Evaluation Of Hardness Strength Of Aluminium Alloy (AA6061 .

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International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE)Volume: 1 Issue: 4ISSN: 2349-7947014– 018Evaluation of Hardness Strength of Aluminium Alloy (AA6061) Reinforced WithSilicon CarbideKrishnaMechanical Department,M.S.Ramaiah institute of technology, MMechanical DepartmentM.S.Ramaiah institute of mAbstract - In the experimentation, AMC specimens were cast by Stir cast method, for different size and percentage ofreinforcing material. Standard size Hardness test specimens were prepared and the properties evaluated. The compositematerials offers a solution to the challenging problem of, developing materials with high performance capability. Due to thelightness of aluminium, its alloys find a wide range of applications. Silicon carbide (SiC) is known for its hardness and highdegree of chemical inertness. In this experimentation, An Aluminium metal matrix composite (AMC) consisting of aluminiumalloy (AA6061), reinforced with SiC is considered for evaluation.Keywards : High performance, Chemical inertness, AMC, Hardness.I.INTRODUCTIONThis experimentation aims at materializing aMMC by reinforcing AA6061 alloy with silicon carbideand studying its Hardness properties. The reinforcement isdone using stir casting technique[1,2]. With the increasingdemands for superior light weight materials, in areas suchas aircrafts, space shuttles, deep sea submarines,hypersonic space planes etc, there is a need to developmaterials with high performance capabilities. Thecomposites approach offers a systems solution to thischallenging problem. The recent advancement in the fieldof material sciences led to the development of species ofmaterials known as composites. Composites are materialsmade from two or more constituent materials withsignificantly different physical or chemical properties, thatwhen combined, produce a material with characteristicsdifferent from the individual components[3,4]. Thecomposites created with metal or a metal alloy as the base,are known as metal matrix composites (MMCs). Thealuminium alloy (AA6061) has proved its usefulness invarious fields ranging from aircraft construction tocommon household equipments such as ladders andwindow frames. Silicon carbide (SiC) is a potentialmaterial for structural applications at high temperatures.Also, it has good hardness and high degree of chemicalinertness.1.1 Literature reviewAA 6061 is a precipitation hardening aluminium alloy,containing magnesium and silicon as its major alloyingelements. Originally called "Alloy 61S," it was developedin 1935[1]. Common applications of AA 6061 are Windowframes, Engine cylinder blocks, Pressure vessels, Aircraftfuselage, Aircraft wings, Household wiring, Yacht andboat construction, Automotive wheel spacer assemblies,Aluminium wrapping foils and cans for food andbeverages and so on. Composite materials are complexmaterials whose components differ strongly from eachother in the properties. Composite materials can be definedas a macroscopic combination of two or more materials,having a recognizable interface between them. The firstfocused efforts to develop Metal Matrix Compositesoriginated in the 1950s and early 1960s. The principalmotivation was to dramatically extend the structuralefficiency of the metallic materials while retaining theiradvantages. Metal matrix composites typically useabrasive grade ceramic grit. Silicon carbide provides thebest strength and stiffness for aluminium alloy matrices,but is slightly more expensive than aluminium oxide. Theintrinsic advantage of Metal Matrix Composites developedby reinforcement of the base alloy is the improvement inmechanical properties, strength and stiffness of the sodeveloped composite material. Y.Sahin[7] has investigatedaluminium alloy containing various particle sizes of 10%and 20% Silicon Carbide particles prepared by moltenmetal matrix and squeeze casting method under argon gas.Microscopic examination, hardness, density and porositymeasurement have been carried out. The uniformdispersion of particles in the matrix alloy has beenobserved. The density decreases with increase in particlesizes, but porosity increases considerably with increase inparticle size. The present study aims at conducting anexperimental analysis of the variation in the hardnessproperties of AA6061 alloy, reinforced with 5%, 10% and15% weights of 400, 320 and 200 mesh sizes of siliconcarbide powders.14IJRMEE November 2014, Available @ http://www.ijrmee.org

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE)7947Volume: 1 Issue: 4018ISSN: 2349014–II.METHODOLOGYdistributing the reinforcement material [5,6]. After theaddition of requisite SiC powder, stirring was done usingmotorized stirrer, as shown in Fig 2. Molten metal is poured into the Die and the Die with solidified MMC is shown in Fig 3and the casting shown in Fig 4. Standard dimensions [6] ofhardness test specimen are shown inFig 5and theIII.EXPERIMENTProcedure followed in stir casting and subsequentevaluation of hardness strength is as follows [7,8]. The reinforcement particles were weighed as perthe experiment’s requirement, preheated to 600ºC ina separate electric furnace and added to AA6061alloy melted to 750ºC. The required quantity ofalloy is weighed and melted in ceramic crucible andThe furnace was totally closed by ceramic wool isused to avoid the escape of heat from the furnace. Degassing tablet (hexachloroethane) was added andthe slag was removed carefully Matrix was kept in the furnace for around fourhours and then the AA6061 alloy was ready for stircasting. The silica wool from the main furnace wasremoved and stirrer setup was brought into itsposition to stir the melt. 450 RPM was set as thestirrer speed using the speed regulator, the preheatedreinforcement material was carefully added. Due tothe stirring speed, vortex was formed and it allowedthe reinforcement to mix properly throughout themelt. The melt was continuously stirred for 10minutes and poured into the pre heated fingermould, coated with chalk powder. Specimens were cooled and separated from thecasting and machined as per the dimensions ofstandard hardness test specimen to be tested onhardness testing machine. Casting is obtained and specimens were preparedfor varying weight percentages (5%, 10%, and 15%)and particle size (200 mesh, 320 mesh and 400mesh) of SiC. A specimen was also cast andmachined, corresponding to basic metal withoutreinforcement and is called “as cast” specimen. Each specimen is mounted on the “Hardness testingmachines” and BHN, HRB and HV were recorded.IV.RESULTS AND DISCUSSIONS.The hardness test was done, in order to determine theRockwell Hardness number (HRB), the BrinellHardness Number (BHN) and the Vickers HardnessAn electric furnace with stirring mechanism, shown inFig1, is used for melting the base metal and uniformlymachined specimen in Fig 6. An “as cast” specimen was alsoobtained for strength comparison. Rockwell hardness, Brinellhardness and Vickers hardness, for as cast and MMC withdifferent % of reinforcing material and different particle sizewere determined.number (HV) for each of the specimen created forthe different sizes and weight percentages of thereinforcement. Fig 7 shows the tested Hardnessspecimen and Fig 8 the corresponding indentations.4.1 Rockwell Hardness TestThe Rockwell hardness test determines the hardness bymeasuring the depth of penetration of an indenter under alarge load compared to the penetration made by a preload[9].The chief advantage of Rockwell hardness is its abilityto display hardness values directly, thus obviating tediouscalculations involved in other hardness measurementtechniques. The determination of the Rockwell hardness ofa material involves the application of a minor loadfollowed by a major load. Release the major load and theDial indicator gives the Rockwell hardness number (HRB).Results are shown in table-1 and the corresponding graphin Fig 9. As expected, the hardness of the material is seento improve with the increasing reinforcement weightpercentages. Particle size has not much effect on hardnessand 320 mesh size gives slightly better results.4.2 Brinell Hardness TestThe Brinell scale characterizes the indentation hardness ofmaterials through the scale of penetration of an indenter,loaded on a material test-piece[10]. The value of theBrinell Hardness Number (BHN) is obtained byperforming calculations using the following formula:Where P Load applied, D Diameter of indenter, d Diameter of indentationThe load used was 60kgf for a duration of 30 seconds. Thereadings and calculations are shown in table 1.Thesereadings have been substantiated by the following graphshown in Fig 10.For 400 mesh particle size, the BHN values are seen toincrease with the increasing reinforcement amounts. Thisindicates an increase in hardness with the increase inweight percentages.15IJRMEE November 2014, Available @ http://www.ijrmee.org

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE)7947Volume: 1 Issue: 4018ISSN: 2349014–For 320 mesh particle size, the BHN values remain almostsame for the first two reinforcement amounts and anincrease is shown in the third reinforcement amount.For 200 mesh particle size, the value show an increasingtrend with increase in the weight percentages of thereinforcement. The BHN value for 5% reinforcementdrops below that of as cast which supports the resultsobtained in the Rockwell hardness tests.The test was performed according to ASTM E92-82 [28].The Vickers Hardness Number (HV) is obtained by thefollowing formula.V.CONCLUSIONS4.3 Vickers Hardness TestThe Vickers test method is similar to the Brinell hardnesstesting method. The principle in this test is that a definedshaped indenter is pressed into the material. The indentingforce is applied for a certain decided amount of time[11].The resulting indentation diagonals are measured andrecorded. The hardness number is calculated by dividingthe force by the surface area of the indentation.As mentioned previously, the principle of the Vickers testis similar to the Brinell test, but the Vickers test isperformed with different forces and indenters. The squarebase pyramidal diamond indenter is forced under apredetermined load ranging from 1 to 129kgf into thematerial to be tested. After the forces have attained staticor equilibrium conditions, further penetration cease, theforce remains applied for a specific time (10 to 15s fornormal test times) and is then removed.The resulting unrecovered indentation diagonals aremeasured and averaged to give the value in millimeter.These length measurements are used to calculate theVickers hardness number (HV).The hardness of the materials also showed a steadyincrease with the increase in the weight percentages ofreinforcements for a certain particle size of thereinforcement. The Rockwell hardness test results suggestthat the maximum hardness was obtained by thereinforcement of the metal alloy matrix with 400 mesh sizesilicon carbide in a weight percentage of 15%.The Brinellhardness test results infer that the maximum hardness wasobtained by the combination of the metal alloy matrix with15% weight percentage of 400 mesh size silicon carbide.The Vickers hardness test result, the most accurate amongthe three hardness tests, also implies the same results. Themaximum Vickers hardness number was obtained for thespecimen which was made of the metal alloy matrixreinforced with 15% weight percentage of 400 mesh sizesilicon carbide which indicated maximum hardness for thesame.VI.ACKNOWLEDGEMENTThe authors gratefully acknowledge the supportand encouragement by the management and the principalWhere, P is the indentation load in kgf and d is the meandiagonal of indentation in mm. The Vickers indenter hasincluded face angles 136 .The load applied was 5kgf for aduration of 10 seconds.The data obtained from the above hardness test resultshave been given in Table1 and the corresponding graphs inFig 11. Generally considered as the most accurate amongthe three tests performed, this test also supports resultsobtained from the previous two tests, thereby confirmingthe increase in hardness of the composite. The graphshows that the hardness value is increasing with theincrease in reinforcement amount which is the same as thatobtained from the previous two tests. The graph for 200mesh size shows that the 5% reinforcement has reducedhardness value which was the same obtained in theprevious two tests. This may be attributed to non-uniformdistribution of the reinforcement in the metal matrix duringstirring and casting.of M S Ramaiah institute of technology, Bangalore,Affiliated to VTU, Belgaum, in carrying out this work.REFERENCES[1] T W Lee, C H Lee, Statistical Analysis forStrength and Spatial Distribution Of Reinforcements inSiC Particulate Reinforced Aluminum Alloy Fabricated byDie-Casting, J.Mater.Sci.35[2] MingzhaoTan,Qibin Xin, Zhengua Li, B Y Zong,Influence of SiC and Al2O3 Particulate Reinforcements andHeat Treatments on Mechanical Properties and DamageEvaluation of Al-2618 Metal Matrix Composites.[3] Munoru Taya, Richard J, Text book of Metal MatrixComposites[4] T W Clyne and P J Withers, Cambridge UniversityPress, Cambridge, U.K, 1993, An Introduction to MetalMatrix Composites,[5] Munoru Taya, Richard J, Text book of Metal MatrixComposites[6] Rohatgi P K, Casting Metal Matrix Composites16IJRMEE November 2014, Available @ http://www.ijrmee.org

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE)7947Volume: 1 Issue: 4018ISSN: 2349014–[7] Y Sahin, Materials and Design 24 (2003) 671-679,“Preparation and Some Properties of SiC ParticleReinforced Aluminum Alloy Composites”[8] Rajeshkumar Gangaram Bhandare, Parshuram MSonawane, International Journal of Engineering andAdvanced Technology (IJEAT), Preparation of AluminiumMatrix Composite by Using Stir Casting Method[9] ASTM E18 – 03E1, Standard Test Methods forRockwell Hardness and Rockwell Superficial Hardness ofMetallic Materials[10] ASTM E10 - 01E1, Standard Test Method for BrinellHardness of Metallic Materials[11] ASTM E92-82, Standard Test Method for VickersHardness of Metallic Materials17IJRMEE November 2014, Available @ http://www.ijrmee.org

International Journal on Recent Technologies in Mechanical and Electrical Engineering (IJRMEE)7947Volume: 1 Issue: 4018ISSN: 2349014–Table 1 Hardness test resultsMATERIAL%WEIGHTHRBAS CAST400 MESH----51015510155101533353740373839343538320 MESH200 MESHBRINELL HARDNESSTESTAVERAGEBHN(3 TRIALS)DIA 1246.8352.273VICKERS HARDNESSTESTAVERAGEHV(3 TRIALS)DIA 65.23657.5663.20864.01118IJRMEE November 2014, Available @ http://www.ijrmee.org

4.1 Rockwell Hardness Test The Rockwell hardness test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload [9].The chief advantage of Rockwell hardness is its ability to display

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