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Electrochemical machining is a modern machining technique that plays an important role in the applications of aerospace, die and electronic industries. Electrochemical machining is used to machine difficult-to-machine materials and complex shapes. Machining of alloy steels especially 20MnCr5 is very important for its wide variety of applications such as piston bolts, spindles, camshafts, gears, shafts and other mechanical controlling parts. Machining of the above components with conventional machine tools is a burdensome task. Hence, in this work, an investigation was made to study the electrochemical machining characteristics of 20MnCr5 alloy steel. Two electrolytes, namely, aqueous sodium chloride (NaCl) and potassium dichromate (K2Cr2O7) mixed aqueous NaCl, were used to investigate the machining performance. K2Cr2O7 was selected for its oxidizing characteristics and was included in small proportions in aqueous NaCl bath. The influence of predominant electrochemical machining process parameters such as applied voltage (V), inter electrode gap and electrolyte concentration was studied on the material removal rate and surface roughness (Ra). Scanning electron microscope photography of surface of the 20MnCr5 specimen machined with electrochemical machining was studied to understand the effect of electrolytes during the machining. The contour plots were generated to study the effect of process parameters as well as their interactions. It was noted in the study that the presence of K2Cr2O7 in aqueous NaCl electrolyte increases the material removal rate significantly. The process parameters are optimized through genetic algorithm-desirability function. Optimized operating conditions were found to be quite close with experimental results.

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Novel Al-6061 hybrid composite materials with varying range of SiC particulate and constant weight percentage of B4C particulate and 1% of magnesium alloy were fabricated by the stir casting technique (liquid metallurgy route). The mechanical and tribological properties of the hybrid composites and that of Al-6061 unreinforced alloy were examined by a Rockwell hardness test machine, pin-on-disc test machine, and Optical Microscope and Scanning Electron Microscope (SEM). A plan of experiment generated through Taguchi's technique was used to conduct experiments based on the L27 orthogonal array. The developed analysis of variance (ANOVA) and the regression equations were used to investigate the influence of parameters like sliding speed, applied load, sliding time, and percentage of reinforcement and their interactions on the dry sliding wear and friction coefficient of the composites. The motto of the present study is ‘the smaller the better’ to identify the optimum conditions for dry sliding wear and the friction coefficient. The results indicate that wear rate and friction coefficient were highly influenced by applied load, sliding speed, percentage of reinforcement and sliding time whereas the interaction between these parameters show only a minor influence in Hybrid Metal Matrix Composites (HMMCs). The wear surface morphology and wear mechanism of the pins were investigated using SEM and were correlated with wear test results. Finally, confirmation tests were carried out to verify the experimental results. It is concluded that Al-6061 hybrid composite can replace the conventional material used in the brake disc of automobiles owing to improved hardness and strength and reduced wear rate.