Quenching sensitivity and precipitation kinetics of 2196 alloy
The time-temperature-transformation(TTT)and time-temperature-property(TTP)curves of 2196 alloy extruded profiles were measured by interruption quenching method.The microstructure transformation and precipitation kinetics of 2196 alloy during isothermal treatment were studied by electron probe microanalysis(EPMA),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and Johnson-Mehl-Avrami(JMA)equation.The results show that the nose temperature of 2196 alloy profiles is 375 ℃,the incubation period is 0.9 s,and the quenching sensitive range is 300-425℃.During the isothermal treatment,the coarse precipitate decomposed from the supersaturated solid solution is T1 phase,and the precipitation rate of the second phase is the largest near 375℃.With the extension of holding time,the T1 phase aggregates and grows,and the nano-precipitated phase decreases after aging,and the precipitation free zone(PFZ)becomes wider,resulting in a significant decrease in mechanical properties.According to the S-shape curve fitted by the precipitation kinetic equation,the reason for the maximum quenching sensitivity of the alloy near 375℃is explained,and the precipitation law of the second phase of the alloy in the quenching sensitive range is analyzed.
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