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Fabrication and Effect on Physical and Mechanical properties of Graphite and Alumina reinforced ZA-27
Alloy Hybrid Composites
Viresh Payak
1, Swati Gangwar
21
M. Tech research scholar,
2Assistant Professor
Department of Mechanical Engineering, Madan Mohan Malaviya University of Technology, Gorakhpur, Uttar Pradesh, 273010, India
ABSTRACT
Metal matrix composites are acting as an extraordinary part in satisfying the requests of different mechanical applications and furthermore producing a wide passion for look into research area. The properties of metal matrix composites depend on the character of reinforcement and consequently addition of various reinforcement can yield new properties and can expand the use of hybrid reinforced composites in various fields. The present investigation is regarding fabrication of metal matrix composite by stir casting method, utilizing Zinc – Aluminum alloy (ZA – 27) as matrix material and (0, 2.5, 5, 7.5) wt. % of graphite and (0, 2.5, 5, 7.5) wt. % of alumina having 30µ particle size as the hybrid reinforcement material, after the fabrication of composites for four different wt. % (0, 3.5, 7, 10.5) of hybrid reinforcement i.e. Graphite and Alumina (GAl) physical and mechanical characteristics has been investigated.
Keywords –
ZA-27 alloy, Graphite, Alumina, Hybrid Composites, Stir casting, Mechanical characteristics
.1. INTRODUCTION
Composites materials are the combination of matrix material and reinforcements, when different types of two or more reinforcements are mixed in matrix then it is known as hybrid composites. Hybrid composites are used to improve properties and reduce the cost of conventional composites, according to the incorporation of component materials the hybrid composites are classified as;
Sandwich hybrids: In this hybrids one material is sandwiched in the layers of other materials.
Interply hybrids: In this hybrids the layers of two or more materials are stacked alternatively in regular manner.
Intraply hybrids: In this hybrids the rows of two or more materials are arranged in regular or random manner.
Intimately mixed: In this hybrids the materials are mixed in such a possible way that there is no concentration between the materials [1].
The commercial use of ZA – 27 alloy increases in various application like as diecasting, valve housing, bearings, high and low speed machines due to the better castability, low melting temperature and good machinability. Under moderate working temperature Zinc aluminum alloys are being substitute for aluminum,
354 | P a g e copper and bronze [2]. ZA – 27 alloys have high strength, low density and low cost compared to lead bronze.
The development of zinc aluminum alloys take place during 1960-1970. The international Lead Zinc Research Organization (ILZRO) had developed ZA – 12 and ZA – 16 during 1960’s whereas Noranda Co. had developed ZA – 8 and ZA – 27 in the late 1970’s [3].
Veera Brahman et. al. studied the effect of (5 wt.%) fly ash and (2, 4 wt.%) of Gr hybrid reinforcement on the characterization of ZA – 27 alloy composite, produced by stir casting technique. Testing have been done by vary the content of Gr 2, 4 wt.% while kept the constant content of fly ash 5 wt%. They find out that maximum value of toughness, tensile strength, Vickers hardness and lower wear rate at 5 wt.% of fly ash and 4 wt.% of Gr particles [4].
Fi chen et. al. investigated the mechanical and tribological properties of ZA – 27 alloy composite reinforced by 1 – 5 wt.% of TiB2 particle, produced by situ fabrication. They got that hardness is improved up to HB 128, ultimate tensile strength increases from 385 to 434 MPa at 5 wt.% of TiB2 reinforcement particle and wear rate reduced from 5.9 × 10-3 to 1.3 × 10-3 mm3/m [5].
Mahdavi et. al. fabricated the Sic and Gr reinforced Al – based hybrid composites by powder processing and found that the increase in Gr content decreases the porosity and hardness of composites [6].
A. Saravanakumar et. al. studied the mechanical properties of 0 – 12 wt.% of alumina and 1 wt. % of Gr filled aluminum matrix composites in as-hardened and as-cast condition and found that hardness, compressive strength, impact strength and three-point bending strength increases up to 6 wt.% of alumina and after this it decreases with the increase of alumina content in both condition [7].
A. Manna et. al. examined the characteristics of Gr/Al2O3 filled Al alloy composites produced by melt stirring technique and found that the addition of alumina particle decreases the impact strength and ultimate tensile strength but increases the hardness of composites [8].
2. MATERIALS AND FABRICATION TECHNIQUE 2.1 Matrix Material
ZA-27 is used as matrix material due to its better mechanical properties, excellent foundry castability, low weight, improved machining properties, corrosion resistance, high hardness and low initial cost. ZA-27 has the highest aluminum content, highest strength, highest melting point and lowest density of zinc-aluminum alloys [9]. The density of ZA – 27 alloy is 4.9 gm/cc. The chemical elements and their wt.% consisted by ZA – 27 alloy is shown in table 1.
TABLE 1 :
Chemical components of ZA - 27 alloy [10].Materials Al Mg Cu Zinc
Wt. % 25-28 0.01-0.02 2-2.5 Balanced
2.1 Reinforcement materials
355 | P a g e 2.1.1 Alumina (Al2O3)
Alumina (Al2O3) is extensively specified, common-purpose technical ceramics. Alumina particles are hard and having resistance to wear, along with a high compressive strength even against extreme temperatures and corrosive environments. Alumina particles are gas tight and also having very good electrical insulation [11]. The density of alumina is 3.90 gm/cc and particle size is 30µ.
2.1.2 Graphite (Gr)
Graphite is the allotrope of carbon, made up of carbon atoms and it is softer in nature. The density of Gr is 1.80 gm/cc and particle size is 30 µ.
The image of ZA – 27, Al2O3 and Gr are presented in fig. 1: -
(a) ZA – 27 (b) Alumina (c) Graphite
Fig. 1:
(a), (b) and (c) show matrix and reinforcements material used for fabrication of composites2.2 Chemical composition of fabricated composites
Three different composition of graphite and alumina reinforced ZA – 27 alloy hybrid composites fabricated and then compression of these three hybrid composites is done with purely fabricated ZA – 27 alloy.
The number of prepared samples, their designations and corresponding composition of fabricated graphite and alumina reinforced ZA – 27 alloy hybrid composites are exhibited in table 2. Measurements of the amount of alloy and reinforcement for the fabrication of ZA – 27 alloy hybrid composites, have done according to the composition shown in table 3.5.
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Table 2:
Chemical composition of ZA-27 alloy compositeNo. of samples
Designations Compositions Hybrid wt. %
of reinforcement
1 ZAlGr – 0 100 wt.% ZA-27 + 0 wt.% Gr + 0 wt.% Al2O3 0
2 ZAlGr – 2 96.5 wt.% ZA-27 + 1 wt.% Gr + 2.5 wt.% Al2O3 3.5
3 ZAlGr – 3 93.0 wt.% ZA-27 + 2 wt.% Gr + 5 wt.% Al2O3 7
4 ZAlGr – 4 89.5 wt.% ZA-27 + 3 wt.% Gr + 7.5 wt.% Al2O3 10.5
2.3 Stir Casting Fabrication Technique
• ZA – 27 alloys melt in a graphite crucible by placing it within the temperature controlled electric furnace. The range of melting for ZA-27 alloy is 376-484 °C.
• To avoid solidification during pouring, it necessary that melt is to be superheated up to a temperature of 540 C and the same temperature to be maintained for some time.
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• After melting of ZA – 27, the reinforcements were taken as per designations given in table 2.
• After weighing reinforcements (i.e. Gr and Al2O3), the reinforcements were mixed with the molten ZA - 27with the help of stirrer made of hardened steel for 30-35 seconds and heated again in furnace. Then crucible is taken out from the furnace and stirred again for 30 - 40 seconds and then poured into the die.
• The mixture of ZA - 27 + Gr + Al2O3 was then poured in a die made of hardened steel having dimension 145 х 90 х 10 mm. The mixture was then allowed to solidify for 2 – 3 minutes and then after taking out from the die, the solidified plate of composite was quenched in cold water.
3. RESULTS AND DISCUSSION
3.1 Effect on density and void contents of graphite and alumina reinforced ZA - 27 alloy hybrid composites
The relative proportion of reinforcing and matrix material in a composite determines the value of density. There is always difference found in the theoretical and measured values of density because of the existence of pores and voids [12]. In this investigation the calculated volume fraction of voids and densities for various compositions of Gr and Al2O3 reinforced ZA – 27 alloy hybrid composites are exhibited in table 3.
Archimedean method is used to find the porosity in terms of volume percent by comparing the theoretical and experimental densities.
In table 3 this can be see that experimental densities are lower than the theoretical densities and this value decreases continuously with increase in reinforcement particle. Void contents of hybrid composites are less than ZA – 27 alloy except than 10.5 wt.% hybrid reinforced composites.
Fig. 2:
Melting of ZA-27 in temperature controlled furnace machineFig. 3:
Pouring of meltFig 4:
CrucibleFig 5:
Permanent Mould358 | P a g e
Fig. 6:
Effect on void content of ZA-27 Alloy compositesTABLE 3:
Measured densities along with the void contents Designations Compositions wt. %(ZA – 27 : Gr : Al2O3)
Theoretical densities (gm/cc)
Experimental densities
(gm/cc)
Void contents
(%)
ZAlGr – 1 100 : 0 : 0 4.90 4.82 1.63
ZAlGr – 2 96.5 : 1 : 2.5 4.79 4.72 1.46
ZAlGr – 3 93 : 2 : 5 4.68 4.65 0.64
ZAlGr – 4 89.5 : 3 : 7.5 4.61 4.52 1.95
The graph between void content and hybrid reinforced ZA – 27 alloy composites is presented in fig. 6. This graph presents that 3.5 wt.% and 7 wt.% hybrid reinforced composites have lower void content than ZA – 27 alloy while 10.5 wt.% hybrid reinforcement has higher void content. Lowest void content is obtained at 7 wt. % of hybrid reinforcement.
The reason of increasing in void content at higher wt.% of hybrid reinforcement can be increasing in stirring time due to the presence of higher weight content of reinforcement, at the ceramics particle sites the presence of pores nucleation, clustering and the effect of lower wettability [13].
Mahdavi et. al. fabricated the SiC and Gr reinforced Al – based hybrid composites and told that the due to presence of hard particles, hybrid composites have more porosity because of the interparticle spacing during pressing but Gr
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Fig. 7:
Hardness of ZA-27 alloy hybrid compositecontent decreases the void content by providing movement and rearrangement facilities to reinforcement because it acts as a solid lubricant [6].
3.2 Effect on mechanical properties of graphite and alumina reinforced ZA - 27 alloy hybrid composites
Table 4 presents the values of different mechanical properties (Hardness, Compressive strength, Impact strength) for different composition of graphite and alumina reinforced ZA - 27 alloy hybrid composites, obtained by operating corresponding testing under controlled lab circumstances.
TABLE 4:
Mechanical properties of the graphite and alumina reinforced ZA - 27 alloy hybrid composites Designations Compositions wt. %(ZA – 27 : Gr : Al2O3)
Hardness (HRB)
Compressive Strength (MPa)
Impact Strength (J)
ZAlGr – 1 100 : 0 : 0 61.3 282 36
ZAlGr – 2 96.5 : 1 : 2.5 67.28 297 39
ZAlGr – 3 93 : 2 : 5 72.1 314 43
ZAlGr – 4 89.5 : 3 : 7.5 59.33 293 33
3.2.1 Effect on hardness of graphite and alumina reinforced ZA - 27 alloy hybrid composites
The Rockwell hardness for B scale is shown in table 4, by taking three readings on every sample and then calculated the average value, have been considered as final HRB of every sample. The graph of hardness (HRB) vs different hybrid reinforcement is plotted in fig. 7. The unfilled ZA – 27 alloy have 61.3 HRB, is increasing up to 72.1 HRB with the increase of hybrid reinforcement till 7 wt.% after this hardness decreases up to 59.33 HRB for 10.5 wt.% for hybrid reinforcement. Suresha et. al. found that when the composite is reinforced up to 2.5 wt.% of each Graphite and SiC particle then hardness increased and after this start to decrease. The increase of
360 | P a g e hardness is due to the hard reinforcement particle and decrease is due the overriding impact of softer Gr particles [14].
3.2.2 Effect on compressive strength of graphite and alumina reinforced ZA - 27 alloy hybrid composites The tendency of the material to resist the load applied on the body that could result in the reduction of size of the material is known as the compressive strength of the material. Every material shows different compression limit; in it some materials reach their maximum limit but other fail early due to the anisotropy of the material.
Fig 8:
Compressive Strength of ZA-27 alloy CompositeThe fig. 8 represents the compressive strength that varies with the varying wt. % of hybrid reinforcement. The compressive strength increases with the increase of hybrid reinforcement up to 7 wt.% and further it decreases for 10.5 wt.% of hybrid reinforcement. The compressive strength for each hybrid reinforcement is greater than unfilled ZA – 27 alloy, and the maximum compressive strength (314 Mpa) is obtained at 7 wt.% of hybrid reinforcement.
3.2.3 Effect on impact strength of graphite and alumina reinforced ZA - 27 alloy hybrid composites
361 | P a g e Under application of shock or impact loading the capacity to absorb and dissipate energies can be defined as the impact strength of material. The variation of impact strength with various hybrid reinforcement is represented in fig. 9. The unfilled ZA – 27 alloy has lower impact strength than filled hybrid reinforcement except than 10.5 wt.% of hybrid reinforcement. The impact strength increases from 36 J to 43 J with the increase of hybrid reinforcement up to 7 wt.% and further it decreases up to 33 J for 10.5 wt.% of hybrid reinforcement. A. Manna
Fig. 9:
Impact Strength of ZA-27 alloy Compositeet. al. studied the behavior of Gr/Al2O3 reinforced Al alloy composite material and found that the addition of alumina particle more than 5 wt.% show decreases in impact strength, because of segregation at some places and brittle nature of reinforcement particle [8].
4.
CONCLUSIONS
For the fabrication of ZA – 27 alloy hybrid composites stir casting can be successfully utilized.
It is seen that 3.5 wt.% and 7 wt.% hybrid reinforced composites have lower void content than ZA – 27 alloy while 10.5 wt.% hybrid reinforcement has higher void content. Lowest void content is obtained at 7 wt. % of hybrid reinforcement.
The unfilled ZA – 27 alloy have 61.3 HRB, is increasing up to 72.1 HRB with the increase of hybrid reinforcement till 7 wt.% after this hardness decreases up to 59.33 HRB for 10.5 wt.% for hybrid reinforcement.
The compressive strength increases with the increase of hybrid reinforcement up to 7 wt.% and further it decreases for 10.5 wt.% of hybrid reinforcement. The compressive strength for each hybrid reinforcement is greater than unfilled ZA – 27 alloy, and the maximum compressive strength (314 Mpa) is obtained at 7 wt.% of hybrid reinforcement.
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The unfilled ZA – 27 alloy has lower impact strength than filled hybrid reinforcement except than 10.5 wt.% of hybrid reinforcement. The impact strength increases from 36 J to 43 J with the increase of hybrid reinforcement up to 7 wt.% and further it decreases up to 33 J for 10.5 wt.% of hybrid reinforcement. The reason of decreasing in impact strength can be segregation at some places and brittle nature of reinforcement particle.
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