Investigation of Mechanical Behavior of Aluminium Alloys Before and After Work Hardening

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Investigation of Mechanical Behavior of Aluminium Alloys Before and After Work Hardening Shreyas S Bhatt1, Ravichandra P V2, Shreyas P M3, Srivathsa B S4, V R Kabadi5, K Kotresh6 UG Student, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India1,2,3,4 Professor, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India 5 Assistant Professor, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India 6

Abstract:

The ever increasing demand from aerospace industries and automotive industries to manufacture components which are lighter and stronger than conventional steel has prompted the significant usage of aluminium alloys. This research work involves the investigation of mechanical properties in aluminium alloys before and after work hardening. The alloy is work hardened using cold forging process. The major alloying elements used in the aluminium alloy are manganese, magnesium and silicon. The aluminium alloy ingots are prepared through gravity casting. After the ingots are air cooled to room temperature, they are work hardened using cold forging method where the ingots are forged at room temperature. The cold forged aluminium alloys are then subjected to tensile tests, wear tests, hardness tests and microstructure analysis using optical Scanning Electron Microscope (SEM). The material properties achieved are compared with the alloys properties that have not been subjected to work hardening. The expected outcome is to achieve a work hardened aluminium alloy that exhibits excellent mechanical properties which can be best suited for numerous industrial manufacturing requirements.

Better ideal properties such as formability, weldability,

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increased hardness and wear resistance are expected from the cold forged alloys.

Keywords: Aluminium alloys, Cold forging, Hardness, Microstructure, Wear resistance, Work hardening.

1. INTRODUCTION Aluminium alloys are used for manufacturing since pure aluminium alone (1xxx series) tends to have weaker material properties and are non hardenable.

Aluminium alloys occur as two types namely, wrought aluminium and cast aluminium. Cast aluminium alloys can be easily heat treated and work hardened unlike wrought aluminium. The cast aluminium is subdivided into heat treatable and non heat treatable alloys. In this research work, castable and heat treatable aluminium alloys are being used.

There are eight alloying groups for aluminium out of which only three groups are of interest to this research work. They are Aluminium-Manganese (3xxx series), Aluminium-Silicon (4xxx series) and Aluminium-Magnesium (5xxx series). When subjected to cold working, different alloying elements exhibit different attributes on the alloy property. The strength of 3xxx series aluminium is moderate. However, they 1|P a g e

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International e-Journal For Technology And Research-2017 have good formability characteristics and can be easily work hardened and also used for anodizing and welding. On the other hand, the 4xxx series aluminium comprises of silicon which is primarily used for its good casting properties. This is because silicon has the capability to reduce the melting point of aluminium without introducing brittleness into the alloy. As in the case of 5xxx series alloy, magnesium is seen to be the primary alloying element. Such alloys have higher strength when compared to that of 3xxx series or 4xxx series alloy. They also have an excellent corrosion resistance property because of which they are preferred in numerous marine industry and naval applications. Because of their high strength, they are most commonly employed in the production of pressure vessels and tanks that can withstand very high pressures.

The overall applications of aluminium alloys prove that it is one of the most versatile materials which are highly sought after. Sometimes basic standards of aluminium might not meet the requirement in an industry level environment.

Therefore aluminium is alloyed with multiple alloying elements together to obtain materials with properties that meet the requirement of purpose. In this research paper, three different alloying elements are used to obtain three unique alloys whose mechanical properties are investigated in detail. The same materials are subjected to work hardening and investigation of mechanical properties is also conducted for the same.

A critical comparison of mechanical properties such as material hardness, tensile strength and wear resistance is performed between the work hardened and non work hardened aluminium alloys. The microstructure is also viewed critically with the help of a Scanning Electron Microscope (SEM) which will provide a better understanding of influence of work hardening on the dendrite formation, distribution and orientation. After the comparison of multiple samples of aluminium alloys are performed, a best work hardened aluminium alloy composition with excellent material properties is suggested which can be best suited for innumerable cross-domain applications in the manufacturing industry.

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MATERIAL SELECTION AND COMPOSITION Various compositions of magnesium, manganese and silicon are used as alloying elements for the aluminium alloys from which specimens are fabricated. Since they play a big role in enhancing the material properties, the following composition table describes the percentage composition in the entire alloy.

Table 1.1: Chemical composition of aluminium alloys

Element

Percentage composition %

Alloys

1

2

3

Si

10

10

-

Mg

0.2

0.6

0.4

Fe

0.8

1

1

Mn

7

-

7

Al

82

88.4

91.60

2. OBJECTIVES According to the requirements and problem definition, the main objectives of this paper are as listed below:  To utilize three different alloying elements and fabricate aluminium alloy ingots by gravity casting.  Subject the ingots to work hardening (Cold forging) and estimate the percentage of work hardening.  Fabricate multiple specimens for investigation of mechanical properties such as tensile strength, wear resistance, hardness.  To calculate the wear rate of alloys using a pinon-disk wear test apparatus.

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Microstructure inspection using Scanning Electron Microscope (SEM).

Comparison of results and providing conclusion based on the test results.

3. METHODOLOGY A prefixed methodology that includes the systematic conduction of various activities of the research work is shown in the form of a hierarchy tree in figure 3.1. It signifies the activities ranging from fabrication of specimen to discussion of results.

If the fabricated specimens upon testing yield excellent mechanical properties, can be implemented in the following industrial scenarios:  Aerospace industries for construction of fuselage and other light weight components.  Automotive industries where light weight chassis construction is of crucial importance to obtain better efficiency.  Weldable components in the marine industry where non corrosive and high strength hull construction is of primary importance.  Light weight engine block headers in race vehicles.  High pressure vessels and storage tanks.

5. OUTCOMES Various tests have been performed to investigate the mechanical properties. The following section depicts various results obtained from conduction of tests such as hardness test, wear test and tensile test. 

HARDNESS TEST The hardness test is conducted using a Brinell hardness testing machine. Hardness is checked mainly for two conditions – before work hardening and after work hardening. The table 5.1 illustrates the comparison of Brinell hardness numbers obtained.

Table 5.1: Hardness test results

Sl. No.

1

2 Fig. 3.1: Research methodology heirarchy

Alloy composition

      

Al (82%) Si (10%) Mg (0.2%) Mn (7%) Al (91.6%) Mg (0.4%) Mn (7%)

BHN before work hardening (N/mm2)

BHN after work hardening (N/mm2)

% increase in hardness

338.967

443.50

23.57

373.787

363.32

-2.8

4. IMPLEMENTATION IDL - International Digital Library

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 Al (82%)  Si (10%)  Mg (0.6%)

286.589

413.22

30.64

In the table 5.1, we can observe that for the Brinell hardness numbers have increased after work hardening. However this does not hold true for the alloy containing 0.4% Mg in which case the hardness value has decreased. This is because the alloy composition turned brittle upon work hardening which in turn resulted in the decrease of Brinell hardness.

The third composition which contains silicon as a dominant alloying element has resulted in significant increase in hardness. Not only silicon but also magnesium percentage has played an important role in the increased hardness. However in the brittle alloy, though the magnesium percentage was fairly high with about 0.4%, the hardness decreased because of the absence of silicon.

When designing automotive components which are subjected to various cyclic loads, it is important to ensure that the component holds up under intense tensile forces. Therefore in this research work tensile tests are performed for aluminium alloys which are work hardened and non work hardened. The tensile test results are as shown in the table 5.2.

The tensile test results clearly signifies that the fracture load of the alloy composition containing 0.4% magnesium has portrayed a higher fracture load after the alloy has been subjected to work hardening.

However in the case of the other two alloy composition there is a minor change in fracture load from which we can signify the brittleness of the material has contributed to the increase in fracture load of the material.

Table 5.2: Tensile test results

Sl. No.

1

2 Fig. 5.1: Graphical representation of hardness test results Figure 5.1 portrays the hardness test results in the form of a bar chart from which it can be clearly seen that there is a negative resultant of hardness for the aluminium-manganese composition. It also showcases that for the compositions with magnesium percentages of 0.2% and 0.6%, the hardness has increased upon work hardening. 

TENSILE TEST Upon work hardening the expected result is for the aluminium alloys to have increased yield strength.

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3

Alloy composition

         

Al (82%) Si (10%) Mg (0.2%) Mn (7%) Al (91.6%) Mg (0.4%)

Fracture load before work hardening (N)

Fracture load after work hardening (N)

% change in fracture load

1108.19

1039.54

6.19

902.24

1255.3

-28.12

1382.79

1363.17

1.41

Mn (7%) Al (82%) Si (10%) Mg (0.6%)

 WEAR TEST Wear properties are one of the most important characteristics that must be tested for a newly alloyed element as the ultimate aim for a component is to have maximum resistance to wear. To investigate the same, a stringent wear test was conducted on all the compositions of aluminium alloys using a pin on disk apparatus. The test parameters were preset with the rotational speed of the disk being 636 RPM and the load being 2Kgs. For these parameters wear test was 4|P a g e

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International e-Journal For Technology And Research-2017 conducted and wear rate is calculated from the slope obtained from graphs (wear vs distance). Figure 5.2 illustrates the wear rate for all three compositions of the aluminium alloy.

It is evident from the figure that the composition with silicon as an alloying element has no significant contribution towards providing better wear resistance. However, in general the work hardening has rendered the alloys to display significant changes in wear rate. The maximum change in wear rate after work hardening has been portrayed by the alloy composition consisting of 0.4 % magnesium.

Although there is absolutely no silicon content in the alloy an excellent wear characteristic is seen which might imply that the magnesium content has a role to play in providing better wear resistance.

hardening and after work hardening. With careful observations of image 5.3, the dendrite formations are easily noticeable. The primary dendrite mainly is comprised of manganese, aluminium and silicon. In this image however, a small length of secondary dendrites have been formed and no tertiary dendrites exist.

After work hardening is performed on the alloy, the microstructure is seem to have a small change in the dendrite formation as shown in figure 5.4 where the formation of secondary dendrites as well as ternary dendrites are prominently seen. All the microstructure images are illustrated at 20 micrometers magnification. In the alloy composition of aluminium and manganese where silicon is absent, the SEM image is as shown in figure 5.5.

Fig. 5.2: Wear rates calculated for all three alloy compositions

Fig. 5.3: SEM image of Al-Si-Mn alloy (before work hardening)



MICROSTRUCTURE ANALYSIS Microstructure analysis is most crucial in investigating the material behavior subjected to multiple operations and tests. One of the most highly sought after methods to conduct a microstructure analysis are through optical microscopy techniques and Scanning Electron Microscopy techniques.

However in this research work a Scanning Electron microscope (SEM) is used to obtain clear microstructure images to investigate the surface characteristics of work hardened and non work hardened alloys.

The following images represent comparisons of microstructure (SEM) images of alloys before work IDL - International Digital Library

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International e-Journal For Technology And Research-2017 Fig. 5.4: SEM image of Al-Si-Mn alloy (after work hardening) In the figure 5.5, the formation of dendrites is eutectic type which are oriented in a pine tree like structure. However they are not randomly oriented.

The dendrites observed here are made from aluminium and manganese alone. Aluminium is the first element to solidify thus resulting in the pine tree like dendrite formation. Here ternary and quaternary dendrites can be easily identified.

The same comment stands for the aluminiummanganese alloy composition after work hardening where the microstructure SEM image as shown in figure 5.6 portrays the formation of numerous continuous dendrites.

Fig. 5.6: SEM image of Al-Mn alloy (after work hardening) The space between two lobes of the dendrides formed is known as the interdendritic region. In this case the interdendritic region consists of manganese and aluminium. In figure 5.7, the SEM image depicting the microstructure of aluminium-silicon alloy without is portrayed. In this type of composition the dendrites are in the form of needles. They are therefore called randomly oriented needle like dendrites. The needle like dendrites is primarily made of silicon and small amounts of aluminium whereas the interdendritic regions are composed of pure aluminium.

Fig. 5.5: SEM image of Al-Mn alloy (before work hardening)

Fig. 5.7: SEM image of Al-Si alloy (before work hardening) IDL - International Digital Library

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



Fig. 5.8: SEM image of Al-Si alloy (after work hardening) Also in figure 5.8 which shows the SEM image of aluminium-silicon alloy also depicts the same needle like structure dendrites which seem to be randomly oriented. However some of the pin like dendrites seems to be discontinuous and this is found to be an effect of work hardening where dendrites get disoriented into simpler structures.

CONCLUSION The important conclusions that can be drawn from this research work are as follows:  Three specimens have been developed containing Mn and Si in Aluminium. Purpose of adding Si is to increase the hardness and wear resistance.

Purpose of adding the Mn is to increase the work hardening effect. From the figure 2 it is observed that hardness of the Al-Si is considerably increased after work hardening. It is understood from the values of the difference in hardness. The corresponding difference wear rate is least which is observed in Fig. 5.2 whereas the difference in hardness before and after work hardening for AlIDL - International Digital Library



Mn alloy is least. The corresponding difference in wear rate is maximum. Also it is observed that the difference in work hardening for Al-Si-Mn is moderate. The corresponding difference in wear rate is also moderate.

The hardness of the aluminium alloys have increased upon work hardening exhibiting mechanical properties significant to the ones which are not work hardened.

The tensile strength of major work hardened alloy comprising of aluminium and manganese is increased upon work hardening. Also among the three compositions it is observed that with varying magnesium composition the engineering stress also increases.

Excellent wear resistance is seen in aluminium alloy which contains magnesium as the alloying element.

REFERENCES [1]. Wei-wen ZHANG, Bo LIN, Pei CHENG, Da-tong ZHANG, Yuan yuan LI. “Effects of Mn content on microstructures and mechanical properties of Al−5.0, Cu−0.5Fe alloys prepared by squeeze casting”.

Elsevier science direct 1525−1531.

[2]. Qinglong Zhao, Bjørn Holmedal, Yanjun Li. “Influence of dispersoids on microstructure evolution and work hardening of aluminum alloys during tension and cold rolling”. Norwegian University of Science and Technology. Thesis for the degree of Philosophiae Doctor.

[3]. Qinglong Zhao, Bjørn Holmedal. “Modeling work hardening of aluminum alloys containing dispersoids”.

Norwegian University of Science and Technology.

Thesis for the degree of Philosophiae Doctor.

[4]. Qinglong Zhao, Bjørn Holmedal.“The effect of silicon on the strengthening and work hardening of aluminum at room Temperature”.Norwegian University of Science and Technology. Thesis for the degree of Philosophiae Doctor.

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International e-Journal For Technology And Research-2017 [5]. Kiran Aithal, Narendranath, Vijay Desai and P G Mukunda. “Effect of L/D Ratio on Al-Si Functionally Graded Material cast through Centrifuge Technique”.

Trans Tech Publications, Switzerland. Advanced Materials Research Vol. 213 (2011) pp 281-285.

[6]. Vipin Kumar, Husain Mehdi, Arpit Kumar.

“Effect of Silicon content on the Mechanical Properties of Aluminium Alloy”. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056.

[14] Chaman Lall and Paul Williamson, Metal Powder Products Company 16855 Southpark Drive, Suite 100, Westfield, IN 46074, USA, “Wear Resistance and Mechanical Properties of Selected PM Aluminum Alloys and Composites”.

[15] Nofal Al-Araji and Hussein Sarhan, Dirasat, Engineering Sciences, Volume 32, No. 1, 2005, “Abrasive Wear of Al-Mn Alloys”.

[7]. S. R. CHANG, J. M. KIM and C. P. HONG. “Numerical Simulation of Microstructure Evolution of Al Alloys in Centrifugal Casting”. ISIJ International journal. , Vol. 41 (2001), No. 7, pp. 738–747.

[8]. Qinglong Zhao, Bjørn Holmedal. “Effect of Si addition on Solid Solution Hardening of Al-Mn Alloys”. Norwegian University of Science and Technology. Thesis for the degree of Philosophiae Doctor.

[9]. H.J Ivey Scientific officer, U.K.A.E.A ; former Department of Mechanical Engineering, University of Bristol. “Plastic Stress strain Relations and Yield Surfaces for Aluminium Alloys”.

[10]. B.K Zuidema, D.K. Subramanyam and W.C Leslie. “The effect of Aluminium on the work hardening and wear resistance of Hadfield manganese Steel”.

[11]. L.M. Cheng, W.J. Poole, J.D. Embury, and D.J. Lloyd “The Influence of Precipitation on the WorkHardening Behaviour of the Aluminium Alloys AA6111 and AA7030”.

[12] D. J. Lloyd’ and D. Kenny’, “The Structure and Properties of Some Heavily Cold Worked Aluminium Alloys”. Alcan Labs Ltd. Banbury. Oxford OX16 7SP. England.

[13] M. Jain, DJ Lloyd and SR Macawen, Alcan International Limited, Kingston R & D Centre, Kingston, Ontario K7L5L9, Canada. “Plastic Stress strain Relations and Yield Surfaces for Aluminium Alloys” IDL - International Digital Library

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