Shear localization and recrystallization in dynamic deformation of 8090 Al-Li alloy

The microstructural evolution in localized shear deformation was investigat ed in an 8090 Al-Li alloy by split Hopkinson pressure bar (strain rate of a pproximately 10(3) s(-1)) at ambient temperature and 77 K. The alloy was te sted in the peak-, over-, under-, and natural-aged conditions, that provide a wide range of microstructural parameters and mechanical properties. Two types of localized shear bands were distinguished by optical microscopy: th e deformed shear band and the white-etching shear band. They form at differ ent stages of deformation during localization. There are critical strains f or the occurrence of deformed and white-etching localized shear deformation , at the imposed strain rate. Observations by transmission electron microsc opy reveal that the white-etching bands contain fine equiaxed grains; it is proposed that they are the result of recrystallization occurring during lo calization. The deformed-type bands are observed after testing at 77 K in a ll heat treatment conditions, but they are not as well defined as those dev eloped at ambient temperature. Cracking often occurs along the localized sh ear at ambient temperature. The decrement in temperature is favorable for t he nucleation, growth and coalescence of the microcracks along the shear ba nds, inducing fracture. (C) 2001 Elsevier Science B.V. All rights reserved.