Study On Texture Optimization Of Extruded And Rolled Mg-Ce(Zn) Alloys

Conventional rolling and pack rolling by Al sheets were carried outon Mg-2Zn-0.5Ce alloy sheets at400℃and450℃, respectively. Besides,Mg-0.5Ce alloy rods were deformed by indirect extrusion at temperaturesof350℃and400℃. The microstructure evolution and mechanicalproperties were investigated of these deformed alloys．The influence of deformation extent, deformation temperature andannealing on the microstructure, texture evolution and mechanicalproperties were investigated，systemically. Optical Microscopy (OM),scanning electron microscopy (SEM) and electron back-scattereddiffraction (EBSD) techniques were used to study the microstructure ofthe alloys. Tensile test was also carried out at room temperature underthree directions for analysis and r-value was calculated based on this test.The main objective of the current research was to optimize texture byadjusting rolling parameters and to develop high formability magnesiumsheets by rolling. Besides, mechanism of texture randomization was alsodiscussed in this study by investigating the microstructure evolution of Mg-Ce alloy by indirect extrusion.When subjected to conventional rolling at the temperature of400℃and450℃, Mg-2Zn-0.5Ce alloy sheets have shown inhomogeneousmicrostructure and a small extent of recrystallization. With thedeformation extent increasing from38%to76%at the temperature of400℃, the microstructure is becoming much more homogeneous and morerecrystallized grains appear. Mg-2Zn-0.5Ce alloy sheets deformed at450℃have shown the similar microstructure evolution discipline. Nevertheless,mechanical properties for sheets deformed at different temperatures byconventional rolling are different． It is shown that450℃deformationlead to better plasticity of rolled sheets, and the elongation at the tensileangle of45°was15.12%. While, it is9.83%for sheets rolled at400℃. Atthe same time, for sheets by conventional rolling, they all have performedan obvious anisotropy when tensioned along three directions of0°,45°and90°to the rolling direction. Annealing treatment was useful to obtainhomogeneous microstructure, but the texture was strengthened. Besides,Mg-2Zn-0.5Ce alloy sheets have exhibited oxidized surfaces and obviousedge cracks, which indicated bad formability.However, for Mg-2Zn-0.5Ce alloy sheets deformed at the sametemperature by pack rolling, they have shown much better formability with smooth surfaces, metallic luster and little edge cracks. Due to theexact temperature control by pack rolling, homogeneous microstructurecan be obtained for Mg-2Zn-0.5Ce alloy sheets. Compared to400℃rolling,450℃rolling sheets have performed a little more coarse grainsize of9.5μm, but a more randomized texture and weaker anisotropy whentensioned along different directions. Also, an obvious “rare earth texture”has been observed when rolled at450℃, which resulted in the goodformability of magnesium alloys. In this case, the elongation isapproximately30%. When annealed at350℃, grains tend to grow largerwith the increase of treatment time. The texture of the pack rolled sheetshas been strengthened after annealing. It can be inferred that pack rollinglead to a more randomized texture than conventional rolling and theductility of the rolled sheets are better for pack rolling.When Mg-0.5Ce was deformed by indirect extrusion at350℃andsubsequent quenching, small recrystallized grains were observed in thegrain boundaries at a small strain. And most grains were deformed alongthe extrusion direction and were elongated. With the increase of strain,more recrystallized grains appeared instead of the deformed grains.However, when extruded at400℃, most of the grains have gone throughrecrystallization and only a few grains are elongated along the extrusion direction remained. Besides, for rods deformed at400℃, they have shown amuch more randomized texture than at350℃and “rare earth texture” wasalso obtained in this case, which might have a correlation with the solutedrag effect and400℃is in the small temperature-stress window ofdynamic strain aging effect. As a result, indirect extrusion at400℃hasexhibited a much better tension-compression symmetry and a largerelongation than at350℃.