2021 年 85 巻 4 号 p. 129-137
Bending-tension deformations were conducted to AZ31B (Mg-3 mass％Al-1 mass％Zn) alloy sheets with weak basal texture intensity and RD (rolling direction)-split texture, which were processed by high-temperature rolling. Effects of process pass number of bending-tension deformation on the texture formation and related room temperature formability were investigated. 1 pass bending-tension deformation contributed to significant increase in the RD-split angle from 13° to 25°, and additional bending-tension deformation only contributed to slight increase in the RD-split angle. 7 pass bending-tension deformation increased basal texture intensity from 2.9 to about 4.5, which was still much lower than those of commercial AZ31B alloy sheets. Specimens subjected to less than 5 pass bending-tension deformations kept significant stretch formability (8.0 mm of Erichsen value). However, specimens subjected to 7 pass bending-tension deformation exhibited deteriorated Erichsen value of 6.7 mm regardless of the high RD-split angle, low basal texture intensity and high average Schmid factor. As a result of microstructural observation, it was revealed that repetition of bending-tension deformation generated area with coarse grains at near surface. In addition, repetition of bending-tension deformation induced duplex microstructure at the surface, where layers of fine grains and coarse grains were distributed along to the RD on the RD-TD (transverse direction) plane. It was suggested that the above microstructural changes induced inhomogeneous deformation at grain boundaries and in double twinning, resulting in the deterioration of the stretch formability of the specimens subjected to 7 pass bending-tension deformation.
