Cast Alloy Soldering Tendency and Corrosion Resistance of Duplex PVD Coatings for Application on Die Casting Tools for Aluminum Alloys Processing

摘要

Wear resistance of die casting tools used for aluminum alloys processing is successfully increased by application of duplex PVD nitride coatings. However, their performance greatly depends on few surface characteristics which are often overlooked. These are coatings topography, growth defects morphology and variable nature of surface chemistry. This investigation concerned Hll steel, plasma nitrided steel, CrN and TiAIN PVD coatings deposited in the form of duplex layers, all prepared on different levels of surface roughness. Soldering and corrosion behavior in cast Al-Si-Cu alloy were evaluated by an ejection test performed on conventional and delayed alloy solidified samples. The coatings outperformed steel and nitrided treatments and exhibited no reaction with the cast alloy in both experimental configurations. By decreasing the coating roughness, the ejection force from the conventionally solidified castings considerably increased. However, the highest ejection force that was recorded for post deposition polished coatings, with delayed solidification, decreased as a consequence of coating oxidation. Corrosion of the nitrided substrate developed through the defects in the coatings, but the observed damage did not compromise coating integrity. In order to achieve the highest coating performance, besides selection of appropriate coating type, focus should be on the surface morphology and transformations of coatings during their use.