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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 17    Special 1    November 2007

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Partial melting and re-solidification in partially melted zone during
 gas tungsten arc welding of AZ91 cast alloy
T. P. ZHU1, Z. W. CHEN2, W. GAO1

1. Department of Chemical and Materials Engineering, University of Auckland, NZ
2. Department of Mechanical and Production Engineering, Auckland University of Technology, New Zealand

Abstract:During the welding of AZ91 cast alloy, the presence of eutectic b-Mg17Al12 phase results in constitutional liquation in the original interdendritic regions and in the formation of a partially melted zone (PMZ). In this study, gas tungsten arc welding (GTAW) and partial melting (simulated using furnace, salt bath and Gleeble) experiments were conducted. The results show that practically there would not be a critical heating rate during the welding to prevent constitutional liquation. The gradual change of the re-solidification microstructure within PMZ from base metal side to weld metal side was characterized. A sharp transition from base metal to PMZ has been observed. It is found that the original partially divorced eutectic has become a more regular eutectic in most of the PMZ, although close to the fusion boundary the re-solidified eutectic is again a more divorced one. Proceeding the eutectic re-solidification, a-Mg re-solidified with a cellular growth resulting in a serrated interface. The morphological change affected by the peak temperature and cooling rate will be presented and explained.

 

Key words: Mg cast alloy, partial melting, divorced and regular eutectic solidification

ISSN 1672-7029
CN 43-1423/U

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