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The rolling direction (RD) and the transverse direction (TD) samples were obtained from an as-rolled ZK60 magnesium alloy sheet with strong anisotropy of initial texture and their mechanical properties were tested at various deformation temperatures. Meanwhile, the microstructure and texture of these samples after fracture were investigated. Results revealed that a higher flow stress along the RD than that along the TD at room temperature were ascribed to the strong anisotropy of transitional texture, and this texture effect was remarkably weakened with the increase of deformation temperature. Deformation structure was dominant at 100 °C, and was replaced by dynamic recrystallization structure when the deformation temperature increased to 200 °C and 300 °C. The texture presented a strong texture (transitional texture in the RD sample and basal texture in the TD sample) at 100 °C, but its intensity visibly decreased and texture components became more disperse at 200 °C and 300 °C. These microstructure and texture results were employed in conjunction with calculated results to argue that raising deformation temperature could increase the activity of non-basal slip by tailoring the relative critical resolved shear stress of each deformation mode and finally result in low texture effect on mechanical anisotropy.

The rolling direction (RD) and transverse direction (TD) samples with distinct difference in initial texture were cut from differential speed rolled ZK60 magnesium alloy sheet and were subsequently subjected to the bending process. The bending behavior, microstructure and texture evolution of the bending samples were investigated to argue the effect of initial texture during the bending process. Results revealed that conspicuous asymmetry in the bending behavior was ascribed to the initial texture, and weaker basal texture was favorable to improve the bending properties. Meanwhile, initial texture remarkably influenced the microstructure characteristics, especially the number and morphology of (10–12) tension twin. Texture results revealed that initial texture in conjunction with the deformation mode led to the difference in texture evolution by influencing the deformation mechanism: (10–12) tension twin for the inner region of the RD sample; basal slip and prismatic slip for the outer region of the RD sample; basal slip and (10–12) tension twin for the TD sample. In addition, the bending behavior was reflected well by finite element method, and was investigated by strain-hardening curves based on experimental tests. Results suggested that the priority of deformation mechanism was dependent on the initial texture.

The AZ31 magnesium alloy sheets obtained by multi-pass hot rolling were applied to cold rolling and the maximum single pass cold rolling reduction prior to failure of AZ31 magnesium alloy was enhanced to 41%. Larger single pass rolling reduction led to weaker texture during the multi-pass hot rolling procedure. The sheet obtained showed weak basal texture, while the value was only 1/3–1/2 that of general as-rolled AZ31 Mg alloy sheets. It was beneficial for the enhancement of further cold rolling formability despite of the coarser grain size. The deformation mechanism for the formation of texture in AZ31 magnesium alloy sheet was also analyzed in detail.

ZK60 magnesium alloy sheets with various texture states were successfully fabricated by controlling the rolling temperature in multi-pass lowered-temperature rolling. The microstructure including texture and the mechanical properties of the resulting sheets were investigated. Results showed that dynamic recrystallization (DRX) during current rolling process could be realized at lower deformation temperature when the thickness reduction per pass was larger than 30%, and with its help, the grain size was significantly refined and the microstructure homogeneity strikingly improved. In this circumstance, deformation temperature mainly influenced the texture state of the resulting sheets, implying that with the increase of deformation temperature the distribution of (0002) basal planes remained stable along the rolling direction but gradually increased along the transverse direction. The calculation results about the friction stress for various deformation modes indicated that the changing ratios of the critical resolved shear stress (CRSS) for the non-basal slip to that for basal slip resulted in this texture difference. Additionally, for the samples with the dominant deformation mode of basal slip, the yield stress gradually decreased and the uniform elongation increased with the weakening of basal texture. However, if dominant deformation mode changed, an abrupt change would occur in their values. This change of yield stress came from the change of CRSS, while uniform elongation from strain hardening rate.

The effects of grain size on the tensile and compressive strain hardening behaviors for extruded ZK61 alloys have been investigated by uniaxial tensile and compressive tests along the extrusion directions. Cylindrical tension and compression specimens of extruded ZK61 alloys with various sized grain were fabricated by annealing treatments. Tensile and compressive tests at ambient temperature were conducted at a strain rate of 0.5 × 10−3 s−1. The results indicate that both tensile strain hardening and compressive strain hardening of ZK61 alloys with different grain sizes have an athermal regime of dislocation accumulation in early deformation. The threshold stress value caused dynamic recovery is predominantly related to grain size in tensile strain hardening, but the threshold stress values for different grain sizes are almost identical in compressive strain hardening. There are obvious transition points on the tensile strain hardening curves which indicate the occurrence of dynamic recrystallization (DRX). The tensile strain hardening rate of the coarse-grained alloy obviously decreases faster than that of fine-grained alloys before DRX and the tensile strain hardening curves of different grain sizes basically tend to parallel after DRX. The compressive strain hardening rate of the fine-grained alloy obviously increases faster than that of coarse-grained alloy for twin-induced strain hardening, but compressive strain hardening curves also tend to parallel after twinning is exhausted.

Multi-pass lowered-temperature rolling was applied on the friction stir welded ZK61 magnesium alloy sheets not only for fabricating wide high-performance wrought magnesium alloy sheets, but also for reducing the sheet inhomogeneity including the microstructure and mechanical properties induced by friction stir welding. Results showed that obvious microstructure inhomogeneity including plannar texture anisotropy between the base metal and the stir zone were introduced in the friction stir welded ZK61 alloy sheets, but can be strikingly weakened by hot rolling deformation via multiple dynamic recrystallization. These led to a uniform fine-grained structure of about 8 µm in average grain size and similar (0002) basal texture in the final 1.4 mm thick sheets, and brought a continuous improvement in the associated property differences, where the relatively lower yield strength in base metal zone was strongly correlated with spreading (0002) texture while higher values in stir zone with stable intense (0002) texture. Moreover, the experimental and calculated Hall–Petch relationships were investigated to explain the different evolution of yield strength between the base metal and the stir zone. Meanwhile, enhanced fracture elongations larger than 20% in both the base metal zone and the stir zone were primarily attributed to grain refinement.

Thin Mg—6.63 wt.%Zn—0.56 wt.%Zr (ZK61) magnesium alloy sheets with fine-grain structure were successfully fabricated by extrusion and multi–pass rolling with lowered temperature from 653 K to 523 K. Relationships between grain size, texture and mechanical properties of as–rolled ZK61 magnesium alloy were investigated. Microstructure homogeneity as well as planar texture anisotropy was strikingly improved by hot rolling deformation via multiple dynamic recrystallization. A uniform fine–grained structure of 6.1 μm in average grain size and a {0002} basal texture were obtained. These led to better strength isotropy in the plane, and high yield strengths of ∼200 MPa, which was related to pyramidal ( ) slip. Enhanced ductility more than 20% in fracture elongation was composed of uniform elongation strongly correlated with basal texture, especially along TD, and post–necking elongation enhanced by grain refinement.

Ductility enhancement up to about 28–39% in fracture elongation with simultaneous strengthening was achieved in fine-grained magnesium and magnesium alloy sheets by multi-pass rolling with lowered temperature suitable for industrial fabrication. Specifically, high strengths at yielding following slip-dominated Hall–Petch relations were achieved owning to the naturally twinning's replacement by pyramidal under intense basal texture. These Hall–Petch relations had a high slope of 190 MPa μm 1/2 and frictional stresses ranging from 40 MPa to 144 MPa. The variation in frictional stress matched well with solid solution hardening and/or precipitation hardening. Enhanced uniform elongation was strongly correlated with improved strain-hardening rate via introducing solid solution and/or fine precipitates in Mg alloys compared with pure Mg, and conversely post-necking elongation (local elongation) as well as cold-workability under compressive stress was strikingly weakened by the restriction of dynamic recovery.

In this work, the influence of various rolling temperatures and thickness reductions on the dynamic recrystallization (DRX) behavior of AZ31 magnesium alloy sheets was investigated. Meanwhile, the texture variation controlled by DRX behavior was analyzed. Results suggested that, with the help of DRX behavior, reasonable matching of rolling temperature and thickness reduction could effectively refine the grain size and improve the microstructure homogeneity. Using the grain refinement and microstructure homogeneity as the reference, the critical rolling process parameters were 400 &deg, C&mdash, 30%, 300 &deg, 30%, and 250 &deg, 40% in the present work. In terms of basal texture variation, the occurrence of twins produced the largest maximum texture intensity. However, for the sheets with DRX behavior, the maximum texture intensity decreased sharply, but would steadily increase with the growth of DRXed grain. Additionally, for DRXed grains, the &lt, 11-20&gt, //RD (RD: rolling direction) grains would gradually annex the &lt, 10-10&gt, //RD grains with the growth of DRXed grains, which finally made their texture component become the dominant texture state. However, when the deformation continued, the &lt, in DRXed grains would rotate toward the RD again. Weighted by the fracture elongation of AZ31 magnesium alloy sheet, the critical thickness reductions were 30&ndash, 40% under the rolling temperature of 400 &deg, C.

In order to investigate the dependence of microstructure and mechanical properties on the rolling process parameters, AZ31 magnesium alloy sheets with different grain sizes, basal texture intensities and twinning types were obtained using hot rolling at various temperatures and reductions. The volume fractions of the extension, contraction and secondary twins in the as-rolled sheets depend on the grain size. The highest volume fractions of three types of twins are obtained at 523 K under the reduction of 10% when the average grain size value is the maximum. The critical reductions for complete dynamic recrystallization are 30% at 523 K and 40% at 473 K. The increase of yield strength is ascribed to both grain-refinement strengthening and basal texture strengthening at the first stage. When the grain size does not decrease with increasing the reduction, the yield strength is mainly influenced by the texture weakening.

An ultra-high strength and high ductility Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr Mg alloy sheet was fabricated by vertical direct chill casting, extrusion, hot rolling and peak-ageing treatment. The peak-aged sheet shows tensile yield strength of 416 MPa, ultimate tensile strength of 505 MPa and superior elongation to failure of 12.8% at ambient temperature. The remarkable improvement of strength is ascribed to the fine β′ phase precipitated within the grains, grains with strong basal texture and the dispersed long period stacking ordered (LPSO) phases located at the grain boundaries.

The Mg-Gd-Y-Zn-Zr sheets with different accumulative rolling reduction were successfully prepared through the multi-passes hot rolling process. The accumulative rolling reduction significantly affects the mechanical properties of the resulting sheets through altering the fraction of dynamic recrystallization (DRX) grains and distribution of the broken interdendritic 14H-LPSO phase. In addition, the precipitated equilibrium β phase at grain boundaries can facilitate the DRX process through the particle-stimulated nucleation (PSN) mechanism. The sub-grain boundaries formed in the vicinity of the grain boundaries and within the coarse deformed grains, and then transformed into the high-angle grain boundaries (HAGBs) through incorporating the adjacent dislocation. The coarse deformed grains were also divided into several grains by the formation of HAGBs and the DRX grains at grain boundaries also spread into the coarse deformed grains, and thus the fraction of the DRX grains improved with the increase of the accumulative rolling reduction. The ambient temperature tensile strength anisotropy of the resulting sheets increases with further accumulative rolling reduction. The effectively broken interdendritic 14H-LPSO phases, which acts as the reinforcing short-fiber, significantly strengthen the tensile yield strength along the RD due to its decreased aspect ratio (d/l) and more dispersed distribution aligned along the RD. Thus, the tensile yield strength along the RD demonstrated the higher increment than that along the TD and 45° with increasing accumulative rolling reduction. The broken interdendritic 14H-LPSO phases aligned along the RD also contribute to the higher fracture elongation along the 45° due to its alignment parallel to the resolved maximum shear stress during tension. Furthermore, the larger accumulative strain is conducive to decreasing the tensile anisotropy of the resulting sheets at elevated temperature.