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 104 ks at 693 K, the average grain size for samples continuous compressed to ε=1.2 and those interrupted compressed to ε=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.

The fine-grained structure development and the resultant mechanical properties during/after hot deformation were investigated in a Mg–2.7Nd–0.5Zn–0.8Zr alloy pretreated in solution and subsequently full aging. The true stress-true strain flow curves show a two-step work hardening during hot compression due to the interactions between dislocations and Mg–Nd precipitates as well as Zn–Zr intermetallics. In as-aging (AA) sample containing statically precipitated particles (SPPs), deformation bands (DBs) are easily developed at low strains and then ultrafine grains (UFGs) are evolved at along the boundaries of DBs and original grains at medium strains and rapidly approaches to a full development of final stable UFGs as the strain goes higher. In as-solution (AS) sample, by contrast, equiaxial UFGs are partially developed even in high strain and the grain sizes are smaller attributed to dynamic precipitated particles (DPPs). Tensile tests were carried out at ambient temperature for both types of sample, the results show that the tensile elongation to fracture of the hot deformed AA sample is higher than that of the AS one, because the former has a higher volume fraction and a weaker texture of UFGs developed. Besides, the AA sample contains a higher 5% proof strength compared with the AS one at low deformation temperature, however, such trend is reversed at high temperature, which may be resulted from the effect of SPPs and DPPs, respectively.

•The Cu–Zr–B alloy is processed by double deformation–aging treatment.•Excellent balance of paradoxical strength and electric conductivity is achieved.•Discontinuous precipitation mode is suppressed and continuous one is promoted.•The precipitates responsible for the age strengthening effect are fcc Cu5Zr.The microstructures, mechanical/electrical properties and precipitation behaviors of Cu–Zr–B alloy manufactured by double deformation–aging process were investigated. The results show that an excellent balance of tensile strength and electrical conductivity, e.g. as high as 575.4 MPa and 79.37% IACS, respectively, can be obtained for the alloy after primary 80% cold rolling and aging at 470 °C for 2 h followed by secondary 40% cold rolling and aging at 360 °C for 2 h. The achievement of such high strength and electrical conductivity can be attributed to the interactions of strain hardening and precipitation behaviors taking place in the course of double deformation and aging treatments. High softening resistance is the outgrowth of the occurrence of limited recovery and recrystallization. After secondary deformation and aging, discontinuous precipitation can be suppressed but continuous one promoted. It is found that the precipitates responsible for strengthening are fcc structure Cu5Zr with the orientation relationship of (101¯)M//(21¯1¯)P and [111]M//[111]P.Graphical abstract

•The AZ61 Mg alloy is deformed at 623 K by bidirectional cyclic bending.•A symmetric gradient distribution of fine grains along the thickness is formed.•The basal texture in the regions near two surfaces is weakened significantly.In this work, the microstructural and textural evolution in the sheets of AZ61 magnesium alloy was studied by means of bidirectional cyclic bending for 8 passes at 623 K. The bended samples were examined by optical microscopy and electron backscatter diffraction analysis. The results showed that a gradient structure with fine grains about 3 μm in the regions near two surfaces and, in contrast, coarse grains in the middle of the sheet were formed. The evident grain refinement was attributed to twin-assisted dynamic recrystallization and continuous dynamic recrystallization induced by kink bands. The texture intensity was clearly reduced, resulting in a negative gradient distribution, with the texture intensity decreases from the center of the sheet to two surfaces. The weakened texture greatly facilitated the reduction of the yield strength. A higher fracture elongation and a slightly improved ultimate tensile strength were achieved concurrently.

•The AZ31 Mg alloy rod is compressed at liquid nitrogen and room temperatures.•The mechanical anisotropy exhibits more evident at liquid nitrogen temperature.•Twinning is likely to be inhibited at liquid nitrogen temperature.•Twinning in certain grains and grain rotation are two of the main mechanisms.The mechanical behavior and deformation mechanisms of AZ31 magnesium alloy at liquid nitrogen temperature were investigated by compressing samples with different original textures to fracture at liquid nitrogen and ambient temperatures with different constant true strain rates. The results showed that the samples compressed at liquid nitrogen temperature exhibit higher strength especially when compression axis parallel to extrusion direction. Mechanical anisotropy is more remarkable during compressing at liquid nitrogen temperature. Twinning tends to be inhibited at liquid nitrogen temperature, regardless of original orientation and strain rate. The two main deformation mechanisms at liquid nitrogen temperature are twinning in several certain grains and grain rotation.

The mechanical properties of AZ31 magnesium alloy compressed at high temperature (623–823 K) are investigated. The alloy was compressed along the rolling direction (RD) at a strain rate of 1 s−1. Optical microstructure observation and electron backscatter diffraction analysis reveal that the grain size and texture have a great influence on the mechanical properties. The fracture elongations (FE) of the compressed AZ31 Mg alloy samples are in the vicinity of 17% when the tensile direction is in the transverse direction (TD). When the tensile direction is in the normal direction (ND), the FE values grew abruptly at above 723 K. The yield stress (YS) value decreased linearly with the increasing deformation temperature along the TD. However, along the ND, the YS values decreased linearly at temperatures below 723 K but decreased more rapidly at temperatures higher than 723 K. The results show that mechanical anisotropy becomes stronger with the increasing temperature. This is because the orientations of the basal planes are rotated 90° from the ND to the RD at lower temperatures but about 45° from the ND to the RD after deformation at temperatures up to 823 K. The effects of grain size and texture on the mechanical properties are analyzed in detail.

Mechanisms of grain refinement were investigated in an extruded Mg–6Al–1Zn alloy during hot compression at 623 K and a true strain rate of 3 × 10−3 s−1. With increasing strain, grain fragmentation gradually took place; the dominant grain refinement mechanism, however, depended on the strain. At strains up to ɛ = 0.1, mechanical twinning contributed notably to grain refinement and to the formation of high angle boundaries. At medium to high strains, continuous dynamic recrystallization took place. Kinking contributed to grain fragmentation at all strains. The latter two mechanisms also increased the fraction of low to medium angle boundaries.Highlights► High temperature deformation behavior of Mg alloy. ► Complicated grain refinement mechanisms in AZ61Mg alloy. ► Grain refinement by twinning, kinking and continuous dynamic recrystallization. ► Strain dependence of the dominant grain refinement mechanisms.

The effect of prior strain on static recrystallization of hot-deformed magnesium alloy AZ31 was investigated at temperatures of 497, 503 and 513 K by optical and SEM/OIM metallographic observation. Ultrafine grains (UFGs) were evolved by grain fragmentation due to continuous dynamic recrystallization (cDRX) during hot deformation. Irrespective of the different microstructures developed at strains of 0.3 and 1.2, the kinetics of grain coarsening taking place during annealing are very similar, while the deformation texture scarcely changes even at longer times. The grain size changes at both the strains are categorized into three stages: i.e. an incubation for grain growth, a rapid and limited grain growth and then normal grain growth. It is concluded that the annealing process occurring in the regions of UFGs evolved is primarily controlled by grain growth accompanied with static recovery, that is continuous static recrystallization.Graphical abstractHighlights► Annealing of Mg alloy hot deformed to various strains. ► Ultrafine grains evolved partially or fully by continuous dynamic recrystallization. ► Grain coarsening takes place in three stages irrespective of the different microstructures. ► The annealing process can be primarily controlled by continuous static recrystallization.