Anisotropía mecánica de aleaciones laminadas y recocidas de los sistemas Mg, Mg-Y, Mg-Nd

Abstract

Magnesium alloy sheets have a significant potential in replacing materials in lightweight designs. Magnesium has the lowest density (1.74) of metallic materials, combined with high specific strength and stiffness. It makes of magnesium and its alloys good candidates to face the challenges of reducing vessel weight in transportation industry, reducing the consume of fuel. Magnesium alloys present poor formability at room temperature, many efforts have been done to improve it. Many author’s have improved magnesium formability by adding RE (rare elements) such as Gd, Nd, Ce,Y, and La, because these RE modify the strong crystallographic texture after the rolling. However, the mechanism(s) by which the texture is modified remains unclear. Therefore in the present study were prepared 2 experimental alloys Mg-1.5wt% Nd, Mg-3wt% Y and pure magnesium with the purpose of comparing the effect of each alloying element during deformation and recrystallization of magnesium sheets. Fully recrystalized and similar grain sizes were obtained in the three experimental sheets. It has been observed that during the annealing treatment of Mg-RE sheets the additions of Y and Nd cause the retardation of recrystalization and grain growth. In addition, the texture intensities of the rolled and annealed Mg- RE sheets were lower than in pure magnesium sheet. During the uniaxial tensile test was evident that the additions of RE improve the mechanical response of Mg. Pure magnesium sheet showed the fracture strain of ~4%, whereas the Mg-RE sheets have a remarkable high ductility with ~24% strain. Moreover, the Erichsen values of the Mg-RE sheets are almost 2 times higher than that of the pure Mg sheet. The high ductility and improved sheet formability with well-balanced work hardening in the Mg-RE sheets can be understood as a result of the weak texture, which is favourable for the deformation in the sheet planar as well as thickness directions. Finally a reduced planar anisotropy (r~1) is observed in the Mg-RE sheets, in comparison to conventional magnesium alloys, this is related to the weaker textures .The n-value in this work was higher than conventional magnesium alloy, n-value is one of the important factors which control metal sheet’s resistance to plastic instability. Thus, low plastic instability should also contribute to the enhancement of stretch formability. The texture and microstructural evolution during tensile test at different loading direction 0°, 45°and 90° respect to rolling direction, showed the formation of a new texture component which corresponds to the activity of tensile twinning. This new component was more evident at 0° than 90°, it´s obeys the Schmid factor criterion.