Thermal-sprayed coatings on aluminium for mould tool protection and upgrade

The aim of the research outlined in this paper was to evaluate a range of thermal spray processes High Velocity Oxy Fuel (HVOF) and Atmospheric Plasma Spraying (APS) for the deposition of coatings for the protection and upgrade of aluminium injection mould tooling, particularly for the low-cost and flexible manufacture of automotive components. A rigourous evaluation of coating properties pertinent to the application, including as-sprayed surface finish, hardness, adhesion to substrate and microstructure, and the effect of the coating process on the fatigue properties of a range of typical aluminium alloys was made. The JP5000 (HVOF) system, on the whole, was found to offer the smoothest, hardest, best bonded coatings with the lowest porosity and most homogeneous microstructure, and has the potential to satisfy the requirements for an easily applied, cost effective hard coating, applicable to a range of aluminium alloys. The properties of coatings deposited via APS were not suitable for this application, as they were in general poorly adhered to the substrate, with poor microstructure. There was no correlation identified between the coating adhesion and the substrate material, and, furthermore, the processing by HVOF was not found to be detrimental to the fatigue life of the aluminium substrate.