Plastic anisotropy and deformation behavior of extruded Mg-Y sheets at elevated temperatures

The plastic anisotropy in terms of tensile mechanical property, Lankford coefficient (r), and microstructure evolution of as-extruded Mg-1Y (wt%) and Mg-5Y (wt%) sheets along the extrusion direction (ED), transverse direction (TD), and diagonal direction (DD) were investigated in detail at temperatures between 25 degrees C (RT) and 300 degrees C. The sheets exhibited anisotropic deformation behavior at lower temperatures, and nearly isotropic for Mg-5Y at 300 degrees C in these three directions. For both sheets, the ultimate tensile strength anisotropy (UA) and elongation anisotropy (EA) was not sensitive to the temperature, while the yield strength anisotropy (YA) decreased significantly from 49.1% (Mg-1Y) and 40.2% (Mg-5Y) at RT to 7.2% and 2.7% at 300 degrees C, respectively. The r values of Mg-1Y in all directions first increased from 0.66-1.4 (RT) to 0.81-1.98 (200 degrees C) then decreased to 0.67-1.56 (300 degrees C), while those of Mg-5Y decreased from 1.04-2.05 (RT) to 1.18-1.35 (300 degrees C) with increasing temperature. Few twins were observed in Mg-5Y after tension at RT while large amounts of twins occurred in Mg-1Y. The huge reduction of twins and the weakened basal texture are believed to increase the r value from 0.66 (Mg-1Y) to 1.04 (Mg-5Y) at RT. At 300 degrees C, dynamic recrystallized (DRX) grains appeared in Mg-1Y while only a few DRX grains showed up in the vicinity of grain boundaries in Mg-5Y, which may be closely related to grain boundary segregation of the yttrium atoms.