Effects of die core treatments and surface finishes on the sticking and galling tendency of Al–Si alloy casting during ejection

In the process of high pressure die casting of aluminium alloys tool surfaces are severely damaged by cast alloy sticking and soldering which promote galling during casting ejection. As a consequence, casting quality is lowered and production efficiency is reduced. Although die casting tools are greatly improved by application of diffusion layers and surface coatings, effects of surface topography on performance of such treated tools are scarcely recognized. This investigation gives an insight in the effects of surface topography on the sticking tendency and galling of Al–Si alloy toward the H11 steel, plasma nitrided steel, and duplex treated steel with CrN and TiAlN PVD top coatings. The sticking tendency was evaluated by ejection test during which the force required to eject the sample from the casting was measured. It was found that the ejection force does not depend on chemical composition of the investigated materials. However, the ejection force of coated samples strongly depends on their surface topography. The coated samples which were polished after the deposition exhibited the highest ejection force. Wear conditions inherent in this specific tribo-system are recognised and interpreted for surfaces with different topography. [Display omitted] •Sticking tendency of cast Al–Si alloy was investigated by employing ejection test.•Hot-working tool steel, nitrided and duplex treated surface layers were examined.•Ejection force is found to be independent of the surface chemical composition.•Ejection force of CrN and TiAlN coated samples increased with decrease in roughness.•Coatings post deposition polishing enhances adhesive wear and raises ejection force.