Plastic strain-induced grain refinement in the nanometer scale in a Mg alloy

• Published in: Acta materialia Vol. 55; no. 3; pp. 975 - 982
• Main Authors: Sun, H.Q., Shi, Y.-N., Zhang, M.-X., Lu, K.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-02-2007; Elsevier Science
• Subjects: Applied sciences; Dynamic recrystallization; Exact sciences and technology; Grain refinement; Magnesium alloy; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; SMAT; Twinning; Twinning; SMAT; Dynamic recrystallization; Grain refinement; Magnesium alloy; Grain size; Mechanical properties; Dynamical recrystallization; Plastic deformation; Microstructure
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2006.09.018

By means of surface mechanical attrition treatment, nanometer-sized grains (with an average size of 30±5nm) were generated in the surface layer of a single-phase AZ91D alloy. Transmission electron microscopy investigations showed that the strain-induced grain refinement process in AZ91D alloy includes three steps. At the initial stage twinning dominates the plastic deformation and divides the coarse grains into finer twin platelets. With increasing strain, double twins and stacking faults form and a number of dislocation slip systems are activated, including basal plane systems, prismatic plane systems and pyramidal plane systems. As a result of the dislocation slip along these systems and of the cross slips, high-density dislocation arrays are formed which further subdivide the twin platelets into subgrains. Obvious evidence of dynamic recrystallization were identified within the high-strain-energy subgrains with a further increase of strain, leading to the formation of nano-sized grains in the surface layer.