Temperature dependence of mode I fracture behaviour of a textured magnesium alloy

Mode I, static fracture experiments and uniaxial tension/compression tests are conducted at three temperatures in the range from 25 to 100 degrees C using fatigue pre-cracked four-point bend and microtensile/compression specimens machined from a rolled AZ31 Mg alloy plate. Digital image correlation technique along with in-situ optical imaging is employed to analyse the specimen surface deformation. It is found that the fracture mechanism which is operative near the tip changes from quasi-brittle cracking caused by tensile twins to ductile void growth and coalescence as temperature is raised above 65 degrees C. This corroborates with reduction in tensile twin development near the crack tip with enhancement in temperature. On the other hand, at higher temperature, more profuse twinning and pronounced texture changes are perceived in the far-edge of the ligament, where compressive normal stress prevails. Simplified analyses are performed to show that the evolution rate of tensile twin volume fraction with energy release rate J near the tip will diminish strongly, while micro-void growth rate will enhance between 25 and 100 degrees C, thereby triggering the observed brittle-ductile transition. The fracture toughness rises dramatically above 65 degrees C and is also accompanied by significant notch blunting. This is rationalized from the transition in fracture mechanism and large plastic dissipation in the ligament far-edge due to twinning.

Automated summary

This study investigates the fracture behavior of AZ31 Mg alloy at different temperatures. Experimental results show that the fracture mechanism changes from brittle cracking to ductile void growth as temperature increases. Increased temperature also leads to increased twinning and texture changes in the far-edge of the ligament.