Improvement of tensile properties of wrought magnesium alloys by grain refining

ECAE process was applied to magnesium alloys containing 3 mass%Al or Zn, and the effect of isochronal annealing after ECAE process on the tensile properties of the alloys was evaluated in order to improve tensile properties of the magnesium alloys. When the investigated alloys are subjected to ECAE process, the grains of 1-pass specimens of all the investigated alloys are elongated towards 30° from the extrusion direction and 4-pass specimens of AZ31 and ZK31 alloys exhibit fine fiberous microstructure. In 1-pass specimens, recrystallization partly occurs by isochronal annealing at 300 °C for 1 h, while complete recrystallization occurs by annealing at 400 °C for 1 h. However, the recrystallized grains coarsen when annealing at 400 °C for 1 h. In 4-pass specimens, the temperatures at which recrystallization finishes become lower, and the grain sizes are finer than those of 1-pass specimens. As a result of the above-mentioned microstructural changes, particularly in grain size by annealing, elongation is improved remarkably and 0.2% proof stress decreases with an increase in annealing temperatures. As-ECAE and 300 °C-annealed samples of 4-pass specimens of ZK31 alloy have tensile properties comparable to fully heat treated 6061 forging alloy due to grain refining by ECAE process.