Enhancing surface integrity and mechanical characteristics of AZ91D magnesium alloy using Cr–Cu electrode assisted electro-discharge deposition

This investigation explores the electro-discharge deposition (EDD) of AZ91D magnesium alloy using a Cr–Cu powder-compacted electrode to improve deposition rate (DR), surface roughness (Ra). Response Surface Methodology (RSM) with Box–Behnken Design was used to conduct the experiments viz discharge current (Id: 3–7 A), pulse-on time (Pon: 50–90 µs), and coating time (Ct: 3–9 min). DR increased from 2.11 mg/min at 3 A and 50 µs to 4.25 mg/min at 7 A and 90 µs. Conversely, Ra increased 3.43 µm to 4.47 µm with higher Id and Pon, indicating that higher discharge energy promoted deeper crater formation. The developed models for DR and Ra exhibited good accuracy with R2 values of 0.9997 and 0.9998, respectively. SEM analysis revealed dense coating morphology characterised by splat structures and minimal microcracks, while cross-sectional SEM confirmed a uniform layer thickness of 94 µm. Microhardness and adhesion strength achieved at the same parametric condition were 328 ± 12 HV and 48 ± 3 N, respectively. EDS examination confirmed the presence of Cr (59.98 wt.%) and Cu (6.66 wt.%) along with minor oxygen content (5.30 wt.%), indicating the formation of oxides that enhanced durability and hardness, making it suitable for biomedical, automotive, and aerospace applications.