The Role of Current Density Distribution on Local Hardening of 20GL Steel During Electrolytic Plasma Processing

This study investigates the influence of current density distribution on the hardening behavior of 20GL cast steel during electrolytic plasma processing (EPP). Experimental and numerical methods were combined to establish the relationship between discharge dynamics, heat flux, microstructural transformation. Electrolytic plasma hardening was carried out at cathodic voltages of 150 V and 250 V in a 20% Na₂CO₃ solution. The transient evolution of current density was analyzed using a 3D COMSOL Multiphysics model incorporating a vapor-gas shell (VGS) represented as a distributed impedance layer with realistic conductivity and permittivity. High-speed video confirmed that microdischarges preferentially initiate at sample corners, where modeling also predicts local current concentration and heat flux up to 12 MW/m². Experimental current density values (3-4 × 10⁴ A/m²) showed good agreement with the simulations. Microhardness tests revealed that increasing voltage from 150 V to 250 V increases the thickness of the hardened layer (from ~250 µm to ~600 µm) and raises surface hardness (up to 750 HV), while polarization tests showed a 40% reduction in corrosion rate. The results highlight that current density distribution governs the non-uniformity of thermal effects and surface strengthening during EPP, emphasizing the importance of electrode alignment and VGS stability for uniform hardening.