Dislocation Activity in AZ31B Magnesium Deformed at Moderately Elevated Temperatures via EBSD

Abstract

Activation of < c+a > type slip in wrought magnesium has typically been associated with forming temperatures of 200°C or higher, while contraction twinning has been observed to be more prevalent at lower temperatures. A recent investigation showed that when AZ31B sheets with strong basal texture were formed in biaxial or plane strain tension at room temperature, contraction twins were observed in banded structures. These banded structures disappeared at moderate forming temperatures of 75°C and 125°C. The hypothesis is that < c+a > type slip was sufficiently activated at the moderate forming temperatures that thinning of the sheet was accommodated less by twinning and more by slip. This paper uses mesoscale electron backscatter diffraction continuum dislocation microscopy in an SEM to determine < c+a > type geometrically necessary dislocation density. Preliminary results suggest that the relative amount of < c+a > geometrically necessary dislocations is unrelated to the onset of twinning.