Towards lube-free aluminum high pressure die casting using duplex AlCrN physical vapor deposition coatings

Abstract

Aluminum high pressure castings (HPDC) were successfully produced on two simple but slightly different H13 steel dies that had been coated with AlCrN physical vapor deposition (PVD) coatings and without the use of conventionally-sprayed die lubricants. Over 200 lube-free (no lubricant) castings were produced in both of the dies. Temperature simulations of the dies matched well with thermal camera measurements taken during the trials, and helped explain the positions where small amounts of soldering and aluminum marks developed. Aluminum build-up on the die surfaces was observed as an intermittent phenomenon and did not lead to soldering. Due to the high gate velocities used in these trials, a large fraction of the AlCrN coating was washed out or cracked. No chemical reaction or intermetallic formation was observed on the analyzed surfaces, suggesting that build-up of aluminum on the die surface occurred by mechanical keying rather than by chemical soldering. A mechanistic model was developed to understand the correlation between surface roughness, wetting angle and HPDC pressure, in an attempt to explain why lube-free aluminum HPDC was possible for these simple die geometries, and to shed light on why it is more challenging for more complex die geometries. This study has demonstrated that lube-free aluminum die casting is possible by coating simple geometry dies with duplex AlCrN PVD coatings and suggests that lube-free castings might extend die life.

Keywords

• AlCrN coating
• Lube-free
• Aluminum high pressure die casting
• Soldering
• Build-up