# Optimization on Tribological Characteristics of Stir-Casted AA7076/Nano Zirconium Dioxide/Boron Nitride Hybrid Composites by Taguchi Method

Authors: S. Shenbaga Ezhil; A. Shanmuganathan; Ganganagunta Srinivas; K. Ashokkumar; Sultan Althahban; S. Mousa; Faez Qahtani; Yosef Jazaa; Nagaraj Ashok
Journal: Journal of Nanomaterials
 (2022)

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## Abstract

Aluminum alloys are currently used in a wide variety of industries, and strong aluminum alloys are required for the creation of new components. As a result, multiple scientists are experimenting with various compositions of hybrid aluminum metal matrix composites. The purpose of this experiment was to generate hybridization on aluminum alloy 7076 using stir-casting and nano zirconium dioxide and BN reinforcements. Taguchi’s approach was used to optimize the stir-casting process criteria in this investigation. The parameters employed in this investigation were agitation speed, agitation time, and temperature. The chosen constraints are the percentage of reinforcement (0–12%), the agitation speed, the agitation time, and the molten state temperature. We used a wear tester and a Vickers hardness tester to determine the wear and microhardness of the produced stir casting materials. By optimizing wear parameters, the least wear rate is determined.


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## Body

## 1. Introduction

Alloys of aluminum have outstanding mechanical qualities and machinability characteristics, as well as the ability to be strengthened by adding the reinforcement elements [1, 2]. The addition of hard ceramic particles improves the alloy materials strength and mechanical qualities, as well as their corrosion resistance, using the AZ91 magnesium alloy with graphite particle accumulation [3–5]. Modern engineering firms have started innovative technology to maintain and thrive in quality at low cost. Manufacturing sectors are continually on the lookout for new materials due to rapid technological advancements and the need for low-cost materials. The tribological and mechanical characteristics of aluminum materials were studied by [6]. Magnesium alloy [7] is infused with graphite at varying volume fraction levels, with the 60 to 100 percent volume fraction resulting in a lower wear rate, and the wear forms is like peeling wear [8]. The basic alloy with 5% graphite may be easily refined and formed into a homogeneous combination.Stir-casting [9] was employed by [10] to create aluminum hybrid composites using silicon carbide and tungsten carbide. The composites’ mechanical strength and wear characteristics are currently being evaluated in-depth in an experimental study by the scientists [11, 12]. SiC and WC materials are uniformly dispersed into an aluminum alloy for microstructural analysis. Owing to the strong merging of the strengthening particles with the base materials, greater hardness values are tested in all measures. The extensive fusing of the tough materials during the stir-casting process greatly improves the composites’ wear resistance [13, 14].Tests on the wear resistance of Al 6061 with B4C and mica particles were conducted by [15]. The abrasive resistance and COF of stir-casted composite samples were determined by a wear test [16]. Friction stir-casting is used to incorporate 70 m boron carbide and 10 m mica particles. In their research, they employed dry sliding wear test parameters with applying loads of 10, 20, and 30 Newtons. For wear resistance and COF, the AA6061/B4C/Mica composites were superior than the AA6061/B4C composites [17, 18].Aluminum matrix composites, including those containing SiC and red mud, were examined by [19] using a stir-casting procedure [20]. Studies rely on Taguchi’s statistical technique, which favors factors like red mud portion, particles size and weight usage, sliding distance, and speed of movement. In their evaluation of wear loss and coefficient friction, the gliding distance and applied load are the most critical parameters [21, 22]. Red mud was discovered to boost wear resistance by increasing the amount of red sludge and decreasing the load and sliding distance.By [23], wear on aluminum 2024 alloys with diverse % of fly ash and SiC was examined. Various reinforcing percentages of fly ash and SiC are combined in equal weight fractions (5 percent, 10 percent, and 15 percent). Researchers analyzed L27 orthogonal arrays. The composites’ wear resistance rises with rising load and sliding distance [24]. It is clear that when comparing wear test to another factors like sliding duration and percentage of reinforcement, applied load had the greatest impact on all three metrics.To improve the mechanical characteristics and strength of various alloy materials for reinforcing hare particles, stir-casting was heavily utilized. To prepare a composite, stir-casting method process parameters play a significant role, with each one having an impact on a different character [25]. Composite characteristics have an impact on the final outcome. Alloy alloys must be tested for wear resistance by wear analysis. In most cases, the wear test is performed in a dry environment. Measurement of the hardness of materials can be done using microhardness testing methods. Hardness can be measured more accurately and less destructively with the Vickers test than with other methods [26]. As a result of careful consideration of all relevant aspects and a thorough review of relevant literature, aluminum metal matrix composites were selected for this investigation. For this experiment, we used aluminum alloy 7076 with nano zirconium dioxide (ZrO2) and micron boron nitride reinforcement particles as foundation element. The stir-casting process is used to make hybrid composites, and the process parameters are optimized using the Taguchi method [27–29]. Investigation of AMMC’s mechanical and tribological properties will be the key focus of this project. In order to estimate wear rate and assess the hardness value of stir-cast parts, Pin-On Disc equipment and Vickers microhardness are used on the stir-cast composites.


## 2. Materials

XRF was utilized to determine aluminum alloy’s constituent makeup (AA7076). Because of its great abrasion resistance, exceptional strength, superior ductility, and outstanding Heat and electrical characteristics, aluminum alloy 7076 was chosen for this study. They are originally wrought alloys, and they have an extremely machinable character. AA7076 alloy is used to build highly stressed components for machines, mobile gadget, hydraulic valves, and air wing parts [30]. This study’s reinforced particles are made from nano zirconium dioxide (30 nm) and micron boron nitride (50 μm) as boron nitride is being used as a lubricant in paints, cosmetics, pencil lead, and dental cement. Reinforced hybrid particles with high tensile strength are mixed into the base material to boost its tensile strength. In materials such as aluminum alloy AA7076, components included in the basic material are listed in Table 1.Table 1
Chemical composition of AA7076.
MaterialPercentage of compositionCopper1.0Iron0.58Magnesium2.0Manganese0.3Silicon0.4Zinc7.0Titanium0.2AluminumBalance


## 3. Experimental Procedure

A stir-casting technique is used to first create an aluminum alloy and reinforced particles, which may then be controlled by varying various process parameters. Further testing will include a wear test and a microhardness test. Using the stir-casting procedure, the following variables and their corresponding values are shown in Table2. Four constraints were employed to cast the AMMC, such as reinforcement percentage, agitation speed (rpm), agitation duration (min), and melting temperature. The L16 OA was successfully completed. Blending base materials and reinforcement particles together via liquid state stir-casting are used in this study. The 5 kilogram crucible is filled with sliced AA7076 plates, and the crucible is then placed into the stir casting machine. The aluminum alloy is melted by heating the crucible to various temperatures (700 °C, 750 °C, 800 °C, and 850 °C). Nano zirconium dioxide and boron nitride are cooked in the muffle furnace simultaneously, and their weight ratios are maintained although their percentage levels differ. In addition, the stir-casting machine’s stirrer and varied agitation rates effectively combine the base material with reinforced particles (450, 500, 550, and 600 rev/min). A variety of agitation time periods (15, 20, 25, and 30 minutes) were used to ensure that the composites were thoroughly mixed. Finally, the crucible’s molten contents were poured into the dies to produce the desired forms.Table 2
specifications and levels for the stir-casting process.
SpecificationsLevels1234Percentage of reinforcement(%)04812Agitation speed(rev/min)450500550600Agitation time(min)15202530Temperature at molten stage(°C)700750800850


### 3.1. Wear Test

As a result of this process, the wear test samples are cast using parameters like 8 percent reinforcement, 600 RPM, and a molten temperature of around 850 °C. Amount of reinforcement, applying load (Newtons), disc speed (meter/sec), and sliding distance are a few of the features stated in Table3. A wide range of values can be assigned to each of the parameters. The DUCOM model was put through a rigorous wear test using a Pin-On-Disc system, which measures the wear on the specimens by sliding them across a dry surface. The specimens were 40 mm long and 12 mm diameter, and they were all put through a wear test in accordance with ASTM G99’s standard protocol. On behalf of the L16 orthogonal array configuration, each specimen was examined using a different set of parameters.Table 3
Wear test process specifications.
S. NoSpecificationsLevel 1Level 21.Percentage of reinforcement042.Applying load (Newtons)15253.Disc speed (meter/seconds)1.01.54.Sliding distance (mm)10001200


### 3.2. Vickers Microhardness Test

One of the optical measurement setups is Vickers microhardness testing, which uses specimens produced in accordance with ASTM standards. Diamond indenter was utilized to make an imprint on the sample’s surface and apply a small load to determine the specimen’s hardness value. When performing the Vickers hardness test, the normal load variation ranges from 10 gm to 1 kgf; however, in this instance, just a 0.5 kgf weight was used.


## 3.1. Wear Test

As a result of this process, the wear test samples are cast using parameters like 8 percent reinforcement, 600 RPM, and a molten temperature of around 850 °C. Amount of reinforcement, applying load (Newtons), disc speed (meter/sec), and sliding distance are a few of the features stated in Table3. A wide range of values can be assigned to each of the parameters. The DUCOM model was put through a rigorous wear test using a Pin-On-Disc system, which measures the wear on the specimens by sliding them across a dry surface. The specimens were 40 mm long and 12 mm diameter, and they were all put through a wear test in accordance with ASTM G99’s standard protocol. On behalf of the L16 orthogonal array configuration, each specimen was examined using a different set of parameters.Table 3
Wear test process specifications.
S. NoSpecificationsLevel 1Level 21.Percentage of reinforcement042.Applying load (Newtons)15253.Disc speed (meter/seconds)1.01.54.Sliding distance (mm)10001200


## 3.2. Vickers Microhardness Test

One of the optical measurement setups is Vickers microhardness testing, which uses specimens produced in accordance with ASTM standards. Diamond indenter was utilized to make an imprint on the sample’s surface and apply a small load to determine the specimen’s hardness value. When performing the Vickers hardness test, the normal load variation ranges from 10 gm to 1 kgf; however, in this instance, just a 0.5 kgf weight was used.


## 4. Results and Discussion

### 4.1. Wear Test

0.238 mm3/m of lowest wear rate was obtained with a 12 percent reinforcement contribution, 25 Newton applied load, 1.5 meter/sec disc speed, and 1200 meter sliding speed (see Table 4 for an experimental overview of the wear test).Table 4
Wear test summary.
ReinforcementApplying loadSpeed on discSliding distanceRate of wear%(Newtons)(meter/sec)(mm)(mm3/m)0151.01000.5680251.51200.3840352.01400.8010452.51600.8354151.01000.5584251.51200.7124352.01400.4264452.51600.8358151.01000.7518251.51200.5048352.01400.4098452.51600.59912151.01000.68612251.51200.23812352.01400.35112452.51600.296It can be seen here that there is a response table for wear test methods in Table5 and a response table for wear test S/N ratios in Table 6. Experiment design is employed to transform all of the input data into wear test mean and S/N ratio values. The sliding distance, applied stress, and disc speed were all strongly influenced by the percentage of reinforcement in the wear test. It was determined that 12 percent reinforcement, 25 Newton applied stress, 1.5 meter/sec disc speed, and 1200 mm sliding speed were the best parameters for the wear test.Table 5
Response table for average.
LevelPercentage of reinforcementApplying load (Newtons)Speed on disc (meter/sec)10.64150.63250.486820.61950.44680.463830.64770.48700.642340.38400.62650.6000Delta0.26010.17960.1826Rank134500Table 6
S/N ratios response table.
LevelPercentage of reinforcementApplying load (Newton)Speed on disc (meter/sec)14.2494.0416.74924.4287.6816.89335.4616.7394.83249.0834.7614.748Delta4.8343.6402.145Rank134.493Wear test main effects plots for mean and S/N ratios are shown in Figures1 and 2. Due to the lack of reinforcement, the specimen’s wear rate was significantly higher. Increasing the reinforcing percentage also helped to reduce the wear rate. Finally, the greater reinforcing percentage (12%) had the lowest wear rate. Applying a greater applied load (25 N) causes the wear rate to drop rapidly at first, but when the applied force is increased, the wear rate rises again. The wear rate increased once again when the applied force was raised from 25 N to 45 N. At 1.5 meter/sec disc speed, wear rate was at its lowest; as disc speed increased, the wear rate increased as well.Figure 1
Average plot effects for wear test.Figure 2
S/N ratio plot effects for wear test.Figure3 shows the wear rate residual graphs. As shown in the residual plot, each parameter has a direct impact on the other three. There are sixteen points on a normal probability plot, but only some of them are close to line, which can be seen in wear rate, which was found by directing accurate experimentations. It is possible to accurately measure the given parameters using the fit plot, as the points are distributed uniformly. They are all very close to each other in a histogram display of the data. There was a simultaneous positive and negative crossing of the mean line plotting the dots in a specific sequence. As a result of these circumstances, the experiment was executed flawlessly, and the parameters were effectively utilized.Figure 3
Wear rate residual plots.Figure4 depicts the wear test’s experimental runs compared to the wear rate. The experimental and anticipated values are analyzed from the wear test. There were just a few values that were closer to or even crossed the projected levels in the sixteen experiments.Figure 4
Experiment numbers vs wear rate.


### 4.2. Vickers Microhardness Test

The Vickers microhardness test yielded a maximum hardness of 126 VHN, as shown in Table7. The highest hardness was impacted by the criteria 12 percent reinforcement, 550 rpm agitation speed, 25 minute agitation time, and a molten temperature of 800 ° C. Through DoE, Vickers hardness test results are transformed into mean as in Table 8 and S/N ratios as in Table 9. Percentage of reinforcement was the most important factor in Vickers hardness test after agitation speed, agitation time, and temperature at molten state. 12 percent reinforcement, 550 rpm agitation speed, 25 minute intervals, and 800 °C temperature were found to be the appropriate Vickers hardness test settings.Table 7
VHN summary.
Experiment numberPercentage of reinforcementAgitation speedAgitation timeTemperature at molten stateVickers hardness number(%)(rev/min)(min)(°C)(VHN)10450157001122050020750913055025800116406003085011454450158001186450020850112745502570011984600307501219845015850124108500208001251185502575012112860030700118131245015750125141250020700120151255025800126161260030850119Table 8
Average response table for VHN.
Level% of reinforcementAgitation speed (rpm)Agitation time (min)Molten temperature (C)1108116112113211411211211531181171171164119115118115Delta12.06.25.43.0Rank1234Table 9
S/N ratio response table.
LevelReinforcementAgitation speedAgitation timeTemperature at molten state(%)(rev/min)(min)(°C)141.242.641.0242.8241.1140.8841.9441.32341.4241.3041.2541.0441.4741.180.2136Delta0.890.424142Rank1234Figures5 and 6 show the Vickers hardness test’s main effects plot for average and S/N ratios. Microhardness value was raised by increasing the reinforcing percentage. Finally, the larger proportion of reinforcement (12 percent) resulted in the greatest microhardness possible. An increase of 500 rpm agitation speed reduced the value of microhardness rapidly. An increase in microhardness was achieved by increasing the speed of rotation from 500 to 550 revolutions per minute. In the agitation time stage, rising the agitation time steadily raised the microhardness value; 25 minutes supplied the maximum hardness values. Microhardness increased as the molten temperature rose, starting at the lowest level and continuing to rise as the temperature grew. As a last point, the microhardness values reached their peak at 800 °C. Vickers hardness residual graphs are shown in Figure 7. The microhardness level and parameters’ influence on it can be seen clearly in a single observation in the residual plot.Figure 5
Main effects plot for average.Figure 6
S/N ratios main plot effects.Figure 7
Residual plots for Vickers hardness.All sixteen points on the typical probability plot lie on the probability line, with only a few closer to the line, and this may be recreated experimentally by manipulating the microhardness. There is no variation in points in the fit plot, which means that under the parameters set, the response values are perfect. All of the rectangular boxes in the histogram plot are so close to one another that they are touching. There were no points in the order plot that did not cross the mean line simultaneously, either favorably or negatively. As a result of these settings, the testing was passed out in an outstanding manner, and the criteria used were effective. Experimental runs versus Vickers microhardness are depicted in Figure8. The experimental and projected results are compared using the Vickers microhardness test. All sixteen experimental runs yielded data that was within the predicted range, although a few were even closer and crossed it.Figure 8
Experimental runs versus Vickers microhardness.


## 4.1. Wear Test

0.238 mm3/m of lowest wear rate was obtained with a 12 percent reinforcement contribution, 25 Newton applied load, 1.5 meter/sec disc speed, and 1200 meter sliding speed (see Table 4 for an experimental overview of the wear test).Table 4
Wear test summary.
ReinforcementApplying loadSpeed on discSliding distanceRate of wear%(Newtons)(meter/sec)(mm)(mm3/m)0151.01000.5680251.51200.3840352.01400.8010452.51600.8354151.01000.5584251.51200.7124352.01400.4264452.51600.8358151.01000.7518251.51200.5048352.01400.4098452.51600.59912151.01000.68612251.51200.23812352.01400.35112452.51600.296It can be seen here that there is a response table for wear test methods in Table5 and a response table for wear test S/N ratios in Table 6. Experiment design is employed to transform all of the input data into wear test mean and S/N ratio values. The sliding distance, applied stress, and disc speed were all strongly influenced by the percentage of reinforcement in the wear test. It was determined that 12 percent reinforcement, 25 Newton applied stress, 1.5 meter/sec disc speed, and 1200 mm sliding speed were the best parameters for the wear test.Table 5
Response table for average.
LevelPercentage of reinforcementApplying load (Newtons)Speed on disc (meter/sec)10.64150.63250.486820.61950.44680.463830.64770.48700.642340.38400.62650.6000Delta0.26010.17960.1826Rank134500Table 6
S/N ratios response table.
LevelPercentage of reinforcementApplying load (Newton)Speed on disc (meter/sec)14.2494.0416.74924.4287.6816.89335.4616.7394.83249.0834.7614.748Delta4.8343.6402.145Rank134.493Wear test main effects plots for mean and S/N ratios are shown in Figures1 and 2. Due to the lack of reinforcement, the specimen’s wear rate was significantly higher. Increasing the reinforcing percentage also helped to reduce the wear rate. Finally, the greater reinforcing percentage (12%) had the lowest wear rate. Applying a greater applied load (25 N) causes the wear rate to drop rapidly at first, but when the applied force is increased, the wear rate rises again. The wear rate increased once again when the applied force was raised from 25 N to 45 N. At 1.5 meter/sec disc speed, wear rate was at its lowest; as disc speed increased, the wear rate increased as well.Figure 1
Average plot effects for wear test.Figure 2
S/N ratio plot effects for wear test.Figure3 shows the wear rate residual graphs. As shown in the residual plot, each parameter has a direct impact on the other three. There are sixteen points on a normal probability plot, but only some of them are close to line, which can be seen in wear rate, which was found by directing accurate experimentations. It is possible to accurately measure the given parameters using the fit plot, as the points are distributed uniformly. They are all very close to each other in a histogram display of the data. There was a simultaneous positive and negative crossing of the mean line plotting the dots in a specific sequence. As a result of these circumstances, the experiment was executed flawlessly, and the parameters were effectively utilized.Figure 3
Wear rate residual plots.Figure4 depicts the wear test’s experimental runs compared to the wear rate. The experimental and anticipated values are analyzed from the wear test. There were just a few values that were closer to or even crossed the projected levels in the sixteen experiments.Figure 4
Experiment numbers vs wear rate.


## 4.2. Vickers Microhardness Test

The Vickers microhardness test yielded a maximum hardness of 126 VHN, as shown in Table7. The highest hardness was impacted by the criteria 12 percent reinforcement, 550 rpm agitation speed, 25 minute agitation time, and a molten temperature of 800 ° C. Through DoE, Vickers hardness test results are transformed into mean as in Table 8 and S/N ratios as in Table 9. Percentage of reinforcement was the most important factor in Vickers hardness test after agitation speed, agitation time, and temperature at molten state. 12 percent reinforcement, 550 rpm agitation speed, 25 minute intervals, and 800 °C temperature were found to be the appropriate Vickers hardness test settings.Table 7
VHN summary.
Experiment numberPercentage of reinforcementAgitation speedAgitation timeTemperature at molten stateVickers hardness number(%)(rev/min)(min)(°C)(VHN)10450157001122050020750913055025800116406003085011454450158001186450020850112745502570011984600307501219845015850124108500208001251185502575012112860030700118131245015750125141250020700120151255025800126161260030850119Table 8
Average response table for VHN.
Level% of reinforcementAgitation speed (rpm)Agitation time (min)Molten temperature (C)1108116112113211411211211531181171171164119115118115Delta12.06.25.43.0Rank1234Table 9
S/N ratio response table.
LevelReinforcementAgitation speedAgitation timeTemperature at molten state(%)(rev/min)(min)(°C)141.242.641.0242.8241.1140.8841.9441.32341.4241.3041.2541.0441.4741.180.2136Delta0.890.424142Rank1234Figures5 and 6 show the Vickers hardness test’s main effects plot for average and S/N ratios. Microhardness value was raised by increasing the reinforcing percentage. Finally, the larger proportion of reinforcement (12 percent) resulted in the greatest microhardness possible. An increase of 500 rpm agitation speed reduced the value of microhardness rapidly. An increase in microhardness was achieved by increasing the speed of rotation from 500 to 550 revolutions per minute. In the agitation time stage, rising the agitation time steadily raised the microhardness value; 25 minutes supplied the maximum hardness values. Microhardness increased as the molten temperature rose, starting at the lowest level and continuing to rise as the temperature grew. As a last point, the microhardness values reached their peak at 800 °C. Vickers hardness residual graphs are shown in Figure 7. The microhardness level and parameters’ influence on it can be seen clearly in a single observation in the residual plot.Figure 5
Main effects plot for average.Figure 6
S/N ratios main plot effects.Figure 7
Residual plots for Vickers hardness.All sixteen points on the typical probability plot lie on the probability line, with only a few closer to the line, and this may be recreated experimentally by manipulating the microhardness. There is no variation in points in the fit plot, which means that under the parameters set, the response values are perfect. All of the rectangular boxes in the histogram plot are so close to one another that they are touching. There were no points in the order plot that did not cross the mean line simultaneously, either favorably or negatively. As a result of these settings, the testing was passed out in an outstanding manner, and the criteria used were effective. Experimental runs versus Vickers microhardness are depicted in Figure8. The experimental and projected results are compared using the Vickers microhardness test. All sixteen experimental runs yielded data that was within the predicted range, although a few were even closer and crossed it.Figure 8
Experimental runs versus Vickers microhardness.


## 5. Conclusions

Stir-casting was used to create hybrid composites comprising aluminum alloy 7076 with nano zirconium dioxide and boron nitride (AMCs). In addition, Pin-On-Disc with Taguchi analysis was used to conduct the wear test. In the end, the wear worn-out surfaces and Vickers microhardness were rigorously evaluated for damage. Finally, the experiment’s conclusion and results were shown as follows:(i)
When it came to a test of how much of a factor reinforcement play, it was shown to have a 12% impact, with the applied load being 25 N and disc speed being 1.5 m/s, as well as the sliding speed being 1200 m. 12 percent reinforcement, 25 N load, 1.5 m/s disc speed, and 1200 m sliding speed were found to be the optimal parameters for the wear test(ii)
The lowest level of load applied and the highest level of strengthening were shown to have the lowest wear rate in the surface plot study. In addition, the least amount of disc speed and the least amount of applied load provided the least amount of wear rate. For a decreased wear rate, a correlation was found between the min sliding distance and the max reinforcement percentage(iii)
The maximum Vickers microhardness was reported as 126 VHN during the testing process. The parameters of 12 percent reinforcement, agitation speed of 550 rpm, agitation period of 25 minutes, and molten temperature of 800 °C had the greatest impact on the highest hardness values produced. The ideal Vickers hardness test parameters were discovered to be 12 percent reinforcement, agitation speed of 550 rpm, agitation period of 25 minutes, and molten temperature of 800 °C(iv)
The higher reinforcement percentage and moderate agitation speed provided outstanding microhardness, as seen by the contour plot analysis. In addition, the greatest hardness was found to be associated with lower agitation speeds and longer agitation times. Finally, the highest hardness value was found to be a combination of a long agitation period and a moderate molten temperature



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*Source: 5706132-2022-07-18.xml*