Despite their excellent specific mechanical properties magnesium-based alloys are not widely used in the industry due to their high affinity to oxygen. Given the need for lightweight design, there are increasing efforts to replace high density materials by magnesium. One way to cope with the high oxygen affinity of magnesium is the use of thermally sprayed anti-corrosion coatings. However, conventional thermal coating processes have various process-related limitations. A case in point is coating of complex geometries and internal coatings with small diameters that often cannot be realized by conventional processes. Due to the changed process order some of the limitations of conventional coating methods can be resolved by the transplantation of thermally sprayed coatings. This method is a composite casting process for the coating of die cast components, where the thermally sprayed coating is applied to the corresponding area of the mold prior to the casting process. The aim of this study is to compare the effectiveness of transplanted thermally sprayed coatings with corrosion protection properties to conventional coatings deposited by thermal spraying and to discuss the ramifications with respect to industrial applications.

Be it to save the environment or to save money, engineers everywhere attempt to use materials which can’t normally withstand the surface stress they will be exposed to on their own. This is one of the reasons for the constant interest in new and innovative coating technologies. One such innovation is the transplantation of thermal sprayed coatings. In the transplantation process the coating is integrated into a high-pressure die casting process. In contrast to the conventional process chain, the coating is not directly applied to the work piece, but to a mold insert. During the pressure casting the melt infiltrates the coating and thus creates a join. This way the coating is indirectly applied to the die-cast work piece after removal from the mold. Additionally, depending on the materials involved, a material bonding connection similar to brazing is possible and results in an increased adhesion of the coating. A potentially very interesting trait of the transplantation process is, turning an internal coating process into an external coating process. This allows the coating of inside diameters well below the usual limit of an internal spray gun. Due to the high geometric accuracy of the process this can be potentially done without any need for additional finishing steps.

Manufacturing a die-cast workpiece with a thermal spray coating usually requires multiple steps. An alternative approach demonstrated in this study integrates the spray process into a high-pressure die casting step, eliminating the need for surface preparation and post processing of the coating. To achieve this, the coating is applied to a mold insert rather than the workpiece. During pressure casting, the melt infiltrates the coating and thus creates a joint. Depending on the coating and substrate, a bonding connection similar to brazing is possible. The ability to manufacture coatings this way makes it possible to coat inside diameters well below the limit of an internal spray gun.