The cyclic stress-strain behaviour of age-hardened CuCo and AlZnMg alloy single crystals

Abstract

The cyclic hardening and softening behaviour of Cu-2.0at.%Co, Cu-1.4at.%Co and Al-2.1at.%Zn-1.3at.%Mg was studied in the underaged and peak-aged states on single crystals at plastic stran amplitudes ranging from 5.5 × 10 −5 to 7.8 × 10 −3. The deformation behaviour is compared with that of pure metals and single-phase alloys. Special emphasis is placed on the formation and development of persistent slip bands which form only when a critical stress value is attained during hardening at sufficiently large plastic strain amplitudes. Softening is only observed after the appearance of persistent slip bands. A constant critical stress for persistent slip band formation and experiments with a stepwise increase in the plastic strain amplitude indicate a limited strain capacity of the persistent slip bands. The softening mechanisms are discussed. From the results it may be deduced that a comparable behaviour can also be expected to occur in other age-hardened materials.