MICROSTRUCTURAL FORMATION MECHANISM OF SEMI-SOLID AZ91D ALLOY
来源期刊：Acta Metallurgica Sinica2005年第4期
论文作者：H.T. Chen W.M.Mao Z.S.Zhen X.Y.Zhong
Key words：AZ91D magnesium alloy; electromagnetic stirring; microstructure; semi-solid;
Abstract: With the help of an electromagnetic stirring device and alloy melt quenching technology, the microstructure of semi-solid AZ9lD magnesium alloy slurry stirred by a rotationally electromagnetic field was studied and the experimental results are shown as the following. The primary α-Mg grains are refined obviously when the slurry is stirred by a rotational electromagnetic field during continuously cooling and they are eventually changed to fine rosette grains or spherical grains. If the above semi-solid slurry is further stirred isothermally .for some time,much more spherical primary α-Mg grains can be obtained. If the melt is first cooled down to a given semi-solid temperature and then starts being stirred by the rotational electromagnetic field, the primary α-Mg dendrites will be large, and a longer time will be taken and a larger stirring power will be needed for the secondary arms of the dendrites to be remelted on the roots to prepare an ideal semi-solid slurry. Theoretical analysis indicates that the strong flow motion leads to a more even temperature field and a solute field and stronger man-made temperature fluctuation in the AZ91D magnesium alloy melt so that the spherical primary α-Mg grains are increased in the slurry. Moreover, all the measures promoting the temperature fluctuation will be favorable to the formation of spherical primary α-Mg grains and all the factors increasing the arm's root remelting difficulty will be favorable to the formation of rosette-type primary α-Mg grains.
H.T. Chen1，W.M.Mao1，Z.S.Zhen1，X.Y.Zhong1
(1.School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing100083, China)
Abstract:With the help of an electromagnetic stirring device and alloy melt quenching technology, the microstructure of semi-solid AZ9lD magnesium alloy slurry stirred by a rotationally electromagnetic field was studied and the experimental results are shown as the following. The primary α-Mg grains are refined obviously when the slurry is stirred by a rotational electromagnetic field during continuously cooling and they are eventually changed to fine rosette grains or spherical grains. If the above semi-solid slurry is further stirred isothermally .for some time,much more spherical primary α-Mg grains can be obtained. If the melt is first cooled down to a given semi-solid temperature and then starts being stirred by the rotational electromagnetic field, the primary α-Mg dendrites will be large, and a longer time will be taken and a larger stirring power will be needed for the secondary arms of the dendrites to be remelted on the roots to prepare an ideal semi-solid slurry. Theoretical analysis indicates that the strong flow motion leads to a more even temperature field and a solute field and stronger man-made temperature fluctuation in the AZ91D magnesium alloy melt so that the spherical primary α-Mg grains are increased in the slurry. Moreover, all the measures promoting the temperature fluctuation will be favorable to the formation of spherical primary α-Mg grains and all the factors increasing the arm''s root remelting difficulty will be favorable to the formation of rosette-type primary α-Mg grains.
Key words:AZ91D magnesium alloy; electromagnetic stirring; microstructure; semi-solid;
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