Microstructure evolution in AZ31B magnesium alloy subjected to tension

Incremental Equal Channel Angular Pressing (I-ECAP) is an incremental severe plastic deformation (SPD) process, which can be used to process continuous bars, plates and sheets. In the current study, commercially available AZ31B magnesium alloy bars were subjected to four passes of I-ECAP using route BC; the process was conducted at 250 °C since fracture was reported at lower temperatures. The obtained fine-grained bars were subjected to side upsetting at 200 °C to produce sheets. The significant height reduction, from 10 mm to 2 mm, was obtained without fracture. Then, flat tensile samples were machined from as-received coarse-grained bars and fine-grained, strongly textured sheets. The samples were polished and etched to enable observation of microstructure evolution during testing. Tensile testing was conducted in the SEM chamber at room temperature with constant tool velocity. It was shown that earlier fracture of coarse-grained samples, comparing to fine-grained ones, can be attributed to twinning as twin-size voids were observed in the fracture zone. Avoidance of twinning was identified as the most important factor for ductility enhancement of fine-grained and strongly textured sheets.