Influence of Cu Addition on the Wear Behavior of a Eutectic Al–12.6Si Alloy Developed by the Spray Forming Method

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Introduction
The cast aluminum alloys are widely used in various industries, such as in the production of chemical vessels, aircraft, and automobiles, due to their lightweight nature, high strength, and excellent wear and corrosion resistance [1][2][3].The most significant

Materials and Methods
The Al-12.6Si and Al-12.6Si-2Cualloys were prepared from the master alloys of Al (99.7%),Al-20Si, and Al-50Cu alloys.Table 1 shows the chemical composition of the alloys.The SF process was used to produce the Al-12.6Si(SF1) and Al-12.6Si-2Cu(SF2) alloys, and the details of the SF process have been described elsewhere [24,25].Table 2 shows the list of the process parameters employed in the present work.A free-fall atomizer was employed to atomize the superheated liquid metal stream using nitrogen gas.The flow diagram of the SF process is depicted in Figure 1.

Materials and Methods
The Al-12.6Si and Al-12.6Si-2Cualloys were prepared from the master alloys of Al (99.7%),Al-20Si, and Al-50Cu alloys.Table 1 shows the chemical composition of the alloys.The SF process was used to produce the Al-12.6Si(SF1) and Al-12.6Si-2Cu(SF2) alloys, and the details of the SF process have been described elsewhere [24,25].Table 2 shows the list of the process parameters employed in the present work.A free-fall atomizer was employed to atomize the superheated liquid metal stream using nitrogen gas.The flow diagram of the SF process is depicted in Figure 1.The samples of the AC and secondary processed SF Al-12.6Si and Al-12.6Si-2Cualloys were prepared [Silicarb Recrystallized Pvt Ltd., Karnataka, India] using standard metallographic techniques and were etched with Keller's reagent for the exploration of The samples of the AC and secondary processed SF Al-12.6Si and Al-12.6Si-2Cualloys were prepared [Silicarb Recrystallized Pvt Ltd., Karnataka, India] using standard metallographic techniques and were etched with Keller's reagent for the exploration of the microstructural features.The microstructural features were studied under an optical microscope and a scanning electron microscope (SEM).The hardness measurement was carried out using an HV-5 VH tester at a load of 300 g and a dwell period of 15 s with a procedures of ASTM E92 (2004).The dry sliding wear testing was carried out on a pin-ondisk tribometer as per ASTM: G99-05 (2016).The disk was made of EN-32 steel with a hardness of 65HRC.The wear specimens were Ø8 × 30 mm in size and were polished and cleaned with acetone before being tested.The wear tests were performed at different loads, ranging from 10 to 40 N, for a sliding distance of 2000 m at sliding velocities of 1, 2, 2.5 and 3 m/s.The topographical features of the worn-out surfaces were analyzed using SEM.

Porosity Measurement
The porosity has been observed to be an inevitable entity in SF alloys.However, depending on the location and processing parameters, its proportion and features in the preform are subject to change.The porosity heavily influences the mechanical, wear, and corrosion properties of the alloys.In the current investigation, hot pressing was used for porosity reduction in the alloys.The porosity values reported are shown in Table 3.In comparison to SF1 alloy, the SF2 alloy exhibits less porosity after hot compaction.The variation in monitoring the process parameters in SF may be the cause for the variation in porosity in the alloys before hot compaction.The increasing surface heat condition of the preforms during deposition has a significant effect on the nature and amount of porosity.As a result, minimizing preform porosity requires careful control of the processing parameters.Many researchers have investigated how porosity develops during SF [26].The high liquid fraction in the spray typically causes gas to become trapped within the liquid, resulting in spherical holes.The SF1 alloy exhibited a higher porosity than did the SF2 alloy before hot compaction.This can be due to the fact that the spray contains a significant amount of liquid.In the spray deposited alloys, the porosity was significantly reduced by hot compaction.

Microstructural Features of AC and SF Alloys
The optical microstructure of the AC1 alloy is shown in Figure 2a.It consists of eutectic Si needles dispersed randomly throughout the α-Al matrix.The EDX (energy dispersive X-ray) spectrum of the AC1 alloy is shown in Figure 2b.The Al and Si peaks in the spectrum are particularly prominent.As shown in Figure 3a, the SF1 alloy microstructure was composed of evenly dispersed, fine eutectic Si particulates.The EDX spectrum of the SF1 alloy is shown in Figure 3b.Additionally, it was found that the matrix of the SF1 alloy included a 7 vol.% of micron-sized porosity and showed an improved solid solubility of Si.The high fraction of liquid in the spray causes the entrapment of gas in the liquid, which results in the formation of pores in the alloy [26].However, the amount of porosity was not significantly influenced by the presence of Cu and Si.The SEM micrograph of the AC2 alloy is shown in Figure 4.The micrograph depicts the random distribution of the eutectic Si phase, the θ-Al2Cu phase, and the Q-Al-Si-Cu phase in the dendritic α-Al matrix.At the grain boundaries of the Al dendrite arms, the intermetallic θ and Q phases were found to be coarse, ranging in size from 50 to 75 μm.Table 4 displays the composition of the AC2 alloy, as determined by EDX analysis at spots 1, 2, 3 and 4 as shown on the microstructure.The SEM micrograph of the AC2 alloy is shown in Figure 4.The micrograph depicts the random distribution of the eutectic Si phase, the θ-Al2Cu phase, and the Q-Al-Si-Cu phase in the dendritic α-Al matrix.At the grain boundaries of the Al dendrite arms, the intermetallic θ and Q phases were found to be coarse, ranging in size from 50 to 75 μm.Table 4 displays the composition of the AC2 alloy, as determined by EDX analysis at spots 1, 2, 3 and 4 as shown on the microstructure.The SEM micrograph of the AC2 alloy is shown in Figure 4.The micrograph depicts the random distribution of the eutectic Si phase, the θ-Al 2 Cu phase, and the Q-Al-Si-Cu phase in the dendritic α-Al matrix.At the grain boundaries of the Al dendrite arms, the intermetallic θ and Q phases were found to be coarse, ranging in size from 50 to 75 µm.Table 4 displays the composition of the AC2 alloy, as determined by EDX analysis at spots 1, 2, 3 and 4 as shown on the microstructure.The SEM micrograph of the AC2 alloy is shown in Figure 4.The micrograph depicts the random distribution of the eutectic Si phase, the θ-Al2Cu phase, and the Q-Al-Si-Cu phase in the dendritic α-Al matrix.At the grain boundaries of the Al dendrite arms, the intermetallic θ and Q phases were found to be coarse, ranging in size from 50 to 75 μm.Table 4 displays the composition of the AC2 alloy, as determined by EDX analysis at spots 1, 2, 3 and 4 as shown on the microstructure.Table 5 displays the composition of the phases.After being hot pressed, the microstructure of the SF2 alloy (Figure 5a) showed eutectic Si and θ phase fragmentation.Additionally, an increase in the volume percentage of the Si phases, a decrease in porosity, and a homogeneous Al-matrix were observed.The fine θ and Q-intermetallic compounds began to precipitate at room temperature as a result of the alloy's rapid cooling during the atomization and deposition process, which maintained all of the solute in a supersaturated state.Table 5 displays the composition of the phases.After being hot pressed, the microstructure of the SF2 alloy (Figure 5a) showed eutectic Si and θ phase fragmentation.Additionally, an increase in the volume percentage of the Si phases, a decrease in porosity, and a homogeneous Al-matrix were observed.The fine θ and Q-intermetallic compounds began to precipitate at room temperature as a result of the alloy's rapid cooling during the atomization and deposition process, which maintained all of the solute in a supersaturated state.

Hardness
Table 6 displays the micro-hardness values of the AC and SF alloys.In comparison to AC alloys, the results show a considerable increase in the microhardness of the SF alloys.The hardness of the SF1 alloy is 36% greater than that of the AC1 alloy, while the hardness of the SF2 alloy is 33% higher than that of the AC2 alloy.The SF2 is invariably 41% harder than that of the AC1 alloy.The small and hard Si particles, which are uniformly dispersed throughout the Al matrix and that resist localized deformation when the indentation is applied, may be the cause for the high hardness of the spray deposited alloys.The plastic deformation was significantly hampered by the fine eutectic Si phase.The high hardness of the SF2 alloy may be attributed to the fine precipitation of the hard Al 2 Cu intermetallic phase, distributed uniformly throughout the Al matrix, and a higher volume fraction of eutectic Si, which causes an obstruction in the indentation and raises the hardness [23].Additionally, the SF process, being a rapid solidification process, has produced more fine precipitates and a hardening effect, which may have contributed to the resulting increased hardness by adding another barrier to the dislocation motion [27].The wear rates of both the AC and SF alloys are shown in Figure 6a-d.The alloys were tested for wear at sliding velocities of 1, 2, 2.5, and 3 ms −1 , with a sliding distance of 2000 m and a load range of 10-40 N. The results show that the wear rate increases for all alloys as the load is increased, regardless of the type of alloy or sliding velocity.Additionally, it was observed that AC alloys consistently exhibit a higher wear rate than that of the SF alloys.Among the tested alloys, the SF2 alloy has the lowest wear rate, while the AC1 alloy has the highest wear rate across the whole range of applied loads and sliding velocities.
During wear testing, the long eutectic Si needles tend to break more frequently than the tiny Si particles.This is due to an increase in the alloy's shear stress as the load increases, which results in easier fracturing of the eutectic Si and deformation of the matrix around it.The size of the eutectic Si may influence the stress concentration caused by deformation, with the interface between Si needles and the α-Al matrix being more susceptible to this effect than the interface between the tiny Si particles and the α-Al matrix.In the present study, this was observed, as coarse eutectic Si fractured easily, leading to the decreased wear resistance of the AC alloys.However, in spray deposition, the eutectic Si is more finely divided and evenly dispersed throughout the α-Al matrix.The wear resistance of AC2 alloy is higher than that of AC1 alloy, and SF2 alloy has a higher wear resistance than the SF1 alloy.This is because of the presence of the θ phase in the ternary alloy.The strengthening effect of the θ phase on the α-Al matrix lowers the possibility of the Si needles peeling off from the matrix, decreasing the wear rate.The secondary processed SF2 alloy has a better wear resistance than does the AC2 alloy.This is because of the uniform distribution of the refined eutectic Si and the fine precipitates of the θ-Al2Cu intermetallic phase in the α-Al matrix.The Si and θ phases in the alloy have been further finely refined by hot compaction, decreasing the wear rate of the alloy [24].The wear rate of the AC and SF alloys is low at a low load (10 N) and a low sliding velocity (1.0 ms −1 ), with no appreciable variation between the alloys (Figure 6a).There will be less contact between the mating surfaces, and at a low contact pressure, the interface temperature is adequate to produce metal oxide film, which will be removed from the pin surface during sliding.Therefore, oxidative wear was responsible for the separation of the oxidized film between the mating surfaces and the removal of oxides from the interface.The clear sign of a change in the wear behavior was the rise in wear rate as the applied load increased (from 10 to 20 N).The slope of the wear rate versus the applied load has been observed to increase at higher loads (greater than 20 N).This demonstrates that the wear process has switched from mild oxidative metallic wear to delamination pure metallic wear.At a high load, the sliding surface is subjected to high shear stress, which causes cracks and spreads beneath the plastically deformed surface, potentially eventually causing the alloy to delaminate from the surface.This underlying wear process causes the wear rate to increase with the load [28].For both the SF and AC alloys, the wear rates increased at a 40 N load.The strengthening effect of the θ phase on the α-Al matrix lowers the possibility of the Si peeling off from the matrix, decreasing the wear rate.The secondary processed SF2 alloy has a better wear resistance than does the AC2 alloy.This is because of the uniform distribution of the refined eutectic Si and the fine precipitates of the θ-Al 2 Cu intermetallic phase in the α-Al matrix.The Si and θ phases in the alloy have been further finely refined by hot compaction, decreasing the wear rate of the alloy [24].The wear rate of the AC and SF alloys is low at a low load (10 N) and a low sliding velocity (1.0 ms −1 ), with no appreciable variation between the alloys (Figure 6a).There will be less contact between the mating surfaces, and at a low contact pressure, the interface temperature is adequate to produce metal oxide film, which will be removed from the pin surface during sliding.Therefore, oxidative wear was responsible for the separation of the oxidized film between the mating surfaces and the removal of oxides from the interface.The clear sign of a change in the wear behavior was the rise in wear rate as the applied load increased (from 10 to 20 N).The slope of the wear rate versus the applied load has been observed to increase at higher loads (greater than 20 N).This demonstrates that the wear process has switched from mild oxidative metallic wear to delamination pure metallic wear.At a high load, the sliding surface is subjected to high shear stress, which causes cracks and spreads beneath the plastically deformed surface, potentially eventually causing the alloy to delaminate from the surface.This underlying wear process causes the wear rate to increase with the load [28].For both the SF and AC alloys, the wear rates increased at a 40 N load.

Variation of Wear Rate with Sliding Velocity at a Constant Applied Load
Understanding how the wear rate changes with sliding velocity at a constant load is crucial (refer to Figure 7a-d).At a low load of 10 N, the wear rate decreased as the sliding velocity increased (Figure 7a).Initially, the wear rate was high at a low sliding velocity of 1.0 ms −1 .The lowest wear rate was found at 2.0 ms −1 for loads of 20 and 30 N, and the wear rate increased somewhat at higher sliding velocities (Figure 7b,c).However, at a high load of 40 N, the lowest measured wear rate was observed at a sliding velocity of 2.0 ms −1 , and beyond 2.0 ms −1 , the wear rate significantly increased (Figure 7d).Due to the friction force, a metal oxide layer forms on the pin surface, which then gets removed during the sliding process.Therefore, at low loads, only oxidative wear takes place.At a higher load of 40 N, adhesive wear takes over, where severe plastic deformation of the surface occurs.This causes a higher interface temperature, which then heats up the worn surface and softens the matrix.Furthermore, the worn surface experiences greater penetration and plastic deformation.As a result, both the AC and SF alloys experienced mixed adhesive and abrasive wear at higher loads.As per the study in Ref. [29], it has been observed that the wear rate decreases as the sliding speed increases up to a critical sliding velocity (2.0 ms −1 ).However, as the sliding speed increases beyond 2.0 ms −1 , the wear rate starts to increase.This happens because the reduced surface contact between the pin and disc initially leads to lower wear rate, but the increase in sliding velocity raises the strain rate, improves the flow strength, and increases the flow rates, which eventually increases the wear rate [30].Moreover, at higher sliding velocities (between 2 and 3 ms −1 ), the interface temperature increases due to the rise in friction heat, which makes the alloy softer.This leads to more surface contact, resulting in a higher wear rate [31].
of 40 N, adhesive wear takes over, where severe plastic deformation of the surface occurs.This causes a higher interface temperature, which then heats up the worn surface and softens the matrix.Furthermore, the worn surface experiences greater penetration and plastic deformation.As a result, both the AC and SF alloys experienced mixed adhesive and abrasive wear at higher loads.As per the study in Ref. [29], it has been observed that the wear rate decreases as the sliding speed increases up to a critical sliding velocity (2.0 ms −1 ).However, as the sliding speed increases beyond 2.0 ms −1 , the wear rate starts to increase.This happens because the reduced surface contact between the pin and disc initially leads to lower wear rate, but the increase in sliding velocity raises the strain rate, improves the flow strength, and increases the flow rates, which eventually increases the wear rate [30].Moreover, at higher sliding velocities (between 2 and 3 ms −1 ), the interface temperature increases due to the rise in friction heat, which makes the alloy softer.This leads to more surface contact, resulting in a higher wear rate [31].
During the SF process, the rapid solidification of alloys led to the development of fine eutectic Si, an increase in the volume fraction of the Si phase, and an increase in the solid solubility of Si in the matrix.This process reduced the stress concentration at the interface between the fine and spherical Si phase and the equiaxed Al matrix, which lowers the likelihood of the formation of subsurface cracks.Additionally, the strong interface bond strength with the matrix might improve the wear resistance of the SF alloys.The Cu addition improved the thermal stability of the Al-Si alloys by generating a hard θ-Al2Cu intermetallic compound in the Al matrix.This resulted in an increase in the transition period for both the SF and AC alloys, leading to mild to severe wear rate.In the SF2 alloy, the development of fine θ-Al2Cu intermetallic precipitates was coherent with the soft Al-matrix, which increased the hardness and wear resistance by resisting the dislocation motion.However, the presence of an extremely hard, coarse, and brittle θ-Al2Cu intermetallic phase, as well as the needle-like eutectic Si phase, in the α-Al matrix resulted in a high wear rate in the AC2 alloy.This faceted structure of intermetallic and Si phases existed as discrete particles that had a relatively weak bond with the matrix and served as stress raisers.The eutectic Si and hard intermetallic phases were also anticipated to have the potential for crack nucleation [32].

Variation of Friction Coefficient with Load at Constant Sliding Velocity
In Figure 8, the relationship between the coefficient of friction (μ) and the applied load at a sliding velocity of 3.0 ms −1 is presented.It was observed that the μ remained almost steady, with a slight decrease over time as the load increased.The results indicate that regardless of the composition, the SF alloys had a lower μ than did the AC alloys.The SF2 alloy in particular had the lowest μ.At a load of 10 N, the SF1 and SF2 alloys exhibited 7% and 4% less μ, respectively, compared to the AC alloys.At a high load of 40 N, the μ of the SF1 and SF2 alloys was 9% and 6% less than that of the AC1 andAC2 alloys, respectively.When the load is low, there is no metal-to-metal contact between the pin and During the SF process, the rapid solidification of alloys led to the development of fine eutectic Si, an increase in the volume fraction of the Si phase, and an increase in the solid solubility of Si in the matrix.This process reduced the stress concentration at the interface between the fine and spherical Si phase and the equiaxed Al matrix, which lowers the likelihood of the formation of subsurface cracks.Additionally, the strong interface bond strength with the matrix might improve the wear resistance of the SF alloys.The Cu addition improved the thermal stability of the Al-Si alloys by generating a hard θ-Al 2 Cu intermetallic compound in the Al matrix.This resulted in an increase in the transition period for both the SF and AC alloys, leading to mild to severe wear rate.In the SF2 alloy, the development of fine θ-Al 2 Cu intermetallic precipitates was coherent with the soft Al-matrix, which increased the hardness and wear resistance by resisting the dislocation motion.However, the presence of an extremely hard, coarse, and brittle θ-Al 2 Cu intermetallic phase, as well as the needle-like eutectic Si phase, in the α-Al matrix resulted in a high wear rate in the AC2 alloy.This faceted structure of intermetallic and Si phases existed as discrete particles that had a relatively weak bond with the matrix and served as stress raisers.The eutectic Si and hard intermetallic phases were also anticipated to have the potential for crack nucleation [32].

Variation of Friction Coefficient with Load at Constant Sliding Velocity
In Figure 8, the relationship between the coefficient of friction (µ) and the applied load at a sliding velocity of 3.0 ms −1 is presented.It was observed that the µ remained almost steady, with a slight decrease over time as the load increased.The results indicate that regardless of the composition, the SF alloys had a lower µ than did the AC alloys.The SF2 alloy in particular had the lowest µ.At a load of 10 N, the SF1 and SF2 alloys exhibited 7% and 4% less µ, respectively, compared to the AC alloys.At a high load of 40 N, the µ of the SF1 and SF2 alloys was 9% and 6% less than that of the AC1 andAC2 alloys, respectively.When the load is low, there is no metal-to-metal contact between the pin and counter surface.Instead, the behavior is influenced by the oxidation process and the adhesion of small protrusions on the contacting surfaces.As the load increases, the µ decreases slightly, which may occur because of metallic contact between the counter face and the pin.This contact leaves no room for imperfections and locks the surface contact area.The slight variation in the µ at higher loads may be attributed to the fact that all alloys contain more aluminum than the alloying elements.At higher loads, the aluminum matrix in the specimens and the counter face come in contact with each other, which determines the effective coefficient of friction.

Variation of Friction Coefficient with Load at Constant Sliding Velocity
In Figure 8, the relationship between the coefficient of friction (μ) and the applied load at a sliding velocity of 3.0 ms −1 is presented.It was observed that the μ remained almost steady, with a slight decrease over time as the load increased.The results indicate that regardless of the composition, the SF alloys had a lower μ than did the AC alloys.The SF2 alloy in particular had the lowest μ.At a load of 10 N, the SF1 and SF2 alloys exhibited 7% and 4% less μ, respectively, compared to the AC alloys.At a high load of 40 N, the μ of the SF1 and SF2 alloys was 9% and 6% less than that of the AC1 andAC2 alloys, respectively.When the load is low, there is no metal-to-metal contact between the pin and counter surface.Instead, the behavior is influenced by the oxidation process and the adhesion of small protrusions on the contacting surfaces.As the load increases, the μ decreases slightly, which may occur because of metallic contact between the counter face and the pin.This contact leaves no room for imperfections and locks the surface contact area.The slight variation in the μ at higher loads may be attributed to the fact that all alloys contain more aluminum than the alloying elements.At higher loads, the aluminum matrix in the specimens and the counter face come in contact with each other, which determines the effective coefficient of friction.

Topographical Features of Worn Surfaces
The worn surfaces of AC and SF alloys at a 40 N load and a sliding velocity of 3.0 ms −1 are as shown in Figure 9.The topography of the worn surfaces indicates that the binary alloys have suffered more damage than the ternary alloys.The worn surface of the AC1 alloy showed several features, including oriented overlapping flaky structures, wear

Topographical Features of Worn Surfaces
The worn surfaces of AC and SF alloys at a 40 N load and a sliding velocity of 3.0 ms −1 are as shown in Figure 9.The topography of the worn surfaces indicates that the binary alloys have suffered more damage than the ternary alloys.The worn surface of the AC1 alloy showed several features, including oriented overlapping flaky structures, wear scars, craters, the crass plastic flow of metal, metallic fracture of the ridges, and edge cracking (Figure 9a).The damaged surface also revealed evident signs of plastic deformation, along with adhesive wear.On the other hand, the AC2 alloy, as shown in Figure 9b, shows wide parallel grooves, compacted oxide patches, and a few discontinuous abrasive grooves on its worn surface.During the wear testing, the sliding of a soft pin surface against a hard disc caused two types of abrasive wear.The first type occurred when the pin penetrated the disc and created continuous parallel grooves.The second type occurred when hard intermetallic phases, such as Si and Al 2 Cu, were introduced between the sliding surfaces.This type of wear caused the formation of surface cavities due to debris detachment, which indicated delimitative wear on the surface layers.As a result, cracks were formed below the surface layers and grew until they joined together, forming plate-shaped particles that detached from the wear surface.In Figure 9c, it is observed that the worn surface of the SF1 alloy displayed a homogenous wear pattern.The surface was smooth, with fine abrasion grooves, a few small dimples, and some scoring marks that extended from end to end.Additionally, the surface showed white patches, indicating the early stages of oxide formation.On the other hand, in Figure 9d, we can see the worn surface of the SF2 alloy, which had small, homogeneous, and continuous grooves.The surface was smooth, with fine scoring marks, and it had no pits or dimples, indicating a low wear-rate [24].
scars, craters, the crass plastic flow of metal, metallic fracture of the ridges, and edge cracking (Figure 9a).The damaged surface also revealed evident signs of plastic deformation, along with adhesive wear.On the other hand, the AC2 alloy, as shown in Figure 9b, shows wide parallel grooves, compacted oxide patches, and a few discontinuous abrasive grooves on its worn surface.During the wear testing, the sliding of a soft pin surface against a hard disc caused two types of abrasive wear.The first type occurred when the pin penetrated the disc and created continuous parallel grooves.The second type occurred when hard intermetallic phases, such as Si and Al2Cu, were introduced between the sliding surfaces.This type of wear caused the formation of surface cavities due to debris detachment, which indicated delimitative wear on the surface layers.As a result, cracks were formed below the surface layers and grew until they joined together, forming plate-shaped particles that detached from the wear surface.In Figure 9c, it is observed that the worn surface of the SF1 alloy displayed a homogenous wear pattern.The surface was smooth, with fine abrasion grooves, a few small dimples, and some scoring marks that extended from end to end.Additionally, the surface showed white patches, indicating the early stages of oxide formation.On the other hand, in Figure 9d, we can see the worn surface of the SF2 alloy, which had small, homogeneous, and continuous grooves.The surface was smooth, with fine scoring marks, and it had no pits or dimples, indicating a low wear-rate [24].

Conclusions
The following conclusions may be drawn from the present study on AC and SF alloys:

•
The microstructure of the SF1 alloy consists of eutectic Si particles ranging from 3 to 7 μm, which are uniformly distributed in the Al-matrix.The SF2 alloy exhibited a uniform distribution of eutectic Si, Al2Cu, and Al-Si-Cu intermetallic phases in the equiaxed Al-matrix.

•
The micro hardness of the SF2 alloy has been improved by 8, 34, and 41% compared to that of the SF1, AC2, and AC1 alloys, respectively.

Conclusions
The following conclusions may be drawn from the present study on AC and SF alloys: • The microstructure of the SF1 alloy consists of eutectic Si particles ranging from 3 to 7 µm, which are uniformly distributed in the Al-matrix.The SF2 alloy exhibited a uniform distribution of eutectic Si, Al 2 Cu, and Al-Si-Cu intermetallic phases in the equiaxed Al-matrix.• The micro hardness of the SF2 alloy has been improved by 8, 34, and 41% compared to that of the SF1, AC2, and AC1 alloys, respectively.• The SF2 alloy exhibits superior wear resistance to that of the SF1 and AC alloys under varying load and sliding velocity conditions.This improvement was attributed to the fine and uniform distribution of the Si and intermetallic phases and to the increased solid solubility.Specifically, at a 40 N load and a 1 ms −1 sliding velocity, the wear resistance of the SF2 alloy is 23, 47, and 62% higher than that of the SF1, AC2, and AC1

Figure 1 .
Figure 1.Flow diagram depicting the details of spray forming of the Al-12.6Sialloy.

Figure 1 .
Figure 1.Flow diagram depicting the details of spray forming of the Al-12.6Sialloy.

Figure
Figure 5a depicts the SEM microstructure of the SF2 alloy.The microstructure of the alloy showed fine precipitates of θ-Al 2 Cu and Q-phases in an equiaxed Al matrix, as well as a uniform, homogeneous distribution of fine eutectic Si particles, with sizes ranging from 3 to 7 µm.The EDS spectra of spots 1, 2 and 3 of Figure 5a are shown in Figure 5b(i,ii,iii) respectively.The EDX analysis of the SF2 alloy has revealed fine eutectic Si, fine precipitates of θ-Al 2 Cu, and Q-Al 74 Si 9 Cu 10 phases.

Figure
Figure 5a depicts the SEM microstructure of the SF2 alloy.The microstructure of the alloy showed fine precipitates of θ-Al2Cu and Q-phases in an equiaxed Al matrix, as well as a uniform, homogeneous distribution of fine eutectic Si particles, with sizes ranging from 3 to 7 μm.The EDS spectra of spots 1, 2 and 3 of Figure 5a are shown in Figure 5b(i,ii,iii) respectively.The EDX analysis of the SF2 alloy has revealed fine eutectic Si, fine precipitates of θ-Al2Cu, and Q-Al74Si9Cu10 phases.

Figure 6 .
Figure 6.The variation in the wear rate of the AC and SF alloys as a function of load and sliding velocity (a) 1.0 ms −1 ; (b) 2.0 ms −1 ; (c) 2.5 ms −1 ; and (d) 3.0 ms −1.

Figure 6 .
Figure 6.The variation in the wear rate of the AC and SF alloys as a function of load and sliding velocity (a) 1.0 ms −1 ; (b) 2.0 ms −1 ; (c) 2.5 ms −1 ; and (d) 3.0 ms −1 .

Figure 8 .
Figure 8. Coefficient of friction versus applied load at a sliding velocity of 3.0 ms −1 .

Figure 8 .
Figure 8. Coefficient of friction versus applied load at a sliding velocity of 3.0 ms −1 .

Table 1 .
The details of the composition of the experimental alloys (wt.%).

Table 2 .
Details of process parameters for spray forming.

Table 1 .
The details of the composition of the experimental alloys (wt.%).

Table 2 .
Details of process parameters for spray forming.

Table 3 .
Porosity values of spray-formed alloys.

Table 4 .
Phase composition of the AC ternary alloy obtained by EDX analysis.

Table 4 .
Phase composition of the AC ternary alloy obtained by EDX analysis.

Table 5 .
Phase composition of SF2 alloy obtained by EDX analysis.

Table 6 .
Hardness values of the AC and SF alloys.
3.4.Wear Characteristics of AC and SF Alloys 3.4.1.Variation of Wear Rate with Load at Constant Sliding Velocity