Microstructure,Tensile Flow Behavior And Anisotropy Of The Mg-Y(0.5-5wt.%)As-Extruded Sheet

Magnesium(Mg)alloys are of great significance in aerospace,automotive industries and high speed trains,due to their potential to provide remarkable mass reduction and improve fuel efficiency.However,their poor formability at room temperature(RT)has significantly limited their application.Latest results have been reported that Y addition is expected to be beneficial for the activation of non-basal slips at RT and a weakened texture,which may also lead to an increase of the elongation to fracture and a reduction of anisotropy.Nevertheless,no systematic results about the effect of yttrium addition and deformation conditions on the anisotropy have been reported.This article investigated the microstructure,texture,tensile deformation behavior and the anisotropy in the extrusion direction(ED,0°),the 45° direction and the transverse direction(TD,90°)of the Mg-Y(0.5-5wt.%)sheets.The main results are as below:The addition of yttrium is beneficial to reduce the grain size,weaken the texture and inhance the(ultimate tensile strength)UTS,the(yield strength)YS and the elongation to fracture.The elongation to fracture of the Mg-1 Y sheet extruded at 300?and 400? was 30.2%±2.1%and 36.8%±3%,respectively.The grain size decreased slightly and the texture was more weakened with increasing extrusion temperature while the texture type(splited into two poles in ED and tilt in TD)was not changed.The UTS and YS decreased while the elongation to fracture increased with increasing extrusion temperature.The flow behavior of this alloy can be described by the Arrhenius hyperbolic sine constitutive equation ? = 4.48×1012[sinh(0.0567?)]27.8exp(-124600/RT)at 25-250?.The average error of experimental stress values and calculated values using the molded constitutive equations was 2.8%.The the activation energy of deformation was 124.6kJ/mol,indicating that the dislocation climb was the rate-controlling mechanism.The strain rate sensitivity exponent m at the strain of 0.1 was 0.026 at RT,which was much higher than that of as-rolled AZ31 sheet(0.0025),indicating that the Mg-1 Y exhibited much better formability at RT.The yield strength anisotropy at 300? decreased from 7.2%(Mg-1Y)to 2.7%(Mg-5Y),the r values in the 0° direction from 0.66?0.88(Mg-1 Y)to 1.04?1.18(Mg-5Y),and the differeces in the three directions of Mg-5Y at 300? was much lower than that of Mg-1 Y,indicating that the anisotropy was reduced with increasing yttrium content.These results may be related to the more weakened texture,depressed twinning and the activation of non-basal slip systems.Microstructure observation suggested that twinning was depressed by increasing the yttrium content and temperature and dynamic recrystallization was also depressed with increasing yttrium content.