The fractal dimensions of primary phase morphology in semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring were calculated,and the effect of pouring temperature on fractal dimension of primary phase morphology in semi-solid A356 alloy was researched.The results indicate that it is feasible to prepare semisolid A356 alloy slurry by low superheat pouring and slightly electromagnetic stirring,and there is an important effect of pouring temperature on the morphology and the grain size of the primary phase in semi-solid A356 alloy,in which the reduction of pouring temperature can obviously improve grain size and shape factor of primary phase in semi-solid A356 alloy under the condition of a certain stirring power.The primary phase morphology of semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring can be characterized by fractal dimension,and the primary phase morphology obtained by the different processing parameters has the different fractal dimensions.Solidification of semi-solid alloy is a course of change in fractal dimension.
With the help of an electromagnetic stirring device and alloy melt quenching technology, the microstntcture of semi-solid AZqlD magnesium alloy slurry stirred by a rotationally electromagnetic fieM 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 slurty 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 army of the dendrites to be remelted on the roots to prepare an ideal semiolid 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 AZglD 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.
