Materials Transactions Online

Materials Transactions, Vol.51 No.09 (2010) pp.1574-1580
© 2010 The Japan Institute of Metals

Clustered Shrinkage Pores in Ill-Conditioned Aluminum Alloy Die Castings

Yoshihiko Hangai1, Osamu Kuwazuru2, Takayuki Yano1, Takao Utsunomiya3, Yozo Murata1, Soichiro Kitahara4, Sujit Bidhar5 and Nobuhiro Yoshikawa5

1Department of Mechanical System Engineering, Graduate School of Engineering, Gunma University, Kiryuu 376-8515, Japan
2Department of Nuclear Power and Energy Safety Engineering, Graduate School of Engineering, University of Fukui, Fukui 910-8507, Japan
3Research Organization for Advanced Engineering, Shibaura Institute of Technology, Saitama 337-8570, Japan
4Gundai Co., Ltd., Isesaki 372-0854, Japan
5Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan

The geometric features of clustered shrinkage pores (CSP) in ill-conditioned aluminum alloy die castings were revealed and their effect on the fatigue strength was discussed. To obtain the geometric features of CSP, an observation using a commercial microfocus X-ray computed tomography (X-ray CT) system was carried out and the position and size of CSP were confirmed. However, the detailed geometry of the CSP could not be clearly observed by X-ray CT, because each pore in the CSP was too small to observe owing to the insufficient resolution of the CT image. We developed a serial sectioning system with a polishing machine and an optical microscope. Observation using the serial sectioning system clearly showed that a CSP consists of many interconnected small pores, which formed an extremely complicated shape. The CSP was thought to grow from relatively large gas pores, which connect to small pores and consequently generate a cavity with a huge volume and a complicated geometry. The complex geometry of CSP resulted in the concentration of stress around CSP, and significantly undermines mechanical properties such as tensile strength and fatigue strength.

(Received 2010/4/26; Accepted 2010/5/28; Published 2010/7/14)

Keywords: casting defect, shrinkage porosity, die casting, aluminum alloy, X-ray computed tomography, fatigue, serial sectioning

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