A study on characterization of Al-18%Si alloy by centrifuge casting

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A study on characterization of Al-18%Si alloy by centrifuge casting Manjunath M D 1, Mallikarjun P S2, Shankar Narayan K3, Rajiv B L4, Harish N5 1234

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Department of Mechanical Engineering, NMIT Yelahanka, Bangalore, Karnataka, India Assistant Professor, Department of Mechanical Engineering, NMIT yelahanka, Bangalore Karnataka, India

Abstract: Aluminum-silicon alloy are characterized by light weight, good strength –to-weight ratio, ease of fabrication of at reasonable cost, high strength at elevated temperature, good thermal conductivity, excellent castability, good weldability, excellent corrosion and wear resistance property. Thus, these types of alloys are well suited for automotive industries, aerospace structural and military applications. In centrifuge casting solidification rate is faster compared to gravity casting, but still solidification depends on various process parameters like, cooling temperature of molten metal, rotational speed of the die and also wall thickness of die. In centrifuge casting the silicon deposition in aluminum varies from top to bottom. Here Al-Si functionally graded material is used and developed under centrifuge casting. The method used in this work to produce functionally graded material is totally different from other centrifugal casting which helped in producing solid cylindrical parts. This report describes about mechanical characterization of Al18%Si at different temperature. At 950°C casting shows good ultimate tensile strength and harder metal compared to other casting.

Keywords: centrifuge casting, mechanical properties, functionally graded material(FGM), AlSi18% centrifuge casting.

1.INTRODUCTION Functionally Graded Material are a new class of inhomogeneous material, whose composition and

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microstructure vary from one end to the other in component. In conventional composites, the constituent phases are evenly distributed thereby the properties on an average will be uniform. However in FGMs, the composition and microstructure vary smoothly in space and the properties and performance therefore vary from one end of the specimen to other end. The FGMs, can be tailored to the specific service requirement thus ensuring the best response of the system. Due to the gradual variation of composition and microstructure, it avoids an abrupt interface which gives smooth transition from one side to the other side avoiding the local stress concentration [1].

This work uses a modified centrifugal casting technique to produce in situ blocky Al/Si FGMs. The process enables the pouring of molten metal in to stationary mould. The principal advantage of this is good mould filling combined with microstructure control, which usually results in improved mechanical properties. Apart from this production rate, time saving, and any kind of casting can be reproducible of any shape.

2.OBJECTIVES As from the literature review promoted for the need of a systematic study of various mechanical properties of Aluminum Silicon alloy can be used for better application and have better composition. This study can lead one to explore the possibility of identify the use of these alloy for engineering applications.

Therefore the work taken up have following objectives: 1. Fabrication of Al-Si by centrifuge casting.

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International e-Journal For Technology And Research-2017 2.

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Microstructure characterization of the alloy using optical microscope.

Evaluation of mechanical, corrosion and wear properties of Al-Si alloy.

Comparing the result of mechanical, corrosion and wear properties of as-cast alloy.

Drawing conclusion based on the obtained result.

is enough scope for further research of Al-Si alloys especially their mechanical properties.

Therefore the objectives of this study are; i. To study of their microstructure. ii. To study of their mechanical properties like hardness, tensile. iii. To study the wear behavior.

3.1 EXPERIMENTAL PROCEDURE The present study is thus aimed at production of MMCs with aluminum and Silicon composite material as centrifuge casting process in order to attain the good mechanical properties, and also attain good application.

3. Materials and Methods Aluminum- Silicon alloy Al-Si alloys are of great importance to many industries as they impart high wear Resistance, high strength to weight ratio, low coefficient of thermal expansion low density etc. Silicon exhibits low shrinkage and high fluidity, which gives these alloys good weldability and castability. Al-Si alloys are given a nomenclature of 4xxx alloys according to the Aluminum.

Association Wrought Alloy Designation System. The major features of the Al-Si alloys are: a. They are moderately heat treatable. b. They show good flow characteristics. c. They are easily wieldable.

The two most important uses of the 4xxx series Al-Si alloys are for forging and weld filler alloy. These applications are feasible due to the good flow characteristics given by relatively high silicon amount.

Effects of Si in the Al-Si alloys can be summed as: i. Silicon reduces thermal expansion. ii. Silicon has a very low effect on magnetic susceptibility and reduces it by a very low amount. iii. Lattice Parameter decreases on adding Si. iv. Silicon is hard and therefore the machinabilty of

Centrifuge casting is used to process the functionally graded Al-Si alloy. The centrifugal force progressively increases the volume fraction of the Si within the liquid Al matrix along the radial direction, owning to the density difference between the two materials. The difference in this design of centrifuge technique from the commonly use centrifugal casting machines is that this device operated horizontally and pouring had to be done while the mold is stationary. Thus, centrifugal forces were not applied immediately as in the traditional casting methods since the mould takes

some time to reach its casting speed. This delay had to be compensated by higher pouring and mould temperatures so that the desired particle segregation could be achieved[1].

these alloys deteriorates.

Although many investigations exist in literature and based on the above discussion, it is evident that there

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IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

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International e-Journal For Technology And Research-2017 Fig. 1. Centrifuge casting setup The equipment used to cast is a modified version of centrifugal casting process based on centrifuge technique. The centrifuge casting machine mainly consists of an arm wherein a mold is allowed to swing at one end and the other end with a counter weight.

This arm is centrally mounted on a motor shaft of 1 HP capacity.

The raw material used in these experiments is Al18wt% Si master Alloy from Fen-Fee Metallurgist.

The matrix alloy is an Al-Si alloy whose composition is (by weight): 18% Si, 0.1% Fe, and the remaining is Al. Al-Si has good cast-ability since Si improves casting characteristics such as fluidity, hot tear resistance, and feeding[3]. Al Alloys can be used in environments where corrosion is a problem, thermal conductivity, high strength. They are used in pistons and bearings due to these properties. Wear resistance of Si added Al alloys is higher than those of other Al alloys [2]. The Alloy was poured into the mold located at one end of the arm. Then the arm is rotated at known speed. A changing of temperature 750°C, 850°C, 950°C casting has been done. And those mechanical properties calculated.

3.2 CHARACTERIZATION

Fig. 2. ASTM E8 standard

4. Result and Discussion

The specimens are cut along the length through the center of the cylindrical block. These specimens were polished by the standard metallographic methods. The microstructures of the specimens were investigated by an optical microscope interfaced with a computer.

Image Analyzer is used for determining the percentage of primary Al-Si phases at different locations along the length of the casting.

Tensile strength was measured by using casted part.

To conduct tensile test a ASTM E8 specimen standard has been used. We found out eng UTS and true UTS[3].

3.3 TENSILE TEST Procedure to conduct tensile test as explained below:

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1. The specimen’s dimensions (thickness/gauge length/total length in mm etc) were measured accurately with a Venire calipers.

2. The details were fed into the testing machine.

3. The distance between the jaws was fixed according to the gauge length of the specimen.

4. The specimen was inserted into the machine and gripped by the jaws.

5. Maximum load was set to 2KN and loading was done till the specimen failed.

6. The corresponding readings generated for Yield Strength, %elongation & Ultimate Tensile Strength was noted.

ASTM E8 standard

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The microstructure and distribution of primary Si particles in a casting depends on several parameters [4]. These parameters are the size, centrifugal force and cooling rate controlled by mold temp, pouring temperature and heat transfer between the mold and melt.

In these experiments the composition of Al-Si18% is same and also RPM(200) parameters are fixed i.e, pouring temperature changes by 750°C, 850°C, 950°C. So three casting has been done at different temperature, then the deposition of Si varies from one end to the other in all three casting. Microstructure has been taken from all three casting, as shown below.

At 750°C

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International e-Journal For Technology And Research-2017 170 160 150

Eng UTS

140

True UTS

UTS130 At 850°C

750°C 850°C 950°C Temperature

Fig. 3. Al Si18% centrifuge casting by varying temperature

1.Test conducted for 7500 C and the load displacement curve is shown below.

At 950°C

Figure 5.8: Load displacement curve at 750°C

Data obtained from test as shown below.

4.1 Tensile test The tensile test has been conducted, and result has taken. As below graph shows strength of material at different temperature. As temperature of the material increases the hardness and strength of material also increases. This aspect is also clearly revealed in their respective microstructure.

Eng UTS : 144.3N/sq mm ; proof stress:50.4 N/sq mm;

2.Test conducted for 8500 C and the load displacement curve is shown below.

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IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

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International e-Journal For Technology And Research-2017

5.Conclusion Among the Al-Si FGM formed at 250G (200rpm) for 750°C, 850°C and 950°C temperature, has yielded best result compared to 750°C and 850°C casting. The gradation in micro structural features is reflected in hardness values also.

The FGM formed for 950°C casting show high volume percentage of Si nearly 26% in the upper region of the cast and a depleted region towards the lower region. The upper region is a hypereutectic microstructure and that the lower region is Hypo.

Figure 5.9: Load displacement curve at 850°C

Data obtained from test as shown below.

Eng UTS : 149.8N/sq mm ; proof stress:52.9 N/sq mm 3.Test conducted for 9500 C and the load displacement

6.References 1. Kiran aithal , P G Mukunda: “Effect of L/D ratio on Al Si Functionally Graded Material cast through Centrifuge technique”.

2. Madhusudhan, Narendranath S: “Properties of centrifugal casting at different rotational speed of the die”.

3. Mohamed Nazirudeen S S, Dhanapal P: “Processing techniques of functionally graded materials”.

4. Anirudh Biswas, D K Balla, Manoj Kumar: “To study the mechanical properties of silicon 18% based aluminum alloy”.

curve is shown below.

Figure 5.10: Load displacement curve at 950°C

Data obtained from test as shown below.

Eng UTS : 156.8N/sq mm ; proof stress:56.4 N/sq mm;

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IDL - International Digital Library Of Technology & Research Volume 1, Issue 3, Apr 2017

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