A composite structure includes a passivated substrate, a sealing layer, a conductive layer, and a coating layer. The passivated substrate includes a substrate body made of a metallic material that is magnesium or magnesium alloy, and a porous passivation layer which is disposed on the substrate body, and which is made of an oxide of the metallic material. The sealing layer is disposed on the porous passivation layer, and is made of a sealing material. The conductive layer is disposed on the sealing layer, and is made of an electrically conductive material. The coating layer covers the conductive layer, and includes an electrophoretic material and/or a metal. A method of making the composite structure is also disclosed.