Pure magnesium and Mg-Y alloy single crystals were subjected to three-point bending tests to investigate the effect of crystal orienta-tion and yttrium on bending deformation behavior. Specimens
whose neutral planes are parallel to (0001) and neutral axes are [1120] de-formed due to basal slips and showed a gull-shape. Their bending yield stresses increased by addition of yttrium and were controlled
by the shear stress on the basal plane. Conversely, when neutral planes are parallel to (1100) and neutral axes are [1120] the specimens deformed due to {1012¯ } twins occurred in the compression side,
basal slips within the twins and nally showed a V-shape. In Mg-Y alloys, rst order py-ramidal <c+a> slips ÿFPCSÿ and {1011¯ }-{1012¯ } double twins were also activated in the tension side. Their bending yield
stresses and bending ductility increased by yttrium addition. Strain induced by {1011¯ }-{1012¯ } double twins in the tension side was very low. FPCS was found to be activated by addition of yttrium and to
increases bending ductility