A Review on Al Si Alloy as a Matrix Material for MMCs 2014

International Journal of Advance Foundation and Research in Science & Engineering (IJAFRSE)

Volume 1, Issue 2, July 2014

13 | © 2014, IJAFRSE All Rights Reserved www.ijafrse.org

A Review on Al-Si Alloy as a Matrix material for MMCs. Ajit Senapati*,Avinash Senapati,Omkarnath Mishra.

Department of Mechanical Engineering,GIET,GUNUPUR [email protected]

A B S T R A C T

Over the last few decades the interest of researchers has shifted from conventional materials to

Metal Matrix composite (MMC). The MMCs are now extensively used in the field of aerospace,

automotive, marine applications etc., instead of conventional materials because of their improved

mechanical and tribological properties like strength, stiffness, abrasion and impact resistance.

MMCs have replaced initially used Bronze alloys and cast iron components but because of their

poor seizure and wear resistance. Experiments have been conducted on the physical behavior of

these composites and are reported by a number of research scholars over the past couple of

decades. In this paper, the change in mechanical properties of Al-Si alloy are taken into

consideration with different reinforcements such as SiCp, Al5TilB, B4C, Quartz, Fly ash and AlN

based on literature review.

Index Terms: MMC, Al-Si alloy, Reinforcement, Wear, Tensile strength and hardness.

I. INTRODUCTION

Recently, metal matrix composites (MMC) have gained importance in the field of engineering and research. MMCs are materials which are made up of combination of metals and non-metals in specific proportions. MMCs exhibit better physical and mechanical properties than conventional materials in terms of density, strength, surface characteristics, microstructure etc. Metal matrix composites (MMC) are composed of an elemental or alloy matrix in which a second phase is embedded and distributed to achieve some property improvement [1]. Based on the size, shape and amount of the second phase, the composite property varies [1]. Aluminium is abundantly available on earth’s crust. It is the 3rd most abundant chemical element and the most abundant metal. Aluminum alloys are broadly used as a main matrix element in Composite materials. Aluminium alloys for their light weight, have been in the net of researchers for enhancing the technology [2]. In this paper Eutectic Al–Si alloy (LM6) is taken as a matrix material, with the reinforcement of fly ash, SiCp, Al5TilB, B4C, Quartz, AlN. LM6 has wide applications in Marine, Automobile, Aerospace industries. But it exhibits. Poor tribological properties [2]. Hence the desire in the engineering community to develop a new material with greater wear resistance and better tribological properties, without much compromising on the strength to weight ratio led to the development of metal matrix composites [2].

Above reinforcements were chosen due to the exhibition of specific properties. Fly ash is available as waste material and can be utilized as the reinforcement. SiC is an excellent abrasive and maintain their strength to very high temperatures [2]. Al5TilB acts as grain refiner and improves mechanical properties of LM6 [3]. B4C increases the hardness and decreases density of base matrix [4].Quartz imparts hardness, corrosion resistance & high chemical stability, in the materials it is reinforced in to [1]. AlN has high thermal conductivity, high strength (greater than alumina), lower thermal expansion and good electrical properties [5]. So, the degree of improvement in the properties with the reinforcement of above materials with LM6 matrix is studied and described in this paper. II. LITERATURE REVIEW




A. WEAR

S. Kumar et al. [6] produced composites of Al-Si alloy reinforced with 0, 5 & 10wt. % TiB2. The Vickers’s hardness of the composite at 5 kg load was determined and for the wear a track diameter of 45mm with specimen pin of 8mm diameter and 15 mm height was taken that slide against AISI 52100 steel disc. It is noted that the friction coefficient decreases with the addition of TiB2 particle irrespective of applied load. The average coefficient of friction of alloy lies in the range of 0.37-0.40 and that of composite is less than that of alloy and ranges between 0.25-0.35. The values of μ mentioned above are measured in the given sliding range under steady state condition and are all mean values. The flow of metal is restricted by the Presence of the second phase such as Si and TiB2. It is also found that the wear rate decreased significantly not only with the increase in TiB2 in the composite but also due to the refined grain size. Fig 1. and Fig 2. Shows the variation of wear rate with respect to normal load and wt. % of TiB2. Prasad Rao et al [7] showed that the size of the silicon particles, grain size or dendritic arm spacing affect the wear rate of Al-Si. The improvement in wear resistance of the composite was not because of the presence of TiB2, but also due to modification and refinement of eutectic Si and refinement of grain size [7].

Fly ash mostly consists of solid particles in the form of sphere known as precipitator fly ash. With precipitator fly ash some partially solid or hollow spherical particles are also present [8]. The cost and density of aluminium and its alloys get reduced with the incorporation of fly ash particles in them [9]. Rohatgi reported that the abrasive wear resistance of aluminium alloy is increased significantly with the addition of the fly ash particles because of the hard alumina silicate constituent present in the fly ash [10]. The twelve volume percent of fly ash shows lower wear rate compared to the alloy under same load condition. Sudarshan et al experimented on the dry sliding wear of the Al-Si alloy and 6 and 12 vol. % fly ash reinforced composite and found that at same load conditions the wear rate exhibited by the 6 volume percent reinforcement shows twice the wear exhibited by 12 volume percent reinforced composite [11].

Figure.1 Figure.2




Figure 3, Shows the deviation of wear curve of composite from Al-Si alloy, under the effect of load calculated by weight loss method. Fig 4. Deals with the variation of particle size range i.e., narrow size range and wide size range and its effect on wear rates. S. K. Dey et al worked on finding out upper limit of the ultra-mild wear in hyper eutectic Al-Si alloy considering a higher load of magnitude 5.0 N and concluded that ultra-mild wear in aluminium alloy with 18.5 %Si occurred due to the abrasive action of exposed Si on top and fracture of larger particles. The mild wear damage was stabilized probably because of the formation of the oil-residue layer after a prolonged sliding [12]. A.K. Prasad Rao et al reported that using various grain refiners such as Al3B, Al1Ti3B, Al5Ti1B and Al3Ti for grain refinement of aluminium alloy significantly improves the wear resistance characteristics of aluminium and aluminium alloys [13]. R.M. Mohanty used boron carbide [B4C] as an alternative reinforcement to SiC and Al2O3 due to its higher hardness. And he found that the composite shows increase in wear characteristics due to presence of hard B4C in the compound [14].

B. TENSILE STRENGTH

Nikhilesh Chawla et al observed that, elastic modulus, microscopic yield and tensile strength of the alloy increases with the increase in volume fraction of the SiC reinforcement coupled with lower ductility [15]. YU Xiao-dong et all experimented on aluminium metal matrix composites reinforced with SiC with higher volume fraction of about 50% and various particle size 10, 28, 40 and 63μm and concluded that bending strength increases with increasing volume fraction and decreasing particle size but fracture toughness increases with increasing particle size [16]. J.R. Gomes et all investigated that SiC reinforced aluminium alloys are widely used because of their effective combination of density, hardness and strength. The SiC reinforced aluminium MMCs exhibits significant increase in elastic modulus, hardness, tensile strength and wear characteristic [17]. M. Mahendra Boopathi et all noted that tensile property and yield strength increases with increase in area fraction of SiC reinforcement in matrix coupled with significant decrease in percentage rate of elongation [18].Ismail Ozdemir et al reported that in reinforced aluminium composite the increase in tensile strength is not profound but after two step forging there is about 40% increase in tensile strength. Up to 17% volume fraction of particulate silicon carbide (SiCp) the yield tensile strength of the composite increases and then decreases with further addition of SiCp strength [8]. Tamer Ozben et al investigated the effect of SiCp reinforced in Al-Si MMC with reinforcement ratio of 5, 10 & 15 wt. %. The result shows an increment in tensile strength, hardness & density of aluminium MMC material with increase in reinforcement ratio but decrement in impact toughness was also noticed [19]. Hayrettin Ahlatci et al , concluded that strength of composite increased without significant loss in toughness as amount of Si increased up to 1% after which the strengths declined with further increase is Si content , when experimented on mechanical properties of Al-Si with 60 vol. % SiC composite[20]. H. C. Anilkumar et al

Figure .3 Figure.4




investigated on mechanical properties of fly ash reinforced Al-Si alloy. Different sizes of fly ash particles (4-25, 45-50, 75-100 micro meter) were used in preparing samples. Each set of samples had three types of composites reinforced with weight fractions of 10, 15 & 20%. It was observed that tensile strength of the composite decreases with increase in particle size and increases with increase in weight fraction of reinforced fly ash particles [21]. Basavarajappa et al noted that, with the increase in weight percentage of fly ash the tensile strength increases. When the dislocation takes place with the application of load, the dislocation front is obstructed by hard fly ash particles that act as barriers [9]. N. Suresh et al investigated on composites reinforced with disperse cenospheres of fly ash (from 1-10 %) in the Al-Si alloy matrix. The increase in ultimate tensile strength for the aluminium composite is of 8.5% for 1% addition (158.8 MPa) and 44.3% for 10% (211 MPa) addition of the cenospheres of fly ash to the aluminium alloy [22]. M. Sayuti et al prepared tensile test sample according to ASTM standards with 5%, 10%, 15%, 20%, 25% and 30% wt. fraction of SiO2 of 65 microns. There is decrease in tensile stress value along with elastic modulus with increase in addition of SiO2 particulate. On the other hand the tensile strength would be increased by decreasing SiO2 particulate less than 30% by weight fraction along with particle size as 230 mesh-65 microns [5]. A. M. S. Hamouda et al experimented on the processing and characterization of SiO2p reinforced Al-Si alloy matrix. From the experiment it was observed that with the increased addition of SiO2p there is a decrease in tensile strength and modulus of elasticity in Al-Si alloy. The Fig 5. Shows the variation of tensile strength with respect to Vol. fraction of SiO2.

Figure 5. Tensile Strength vs. Vol. Fraction of SiO2 Figure 6. Young’s Modulus vs. Vol. Fraction of SiO2

Fig 6. Explains the variation of average Young’s Modulus with respect to increase in Vol. fraction of SiO2 [23]. S. Sulaiman et al studied the mechanical properties of Al-Si alloy by varying the Vol. fraction of SiO2 reinforcement from 5% to 30%. It was observed that split tensile strength and Young’s modulus decreased with increase in Vol. fraction of SiO2 in the composite. The reason behind the decrease in mechanical behavior is the compressive strength of the quartz particulate reinforced in the alloy matrix. It was noticed that the compressive strength of the composite increased significantly with increase in SiO2. It is clear that, due to the influence of quartz (SiO2) particles, the compressive strength effectively dominates its influence over tensile strength [31]. M. Kok prepared Al-Si metal matrix composite with three different sizes of Al2O3 particles and also with three different wt. fractions ranging up to 30% wt. fraction. The effect of Al2O3 particles on the mechanical properties such as hardness and tensile strength of the composite were investigated. He noticed that, the tensile strength of the Al2O3 reinforced aluminium alloy increases with decreasing size and increasing weight percentage of the particles, but the elongation of the MMCs decreases [24]. Lim Ying Pio et al investigated on the effect grain refiners such as Al5Ti1B on the casting quality and also on the mechanical properties. For experiment, samples were prepared varying Al5Ti1B from 0 wt. % to 1 wt. %, incremented by 0.25 wt. %. It was found that the inoculation of aluminium alloy with Al5Ti1B significantly improves the tensile strength (by 39%) and this improvement is achieved with optimal addition level of grain refiner of 0.5% [3].




C. HARDNESS

The resistance to indentation is known as hardness. Instruments like Brinnell’s, Rockwell’s and Vicker’s are used for measuring hardness of materials. M. Singh et al studied the effect of addition of ceramic particles in the composites and concluded that the addition of ceramic particles increases the hardness of composites [25]. Y. Sahin et al investigated that there is more or less a linear relationship between the increase in hardness of Al-Si composite and the volume fraction of particulates in the alloy matrix due to increase in ceramic phase in the matrix [26]. Rabindra Behera et all studied the effect of different weight fractions of SiCp reinforced in Al-Si alloy and their influences on machining parameters were noted. It was seen that there is an increase in the cutting forces at the same cutting conditions with the increase in weight fraction of SiCp in the MMC and the hardness varies linearly with weight fraction [27]. Rabindra Behera et al carried out machining tests on Al-Si MMCs with different cutting speeds (30, 68 and 103 m/min) and depth of cut (0.5, 1 and 1.5 mm) at constant feed of 0.05 mm/rev, and found that there is a decrease in cutting force components Ft , Ff and Fr with increase in cutting speed of the composite reinforced with 7.5 wt%,10 wt%,12.5wt% of SiCp under same cutting conditions .It also reveals that there is linear increase in weight percentage of SiCp in composite [28]. Ramachandra et al studied the mechanical properties of hypoeutectic Al-Si fly ash reinforced composite and concluded that there is an increase in hardness, tensile strength and decrease in density as the fly ash content increased [29].Wong W.L.E. et al have reported that the reason behind the increase in hardness is the presence of very hard ceramic reinforcements which acts as barrier to the dislocation movement within the matrix and thus exhibit greater resistance to indentation [30]. N. Suresh et al produced Al-Si composites reinforced with cenospheres of fly ash and studied its mechanical properties. It was observed that the hardness increases by 8.6% for 1% fly ash and by 34.7% for 10% fly ash based composite, compared with the base alloy [22]. M.N. Wahab et al studied the Characteristic of aluminium metal matrix composite reinforced with aluminium nitrate and found that hardness of the matrix increased to 89Hv from 44Hv as the Al composite reinforced with 5 wt% AlN powder. The increase in hardness value was an indication of the contribution of AlN particles towards the improvement of hardness of the matrix [2]. S. Sulaiman et al studied Quartz particulate reinforced Al-Si MMC by varying particulate addition by volume faction and conducted tensile test, hardness test and scanning electron microscopic studies. Based on the experiments conducted upon the variation in hardness of the Al composites corresponding to the variation in the volume fraction of Quartz particulate, it is found that value of hardness of composite increases with the increase in Quartz particulate by volume fraction % [31]. M. Sayuti et all reported that for 30% weight fraction addition of SiO2 the maximum hardness value based on Rockwell superficial 15N-S scale was 67.85 [5]. A. M. S. Hamouda et al determined hardness value for different composite reinforced with different volume fraction of quartz in Al-Si alloy. It was observed that the hardness value of the Quartz reinforced composites increased with increase in Quartz particulate by volume fraction [23]. The variation of the hardness value vs. volume fraction of Quartz particulate is shown in Fig.7.

Figure 7 Hardness Rockwell Superficial 15T VS Quartz




Ling Ying Poi et al 2005 investigated the effect of Al5Ti1B grain refiner on the mechanical property of Al-Si alloy and found out that the highest hardness is achieved at 0.5 wt% of grain refiner and no significant improvement was observed above the level of addition. The hardness was increased to 60 Rockwell HRD because of the effect of the grain refinement on Al-Si alloy [3]. M. N. Wahab et al carried out an experiment to study preparation and characterization of Al-Si metal matrix composite reinforced with aluminium nitride. The hardness of the Al-Si was found to be 44 Hv which increased to 89 Hv for composite reinforced with 5% wt. % AlN powder. With the addition of AlN powder a significant increase in hardness of the alloy was observed. The higher value of hardness indicates that the hardness of the composite is improved with the existence of particulates in the matrix. As aluminium is soft, reinforcements especially ceramics material being hard, possibly contribute towards hardness positively. The constraint to the plastic deformation of the matrix during the hardness test increases due to the presence of stiffer and harder AlN reinforcement [2]. III. CONCLUSION

In this study, the properties of Al-Si alloy based MMCs with different reinforcements like SiCp, Al5TilB, B4C, Quartz, Fly ash and AlN are accounted. These reinforcements showed changes in various properties like wear, tensile strength, hardness as noted below: (a)Wear

It is found that the wear rate decreased significantly with the increase in TiB2 in the composite and also due to the refined grain size. The abrasive wear resistance of aluminium alloy increases significantly with the addition of fly ash particles because of the hard alumina silicate constituent present in the fly ash. Dry slide wear decreases with increasing volume fraction of fly ash in the composite. Ultra-mild wear in aluminium alloy with 18.5 %Si occurred due to the abrasive action of exposed Si on top and fracture of larger particles. The mild wear damage was stabilized probably because of the formation of the oil-residue layer after a prolonged sliding. Reinforcement of various grain refiners such as Al3B, Al1Ti3B, Al5Ti1B and Al3Ti etc. significantly improves the wear resistance characteristics of aluminium alloys. The composite shows increase in wear characteristics due to the presence of hard B4C in the compound. (b)Tensile Strength

It is concluded that tensile strength of the alloy increases with the increase in volume fraction and area fraction of SiC reinforcement coupled with lower ductility and significant decrease in percentage rate of elongation respectively. The yield tensile strength of the composite increases up to 17% volume fraction of particulate silicon carbide (SiCp) and then decreases with further addition of SiCp. Tensile strength of the composite decreases with increase in particle size and increases with increase in weight fraction of reinforced fly ash particles. There is a decrease in tensile stress value along with elastic modulus with increase in addition of SiO2 particulate. The reason for the decrease in tensile strength is the dominance of compressive strength of the SiO2 reinforced alloy matrix over the tensile strength. On the other hand the tensile strength would be increased by decreasing SiO2 particulate less than 30% by weight fraction along with particle size as 230 mesh-65 microns. Tensile strength of the Al2O3 reinforced aluminium alloy increases with decreasing size and increasing weight percentage of the particles with the decrement in elongation of the MMCs. Inoculation of aluminium alloy with grain refiners like Al5Ti1B improves the tensile strength significantly with optimal addition level of this grain refiner. (c) Hardness




There is an increase in the cutting forces at the same cutting conditions with the increase in weight fraction of SiCp in the MMC. Also hardness varies linearly with weight fraction. There is an increase in hardness as the fly ash content increases in the composite. Addition of ceramic particles increases the hardness of composites. The reason behind the increase in hardness is the presence of very hard ceramic reinforcements which acts as barrier to dislocation movements within the matrix and thus exhibit greater resistance to indentation. Reinforcement of Quartz particulates and AlN particles increases hardness of the matrix

Thus different desirable properties can be achieved with different types of reinforcements in the base alloys. With properties like better wear resistance, hardness, less density, better tensile strength etc., aluminium MMCs prove to be vital in the development of future technology. Hence study of these MMCs is important for development of new products in industrial sectors like automobile, aerospace, marine and many more.

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A Review on Al Si Alloy as a Matrix Material for MMCs 2014