High strain rates deformation behavior of an as-extruded Mg–2.5Zn–4Y magnesium alloy containing LPSO phase at high temperatures

Abstract

Mg–Zn–Y magnesium alloys comprising long-period stacking ordered (LPSO) phase have shown excellent strengthening effects, however, their deformation behavior and microstructure evolution under different strain rates and temperatures have not yet been thoroughly investigated. This work is based on the investigation of elevated temperature and high strain rate deformation behavior of an as-extruded Mg–2.5Zn–4Y magnesium alloy comprising LPSO phase, with the strain rates lying in the 700 s−1 to 2100 s−1 range, and temperature ranging from 293 K to 623 K. Electron backscattering diffraction (EBSD), scanning electron microscopy (SEM), and optical microscopy (OM) was employed for investigating the deformation microstructure. The results show that at early deformation the extension twinning coordinates the plastic deformation first, subsequently, pyramidal < c+a > slip and kinking of LPSO phase can also coordinate deformation for the experimental alloy at high strain rates at high temperatures. A peculiar phenomenon of misaligned LPSO phase structures (1600 s−1, 623 K) was also discovered. The fracture mode of the experimental alloy is mainly the cleavage fracture or the mixed ductile-brittle fracture during high-speed impact. A modified Johnson–Cook (J-C) constitutive model of the as-extruded Mg–2.5Zn–4Y was found to appropriately analyze the stress–strain values by comparing the computed results with the experimentally obtained data. It was, thus, demonstrated that the modified J-C model can make a reasonable prediction about the dynamic mechanical behavior of a Mg–2.5Zn–4Y magnesium alloy in its as-extruded condition throughout a range of high temperatures and strain rates with a high degree of accuracy.