| With the continuous development of science and technology in the world,the requirements for metal materials are becoming higher and higher nowadays.The consumption of magnesium alloy ranks third after steel and aluminum alloy.The magnesium alloy has many advantages such as low density,high specific strength,high specific stiffness,good electromagnetic shielding performance,and easy to be recycled.So,it is one of the green materials in the 21 st century with great potential.However,the mechanical properties of magnesium alloys,especially the low plasticity,limit their further applications.The addition of rare earth elements,such as Nd and Y,can improve plasticity by activating non-basal slips,which is one of the important ways to improve the plasticity of magnesium alloys in recent times.Therefore,for the further development of magnesium alloys,it is important to understand how the rare earth elements Nd and Y affect the properties and deformation mechanism of magnesium alloys.In this paper,Mg-6Zn-1Nd-0.5Zr,Mg-6Zn-1Y-0.5Nd-0.5Zr and Mg-6Zn-1Y-0.5Zr were prepared and followed by hot extrusion.The microstructure,texture and mechanical properties of these three alloys were studied,and the effects of Nd,Y addition on the deformation mechanism of the alloys during hot extrusion were investigated.The experimental results show that the textures of the three alloys have a common feature:they more or less distribute along the TD direction,i.e.,the characteristic of fiber texture.In order to further investigate the role of Nd,Y played on the formation of fiber texture during hot extrusion,the contribution of activated prismatic slips in the formation of fiber texture was elucidated in detail by calculating Schmid factor and utilizing intragranular misorientation axis(IGMA)analysis method.The main findings are listed as follows:(1)After hot extrusion,the second phase in Mg-6Zn-1Nd-0.5Zr is finely dispersed and the Nd of Mg-6Zn-1Nd-0.5Zr is almost completely dissolved in the matrix,which promotes the generation of twins and a few prismatic slips.The mechanical properties of Mg-6Zn-1Nd-0.5Zr along the ED and TD directions do not have much difference-the elongations both exceed 20% and the tensile strengths are both above 230 MPa;the Y and Nd of Mg-6Zn-1Y-0.5Nd-0.5Zr form second phases in large quantities,but there is still a small amount of Y that dissolves in the α-Mg matrix,which promotes a certain amount of prismatic slips.The grains of Mg-6Zn-1Y-0.5Nd-0.5Zr are fine,while the second phases are coarse and almost uniformly distributed,in addition,there are certain residual stresses in most of the grains.The elongation along the ED direction is the lowest,which is only 10.3%,and the elongation in the TD direction is slightly higher,reaching 18.8%.However,the tensile strengths in the ED and TD directions are almost the same,which is297 and 291 MPa,respectively;Mg-6Zn-1Y-0.5Zr also has a certain amount of the second phase,which is distributed along ED direction,but the number of second phase is relatively small,which means the solid solubility of Y in Mg-6Zn-1Y-0.5Zr is much larger than Mg-6Zn-1Y-0.5Nd-0.5Zr.As a result,more prismatic slips are activated,which promote the formation of the weakened fiber texture along the TD direction.Along the TD direction,the alloy has the highest elongation of 26.4% but a relatively low tensile strength of 269 MPa.While along the ED direction,the elongation is only 21.0%,but the tensile strength is as high as 313 MPa.(2)For the prismatic slips activated by Nd,Y,this paper summarized the previous experience and proposed new methods to identify the slip directions.These methods demonstrated how the activated prismatic slips affect the formation of fiber texture distributed along the TD direction: the formation of fiber texture is owing to the interaction between prismatic slip and basal slip.The function of the prismatic slip is to inhibit the continuous movement of the basal slip and make the grain rotate around the[0001] axis,so,in the crystal coordinate system,the ED direction is perpendicular to a certain prismatic plane,and the TD and ND directions are located at the intersection point of two certain prismatic planes.It can be seen from the top view of the close-packed hexagonal structure that the loading force is often projected on an intersection line of a prismatic plane and the basal plane,and the prismatic plane activated is just close to the projected loading force.From the top view of the close-packed hexagonal structure,the direction of the prismatic slip points to the location of the loading force,which causes the grains to rotate in the opposite direction to the prismatic slip direction and finally leads to the formation of texture distributing along the TD direction,and when the prismatic slips reach a certain amount,a fiber texture distributed along the TD direction is formed. |
PDF Full Text Request