Abstract
Friction stir processing (FSP) has evolved as an important technique in fabrication of metal matrix composites. The surface properties enhancement is obtainable by insertion of desired discontinuous particular reinforcements into base alloy using FSP. Despite having high specific strength, more applications of Al alloys are restricted due to their poor surface properties under various loading conditions. In this study, the main focus is on enhancing the microhardness and wear properties of Al 7075 base alloy by means of uniform dispersion of silicon carbide and graphite (SiC/Gr) nano particles into the base alloy using the FSP technique. The tool rotational speed (w: 500, 1000, 1500 rpm), tool traverse speed (v: 20, 30, 40 mm/min), reinforcement particles hybrid ratio (HR: 60:40, 75:25, 90:10) and volume percentage (vol%: 4%, 8%, 12%) are used as independent parameters. The effect of these parameters on microstructure, micro hardness and wear properties of surface composites are studied in detail. For desired wear rate and microhardness as responses, the aforementioned independent parameters are optimized using response surface methodology (RSM). The significance of factors and their interactions for maximizing hardness and minimizing wear rate and coefficient of friction (COF) were determined. Analysis of variance (ANOVA) for responses has been carried out, and the models were found to be significant in all three responses. The minimum wear rate of 0.01194 mg/m was obtained for parameters w 1500 rpm, v 40 mm/min, HR 60:40, vol% 4 (Run 10). The maximum micro hardness of 300 HV obtained for parameters w 1000 rpm, v 30 mm/min, HR 75:25, vol% 12 (Run 14). The presence and uniform distribution of SiC and Gr into the base alloy was confirmed through field-emission scanning electron microscopy (FESEM) imaging, energy-dispersive X-ray spectroscopy (EDX) and mapping tests. The wear rate and COF decreased significantly due to graphitized mechanically mixed layer developed at the sliding contacts. The microhardness of resultant composites observed to be dependent on effect of the independent parameters on extent of inherent precipitates dissolution and grain size strengthening in the resultant materials.
Highlights
In the engineering materials field, the fabrication of composite materials, related design and manufacturing technology is a significant advance in the area of engineering materials
It has been noted that metal matrix composites (MMCs) offer such tailor-made property combinations required in a wide range of engineering applications [2]
The indentation was measured on two diagonals (d1 and d2 in μm). 5 readings each were recorded on the stir zone (SZ) and the average value is utilized for further analysis
Summary
In the engineering materials field, the fabrication of composite materials, related design and manufacturing technology is a significant advance in the area of engineering materials. The bulk metal matrix composites are produced by using the conventional methods like stir casting [13], powder metallurgy [14], mechanical alloying [15], etc These fabrication techniques have many disadvantages such as reinforcement agglomeration, formation of detrimental phases, and interfacial reactions due to processing above melting point temperature [16,17]. The fabrication of hybrid composites on Al alloys using FSP in order to improve their mechanical and tribological properties is found to be an effective method used by many researchers as discussed before. Attempts with the addition of hard SiC nano particles along with soft solid lubricant Gr nano particles reinforcement with Al 7075 as a base alloy using FSP, in order to improve its tribological properties is not yet reported.
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