Study On The Solidification Behavior Of The Immiscible Cu-Co Alloy Under Electromagnetic Stirring

The fabrication of immiscible alloys has always been a hard target for solidification researchers, because immiscible alloys are easy to get serious segregation. Many of immiscible alloys have good physical and chemical properties. This research prefer Cu-Co alloy, which is a good contact material and giant magnetoresistance material, but its application needs second phases to be homogenously distributed in the matrix.The technique of electromagnetic stirring (EMS) has the effect to refine crystal grains, and break up large dendrites and droplets. This thesis prefers Cu-15at%Co alloys, to study the effect of EMS on the distribution of second phases and its mechanisms. The morphology of transforming Co-rich phases in deformed Cu-Co alloys has also been studied, together with the electrical property and mechanical property. The thesis has the following results:In this experiment the Cu-Co alloy has a non-equilibrium structure, in which Co-rich phase did not transformed from a-Co into s-Co due to f.c.c.â†'h.c.p. as a structure for pure Co at room temperature, and it has a Cu solute percentage of 15～20%. The average size of Co-rich phase increase with decreasing cooling rate. The length and width of Co-rich dendrite also decrease with decreasing cooling rate. The decreasing of cooling rate is benefit to have small amount of droplets structure, which result in the coarsening of dendrites.The electromagnetic stirring is benefit to inhibit the liquid segregation, and reduce the percentage of liquid Co-rich droplets during solidification. With increasing stirring strength, the length of dendrites tends to decrease because EMS breaks up long dendrites. A proper strength 100-200A EMS tends to get smaller dendrite widths, but EMS with very large strength increase the width of dendrites. A proper strength of 200A EMS is benefit to the deformation strain of Co-rich phases, and increase the hardness and conductivity.