wear behaviour of aluminium metal matrix …
TRANSCRIPT
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WEAR BEHAVIOUR OF ALUMINIUM METAL MATRIX COMPOSITES
REINFORCED WITH COPPER AND GRAPHITE
B. N. V. SRINIVAS1, K. DORATHI2, Dr. N. TULASI RADHA3 & G. RAMAPRASAD4
1,2,4Assistant Professor, Department of Mechanical Engineering, Sri Vasavi Engineering College, Tadepalligudem, Andhra
Pradesh, India
3Scholar, Department of Mechanical Engineering, GITAM University, Visakhapatnam, Andhra Pradesh, India
ABSTRACT
A low cost system of Al 6063 4%Cu xGr (x = 2, 4 and 6 wt. %) metal matrix composites (MMCs) were fabricated by stir
casting technique. These fabricated composites were characterized by using scanning electron microscope. The dry sliding
wear behaviour of the prepared composite was investigated by using a Pin on Disc method at applied loads of 50 N. Wear
tests were carried out with no lubrication at room temperature (30–36°C). The ageing of the MMCs was done followed by
air cooled and water cooled. The results indicate that the wear rate is less for Al4CU4Gr air cooled.
KEYWORDS: Al6063, Stir casting, Graphite, Copper, Metal matrix composites, Wear & Ageing
Received: Jun 10, 2020; Accepted: Jun 30, 2020; Publibshed: Aug 31, 2020; Paper Id.: IJMPERDJUN2020990
1. INTRODUCTION
Discontinuous reinforced aluminum metal matrix composites (DRAMMCs) are a class of composite materials with
desirable properties, including low density, high specific rigidity, high specific strength, controlled thermal
expansion co-efficient, increased fatigue resistance and superior dimensional stability at high temperatures,
etc.[1,2]. Such materials have emerged as the essential class of advanced materials that offer the ability for
engineers to adapt the material properties to their needs. Such materials fundamentally vary from the typical
manufacturing materials from the homogeneity point of view. Controlled application of one or more reinforcement
materials in continuous metal matrix process is possible in composites. The vast majority of these composite
materials are metallic components reinforced with high strength, high modulus and brittle ceramic phases which can
be either continuous in the form of fibre, discontinuous in the form of whiskers,
Platelets or particulate reinforcements embedded in a matrix [3-6]. Over the past two decades, wear
performance of DRMMCs
Reinforced with various reinforcements ranging from very soft materials such as graphite, talc etc. to
highly hardened ceramic particles such as SiCp, Al2O3 etc., [3 – 6] was reported to be superior to their respective
unreinforced alloys. A large number of experiments were done independently on the Al / SiCp [4 – 6] and Al /
Graphite [3, 7]. The outer lubricant traditionally plays an important role in wear behaviour. Al alloy wear behavior
strengthened with SiCp-Graphite particles has not been newly understood. As a result, the present study used a
mixture of high-hardened SiC particles and soft graphite to examine the wear actions of the Al alloy reinforced with
SiC particles and graphite. It was observed that wear test volume losses of Al – Mg – Cu alloy continuously
decrease to 5%. It has also been found that silicon carbide particles play a significant role in improving the Al – Mg
– Cu alloying system's wear resistance. All Al – Mg – Cu alloys and Al – Mg – Cu / SiC composites were found to
Orig
inal A
rticle International Journal of Mechanical and Production
Engineering Research and Development (IJMPERD)
ISSN (P): 2249–6890; ISSN (E): 2249–8001
Vol. 10, Issue 3, Jun 2020, 10339-10350
© TJPR Pvt. Ltd.
10340 B. N. V. Srinivas, K. Dorathi, Dr. N. Tulasi Radha, G. Ramaprasad
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
form mechanically mixed layer (MML) due to the move of Fe from counter face disk to plate [8]. In their analysis on the
sliding wear of in situ composites Al–4Cu – TiB2, Mandal et al[9] reported that TiB2 particles greatly improved the wear
efficiency of the alloy Al–4Cu. The reaction mixture of K2TiF6 and KBF4 with molten alloy prepared a low-cost system
of Al 6063 xTiB2 (x = 0, 5, 10 wt. per cent) in situ metal matrix composites (MMCs). Such composites prepared in situ
were characterized by the use of scanning electron microscope, X-ray diffractometer and study of micro hardness. The
prepared composite’s dry sliding wear behavior was investigated using a Pin on Disc method at different applied loads of
9.8, 19.6 and 29.4 N for different temperatures (100, 200 and 300 C). The findings show that with the change in the weight
percentage of TiB2 the wear rate decreases, although it increases with the rise in the load added [10]. Roy et al. [11]
compared aluminum wear resistance reinforced with TiC, TiB2, B4C, SiC powder metallurgy route synthesized. TiB2 had
been reported to show better wear resistance than other dispersoids. However, limited work has been reported on the wear
and friction behavior of these composites at high temperatures [12–22]. Jianxin et al. [12] reported Al2O3–TiB2 / SiC
composites wear conduct at a temperature of up to 800 C. It has been emphasized that at higher temperatures oxidative
wear was regulated. Oxidation of the materials plays a significant role in sliding contact of materials under conditions
when the operating temperature is high, causing changes in overall wear rate. Several researchers have established the
value of oxidation during wear of metallic materials and a classification of moderate and extreme wear was suggested
based on contact resistance assessment, wear debris analysis and microscopic inspection. Quinn et al.[13] and Lim and
Ashby[14] extensively discussed the role of the oxide scale for ambient temperature wear. Many investigators have also
studied the impact of applied load on the wear rate of Al-based composite prepared by other routes [22–33]. It was stressed
that the rate of wear increases with the load applied.
2. EXPERIMENTATION
Preparation of Composite
Stir casting is a two – step mixing process. In this process, the matrix material is heated to above its liquid temperature so
that the metal is totally melted. The melt is then cooled down to a temperature between the liquids and solidus points and
kept in a semi solid state. At this stage, the preheated particles are added and mixed. The slurry is again heated to a fully
liquid state and mixed thoroughly. This two – step mixing process has been used in the fabrication of aluminium. Among
all the well – established metal matrix composite fabrication methods, stir casting is the most economical. For that reason,
stir casting is currently the most popular commercial method of producing aluminium based composites.
Figure 1: SEM Image of Al 6063
Wear Behaviour of Aluminium Metal Matrix Composites Reinforced with Copper and Graphite 10341
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Muffle furnace is used as a pre heated furnace for the matrix materials copper and graphite which is heated at
4000c for 1 hour.. The powder samples are indicated below.
Figure 2: Copper and Graphite Powders
The copper and graphite powder samples are taken into a bowl and mixed. The mixed powder is placed in muffle
furnace for pre-heating purpose. This is done in order to remove moisture content because the presence of moisture content
might result in formation of air gaps in the final mould.
Stir Casting Procedure
The experimental setup consist of an assembled coupling gear box motor and mild steel four blade stirrer. The melting of
the aluminium (Al6063) pieces and copper, graphite powder are carried out in a graphite crucible. The capacity of the
crucible is 1kg. First the pieces of aluminium in their respective composition are placed in the furnace by keeping them in a
crucible. The temperature of the furnace is set to reach 7000c because the melting point of aluminium is 6500c and this is
done to compensate losses during stirring and other heat losses. The rising temperature of the furnace is checked from time
to time. Copper and graphite powders are taken in a bowl and mixed thoroughly and placed in a muffle furnace for pre-
heating. The pre-heating ensure elimination of moisture content so that the mould obtained does not have any air gaps.
During the melting of aluminium there is formation of film above the molten metal. The film formed is removed by using a
cast iron rod and the process is made to progress. After the temperature reaches 7000c the furnace door is opened, the
power supply is switched off and the pre-heated copper and graphite mixture is poured carefully into the crucible.
Figure 3: Stir Casting Equipment Setup
The mixture is now thoroughly stirred by using the stirrer which is operated by a motor and rotates at 200rpm. the
stirring process is carried out for 10 minutes. Now the furnace power supply is again switched on because the molten metal
losses heat during the stirring process. So the process is again carried out until the furnace reaches 8000c. the temperature is
10342 B. N. V. Srinivas, K. Dorathi, Dr. N. Tulasi Radha, G. Ramaprasad
Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11
now being raised to 8000c because the re-crystallization temperatures of graphite and copper are higher than that of
aluminium. The actual melting points of copper and graphite are 10830c and 35000c respectively. But the temperature is
only maintained at 8000c because only minute quantities of copper gets mixed up. The main aim of the project is to
continue the properties of aluminium and also imparting strength and conductivity properties by adding copper and
graphite. So only lesser weight quantities of copper and graphite are added because higher quantities may affect the
properties of aluminium. Now as the temperature reaches 8000c the crucible is taken out and the molten metal mould is
poured into the die carefully. The pouring should be continuous or otherwise there will be formation of air gaps and also
uneven distribution of the molten metal in the die takes place which may lead to cracks or even breakage of the material
after solidification of the material. Three composites were fabricated by taking copperas 4% and graphite is taken as 2%,
4%, 6% and according to that aluminium is arranged. The total composition is taken as 750 grams and as per that weight
percentages were calculated and weighed by using weighing machine. In this way, stir casting setup is used for all the three
compositions as stated above.
The die is now kept in air for half an hour. During this time the mould solidifies. The mould is now taken out by
removing the bolts of the die and removed carefully. The obtained mould is separated into pieces and then machined for
better finish. Now the machined piece again cut into different cross-section required for the different tests to be conducted
on them. The mould cavity is used to make the molten metal into a desired shape and size based on our requirements. The
permanent die made up of cast iron. The depth of the cavity is 100mm and the diameter is 15mm.
The matrix composite mixture is poured into the mould. The die is fixed by nut and bolt arrangement. After that
the metal matrix samples are formed and it is cut into required sizes.
Figure 4: MMC Specimens
The formed samples are cut into required sizes by using abrasive cutting machine and then they are taken for
different tests.
The final obtained metal matrix samples are of diameter about 15mm and 100mm in length.
3. RESULTS AND DISCUSSION
Experimental Wear Tests
Pin-on - disk monitoring is used to determine the slipping wear behaviour. The simple wear test equipment design is shown
in Fig. This consists of a screw connected to a spinning disc. The test piece of concern can be either the pin or the tape. The
pin's touch surface can be spherical, or square. Such tests have been performed in compliance with ASTM G99, which
Wear Behaviour of Aluminium Metal Matrix Composites Reinforced with Copper and Graphite 10343
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requires the use of a rounded pin, but does not define precise values for the parameters, and thus these are chosen by the
users to match the method.
This is lightweight equipment designed specifically for testing wear under sliding pressure. Typically, slipping is
between a fixed pin and a spinning disk. The disk rotates with the help of a D. C. Motor; has a frequency of 0–2000rpm
with a wear track diameter of 20–150 mm, and may achieve sliding speeds of 0 to 30m / sec. Load is to be placed by dead
weight arrangement on pin (specimen). The machine has a maximum 1000N loading capacity. The substrate / coated
samples used the cylindrical pins (10 mm diameter and 25 mm height) as test material. The polished chromium steel disk
(100Cr6) was used as the coating on the counter side. The wear checks were conducted at 50N, sliding speed held at
600rpm. Wear tests were carried out with no lubrication at room temperature (30–36°C). Weight of the specimens before
and after the experiment was taken. This test was done before and after ageing. After ageing, cooling was also done in two
ways such as Air cooled and water cooled.
Figure 5: Wear Test Samples
Figure 6: Wear Test Machine
10344 B. N. V. Srinivas, K. Dorathi, Dr. N. Tulasi Radha, G. Ramaprasad
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Figure 7: Graph of Al 4%Cu2%Gr – Before Ageing
Figure 8: Graph of Al 4%Cu2%Gr – After Ageing (air cooled)
Figure 9: Graph of Al 4%Cu2%Gr – After Ageing (water cooled)
Wear Behaviour of Aluminium Metal Matrix Composites Reinforced with Copper and Graphite 10345
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Figure 10: Graph of Al 4%Cu4%Gr – Before Ageing
Figure 11: Graph of Al 4%Cu4%Gr – After Ageing (Air Cooled)
Figure 12: Graph of Al 4%Cu4%Gr – After Ageing (Water Cooled)
10346 B. N. V. Srinivas, K. Dorathi, Dr. N. Tulasi Radha, G. Ramaprasad
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Figure 13: Graph of Al 4%Cu6%Gr – Before Ageing
Figure 14: Graph of Al 4%Cu6%Gr – After Ageing (Air Cooled)
Figure 15: Graph of Al 4%Cu4%Gr – After Ageing (Water Cooled)
Wear Behaviour of Aluminium Metal Matrix Composites Reinforced with Copper and Graphite 10347
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Table 1: Wear of Materials with Varying Ageing and Cooling
% of Samples Before Ageing
(gms)
After Ageing(gms)
Air Cooled Water Cooled
Al4%Cu2%Gr 0.33 0.05 0.25
Al4%Cu4%Gr 0.77 0.56 0.02
Al4%Cu6%Gr 0.59 0.25 0.1
Figure 16: Graph of Wear of Various Samples
Wear behaviour of Al4%Cu4%Gr was studied and analyzed using the SEM images. From the above graph, we
can observe that the wear rate increases with the increase of both frictional force and time. But by observing, frictional
force vs time, we can clearly say that, as the time increases the frictional force is constant and decreases and again remains
constant.
10348 B. N. V. Srinivas, K. Dorathi, Dr. N. Tulasi Radha, G. Ramaprasad
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Figure 17: SEM Images of the Worn Surfaces of Al4Cu4Gr a) Before Ageing b) After Ageing (Air Cooled) c) After
Ageing (Water Cooled)
4. CONCLUSIONS
Al4Cu4Gr4 has shown a typical trend during the ageing and the cooling process.
Al 92% Cu 4% Gr4% i.e 0.02 grams (after ageing and water cooled) has less wear rate.
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