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EFFECTS OF BIODEGRABLE OILS ON THE PROPERTIES OF
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ALUMINIUM DURING SOLUTION HEAT TREATMENT
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Odusote Jamiu Kolawole; 2Adekunle, Adebayo Salaudeen and
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Rabiu, Abdulkarim Baba
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Department of Mechanical Engineering, Faculty of Engineering and Technology, University
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of
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Ilorin,
Ilorin,
Nigeria.
E-mail:
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odusote.jk@unilorin.edu.ng,
rabiu.br@unilorin.edu.ng
* Corresponding author
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Abstract
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This paper presents the effects of rate of heat extraction by groundnut, melon,
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palm kernel, shea butter and palm oils on the mechanical properties of various
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samples of pure commercial aluminium heat treated at 200°C, 250°C, 300°C and
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350°C. Muffle furnace equipped with digital thermometer and thermocouple
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was used for the solution heat treatment. Tensile strength and hardness tests
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were carried out using Instron Universal Tester and Vickers hardness methods,
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respectively. Results obtained from the experiment were presented graphically.
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The results showed that palm kernel oil cools faster at 200°C and 250°C, while
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palm oil and shea butter oil quench faster at 300°C and 350°C, respectively.
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Solution heat treatment with palm kernel oil offerred the highest percentage
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elongation at 200°C, while at 350°C shea butter oil gave the best percentage
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elongation. The best among the bio-quenching oils in providing good ductility is
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shea butter oil at 200°C, while at 300°C and 350°C groundnut oil give the best
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result. Highest hardness values were obtained from samples quenched in melon
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oil between 200°C - 300°C. However, these values decreased with increased
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heating temperature, probably due to density and viscosity variation with
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temperature rise. Similar observations were made on most of other samples
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quenched in other bio-quenching oils used in this experiment. This study shows
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that these locally available vegetable oils have promising potentials to serve as a
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possible replacement for non-biodegradable mineral oils in many applications.
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Keywords: Mineral oils, vegetable/biodegrable oils, heat treatment, quenching
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media, aluminium
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Introduction
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Aluminium is widely used in electrical, chemical, food packaging, petrochemical and
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construction industries on account of its excellent corrosion resistance, high thermal
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and electrical conductivities and good formability (John, 2007). One major drawback
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to the use of pure commercial aluminium is its low strength. It has been established
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that mechanical properties of metals and alloys can be effectively improved through
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alloying and heat treatment (Krauss, 1990). However, the choice of effective
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quenching medium after heat treatment is very critical in ensuring the achievement of
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desired mechanical properties (Feng and Khan, 2008). The most common quenching
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medium for metals and alloys is mineral oil, and it possesses excellent cooling
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capacity (Grishin and Churyukin, 1986). However, but they are relatively expensive,
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toxic and non-biodegradable. There have been considerable studies focused on
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possibility of reducing or replacing mineral oil with less expensive water-based or
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polymer-based quenching media (Tolstousov and Bannykh, 1981). Cooling capacity
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of aqueous solutions of different substances was examined in order to determine their
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suitability as quenching media, and it was observed that aqueous 6-7 % monosulfite
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liquor (MSL) with 1 % phenol could serve as a possible replacement for mineral oils
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(Grishin and Churyukin, 1986). Protsidium et al. (1988) studied the quenching
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capacity of spent and regenerated minerals oils, and observed that addition of 0.3 %
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antioxidant lonol to regenerated oils improved their quenching capacity. The
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effectiveness of polymer based quenching medium, UZSP-1, was examined, and it
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was found that UZSP-1 of varying concentrations was effective as a quenching
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medium for only low-carbon ball-bearing steels (Goryushin et al., 1991) but not well
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suitable for high-carbon ball-bearing steels. The present study was undertaken with
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the objective of replacing mineral oils with local biodegradable oils, which are more
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readily available, relatively cheaper and environmental friendly. These oils also have
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many other good natural properties, which made them attractive as lubricants and
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other applications (Xia and Larock, 2010). This was done by examining the
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mechanical properties of heat-treated pure commercial Al after quenching with
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several locally available biodegradable oils.
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Materials and Method
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The material used for this investigation was pure commercial Al, with percentage
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composition of 99.83% aluminium and traces of other elements as shown in the Table
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1. The samples were obtained from a local aluminium smelting company based in
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Lagos. The as-received samples were cut into experimental work pieces prior to heat
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treatment. Heat treatment of the samples was performed at 200ºC, 250ºC, 300ºC and
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350ºC, using a muffle furnace. After heat treatment, the samples were soaked for 60
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minutes inside the furnace and then quickly transferred into a quenching bath
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equipped with a digital thermometer and thermocouple. The quenching bath was
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filled separately with 50 cm3 of groundnut oil, melon oil, palm oil, palm kernel oil
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and shea butter oil as quenchants. The heat losses by the heat treated pure commercial
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aluminium were recorded by the digital thermocouple at various time intervals from
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30 s to 300s.
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After quenching, approximately 10 mm long and 9 mm in diameter specimens
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were cut from the quenched samples. The specimens were ground and polished down
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with 4000-grit SiC paper and 1 µm diamond paste finish respectively. After
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polishing, the specimens were cleaned ultrasonically in acetone, followed by alcohol
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and immediately dried before hardness and other mechanical tests.
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Mechanical Test
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Tensile Testing
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Tensile tests were carried out on the quenched specimens using Instron
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Universal Tester. Each of the specimens was loaded till fractured, and the fracture
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load for each sample was recorded as well as the diameter at the point of fracture and
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the final gauge length. The initial diameter and initial gauge length for each sample
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was noted before the application of the uniaxial load. The percentage elongation of
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each test sample was determined, as well as the tensile strength.
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Hardness Test
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Vickers hardness method was used for the determination of the hardness of
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the quenched samples. Each of the test specimens were prepared metallographically
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after different heating and quenching regimes, and then mounted on the anvil. The
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specimens were brought in contact with the pyramid indenter and allowed to rest for a
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dwell time. The hardness of the specimens were indicated by the penetration of the
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indenter on the test specimens, and displayed by the machine. Average values were
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recorded after repeating the test for each of the test specimens.
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Results and Discussion
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Cooling Rate
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Figures 1-4 show the rate of heat extraction by each of the quenching medium
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namely; groundnut, melon, palm, palm kernel and shea butter oils, from the heat-
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treated pure aluminium samples after heating at 200°C, 250°C, 300°C and 350°C,
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respectively. Figure 1 shows that at 200°C, palm kernel oil extracted heat to an
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elevated temperature of 31.9°C at 160s, while groundnut, melon, shea butter and
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palm oils extracted heat to 31.6°C at 185s, 31.8°C at 245s, 31.8°C at 205s, and
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31.6°C at 265s, respectively. This indicates that palm kernel oil extracted heat and
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reached equilibrium with the samples faster than the other oils at this heating
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temperature, while the least heat was extracted by palm oil at this heating
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temperature. However, the temperature of each of the quenchants remained constant
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after getting to their elevated temperature during the quenching process. As shown in
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Figure 2, the temperatures of both palm kernel and melon oils were raised to 32.5°C
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from 30.8°C at 175s and 250s respectively, during quenching of aluminium samples
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heated to 250°C, while those of groundnut, shea butter and palm oils were raised to
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32.4°C at 165s, 32.2°C at 145s and 31.7°C at 280s, respectively. Thus, showing that
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palm kernel oil extracted faster than other oils, while palm oil extract least heat at
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250°C. However, at 300°C, palm oil cools the heated aluminium faster, as more heat
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were extracted as shown in Figure 3. Similarly, at 350°C, shea butter oil removed
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heat and cooled the heated aluminium faster compared with other oils, as shown in
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Figure 4.
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Percentage Elongation of the Quenched Samples
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Figure 5 shows the percentage elongation of the investigated samples after
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quenching in various bio-quenching oils at different exposure temperatures.
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Comparing the value of elongation of the quenched samples at different heating
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temperatures with the as-received sample of 14.09 mm, it was evident that in most
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cases the percentage elongation of the quenched samples increased with increasing
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heating temperature, as shown in Figure 5. This indicates possible improvement in
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the ductility of the quenched samples at higher heating temperatures. The least
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elongation value of 6.92 mm was obtained after quenching in groundnut oil at 250°C,
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while shea butter oil produces samples with highest ductility at 350°C. As shown in
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the graphs, all the samples heated at 200°C and 250°C and quenched in the various
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oils are brittle, except those quenched in shea butter oil at 200°C, which are slightly
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ductile. Samples heated at 300°C and quenched in groundnut and shea butter oils are
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also ductile, while those quenched in other oils are brittle. However, at 350°C, all the
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quenched samples exhibited ductility, with highest elongation of 22.25 mm was
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displayed by those quenched in shea butter oil.
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Tensile Strength of the Quenched Samples
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The tensile strength of the as-received commercial Al sample is 60.04 MPa,
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which is higher than those obtained from the quenched samples at some of the
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heating temperatures (Figure 6). At 200°C, samples quenched in groundnut and
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melon oils displayed lower tensile strenght compared with that of the as-received
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sample, while shea butter oil exhibited highest tensile strength value of 67.38 MPa.
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This value is higher than 65.62 MPa and 61.21MPa of palm kernel and palm oils,
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respectively. At 250°C, all the quenched samples gave lower tensile strength value
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compared with that of as-received sample, with sample quenched in groundnut oil
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showing lowest tensile strength value. However, at 300°C and 350°C, heat treated
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samples quenched in groundnut oil displayed highest tensile strength value, followed
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by those quenched in shea butter oil, with the least value obtained from samples
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quenched in melon oil at 300°C, and in palm oil at 350°C. Thus, quenching in
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groundnut oil after heating at 350°C, resulted in sample with best tensile strength.
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Variation of the Hardness of the Quenched Samples
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The highest Vickers hardness value of the samples quenched in the various
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quenching oils were obtained at 200°C, with peak value from the sample quenched in
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melon oil, as shown in Figure 7. However, at 250°C, the hardness values of all the
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quenched samples decreased, with those quenched in melon, palm kernel and shea
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butter oils became lower than that of the as-received sample, which is 30.9 Hv. The
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hardness values of all the samples increased at 300°C above that of the as-received,
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but later decreased when quenched after heating up to 350°C, except that of the
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sample quenched in melon oil. This indicates that the best heating temperature to
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obtain highest hardness value will be 200°C, with melon oil as the quenching
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medium.
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Conclusions
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The possibility of using some biodegradable oils for solution hardening of pure
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commercial aluminium was established, in order to improve its mechanical
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properties. Quenching with palm oil cools faster at 200°C and 250°C, while Shea
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butter oil cools faster at 350°C. It was discovered that heat treatment with palm
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kernel oil offered the highest percentage elongation at 200°C, while shea butter oil
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was found to produce highest percentage elongation at 350°C. Also, shea butter oil
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offered the best ductility at 200°C, while groundnut oil produced pure commercial
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aluminium with best ductility after heat treatment at 300°C and 350°C. However,
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groundnut oil can be used for quenching to improve the tensile strength at 350°C. The
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best bio-quenching oil in providing the highest hardness value for the aluminium
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sample was melon oil during heat treatment between 200-300°C.
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References
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Feng, C. and Khan, T.I. (2008). The effect of quenching medium on the wear
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resistance of a Ti-6Al-4V alloy. J. Mater. Sci. Technol., 43:788-792.
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S.Y. (1991). Met. Sci. Heat Treat., 41(1-2): 3-7.
Grishin, S.A. and Churyukin, Y.N. (1986). Evaluation of the cooling capacity of
quenching media based on water. Met. Sci. Heat Treat., 30(5):86-88.
John, A.S.G. (2007). Aluminium Recycling and Processing for Energy Conservation
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Krauss, G. (1990). Steels: heat treatment and processing principles. ASM Int., Ohio,
p. 125-345.
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Kulikov, A.I. (1997). A new quenching medium for metals and alloys. Met. Sci. Heat
Treat., 39(11-12): 528-530.
Protsidim, P.S., Rudakova, N.Ya., and Shevemeta, B.K. (1988). Regenerated Oils as
Base for Quenching Media. Met. Sci. Heat Treat., 4(1-2): 3-7.
Tolstousov, A.V. and Bannykh, O.A. (1981). New Quenching Media Based on
Water-Soluble Polymers. Met. Sci. Heat Treat., 23(2): 104-106.
Xia, Y. and Larock, R.C. (2010). Vegetable oil-based polymeric materials: synthesis,
properties, and applications. Green Chem. 12:1893-1909.
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Table 1. Percentage composition of aluminium specimen used by weight
Al
Cu
Si
Mn
P
S
Cr
Zn
Ni
99.83
0.00
0.07
0.02
0.02
0.002
0.00
0.04
0.002
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