This paper reports the microstructure observation and crystal orientation change during Erichsen test on Mg-Y extruded alloy sheets. The Erichsen value of Mg-Y alloy was 4.2 which was higher than 1.8 of AZ31 commercial alloy rolled sheet. The result shows Mg-Y alloy has high formability than AZ31 rolled sheet.
  From the EBSD results of their crystal orientation change, tensile twin formed from early deformation stage and the area fraction of tensile twin increased with increasing the Erichsen value. In this time, crystal orientation changed to c axis parallel to nominal direction. During the Erichsen test, the randomly crystal orientation change to strong basal texture due to tensile twin. On the other hand, compression and their double twins formed on the strong basal textured grains from medium deformation stage. These compression twins easily formed the grains because of high Schmid factor for compression twin. The area fraction of these compression twins increased to 5% with increasing the Erichsen value. It was reported that double twins accompanied localized severe deformation and triggered premature failure in strong basal texture Mg alloy. Therefore, even in Mg-Y alloy with randomly crystal orientation, the crystal orientation change to strong basal texture due to tensile twin and it is presumed that these double twins also triggered premature failure.