Bi-layered functional coatings were developed to modify the surface of AZ31 and ZE41 Mg alloys intended as biodegradable implant materials for bone repair applications. An inner silane-TiO2 coating was designed to slow down the degradation rate of Mg alloys while a top-most biopolymer layer, composed of collagen or chitosan, was intended to improve bioactivity and biocompatibility of the alloys. Scanning vibrating electrode technique (SVET) and scanning ion-selective technique (SIET) were used to study the localized corrosion phenomena and localized pH evolution of silane-TiO2 coated Mg alloys. Electrochemical impedance spectroscopy (EIS) evaluation of bi-layered alloys in simulated body fluid (SBF) showed that the presence of the biopolymers promotes formation of carbonated compounds within the corrosion products. Localized electrochemical impedance spectroscopy (LEIS) results revealed that the top-most biopolymer layers do not have a detrimental effect on the barrier properties of the silane-TiO2 coating. Indeed, formation of gas pockets evidenced that collagen and chitosan layers trap evolved H2 avoiding its release into the solution at early stages of immersion. The here reported results contribute to elucidate the corrosion mechanisms of AZ31 and ZE41 Mg alloys on the long term in a biological context and provide promising insights into their control via a multilayered coatings.