Study On The Dendrite Refinement And Properties Of CuNiMnFe Alloy

III As one of high strength and nonmagnetic materials,CuNiMnFe alloy is widely used especially in military field.While in the process of the application,the master alloy remelted will cause its dendrite microstructure becoming bulky and primary precipitate dispersing seriously,which will lead poor plasticity and toughness after strenthening by solution and aging treatment.In this paper,the refinement mechanism of microstructure is studied by adjusting the high melting point element Fe content in the alloy,and changing the cooling conditions after the alloy remelted.IPP software is used to calculate the length of primary dendrites arms and the spacing between secondary dendrite arms.Then analyse the relationship between the refinement of the branch crystal size and the composition of the alloy.The microstructure observed by metallurgical microscope and scanning electron microscopy(SEM),the phenomenon,dendritic segregation,was investigated by the energy disperse spectrum(EDS),the solid solubility and the lattice change were analyzed by X-ray diffraction.The results showed that:(1)When the CuNiMnFe alloy after secondary remelted under furnace cooling condition,the dendrites microstructure becomes bulky,the spacing between secondary dendrite arms increases from 24.32?m to 65.73?m,in addition,the segregation degree of high melting point element Fe increases,which will form primary phase FeMn,about 1?m,gathering in the dendrite and grain boundary causing the hardness and tensile strength decreased.(2)With the content of Fe in the CuNiMnFe alloy increasing,the number of nucleation increases and the dendrite size becomes smaller,which shows that the dendrite arms in the structure become shorter.Tensile strength of as-cast alloy increases and elongation rate is about 50%.After aging treatment,hetensile strength and hardness of the alloy show a growth trend,while the elongation of the alloys is stable at 5~6%.(3)During the solidification process of CuNiMnFe alloy after secondary remelted,the dendrite structure of CuNiMnFe alloy turns to be refined significantly with the cooling capacity of medium increases,the spacing between secondary dendrite arms decreases obviously.Back stepping by Kirkwood secondary arm coarsening model,it can be learned that when the cooling rate is between 0~50k/s,the secondary dendrite arms spaces change significantly.When the cooling rate is over 50k/s,the secondary dendrite arms spaces decreases slowly.