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Background: Machining hybrid composites through conventional machining technique was a challenging task as it produces excessive tool wear and exhibits poor surface roughness. In this research work, an attempt was made to electric discharge machining of AA7075/SiCP/B4CP Hybrid Composites produced through the stir casting route. Objective: The used engine oil was as the dielectric fluid with the objective of obtaining wealth from waste. The experiments were performed by varying distinct Electric Discharge Machining (EDM) process parameters with the goal of obtaining a high Material Removal Rate (MRR), low Tool Wear Rate (TWR) and least Surface Roughness (Ra). The experimental runs were optimized using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) optimization techniques. Methods: Experimental runs were designed using the L20 Taguchi orthogonal array in which Powder concentration, Current and Pulse on time were varied for three different levels, and two various dielectric fluids were used for investigation. The characteristics of the Used Engine Oil (UEO) were assessed to find its feasibility as a dielectric fluid. Results: In comparison to EDM oil, the specimen machined in UEO dielectric medium has a somewhat greater MRR. Regardless of the kind of dielectric fluid employed, adding Al2O3 particles increases the MRR because of the bridging effect. Due to its high thermal conductivity, UEO oil produced electrodes with a TWR that was greater than that of EDM oil. The TWR decreases with the addition of Al2O3 particles due to an increase in the spark gap. In comparison to EDM oil, the specimen machined under UEO displays a lower Ra value. Ra decreases with the inclusion of Al2O3 particles due to the thorough flushing of machining waste. Conclusion: The specimen machined under Al2O3 mixed UEO dielectric medium, with the process parameters tuned at 3A current and 20µs Ton, offers better machining performance and was recommended for EDM sector.

The study is fundamentally geared toward the investigation of the influence of Manual Metal Arc (MMA) welding on the mechanical and microstructural properties of low carbon steel immersed in a 0.5 M nitric acid environment having a pH of 0.3. The corrosion and mechanical behavior of the substrates are investigated prior to and after 336 h of immersion in the test environment. The outcome of the experiment shows that the structural integrity of the immersed substrates is affected due to corrosion in the test environment. Prior to immersion, the bending resistance is seen to decrease at the welded joints relative to the blank sample and then decrease further after immersion in the test solution respectively as 3.95, 3.53, and 4.21KN. Similarly, the tensile strength of the immersed substrate decreases as compared to the unexposed and blank samples; exposed to test environment (30.60%), welded unexposed to test environment (33.25%) and for the control sample (36.33%). Furthermore, the hardness value is observed to be higher at the heat‐affected zone (HAZ) of the test substrate than at the weldment and parent metal, respectively, as 11.3, 17.7, and 15.7HV. Optical micrographs prior to and after immersion have evidently revealed that heat input during welding has caused recrystallization leading to coarser grains at the HAZ.