EFFECT OF TEMPERATURE ON THE MODE I FRACTURE BEHAVIOR OF A ROLLED MAGNESIUM ALLOY

The temperature dependence of the mode I fracture behavior of a rolled Mg AZ31 alloy having near basal texture is studied in this work through four-point bend fracture experiments in the temperature range from 25 to 100 deg Celsius. It is found that the operative fracture mechanism changes from twin-induced quasi-brittle cracking to one mediated by ductile void growth and coalescence as temperature is raised above 65 deg Celsius. A concomitant reduction in tensile twin development near the crack-tip is observed with enhancement in temperature, while at the specimen far-edge it increases, resulting in pronounced texture changes at higher temperature. The reduction in tensile twin evolution with energy release rate and enhancement in micro-void growth rate near the crack-tip over the above temperature range are rationalized through simplified analyses. The change in fracture mechanism from brittle to ductile and higher dissipation due to tensile twinning at the specimen far-edge as temperature increases results in significant enhancement in fracture toughness.
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