Ruling Factors of ZDC2 Zinc Alloy Melt Fluidity in Die Casting

This paper describes the effects of casting variables on the fluidity of thin wall ZDC 2 (ASTM-AG40A) zinc alloy die casting using a hot chamber die casting machine. The fluidity was evaluated with the filling weight of 70×100mm square test plates of 0.2 to 1.5mm wall thickness. The fluidity was improved by increasing plunger speed. However, complete filling was not achieved with the 0.2mm thickness plate at any plunger speed when a die lubricant diluted 500times with kerosene was used in usual production. A trial for spraying undiluted oil-type die lubricant on a die cavity shows that complete melt filling is possible even if the wall is as thin as 0.2mm. The effect was confirmed by a heat transfer simulation based on the cooling rate which was obtained by measuring the secondary dendrite arm spacing of the specimen when the zinc alloy was gravity-cast in the test mold sprayed with these two different die lubricants. The result shows that the heat transfer coefficient between the melt and die surface clearly decreased by a thick gas film produced by the thermal decomposition of the undiluted die lubricant; thus the fluidity remarkably improved.