A study was carried out with AlSn alloys having eutectic system aiming at understanding the hot-cracking mechanism considering the factors of temperature, stress and element distribution in the vicinity of cracks. According to the temperature measurement in the cast Al30 mass%Sn alloy, cracking was initiated at 820K (547°C) which corresponded to 0.9 in solid fraction. It was observed that the crack was initiated at the position close to the center but a little bit mold side and propagated toward the Cu and refractory sides. The crack became longer with an increase in Sn content. According to the residual stress distribution, almost zero stress remained in the Sn phase along the hot-crack indicated that the crack was attributed to the liquid film of the Sn phase. On the other hand, compressive stress remained in the both Al and Sn phases beyond the crack-tip indicating ductile behavior in this region. Observation of the fracture surfaces showed that the Sn phases exhibited globular shapes indicating that Sn melted consistently with the results of stress measurement showing almost zero stress values. Therefore, hotcracking mechanism was clarified as a fracture firstly took place at 0.9 in solid fraction due to the liquid film of Sn. After that, ductile fracture occurred at the positions almost solidified when the crack was initiated.
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