Mg-6.6%Y-2.3%Zn (WZ62, mass fraction) magnesium alloys were fabricated by equal-channel-angular-extrusion (ECAE), and ECAE followed by forging processing, respectively. The “necklace” structure that is composed of fine recrystallized and coarse initial grains was found. The process of dynamic recrystallization (DRX) is associated with the strain localization. With increasing ECAE passes, the tensile test results reveal that both the strength and elongation are enhanced. A typical non-basal texture component in the (0002) pole figures with tilted peaks at about 45° was observed. After ECAE followed by forging processing, the strength increases greatly with sacrificed ductility. That is attributed to the change in the texture: the majority of basal planes is rotated to be normal to the normal direction. The non-basal texture induced by ECAE is modified by the secondary forging processing.

Repeated unidirectional bending (RUB) was carried out to improve the texture of commercial AZ31B magnesium alloy sheets. All specimens were prepared in the rolling direction. The forming limit diagrams (FLDs) of AZ31B magnesium alloy sheet were determined experimentally by conducting stretch-forming tests at room temperature, 100, 200 and 300 °C. Compared with the as-received sheet, the lowest limited strain of AZ31B magnesium alloy sheet with tilted texture in the FLD increased by 79% at room temperature and 104% at 100 °C. The texture also affected the extension of the forming limit curves (FLC) in the FLD. However, the FLCs of two kinds of sheets almost overlapped at temperature above 200 °C. It can be concluded that the reduction of (0002) texture intensity is effective to the improvement of formability not only at room temperature but also at low-and-medium temperature. The effect of texture on FLDs becomes weak with increasing temperature.

The effect of the repeated unidirectional bending (RUB) process and annealing on the formability of magnesium alloy sheets was investigated. The RUB process and annealing treatments produce two effects on microstructure: grain coarsening and weakening of the texture. The sheet that underwent RUB and was annealed at 300 °C exhibits the best formability owing to the reduction of the (0002) basal texture intensity, which results in low yield strength, large fracture elongation, small Lankford value (r-value) and large strain hardening exponent (n-value). Compared with the as-received sheet, the coarse-grain sheet produced by RUB and annealing at 400 °C exhibits lower tensile properties but higher formability. The phenomenon is because the deformation twin enhanced by grain coarsening can accommodate the strain of thickness.

Ring hoop tension test and tube bulging test were carried out at elevated temperatures up to 480 °C to evaluate the formability of AZ31B extruded tube for internal high pressure forming (IHPF) process. The total elongation along hoop direction and the maximum expansion ratio (MER) of the tube were obtained. The fracture surface after bursting was also analyzed. The results show that the total elongation along hoop direction and the MER value have a similar changing tendency as the testing temperature increases, which is quite different from the total elongation along axial direction. Both the total elongation along hoop direction and the MER value increase to a peak value at about 160 °C. After that, they begin to decrease quickly until a certain rebounding temperature is reached. From the rebounding temperature, they begin to increase rapidly again. Burnt structure appears on the fracture surface when tested at temperatures higher than 420 °C. Therefore, the forming temperature of the tested tube should be lower than 420 °C, even though bigger formability can be achieved at higher temperature.

The hot working behaviors of Mg-9Y-1MM-0.6Zr (WE91) magnesium alloy were researched in a temperature range of 653−773 K and strain rate range of 0.001−1 s⁻¹ on Gleeble−1500D hot simulator under the maximum deformation degree of 60%. A mathematical model was established to predict the stress—strain curves of this alloy during deformation. The experimental results show that the relationship between stress and strain is obviously affected by the strain rates and deformation temperatures. The flow stress of WE91 magnesium alloy during high temperature deformation can be represented by Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation, and the stress—strain curves obtained by the established model are in good agreement with the experimental results，which prove that the model reflects the real deformation characteristics of the WE91 alloy. The average deformation activation energy is 220 kJ/mol at strain of 0.1. The microstructures of WE91 during deformation processing are influenced by temperature and strain rates.

A high strength GW94 alloy with fully recrystallized microstructure and equiaxed ultrafine grains of submicron size was produced by multiaxial forging and ageing. The alloy exhibits an ultimate tensile strength of 377 MPa, proof stress of 295 MPa and elongation to failure of 21.7%. The ductility is improved in comparison with that of the conventional extrusion processing. Superplastic ductility is achieved in tensile testing at 573 K with a maximum elongation of 450%. These high ductility and high strength are attributed to the coexistence of fully recrystallized grains and nanoscale Mg₅(Gd, Y) particles dynamically precipitated at grain boundaries.

The relative effect of Zn addition to Mg-2%Ca based alloy on the creep and corrosion characteristics was compared with Al addition. The creep resistance of Mg-2%Ca based alloy at 175 °C was improved by Zn addition more significantly than by Al addition. However, the Al addition showed more effective in enhancing corrosion resistance. Since the solidification range for Zn-added alloy was considerably wide, the cautious casting design may be necessary to produce high-quality castings.

The microstructure and mechanical properties of the cast and extruded Mg-12Zn-1.5Er alloys were investigated. The I-phase observed in the cast Mg-12Zn-1.5Er alloy was broken during hot extrusion. The microstructure of the alloy was refined due to the dynamic recrystallization, and the equiaxed grains have size in the range of 2−5 μm. Moreover, a great deal of nano-scale particles precipitate in the recrystallized grains. Compared with the cast one, the extruded alloy shows a great improvement on the mechanical properties as the result of refined microstructure, the dispersed I-phase and the fine precipitates. The ultimate tensile strength and the yield tensile strength of this extruded alloy are 359 and 318 MPa, respectively.

The effects of texture and abnormal large grains on the plastic anisotropy and fracture behavior of hot-rolled AZ31 magnesium alloy were investigated. Uniaxial tensile deformation behaviors of samples with tensile axis tilting 0°, 15°, 30°, 45°, 60°, 75° and 90° to normal direction (ND) respectively were addressed. Tensile deformation anisotropy was observed for samples with different angles to ND. The results show that the specimens with the angle from 0° to 30° exhibit relatively lower yielding strength due to the  extension twinning. However, basal slip and prismatic slip are the dominant deformation modes for the specimens with angles larger than 45°. Macro-fractures are parallel to the length direction of abnormal large grains in the specimens with angles less than 60°, while those are serrated fracture edge for specimens with angles 75° and 90°.

Neural network models of mechanical properties prediction for wrought magnesium alloys were improved by using more reasonable parameters, and were used to develop new types of magnesium alloys. The parameters were confirmed by comparing prediction errors and correlation coefficients of models, which have been built with all the parameters used commonly with training of all permutations and combinations. The application was focused on Mg-Zn-Mn and Mg-Zn-Y-Zr alloys. The prediction of mechanical properties of Mg-Zn-Mn alloys and the effects of mole ratios of Y to Zn on the strengths in Mg-Zn-Y-Zr alloys were investigated by using the improved models. The predicted results are good agreement with the experimental values. A high strength extruded Mg-Zn-Zr-Y alloy was also developed by the models. The applications of the models indicate that the improved models can be used to develop new types of wrought magnesium alloys.

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies. The research activities are funded primarily through four government-supported programs: the Key Technologies R&D Program of China, the National Basic Research Program of China, the National High-tech R&D Program of China, and the National Natural Science Foundation of China. The key R&D activities for the development of new wrought magnesium alloys in China are reviewed, and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys. Some novel plastic processing technologies, emerging in recent years, which aim to control deformation texture and to improve plasticity and formability especially at room temperature, are also introduced.

The mechanical properties of the Mg97Zn1Y2 extruded alloy containing the long-period stacking ordered phase, the so-called LPSO-phase, with a volume fraction of 24%−25%, were examined by compression tests and cyclic tension−compression deformation tests. The plastic behavior of the extruded alloys with compositions of Mg99.2Zn0.2Y0.6 and Mg89Zn4Y7 (molar fraction, %), which were almost the same compositions of Mg matrix phase and LPSO phase in Mg97Zn1Y2 Mg/LPSO two-phase alloy, respectively, were also prepared. By comparing their mechanical properties, the strengthening mechanisms operating in the Mg97Zn1Y2 extruded alloy were discussed. Existence of the LPSO-phase strongly enhanced the refinement of Mg matrix grain size during extrusion, which led to a large increment of the strength of alloy. In addition, the LPSO-phases, which were aligned along the extrusion direction in Mg97Zn1Y2 extruded alloy, acted as hardening phases, just like reinforced fibers.

The static recrystallization of hot-deformed magnesium alloy AZ31 during isothermal annealing was studied at temperature of 503 K by optical and SEM/EBSD metallographic observation. The grain size change during isothermal annealing is categorized into three regions, i.e. an incubation period for grain growth, rapid grain coarsening, and normal grain growth. The number of fine grains per unit area, however, decreases remarkably even in incubation period. This leads to grain coarsening taking place continuously in the whole period of annealing. In contrast, the deformation texture scarcely changes even after full annealing at high temperatures. It is concluded that the annealing processes operating in hot-deformed magnesium alloy with continuous dynamic recrystallized grain structures can be mainly controlled by grain coarsening without texture change, that is, continuous static recrystallization.

In order to realize cold forging of magnesium alloys in practical application, some methods for ductility improvement of a commercial wrought AZ31B magnesium alloy (Mg-3%Al-1%Zn, mass fraction) at room temperature were suggested. The effects of heat treatment before forging and hydrostatic pressure during forging on the ductility were investigated in cold upsetting and cup forging. High-temperature annealing was effective to reduce the degree of the texture anisotropy of the specimen, and it was found that the forging limit of the annealed specimen was improved in cold forging. On the other hand, cold cup forging of the annealed specimen was carried out with applying counter pressure. By applying counter pressures of 100−200 MPa during forging, the critical punch stroke for forging limit of the specimen without crack was improved by 25% in punch stroke.

Stress intensity factors of thin AZ31B magnesium alloy sheet under biaxial tension loading were analyzed by modified Dugdale model. K-values with crack angle of 90˚ obviously show that there is no influence of the loading condition in Mode-I. In the 45˚ case, K_Ⅰ values are obtained within 10% errors when they are calculated by modified Dugdale model under biaxial loading. It is concluded that the modified Dugdale model is one of effective ways to evaluate stress intensity factor of AZ31 magnesium alloy sheet appropriately.

In tube hydroforming with axial feeding, under the effect of coupled internal pressure and axial stress, wrinkles often occur and affect the forming results. Wrinkling behavior of an AZ31B magnesium alloy tube was experimentally investigated with different loading paths at different temperatures. Features of wrinkles, including shape, radius and width, were acquired from the experiments, as well as the thickness distribution. Numerical simulations were carried out to reveal the stress state during warm hydroforming, and then the strain history of material at the top and bottom of the wrinkles were analyzed according to the stress tracks and yielding ellipse. Finally, effects of loading paths on expansion ratio limit of warm hydroforming were analyzed. It is verified that at a certain temperature, expansion ratio limit can be increased obviously by applying a proper loading path and realizing enough axial feeding.

AZ61Mg alloy was multi directionally forged (MDFed) during decreasing temperature condition from 643 K to 483 K at a true strain rate of 3×10⁻³ s⁻¹ up to cumulative strain of ∑∆ε=4.0 at maximum. A pass strain of ∆ε=0.8 was employed. While average grain size decreased gradually with increasing cumulative strain, the evolution of fine-grained structure strongly depended on the MDF temperature. Under the condition where the temperature was higher than the most adequate one, grain coarsening partially took place during MDF. In contrast, at lower temperature, inhomogeneous microstructure composed of the initial coarse and newly appeared fine grains was evolved. After straining over ∑∆ε=3.2 (i.e., over 4 passes of MDF), equiaxed ultrafine grains (UFGs) having average size of about and lower than 1 μm were uniformly evolved. While the MDFed alloy to ∑∆ε=4.0 possessed relatively high hardness of HV 99, and it accepted further about 20% cold rolling almost without cracking. Because of the superior formability of the UFGed AZ61Mg alloy, the hardness was further easily raised to HV 120 by following cold rolling.

The influence of impurity content on the microstructure and mechanical properties of ZK60 magnesium alloys was investigated by optical microscopy, scanning electron microscopy and tensile test. ZK60 alloys were prepared by changing holding time of alloy melt during semi-continuous casting in order to control the content of impurity elements. The alloy with lower purity content is found to have less second precipitates and larger grain size in the as-cast state. However, in the as-extruded state, reducing impurities brings about a decrease in grain size and an increase in yield strength from 244 MPa to 268 MPa, while the elongations in the as-extruded alloys with different contents of impurities are almost the same. After T5 treatment, impurity content is found to have more obvious effect on the yield strength of ZK60 alloy. The yield strength of ZK60-45 alloys with low impurity content is increased up to 295 MPa after T5 treatment.

The influence of impurities on damping capacities of ZK60 magnesium alloys in the as-cast, as-extruded and T4-treated states was investigated by dynamically mechanical analyzer at room temperature. Granato and Lucke dislocation pinning model was employed to explain damping properties of the alloys. It is found that reducing impurity content can decrease the amount of second-phase particles, increase grain size and improve damping capacity of the as-cast alloy slightly. The as-extruded alloy with lower impurity content is found to possess obviously higher damping capacity in the relatively high strain region than that with higher impurity concentration, which appears to originate mainly from different dislocation characteristics. The variation tendency of damping property with change of impurity content after solution-treatment is also similar to that in the as-extruded and as-cast states. Meanwhile, the purification of the alloy results in an evident improvement in tensile yield strength in the as-extruded state.

The solution-treated Mg-4Y-4Sm-0.5Zr alloy was extruded at temperatures from 325 ˚C to 500 ˚C. Dynamic recrystallization (DRX) completely occurs when the alloy is extruded at 350℃ and above. The grains of the extruded alloy are obviously refined by the occurrence of DRX. The average grain size of the extruded alloy increases with increasing the extrusion temperature, leading to a slight decrease of the ultimate tensile strength (UTS) and the yield strength (YS). On the contrary, the UTS and YS of the extruded and aged alloy increase with increasing the extrusion temperature. Values of UTS of 400 MPa, YS larger than 300 MPa and elongation (EL) of 7% are achieved after extrusion at 400 ˚C and ageing at 200 ˚C for 16 h. Both grain refinement and precipitation are efficient strengthening mechanisms for the Mg-4Y-4Sm-0.5Zr alloy.

Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10⁻³ to 2×10⁴ s⁻¹. The results show that the compressive behavior and deformation mechanism of AZ31 depend largely on the temperature and strain rate. The flow stress increases with the increase of strain rate at fixed temperature, while decreases with the increase of deformation temperature at fixed strain rate. At low temperature and quasi-static condition, the true stress—true strain curve of AZ31 alloy can be divided into three stages (strain hardening, softening and stabilization) after yielding. However, at high temperature and high strain rate, the AZ31 alloy shows ideal elastic-plastic properties. It is therefore suggested that the change in loading conditions (temperature and strain rate) plays an important role in deformation mechanisms of AZ31 alloy.

The microstructure and mechanical properties of Mg-xSn (x=3, 7 and 14, mass fraction, %) alloys extruded indirectly at 300 ˚C were investigated by means of optical microscopy, scanning electron microscopy and tensile test. The grain size of the α-Mg matrix decreases from 220, 160 and 93 μm after the homogenization treatment to 28, 3 and 16 μm in the three alloys after extrusion, respectively. The results show that the grain refinement is most remarkable in the as-extruded Mg-7Sn alloy. At the same time, the amount of the Mg₂Sn particles remarkably increases in the Mg-7Sn alloy with very uniform distribution in the α-Mg matrix. In contrast, the Mg₂Sn phase inherited from the solidification with a large size is mainly distributed along grain boundary in the Mg-14Sn alloy. The tensile tests at room temperature show that the ultimate tensile strength of the as-extruded Mg-7Sn alloy is the highest, i.e., 255 MPa, increased by 120% as compared with that of as-cast samples.

The process of mechanically assisted hydriding and subsequent thermal dehydriding was proposed to produce nanocrystalline Mg and Mg alloy powders using pure Mg and Mg-5.5%Zn-0.6%Zr (mass fraction) (ZK60 Mg) alloy as the starting materal. The hydriding was achieved by room-temperature reaction milling in hydrogen. The dehydriding was carried out by vacuum annealing of the as-milled powders. The microstructure and morphology of both the as-milled and subsequently dehydrided powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), respectively. The results show that, by reaction milling in hydrogen, both Mg and ZK60 Mg alloy can be fully hydrided to form nanocrystalline MgH₂ with an average grain size of 10 nm. After subsequent thermal dehydriding at 300 ˚C, the MgH₂ can be turned into Mg again, and the newly formed Mg grains are nanocrystallines, with an average grain size of 25 nm.