Study On Deep Supercooling Solidification Process And Microstructure Of Jinchen Eutectic Alloy By Overlapping Process

Superheating recyle method as a kind of high undercooling solidification,It is not limited by the heat transfer process.In the solidification process, the nucleation can be inhibited and alloyes get high undercooling.Not only the large size alloy can get high undercooling, but also the solidification behavior and microstucture of the alloy by this method have different from equilibrium conditions.In this study, the relationship of the performance which includes the multicomponent cleansing agen、superheating、recyle times and soaking time with the Au-20Sn eutectic undercooling was obtained to explore the largest undercooling. The solidification behavior and evolution in different undercooling solidification microstructure are studied by XRD,SEM and EDX. Main conclusions are drawn as follows:(1) The performance conditions of multicomponent cleansing agen、recyle times、 superheating and soaking times have influence on alloy undercooling.The Au-20Sn has higher undercooling with silicone oil than molten salt. With increaseing the viscosity of silicone oil, the undercooling of Au-20Sn increases first and then decreases.With increasing the superheating, the undercooling of Au-20Sn increases first and then decreases.With increasing the soaking time and recyle times, the undercooling of Au-20Sn increases first and keeps constant, then decreases.(2) Indicated by the theoretical analysis and the experimental result, with the1000cs silicone oil、210K superheating%3min-6min soaking time and2-4recyle times, the Au-20Sn alloy can obtain above0.2Tm (55K) undercooling.(3) The cooling curve shows:①There have three stages in Au-20Sn cooling curve:continuous cold stage,recalescence stage and slow solidification stage.②The recalescence time and velocity is the key difference under different cooling curve. With the increasing the undercooling, the recalescence time decreases and recalescence velocity increases. (4) The study of the Au-20Sn solidification microstructure shows that:①The solification microstructure consists of primary ζ’-Au5Sn phase and matrix organization②With increasing of the undercooling,the size of the primary ζ’-Au5Sn phase is decrease. The morphology of undercooled Au-20Sn alloy from dendrites to sphere,then disappered.③When the undercooling is below28K,the microstructure is regular lamellar structure.When the undercooling is38K～48K, the lamellar structrure is disturbed and the grid structure is formed.When the undercooling is above58K, the anomalous eutectic appeaers.(5) Combined with solidification microstructure evolution and theory of undercooled shows that:When the undercooling is small,δ-AuSn and ζ’-Au5Sn are coupled growth,at last, lamellar structure is formed.When the undercooling is large, two phase symbiotic growth condition is broken and the irregular eutectic is formed.(6) The dendrite remelting model show that:δ-AuSn and ζ’-Au5Sn have different crystalline structure and melting entropy.The simpler crystalline of the δ-1AuSn phase as dendrite nucleas first and grows.Then with the reclensec process, the δ-AuSn phase is fused from the neck of dendrite,which is surrounded by the latter nucleation of ζ’-Au5Sn phase.At last, the irregular eutectic is formed.