Estimation of multiple heat-flux components at the metal/mold interface in bar and plate aluminum alloy castings

In the present investigation, a serial solution of the inverse heat-conduction problem (IHCP) is extended for Al-3 pct Cu-4.5 pct Si alloy square bars and rectangular plates cast in metal molds. The metal/mold interface was divided into three segments, viz., the half face, the quarter face, and the corner. The heat-flux transients during casting solidification were then estimated at these segments. Three configurations were considered, viz., (1) one boundary segment for the whole length on the interface, (2) two boundary segments delineating two heat-flux components, and (3) three boundary segments leading to three heat-flux components. In order to identify the most acceptable spatial distribution of interface heat flux, two types of analyses were performed on the results of the IHCP, viz., convergence of absolute error in the computed and the measured temperatures at the sensor locations and total heat energy transferred across the boundary from the casting to the mold. The error convergence at the thermocouple locations was more or less identical for all the three cases in both bars and plates. However, the total heat absorbed by the mold, in the case of the one-segment model in bars and the three-segment model in plates, was found to be a minimum. This indicated that the interface heat flux did not show any spatial distribution in the case of bars, while a distinct spatial distribution could be identified in the case of plates. The individual heat fluxes at the different interface segments for the plate casting showed a peak within 3 to 3.5 seconds of pouring, after which it reduced and reached stable values in about 200 seconds. The maximum heat flux occurred at the corner segment. The analysis of heat-flux gradients showed that the air gap initiated at the corner and spread toward the center.