Copper coating of magnesium alloy AZ31 using conventional electrode EDM for enhanced corrosion resistance

Magnesium alloys such as AZ31 are promising for biomedical applications; however, their rapid corrosion in physiological environments limits their use. Many surface modification techniques for improving corrosion resistance, including powder-mixed electrical discharge machining (EDM), involve added process complexity and limited reproducibility. In this study, copper surface modification of AZ31 magnesium alloy was achieved using conventional electrode EDM without the use of external powders. A Taguchi L9 experimental design was employed to investigate the influence of peak current, pulse-on time, pulse-off time, and gap voltage on surface integrity, mechanical response, and corrosion behaviour. Surface and phase characterization were conducted using SEM, EDS, and XRD, while corrosion performance was assessed through potentiodynamic polarization testing in phosphate-buffered saline (PBS). The results show that EDM processing produced a continuous copper-coated surface layer (with a thickness of approximately 50-60 μm) with reduced surface roughness and increased surface hardness under optimized conditions. Electrochemical testing indicated a reduction in corrosion current density from 9.49 to 2.42 µA/cm², corresponding to a decrease in corrosion rate from 0.111 mm/year to 0.028 mm/year; an improvement of approximately 75%. These findings demonstrate that conventional electrode EDM is a practical approach for modifying the surface characteristics and improving the corrosion behavior of AZ31 magnesium alloy, with potential relevance for biodegradable implant-related applications.