Mg-Zr合金の温間深絞り成形における応力状態と変形組織

抄録

The relationship between the stress state and the deep-drawn deformation structure of Mg-1.5Zr alloy was studied. The alloy blanks, made from cast material, were deep-drawn at 300°C with a drawing ratio of 1.7. A series of circular laser-etched marks, made on the blank surface from the center to the rim of the blank, were used to measure strains in various directions caused during deep-drawing. The results indicated that since no shear stress is generated at the bottom of the cup due to equal biaxial tension, slip deformation is unlikely to occur and hence no development of basal texture is observed, however a large number of twins were formed. The R part of the cup is also biaxially tensioned, but the shear stress is |σ_r-σ_θ| and conjugated shear stress is generated due to bending, which promotes the formation of new crystals and twin deformation. Along the side wall from the R toward the rim areas of the cup, there is a transition area where σ_θ changes from tension to compression and as compression strain increases, basal texture develops significantly. The main deformation mechanism is by twin when σ_θ is “tensile” and by slip when σ_θ is “compression”.