Compaction sintering and mechanical properties

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  • 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) IAEMEAND TECHNOLOGY (IJMET)ISSN 0976 6340 (Print)ISSN 0976 6359 (Online) IJMETVolume 3, Issue 3, September - December (2012), pp.565-573 IAEME: Impact Factor (2012): 3.8071 (Calculated by GISI)IAEMEwww.jifactor.comCOMPACTION, SINTERING AND MECHANICAL PROPERTIES OF Al-SiCp COMPOSITES Jeevan.V1, C.S.P Rao2 and N.Selvaraj31,2,3Department of Mechanical Engineering, National Institute of Technology Warangal, Warangal, Andhrapradesh, India.Email: ABSTRACT A trend has been observed in the field of aluminum based composite materials to employ silicon carbide as reinforcement material in developing composites of unique properties. In the present study, an attempt has been made to fabricate the unreinforced Al and its composites were synthesized using the Powder Metallurgy (P/M) manufacturing route with blending, pressing and sintering allows the near net shape fabrication of precision parts. The composites are further solution heat treated at 5290C for two hours and artificially aged at 1750C for 18 hours. Optical Microscopy, Scanning Electron Microscopy has been carried out to analyze powder morphology and composite structure. An increasing trend towards micro-hardness and compressive strength with increase in weight percentage of silicon carbide has been observed. KEYWORDS: Al-SiCp, Mechanical Properties, Microstructure, Powder Metallurgy. 1. INTRODUCTION Particulate Reinforced Aluminum Matrix Composites (PR AMCs) have evoked a vehement interest in recent times for potential applications in aerospace, defence and automotive industries. PR AMCs exhibit improved physical, mechanical and wear resistant properties such as higher stiffness, superior strength-to-weight ratio, improved wear resistance, increased creep resistance , low coefficient of thermal expansion, improved high- temperature properties, and high workability of the composites over those of the monolithic metals oralloys [1-5]. Earlier studies on Metal Matrix Composites (MMCs) addressed the behaviour of continuous fiber reinforcement composite based on aluminum, zinc and titanium alloys matrices. The wide usage of these composites is restricted because of high production cost of composite and composite fiber. MMCs that include both particulate and whiskers have attracted considerable attention than fiber reinforced MMCs, because of their low cost and considerable ease of manufacturing. A wide range of PR AMCs manufacturing processes has565

2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) IAEMEbeen developed. These are generally manufactured either by solid state (Powder Metallurgyprocessing) or by liquid state (stir casting) processes effectively [6].To fabricate PR AMCs, among the various manufacturing technologies powder metallurgy isone the most advantageous techniques to fabricate isotropic distribution of particles in matrix, gooddimensional accuracy, complex, net shape lightweight components can be produced cost effectively.Powder metallurgy is especially suitable for producing PR AMCs as it prevents some wettabilityproblems of silicon SiCp and deleterious reactions that may appear during casting routes. Blendedfine powder mixtures in the solid state with particulates, whiskers or platelets along with bindersproduce materials of uniform microstructure. The conventional powder metallurgy process can easilyformulate different composition by mixing elemental or premixed powders along with reinforcement,and pressing the powder mixture to form green compact by applying hydraulic pressure and sinteringthe green compact in inert gas atmosphere. Few microstructural parameters control and contribute tothe advancement in the properties of PR AMCs. These involve the matrix alloy, the morphology, size,and weight fraction of the reinforcement particulate; the material processing technique; and the heattreatment adapted [1-7].PR AMCs powder is highly compressible. Mostly, green densities of more than 90 % oftheoretical can achieve utilizing low compacting pressures around 200MPa, allowing the use ofpresses with smaller capacity. Sintering of PR AMCs parts is more economical than for most otherPM materials due to the relatively low sintering temperatures. Due to the low density of PR AMCs,more than twice number of parts can be produced from unit weight of powder as compared to ferrous,copper and tungsten based powders. During last decade, several researchers have reported the fabrication of Al-SiCp compositesand testing of their properties such as tensile strength, hardness, wear resistance and microstructuralcharacterization. Most of the researchers have observed that an increase in tensile strength, hardnessand wear resistance while decrease in ductility with increase in reinforcement content and aluminumalloy powders are difficult to sinter because of the stable aluminum oxide film covering the powderparticles and thus reducing sinter-ability. In addition, the presence of hard ceramic particles inaluminum ductile matrix increases the processing difficulty. Related work carried out on aluminumalloy by reinforcing ceramic particles such as SiC, Al2O3, ZrO2, TiO2 etc., with varyingreinforcement sizes, volume/weight fractions, lubricants, compaction pressures, sinteringtemperatures, sintering time, and sintering atmospheres. By varying these parameters will resultoptimal set of parameters lead to resultant microstructure and properties [7-22]. The 6xxx series aluminum alloys have a widespread application, especially in the building,aircraft and automotive industry due to their properties. Increasing demand for these materials haveresulted in increasing research and development for high strength and high-formabilityaluminum alloys. Among 6xxx series aluminum alloys AA6082 one of the most common engineeredaluminum alloy. It offers a combination of better corrosion resistance and weldability due to its lowerstrength values in the welding zone. In numerous applications, AA6061 can be replaced with AA6082due to its higher strength [11-12].The objective of the present investigation is to fabricate the unreinforced Al and itscomposites. Hence, the present studies are aimed at fabrication of Al and Al-5 wt% of SiCpcomposite that is fabricated by powder metallurgy route followed by solution heat treatment andartificially aged. Microstructure, micro-hardness and compressive strength of the developedunreinforced Al and its composites are studied. alloys [1-5]. 566 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME2. EXPERIMENTAL PROCEDURE2.1 Materials It is necessary to select pure metal powder and optimal processing parameters for thepreparation of specimens. Commercial pure aluminum is obtained from M/S Metal PowderCompany Ltd, Tamil Nadu, India. Silicon, Magnesium, and Manganese are supplied bypremier industrial corporation limited Maharashtra, India. Silicon carbide is obtained fromoutside vendor at Tamil Nadu, India. The morphology of raw powders (Al, SiCp) was madewith Scanning Electron Microscopy (SEM), JSM-6390 Model (JOEL) shown in figure 1(A),1(B), 1(C), 1(D) and 1(E). The EDAX analysis has shown in figure 2(A) and 2(B).Particlesize and purity details for raw materials are given in table 1. Fig. 1(A) SEM of Aluminum PowderFig. 1(B) SEM of Silicon Powder Fig. 1(C)SEM of Magnesium PowderFig. 1(D)SEM of Manganese Powder567 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME Fig. 1(E) SEM of Silicon Carbide Powder Fig. 2(A)EDAX of Aluminum Powder Fig. 2(B)EDAX of Silicon Carbide Powder Table 1: Details of Raw MaterialSl.No Raw Material Particle SizePurity1Aluminum-200/+325 mesh99.50%2Silicon -325 mesh 99.57%3Magnesium -150 mesh 99.67%4Manganese -325 mesh 99.78%5Silicon Carbide -1200 mesh98.0%2.2MixingThe chemical composition of the AA6082 prepared by elemental mixing is as follows: Al1.0Si0.9Mg0.7Mn/5.0 SiCp (all concentrations by weight). Contech Precision Balance (Type: CA223) is used for weighing elemental powder. Metal and ceramic powders were blended in a Turbulamixer with Jar container. Blending is one of the crucial processes in powder metallurgy where themetallic powders have mixed with the ceramic reinforced particles.Good blending produces noagglomeration of both the metallic and ceramic powders. 1.5% of acrawax by weight was added to thebase Aluminum powder and mixed separately for 15 minutes. In general lubricant was added andhomogeny blended to reduce friction between the powder mass and the surface of the die and obtain agood compaction. Addition of 1.0 Si, 0.9 Mg, 0.7Mn as elemental were made to the lubricated basepowder and mixed for 15 min each, after which a composition similar to that of wrought 6082 Alalloy was gained. Finally by addition of 5% of SiC particulates by weight to the 6082 Al alloy powderand mixed for 20minutes. The obtained powder mixtures with ceramics were homogeny atmacroscopic level.568 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) IAEME2.3 The Specimens Compacting For pressing, a hydraulic press (Model: plus one machine fabric) was used to obtaingreen compacts. Die wall is brushed with zinc stearate powder for easy ejection of pallet andto reduce the friction between them. Blended Powders were compacted at 200 5 Mpa in ahardened steel die. In order to avoid damage of the samples during ejection, the compac