Microstructure and Mechanical Behaviour of A356/SiC/MoS 2 Hybrid Composites for an IC Engine Block Application

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1 Volume-6, Issue-5, September-October 2016 International Journal of Engineering and Management Research Page Number: Microstructure and Mechanical Behaviour of A356/SiC/MoS 2 Hybrid Composites for an IC Engine Block Application S. Mohamed Jameen Assistant professor, Department of Automobile Engineering, K.L.N college of Engineering, Madurai, INDIA ABSTRACT The application of aluminium composites in the automotive industry has changed the use of traditional grey cast iron for engine cylinder blocks. Use of aluminium composites as a substitute for grey cast iron has positive aspects such as reduction of engine mass, lower fuel consumption and therefore reduced pollution. Unfortunately most aluminium alloys do not have satisfactory wear resistance. Also neglecting grey cast iron results in loss of natural self-lubricating property, which is very much needed in engine block applications. The focus of this research paper will be to select a suitable aluminium metal matrix composite which should have high strength, wear resistance and selflubricating property. It is noted that A356 (an aluminium grade) is preferred for engine block applications. Silicon carbide is known for its high strength and molybdenum disulfide is a very good self-lubricator. In this paper, microstructure and mechanical properties of A356/SiC/MoS 2 hybrid composites have been analyzed. It is proposed to use this hybrid composite for engine block applications. Keywords Aluminium MMC s, A356/SiC/MoS2 hybrid composites, microstructure and mechanical behaviour, Automotive engine block application. I. INTRODUCTION Aluminium based hybrid composites are being used in automotive applications like pistons, brake rotors and engine-block cylinder liners.tribological behaviour is an important aspect in the use of aluminium metal-matrix composites in automotive applications. Prasad et al [1] described the tribological behaviour of aluminium metal matrix composites reinforced with hard particles, short fibers and solid lubricants. Vinoth et al [2] investigated the mechanical and tribological characteristics of aluminiummolybdenum disulphide self-lubricating composites and compared to the Al-Si10Mg alloy, Al-Si10Mg/4MoS 2 shows the finest microstructures due to a higher fraction of MoS 2 added. Al-Si10Mg/2MoS 2 and Al-Si10Mg/4MoS 2 showed an enormous decrease in the wear rate by 55 % and 65 %, respectively, compared with the Al-Si10Mg alloy. The decrease in the wear occurs due to the presence of a MoS 2 layer, which forms a film on the wear surface.bhargavi Rebba et al [3] have reported the results of an experimental investigation on the mechanical properties of molybdenum disulphide (MoS 2 ) powders reinforced in aluminium alloy (Al-2024) composite samples. From the literature review it is observed that by implementing aluminium metal matrix composites instead of grey cast iron for IC engine cylinder block, the engine efficiency is improved. Also fuel economy is achieved due to reduction of engine weight. Most of the researchers concentrate on the aluminium metal matrix composites for manufacturing of IC engine cylinder block. Based on various reviews this project concentrates on aluminium metal matrix composites. II. MATERIALS In this study, A356 alloy has been selected as matrix alloy since it has very good mechanical strength, ductility, hardness, fatigue strength, pressure tightness, fluidity and machinability. Table I shows the chemical composition of A356 alloy.silicon carbide (SiC) has been chosen as one of the reinforcement material. This produces a very hard and strong material. The high thermal conductivity coupled with low thermal expansion and high strength gives this material exceptional thermal shockresistant qualities. Another reinforcement material used is molybdenum disulfide (MoS 2 ). It is considered as sacrificial lubricant and transfers material between the two mating surfaces involved, which is aimed to increase wear resistance. These sacrificial layers, and its lubricating properties, give the coating its low coefficient of friction. On the basis of the literature review and the results based on pilot investigations, the compositions of 257 Copyright Vandana Publications. All Rights Reserved.

2 reinforcements (SiC and MoS2) were selected and are shown in Table II. The total percentage of both reinforcements varies from 0 to 20 % wt. fraction in metal matrix. If the wt% of reinforcements increases more than 20 % there is no more effect on physical and chemical properties of hybrid metal matrix composite. TABLE I CHEMICAL COMPOSITION OF A356 ALLOY (%) Si Fe Cu Mn Mg Zn Ti Al Figure 3: Sample I Figure 4: Sample II TABLE II THE VARIOUS COMPOSITIONS OF MATRIX AND REINFORCEMENTS Sample I 85% A356 15% SiC 0% MoS 2 Sample II 85% A356 13% SiC 2% MoS 2 Sample III 85% A356 11% SiC 4% MoS 2 III. METHODOLOGY Fabrication of hybrid metal matrix composite was done by stir casting method. Stir Casting is a liquid state method of composite materials fabrication, in which a dispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal by means of mechanical stirring. Stir Casting is the simplest and the most cost effective method of liquid state fabrication. The liquid composite material is then cast by conventional casting methods and may also be processed by conventional Metal forming technologies. Figure 1 and Figure 2 show the manual stir casting method and green sand die respectively. The molten hybrid composite material is poured into the green sand die whose mould cavity is (150mm X 150mm X 10 mm) in dimension. Three samples were produced with 3 different compositions of A356/SiC/MoS 2.Figures 3, 4, 5 show the samples I, II and III respectively. IV. Figure 5: Sample III RESULTS AND DISCUSSIONS Microstructure analysis: The optical micrographs of 3 samples were obtained using scanning electron microscope (SEM).The SEM images of samples I, II, III are shown in figures 6, 7, 8 respectively. All the three samples show as-cast (dendritic) structures consisting of silicon carbide particles in an eutectic A356 matrix. The sample III exhibits the finest microstructure due to the higher fraction of MoS 2 added. Figure 6: Sample I Figure 7: Sample II Figure 1: Manual stir casting method Figure 2: Green sand die Figure 8: Sample III Hardness: For hardness testing, the samples of A356/SiC/MoS 2 hybrid metal matrix composites have been prepared as per dimension (10 mm X 10 mm X 25 mm). Also the three samples are heat treated at 500 C for 5 hours and quenched. For hardness test, Brinell hardness testing machine is used. The load applied is 500kgf using a ball indenter of 10 mm diameter for about 30 seconds. The measured values of hardness of different compositions for as-cast and as heat-treated hybrid composites are 258 Copyright Vandana Publications. All Rights Reserved.

3 summarized in Table III. Figure 9 show the Comparison of hardness of samples I, II and III. TABLE III COMPARISON OF AVERAGE VALUES OF HARDNESS OF 3 DIFFERENT SAMPLES Samples Hardness as cast (BHN) Hardness as heat treated (BHN) Improved hardness (BHN) I II III TABLE IV COMPARISON OF AVERAGE VALUES OF TENSILE STRENGTH OF 3 DIFFERENT SAMPLES Ultimate break load Samples Tensile strength (N/mm 2 ) (kn) I II III Figure 12: Comparison of tensile strength of samples I, II and III Figure 9: Comparison of hardness of samples I, II and III Tensile Strength: For tensile testing of A356/SiC/MoS 2 hybrid metal matrix composites material, three samples were prepared as per ASTM. Figure 10 and 11 show the tensile test samples before and after test. The tensile samples were tested at room temperature. The tests revealed that, the ultimate tensile strength gradually increased by the increase in wt. % of the reinforcement added to the metal matrix. The maximum tensile strength was observed at 2% MoS 2. Wear Resistance: A pin-on-disc tribometer is used to perform the wear experiment. The results show that the sample I attained high wear of 191µm. The sample II attained 49µm of wear, which is the lowest value when compared to all other samples. This is due to the presence of 2% MoS2 powder in sample II. Figure 13: Wear test samples TABLE V INPUT PARAMETERS FOR WEAR TEST Figure 10: Tensile test samples before testing Wear testing machine Length of the pin Diameter of the pin Diameter of the disc Input load Speed Pin on disc 25 mm 8 mm 150 mm 5 N 500 rpm Figure 11: Tensile test samples after testing TABLE VI COMPARISON OF MAXIMUM WEAR OF THREE SAMPLES Samples Maximum wear (µm) I 191 II 49 III Copyright Vandana Publications. All Rights Reserved.

4 Figure 14: Comparison of wear of three samples Impact strength: The Charpy V-notch test is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. The input parameters for impact testing machine is shown in table VII. The impact test results are summarized in table VIII. The results show that sample I has greater impact strength of 100 kn/m when compared to other samples. This is due to the presence of more SiC material in sample I. Figure 16 represents the variation of impact strength for samples I, II and III. Corrosion resistance: The simplest and longestestablished method of estimating corrosion losses is weight loss analysis. The weighed samples of the metal or alloy under consideration is introduced into the process, and later removed after a reasonable time interval. The samples are then cleaned of all corrosion products and are reweighed. The corrosion test samples are shown in figure 17. Table IX represents the input parameters for corrosion test. Three samples I, II and III were hanged into a 100 ml beaker with normal bore water as shown in figure 18. After 24 hours of time interval the samples are take out and dried in an oven at 50 C.The dried samples are then weighed again. The table X shows the comparison of weight of three different samples before and after test. The result shows that there is not much difference in the weight of the samples. Thus the three samples are corrosion resistant in nature. Figure 17: Corrosion test samples Figure 15: Impact test samples TABLE VII INPUT PARAMETERS FOR IMPACT TEST Machine name Charpy impact testing machine Capacity 300 joules Least count 2 joules Size of the specimen 60 X 10 X 10 mm TABLE VIII IMPACT TEST RESULTS Samples Energy absorbed (J) Impact strength (kn/m) I II 4 50 III 2 25 Figure 18: Corrosion test-weight loss method TABLE IX INPUT PARAMETERS FOR CORROSION TEST Testing method Weight loss method Testing medium Normal bore water Testing time 24 hours Quantity of water 100 ml TABLE X CORROSION TEST RESULTS Figure 16: Comparison of impact strength of samples I, II and III Samples Weight of sample before test (g) Weight of sample after test (g) I II III V. CONCLUSION In this research work, A356/SiC/MoS 2 hybrid composites with 3 different compositions were fabricated using stir casting technique and the microstructure and 260 Copyright Vandana Publications. All Rights Reserved.

5 mechanical behaviour were studied.the following important observations can be noted: 1. Microstructures of A356/SiC/MoS 2 hybrid MMC sshow that the sample II exhibits better distribution of SiC and MoS 2 particlesin the matrix (A356). 2. The hardness of A356/SiC/MoS 2 hybrid composites samples is increased after heat treatment process. In both cast and heat treated samples, sample III attained a highest value of and Brinell hardness number (BHN) respectively. 3. The ultimate tensile strength is gradually increased by the increase in wt. % of the reinforcement added to the metal matrix. The 2 maximum tensile strength of 61 N/mm was obtained in sample II (2% of MoS 2 ). 4. The wear test results show that the sample I attained high wear of 191µm. The sample II attained 49µm of wear, which is the lowest value when compared to all other samples. This is due to the presence of 2% MoS2 powder in sample II. 5. The impact test results show that sample I attained greater impact strength of 100kN/m when compared to other samples. 6. All the three samples are corrosion resistant in nature. 7. On considering all the results, the sample II has good mechanical and wear properties and it is suitable for IC engine block applications. Aircrafts:A Review, Materials And Design,Volume-46 (2013) Pages REFERENCES [1] S.V. Prasad and R. Asthana et al Aluminium metal matrix composites for automotive applications: tribological considerations, Tribology Letters (2004), Vol.17, No. 3. [2] Kannappan Somasundara Vinoth, Ramanathan Subramanian, Somasundaram Dharmalingam, Balu Anandavel et al Mechanical and Tribological Characteristics of Stir-Cast Al-Si10Mg and Self- Lubricating Al-Si10Mg /Mos2 Composites, Materials and technology 46 (2012) 5, [3] Bhargavi Rebba et al Evaluation of Mechanical Properties of Aluminium Alloy (Al-2024) Reinforced with Molybdenum Disulphide (MOS2) Metal Matrix Composites, Procedia Materials Science 6 (2014), [4] R. L. Deuis, C. Subramanian, J. M. Yellup et al Dry Sliding Wear Of Aluminium Composites-A Review Composites Science and Technology 57(1997) [5] Haizhi Ye et al An Overview of the Development of Al-Si-Alloy Based Material for Engine Applications, Journal of Materials Engineering and Performance (2003) Volume 12(3) [6] Zainul Huda, Prasetyo Edi et al Materials Selection In Design Of Structures And Engines of Supersonic 261 Copyright Vandana Publications. All Rights Reserved.