Grain Refinement in the Surface Layer of AZ31 Mg Alloy Sheet Processed by Cyclic Bending

摘要

Grain refinement in the sheets of magnesium alloy AZ31 was studied by means of cyclic in-plane bending at 423K. The deformed and subsequent annealed microstructures were investigated by optical and SEM/EBSD metallographic observation. Deformation twins are frequently formed in the original grain interiors. Bending induces a gradient structure with high-density twins in the surface layer and, in contrast, lower density ones in the center. The grain size in the surface layer is refined steadily with increasing strain passes due to operation of twin dynamic recrystallization based on twin intersections. After bending of 6 passes at 423K followed by a subsequent annealing at 523K, the average grain size in the surface layer was reduced to about 10 μm from the original size of 46 μm. In particularly, the relative intensity of the strong texture developed in the sheets was severely weakened by repeated bending.