Quantitative analysis of the deformation modes and cracking modes during low-cycle fatigue of a rolled AZ31B magnesium alloy: The influence of texture

Abstract

The anisotropy of mechanical behavior, as extensively reported in wrought Mg alloys, is ultimately associated with the variation of deformation modes. The influences of texture on the slip/twinning-detwinning activity, cracking modes and mechanical behaviors of a hot-rolled AZ31B alloy during strain-controlled low-cycle fatigue were investigated quantitatively and statistically by quasi-in-situ electron back-scattered diffraction (EBSD) analysis and scanning electron microscopy (SEM) observations coupled with slip trace analysis. The fundamental difference in the cracking modes and fatigue behaviors between the 0°, 45°, and 90° samples (i.e., under loading directions of the normal direction (ND), 45°, and rolling direction (RD)) is ascribed to the distinct activation sequences of deformation modes. The cyclic deformation-mode transitions throughout the whole fatigue life can be summarized as: (I) the 0° sample: basal slip + tension twinning→detwinning + basal slip; (II) the 45° sample: basal slip→ basal slip; (III) the 90° sample: tension twinning → detwinning + basal slip. The underlying mechanism for the texture-dependency of deformation modes is discussed. Cracking modes are also closely related to the texture. Intergranular cracking was the primary cracking mode for the 0° and 45° samples, while tension twinning (TTW) cracking was the major cracking mode in the 90° sample. The factors governing the site where microcracks were nucleated are analyzed.