SUPERPLASTIC FORMABILITY OF FINE-GRAINED AZ61 AND AZ31 MAGNESIUM ALLOY SHEETS AND DEFORMATION MECHANISM MAPS FOR MAGNESIUM ALLOYS

摘要

Rolling processes of fabricating thin AZ61 and AZ31 alloy sheets adequate for superplastic forming have been developed. Superplastic behavior of the sheets was evaluated in the temperature range of 573K-693K and compared with the initial materials with relatively coarse grains. Existing deformation mechanism maps for f.c.c. and b.c.c. metals were reviewed and found to be deficient in predicting the deformation behavior of Mg alloys with h.c.p crystal structure. Using the experimental data for a number of Mg alloys, which are associated with various deformation mechanisms competing at elevated temperatures, deformation mechanism maps for Mg alloys could be constructed. Excellent prediction capability of the maps was verified at temperatures of 573K-673K. Superplastic formability of the rolled AZ61 alloy was demonstrated by forming a sheet into a hemi-spherical dome using N_2 gas pressure and into an indented plate using mechanical pressure by hot press.