Microstructure and mechanical properties of cryorolled AZ31 magnesium alloy sheets with different initial textures

AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.

Twinning Behavior of a Basal Textured Commercially Pure Titanium Alloy TA2 at Ambient and Cryogenic Temperatures

Twinning greatly affects the microstructure and mechanical performance of titanium alloys.The twinning behavior of a basal textured commercially pure titanium TA2 plates rolled to 4% reduction at the ambient and cryogenic temperatures has been investigated.Microstructures of the rolled samples were investigated by optical microscope（OM）and the twinning analysis was carried out based on orientation data collected by electron back-scatter diffraction（EBSD）.{1122}contraction twins,{1124}contraction twins and {1012}extension twins have been observed.Twinning mode activity varied with rolling temperature.Twinning is considered as the dominant deformation mechanism during rolling at both temperatures for the strain condition.Larger proportion of grains activates twinning during cryorolling,and greater number and more diverse types of twins are observed;manifestly related to the suppression of dislocation slips at the cryogenic temperature.{1122}contraction twins are the dominate twin type within samples rolled at both temperatures.Several{1124}contraction twins are observed in the cryorolled sample while there are only a few in the sample rolled at room temperature.A few tiny{1012}twins have been identified in both samples.{1124}contraction twins are preferentially activated at cryogenic deformation temperature and the{1012}extension twins may result in local strain accommodation.

Effects of different types of twinning on microstructure and mechanical properties of a strongly textured TA2 commercially pure titanium alloy subjected to rolling at ambient and cryogenic temperatures

Strongly textured commercially pure titanium alloy TA2 plates with different initial textures have been rolled at cryogenic and ambient temperatures to 4% reduction and then post-annealed at 50℃ for 12 h. Microstructures of the samples were investigated using electron backscatter diffraction. The mechanical property of the sheets was tested via quasi-static uniaxial tensile tests along the rolling direction at room temperature. The effects of initial texture and rolling temperature on twin activity and mechanical property have been investigated. Twinning is very active in TA2 titanium during rolling at either room or cryogenic temperature. {1122} contraction twins can be observed in all the sheets and are the dominant twin mode for the sheets with an initial texture having c-axes parallel to the normal direction （ND）. Extension twins have rarely been seen in sheets having an initial texture with c-axes parallel to ND, but play quite an important role in the sheets having an initial texture with c-axes perpendicular to ND. The initial texture of the sheet is considered to determine the twin mode while the cryogenic rolling temperature is found to increase the numbers of twins. Post-annealing does not change obviously the rolled microstructure. After annealing, the strength decreases and elongation to fracture slightly increases. The cryorolled sample has the better strength with little loss in elongation, and this mechanical enhancement is attributed to massive twinning.