Abstract
In this research, the main aim is to focus the enhancement of aluminium-based metal matrix composites for improving the attributes of light weight metals, aerospace structures and other tailor blank material properties. By this way, the friction stir processing (FSP) was the suited alternate technique to enhancing the mechanical attributes and superior microstructural amendment in the processed MMCs. Therefore, this study investigates the dispersion of ceramic-based strengthening particles of chromium oxide (Cr2O3) in the aluminium base matrix of A356 alloy. During the processing, the different tool pin sizes having the conical threaded tool pin profiles. Similarly, the tool spinning speed and tool travel speed also varied while in FSP. Before the processing, the A356 alloy was prepared by the grooved surfaces for packing the chromium oxide particles to compose the aluminium metal matrix composites. The tensile strength and hardness was employed to carry out from the friction stir processed A356 alloy with influencing of Cr2O3. The maximum occurred tensile processing parameters are 1500 rpm of spinning speed, 6 mm of tool pin sizes and 90 mm/min of tool travel speed. Similarly, the maximum obtained hardness processing parameter are 2000 rpm of spinning speed, 5 mm of tool pin sizes and 90 mm/min of tool travel speed. A scanning electron microscope was utilized to investigate the dispersed Cr2O3 in the A356 alloy for confirming the refinement grains in the nugget zones of FSPed A356 alloy. The increased grain boundary by the influence of different tool pin sizes was the major reason to produces the better mechanical properties in the processed A356/Cr2O3.
1. Introduction
In various engineering industries such as aerospace, automobile, and other light weight-related manufacturing applications, aluminium plays the major role to produce the light weight structures by the utilization of various processing technologies [1–5]. Normally, the aluminium alloys had better mechanical attributes due to their enhanced corrosion, recyclability, low weight, and alleviate to formability. In the normal aluminium alloys, the mechanical strength and its wear performances are improved minimally when the reinforcements were not added up together. While in the process of fabrication in the lightweight materials, reinforcement is very captious role for improving the mechanical attributes and also the wear properties [6–10].
Right now, the aluminium-based metal matrix composites with strengthened particles are extensively utilized in the aerospace and defense related applications in the assembly unit due to their reinforcement particles which assisted to advances in strengthening. During the processing of liquefying and other casting methods, AMCs with their ceramic-based tools have lesser toughness and ductile strength owing to weaken wettability in the composed interfaces composites [11–14]. While in the process of AMCs with their ceramic products, other major disputes like uneven homogeneous dispersion and porosity defects among the ceramic reinforcements and aluminium alloy are generated. It has been accredited that the transforms in mutually the character of strengthening particles and fabrication process will be advantageous to attaining the AMCs with enhanced attributes [15–19].
The following materials like molybdenum, tungsten, vanadium, stainless steel, aluminium nitride, and aluminium-based titanium are the materials which successfully composed the aluminium metal matrix composites by the supporting ceramic reinforcement particles. Due to the wettability, disputes are easily resolved from the different researchers. The above challenging disputes are easily resolved by the friction stir processing, because this process is totally differed from the usual friction stir welding process [20, 21]. The FSP produces the evenly dispersed particles of the reinforcement in the base matrix of aluminium alloy and also resolves the major complicated wettability issues [22–24].
The modifying the tool sizes and shapes of the FSP tool are acknowledged as the most significant technique of justifying the fabrication issues like smaller and larger sized pores in the processed metals. Different pin sizes of the FSP tool on the aluminium alloy with ceramic based composites was indicated by the various researchers. It was confirmed that the different pin having cylindrical threads caused in the better microstructure variations in the expressions of evenly dispersed particles and better grain reducing while the process of FSP [25–27]. At the same time diminishes the maximum angle boundaries of grain and produces the uninterrupted dynamic recrystallization in the welded region statements was reported by the various researchers [28–30].
To enhance the extent of blended materials and the mechanical properties are achieved maximum when utilizing the different sized FSP tools. It was exposed that the different tool pin sized with cylindrical profiles enhances the grain development in the reduction of sizes, mechanical attributes and hardness owing to considerable materials blending. From the literature, different tool pin profile sizes are the novel method to establish the intermetallic particles in the processed aluminium metal matrix composites by the FSP process [31]. On the basis of maximum speed, the joint efficiency of the AA2024-T3 plates was examined [32]. Analyses were done on the effects of nano-/micro-TiO2 on several composites, including glass and kenaf [33]. Using mechanical tests, the volume percentage of glass and banana fibre was estimated [34]. Finite element analysis was used to evaluate the AISI 4130, EN8 forged steel composite materials and estimate the stress fluctuations [35, 36].
The prominent research gaps like the effect of different sized tool pin profiles on the mechanical attributes, microstructure evolution, wear properties and corrosion behaviors performances are fulfilled by the ceramic based particles which are strengthened by the aluminium alloy in the composites processing. But it has weakened the tribo mechanical properties. Now the aluminium alloy A356 is the suitable material for replacing the 6061 aluminium alloy and this material broadly used in the truck chassis, impellers, nuclear energy implementation, aircraft structures and maximum velocity boilers.
Therefore this research is aimed to investigate the mechanical properties and microstructure examinations on the A356 aluminium alloy by the presences of ceramic particles on the V grooved surfaces of the A356 through the different pin sized threaded cylindrical FSP tool pin profiles. In this research, all the processing is produced by the friction stir processing technique with various sized threaded pin shape tool. Similarly, the microstructure and mechanical properties are majorly investigated on the FSPed A356 aluminium alloy.
2. Experimentation
In this experiments, the aluminium alloy A356 was chosen as the base matrix for composing the aluminium metal matrix composites. During the process, the A356 having the sizes of 150 mm of length, 150 mm of width and 10 mm of thickness plate was utilized and ceramic based chromium oxide nano powders having the size of 80 nm was utilized as the strengthening particles in the FSP process. The chemical composition of A356 aluminium alloy is 0.1 of manganese, 0.35 of magnesium, 0.2 of iron, 7 of silicon, 0.2 of copper, 0.1 of zinc and remaining 92.05 of aluminium, respectively. The properties of chromium oxide particles are 197°C of melting point, 99.99 g/mol of molar mass and 2.7 g/cm3 of density, respectively. Before conducting the process of FSP, the base plate of A356 was engaged to prepare the grooves having the sizes of 3.5 mm of depth and 0.75 mm of width throughout the A356 plates. The arranged grooves were occupied by the Cr2O3 particles by manually. The tool material is the significant one for composing the better FSP specimen. In this research, after created the grooved surfaces on the A356 alloy, the chromium oxide particles are packed manually and then pin less tool was packing the particles without any splitting out the reinforcements during the FSP initiation. Then the onion ring structure was formed on the A356 alloy [33].
Figure 1 shows the configuration of preparing the ceramic based nano particles on the A356 aluminium alloy with grooved surfaces. In this experimentation, the appropriated tool material of high carbon high chromium steel material was the tool material to generating the different tool pin profiles [6]. The different tool pin sizes like 4, 5 and 6 diameter of tool pin sizes with conical threaded cylindrical shapes tool was utilized for secondary process of the FSP with different processing conditions. During the FSP, tool rotational speed, cross speed and axial forces are significant processing parameters of FSP. Now in this experimentation, as per the standard literature, 90 to 110 mm/min of cross or traverse speed and various tool spinning speed from 1000 to 2000 rpm, respectively. In this research, after processed specimen of A356, samples were subjected to conduct the microstructure analysis and some necessary actions like barkers reagent was takes place on the processed samples under the 150 V with holding time of 150 seconds. Then, the etched samples are taken for the SEM analysis. The mechanical performances test like microhardness and tensile experiments was conducted on the processed A356 alloy. During the microhardness test, the processed regions like stirred region, thermomechaically affected zone, heat affected zone and unprocessed A356 alloy was location for analyzing the hardness studies. As per the ASTM E8 standards tensile specimen was prepared for conducting the tensile tests. The UTM machine with model of Instron with 1 mm/min of displacement rate was maintained for all the specimens. In this FSP preparation study, tool spinning speed is increased from 1000 to 2000 rpm, different tool pin sizes like 4 to 6 mm of conical cylinder threaded profiles and various tool travel speed from 90 to 110 mm/min, respectively. From these levels of processing parameters, Taguchi L9 was suitable for designing the parameters for conducting the friction stir processing [37, 38]. Tables 1 and 2 show the three level of processing constraints for FSP and its detailed levels, respectively. Figure 2 displays the experimentation details by the graphical view.
3. Results and Discussion
From the detailed array of L9 parameters table, all the processing constraints are conducted on the A356 alloy through the friction stir processing. Table 3 shows the overall Taguchi table for FSP processing with their outputs of tensile values and micro hardness strength values. The packed ceramic particles are well dispersed in the stirred region from the entire processing parameters. As per the detailed level of L9 Taguchi, the entire specimen was prepared by the FSP conditions. From Table 3, overall hardness and tensile was easily revealed that the increasing of spinning speed with medium level of tool pin sizes and decreasing of too travel speed achieves the better mechanical attributes than the other level processing factors. The minimum and maximum of tool pin sized FSP tool did not dispersed the ceramic particles evenly during the FSP, by this way this major reason for diminishing the hardness on the stirred areas on the A356 alloy. But the increment of tool spinning speed and reduced tool travel speed produces the finer with evenly dispersed Cr2O3 in the grooved surfaces of the A356 alloy. While in the medium of tool spinning speed and reduced tool travel speed with moderate sized tool pin sizes obstructing the migrating for the grain boundaries. Therefore, the hardness load and superior hardness was accumulated against hindered migration of the dislodgment during the tests. According hall Petch relationship, above the enhanced hardness values is confirmed. At the same time, stirred zones provides the refined grains and also defended from thermal heat input and also this is the confirmations for producing the maximum hardness in the particular stirred zones. In the dislodgment density of the refined grain structure area, there is an essential betterment in that dislodgment which also confirmed from the Orowan strengthening mechanism by the confirmation. From the various nine processing parameters, all the processing parameters achieved better tensile properties than the unprocessed base materials. The greater maximum spinning speed of the tool, lesser tool travel speed and medium of tool pin sizes composes the maximum tensile strength on the processed regions of A356 alloy. The maximum greater efficient of fine grain structure composes the excellent grain boundaries in the stirred regions and then enhanced grain boundaries produces the maximum obstruct to dislodging transferring of particles which is openly superior to the obstruct per unit length of dislodging in the processed ceramic based composites. The connected strengthening particles highly praised to protect the dislodging shifting and migrated stress from the A356 to Cr2O3 particles. Figures 3 and 4 shows the outputs of FSPed A356 alloy. Figure 5 shows the hardness on the various processed zones of friction stir processed A356 and Cr2O3.
3.1. Contour Analysis of Tensile and Hardness of Friction Stir Processed A356 and Cr2O3
Figures 6–8 show the contour or interaction effects of different processing of FSP parameters; like tool spinning speed, tool pin sizes and tool travel speed on the friction stir processed A356 alloy and chromium oxide strengthens particles. Figure 6 shows the tool spinning speed and tool pin sizes with conical cylindrical profiles on the attained tensile strength of A356 and chromium oxide particles by the FSP. From Figure 6, it is revealed that the increment of tool spinning speed (1500 to 2000 rpm) and medium sizes of the tool pin sizes (5 mm) shows the maximum tensile strength on the FSPed A356/chromium oxide particles. Figure 7 shows the tensile strength of processed A356 alloy with chromium oxide particles with conducting the different processing factors of tool pin sizes and tool travel speed. Form Figure 7, it is exposed that the mechanical properties are improved between the improved of tool pin sizes from 4 to 5 mm and lesser tool travel speed creates the plasticized region on the stirred zones was the major reason to improves the mechanical strength. Figure 8 exhibits the different processing parameters of FSP like tool travel speed and spinning speed on the processed A356 and chromium oxide particle through the FSP for producing the tensile properties on the stirred portions. From Figure 8, it uncovered that the maximum of tensile values are correlated between the 2000 rpm of tool spinning speed and 90 mm/min of travel speed of tool creates.
Figures 9–11 show the contour or interaction effects of remarkable processing of FSP parameters; like tool spinning speed, tool pin sizes and tool travel speed on the friction stir processed A356 alloy and chromium oxide strengthens particles. Figure 9 shows the tool spinning speed and tool pin sizes with conical cylindrical profiles on the accomplished hardness of A356 and chromium oxide particles by the FSP. From Figure 9, it is discovered that the increment of tool spinning speed (1500 to 2000 rpm) and maximum of the tool pin sizes (6 mm) shows the maximum hardness strength on the FSPed A356/chromium oxide particles. Figure 10 shows the hardness strength of processed A356 alloy with chromium oxide particles with performed the different processing factors of tool pin sizes and tool travel speed. Form Figure 10, it is showing that the mechanical properties are enhanced between the improved of tool pin sizes from 5 to 6 mm and minor tool travel speed generates the well plasticized region on the localized processed zones was the main motivation to advances the mechanical potency. Figure 11 displays the various processing parameters of FSP like tool travel speed and spinning speed on the processed A356 and chromium oxide particle through the FSP for producing the hardness strength on the stirred portions. From Figure 11, it is discovered that the maximum of hardness values are correlated between the 1500 to 2000 rpm of tool spinning speed and 90 mm/min of travel speed of tool creates the consistently dispersed particles on the nugget portion of the intermetallic phases in the processed zones.
3.2. Microstructures
In this investigation, maximum of tensile and hardness attained friction stir processed samples of A356 alloy and chromium carbide particles with influences of processing parameters 1500 rpm of spinning speed, 6 mm of tool pin sizes and 90 mm/min of tool travel speed and 2000 rpm of spinning speed, 5 mm of tool pin sizes and 90 mm/min of tool travel speed, respectively, was conducted for the SEM analysis. Figures 12 and 13 show the SEM image of maximum attained specimens of tensile and hardness. Both the SEM image reveals that the surface appearances are getting finer and smoother. It is fully related to the maximized plastic deformation and sufficient material flow was accomplished by the conical threaded tool pin profiles. when compared to lower dimension of tool pin size like 4 mm, the 5 and 6 mm tool pin sizes creates the better plasticized deformation on the processed region of A356 alloy and also provides the additional shearing impact on the stirred regions. The maximum accumulation of plastic and shearing impacts was the major significant reason for enhancing the hardness and tensile strength. When increasing the tool pin sizes from 4 to 6 mm composes the better dispersed chromium oxide particles in the A356 alloy matrix and also aid to generate the greater mechanical mixing in the FSP.
4. Conclusion
In this investigation, the A356 aluminium alloy and ceramic-based chromium oxide particles were successfully processed by the friction stir processing. The different FSP processing parameters such as tool spinning speed, tool pin sizes, and tool travel speed composes the better smooth finishing surfaces on the processed A356 alloy with reinforcing particles. Out of the different processing constraints, the maximum of tool spinning speed and minimum and maximum of tool pin sizes like 5 and 6 mm and minimum tool travel speed produces the better mechanical properties of tensile and micro hardness. The selected chromium oxide particles creates the sufficient heat while in the FSP and reduces the friction that would generate the more plasticized in the processed zones. The maximum tensile was attained at the processing parameters was 1500 rpm of spinning speed, 6 mm of tool pin sizes and 90 mm/min of tool travel speed. The maximum hardness was accomplished at the process parameters of 2000 rpm of spinning speed, 5 mm of tool pin sizes and 90 mm/min of tool travel speed, respectively. The SEM image reveals that the presence of chromium oxide particles dispersed evenly in the A356 aluminium matrix and it was the major causes for improving the tensile and hardness.
Data Availability
The data used to support the findings of this study are included in the article. Should further data or information be required, these are available from the corresponding author upon request.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Acknowledgments
The authors thank Villa College, Maldives, for providing characterization support to complete this research work.