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Top1. Introduction
Numerous materials such as Magnesium and its alloys which in addition to the lightweight, have considerable industrial applications in the air transport, electronic gadgets, automobile sector, and human body curing. No Engineering material can possess all the properties and hence the need to combine two or more elements materials arises to possess ideal values of properties to meet design requirements at minimum cost (Azushima et al., 2008; Brama et al., 2007; Hagen, Hort, Dieringa, & Kainer, 2008). Chang et al have first reported FSP of Mg–Al–Zn wherein, the affected zone attains the plastic stage due to heat produced by friction which consequences in recrystallization of the partially melted material, further fused by axial force of the FSP tool. It resulted in enhanced surface properties like hardness to 150 Hv, which was around thrice the value of the matrix. (Chang, Du, & Huang, 2008; Mishra & Mahoney, 2001).
FSP has been successfully applied to produce Al/SiC surface composites with unlike volume fractions of reinforcements and to enhance the microhardness of these composites by sometimes double the value 173 HV compared with 85 HV of 5083Al alloy and the average grain size of 0.7 µm (Mishra, Ma, & Charit, 2003). Sinha et al have tested the scratch hardness of Magnesium based metal–matrix composites adding submicron SiC (4.8–15.4 wt%) and micron-sized Titanium particulates which slightly enhanced the scratch resistance of the composites. At the maximum percentage of SiC, the scratch hardness was found to be approximately 973 MPa compared with the corresponding value of about 721 MPa for pureMg at a normal load of 0.55 N (Sinha, Reddy, & Gupta, 2006). Karthikeyan et al. investigated the role of FSP parameters in the processing of Aluminum alloy A319 by processing its surface at three transverse feed rates and tool rotation with five levels. Tensile strength of the FSPed alloy improved by about 50% and the microhardness improved by nearly 20% as compared to the as-received Al alloy. An increase from 1.5 to 5 by a factor was reported in the ductility of the FSPed alloy (Karthikeyan, Senthilkumar, & Padmanabhan, 2010). Chen et al. examined composite produced by FSP with an in-situ Al-Al11Ce3-Al2O3 reinforcement for the influence of processing factors on mechanical properties and the microstructure (Chen, Kao, Chang, & Ho, 2010). Asadi et al fabricated magnesium-based SiC and Al2O3 reinforced nanocomposite using FSP and analyzed the effects of the number of passes of FSP tool and particle types. SiC reinforcement exhibited better wear resistance after 1,2,4 and 8 passes of FSP as compared to Al2O3 reinforcement which valued at nearly 5x10-3 mm/Nm in comparaison to 17x10-3 mm/Nm in case of base metal (Asadi, Faraji, Masoumi, & Givi, 2011).
Arora et al carried out a parametric study for processing AE42 alloy by FSP. Process parameters were optimized using five-factor and three levels Taguchi L27 array by taking microhardness as output response. (H. Arora, Singh, & Dhindaw, 2012). Asadi et al examined the FSPed AZ91 magnesium alloy for effects of water cooling, the number of FSP tool runs and direction of tool rotational on the microstructure and mechanical properties. Grain size was refined from 150 to ~4 μm enhancing the hardness from 63 to 98 HV and an increase in tensile strength was registered from ~130 to ~250 MPa (Asadi et al., 2012). Taguchi’s technique for the experimental design was applied by Ahmadkhaniha to find the significant controlling FSP parameters including travel speed, tool rpm, its tilt angle and penetration of tool shoulder on hardness value of Mg. Process variables were optimized as 1600 rpm, 63 mm/min, 0.1 mm and 2o respectively for tool rotation, tool feed and tool tilt angle (Ahmadkhaniha, Sohi, Zarei-Hanzaki, Bayazid, & Saba, 2015). Saikrishna et al. studied the corrosion resistance of processed AZ31 Magnesium alloy sheets by FSP to find the effect of the grain refinement and grain size distribution. Grain refinement enhanced the hardness slightly in the nugget zone (Saikrishna, Reddy, Munirathinam, & Sunil, 2016). Titanium (Ti) particles (0,7,14 and 21 vol%) were reinforced into magnesium alloy AZ31 using friction stir processing (FSP) performed by a conventional sturdy vertical milling machine.