Studies on Microstructure and Mechanical properties of Aluminium Foam prepared by Spray Forming Route

Available online at www.sciencedirect.com Available online at www.sciencedirect.com

ScienceDirect ScienceDirect

Procedia Manufacturing 00 (2019) 000–000 Procedia Manufacturing 00 (2019) 000–000

Available online at www.sciencedirect.com

ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Manufacturing 35 (2019) 861–865

2nd International Conference on Sustainable Materials Processing and Manufacturing 2nd International Conference on Sustainable Materials Processing and Manufacturing (SMPM 2019) (SMPM 2019)

Studies on Microstructure and Mechanical properties of Aluminium Studies on Microstructure and Mechanical properties of Aluminium Foam prepared by Spray Forming Route Foam prepared by Spray Forming Route Amarish Kumar Shukla, J. Dutta Majumdar* Amarish Kumar Shukla, J. Dutta Majumdar*

Department of Metallurgical & Materials Engineering, Indian Institute of Technology Kharagpur- 721302, India Department of Metallurgical & Materials Engineering, Indian Institute of Technology Kharagpur- 721302, India

Abstract Abstract In the present study, attempts have been made to develop aluminium foam using cenosphere as a space holder by spray forming route. main process variables gasaluminium pressure, and of space holders. Detailed investigation In the The present study, attempts havewere, beenapplied made tocurrent, develop foamweight using fraction cenosphere as a space holder by spray forming of the The effect of process on the microstructures undertaken to optimize zoneDetailed for the investigation development route. main process parameters variables were, applied current, gaswere pressure, and weight fractionthe of processing space holders. Theof mechanical properties on in terms of micro hardness, strength have evaluated in of foam. the effect process parameters the microstructures were compressive undertaken tostrength, optimizeand thetensile processing zone forbeen the development details. the deformation behaviour ofof themicro aluminium foam has been established. of foam.Finally, The mechanical properties in terms hardness, compressive strength, and tensile strength have been evaluated in details. Finally, the deformation behaviour of the aluminium foam has been established. © 2019 The Authors. Published by Elsevier B.V. © 2019 Published B.V. Peer-review under responsibility ofElsevier the organizing © 2019 The The Authors. Authors. Published by by Elsevier B.V. committee of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019. Keywords: Aluminium foam, compressive strength, fractography, micro hardness, spray forming, tensile strength. Keywords: Aluminium foam, compressive strength, fractography, micro hardness, spray forming, tensile strength.

1. Introduction 1. Introduction Metal foam is a new class of engineering material containing pores and is promising for structural application, Metaloffoam is a new class of engineering material containing and is promising for structural application, because its light weight, excellent energy absorption capacity, pores good stiffness, higher sound absorption capacity, because of its light weight,higher excellent energy absorption stiffness, higher sound better crushing strength, thermal insulation andcapacity, dampinggood strength in comparison to absorption their solid capacity, material better crushing strength, higher thermal insulation and strength their solidindustries, material counterpart [1–5]. Aluminium foams are extensively useddamping in various fields in viz.,comparison automotive,to aerospace counterpart Aluminium foams extensively used in various fields viz.,mechanical automotive, railway, and[1–5]. structural application for are passenger safety, because of their unique andaerospace physical industries, properties railway, and structural application for passenger safety, because their unique and powder physicalmetallurgy, properties [6,7]. Several methods have been attempted to synthesize foamed of aluminium, likemechanical melt-foaming, [6,7]. Several have been etc. attempted to synthesize aluminium, like melt-foaming, powder metallurgy, spray forming,methods melt infiltration, [7]. Among these allfoamed methods, spray forming gets a less attention to prepare spray forming, melt infiltration, etc. [7]. Among these all methods, spray forming gets a less attention to prepare * *

*Corresponding author. Tel.: +91 3222 283288; fax: +91 3222 282280. *Corresponding author. Tel.: +91 3222 283288; fax: +91 3222 282280. E-mail address: [email protected] E-mail address: [email protected]

2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review the organizing committee 2351-9789 ©under 2019responsibility The Authors. of Published by Elsevier B.V. of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019.

2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of SMPM 2019. 10.1016/j.promfg.2019.06.032

862 2

Amarish Kumar Shukla et al. / Procedia Manufacturing 35 (2019) 861–865 Author name / Procedia Manufacturing 00 (2016) 000–000

aluminium foam by using cenosphere as space holder. Spray forming is an advanced technique, which involves atomization of a liquid metal stream into variously sized droplets, which are then propelled away from the region of atomization by fast flowing atomization gas. These droplets are then allowed to solidify over a substrate into a near fully dense preform. Large preforms can be produced by continuous movement of substrate relative to atomizer [7]. The advantages of spray forming over other conventional techniques are development of refined structure, near zero segregation and improved mechanical properties resulting from rapid solidification. This process is intermediate in terms of cost between stirring and powder metallurgy route. Spray forming offers a combination of low-cost manufacturing with enhanced properties and performance hence this process is commercially viable and sustainable in terms of manufacturing of various engineering components [8]. However, presence of cenosphere as a space holder develops closed porosity with porosity ranging in the micro range. In the present work, 35 weight percentage of cenosphere, constant current (400Amp), and varying hydrogen pressure (5, and 10 Psi), has been used to develop aluminium foam by spray forming route. A detailed investigation of the effect of spray forming parameters on the microstructures was undertaken to optimize the process parameters for spray forming. Finally, the mechanical properties like microhardness, tensile strength, and compressive strength have been evaluated and the mode of failure has been established through a detailed analysis of fractured surface. 2. Materials and Design 2.1 Process description Commercially pure (CP) Aluminium powder (Aldrich, -200 Mesh, 99%), and cenosphere powders (Cenosphere India Ltd., Kolkata) of 60 µm average particle size premixed in the weight ratio of 65:35 was used as precursor powder to prepare foam by using spray forming technique. In this technique, argon (40 Psi) gas was used for arc initiation, and hydrogen (5 Psi and 10 Psi) was used as an auxiliary gas. Argon causes a rapid heat transfer between a plasma jet flame and the heated object. Besides, argon also protects powder particles against oxidation. As a result, the role of argon and hydrogen gas is of prime importance in present work. The used process parameter, for preparation of foam sample is mentioned in Table 1. 2.2 Microstructural Examination For microstructural examination, the representative foam samples were polished by the standard metallographic practice followed by etching with Keller’s regent, and gold sputtered prior to microstructural study using scanning electron microscopy (Field Emission Gun: Carl Zeiss). After compressive and tensile failure, the foam samples were carefully mounted and observed by scanning electron microscopy. In case of compressive, the samples were kept as it is, and for tensile specimen the fractured portion was kept in top, and then observed by scanning electron microscopy to evaluate the deformation mechanism of foam samples and crushing behaviour of cenosphere during deformation. 2.3 Microhardness measurement Microhardness of the foam sample was measured using Vickers micro-hardness tester (UHL-VMHT 001) using a load of 100gmf, and dwell time of 10 second. The distance between the two indentation measurement points was twice as that of the size of indentation. The average hardness was calculated by taking the mean of the hardness at 15 different regions on the sample. 2.4 Compression and Tensile Test Uniaxial compressive samples of size 10 mm × 10 mm × 5 mm were used for the compression testing. The test was carried out by using a Universal Testing Machine (UTM Instron model: 1344) at a strain rate of 0.01/s at



Amarish Kumar Shukla et al. / Procedia Manufacturing 35 (2019) 861–865 Author name / Procedia Manufacturing 00 (2016) 000–000

863 3

room temperature. For tensile tests, the flat samples of the dimension of 20 mm × 10 mm × 3 mm were subjected to loading using a Universal Testing Machine (UTM Instron model: E 1000) at a strain rate of 0.01/s at room temperature. Teflon tape was used on the surface of the compressive foam sample to reduce the friction between sample and anvil. The load displacement data was recorded during the test, and it was converted to stress-strain graph. The yield strength (y), plateau stress (pl), and energy absorption (Eab) were determined from stress-strain curves. The tests were repeated for three times for different samples to calculate the average mechanical properties of the samples. 3. Results and Discussion 3.1 Microstructural characterisation of foam Figures 1(a, b) show the scanning electron micrographs of aluminium foam using cenosphere as space holders developed by spray forming route at a hydrogen pressure of (a) 5 psi and (b) 10 psi. From Figure 1, it may be noted that there is uniform distribution of cenosphere into the matrix. In addition, there is a strong interfacial bonding between cenosphere and the aluminium matrix. Application of higher hydrogen pressure causes formation of micro-pores and deep impingement of the cenosphere particles in aluminium matrix. Few cenosphere were found to be damaged during spraying for both the cases. In addition, cluster of cenosphere was also observed in the microstructure. Table .1: The processing parameters, and physical properties of foam Sample Name

composition

H2

Density

(Psi)

(g/cm )

Porosity (%)

Hardness (HV)

3

S1

Al+Cenosphere

5

1.896±0.06

28.22±2.09

35.16±4.11

S2

Al+Cenosphere

10

1.917±0.11

26.79±3.51

37.8±3.81

Fig.1. SEM micrograph of, (a) S-1, and (b) S-2 foam sample prepared by spray forming route.

3.2 Hardness The Vickers hardness of the foam samples are shown in Table.1. The hardness of the foam sample depends on density, the bonding between the powder particles. The hardness of S-2 foam sample is relatively higher as compared to S-1, because of increased density and the less micro porosity generated due to more hydrogen pressure. The addition of Cenosphere increases the hardness of foam because its higher hardness as compared to aluminium [9].

Amarish Kumar Shukla et al. / Procedia Manufacturing 35 (2019) 861–865 Author name / Procedia Manufacturing 00 (2016) 000–000

864 4

3.3 Compression and Tensile Test Compression testing was performed to find out the behaviour of Al foam under the common structural loading. The compression test was used to illustrate the energy absorption properties of foam, and highlights its strength in this area. The compressive and tensile behaviour of foam are shown in Fig.2 (a), and Fig.2(b). Figure 2(a) shows that initially, the stress-strain diagram shows linear kinetics following which there is increased strain with stress due to deformation of the material. At a stress higher than the fracture strength of cenosphere, there is fracture of cenosphere wall causing serration and discontinuity in the stress-strain diagram. The yield strength, plateau stress, and densification strain are estimated from the stress–strain curve and are listed in Table 2. The yield stress, (σy) is the upper limit of the elastic region beyond which the foam undergoes irreversible deformation, and the offset of 0.2% is used to find out the value of yield strength of all compressive samples. The plateau stress (σ pl), was calculated as the average stress value between 5% and 30% engineering strain [10]. Area under the curve has been used to obtain energy absorption (Eab), capability of the foamed samples. The deformation of foam starts with the collapse of cenosphere wall. The continued application of compression causes the cavity to be filled by the collapsing walls of cenosphere and surrounding matrix materials followed by the crack propagation [5]. The crushing process of cenosphere enhances the energy absorption capabilities of foam leading to better damage tolerance of these materials. It is observed that the overall mechanical properties depend on load carrying capabilities of hollow cenosphere particles and hard cenosphere cell wall thickness. Therefore, the foam exhibits higher energy absorption behaviour. The tensile behaviour of foam sample is depicted in Figure 2 (b). The tensile strength of foamed sample is proportional to the bond strength between matrix and cenosphere. As bonding increases tensile strength also increases. However, samples processed under both 5 psi and 10 psi hydrogen pressure fails prematurely even before reaching 0.02% strain. The premature failure under tensile loading is due to failure of cenosphere, causing crack initiation sites and leading to failure of aluminium foam. A detailed fractography analysis was carried out to study the mode of failure, and fracture characteristics of compressive and tensile loaded sample.

Fig.2: (a) Compressive, and (b) Tensile stress behaviour of spray formed sample. Table .2: The mechanical properties of foam samples, prepared by spray forming route Sample Name

Yield strength

Plateau strength

Energy absorption

Tensile strength

(compressive)

(compressive)

(compressive)

(MPa)

(MPa)

(MPa)

(MPa)

S1

65.67±1.62

113.16±11.06

38.6±2.9

23±2.39

S2

68.09±1.5

122.9±8.5

47.8±1.9

11.13±2.04



Amarish Kumar Shukla et al. / Procedia Manufacturing 35 (2019) 861–865 Author name / Procedia Manufacturing 00 (2016) 000–000

865 5

3.4 Fractography of foam sample The fractographs of compressive and tensile sample have been observed by scanning electron microscopy, and are shown in Fig. 3 (a), and 3(b). Figure 3 (a), reveals that the foam resists the load until cenosphere particles cell wall is continuous. It is also observed that, mostly large size particles collapse, however, small size particles are also clearly observed in micrograph. It might be because of cavity is filled by small particles, and which further enhance the strength of foam. During compression, mixing of fine particles of fragmented cenosphere, leads to increase in elastic modulus. It may further be noted that cenosphere particles are broken almost in two parts, which confirms the brittle nature of cenosphere.

Fig.3: Fractography of foam samples after (a) compressive, and (b) Tensile failure.

4. Conclusion In the present study aluminium foam has been successfully developed by spray forming route by using cenosphere as space holder. From the detailed investigation it has been observed that the porosity generated into the foam sample is because of presence of cenosphere as space holder and generation of micro voids due to spraying. The hardness, and the strength of foamed sample depends upon the density and bonding between cenosphere space holder and aluminium matrix. The strength of foam sample is better in compression, however, localised fracture has been observed during tensile test. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

S.S.M. Nazirudeen, A Development of Technology for Making Porous Metal Foams Castings, Jordan J. Mech. Ind. Eng. 4 (2010) 292– 299. J. Banhart, Aluminium foams for lighter vehicles, Int. J. Veh. Des. 37 (2005) 114. A. Salimon, Y. Bréchet, M.F. Ashby, A.L. Greer, Potential applications for steel and titanium metal foams, J. Mater. Sci. 40 (2005) 5793–5799.. Sudarshan, M.K. Surappa, Dry sliding wear of fly ash particle reinforced A356 Al composites, Wear. 265 (2008) 349–360. S. Birla, D.P. Mondal, S. Das, D.K. Kashyap, V.A.N. Ch, Effect of cenosphere content on the compressive deformation behaviour of aluminum-cenosphere hybrid foam, Mater. Sci. Eng. A. 685 (2017) 213–226. N. Jha, D.P. Mondal, J. Dutta Majumdar, A. Badkul, A.K. Jha, A.K. Khare, Highly porous open cell Ti-foam using NaCl as temporary space holder through powder metallurgy route, Mater. Des. 47 (2013) 810–819. M.F. Ashby, A.G. Evans, N.A. Fleck, L.J. Gibson, J.W. Hutchinson, H.N.G. Wadley, Metal Foams : A Design Guide Metal Foams : A Design Guide, (2000). A.R.E. Singer, Metal Matrix Composites Made by Spray Forming, Mater. Sci. Eng. a-Structural Mater. Prop. Microstruct. Process. 135 (1991) 13–17. D.P. Mondal, S. Das, N. Ramakrishnan, K. Uday Bhasker, Cenosphere filled aluminum syntactic foam made through stir-casting technique, Compos. Part A Appl. Sci. Manuf. 40 (2009) 279–288. V.K. Jeenager, V. Pancholi, B.S.S. Daniel, Influence of cell wall microstructure on the energy absorption capability of aluminium foam, Mater. Des. 56 (2014) 454–459.