Abstract:N06625 alloy contains a large number of strengthening elements, and solute redistribution and component supercooling will occur during solidification, which will have a significant impact on the microstructure of alloy. The influence of magnesium content on phase transformation behavior and the changes of main elements concentration in the residual liquid phase of N06625 alloy during non-equilibrium solidification was analyzed by Thermo-Calc thermodynamic software, and the effect for different mass fractions of magnesium (0, 0.005 2%, 0.008 1% and 0.025 0%) on the as-cast structure of N06625 alloy were studied by optical microscope (OM) and field emission scanning electron microscope (FESEM). The results show that the solid-liquid phase temperature range increases with the increase of magnesium content, and the precipitation temperature of each phase is changed, but not the precipitation phase type. With the increase of magnesium content, the concentrations of Ni and Mg elements in the residual liquid phase increase, while the concentrations of Cr, Mo, Nb and C elements decrease. When magnesium is not added, the secondary dendrite spacing is larger, and the precipitated phase precipitates in interdendritic area in the form of strip and block, with larger average area fraction and size. When the mass fraction of magnesium in the alloy increases from 0 to 0.005 2% and 0.008 1%, the secondary dendrite spacing is refined, the average area fraction of precipitated phase decreases, and refinement and spheroidization effects occur, the distribution is more dispersed and the degree of element segregation for Ti, Cr, Mo and Nb is weakened. When the mass fraction of magnesium increases to 0.025 0%, the refinement of the secondary dendrite spacing is not obvious, the average area fraction of precipitated phase increases slightly, the refinement and spheroidization effects decrease and the degree of element segregation for Ti, Cr, Mo and Nb increases. Therefore, it is necessary to add an appropriate amount of magnesium elements to N06625 alloy to provide some degree of theoretical reference for optimizing N06625 alloy.
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