Production of ultra-fine grain microstructures in Al-Mg alloys by coventional rolling

The conditions under which micron-scale grain structures can be developed in two Al-3%Mg alloys by a process of continuous recrystallization, during rolling and plane strain compression to large strains, have been investigated using high resolution electron backscatter diffraction (EBSD). In an Al-Mg-Cr-Fe alloy, it was found that a lower limit to the processing temperature for forming ultra-fine grain structures is imposed by the low mobility of grain boundaries, whilst an upper limit is imposed by grain growth. In an Al-Mg-Sc-Zr alloy containing stable second-phase dispersoid particles, a fine-grained microstructure is formed only at larger strains and higher temperatures due to the interaction of grain boundaries with the dispersoids. It is concluded that although micron-scale grain structures can be produced in Al-3%Mg alloys by deformation processing in plane strain compression, the processing window, which is controlled by both the solute and particle content, is severely restricted. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.