Fracture morphology and crack mechanism in pure polycrystalline magnesium under tension–compression fatigue testing

Abstract

The fatigue fracture was characterized and the fracture behavior was analyzed, using scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD), the fatigue tests of two strain amplitude at room temperature were 0.5% and 1.0% respectively, and the results showed that the fatigue deformation of different strain amplitude produced two typical fatigue fracture morphology, and when the strain amplitude was 1.0%, fatigue fracture mechanism of AZ31 magnesium alloy induced by $$\\{ 10\\bar{1}2\\}$$ { 10 1 ¯ 2 } twins, when the strain amplitude is 0.5%, it was induced by $$\\{ 10\\bar{1}2\\} - \\{ 10\\bar{1}2\\}$$ { 10 1 ¯ 2 } - { 10 1 ¯ 2 } double twins. In the present study, the average thickness of primary twin is\u2009~\u200920\xa0μm at amplitude of 0.5% and\u2009~\u200980\xa0μm at amplitude of 1.0%. The thickness of $$\\{ 10\\bar{1}2\\}$$ { 10 1 ¯ 2 } primary twins was large enough to activate $$\\{ 10\\bar{1}2\\} - \\{ 10\\bar{1}2\\}$$ { 10 1 ¯ 2 } - { 10 1 ¯ 2 } secondary twins at a high strain amplitude, while the thickness of $$\\{ 10\\bar{1}2\\}$$ { 10 1 ¯ 2 } primary twins was too narrow to activate $$\\{ 10\\bar{1}2\\} - \\{ 10\\bar{1}2\\}$$ { 10 1 ¯ 2 } - { 10 1 ¯ 2 } secondary twins at a low strain amplitude.