Effect Of Electromagnetic Field On The Solidification Structure Of LW6807Alloy

Synchronizer ring gear transmission system is a key part of automotive. Chinese automotive industry started to equip the variable-speed system with synchronizer since1960s. Brass containing Mn, Fe, Si is widely used in producing synchronizer ring, but the macrosegregation in semi-continuous casting alloy greatly decreases the life time of the product. Northeastern University has done many works on refining casting structures of alloys. In the present work, the microstructures of the semi-continuously casting LW6807alloy and the effects of electromagnetic field on the solidification structures are investigated, and the main results are as follows:1. The microstructure of the semi-continuous casting alloy LW6807alloy consists of equiaxed matrix β and second phases with different sizes and shapes. The grain size increases from the edge to the center of casting.2. There are two kinds of second phases in the cast alloy. One is coarse acicular or blocky (Mn, Fe)5Si3and the size of it becomes smaller and the amount gets more from the edge to the center of casting. The other is Mn5Si3and much smaller (<10μm), has the shape of needle, globe or skeleton, and homogeneously distributes in the matrix.3. The alloying elements of Al and Zn completely dissolve in the matrix, while, nearly all the Fe and Si form compounds, Some Mn solute in the matrix and the others form compounds.4. Electromagnetic field can significantly refine the grain of LW6807alloy, restrict the formation of coarse needle and bulk shape phases, decrease the size of compound and make them homogeneous. The above effects become obvious with increasing the current intensity or current frequency.