Annealing of Cold and Warm Rolled AZ31B Magnesium Alloy Sheets

Abstract

Annealing experiments have been performed on warm and cold rolled AZ31B magnesium alloy sheets at 200°C in several time intervals. The effect of the amount of deformation, the annealing time, and the presence of intermetallic phases were evaluated to obtain a microstructure constituted of fine recrystallized grains. Micro structural evolution was followed using optical microscopy, scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction and Vickers hardness measurements. After annealing for 60 min, it was found that static recrystallization mostly takes place on cold-rolled sheets with high thickness reduction, refining the grain size below 10 urn. Twins that were observed in warm rolled specimens nearly disappear and micro structure became suitable for further rolling process. Coarse phases of Mg₁₇Al₁₂ were found inside grains and fine precipitation of Al₄Mn and AlMn were detected at grain boundaries, which presented strong pinning effects to prevent the grain growth.