Materials Transactions Online

Materials Transactions, Vol.59 No.06 (2018) pp.908-916
© 2018 The Japan Institute of Metals and Materials

Hot-Cracking Mechanism in Al-Sn Alloys from a Viewpoint of Measured Residual Stress Distributions

Youichi Saito1, Hidekazu Todoroki1, Yusuke Kobayashi1, Natsuki Shiga1 and Shun-Ichiro Tanaka2

1Technical Research Center, Nippon Yakin Kogyo Co., Ltd., Kawasaki 210-8558, Japan
2New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan

A study was carried out with Al-Sn 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 Al-30 mass%Sn alloy, cracking was initiated at 820 K (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, hot-cracking 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.

[doi:10.2320/matertrans.M2018011]

(Received 2018/01/09; Accepted 2018/03/09; Published 2018/05/25)

Keywords: hot-crack, Al-Sn alloy, X-ray, residual stress, liquid film

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