Microstructure and texture evolution of Mg–7Y–1Nd–0.5Zr alloy sheets with different rolling temperatures

The extruded Mg-7Y-1Nd-0.5Zr(wt%)alloy were performed to the same strain hot rolling with different temperatures.The microstructure and texture evolution of the sheets were investigated by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron back-scattered diffraction(EBSD).The results indicate that the microstructure becomes homogeneous after hot rolling process and precipitated phase distributes at grain boundaries along rolling direction.With the increase in rolling temperature,the grains of sheet grow up.The sheet rolling at 400℃is composed of recrystallization grains,the necklace of the precipitated phase in the grain boundaries and excessive dislocations.The structure of necklace of the precipitated phase is fcc structure with lattice constant of a=0.75 nm.With rolling temperatures increasing from 400 to 450℃,the content of recrystallized grains in volume fraction with relatively random orientations increases significantly.Compared with the rolling process at 400℃,the amount of precipitated phases is reduced at the grain boundary,and the precipitated phase begins to appear in the grain interior when rolling at 450℃.The structure of the precipitated phase is fcc with lattice constant of a=2.22 nm.The recrystallization grains begin to grow in the rolling process at 500℃.The basal texture is obviously produced during the rolling process at 400 and 450℃;however,the basal texture is weak in the rolling process at 500℃.

Homogenization heat treatment of Mg-7.0 wt%Y-1.0 wt%Nd-0.5 wt%Zr alloy

The microstructures and mechanical properties of Mg-7.0 wt%Y-1.0 wt%Nd-0.5 wt%Zr magnesium alloy were investigated both in as-cast condition and after homogenization heat treatment by differential scanning calorimetry(DSC),optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM)and hardness measurement.The results indicate that the ascast alloy consists ofα-Mg matrix,Mg24 Y5 and Mg41 Nd5 phases,which are eutectic phases(cubic Y-rich phase).With the increase in homogenization temperature and time,the Mg24 Y5 and Mg41 Nd5 phases are completely dissolved into matrix,and only yttrium of intermetallic compounds leaves around boundary.After homogenization heat treatment,the elements distributed uniformly and the grains grow up not obviously,only yttrium element of intermetallic compounds left around boundary.The optimum homogenization condition is at 537℃for 16 h.The mechanical properties are improved after homogenization,with tensile strength ofσb=181 MPa,yielding strength ofσ(0.2)=144 MPa and elongation ofδ=5.5%,which are better than those of as-cast alloy.