Search

The quenching sensitivity of an Al–Zn–Mg–Cu alloy containing trace amounts of Sc and Zr is studied by interrupted quenching experiments. Electrical conductivity of the quenched samples and the hardness of the samples subjected to one-stage and two-stage aging, are measured to construct the time–temperature–transformation (TTT) curves and the time–temperature–property (TTP) curves. It is revealed that the quenching sensitivity of the alloy is mainly influenced by the precipitation of coarse η phases during slow quenching, which preferentially nucleate and grow at grain boundaries and at the Al3(Sc, Zr) dispersoids that are incoherent with the matrix. The quenching sensitivity increases with the size and quantity of the coarse η phases. The nose temperature is 290 °C for both TTT and TTP curves, where the phase transformation rate is the fastest and the quenching sensitivity is the highest. Compared to one-stage aged samples, two-stage aged samples exhibit lower quench sensitivity due to the reduced transformation rate from η′ phases to η phases after slow quenching. The quenching sensitive temperatures range from 206 to 358 °C for the one-stage aged samples and from 213 to 352 °C for the two-stage aged samples. Moreover, based on the simulated TTT and continuous cooling transformation curves, an optimized quenching process is proposed in the present work. [ABSTRACT FROM AUTHOR]

The intergranular corrosion (IGC) resistance of the Al–Mg–Si alloy with low Zn addition treated by the interrupted aging treatment (T6I6) was investigated. The IGC results of the Al–Mg–Si alloy show that IGC resistance is enhanced by T6I6 aging treatment. The EIS results reveal that the T6I6-treated Al–Mg–Si alloy has lower double layer capacitance and higher charge transfer resistance than the T6-treated alloy. The superior IGC performance of the T6I6-treated alloy may be attributed to the finer and more densely distributed precipitates within the grains, smaller and discretely distributed precipitates along the grain boundaries and narrower precipitate-free zones (PFZs) compared to the T6-treated alloy. [ABSTRACT FROM AUTHOR]