Selection of Initial Mold–Metal Interface Heat Transfer Coefficient Values in Casting Simulations—a Sensitivity Analysis

Mold–metal interface heat transfer coefficient values need to be determined precisely to accurately predict thermal histories at different locations in automotive castings. Thermomechanical simulations were carried out for Al-Si alloy casting processes using a commercial code. The cooling curve results were validated with experimental data from the literature for a cylindrical-shaped casting. Our analysis indicates that the interface heat transfer coefficient (IHTC) initial value choice between chill–metal and the sand mold–metal interfaces has a marked effect on the cooling curves. In addition, after choosing an IHTC initial value, the solidification rates of the alloy near the chill–metal interfaces varied during subsequent cooling when the gap began to form. However, the gap formation, which results in an IHTC change from the initial value, does not affect the cooling curves within the vicinity of the sand–metal interface. Optimized initial IHTC values of 3000 and 7000 W m⁻²-K⁻¹ were determined for a sand–metal interface and a chill (steel or copper)–metal interfaces, respectively. The initial IHTC had a significant effect on the prediction of secondary dendrite arm spacing (SDAS) (varying between approximately 15 microns and 70 microns) and ultimate tensile strength (UTS) (varying between approximately 250 MPa and 370 MPa) for initial IHTC values that were less than the optimized value of 7000 W m⁻² K⁻¹ for the chill–metal interfaces.