scratch free and low wear aluminium panel: from scrap to

SCRATCH FREE AND LOW WEAR ALUMINIUM PANEL: FROM SCRAP TO BOEING

R.M. Nasir 1School of Mechanical and Aerospace Engineering,

Engineering Campus Universiti Sains Malaysia(USM), 14300, Nibong Tebal, Seberang

Perai Selatan, Pulau Pinang, Malaysia

2Cluster of Polymer Composite (CPC), Science and Engineering Research Centre (SERC), Engineering Campus, Universiti Sains Malaysia, Nibong Tebal,

14300, Malaysia

A.Y.Saad School of Mechanical Engineering,

Engineering Campus Universiti Sains Malaysia(USM), 14300, Nibong Tebal, Seberang Perai Selatan, Pulau Pinang,

Malaysia

ABSTRACT Recycled aluminium is known as secondary aluminium, but

maintains the same physical properties as primary aluminium.

Secondary aluminium is produced in a wide range of formats and

is employed in 80% of alloy injections. Another important use is

for extrusion. To improve aluminium recycling, one can use the

process such as physical separation, magnetic, air separation,

eddy current separation and sink float separation. Recycled

aluminium had been studied due to its wear and friction

resistance, strength, energy consumption and environmental load

lesser than the primary metal. In this work, wear rate, coefficient

of friction, hardness, wear mechanism and elemental analysis or

chemical characterization of the pure and recycled aluminium

were monitored using pin-on-disk tester, Vickers hardness test,

scanning electron microscope (SEM) and Energy-dispersive X-

ray spectroscopy (EDX) respectively. The outcome verified that

the percentage increase in wear resistance of recycled aluminum

compared with pure aluminum is better by 33% at 20N, 27% at

35N and 11% at 50N load imposed. While the average coefficient

of friction for recycle aluminum decreases linearly whereas for

pure aluminium is non-linear. There is also an increase in

hardness of recycled aluminum ranging from 10 to 23 %

compared to pure aluminuim due to high concentration of ferrous

element (maximum of 22 wt. %).

INTRODUCTION

Aluminium recycling brings many environmental and

economical benefits, such as reduce in greenhouse gas

emission, increase in energy efficiency and increase in

material efficiency. Recycling of aluminium involves melting

the scrap, a process that requires only 5% of the energy used

to produce aluminium from ore. 42% of beverage cans, 85%

of construction materials and 95% of transport vehicles was

reported using recycled aluminium[1]. In general, the non-

recycled aluminium has better material properties than the

recycled aluminium due to the present of impurities and other

Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014

November 14-20, 2014, Montreal, Quebec, Canada

IMECE2014-36727

1 Copyright © 2014 by ASME

materials [1]. Besides that, the recycling process may also

cause porosity in the aluminium. Hypothetically, the

mechanical properties and wear resistance of recycled

aluminium should be better than non-recycled aluminium. In

this project, the work is focused on finding out the wear and

friction as well as the hardness of recycled aluminium and

then the results was to be compared the properties to the non-

recycled aluminium. Besides that, hypothetically to prove that

properties of recycled aluminium that undergone many

treatment are better than the aluminium that is not recycled

and undergone lesser treatment.

Nowadays, wear properties are significant as metals are

applied for many applications, for examples; automobile,

sports, medical apparatus unto aircrafts and space vehicles.

Wear is always been refer to the material removal from the

surface due to the relative motion such as sliding with/on

another material and it is caused by some mechanisms such as

abrasion, fatigue, erosion, oxidation and scratching [2]. The

factors that affect wear rate of metals are type of material

used, speed of sliding, roughness of surface, temperature,

magnitude of normal load, friction and vibration[3]. It was

found that as the normal load and sliding speed are increasing,

the value of wear rate of metals increases with noticeable

incremental in thermal and frictional values depending on the

hardness value of metal alloys, the velocity employed and

contact time[4]. This is because at higher velocity, there are

more relative pressure moving in the normal direction, hence,

more upward force produced to the upper surface and this will

increase the separation between the contact surfaces [5].

Stephen L. Rice found that the flat-ended specimen of

aluminium has been impacted on stainless steel counter-face

under normal impact and transverse impact shows the

hardness of metals depends on the microstructure of the

specimen[6]. By increasing normal impact force and

transverse impact velocity causing in the weight loss of

specimen [7]. The schematic view of pin-on-disk testing

machine was detailed by the author in previous work [8].

Fig. 1 Schematic view of pin-on-disk testing machine [8]

Coefficient of friction can be determined according to the

applied load and the frictional force [8-10].The conditions of

the pin-on-disk wearing test without lubricant, at constant

rotational speed, with specimens of the same size and was

cleaned and dried. Wear rate normally calculated as in

equation 1.

(1)

where Ai= area above the profile at four different sections (i=

1-4) in mm2.

Hardness depends on the grain size of metals. As the grain

size becomes smaller, the layers between the grain boundaries

increase the slippage-resistance in the metal microstructure

and vice-versa. In order to increase the hardness, treating the

metal to re-crystallization temperature is needed to reduce its

grain size. During dry sliding, the frictional force transforms

into heat energy, therefore, the thermal conductivity of the

specimens must be avoided to prevent thermal shock[9].

Hence, in order to abrade/polish/cut the metal, the hardness of

the abrading/polishing/cutting tool must be as least 1.2 times


harder than the metal[10]. Most of the Vickers hardness

testing machine such as diamond indentor, has square shaped

pyramid with 136 degree angle between opposite surfaces[11-

13]. In Vickers hardness test, the hardness is measured as in

equation

2.

(2)

EXPERIMENT Pure aluminium was obtained from XXX and recycled

aluminium was prepared using sand casting method. Firstly,

fabrication of casted recycle aluminium from used aluminium

beverage cans was done using high temperature oven furnace

around 1400oC. The aluminum scraps, sand and binders were

melted in the furnace. The mixer was stopped for several times

and a piece of metal was used to mix the sand and binder at

the bottom of the container to form homogeneous molten

metal. Powder was put on the mold and the rack. Next,

mixture was poured into the mold. The mixture was punched

using puncher so that it is fixed to the mold. Some holes were

made on the mixture using the metal stick. The carbon dioxide

was allowed to enter the holes twice to cure the binder through

a pipe. The gas was inlet to fill in the holes for 10 seconds for

the first time. Then, the gas was left to fill in the holes for

another 5 seconds. From the other side of the mold, the ingot

was poured again. Steps 3 to 9 were repeated. Next, the ingot

and mold were removed. Molten aluminium was poured into

the sand mold and allowed to cold down for half a day. Then

the sand mold was removed and recycled aluminium was been

taken out from the cast as in Fig. 2 (a+b). Afterwards, both

pure and recycled aluminium was cut using CNC machine into

smaller pieces with dimensions of 10mm x 10 mm x 30mm.

Then, both pure and recycled aluminium samples were

polished and cleaned prior to wear, friction and hardness tests

as in Fig.2 (c+d). Afterwards, the analysis and comparison

was made between recycled aluminium and non-recycled

aluminium. Three samples were ran for each wear specimen

was tested at five different speeds (100rpm, 200rpm, 300rpm,

400rpm and 500 rpm) and different loads (10N, 20N, 30N,

40N and 50N) using Ducom Tribo-tester as in Fig.3.

The specimens were indented by a square-shaped pyramid

diamond indenter subjected to a load for 5 to 10 seconds. The

two diagonals of the indentation are measure using

microscope and the average values of Vickers hardness were

obtained. Then, the abraded specimens were placed into the

Hitachi S-3400N Scanning Electron Microscope (SEM) for

scanning its morphology. The magnification used were 250x

and 500x. EDAX was determined to identify the elemental

compositions present in the specimens.

(

(a)

Fig. 2(a) Pure aluminium (b) recycled aluminium (c+d) shape of specimens after cut

(c)

(

(a)

(

(a)

( (b) (a) (d)

(

(a)

(

(a)


Fig.3 Pin-on-disk test machine

Fig. 4 Wear rate for pure Aluminium at 400 rpm and at 500 rpm in comparison to recycled Aluminium at 400 rpm and at 500 rpm

RESULTS AND DISCUSSION Effect of speed and load on wear rate In order to make a comparison on the effect of speed and load

on the wear rate of pure and recycled aluminium, different

load parameters were applied at 1400th

. second and at 400 rpm

and 500 rpm respectively as shown in Figs. 4The results of the

specimens of pure and recycled aluminium at 400 rpm are

closer to the ideal results. The results of specimen of pure and

recycled aluminium at 500 rpm are not ideal due to the

composition of the recycled aluminium.

In general, the wear rates of both type of aluminium increase

as the speed of the wearing surface between the specimen and

the rotating disk. This is mainly due to the fact that greater

speed creates greater sliding force (Fs) that will remove the

specimen significantly. Hence, the wear rate increases.

Besides, from the results, the wear rate of both aluminium

increases as the load applied increases. Similarly, greater load

applied to the specimen creates higher pressure per velocity

(P/v) to overcome the frictional force between the surfaces.

Hence, the greater the load, the greater the wear rate of the

specimen.

0

50000

100000

150000

200000

250000

300000

10N 20N 30N 40N 50N

We

ar r

ate

(m

3 /s)

Load (N)

400rpm-pure

500rpm-pure

400rpm-recycled

500rpm-recycled


Fig. 5 Comparative results of wear rate against load at 400 rpm

In Fig. 5, comparative results was extracted from

both type of aluminium at 400 rpm, the specimen of

recycled aluminium shows greater resistance to wear

compared to the pure aluminium under the same

speed and same load. Therefore, the recycled

aluminium has better resistance to wear compared to

the pure aluminium under the same speed and load.

For example, under load of 50N, the wear rate of

specimen of recycled aluminium is 180000 mm3/s,

but the wear rate of specimen of pure aluminium is

200000mm3/s.

Effect of speed and load on average coefficient of friction In order to compare the effect of speed and load on

the average coefficient of friction of pure and

recycled aluminium, the average value of coefficient

of friction at 200 rpm and 500 rpm at different loads

was monitored as shown in Figs.6 The average value

of frictional force depends on the contact surface

between the specimens and the rotating disk. So,

greater frictional force needed to be overcome

between the surfaces if the value of coefficient of

friction is greater. The results of specimen as shown

in Fig 6 show pure and recycled aluminium at 200

rpm and 500 rpm is linear. The values of average

frictional force decreases as the speed and loading of

the wearing surface and the rotating disk increases.

This is because the greater speed creates inertia that

helps to overcome some of the frictional force

between the surfaces. Hence, the value of frictional

force decreases as the speed and load increased.

Fig. 6 Average Frictional Force for pure Aluminium at 200 rpm and at 500 rpm in comparison to recycled

Aluminium at 200 rpm and at 500 rpm

y = -44.28x + 562.74 R² = 0.9722

0

100

200

300

400

500

600

10N 20N 30N 40N 50N

CO

F (x

10

-3)

Load (N)

400rpm-pure

500rpm-pure

400rpm-recycled

500rpm-recycled

Linear (400rpm-recycled)


Fig. 7 AFF against load at 500 rpm

As extracted from Fig. 7 for both type of aluminium

at 500 rpm, the specimen of recycled aluminium has

greater value of average frictional force compared to

pure aluminium under the same speed and same load.

Therefore, the recycled aluminium has better anti-

friction to wear. For example, at 500 rpm, under load

of 10N, 20N, 30N and 40N, the value of average

frictional force of recycled aluminium is greater than

the pure aluminium. The hardness values of pure and

recycled aluminium are determined using Vickers

hardness test machine as shown in Table 1 and

plotted in Fig. 8. Generally, the hardness values of

the specimens of recycled aluminium are having

greater value compared to the specimens of pure

aluminium. This shows that the hardness properties

of recycled aluminium are better than the pure

aluminium hence its wear resistance, as argued by

author previously [8].

Table 1 Hardness value for pure and recycled aluminium

Speed (rpm.) Average hardness value for pure

aluminium

Average hardness value for

recycled aluminium

100 137.3 144.5

200 145.8 163.1

300 135.9 157.3

400 150.3 196.4

500 140.9 146.9

Fig. 8 Vickers Hardness Value

Scanning electron microscope (SEM) test and EDX

analysis were carried out on the worn surface of the

specimens of pure and recycled aluminium at 400

rpm and 500 rpm as shown in Figs. 9(a-d) and EDAX

analysis in Figs.10 (a-d).


Fig. 9 Scanning electron microscope of (a) pure aluminium at 400 rpm (b) pure aluminium at 500 rpm (c) recycled

aluminium at 400 rpm (d) recycled aluminium at 500 rpm (arrow indicates direction of sliding)

Fig. 10 EDAX analysis of specimen (a) pure aluminium at 400 rpm (b) pure aluminium at 500 rpm (c) recycled

aluminium at 400 rpm (d) recycled aluminium at 500 rpm

In Figs. 9 (a-d), the abraded surfaces shows wear mechanism

with intragranular fractures and adhesive wear. In energy

dispersive x-ray spectroscopy (EDAX) analysis on the area of

adhered surface in Figs. 10 (a-d), show the composition of

aluminium is higher in the pure aluminium and the

composition of ferum is higher in the recycled aluminium. The

existence of higher amount of ferum in the composition of

recycled aluminium increases the wear resistance of the

recycled aluminium. The existence of ferum in the

microstructure increases the resistance between the layers of

grain boundaries. The grain boundaries need more force to

overcome the frictional force or friction. Hence, the recycled

aluminium has greater wear resistance compared to the pure

aluminium. Besides, there are other materials exist in the

(a) (b) (c) (d)

(a)

(b)

(d)

(c)

Intragranullar fracture


composition of recycled aluminium which also improve the

wear resistance of recycled aluminium as their existence

increase the resistance of the layers between grain boundaries.

In some regions, as the one of Fig. 9(b), a similar thin adhered

layer is found, while in the others the surfaces appear clearer,

as in the Fig. 4 (a and d), due to continuous formation and

removal of the tribolayer [14].

High ratio of composition for aluminium/ferum in the

specimens causes less resistance of the layers between the

grain boundaries, therefore, there is less force needed for the

layers to sliding over each other (as shown in Fig.11). Hence,

pure aluminium is easily polished compared to recycled

aluminium. Besides that, there are less composition of other

material exist in the composition of pure aluminium specimen

which also contribute to the weak Van de Waals bonding

leading to initiation of slippage, crackage and breakage.

Fig. 11 Effect of impurities on grain boundaries

CONCLUSION The study of wear resistance properties of recycled and pure

aluminium depends significantly on the normal load applied

and the sliding velocity of the contacted surfaces. The wear

rate of pure and recycled aluminium increase when the applied

load and the sliding speed. Recycled aluminium shows the

better wear resistance compared to the pure aluminium ranges

from 11-33% based on applied load from 20 to 50N. Mean

while for average frictional force reduced linearly (3.5428) for

recycled aluminium compared to pure aluminium which

shows drastic exponential reduction of COF gradient. This is

mainly due to impurities and thermal treatment process in

fabrication hence microscopically has altered the composition

in the recycled aluminium that improves its wear resistance. In

Vickers hardness test, the hardness value of recycled

aluminium is greater compared to pure aluminium by 23%

maximum due to the present of 22 wt.% of ferrous element in

the recycled aluminium leading to better hardness compared to

pure aluminium. ACKNOWLEDGEMENT

The authors gratefully acknowledge the Universiti Sains

Malaysia for the funding of this entire research with the grant

number of 304/PMEKANIK/60311052.

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Estimated of eight million pounds of recycled aluminum is to be melted and reshaped into new aerospace materials by

Boeing's sub-contractors. Alcoa Aerospace, Transportation and Industrial Rolled Products director of supply chain Leslie

Shuman quoted: "This programme will maximise the value of aluminum scrap materials throughout the supply chain while

also reducing waste."


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scratch free and low wear aluminium panel: from scrap to

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