Preparation and in vitro degradation of the composite coating with high adhesion strength on biodegradable Mg-Zn-Ca alloy

► A composite coating is prepared on the magnesium alloy using combined MAO and ED. ► The composite coating is composed of MgO, Mg3(PO4)2, HA and OCP. ► The composite coating has high adhesion strength with the substrate. ► The composite coating improves the corrosion resistance and the surface bioactivity.