The anions should not react with the anodic metal to generate a passive film on the anodic surface. The cations in the electrolyte solution should not deposit on the cathode surface, so that the cathode shape remains unchanged. To satisfy this requirement, electrolytes with alkaline metallic cations, such as potassium and sodium, are used. The electrolyte should have a high electrical conductivity and low viscosity to reduce the power loss due to electrolyte resistance and heat generation and to ensure good flow conditions in the extremely narrow interelectrode gap. The electrolyte should be safe, nontoxic, and less erosive to machine.
Neutral salts are preferred.
Acid electrolytes are used only for small hole drilling when the reaction products need to be dissolved into the electrolyte. The electrolyte should be able to maintain its stable features, such as its ingredients and pH value, during the machining period, and its conductivity and viscosity should have small variation due to temperature. The electrolyte should be cheap and easily available. The electrolyte plays an important role in ECM dimension control. The most important feature of the electrolyte in this regard is the relationship between the current efficiency and current density.