In this work we present deformation experiments of polymer-coated polycrystalline aluminium sheets. We observe that the straining is accompanied by the development of microstructural defects at the sample surface as well as in the interface between the metal and the different polymers. These defects are due to a variety of dynamical mechanisms which are essentially induced by bulk plasticity of the metal substrate. They micromechanically interact with the polymer coating and transfer some of the metallic roughness to the coating and to the surface.