Twinning, recrystallization and texture development during multi-directional impact forging in an AZ61 Mg alloy

Multi-directional impact forging (MDIF) with high strain rate shows high grain refinement efficiency and texture randomization effect in magnesium alloys. AZ61 Mg alloy was subjected to MDIF process, and the related grain refinement mechanisms and texture development were investigated. MDIF resulted in a homogeneous microstructure with fine grains of 11 mu m and non-basal texture, which was ascribed to the consecutive twinning and dynamic recrystallization (DRX). During the early forging passes, twin-induced DRX associated with {10-11} contraction and {10-11}-{10-12} double twins, and the coalescence and intersection of {10-12} extension twins with various variants effectively refined the coarse original grains and randomized the texture. With continuous forging, continuous and discontinuous DRX subsequently took place and eventually led to the fully DRXed microstructure and double-peak texture. Besides, fine spherical beta-Mg17Al12 particles were dynamically precipitated along the original grain boundaries, acting as the preferred nucleation sites for DRX by particle-stimulated nucleation mechanism (PSN). Meanwhile, these particles became effective pinning obstacles for suppressing the DRXed grain growth. (C) 2015 Elsevier B.V. All rights reserved.