Anisotropy of flow during isothermal forging of rolled AZ31B magnesium alloy rolled plate in three orthogonal directions: Correlation with processing maps

A rib-web shape has been forged in AZ31B magnesium alloy rolled plate keeping the forging direction parallel to the rolling direction (RD), the transverse direction (TD) and the normal direction (ND) with a view to evaluate the anisotropy of flow due to the texture in the plate. Forging was conducted at speeds of 0.01–10 mm s−1 in the temperature range of 300–500 °C under isothermal conditions. Forging parallel to RD or TD at temperatures lower than about 400 °C produced elliptical cup-shapes with the major axis aligned with TD or RD respectively. On the other hand, forging parallel to ND at all temperatures resulted in a nearly symmetrical cup-shape. The anisotropy of flow has been attributed to the strong basal texture ({0002}〈101¯0〉) in the rolled plate and the dominance of prismatic slip at lower temperatures. At temperatures higher than 400 oC or when forged parallel to ND, pyramidal slip dominates along with cross-slip as the recovery mechanism, which destroys the initial texture and restores the symmetry of flow. The grain size variations for forgings validated the predictions of the processing maps both in the dynamic recrystallization domains and bifurcations for all the three orientations.