Tensile flow and work hardening behaviors of ultrafine-grained Mg-3Al-Zn alloy at elevated temperatures

摘要

Tensile flow behavior of ultrafine-grained Mg-3Al-Zn alloy processed via mechanical milling, hot-press consolidation followed by extrusion has been determined in the temperature range from 300 K to 523 K and strain rate range from 10~(-2) to 10~(-4) s~(-1). The effects of temperature and strain rate on the work hardening behavior are successfully analyzed by the derived Lukac and Balik expression. The micro-structure evolution shows that the dislocation density increases from 1.59 × 10~(16) m~(-2) to 3.04 × 10~(16) m~(-2) in work hardening stage and decreases to 3.97 × 10~(15) m~(-2) in work softening stage, which is in accordance with Lukac and Balik expression. The apparent activation energy value of 66.71 kJ/mol in the strain rate range from 10~(-2) to 10~(-4) s~(-1) at 523 K suggests that the dominant mechanism is GBS accommodated by slip controlled by grain boundary diffusion, which is further proved by the formation of cavities and filaments during tensile test. The analysis of work hardening behavior indicates that dislocation multiplication contributes to the hardening process, while cross slip and climb of dislocations as well as GBS play a role in the softening process.