Soldering in high pressure die casting (HPDC), performance evaluation and characterisation of physical vapour deposition (PVD) coatings

During high pressure die casting (HPDC) of aluminium alloys there is a tendency for the molten alloy to react with the steel die, core pins and inserts. This occurrence within the HPDC industry is referred to as ‘soldering’. This is of concern to high pressure die casters because of down-time, due to regular removal of the soldering, reduced die life and degradation of casting quality. The reaction between the tool steel (usually H13) and the molten aluminium involves inter-diffusion and the formation of intermetallic phases. To remove this problem the possibility exists of applying a surface treatment to act as a barrier between molten alloy and the die. During the course of this research project several surface treatments were investigated namely PVD (TiN, CrN, TiCN), Duplex PVD (TiN, CrN, TiCN) and Gas Nitriding for soldering prevention during HPDC with aluminium alloy, and their results are compared to uncoated core pins. The coating selection criterion was based on commercial availability of surface treatments in Australia and suitability of coating properties with H13 tool steel used in molten aluminium alloy (ADC-12). One of the most important findings made during these experiments was the distinction and characterization of build-up on the surface of PVD coatings. It was found that build-up did not necessarily represent formation of intermetallics (soldering) for PVD surface engineered core pins. It addition build-up did not grow in thickness as previously thought and that build-up was influenced by high fluid flow and temperature during HPDC. The characterization of build-up was a fundamental important step in prolonging the performance of PVD surface engineered core pins in HPDC. The experimental results were confirmed by conducting in-plant HPDC trials at Nissan Casting Plant Pty Ltd Australia. The results demonstrate that PVD coatings can improve the resistance to soldering compared to conventional nitrided and un-coated core pins and the need for polishing was eliminated. Knowledge gained during this research program was transferred to NCAP and a guideline for using PVD coatings in HPDC was prepared. A seminar on PVD coating for HPDC was also given to the Australian die casting industry organized by the Australian Die Casting Association (ADCA).