Influence of hard plate hot forging temperature on the microstructure, texture and mechanical properties in a lean Mg-Zn-Al alloy

A lean Mg-Zn-Al alloy has been developed through melting-casting and subsequently thermo-mechanically processed within the temperature range of 523 K-723 K, by employing a novel 'hard plate hot forging' method. The elevated temperature deformation not only instigates dynamic recrystallization (DRX) and dissolution of second phase particles, but also transforms the solidification texture into basal fiber texture in the forged alloy. The DRX fraction increases as the forging temperature is raised from 523 K to 623 K, which increases the fraction of fine grains and weakens the strong basal fiber of the deformed alloy. However, further raising the forging temperature to 723 K promotes growth of the recrystallized grains along with nucleation of new ones, which eventually increases the average DRX grain size and re-strengthens the basal fibers. The specimen forged at 523 K exhibits considerably high strength (similar to 306 MPa) due to the larger size and higher area fraction of nano-sized tau-Mg-32(Al, Zn)(49) particles that contribute to stage IV hardening through Orowan mechanism. Conversely, the weakened basal texture resulting from a high DRX fraction lead to an improved ductility (similar to 10.7%) in the specimen forged at 623 K. (C) 2019 Elsevier B.V. All rights reserved.