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

IDL - International Digital Library Of
Technology & Research
Volume 1, Issue 3, Apr 2017 Available at: www.dbpublications.org
International e-Journal For Technology And Research-2017
IDL - International Digital Library 1 | P a g e Copyright@IDL-2017
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, India5
Assistant Professor, Department of Mechanical Engineering, NMIT Bangalore, Karnataka, India6
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,
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

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.
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 pin-
on-disk wear test apparatus.

 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.
Fig. 3.1: Research methodology heirarchy
4. IMPLEMENTATION
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.
Alloy
composition
BHN
before
work
hardening
(N/mm2
)
BHN after
work
hardening
(N/mm2
)
%
increase
in
hardness
1
 Al (82%)
 Si (10%)
 Mg (0.2%)
 Mn (7%)
338.967 443.50 23.57
2
 Al (91.6%)
 Mg (0.4%)
 Mn (7%)
373.787 363.32 -2.8

3
 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.
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.
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.
Alloy
composition
Fracture
load
before
work
hardening
(N)
Fracture
load after
work
hardening
(N)
% change
in fracture
load
1
 Al (82%)
 Si (10%)
 Mg (0.2%)
 Mn (7%)
1108.19 1039.54 6.19
2
 Al (91.6%)
 Mg (0.4%)
 Mn (7%)
902.24 1255.3 -28.12
3
 Al (82%)
 Si (10%)
 Mg (0.6%)
1382.79 1363.17 1.41
 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

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.
Fig. 5.2: Wear rates calculated for all three alloy
compositions
 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
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. 5.3: SEM image of Al-Si-Mn alloy (before
work hardening)

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 aluminium-
manganese alloy composition after work hardening
where the microstructure SEM image as shown in
figure 5.6 portrays the formation of numerous
continuous dendrites.
Fig. 5.5: SEM image of Al-Mn alloy (before
work hardening)
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. 5.7: SEM image of Al-Si alloy (before
work hardening)

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 Al-
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.
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