Interplay among Coating Thickness, Strip Size, and Thermal and Solidification Characteristics in A356 Lost Foam Casting Alloy

Abstract

The aim of this research was evaluation of the solidification parameters of A356 alloy, e.g., dendrite arm spacing (DAS), correlation between cooling rate (CR) and DAS, hot tearing, and microstructural analysis at different coating thicknesses and strip sizes during the lost foam casting process (LFC). To achieve this goal, the DAS was measured at six coating thicknesses and six different strip sizes. In addition, thermal characteristics, such as the CR, temperatures of start and finish points of solidification, recalescence undercooling, and hot tearing susceptibility (HCSC), at five coating thicknesses were recognized from the cooling curves and their first derivative and the solid fraction curves, which have been plotted through the thermal analysis technique. The pouring temperature and strip size were fixed at 1063 K (790 °C) and 12 mm, respectively. Besides, to derive a numerical equation to predict the CR by measuring the DAS in this alloy, a microstructural evaluation was carried out on samples cast through 12-mm strip size. The results showed that both coating thickness and strip size had similar influences on the DAS, in which, by retaining one parameter at a constant value and simultaneous enhancement in the other parameter, the DAS increased significantly. Furthermore, at thinner coating layer, the higher amount of the CR was observed, which caused reduction in the temperatures of both the start and finish points of solidification. Also, increasing the CR caused a nonlinear increase in both the recalescence undercooling and the HCSC.