Effects of texture and stress sequence on twinning, detwinning and fatigue crack initiation in extruded magnesium alloy AZ31

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2021-10, Vol.826, p.141941, Article 141941
• Main Authors: Nakai, Yoshikazu, Kikuchi, Shoichi, Asayama, Kaito, Yoshida, Hayata
• Format: Article
• Language: English
• Subjects: Basal plane; Compression loads; Compression tests; Compression–compression fatigue; Compressive properties; Compressive strength; Crack formation; Crack initiation; Crack propagation; Electron backscatter diffraction; Extrusion; Fatigue cracks; Fatigue failure; Fatigue tests; Fracture mechanics; High cycle fatigue; Magnesium alloy; Magnesium alloys; Magnesium base alloys; Orientation; Tensile stress; Texture; Twinning–detwinning; Yield strength; Yield stress
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2021.141941

Several types of cyclic stress were applied to specimens made of an extruded magnesium alloy, AZ31, to elucidate twinning, detwinning, and fatigue crack initiation mechanisms by electron backscattered diffraction analysis. In both the texture and the random orientation, twinning occurred under compressive stress exceeding the compressive yield strength. Detwinning occurred only in the texture upon the subsequent application of tensile stress less than the tensile yield strength of monotonic loading, whereas detwinning did not occur in the structure with random orientation. Under compression–compression fatigue test, successive twinning occurred, which changed the orientation of the basal plane. As a result, the random orientation of grains changed to the texture in which the normal of the basal plane was parallel to the loading direction. Cracks were formed along the boundary of grains with a high Schmid factor of the basal slip system and the misfit of grain on both sides was large. Near the crack initiation site, twin bands were observed; however, detwinning did not occur under the tensile stress after the cyclic compression loading. •Detwinning occurred in texture, but not occurred in random orientation.•Under compression fatigue test, random orientation changed to texture.•Compression fatigue cracks initiated in boundary of high Schmid factor grain.•No detwinning occurred by tensile stressing after compression fatigue.