Dynamic continuous recrystallization characteristics in two stage deformation of Mg-3A1-lZn alloy sheet

Dynamic recrystallization (DRX) characteristics of a Mg-3Al-1Zn (AZ31) alloy sheet were investigated at temperatures ranging from 200 similar to450 degreesC and constant strain rates of I x 10(-4) -2 x 10(-4) s(-1). The average grain size of the as-received alloy was 12 mum and can be refined to 6 mum via deformation at 250 degreesC, 1 X 10(-4) S-1 to a strain level of 60%. Grain refinement was less effective at higher temperatures due to rapid grain growth. The grain refinement was attributed to dynamic continuous recrystallization which involves progressive increase in grain boundary misorientation and conversion of low angle boundaries into high angle boundaries. During DRX, subgrains were developed through the conversion of dislocation cell walls into subgrain boundaries. The presence of precipitates was not essential for dynamic recrystallization in the magnesium alloy being investigated because of its limited slip systems, low stacking fault energy and high grain boundary diffusion rate. (C) 2003 Elsevier Science B.V. All rights reserved.