A study of PVD coatings and die materials for extended die-casting die life

Abstract

There have been some applications of PVD coatings to extend die-casting die life, mainly by reducing molten metal corrosion and erosion to the die. However, die steel heat checking (or thermal cycling induced cracking) resistance is affected significantly by the PVD coatings. This paper presents the results of a systematic study involving three H series and two maraging hot work tool steels with and without TiN, TiAlN and CrN PVD coatings, in terms of heat checking resistance, hardness and impact toughness changes, as well as molten aluminum corrosion resistance. TiN, TiAlN, and CrN PVD coatings can provide significant corrosion and erosion resistance to molten aluminum. However, TiN coating does not last long because of its lower oxidation temperature. The influence of a coating on heat checking resistance is determined by the substrate material and coating variables. Of H10, H13, H19, Marlok and HWM steels, only H19 steel has a significant reduction in heat checking resistance because of the coatings. H19 and HWM steels have much lower impact toughness than H10, H13 and Marlok steels. However, HWM and uncoated H19 steels have much higher heat checking resistance than other steels. HWM has the smallest change in impact toughness and hardness after thermal cycling. The applications of a specific die steel in combination with a PVD coating to address specific problems are also discussed. This die-life extension and cost saving approach is very important because different failure mechanisms occur in different areas in the same die cavity. It is especially true for large and complex automotive dies.