Investigation of microstructure evolution and quench sensitivity of Al-Mg-Si-Mn-Cr alloy during isothermal treatment

摘要

The quench sensitivity of Al-Mg-Si-Mn-Cr alloy was studied through time-temperature-transformation (TTT) and time-temperature-property (TTP) curves. The high quench sensitive region ranges from 250 degrees C to 430 degrees C with nose temperature at about 350 degrees C, where the quenching rate is required to higher than 9 degrees C/s for avoiding the formation of quench-induced precipitates. B'(Al3Mg9Si7) precipitates from the supersaturated solid solution, and gradually transforms to equilibrium beta (Mg2Si) and excess Si phase with increasing isothermal time at 350 degrees C. The loss of the solute atoms in matrix results in the reduction of the aging hardening precipitation and the formation of the precipitate-free zones (PFZs) during artificial aging. The nucleation rate of the quench-induced precipitation is studied by nucleation theory, and the phase transformation kinetics is analyzed through Avrami equation. The Al(MnCrFe)Si dispersoids, (sub)grain boundaries and dislocations are the preferential heterogeneous nucleation sites for quench-induced precipitation. (C) 2020 Elsevier B.V. All rights reserved.