Annealing behavior of a cast Mg-Gd-Y-Zr alloy with necklace fine grains developed under hot deformation

Abstract

The microstructure and texture development of a cast Mg-Gd-Y-Zr alloy during hot deformation and subsequent annealing were investigated by optical microscopy (OM) and electron backscattered diffraction (EBSD) technology. Initial microstructures with partially and fully developed new fine grains (NFGs), separately attended by continuous or interrupted hot forging, were various mixed grain structures composed of NFGs in necklace and retained coarse grains. It is shown that, during annealing, the development of grain size can be divided into three stages: i.e. an incubation of grain growth, a rapid coarsening and a normal grain growth. After a long time annealing of over 10 4 ks at 693 K, the average grain size for samples continuous compressed toε= 1.2 and those interrupted compressed toε= 1.6 were close. Moreover, orientations of such strain-induced fine grains were relatively randomly distributed, leading to a weakened basal texture, while the basal plane of retained coarse grains were perpendicular to the forging direction. Such texture even became weaker during subsequent annealing. The results show that the development of necklace NFGs during hot deformation can be effective for homogeneous grain refinement under subsequent annealing.

Grain fragmentation associated continuous dynamic recrystallization (CDRX) of hexagonal structure during uniaxial isothermal compression: High-temperature α phase in TiAl alloys

“…It was found that Mg alloys usually display typical features of CDRX during hot deformation [18][19][20][21][22], i.e., low angle boundaries were introduced due to the accumulation of dislocations, and then new fine grains were developed progressively from grain boundaries to grain interiors with the gradual increase in misorientation at sub-boundaries. Due to the lack of slip systems, twinning [22][23][24][25][26] and kinking [19][20][21][22] served as additional mechanisms for rapidly introducing large misorientations in deformation substructures and accelerating the formation of new fine grains. For the DRX behavior of CP-Ti, investigations [27][28][29] indicated that DRV was the dominant softening process for the annihilation of dislocation during high temperature deformation.…”

Simultaneously Improving Ductility and Stretch Formability of Mg-3Y Sheet via High Temperature Cross-Rolling and Subsequent Short-Term Annealing

“…The average KAM value of Mg-3Y-R sheet is found to be higher and drops from 1.57 to 0.38 remarkably after subsequent short-term annealing. Therefore, most of the areas nearly exhibit a strain-free state, indicating that SRX is a process of softening the work hardening effect [49,50]. The release of residual stress is beneficial to the improvement of ductility and stretch formability of Mg-3Y sheets.…”

Effect of Loading Direction on the Tensile Properties and Texture Evolution of AZ31 Magnesium Alloy

“…The KAM diagram is used to indicate the local dislocation density and strain degree in the microstructure. The darker the color, the greater the local misorientation [25]. The average local misorientation angles of the T0, T45, and T90 samples are 0.81, 0.87, and 0.76, respectively.…”