27-08-2014, 12:07 PM
THERMAL ANALYSIS OF AUTOMOTIVE CYLINDER HEAD MADE BY ALUMINIUM METAL MATRIX COMPOSITE REINFORCED WITH NANO ALUMINA
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Abstract—
Metal Matrix Nano Composites (MMNC’s) have been developed to meet the demand for lighter materials with significant improvements in mechanical and physical properties like high strength, excellent wear resistance, good thermal conductivity, low thermal expansion coefficient with particulate reinforcements. Aluminium based nano composites (AA356 – nano Al2O3) with three different percentage (1%, 1.5%, 2.5% Wt) of nano – alumina particulate reinforcement (~40 nm) were fabricated using in-situ stir casting technique. Mechanical properties characterization which strongly depends on microstructural properties of reinforcement revealed that the presence of nano – alumina particulates lead to simultaneous increase in hardness, UTS, wear behaviour. The results revealed that UTS, Hardness, Wear behaviour increases with the increase in the percentage of reinforcement of nano – Al2O3 whereas the thermal conductivity drops with increasing percentage of reinforcement when compared to the base alloy AA356. An attempt is made in the present study to review the opportunities of using such a MMNC developed in automotive brake drum replacing the current system using cast iron.
I. INTRODUCTION
Aluminium composites are used for making various components such as brake drum, cylinder liners, cylinder heads, cylinder blocks etc. Aluminium alloy MMNC is becoming potential engineering materials offering excellent combination of properties. Because of their excellent properties, they are being used in various engineering applications . Particulate reinforcement by employing double layer feeding - stir casting technique proves to be a promising technique in developing MMNC. The properties of MMNC developed are critically governed by selection of type of reinforcement and its compatibility with metallic matrix. Reinforcement of Nano Al2O3 ensures uniform distribution and minimal porosity .
II. EXPERIMENTAL PROCEDURE
A. Materials and processing
Aluminium Alloy AA356 and nano – Al2O3 were chosen as Matrix alloy and reinforcement respectively. AA356 is selected as the matrix alloy which has fewer tendencies to drag than with high silicon alloys containing no other alloying elements. AA356 Alloy has high Resistance to corrosion attack under normal atmospheric condition. Nano alumina particulates were reinforced with matrix alloy in different weight percentages of 1%, 1.5% and 2.5% respectively. The matrix was preheated at 200 °C and the reinforcements were added to the matrix material using double layer feeding mechanism . The mix was then melted to liquidus temperature of 600°C – 700°C and motor stirrer at 90RPM. The spectro- analysis test report of the matrix alloy is given in Table
A. MMNC Samples
The MMNC samples prepared shows presence of porosity reduces with increase in the percentage of reinforcement. Samples prepared for hardness shows the presence of porosity clearly through the visual investigation. Fig. 2 shows the surface of the samples. The presence of porosity reduces as the reinforcement increases since the interfacial bonding between the aluminium matrix and the Al2O3 particulates is high for higher percentage of reinforcements.
C. Mechanical test results
It was observed that the MMNC samples with higher percentage of reinforcement shows higher hardness. The hardness values of the test samples were shown in Fig. 5. In case of tensile tests, the results revealed that breaking strength and ultimate tensile strength was at a peak for MMNC with 2.5% nano alumina reinforcements. The property of the material changes from ductility to brittle nature on addition of reinforcements in further. The tensile test result plots were shown in Fig. 6.
IV. CONCLUSIONS
The Aluminium alloy (AA356) hard particle MMNC can be synthesized successfully using the double layer feeding - stir casting solidification process. The MMNC thus prepared exhibits good wear resistance compared to the ethnic materials. Beyond the critical load the MMNC may exhibit the same characteristics as that of base alloy. Further, frictional heating and coefficient of friction are noted to be considerable less in composite as compared to that in the alloy.
Additionally the temperature rise in the MMNC cylinder head is considerable less compared to that of the cast iron cylinder head during the high condition. Also the various mechanical test results revealed that MMNC can be employed promisingly in the field of development of automobile engineering as a replacement to the existing materials. The results revealed the potential to replace the existing components by using the MMNC so far discussed.