Deformation and fracture behaviors of AZ31B Mg alloy at elevated temperature under uniaxial compression

Abstract

The deformation and fracture behaviors of as-cast AZ31B Mg alloy were studied by uniaxial compression experiments and finite element simulations with wide ranges of temperature and strain rate. The strain-rate and temperature sensitivities of flow stress, fracture morphology, critical strain to fracture, fracture criteria and related mechanism were discussed. Results show that the observed sharp in stress caused by micro-cracks initiation and propagation can be readily produced at relatively low temperatures and high strain rates. Shear deformation bands are easily formed along the shear direction under uniaxial compression, which are the main reasons for approximately 45° shear cracking during the compression, and the presence of spheroidal precipitates makes a great contribution to the formation of crossed shear cracks. There exists a strong correlation between the fracture mode and power dissipation efficiency, i.e., the crossed and parallel shear cracking can significantly reduce the efficiency. Freudenthal fracture criterion is applicable to hot forming of AZ31B alloy due to its accurate prediction of the cracking initiation and fracture position under uniaxial compression. The critical cracking strain and further the critical damage value of Freudenthal criterion can be successfully achieved by combining the high-speed photography and numerical simulation. The present mathematical analysis indicates that a linear relationship exists not only between the critical cracking strain and Ln(Zener-Hollomon parameter, Z) but also between the critical damage and LnZ. In response to high strain-rate and temperature sensitivities of AZ31B alloy, the Freudenthal fracture criterion should be optimized.