An experimental study of anisotropic fracture behavior of rolled AZ31B magnesium alloy under monotonic tension

Abstract

Wrought magnesium (Mg) alloys display pronounced anisotropy in their room-temperature mechanical responses. The fracture behavior of Mg alloys, especially its reliance of material orientation, has not been well explored. The current work is an investigation of the anisotropic fracture behavior in a rolled AZ31B Mg alloy by carrying out monotonic tension experiments of specimens taken from the rolled Mg plate with five different material orientations (θ = 0°, 22.5°, 45°, 67.5° and 90°) with respect to the rolled direction (RD). Significant anisotropy is exhibited in the tensile fracture of the rolled Mg alloy. At the macroscopic scale, shear fracture displaying relatively flat fracture surface is exhibited from tension at θ = 22.5° and 45°. Microstructural analysis reveals that fracture at these two material orientations is a result of localized shearing accommodated by basal slips from which both crack initiation and propagation are originated. In contrast, under tension at θ = 0°, 67.5° and 90°, brittle-like fracture is shown where irregular-shaped surfaces composed by ridges and islands are observed. For θ = 0°, microstructural analysis in the vicinity of microcracks confirms that crack forms at the tip and/or boundary of compression and compression-tension double twins. For the cases of θ = 67.5° and 90°, microcrack initiation is due to high-angle grain boundary cracking, which is likely caused by stress concentration due to impingements of none co-zone twin-twin boundaries and tertiary tension-compression-tension twins on the high-angle grain boundaries.