INFLUENCE OF NANO-Al 2O3 AND MICRO-ZrO2 PARTICLES ON ... · bystircasting and squeeze casting process. The last process provide highly successful in producing both porosity-free castings

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT Guwahati, Assam, India

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INFLUENCE OF NANO-Al2O3 AND MICRO-ZrO2 PARTICLES ON

MECHANICAL PROPERTY OF A356 BASED COMPOSITE

FABRICATED BY COMBINATION EFFECT OF STIR AND SQUEEZE

CASTING

Rajeev Ranjan1*,SukeshaV2,G.Nagesh3,K Sekar4

MED, NIT Calicut, 673601, [email protected] MED, NIT Calicut, 673601, [email protected]

MED, NIT Calicut, 673601, [email protected] MED, NIT Calicut, 673601, [email protected]

Abstract

Aluminium Metal Composites(AMCs) is having better property compared to unreinforced materials like greater strength,improved stiffness, reduced weight, improved properties at elevated temperature ,controlled thermal expansion coefficientbehavior, enhanced electrical performance, improved abrasion and wear resistance and improved damping capabilities.In the present work A356 has been casted with reinforcing nano-Al2O3 and micro-ZrO2 ceramic powders. The reinforced powders is having high level of hardness and toughness known as ceramic steel and having good strength at high temperature. Fabrication were done in a resistance furnace equipped with stir and squeeze system. Furnace temperature was kept at 850˚C and stirring was done at 300 rpm for 14 min.Ceramics were preheated at 600˚C for 30 min.A squeeze pressure of 45MPa was applied in the semi solid state.Samples were prepared for testings like hardness, double shear,bending strength and for wear test.A short term heat treatment technique is applied for the heat treatment of specimen (solution heat treatment at 560˚C for 2 hr and aging at 200˚C for 2 hr).For hardness testBrinell hard test was used and4 indentations were done on each specimen to obtain data of hardness. Heat treated specimen shows better mechanical property. Wear test was conducted on all the specimen, ceramic reinforced specimen shows improved wear resistance. Worn surface morphology shows the behavior of specimen at different loads and at different distances. Keywords: AMC; Stir and Squeeze casting;

1 Introduction Recently, the demands for lightweight

materials, having high strength and stiffness, have attracted much interest in the development of fabrication processes of metal matrix composites (MMCs) as reported by M. Karbalaei Akbari et al

(2013). MMCs combine metallic properties of

matrix alloys with ceramic properties of reinforcements like high strength and high modulus which leading to greater strength and higher service temperature capabilities. Particle reinforced aluminium matrix composites can be fabricated by using conventional material manufacturing methods with improved mechanical and physical properties. These properties include improved strength, high elastic modulus, creep strength, fatigue strength, hardness and wear resistance, corrosion resistance and low thermal expansion, as studied by Hossein Abdizadeh (2013). Among the manufacturing processes for aluminium matrix composites, the stir

and squeeze casting technique has been developed to manufacture a wide range of these composites. However, the improper control of some process parameters in this technique could produces the composites with defects such as porosity, weak bonding between reinforcement and matrix, non-uniform distribution of the particles in the matrix, which may result in decreasing mechanical properties. Although a great deal of work has been conducted on the aluminium matrix composites, there is limited information over the effect of manufacturing variations on fracture behavior of these materials.S.A. Sajjadi et al (2012), studied on compocasting of A356 alloy by adding macro and nano Al2O3 particles. To improve the wettability, the ceramic particles were preheated at 3000C in the presence of argon gas. The porosity % increases with increasing the Al2O3 wt. %after certain and decreasing particle size. By increasing the stirring timeup to certain limit, homogeneous distribution

INFLUENCE OF NANO-Al2O3 AND MICRO-ZrO2 PARTICLES ON MECHANICAL PROPERTY OF A356 BASED COMPOSITE

FABRICATED BY COMBINATION EFFECT OF STIR AND SQUEEZE CASTING

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ofAl2O3 in the aluminium matrix was foundby increasing stirring speed up to 300 rpm hardness increases and when speed reaches above 450 rpm the hardness decreases due to particles dispersed out of the crucible and particle addition was not desirable.M.T.Abou et al (2007), has reported that The Al/ ZrO2composite can be fabricated bystircasting and squeeze casting process. The last process provide highly successful in producing both porosity-free castings and sound composites when compared with other methods. A new method stir with squeeze casting is developed for casting of MMC which is having advantage of both stir and squeeze system.

2 Experimentation In this present experiment A356 aluminium alloy

is used as matrix in order to manufacture the composites, the alloy wasmeltedat850˚C using an electrical furnace and an impeller which was made of graphite. Themelt was stirred ataspeedof300-350rpmfor14minandthedifferent wt. fraction of zirconia particles(0.5,1,and1.5wt% respectively) were added into the molten alloy. In order to improve the wettability ceramic particles were heat treated at 600˚C for 30 min in the controlled atmosphere tube furnace and then after stirring was done for 2more minutes and the molten composites were poured ina metallic mold (cylindrical shape with 25cm height and 5 cm dia.)and a low pressure of 45 MPa was applied in semi-solid state for better densification of solution.Zn,Mg and slag forming agent were mixed in the solution for better property of casting.Fig.1 showing one of the casted product. Total four castings were done. Table 1shows the number of castings with their compositions. Samples were prepared under both without heat treated(WHT) and heat treated(HT) conditions for hardness, bending strength and double shear test. Also samples were prepared for wear test under dry conditions. A short term heat treatment(solution heat treatment at 560˚C for 2 hr and aging at 200˚C for 2 hr) was done for the specimen.

Table1 Composition of cast composite

Sample composition

1 A356

2 A356+1%Al2O3+.5%ZrO2

3 A356+1%Al2O3+1%ZrO2

4 A356+1%Al2O3+1.5%ZrO2

Figure 1 One of the casted product

Hardness test for all samples were carried out after grinding and polished them down to 1µm.Aloadof500 kg was applied to determine the hardness ( B H N ) of all samples. Four indentations were made on each sample for hardness measurement and the average of hardness values was reported. Microstructural analysis of weared samples was studied.

3 Results and Discussions

3.1 Hardness test

Figure 2 showing the variation in hardness values on increasing varying the wt% of ZrO2 as the fraction of Al2O3 is kept constant.It seems thathardnessofallcompositesishigher than the A356 aluminumalloy.Due to the presenceofceramicparticles(1%Al2O3+.5%ZrO2)in the matrix the hardness value of A356 as cast alloy increases by 30% when not heat treated and increases by 38% when heat treated and hardnessincreases to was 118 BHN when 1wt% Al2O3 and 1.5 wt% ZrO2 was added. The reason can be higher hardness of ZrO2 and Al2O3 particle as compared to aluminium alloy.Secondary the coefficient of thermal expansion of ceramic particles are less compared toaluminium alloy so dislocation generated at the particle-matrix interphase which causes higher hardness values as studied in paper by A.Mandal et al.The hardness value upto 1 wt% of ZrO2 shows excellent results but after 1wt % it remains almost constant.Thisbehaviorcanbeattributedtotheeffect of particles content in the matrixwhich raisesthe hardness and volume content ofvoids. Therefore, inthe range of 0.5-1wt%, the ceramic reinforcement content is the dominate factor,whileintherangeover1wt%themain factor which controls the hardnessvariations is voids content.


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Figure 2 Hardness value

3.2 Bending and Double shear test

Figure3 Variation of bending strength of

samples

Fracture toughness means capability to prevent

and stop crack growth of a specimen which depends upon three parameters: bridging of cracks, crack deflection and crack branching. Increase in Bending Strengthand Double Shear was found to be 16.7% and 19.5% respectivelyin sample 1 and increase to max.of 36% in 4th sample after heat treatment. Sample with 1 wt.% addition of both ceramic shows better results but after 1 wt.%, addition of ZrO2 is not desirable.

According to a book by Balasubramaniam (2011), For many materials yield strengthand grain size could be described by the expression:

Hall – Petch equation σ0 = σi+k/√d (1)

Where σ0 and K are the constants for a particular material, d is the grain sizeThe expression suggested that the strength of the material will decrease as the size of grains increases. Also, a large size of eutectic silicon phase degrades the strength of the MMCs, As the silicon phase is brittle so that cracks will generate

first near the silicon particles and then propagate rapidly through the ceramic particles and then to the matrix leading to failure of composite.

Figure 4 Variation of double shear strength of

samples

But because of the squeeze pressure while

casting Si get spheroids and the grain size of particle decreases as suggested in a paper by S.A.Sajjadi(2012), The results shows improved property in the strength. Same reason is applicable for results of shear test also. However,inthe entire testing weight fraction more than1wt% of ZrO2does not show much improvement in the property because of the agglomeration of ceramic particle in the matrix.

3.3 Wear test Dry sliding wear tests were carried on a

pinondiscwear testing machine (TR-20,DUCOM) according to the ASTM G99-04 Standard with specimen as cylindrical pins (8 mm diameter and 30 mm height).The hardened chromium steel (R62) was used as the counter disc face material. The tests were carried out at different loads (4kg, 8kg,10kg), which correspond to nominal contact stress of 0.77, 1.56 and 1.94MPa respectively. The track radius was fixed at 50 mm and the sliding speed was maintained at 250 rpm. All tests were carried out in ambient temperature. Mass loss of samples was calculated by varying distance from 250m to 1000m. Graph (Fig.5-10)has been plotted between mass lossvs. distance at different loads.It has been found that there is a gradual increase in the mass loss for the alloy as well as composites at lower loads of 4 and 8 kg. But the loss increases sharply at 10 kg and as the distance increases to 1000m.Composite shows less wear loss compared to alloy the reason can be attributed to the resistance offered by hard Al2O3 and ZrO2 particles and the composite with higher wt % of ZrO2

experiences a lower wear rate. Monolithic A356

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alloy shows sharp increase in wear loss as the load and distance increases.

Figure5 Mass loss of Heat treated samples at

40 N

Figure 6 Mass loss of without Heat treated

samples at 40 N

Figure 7 Mass loss of Heat treated samples at

80 N

The heat treated samples shows improved

property in all the cases as the slope for wear loss in heat treated sample is less compared to that of non heat treated sample. Adding 1wt.%Al2O3 and 0.5 wt % ZrO2 shows tremendous decrease in wear loss

then after it shows only slight increase in wear resistant.


80 N


100 N

Figure 10 Mass loss of without Heat treated

samples at 100 N

It is can also been inferred from the graph that

as the distance increases from 750m to 1000m wear loss is more in all the samples (reason may be because of increase in heat generation) at all the loads except at 10 kg which shows sharp increase in

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loss in all components which shows that materials may fail when subjected to load more than 10 kg.

3.4 Wear surface Morphology

Worn surfaces of the monolithic A356 aluminum alloy and A356 reinforced with ceramic particles were examined with SEM to understand the wear mechanisms of each sample. In monolithic A356 alloy wear track morphologies arerough withcontinuous wear grooves.Debris particles (cutting and ploughing) in figure 11-15characterize the morphology. During sliding at higher loads, a rough wearedsurface signifies abrasive wear as materials are being pulled out from the surface and forms loose abrasive particles while a smooth and less grooved surface indicates adhesive wear from plastic deformation with very less material removed from the surface at lower loads. Figure 11 shows the wear characteristics ofsample 1 after exposure to a load of 80 N at 250RPM for 1000m.Wear mechanisms andadhesive wear are visible along the wear track. The abrasive wear is shown at higher magnification which signifies rough surface

dispersed with small particles of debris.Figure 12

shows the debries of ceramic particle being pulled out when higher load of 100 N was applied a very rough surface were observed at this load. Heat treated sample with 1wt% Al2O3 and 1.5wt% ZrO2 are shown in figure 14 which infers from surface roughness that wear resistance is more of this sample as very less grooving is present alsothere is not ploughing of debries from the sample.

Figure 11 Wear surface of without heat treated

monolithicA356 alloy at 80 N loads

The reason can be attributed to the presence of hard Al2O3 and ZrO2particles whose hardnessis much greater than that of the as-cast Al substrate. Ceramic particles provides wear resistance by strengthening the Almatrix which limits the deformation and resists the penetration and cutting ofthe slider into the surface butwhen tested at 100 N ploughing action were found as shown in figure 15.High ploughing action and high wear rate at

100N load inferences that the material cannot sustain the load for 1000m.Figure 13 shows the EDS analysis of worned surface of sample 3.which shows the presence of ceramic particle in the matrix.

Figure 12 Wear surface at higher

magnification of withoutHeat treated

A356+.5wt%alloy at 100 N load

Figure 13 EDS analysis of a worned

surfaces

Figure 14 Wear surface of heat treated

composite(sample 4) of particles at 80 N

loads



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Figure 15 Wear surface at higher magnification of

sample 4 with reinforcement at 100 Nload

4 Conclusion

In this investigation,A356 alloy were successfully casted on an electrical furnace withvarying wt. percentage of ZrO2 however the fraction of Al2O3 were kept constant.Hardness, bending and double shear strength were calculated.Dry sliding wear tests werecarried on a pin ondisc wear testing machine Characterizationof weared surface were studied and the results were reported as follows:

• With the presence of only 1 and 0.5 wt% Al2O3 and ZrO2 respectively improved the property of A356 alloy.

• Hardness value increases to max of 38% with increase in percentage of ceramic as compared to as cast A356 composite, also there is increase in bending and double shear strength. There is not much improvement in property after 1 wt% addition of ZrO2.

• Heat treated samples shows better results in all conditions shows an average of 6% in hardness and 5% in bending strength and 5.7% in shear strength.

• Wear test also shows significant improvement on increasing the fraction of ceramic powders into the alloy.

• Mass loss study shows that the wear rate strongly depends on the reinforcement of ceramic powder rather than overall hardness of composite. However wear rate at higher loads shows similar effect in all samples.

References A.Mandal, B.S.Murthy, M.Chakraborty, (2009),Sliding wear behavior of T6 treated A56-TiB2 in-situ composites, Wear 266 pp.865-872 HosseinAbdizadeh,MohammadAminBaghchesara(2013), Investigation on mechanical and fracture behavior of A356 aluminium alloy based ZrO2 particle reinforced metal matrix composite, Ceramic International 39 pp.2045-2050 KyuhongLee,Yong Nam Kwon,Sunghak Lee (2008),Correlation of micro with mechanical properties and fracture toughness of A 356 aluminum alloys fabricated by low-pressure-casting, rheo-casting, and casting–forging processes Engineering Fracture Mechanics. 75 pp.4200–4216 M.KarbalaeiAkbari, O. Mirzaee, H.R.Baharvandi(2013), Fabrication and study on mechanical properties and fracture behavior of nanometricAl2O3particle reinforced A356 composite focusing on the parameters of vortex method, Mater. Design 46 pp.199-205 M.T.Abou, EI-Khair, A. Abdel Aal(2007) Erosion-Corrosion and surface protection of A356 Al/ZrO2 composite produced by vortex and squeeze casting, Material Science and Engineering A454-455pp.156-163 Mazahery, H. Abdizadeh, H.R. Baharvandi(2009), Development of high performance A356/nano- Al2O3 composite.Mater.Sci. Eng. A518 pp.61-64 S.A.Sajjadi,M.TorabiParizi,H.R.Ezatpour,A.Sedghi(2012), Fabrication of A356 composite reinforced with micro and nanoAl2O3 particle by a developed compocasting method and study of its properties. Journal of Alloys and Compounds 511 pp.226–231 R.Balasubramaniam(2011),Callister’s Materials Science and Engineering,Wiley India(P) Ltd.

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INFLUENCE OF NANO-Al 2O3 AND MICRO-ZrO2 PARTICLES ON ... · bystircasting and squeeze casting process. The last process provide highly successful in producing both porosity-free castings