Characterization and kinetic modeling of secondary phases in squeeze cast Al alloy A380 by DSC thermal analysis

Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C·min^(-1) were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy(SEM) with energy dispersive X-ray spectroscopy(EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al_2Cu), β(Al_5Fe Si) and Al_(15)(FeMn)_3Si_2. Two kinetic methods are employed to calculate the activation energies of the three common troughs and three common peaks in DSC curves of SC A380. The activation energies of the identified reaction θ_(CuAl_2) = α(Al)+β(Si) is 188.7 and 187.1 k J?mol^(-1) when the activation energies of reaction α(Al)+β(Si)→θCu Al_2 is^(-1)22.7 and^(-1)21.8 k J?mol^(-1), by the Kissinger and Starink methods, respectively.

Si_3N_4-doped Zr_(50)Al_(15)Ni_(10)Cu_(25) glassy alloy by mechanical alloying and sintering process

Zr50Al15Ni10Cu25 amorphous powder was synthesized by mechanical alloying.The effect of Si3N4 addition on the crystallization behavior of the alloy during sintering process was studied.Thermal stability of the powders was performed by differential scanning calorimetry(DSC).The phase and microstructure of the powders and bulk specimens sintered were determined by X-ray diffractometry(XRD) and scanning electron microscopy(SEM).The results show that,introducing 0.05%(mass fraction) Si3N4 can enhance the crystallization activation energy of the Zr50Al15Ni10Cu25 amorphous powders,which indicates that Si3N4 addition has hindrance effect on forming crystals from Zr50Al15Ni10Cu25 amorphous powder.However,0.10% Si3N4 results in the decrease of the crystallization activation energy,which makes its crystallization process easy to occur.

Static recrystallization process comparison of AZ31 magnesium alloy deformed by cold compression and cold forging

We deformed AZ31 magnesium alloys by cold forging and cold compression process,and investigated their static recrystallization kinetics during the annealing process.The results demonstrate that the relationship between the annealing time and the fraction of recrystal grains can be described by the Johnson-Mehl-Avrami-Kolmogorov(JMAK)equation.Based on the kinetics analysis,we calculated that the activation energy of recrystallization by cold forging and cold compression were about 53.5 kJ/mol and 85.0 kJ/mol,respectively.The activation energy of cold compression process was higher than that of the cold forging process because the latter had high-rate deformation,which caused more energy storage during deformation.