MICROSTRUCTURAL DEVELOPMENT DURING FATIGUE OF A POLYCRYSTALLINE 3003-ALUMINUM-ALLOY

Polycrystalline 3003 aluminum alloy has been cyclically deformed at ro om temperature with constant plastic-strain amplitudes in the range 1 x 10(-4)-5 x 10(-3). At any strain amplitude, stress saturation was no t observed: A monotonic hardening occurred at low plastic-strain ampli tudes less than 5 x 10(-4). Sequence of hardening, softening and secon dary hardening was found at medium strain amplitudes in the range 1 x 10(-3)-3 x 10(-3) Dislocation configurations in fatigued samples depen ded on the strain amplitudes and the number of cycles. At low strain a mplitudes less than 1 x 10(-3), loop patches with a particular periodi city in dislocation arrangement were formed during the first hardening stage, The labyrinth structure composed of dislocation walls periodic ally arranged along the {100} planes was formed during the softening s tage at the medium strain amplitudes. The stable dislocation configura tion after the secondary hardening was found to be the cell structure. The microstructural analysis using transmission electron microscopy i s well applicable to the fatigue life assessments of the 3003 aluminum alloy.