| Wrought magnesium alloys have found wide applications in many different fields, due to its light weight, high specific strength and stiffness, and good damping capacity. In order to reduce defects of wrought magnesium alloy ingots and the macro-segregation of alloying elements, and improve the quality of wrought magnesium alloy ingots, some new continuous casting technologies appear, such as hot top casting, electromagnetic continuous casting and so on. But their facilities are complex and cost too much, and the universal degree is much less than that of the conventional semi-continuous casting.As the main part of the"973"project called microstructure characterization and quality evaluation of magnesium semi-continuous casting ingots, supported by the national basic research program of China, the present study is devoted to study the microstructure and element macro-segregation of typical wrought magnesium semi-continuous casting ingots under different secondary cooling water, casting speeds, and ingot diameters, and the influence of Ce on ZK20 alloy, by means of the metallurgical phase analysis, scanning electronic microscopy (SEM), XRD and DSC analysis. Then the quality of the microstructure of ingots under various conditions was evaluated to provide guidance for the mass production of wrought magnesium semi-continuous casting.The obtained results indicate that,①In the condition of conventional semi-continuous casting, the microstructure can be fined with the increase of the secondary cooling water and casting speed. Uniform and compact structure of AZ31 ingots with completely cracked dendrites can be obtained when the secondary cooling water is 58L/min, and the casting speed is 16cm/min.②From microstructures in the cross section of AZ series magnesium semi-continuous casting ingots, we can see an abnormal phenomenon that, the crystal grains in the edge of the semi-continuousΦ100AZ31 ingot are coarser than those in the center; While other ingots with different diameters have the typical as-cast structure of ingot, which is the structure in the center of ingot is coarser than that in the edge of ingot; there are very obvious and large columnar crystal area near the edge ofΦ165 andΦ170 magnesium ingots; the radial microstructure of ingots becomes more and more uniform with the increase of the diameter of ingots, however, the dimension of AZ91 ingot is so large that the center of ingot can be hardly influenced by the secondary cooling water, and the radial microstructure of the ingot shows obvious differences, so the overall evenness decreases.③The analysis of the longitudinal section of AZ series magnesium semi-continuous casting ingots, show that some dendrites exist near the edge of ingots in the longitudinal section, because of the influence of unidirectional heat conduction caused by the secondary cooling water.④The solute element macro-segregation degree decreases with the AZ series magnesium ingot diameter, and when the diameter of ingot is 300mm, the microstructure and solute distribution is most uniform, and the solute element macro-segregation degree is smallest.⑤Ce has a refining effect on magnesium alloys grains. 0.3%Ce addition into Mg-1.5Zn-0.2Zr semi-continuous casting alloy is found to have the best refining effect; from center to periphery of the ingot, the amount of granular precipitates in the grain reduces and even disappears.
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