► Chemical conversion treatment in HF slows down biodegradation of Mg materials. ► In cell culture medium, MgF 2 coating retards corrosion process for at least a week. ► Coated cast Mg and AZ31 are promising candidates for biodegradable implants. Mg-based materials are especially attractive as biodegradable implants, although they degrade so fast in physiological media that corrosion protection is needed. In this work, biodegradation kinetics of powder metallurgy Mg, cast Mg and AZ31 alloy were evaluated by EIS measurements in cell culture medium (DMEM), which simulates closely the physiological media. To reduce their degradation rate, a chemical conversion treatment in HF was applied to form MgF 2 coatings. Results confirmed that this coating slows down the biodegradation rate, especially when formed on cast Mg and AZ31, retarding the corrosion process in the cell culture medium for at least a week.