the control sample. The cold rolled samples were also seen to show increase in hardness values peaked at 43.9 HB at 35% reduction and 20 wt.% clay with 250µm particle size. The UTS of the composite samples as shown in Figure 3 increases as the addition of clay increases to a peak value of 51.36 MPa at 20 wt.% clay particle addition over the conventional AA1070 of 36.91 MPa. The cold rolled samples also show considerable increase in the UTS values with the maximum value of 116.39 MPa at 35% reduction and 10 wt.% clay with 250µm particle size. Further increase in clay particle addition to 20wt.% clay resulted in a decline in the UTS values. The improvement of the UTS and micro hardness with the increment in the volume fraction of clay particles may be due to the presence and pinning effect of the clay particles (Khraisat and Abu Jadayil, 2010; Essam et al., 2010; Devaraju et al., 2013) which serve as impingement for the movement of dislocations and as a result restrict the sliding of the grain boundaries. Element Si Mg Fe Cu Mn Zn Pb Na Ti B Al % composition 0.0914 0.0037 0.177 0.0005 0.0019 0.0035 0.0013 0.0008 0.0057 0.0003 99.72 Parameters SiO2 Al2O3 Fe2O3 MnO MgO Na2O CaO K2O BaO SO3 LOI Level detected (%) 45.62 33.74 0.43 0.01 0.06 0.05 0.04 0.63 0.01 0.03 4.545 Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 41 0 10 20 30 40 50 0 10 20 30 B ri ne ll H ar d ne ss Clay (wt.%) 250µm @ 0% reduction 177µm 150µm 250µm @ 25% reduction 177µm Figure 2: Brinell Hardness (HB) of Al-Clay composite samples at varying particle sizes and cold rolling conditions Figure 3: Tensile strength of Al-Clay composite samples at varying particle sizes and cold rolling conditions Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 42 Figure 4: Impact energy of Al-Clay composite samples at varying particle sizes and cold rolling conditions The results of the impact test as shown in Figure 4revealed that an increase in the weight percent fired clay particles resulted in increase in impact energy with respect to the base metal. This is due to proper dispersion of fired clay particles into the matrix and also strong interfacial bonding between the base metal and fired clay interfaces. It was also observed that samples with 150µm particle size significantly show superior impact energy with respect to samples with 177µm and 250µm. Cold rolled samples also show considerable increase in the impact energy values with the maximum value of 139J at 35% reduction and 20 wt.% with 150µm particle size. 3.2 Wear characteristics The result of the wear test of the composites with various volume fractions of Al and cold rolled conditions are displayed in Figure 5. The wear rate decreases with increase in the volume fraction of the reinforcing agent (clay) as compared to conventional AA1070. The lower wear rate observed at optimum condition of 20 wt.% clay is due to enhanced hardness by the dispersion of the hard intermetallics over the AA1070 matrix, which acted as load supporting elements (Essam et al., 2010; Devaraju et al., 2013; Kumar and Balasubramanian; 2008). Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 43 Figure 5: Wear rate of Al-Clay composite samples at varying particle sizes and cold rolling conditions Material removal in a ductile material such as aluminum matrix is due to the indentation and ploughing action of the sliding disc. Incorporation of hard fired clay particles in the AluminiumAA1070 restricts such ploughing action and improves the wear resistance. The improvement in wear resistance properties of the developed composites can also be attributed to the release of the clay particles on the surface during wear process, which to an extent may prevent metal to metal contact and also serve as solid lubricants (Tjong et al., 1999). On the other hand, the wear rate increases with increase in the normal load and sliding speed. This trend was also observed in the work of Devaraju et al., (2013). 3.3 Microstructure The results of the metallographic examination of all the samples are displayed in Plates1-2. The clay particles are fairly distributed along the grain boundaries of the AluminiumAA1070 matrix. The addition of the clay particles is observed to have enhanced the formation of finer grains Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 44 Plate 1: Optical microstructure of the Al-Clay composite samples with 250µm particle size (a) As cast AluminiumAA1070, (b) 5% clay, (c) 10% clay, (d) 15% clay, (e) 20% clay Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 45 Plate 2: Optical micrograph of Al-Clay composite with 20% Fired clay of 250µm at (a) 20% reduction (b) 35% reduction The microstructure as revealed in Plate 2 show that increase in the percentage reduction in cold roll promotes the formation of finer grains which can be attributed to the improvement in the mechanical and wear properties of the developed composites. 4.0 CONCLUSIONS The conclusions drawn from the present investigation are as follows: 1. The results obtained clearly shows that Al-Clay composite can be produced by stir casting and possess superior properties to the Aluminium AA1070 in terms of wear properties, impact energy, tensile strength as well as hardness. 2. Increase in fire clay additions also resulted in an increase in tensile strength, impact energy, and the hardness of the developed composite. 3. Increase in the particle size of fired clay causes a reduction in the impact energy. 4. The formation and distribution of the second phase particles is uniformed around the grain boundaries of the microstructure and generally improve the mechanical properties of the developed composite. 5. Cold worked samples show superior mechanical and wear properties as compare to as-cast samples. Unilag Journal of Medicine, Science and Technology (UJMST) Vol. 5 No 2, 2017 46 5.0 REFERENCES Allison, J.E. and Cole, G.S. (1993). “Metal Matrix Composite in Automotive Industry: Opportunities and Challenges”, Journal of Mechanical Science. 45: 19-24. Devaraju, A., Kumar, A., Kumsrswamy, A, Kotiveerachari, B. (2013). “Influence of reinforcements (SiC and Al2O3) and rotational speed on wear and mechanical properties of aluminium alloy 6061-T6 based surface hybrid composites produced via friction stir process.” Materials and Design. 51: 331-341. Esezobor D. E., Obidiegwu E. O. and Lawal G. I. (2014). “The influence of agro- forestry waste addictive on the thermal insulating properties of Osiele clay”. Journal of Emerging Trends in Engineering and Applied Sciences. 5, (5): 305-311 Essam, R. I., Makoto, T., Tishiya S. and Kenji I. (2010). “Wear characteristics of surface hybrid MMCs layer fabricated on aluminium plate by friction stir processing”. Wear.268:1111-21. Khraisat W. and Abu Jadayil W. (2010).“Strengthening aluminium scrap by alloying with iron.”Jordan Journal of Mechanical and Industrial Engineering. 4, (3): 372–377. Kumar S. and Balasubramanian V. (2008). “Developing mathematical model to calculate wear rate of AA7075/SiCp powder metallurgy composite”.Wear.264:1026-34 Ries H. (1927).Clays: Their Occurrence, Properties, and Uses, (3rd Edn). John Wiley, New York.