Tailoring Thermal Properties of Plasma Spray Ceramic Coatings for Aluminum Molding

Coatings applied on steel molds used for casting aluminum parts have two main purposes: avoid mold metal reaction and modify thermal transfer. The coatings widely known to foundry operators are water-based sodium silicate bonded ceramic suspensions; they are air sprayed and cured on the mold surface and last typically for 100 casting cycles. Why are thermal sprayed coatings that can last over 5000 casting cycles not yet the preferred (standard) mold protection method? They certainly can handle contact with molten aluminum; however their thermal transfer properties are not known to the foundry engineer. This is a major concern since the coating is not sprayed on the shop floor and adjustments are difficult to perform with thermal sprayed coatings. This study aims at developing a knowledge base of the thermal transfer properties obtained using air plasma sprayed magnesium zirconate powders. The thermal transfer properties were assessed on an instrumented mold using the inverse technique for different conditions of coating roughness, thickness and porosity.