Degradation mechanisms of Die coatings used in aluminum pressure Die casting

The degradation behavior of five optimized commercial coating systems, deposited by different PVD processes, on H13 hot working steel, has been studied. Data have been generated from both laboratory and in-plant trials with the primary objective of systematically understanding coating degradation mechanisms that occur during aluminum pressure die-casting. The coatings were characterized both before and after subjection to die casting with respect to stress, phase structure and chemical interaction using optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), and glancing incident X ray diffraction. The results show that each of the commercial coatings provided improved die performance and die life compared with ferritic nitrocarburized surface treatment only of the H13 tool steel. The mechanisms of degradation, cracking and failure of uncoated and coated H13 dies during aluminum pressure die-casting is proposed. The conjoint action between chemical attack of the liquid aluminum alloy and thermal fatigue cracking in the H13 substrate played an important role in the degradation process.