Development of duplex nitrided and closed field unbalanced magnetron sputter ion plated CrTiAlN-based coatings for H13 aluminium extrusion dies

Extruded aluminium alloy is already a ubiquitous engineering material, but there is increasing demand for aluminium-based metal matrix composites (MMCs) with improved stiffness and wear resistance to further extend the material's range of application. The extrusion of MMCs containing significant quantities of hard, second-phase particulates places particular demands on the die, which must obviously maintain its critical mechanical and tribological characteristics, while resisting chemical and abrasive wear during exposure to the flowing aluminium MMC under conditions of high temperature and pressure. Many advanced applications demand the fine control of both the dimensional tolerance and surface finish of the extrudate, while maximising the productive lifetime of the associated die and minimising scrap, setup costs, etc. The development of an advanced duplex treatment for H13 steel extrusion dies, combining gas nitriding and closed field unbalanced magnetron sputter ion plating (CFUBMSIP) of high-performance CrTiAlN-based coatings, is described. Both the intended application and the detailed laboratory testing of coated substrates, using the pin-on-disc and abrasive wear testing are reported.