A hot extruded AZ61Mg alloy was multi directionally forged (MDFed) under decreasing temperature conditions using a die. MDFing was successfully carried out, and the coarse initial grains with an average grain size of 21.6 mm were gradually fragmented to 0.3 mm in average at cumulative strain of∑De=7.2. It showed quite high hardness of 958 MPa and tensile strength of 465 MPa with ductility of 15. The tensile behavior of the ultrafine grained AZ61 Mg alloy exhibited large temperature and strain rate dependency irrespective of temperature. Superplasticity of 680 elongation to fracture could be achieved at 423 K and at strain rate of 1.0×10 -4 s -1 . Such mechanical properties depending on temperature and strain rate were reasonably understood by considering the effect of grain boundary sliding. The tensile strength of the MDFed AZ61Mg alloy was further raised to 490 MPa by additional cold rolling. Fig. 1(a)),アムスラー型万能試験機を用いて初 期ひずみ速度 3.0×10 -3 s -1 ,パス間ひずみ De=0.8 として, MDF 温度を 603~393 K まで鍛造パスごとに逐次降温しな
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