Microstructure and Texture Evolution during Severe Plastic Deformation at Cryogenic Temperatures in an Al-0.1Mg Alloy

The deformation structures formed in an Al-0.1Mg single-phase aluminium alloy have been studied during plane strain compression (PSC) down to liquid nitrogen temperature, following prior equal channel angular extrusion (ECAE) to a strain of ten. Under constant deformation conditions a steady state was approached irrespective of the temperature, where the rate of grain refinement stagnated and a minimum grain size was reached which could not be further reduced. A 98% reduction at 77 K (-196 & DEG;C) only transformed the ECAE processed submicron grain structure into a microstructure with thin ribbon grains, where a nanoscale high angle boundary (HAB) spacing was only approached in the sheet normal direction. It is shown that the minimum grain size achievable in severe deformation processing is controlled by a balance between the rate of compression of the HAB structure and dynamic recovery. The required boundary migration rate to maintain a constant boundary spacing is found far higher than can be justified from conventional diffusion-controlled grain growth and at low temperatures, a constant boundary spacing can only be maintained by invoking an athermal mechanism and is considered to be dominated by the operation of grain boundary dislocations.

Automated summary

Research has shown that in an Al-0.1Mg single-phase aluminum alloy, after equal channel angular extrusion, the minimum grain size reached during plane strain compression at low temperatures cannot be further reduced, leading to the formation of a microstructure with thin ribbon grains. It has also been found that a high boundary migration rate is required to maintain a constant boundary spacing, which exceeds the rate justified by conventional diffusion-controlled grain growth.