Figure 7. A schematic illustration of the degradation process of polymer-coated samples.
The penetrated solution through PLLA coating (a) or HM/PLLA coating (c) into the interface between the coating and the substrate erodes the Mg substrate and produces H2; (b) PLLA coating is compact and dense, retarding the release of H2 and the H2 accumulated at the interface, leading to peeling and delamination of the coating; (d) the presence of Mg(OH)2 particles deteriorates the density of the polymer coating, providing passages for H2 release, thus avoiding the formation of gas pockets and the delamination of the composite coating.