The deformation behaviors of extruded-rolled (ER) AZ31 Mg alloys with different rolling reduction and heat treatment were investigated. The results show that the accumulation of rolling reduction increases the density of twins, and refines the grain structures, which are in accordance with the enhanced strength and degraded plasticity. Tensile strength and plasticity of the alloy depend mainly on rolling reduction, while heat treatment temperature plays a more important role than heat treatment time at the same rolling reduction. With the increase of rolling reduction, the plasticity becomes more sensitive than strength on heat treatment. Recrystallization of extruded-rolled alloys will occur easily with deformation increasing, which is induced by addition of distortion energy.

An experimental Mg₉₇Zn₁Y₂ (molar fraction, %) alloy was produced by rolling the as-cast alloy. The microstructure of the alloy is composed of the α-Mg (also marked as 2H-Mg with reference to long-period stacking structure according to hexagonal close packed structure) and long-period stacking (LPS) phase. Tensile tests of Mg₉₇Zn₁Y₂ alloy in comparison with pure Mg were conducted. The fracture morphologies of the tensile specimens were characterized and the microstructures near fracture surface were observed. The results show that the rolled Mg₉₇Zn₁Y₂ alloy shows a mixed fracture mode including dimples indicating a ductile fracture pattern and a small fraction of cleavage planes indicating a brittle fracture pattern, which is different from the single brittle fracture of the as-cast alloy. In addition, the plastic deformation is mainly from dislocations induced strain with small strengthening effect during plastic deformation in the as-cast Mg₉₇Zn₁Y₂ alloy, and the strain hardening rate is similar to that of the as-cast pure magnesium. The deformation mechanism of Mg₉₇Zn₁Y₂ alloy is different from that of the pure magnesium according to a metallographical observation that whether twins are found or not. The strengthening effect hardly exists in the rolled Mg₉₇Zn₁Y₂ alloy under the same dislocations induced strain, which is different from that of the as-cast alloy with moderate strengthening effect.

The microstructure and tensile properties of the Mg-1.0%Sn-xY(x=1.5%, 3.0%, 3.5%, atom fraction) alloys extruded indirectly at 350 ˚C were investigated by means of optical microscopy, scanning electron microscopy and tensile test. The mean grain sizes of α-Mg matrix in the three extruded alloys are 6, 8 and 12 μm, respectively, slightly increasing with the addition of Y. The relationship between microstructure and strength was discussed in detail. The results show that the addition of Y has little effect on the grain refinement of the as-extruded Mg-Sn based alloys above. The only MgSnY phase is detected in the Mg-Sn-1.5%Y alloy, and the Sn₃Y₅ phase in the Mg-Sn-3.5%Y alloy, whereas both of them simultaneously exist in the Mg-Sn-3.0%Y alloy. The particle shape of MgSnY and Sn₃Y₅ phase, inherited from the solidification, has little change before and after hot extrusion. Mg-Sn-3.0%Y alloy has the highest ultimate tensile strength (UTS), 305 MPa, by over 50% compared with that of the other two alloys.

A mini-type rolling machine was employed for multi-passes rolling of a Mg-5Zn-3Nd(-Zr)(mass fraction, %) wrought alloy. For the sake of providing experimental basis for magnesium alloy rolling process, optical microscopy, SEM and TEM observations were used to study the microstructure evolution of magnesium alloys subjected to different rolling reductions before and after annealing. Investigations show that multi-passes can be achieved for this alloy at ambient temperature, but 330 ˚C, 15 min annealing was needed for next pass rolling, and total deformation degree was 66%. With the increase in total deformation degree, rolling streams form and the average grain size decreases gradually. The microstructure after rolling is mainly composed of twining, and multiple twining in parallel distribution is also observed. The average grain size in the as-cast condition is about 50 μm and decreases to about 10−20 μm after rolling, whereas the twinning spacing is limited to 1−2 μm. SAED analysis in the twinning area indicates that twinning takes place at {10 1} plane. Complete recrystallization can occur in Mg-5Zn-3Nd(-Zr) alloys with various rolling reductions and after 200 ˚C, 120 min or 300 ˚C, 10 min annealing. Meanwhile, grain growth is apparent under heat treatment at 300 ˚C.

Al-5Ti-1B master alloy was added into Mg-14Li-1Al (LA141) alloy and then LA141 sheets were prepared by extrusion and cold rolling. The effect of the addition level of Al-5Ti-, 1B master alloy on the grain size of LA141 alloy was investigated as well as the effects of the total reduction of cold rolling and the annealing temperature on microstructure, mechanical properties and plastic formability of the LA141 sheets. The results show that the optimal addition level of Al-5Ti-1B master alloy into LA141 alloy is 1.25% (mass fraction) and LA141 alloy has the finest grains. With the increase of the total reduction of cold rolling, the grains of the as-rolled LA141 sheets were flattened gradually. A proper anneal temperature of 200 ˚C is obtained for the cold rolled LA141 sheets. Under this condition, microstructure of the LA141 sheets consists of fine and uniform equiaxed grains and has higher Erichsen cupping index (IE).

The Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy ingot and sheet were prepared by casting and hot extrusion techniques, and the microstructure, age hardening behavior and mechanical properties were investigated. The results show that the as-cast alloy mainly contains α-Mg solid solution and compounds of Mg₅RE and Mg₂₄RE₅ (RE=Gd, Y and Nd) phases. The grain size is refined after hot extrusion, and the Mg₅RE and Mg₂₄RE₅ compounds are broken during the extrusion process. The extruded alloy exhibits remarkable age hardening response and excellent mechanical properties in the peak-aging state. The ultimate tensile strength, yield strength and elongation are 310 MPa, 201 MPa and 5.8% at room temperature, and 173 MPa, 133 MPa and 25.0% at 300 ˚C, respectively.

A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca (AZ41, mass fraction, %) magnesium alloy was put forward. The results show that the dynamic material model can characterize the deformation behavior and microstructure evolution and describe the relations among flow stress, strain, strain rates and deformation temperatures. Statistical analysis shows the validity of the proposed model. The model predicts that lower deformation temperature and higher strain rate cause the sharp strain hardening. Meanwhile, the flow stress curve turns into a steady state at high temperature and lower strain rate. The moderate temperature of 350 ℃ and strain rate of 0.01 s⁻¹ are appropriate to this alloy.

The plastic deformation processes of magnesium alloys near a void at atomic scale level were examined through molecular dynamics (MD) simulation. The modified embedded atom method (MEAM) potentials were employed to characterize the interaction between atoms of the magnesium alloy specimen with only a void. The void growth and crystal failure processes for hexagonal close-packed (hcp) structure were observed. The calculating results reveal that the deformation mechanism near a void in magnesium alloy is a complex process. The passivation around the void, dislocation emission, and coalescence of the void and micro-cavities lead to rapid void growth.

Fatigue strength, crack initiation and propagation behavior of rolled AZ31B magnesium alloy plate were investigated. Axial tension−compression fatigue tests were carried out with cylindrical smooth specimens. Two types of specimens were machined with the loading axis parallel (L-specimen) and perpendicular (T-specimen) to rolling direction. Monotonic compressive 0.2% proof stress, tensile strength and tensile elongation were similar for both specimens. On the other hand, monotonic tensile 0.2% proof stress of the L-specimen was slightly higher than that of the T-specimen. Moreover, monotonic compressive 0.2% proof stresses were lower than tensile ones for both specimens. The fatigue strengths of 10⁷ cycles of the L- and T-specimens were 95 and 85 MPa, respectively. Compared with the monotonic compressive 0.2% proof stresses, the fatigue strengths were higher for both specimens. In other words, the fatigue crack did not initiate and propagate even though deformation twins were formed in compressive stress under the cyclic tension−compression loading. The fatigue crack initiated at early stage of the fatigue life in low cycle regime regardless of specimen direction. The crack growth rate of the L-specimen was slightly lower than of the T-specimen. Consequently, the fatigue lives of the L-specimen were longer than those of the T-specimen in low cycle regime.

The mechanical properties and deformation mechanism of semi-continuously casting and as-extruded AZ70 magnesium alloys in a wide range of grain sizes (from 14 to 103 μm) were investigated at 653 K and 1×10⁻³ s⁻¹. It is discovered that with reducing grain size, flow stress is weakened and plasticity is improved and even superplasticity exhibits. SEM and OM were used to clarify the deformation mechanism. It is suggested that dynamic recrystallization (DRX) is the coordination deformation mechanism of grain boundary sliding (GBS) for coarse grain, and cavity and intracrystalline slip are the coordination deformation mechanisms of GBS for fine grain.

The low cycle fatigue(LCF) properties of as-extruded AZ31 Mg alloy were investigated under total strain amplitudes in the range of 0.4%−1.2% with strain rate of 1×10⁻² s⁻¹. Due to the twinning effect in compression during loading and the detwinning effect during unloading, the alloy showed an asymmetric hysteresis loop. The cyclic stress response exhibited cyclic hardening at high total strain amplitudes. The cyclic deformation behaviors were discussed using the Coffin-Manson plot, which divided the plastic strain amplitudes into the tension side and the compression side. Through the LCF tests that were started from either tension or compression under a total strain amplitude of 1.0%, the interaction between the twinning effect and dislocation was analyzed. The twinning effect during the LCF test and the variation of the dislocation density were investigated using optical microscopy and transmission electron microscopy, respectively.

High temperature tensile ductilities and deformation mechanisms of an extruded and rolled AZ31 Mg alloy were investigated. Elongation-to-failure tests were conducted under constant T-head velocity and constant temperatures ranging from  300 ˚C to 450 ˚C. Strain-rate-change tests were conducted under varying strain rate from 5×10⁻⁵ s⁻¹ to 2×10⁻² s⁻¹ and constant temperature from 300 ˚C to 450 ˚C. Experimental results show that the maximum elongation of the AZ31 alloy with an average grain size of about 19 μm is 117% at strain rate of 10⁻³ s⁻¹ and temperature of 450 ˚C. Stress exponent and activation energy were characterized to clarify the deformation mechanisms. The enhanced ductility is dominated by solute drag dislocation creep, and the major failure mechanism is cavity growth and interlinkage.

Tensile creep behaviors of the ageing hardened Mg-10Gd-3Y alloy (referred to GW103) were investigated at temperatures up to 300 ℃. The extruded-T5 specimen exhibited high creep resistance, i.e. the low steady-state creep rate and long creep rupture time, while the better creep properties were observed in the cast-T6 one. The low steady-state creep rate of 1.71×10⁻⁹ s⁻¹ is obtained at 200 ℃ and 80 MPa for the extruded-T5 GW103 alloy. In addition, the microstructure development of GW103-T5 alloy was also examined after creep exposure at different temperatures. On the other hand, the stress exponent and activation energy were studied in the temperature range of 200−300 ℃ for the extruded-T5 specimens, and the creep mechanism was also discussed.

The microstructures and mechanical properties of Mg-8Li and Mg-8Li-2Al-2RE alloy sheets were evaluated after cold rolling. Both alloys contain α-phase and β-phase which consists of a solid solution of Mg in BCC Li. The proportion of β-phase in both alloys is approximately 60%. The α-phase and β-phase are elongated approximately parallel to the rolling direction and there is no sign of recrystallization even after being annealed at 200 ℃ for 1 h. The yield strength of Mg-8Li-2Al-2RE sheets is about 165 MPa with elongation of 35% along rolling direction, while the yield strength is about 187 MPa with elongation of 21% along the direction titled 45˚ to rolling direction. The α-phase in both alloys exhibits basal texture, and the intensity of basal texture in Mg-8Li is larger than that in Mg-8Li-2Al-2RE. However, the β-phase shows (100) texture, and the intensity of (100) texture in Mg-8Li is twice of that in Mg-8Li-2Al-2RE. It could be attributed to the existence of RE-containing particles in Mg-8Li-2Al-2RE.

Both Mg-1Mn-3.5Y and Mg-1Mn-1Y-2.5Nd alloys (mass fraction, %) were extruded at 380 ˚C. Most of the ( ) crystal planes in the Mg-1Mn-3.5Y alloy are parallel to the normal direction, while most of the ( ) crystal planes in the Mg-1Mn-1Y-2.5Nd alloy are parallel to the normal direction. The tensile tests at room temperature, 100 ˚C and 200 ˚C show that the Mg-1Mn-3.5Y alloy exhibits higher yield strength, but lower elongation to failure as compared with the Mg-1Mn-1Y-2.5Nd alloy. These differences in the tensile mechanical properties between the two alloys are mainly attributed to their different texture types and amount and distribution of the Mg₂₄Y₅ precipitates. The serration flow behavior is observed in the Mg-1Mn-1Y-2.5Nd alloy at 200 ˚C, but does not occur in the Mg-1Mn-3.5Y alloy. The Mg-1Mn-3.5Y alloy shows the cleavage fracture mode, while the Mg-1Mn-1Y-2.5Nd alloy exhibits the dimple fracture mode.

The micro orientation theological behavior of AZ61 Mg alloy during net-shape forming of tensile specimens via close-die pressing of extruded preformed and the effect of the press deformation rate on the microstructure characteristics were characterized with electron back-scattering diffraction (EBSD) orientation imaging microscopy and metallography. The results indicate that the intensity distribution of basal {0001}< > texture on the cross-section of the extruded perform is uniform and parallel to the extrusion direction. Subjected to pressing in extrusion direction, deformation shear stress leads to grain rotation and basal texture {0001}< > deviation from the extrusion direction, spreading in the direction perpendicular to pressing direction. The texture intensity increases with the press deformation rate and reaches its peak value at 50%, which is considerably lower than the value reached in extrusion deformation. Then, the texture intensity decreases with the press deformation rate reversely.

The phase structure of ZK60-1Er magnesium alloy thermally compressed at the temperature of 450 ˚C and the strain rate of 1×10⁻⁴ s⁻¹ was determined by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The results show that this magnesium alloy contains many new W phases (Mg₃Zn₃Er₂, FCC structure) in the matrix. Those new W phases have two morphologies, either irregularly rectangular or rod morphology. Lattice constants of the two new W phases are slightly higher than those of W Phase (Mg₃Zn₃Y₂) containing rare earth element of yttrium.

Aging behaviors of extruded and rolled AZ80 and AZ31 Mg alloys were investigated under conditions similar to the paint-bake cycle currently used in automotive industry. Artificial aging at 170 ˚C from 0.5 to 12 h was conducted on solution-treated specimens to study the effects of aging on mechanical properties. SEM observations and EDS data show that β-phase of Al₁₂Mg₁₇ precipitates continuously or discontinuously from α-Mg matrix and distributes along grain boundaries of the AZ80 alloy during artificial aging. Data of tensile tests and Vickers hardness tests show that an optimum mechanical property is achieved after baking at 170 ˚C for 6−8 h when Vickers hardness, tensile strength, and elongation are increased by 6.35%, 15.30%, and 7.88%, respectively, while the AZ31 alloy does not exhibit significant hardening behavior over the aging period.

For 7475 Al alloy, there were micrographs showing filaments or whiskers formation during the separation stage of superplastic elongation. This indicates the presence of liquid phase which accommodates grain boundary sliding to reach superplasticity. On the other hand, there is no such phenomenon reported regarding Mg alloy in literatures. Scanning electron microscopic (SEM) fractography exceptionally exhibits a mark of grain boundary sliding and its accommodating mechanism of inter-granular liquid phase. Under the testing conditions of 350 ˚C and 1×10⁻⁴ s⁻¹, the initially fine-grained structure (3.7 μm) yields 642% superplastic elongation and exhibits fluffy appearance on the fractured surface. For other specimens showing less superplasticity, their fractured surfaces exhibit partial fluffy appearance.

A series of AZ80 billets were compressed with 60% height reduction on hot process simulator at 250, 300, 350, 400 ℃ under strain rates of 0.01, 0.1, 1 and 10 s⁻¹. In order to predict the occurrence of surface fracture, the values of the Cockcroft-Latham equation were calculated by the corresponding finite element numerical algorithm developed. A concept about damage incremental ratio in plastic deformation was defined as the ratio of damage increment at one step to the accumulated value. A method of finding the intersection of incremental ratio varying curve and simulation step axis was brought forward to make the fracture step certain. Then, the effects of temperature and strain rate on critical damage value were achieved. The results show that the critical damage value is not a constant but changes in a range of 0.021 8−0.378 0. It decreases significantly with the increase of strain rate at a certain temperature. While under a certain strain rate, the critical damage value has little change with the increase of temperature.

The dynamic recrystallization refinement of magnesium alloy AZ80 by compression tests was studied, and its effect on the mechanical properties was investigated. It is observed that the microstructure of the as-cast billet with grain size of 240 µm becomes refined to about 120, 110, 94 and 50 µm after upsetting at 350 ˚C under strain rates of 0.01, 0.1, 1 and 10 s⁻¹ respectively. The changes in the mechanical properties according to grain size show that yield strength significantly decreases with grain size increasing, while strain hardening exponent and micro hardness increase very sharply. Further, the grain size vs strain rate and change in Vickers micro hardness according to the various strain rates show that grain size and micro hardness decrease with strain rate increasing.

Two rolling ways, unidirectional rolling and cross rolling, were carried out on twin roll cast AZ31 alloy sheet to study the influence of strain path change on the evolution of the rolling microstructure and texture as well as the anisotropic properties of AZ31 alloy sheet with microscopy, X-ray diffraction technique and tensile tests. It is found that cross rolling gives rise to more uniform microstructure and stronger texture intensities compared with unidirectional rolling. The differences in the microstructure and texture intensities are reflected in the anisotropy characterized by the difference in the yield stress and the fracture elongation that were measured along directions in the rolling plane at angles of 0˚, 45˚ and 90˚ from the rolling direction.

In order to investigate the effects of strain rate and temperature on the microstructure and texture evolution during warm deformation of wrought Mg alloy, AZ31 extruded rods were cut into cylinder samples with the dimension of d8 mm×12 mm. The samples were compressed using a Gleeble 1500D thermo-mechanical simulation machine at various strain rates (0.001, 0.01, 0.1, 1 and 5 s⁻¹) and various temperatures (300, 350, 400 and 450 ˚C). The microstructure and texture of the compressed samples at the same strain under different deformation conditions were studied and compared by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). The results show that the size of recrystallized grains in the deformed samples generally increases with the decrease of strain rate and the increase of temperature. After 50% reduction, most basal planes are aligned perpendicular to the compression direction at relatively high strain rate (>0.01 s⁻¹) or low temperature (<350 ˚C). The optimized strain rate is 0.1 s⁻¹ for uniaxial compression at 300 ˚C, which produces about 80% of small grains (<5 μm).

The recent research and development of forged magnesium road wheel were reviewed. Methods of flow-forming, spin forging of manufacturing a forged magnesium alloy wheel were introduced. A new extrusion method was investigated especially. Extrusion from hollow billet was proposed in order to enhance the strength of spoke portion and reduce the maximum forming load. By means of the developed technique, the one-piece Mg wheels were produced successfully by extrusion from AZ80+ alloy. At the same time, the existing problems on the research and development of forged magnesium road wheel were analyzed. The impact testing, radial fatigue testing and bending fatigue testing results show that AZ80+ wheel can meet application requirement in automobile industry.

AZ91 Mg alloy recycled by a solid state process and equal channel angular pressing (ECAP) exhibited a superior strength. The mechanical properties of AZ91 Mg alloy recycled from machined chips by extrusion at 623 K and ECAP at 573 K and 623 K were compared with those of the reference alloy which was produced from an as-received AZ91 Mg alloy block under the same conditions as the recycled alloy. The recycled specimens show a higher strength at room temperature than the reference alloy. The improvement of the tensile properties is attributed not only to the small grain size, but also to the dispersed oxide contaminants.

Electric product house of magnesium alloy sheet is usually obtained by warm stamping owing to its poor plasticity and formability at room temperature. The formability of AZ31B magnesium alloy sheet can be improved by repeated unidirectional bending (RUB) process through control of (0002) basal texture. Compared with as-received sheet, the Erichsen value (IE) of the sheet underwent RUB process increases to 5.90 from 3.53 at room temperature. It is also confirmed that cell phone houses could be stamped successfully in crank press with AZ31B magnesium alloy sheets underwent RUB process. It provides an alternative to the electronics industry in the application of magnesium alloys.

In order to improve the mechanical properties and corrosion resistance of Mg alloys, the equal channel angular extrusion (ECAE) was employed to fabricate the Mg-5Gd-5Y/Mg-2Zn-1Gd (GW55/ZG21) laminated composites. After fabrication and annealing treatment, the microstructural evolution, phase constitution, microhardness, and bonding strength were investigated on the bonding interface zone of GW55/ZG21 laminated composites. The bonding interface zone of GW55/ZG21 laminated composites comprises a lot of Mg₃(Y, Gd)₂Zn₃ particles along the bonding interface, some rod Mg₂₄(Y, Gd)₅ phases on GW55 side, and a precipitation free zone (PFZ) on ZG21 side. After annealing treatment, Mg₃(Y, Gd)₂Zn₃ particles along the bonding interface increase, rod Mg₂₄(Y, Gd)₅ phases on GW55 side decrease, and PFZ is broadened. Meanwhile, the hardness on the bonding interface zone decreases and the bonding strength increases from 126 MPa to 162 MPa.

Dissimilar friction stir welding between 5052 Al alloy and AZ31 Mg alloy with the plate thickness of 6 mm was investigated. Sound weld was obtained at rotation speed of 600 r/min and welding speed of 40 mm/min. Compared with the base materials, the microstructure of the stir zone is greatly refined. Complex flow pattern characterized by intercalation lamellae is formed in the stir zone. Microhardness measurement of the dissimilar welds presents an uneven distribution due to the complicated microstructure of the weld, and the maximum value of microhardness in the stir zone is twice higher than that of the base materials. The tensile fracture position locates at the advancing side (aluminum side), where the hardness distribution of weld shows a sharp decrease from the stir zone to 5052 base material.

The Mg-Ni-based ternary alloys Mg_2-xTi_xNi(x=0, 0.2, 0.4) and Mg₂Ni_1-xZr_x(x=0, 0.2, 0.4) were successfully synthesized by mechanical grinding. The phases in the alloys and the hydriding/dehydriding properties of the alloys were investigated. Mg₂Ni and Mg are the main hydrogen absorption phases in the alloys by XRD analysis. Hydriding kinetics curves of the alloys indicate that the hydrogen absorption rate increases after partial substitution of Ti for Mg and Zr for Ni. According to the measurement of pressure-concentration-isotherms and Van’t Hoff equation, the relationship between ln p(H₂) and 1 000/T was established. It is found that while increasing the content of correspondingly substituted elements at the same temperature, the equilibrium pressure of dehydriding increases, the enthalpy change and the stability of the alloy hydride decrease.