Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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Transactions of Nonferrous Metals Society of China

Vol. 20    No. 2    February 2010

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Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting
WANG Kai(王 开), LIU Chang-ming(刘昌明), ZHAI Yan-bo(翟彦博), ZOU Mao-hua(邹茂华)

College of Materials Science and Engineering, Chongqing University, Chongqing 400045, China

Abstract:Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like α-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, α-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in cavity, microstructural segregation of unmelted α-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.


Key words: AZ91D magnesium alloy; microstructure; semi-solid die casting process; morphology

ISSN 1004-0609
CN 43-1238/TG

ISSN 1003-6326
CN 43-1239/TG

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