2024 aluminum alloy ultrahigh-strength sheet due to two-level nanostructuring under cryorolling and heat treatment
(Institute for Metals Superplasticity Problems, Russian Academy of Sciences, 39 Khalturin str., Ufa 450001, Russia)
Abstract: The effect of rolling to a total effective strain of 2 at the liquid nitrogen temperature and subsequent natural and artificial aging on the structure and service properties of the pre-quenched hot-pressed 2024 aluminum alloy was investigated. Using optical and electron microscopy, and X-ray analysis, it was found that the cryorolling did not qualitatively change the type of the initial coarse-fibered microstructure, but produced a well-developed nanocell substructure inside fibers. Further aging led to decomposition of the preliminary supersaturated and work-hardened aluminum solid solution and precipitation of strengthening phases in the statically recovered and/or recrystallized matrix. As a result, the rolled and naturally aged alloy demonstrated the yield and ultimate tensile strengths (YS= 590 MPa, UTS=640 MPа) much higher than those in the pressed and Т6-heat treated alloy at equal elongation to failure (El~6%). Artificial aging at a temperature less than conventional T6 route could provide the extra alloy strengthening and the unique balance of mechanical properties, involving enhanced strength (YS=610 MPa, UTS=665 MPа) and ductility (El ~10%), and good static crack resistance (the specific works for crack formation and growth were 42 and 18 kJ/m2, respectively) and corrosion resistance (the intensity and depth of intercrystalline corrosion were 23% and 50 μm, respectively).
Key words: aluminum alloy; cryogenic rolling; heat treatment; nanostructure; mechanical behavior; intergranular corrosion