The development of coating selection criteria to minimize die failure by soldering and erosion during aluminum high pressure die casting

• Published in: Journal of materials processing technology Vol. 316; p. 117954
• Main Authors: Campos Neto, N.D., Korenyi-Both, A.L., Vian, C., Midson, S.P., Kaufman, M.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-07-2023
• Subjects: Aluminum die casting; PVD coatings; Si-DLC; Soldering; Wear resistance; Wetting; Wear resistance; PVD coatings; Si-DLC; Wetting; Soldering; Aluminum die casting
• ISSN: 0924-0136
• DOI: 10.1016/j.jmatprotec.2023.117954

The steel dies used in aluminum high pressure die casting (HPDC) typically degrade and fail due to the occurrence of different soldering mechanisms or to heat checking. Core pins located directly in front of the gate are especially vulnerable to soldering and premature failure. In this study, four sets of core pins were coated with different PVD/CVD coatings and tested in a die used to produce a large automotive die casting. After production of thousands of castings, the failure mechanisms of these core pins were identified as: mechanical erosion, chemical soldering, gross chemical soldering, aluminum build-up on intact coatings, and coating spallation. The fraction of the core pin surface that suffered soldering was measured and correlated with coating wear resistance and coating wettability by liquid aluminum. These observations were used to establish criteria for coating selection aimed at minimizing failure of the die components by any of the observed mechanisms. These include: a maximum coefficient of friction (COF) of 0.40, a wear rate below 10−8 mm3N−1m−1, and a pin scar diameter ratio (Δd/D) below 0.22. Moreover, coatings that exhibit the lowest wetting angles (low cos(ϴ)) by liquid aluminum tended to minimize the chemical and mechanical degradation that led to soldering. This is the first time that numerical criterion have been developed in an attempt to guide coating selection for aluminum HPDC dies and the results sheds light on possible approaches for extending die component life in aluminum die casting.
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•Several die failure mechanisms were found operative during Al HPDC regardless of the type of protective coating applied.•The best coatings have a COF< 0.40, a wear rate < 10−8 mm3N−1m−1, and Δd/D < 0.22.•The most protective coatings also exhibited low wetting by molten Al.•A Si-DLC PACVD coating outperformed the other coatings studied.