The Effect Of Solute Drag On Texture Evolution And Mechanical Properties In Mg-Gd-(Y) Alloys

Basal slip and twinning are the main deformation modes in Mg alloys,which is the main cause of strong basal texture in Mg alloys.The addition of rare earth elements in Mg alloys can weaken the texture efficiently and then improve the formability of Mg alloys.But the texture evolution of Mg-RE alloys still depends on elements addition and heat processes.It is significant to study the mechanism of texture weakening in Mg alloys.The solute drag effect was critical for recrystallization nuclei that could determine the crystallographic texture.And the solute drag of rare earth elements would result in dynamic strain aging(DSA)effect which manifests as serrated yield in tensile curves,so solute drag effect has great influence both on texture evolution and mechanical properties of Mg alloys.However,there are few reports provide direct experimental observation of solute drag effect in Mg-RE alloy.In this paper,we studied the effects of solute drag on texture evolution and mechanical properties in Mg-Gd-(Y)alloys by Electron Back Scattering Diffraction(EBSD),High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy(HAADF-STEM)and high temperature tensile test.The results present as following:Under the same processing condition,the texture of Mg-1wt.%Gd is weaker than that in AZ31 alloy.The EBSD results of Mg-1wt.%Gd extruded at different temperatures show that the RE-texture <2111> first appeared in sample extruded at 400?.In Mg-1wt.%Gd alloy extruded at 400?,a large number of shear bands in which there are many dislocations forming hexagonal dislocation network were observed.The large number of <c+a> non-basal dislocations and the generation of these multiple <c+a> non-basal dislocations could be ascribed to the plentiful Gd-segregated low-angle grain boundaries within shear bands,where dislocations with Burgers vector of 1/3<1120> were commonly found with Gd clusters.It is believed that these Gd-segregated low-angle boundaries can strongly obstacle basal dislocation slip and enhance the mobility of non-basal dislocations,which in turn weakens the overall texture in Mg-1wt.%Gd alloys.DSA effect has been observed during tensile test at temperature of 200? and 250? in Mg-2wt.%Gd and 150?,200? and 250? in GW83,showing as the serrated yield in stress-strain curves.DSA is caused by the interaction between solute atoms and dislocations.At room temperature,the solute diffusion velocity may be too slow to produce cottrell atmosphere near the dislocation core,and thus there is no enough solute drag force to cause DSA effect.But at higher temperature,solute atoms have great drag effect on dislocations and produce DSA effect.At the same time,the temperature shows DSA effect first in GW83 is 150? which is lower than that of Mg-2wt.%Gd alloy.And during hot tensile test of GW83,the yield strength at 200? increased abnormally compared with that at 150?.This is because the solute concentration of GW83 is higher,which produces stronger drag effect on dislocations.