Process optimisation, surface integrity, and microstructural characterisation of EDM-Machined AZ31, AA6061, Al6082-Si ₃ N ₄ composite, and cupronickel alloys using multiple electrodes: A Taguchi–Grey relational analysis approach

This study investigates the machinability of four non-ferrous materials alloys such as AZ31, AA6061 aluminum alloy, Al6082–10%Si3N4 metal matrix composite, and Cupronickel, using electrical discharge machining (EDM) with copper, brass, graphite, and cryogenically treated copper electrodes. A Taguchi L16 orthogonal array combined with Grey Relational Analysis (GRA) was employed to optimize four performance responses: surface roughness (Ra), machining time (MT), material removal rate (MRR), and tool wear rate (TWR). Discharge current was identified as the most influential parameter, contributing 42.7% to MRR and 51.6% to TWR. The lowest TWR of 0.00017 g/min and minimum surface roughness of 6.77 µm were achieved using Cupronickel and brass electrodes, respectively. The statistical adequacy of regression models was confirmed with high coefficients of determination R² > 0.97 and validated using Shapiro–Wilk residual normality tests. Multi-response optimisation through GRA yielded a maximum grey relational grade of 0.706, verified through confirmation experiments showing improvements of 59.3% in Ra and 73.1% in TWR. SEM analysis revealed crater formation, recast layers, and electrode material transfer. XRD confirmed phase transformations, including MgO in AZ31, CuAl2 in AA6061, MgAl2O4 spinel in Al6082 composite, and oxide layers in Cupronickel.