Microstructure Evolution Of Al-Al₂Cu Eutectic Alloy Under Different Solidification Conditions

Eutectic alloy due to its excellent mechanical properties and forming industrial flexibility,widely attention and application in life,they can be used as a function of in situ composite material or structure in situ composites.In the process of eutectic solidification,the microstructure evolution will under the condition of different into various forms of organization.The properties of alloy materials are closely related to their microstructure to a large extent.For eutectic alloy during directional solidification organization a lot of research is in the ideal conditions for the qualitative analysis of the factors which influence,but in the practical application of the influence factors of alloy solidification structure evolution is not a complete unified growth mechanism to explain,further studies are needed.In this paper,on the basis of predecessors'research work,in order to Al-Cu eutectic alloy as the research object,using the vacuum arc furnace,high vacuum drop-down area,directional solidification furnace experiment mainly analyzes directional solidification are discussed under the condition of different initial composition,alloy at different cooling rate,different draw speed,power and transition acceleration of Al-Cu eutectic alloy solidification microstructure evolution.Al-Cu alloys with copper content of 30.2wt%,33.2wt%and 38.2wt%were selected for directional solidification experiment in vacuum arc melting furnace.The effects of different initial composition and different cooling rate on the microstructure evolution of the alloy were studied.Under the same composition,with the increase of cooling rate,the layer with the reduce of eutectic spacing and the for the Al-38.2wt%of Cu alloy,the increase of cooling rate,can inhibit the precipitation of primary phase Al₂Cu and grew up,the primary Al₂Cu phase by elongated ellipsoid to tiny change,its growth mode also will be a small plane into a small plane.The alloy with initial composition of Al-33.2wt%Cu was selected to conduct directional solidification experiments with different pull-down and transition speeds in a high-vacuum zone directional solidification furnace.Mainly studied the different power and the influence of different speed on microstructure morphology evolution.Results show that by alloy solidification of the highest interface growth temperature theory,we calculate to get fully coupled growth of the eutectic organization,its draw speed need to be less than 1.02?m/s,and in the setting of the speed,the primary Al₂Cu phase general ahead of two coupled growth of the eutectic phase;With the increase of the pulling rate,the cytoplasmic eutectic structure gradually changed into the shape of rod-shaped eutectic structure and cytoplasmic dendritic structure,and the morphology of the irregular ribbed planar primary phase Al₂Cu became larger,and its growth characteristics changed from planar to non-small plane,and the lamellar eutectic spacing became smaller,and the eutectic phase grew closer to the direction of heat flow.The bifurcation and re-nucleation of Al₂Cu phase is one of the reasons why the eutectic spacing decreases with the increase of speed.The flow of hot solute will gradually reduce the primary Al₂Cu phase during the pulling process of the alloy.The transition to accelerate the directional solidification experiment with the initial composition of Al-33.2wt%Cu was carried out in a pull-down vacuum high pressure zone directional solidification furnace,we found that the sudden increase of draw rate can change the morphology of primary phase Al₂Cu,and generate some stick eutectic organization;Transition to speed up the layer of eutectic spacing ratio under the same constant speed more small;Warp speed will produce a large number of tissue defect,and mismatch moving boundary is adjustment layers piece the size of the eutectic spacing of a mechanism.