EVALUATION OF THE SURFACE HEAT FLUX IN THE SECONDARY ZONE DURING THE DIRECT-CHILL CASTING OF MAGNESIUM ALLOY AZ31

摘要

Accurate knowledge of the boundary conditions is essential when modelling the Direct-Chill (DC) casting process. Determining the surface heat flux in the secondary cooling zone, where the majority of the heat removal takes place, is therefore of critical importance, particularly for the process start-up phase. Industrially DC cast AZ31 magnesium alloy samples were instrumented with thermocouples, preheated in an electrical furnace and sprayed with water jets to simulate the secondary cooling zone of the DC casting process. The surface heat flux in both the water jet impingement zone and the water film free-falling zone was then evaluated using the measured thermal history data in conjunction with a two-dimensional inverse heat conduction (IHC) model developed at the University of British Columbia. For the set of conditions studied, the water flow rate was found to exert no significant effect on the surface heat flux when the sample temperature lies below 350℃ at the start of a cooling experiment.