Dynamics of deformation band formation investigated by high-speed techniques during creep in an AlMg alloy

Dynamics of the deformation band formation during creep in an Al–Mg alloy was investigated by simultaneous high-speed video recording of deformation bands with an extremely high time resolution of 40 μs and measurement of the concomitant acoustic emission. The results are consistent with the mechanism where the trigger of a strain step on the creep curve is the nucleation and rapid widening of a primary deformation band, generating an acoustic emission signal within 1 ms. Correlations between various stages of the deformation band formation, acoustic emission, and stress response are explored in detail. Notably, the stress drop rate and the amplitude of the acoustic emission signal are found to be linearly related. The mechanism of the acoustic emission associated with the initial rapid stage of the band development is discussed. [Display omitted] •Deformation band formation consists of fast transverse growth of an embryo followed by slow lateral widening.•Embryo band has a needle-like form with a parabolic tip shape.•Tip velocity of the embryo band reaches values about ten m/s.•Strong acoustic emission occurs when the embryo band has grown through the specimen.•Linear relation between the stress drop rate and AE signal amplitude is revealed.