| Strong texture generally develops in magnesium alloy sheet,resulting in strong anisotropy in their mechanical properties(as plasticity,strength)and limited formability,which has become a choke point to its wide range of application.Weakening basal texture of magnesium alloy sheet is the key to solve the problem.Extensive research has shown that the additions of rare earth elements at low alloying levels generally result in significant texture weakening of Mg sheets.However,the mechanism responsible for the texture weakening is still unclear.The projects lay great emphasis on on the texture evolution in Mg-2Zn-0.8Gd,Mg-2Zn(wt.%)alloys during cold rolling and static recrystallization.In order to study the effect of the cold rolling parameters and annealing parameters on microstructure and texture of the annealed alloys,six kinds of rolling reductions(4%,8%,12%,16%,20% and 24%),three temperature(275℃、350℃、400℃)are designed respectively.The recrystallization texture is monitored using a quasi-in-situ electron backscatter diffraction(quasi-in-stiu EBSD)method.In-depth study and exploration of magnesium alloy texture weakening mechanism and deformation behavior are of great significance for the development of Mg-RE alloys with high formability and the basic plastic deformation theory of magnesium alloy.The results show that:(1)It shows that the critical cold-rolling reduction is 24%,and if the reduction is larger than that,the sample will be cracked.During the cold rolling process,grain orientation is more and more concentrated and form a intensive basal texture with the increase of rolling reduction.Rare earth element has no weakening texture effect at the ambient temperature.After annealing,rare earth magnesium alloy develops a TD bimodal texture,whereas Mg-2Zn alloy remains basal texture orientation.The recrystallization texture has no differences in the Mg-2Zn-0.8Gd alloy when change the thickness reduction or annealing temperature.This observation suggests that the texture weakening in the Mg-Zn-RE alloy is primarily influenced by the alloy composition,not the thickness reduction or thermomechanical processing conditions.(2)The addition of Gd has a significant effect on the recrystallization,grain growth behavior and texture evolution of Mg sheet during static annealing.The quasi-in-situ EBSD results show that most of recrystallized grains formed in the high strain area such as twins,grain boundary in priority,and these grains have randomised orientations in the Mg-2Zn-0.8Gd alloy and they grow uniformly during the recrystallization process.Ultimately,a weak texture forms in Mg-2Zn-0.8Gd because of the formation and uniform growth of these recrystallized grains with randomized orientations.A weak recrystallization texture also forms in the early stage of recrystallization in the Mg-2Zn alloys,but it is gradually replaced by a strong basal texture via the preferential growth of recrystallized grains with <11 0> axes are nearly parallel to the RD and c-axes are almost parallel to the c-axes of the deformed parent grains.After full recrystallization,the average grain size of Mg-2Zn-0.8Gd alloy is 18.964μm,smaller than Mg-2Zn alloy which is 35.243μm,and the grain size distribution in the ternary alloy is significantly narrower. |
