A Study on Mechanical Properties of Aluminium LM25- Si c Composites Fabricated Using Stir Casting Technique.Satyanarayen 1, Dominic Roystan 2, M.Shreesaravanan 3 Balaguru 4, C.Devanathan 5 1,2,3,4 UG Students, Department of Mechanical Engineering, Jeppiaar Institute of Technology, Kunnam 5, Assistant Professor, Department of Mechanical Engineering, Jeppiaar Institute of Technology, Kunnam Abstract: Aluminium Matrix Composites (AMCs) refer to the kind of light weight high performance aluminium centric material system. AMCs consist of a non metallic reinforcement which included into aluminium matrix which offers advantageous properties over base material. Reinforcements like si c, B 4 C, Al 2 O 3, Ti c, TiB 2, TiO 2 are normally preferred to improve the mechanical properties. Here aluminum LM25 is selected as matrix material, while silicon carbide is selected as reinforcement material. The Silicon Carbide is added in 3%, 6% and 9% of weight to LM25 alloy to fabricate the MMC. The fabrication of Aluminium matrix is done by Stir Casting method. Stir Casting is a liquid state method of composite materials fabrication, in which a dispersed phase is mixed with a molten matrix metal by means of stirring. The fabricated samples were tested for its tensile strength, wear resistance, and hardness to investigate the effect of silicon carbide in matrix material. Keywords: LM25 Aluminum alloy, Sic, Stir Casting Method, Tensile test, Wear Resistance, Hardness Test. Introduction: Conventional monolithic materials have limitations in achieving good combination of strength, stiffness, toughness and density. To overcome these shortcomings and to meet the ever increasing demand of modern day technology, composites are most promising materials of recent interest. Composite material is a material composed of two or more distinct phases (matrix phase and reinforcing phase) and having bulk properties significantly different from those of any of the 45
constituents. Favourable properties of composites materials are high stiffness and high strength, low density, high temperature stability, high electrical and thermal conductivity, adjustable coefficient of thermal expansion, corrosion resistance, improved wear resistance etc. On the basis of matrix, the composites are classified as metal matrix composites, Ceramics matrix composites, and polymer matrix composites. Metal Matrix Composites are composed of a metallic matrix (aluminium, magnesium, iron, cobalt, copper) and a dispersed in the ceramic (oxides, carbides) or metallic (lead, tungsten, molybdenum) phase. Driving force for the utilization of AMCs in areas of aerospace and automotive industries include performance, economic and environmental benefits. LM25 is mainly used where good mechanical properties are required in castings of shape or dimensions requiring an alloy of excellent castability in order to achieve the desired standard of soundness.[2] LM25 finds applications in the food, chemical, marine, electrical and many other industries, and above all - in the automotive industry where it is used for wheels, cylinder blocks and heads. S.Tzamtzis et.al used conventional stir casting technique to prepare the cast A356/SiC composites and found a good combination of improved ultimate tensile strength and tensile elongation [1]. Akhilesh et.al carried out property analysis of aluminium(lm25) metal matrix with SiC as reinforcing materials and concluded that functionally graded composite cylinder shows improved hardness towards outer periphery, due to the presence of higher volume fraction of SiC particles[2]. Elango et.al investigated the wear behaviour of LM25 and its composites reinforced with SiC and Titanium Dioxide (TiO 2 ). The results revealed that the reinforcement has improved the wear resisting property of LM 25 alloy [3]. Sathyabalan et.al studied the wear behaviour of aluminium silicon carbide (SiC) composites and concluded that higher the volume fraction of SiC reduces the weight of the aluminium alloy as well as wear rate [4]. Shubham Mathur et.al studied the influence of process parameters of stir casting in making aluminium metal matrix composites
with 5% SiC of 400 grit size and observed that the mechanical properties such as hardness, impact strength, tensile strength of the composites found increased with increasing the grit size [5] The main focus of the proposed work is to study the influence of percentage volume fraction of SiC in matrix aluminium on mechanical properties such as tensile strength, hardness and wear resistance. Experimental Procedure a) Selection of Material The Aluminum Silicon Magnesium (LM25/ 365) was chosen as the material for the matrix. SiC is selected as the reinforcement for its major advancements such as low density, high strength, high thermal conductivity and higher elastic modulus. The table 1 shows the chemical compositions of the LM25. Mechanical Properties of the LM 25 is shown in the table 2. Table 1: Composition of Aluminium Alloy (LM25) % Wt. Cu Si Mg Fe Mn Ni Zn Pb Sn Ti Al 0.20 7.50 0.06 0.50 0.30 0.10 0.10 0.10 0.05 0.02 Balance b) Preparation of the Composite The composites were mainly fabricated using liquid stir casting technique which was initiated in 1968 when S.Ray introduced alumina particles into aluminium melt by stirring molten aluminium alloys containing the ceramic powders. Stir casting is suitable for manufacturing composites with up to 30% volume fraction of the reinforcement. Fig.1 shows the Stir Casting apparatus used for making the composites.
Fig.1. Stir Casting Apparatus Initially, Matrix metal LM25 Al alloy was charged into the crucible. The furnace temperature was first raised above the melting point of aluminium LM 25(450 C) to melt the aluminum alloy completely and then cooled down just below the liquidus temperature to maintain the slurry in a semi-solid state. The reinforcement particles silicon carbide (SiC) was preheated to a temperature of 800 C in a brick walled furnace. The preheated reinforcement material were added and mixed. Mechanical mixing was the preferred stirring technique to ensure the proper mixing of the reinforcement in matrix metal. The mixing was carried out for several minutes at a normal stirring speed of 420-480 rpm. Then the molten mixture was poured in the pre heated die to prepare the casted workpiece. The samples were prepared with different volume fraction of SiC (3%, 6%, and 9 %.). The prepared samples are shown in the Fig.2. The prepared samples were tested for tensile strength, hardness, and wear resistance.
Results and Discussion: a) Tensile Test: Fig. 2. Prepared Samples The tensile test was carried out at room temperature on 5 tonne Universal Testing Machine. To carry out the test the samples were prepared as per ASTM standards which is shown in the Fig.3 shows the tensile test specimen details as per the standard. Fig.3. ASTM Standards The tensile test results are given in the table 2. and result clearly shows that increasing the volume fraction of the reinforcement, increases the tensile strength of the composite. % of Reinforcement Ult.Break Load KN Area mm 2 Ult. Stress Mpa Yield Stress Mpa 3 6.165 28.38 217 148
6 6.165 27.82 222 156 9 2.490 27.35 235 162 Table 2: Tensile Test Results Hardness Test: Hardness test was carried out on the composites prepared. The result of the hardness test is given in table 3. The Brinell hardness was measured on the polished samples using steel ball indenter of 10mm diameter with a load of 500kgf. The reported value is an average of 3 readings taken at different locations on the specimens. A significant increase in hardness of the alloy matrix was seen with the addition of SiC particles. This indicated that the existence of particulates in the matrix improved the overall hardness of the composites. This is due to the fact that aluminum is a soft material and the reinforced particles being hard, contribute positively to the hardness of the composites. Fig.4 shows the results of Brinell hardness tests conducted on aluminium LM 25 composites containing different weight percentages of SiC particles. Table 3. Results of Hardness test Sample No. Sample Name Micro Vicker Hardness Test Trial 1 Trial 2 Trial 3 Mean Hardness 1. Pure Aluminium 60.5 60.4 60 60.3 2. 3 %SiC 73.2 72.8 73.9 73.3 3. 6 %SiC 72.3 71.2 71.3 76.27 4. 9 %SiC 78.1 76.7 76.0 77.27 Fig.4. Hardness of the composites
Wear Test: Pin-on-disc is one of the widely used methods to analysis the wear of the composites. For the pin-on-disk wear test, two specimens are required namely a pin, and a flat circular disk. The test machine causes the pin specimen to revolve about the disk center. The prepared pin and disc is shown in the fig. 5 and 6. Fig.5. Sample Pin Fig.6.Sample Disc Table 4. Wear Test results Weight before testing (gms) SiC (%) Speed (rpm) Time (min) Load (kg) Weight After Testing (gms) Material Loss 4.475 3 500 10 2 4.465 0.01 4.521 6 500 10 2 4.513 0.008 4.526 9 500 10 2 4.521 0.005 4.516 3 600 10 2 4.513 0.103 4.5 6 600 10 2 4.493 0.007 4.48 9 600 10 2 4.477 0.003
Wear test was conducted by maintaining the time and load constant for two different speed of 500 rpm and 600 rpm. The results were given in the table 4. The result clearly shows that increasing the reinforcement content in the matrix material reduced the material loss and in turn increases the wear resistance of the composite material. Conclusion: The following conclusion can be drawn from the present work: Stir casting technique can be considered as an effective liquid based technique for making the Aluminium metal matrix composites. Mechanical properties such as tensile strength and hardness increases with increasing the percentage contribution of SiC reinforcement. During the pin on Disc wear test it was found that, increasing the SiC particles content in matrix reduces the material loss so that the wear resistance of the material improves to the considerable extend. References: [1] J Hashim, L Looney, M.S.J. Hashim The Enchancement Of Wetability Sic Particle In Cast Aluminium Matrix Composite Journal of material processing technology 119,(2001), 329-335 [2] Akhilesh Jayakumar, Mahesh Rangaraj, Property Analysis of Aluminium (LM-25) Metal Matrix Composite, International Journal of Emerging Technology and Advanced Engineering, Volume 4, Issue 2, February (2014), 495 501 [3] Elango, G.; Raghunath, B.K.; Palanikumar, K.; and Tamizhmaran, K. (2013).Sliding wear of LM25 aluminium alloy with 7.5% SiC +2.5% TiO2 and 2.5% SiC + 7.5% TiO2 hybrid composites. Journal of Composite Materials,2(1), [4] Sathyabalan, P.; Sakthivel, P.; and Selladurai, V. (2001). ANN based prediction of effect of reinforcements on abrasive wear loss and hardness in a hybrid MMC. American Journal of Engineering and Applied Sciences, 2(1), 50-53.
[5] Shubham Mathur, Alok Barnawal, Effect of Process Parameter of Stir Casting on Metal Matrix Composites, International Journal of Science and Research, Volume 2 Issue 12, December 2013, 395-398 [6] Radhika n,balaji. T. V, Palaniappan. S, studies on mechanical properties and tribological behaviour of LM25/SiC/Al 2 O 3 composites Journal of Engineering Science and Technology, Vol. 10, No. 2 (2015)134 144 [7] Mr. Prasanna, Mr. Devraj, Mr. Rakeshkumar, Mr. Mahadevappa, Sharanabasappa R P, A Study on Mechanical Properties of Silicon Carbide, E-Glass and Red Mud Reinforced Aluminium (LM25) Composite, IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE), Volume 11, Issue 3 Ver. VIII (May- Jun. 2014), PP 08-19 53