Using the Method of an In-situ Thermal Analysis Array in a Cast Section of an Engine Block Casting to Diagnose the Cause of Shrinkage Porosity

摘要

Hot spots are undesirable occurrences during the cast solidification process since they lead to a higher level of porosity in the cast structure. Many techniques have been developed to identify the propensity of hot spots and they include using thermocouple arrays in cast moulds. This work was done in order to determine the specific solidification kinetics, which occurred in the cast section of interest, that yielded the observed shrinkage porosity. The observation of, what will be described in this work as, a latent heat generated hot spot phenomenon was made. This phenomenon resulted in cooling rates for the primary α-Al dendritic phases and for the Al-Si eutectic to change from one cast section to another. This was the result of the accumulative heat extraction by the mould wall and the partially solidified metal and the latent heat release of the solidifying Si crystals.