Dislocation creep in super-light solid solution base Mg-6Li-3Zn alloy

Mg-6Li-3Zn alloy was prepared by Jackson's melting and casting method and the sheets of 1.2 mm in thickness processed by hot rolling at 573 K and cold rolling with a total reduction of more than 92% were obtained. The high-temperature mechanical behavior at temperatures ranging from 423 to 673 K and initial strain rates ranging from 1.67 × 10-3 to 5 × 10-2 s-1 were investigated. The microstructure evolution, such as grains, subgrains, dislocations, cavities and fracture morphology, were investigated by OM, TEM and SEM. Yavari-Langdon model describing the transition between dislocation viscous glide and dislocation climb was used to construct a new dislocation creep mechanism map which consists of Cottrell's solute atmosphere breakaway dislocation climb regime, dislocation viscous glide regime and Cottrell's solute atmosphere incorporated dislocation climb regime. A new cavity growth map considering cavity coalescence was obtained according to the cavity growth models. The maximum elongation to failure of 300% was demonstrated at 623 K and an initial strain rate of 1.67 × 10-3 s-1. Significant dynamic recrystallization occurred in band-like structure at 573 K and an initial strain rate of 1.67 × 10-3 s-1, the subgrain contour was ambiguous and dislocation distribution was relatively uniform. Fracture mode of the alloy at 573-623 K and an initial strain rate of 1.67 × 10-3 s-1 is ductile fracture. It is shown by the dislocation creep mechanism map that the high-temperature deformation mechanism in Mg-6Li-3Zn alloy sheet with bad-like structure at 573 K and an initial strain rate of 0.67 × 10-3 s-1 is dislocation viscous glide controlled by lattice diffusion, the stress exponent is 3 (strain rate sensitivity exponent 0.33) and deformation activation energy is 134.8 kJ/mol, which is the same as the lattice diffusion activation energy of Mg. The cavity growth mechanism of the alloy at 573 K and initial strain rate of 1.67 ×10-3 s-1 is plasticity controlled cavity growth. ©.