The dynamic plastic response and deformation behavior at high strain rate regimes is examined on Mg and various dilute binary Mg alloys with fine-grained structure. Nine types of solute atoms (Ag, Al, Ga, In, Li, Mn, Sn, Y and Zn) are selected for alloying in Mg binary alloys with a chemical content of 0.3 at.%. Flow stress and ductility are affected by alloying elements and strain rates. Previous studies have provided that fine-grained Mg and Mg-Mn alloy exhibit huge ductility at low and quasi-static strain rates, attributable to the contribution of grain boundary sliding partially. However, the tensile ductility is determined to be between 5 % and 20 % at present strain rates of 1/s to 1000/s. In addition, regardless of the alloying elements, the strain rate sensitivities at high strain rate regimes are determined to be approximately 0.01-0.05, suggesting dislocation glide as the major deformation mechanism. Microstructural observations reveal and/or dislocation slips, as well as basal dislocation slips, instead of deformation twin formations.

The influence of different wrought processes on the mechanical properties of AZ31 magnesium alloy was investigated in terms of the strain state induced during these processes using a combination of finite element method (FEM) analysis and tensile testing. A process with a large compressive strain develops an intensive basal texture, leading to high strength and poor ductility.

The effects of reinforced particles on the frictional behavior and mechanical properties are examined using extruded Mg matrix composites. The powder metallurgy route using a sheath is applied to fabricate bulk Mg matrix composites in lengths of more than 350 mm. Five types of ceramics are selected as the reinforced particles, Al2O3, MnO2, SiO2, Si3N4 and Y2O3. Despite the types of ceramic, the dispersion of these reinforced particles plays a role in increasing the hardness and enhancing the wear rate. In addition, the hardness is closely related to the wear rate, which is known as the Archard law. Regarding the frictional behavior, it is interesting to notice that the friction coefficient is suddenly down to similar to 0.1 as the friction progresses. The sliding distance (in other words, wear testing period), at which this unique behavior occurs, differs for the various types of reinforced ceramic particles. The difference in surface energy between Mg and the reinforced particle tends to affect the sliding distance required to suddenly decrease the friction coefficient, and this physical parameter is one of the guidelines for selecting the reinforced particle.

The effects of extrusion and dispersed particles (SiC or SiO2) on the mechanical properties are examined on aluminum (Al) based composites prepared from powder metallurgy. Extrusion is effective for i) grain refinement of the alpha-Al matrix and ii) producing high quality bulk specimens on a large scale. This is because of a high applied stress during hot-extrusion contributes to the degradation of oxide films covering the powder particles, leading to the creation of new real surfaces. Microstructural observations show that powder-based extruded Al and its composites have fine-grained structures, i.e., an average grain size of less than 5 mu m in the alpha-Al matrix. Accordingly, associated to these microstructures, they show higher strength ( 30 MPa) and hardness ( 10 Hv) than those of cast Al and its composite. In addition to beneficial mechanical properties, the extrusion process does not give a negative impression as for wear property, i.e., the wear rate. Plasticity-controlled void growth mechanism is focused to consider the impact of extrusion on bonding quality. The time required to shrink voids is estimated, and this value is consistent with the actual processing duration. [doi:10.2320/matertrans.MT-M2025050]

The effects of dispersed polymer particles on the mechanical properties are examined using extruded Mg/ polymer composites, where five types of polymers are selected as polyamide (hereafter denoted as PA), polyimide (PI), polyethylene (PE), polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA). Even with powder metallurgy routes, some of the Mg/polymer composites (e.g., PA, PI and PMMA) are successfully fabricated by hot extrusion using a sheath. This process provides a significant avenue for producing new metal/polymer composites, given that metals and polymers are well-known to have different construction in atomic levels. The aforementioned three types of Mg/polymer composites exhibit good mechanical properties including superior strength and wear loss rate as compared to Mg/ceramic composites fabricated by the same procedure, in addition to good compressibility. These Mg/polymer composites also exhibit a unique friction behavior, i.e., a sudden drop in the friction coefficient from similar to 0.4 to 0.1 during the wear tests. The sliding distance required for sudden reduction in friction coefficient depends on the difference in surface energy of polymer compared to that of the matrix. For the PE and PTFE, they are not applicable for the dispersed particles in the Mg matrix composite. Rather than focusing on bonding with the matrix, these polymers are useful for use as lubricants for Mg.

Deformation mechanism at room-temperature of fine-grained Pure Mg, AZ31 and Mg-Mn alloys is examined through in-situ neutron diffraction method and postmortem microstructural observations. Extension twins do not form in any of the specimens. In the AZ31 alloy, lattice strain and integrated intensity of individual planes change differently with progression of tensile tests, indicating large plastic anisotropy. This is due to large number of dislocation slips on not only basal but also prismatic planes. Whereas, Pure Mg and Mg-Mn alloy show a small difference in lattice strain and integrated intensity between diffraction peaks, because grain boundary sliding plays a role in relaxation of stress accumulations at grain boundaries, with less dependence on crystallographic orientation. Neutron diffraction analysis in Pure Mg and Mg-Mn alloy reveals that dislocation slips (on mainly basal plane) are generated by mechanisms associated with both accommodation process for grain boundary sliding and general intragranular plastic deformation.

Effect of grain boundaries on {1012} twin formation and its mechanical response in Mg is investigated through in-situ TEM compression test. Compression direction is set to be normal to the -axis, which is a favorable orientation to form {1012} twins. In case of a single crystal, {1012} twins form in the vicinity of the contact region of compression-tip with the specimen, as reported in previous studies. On the contrary, when the specimen has a grain boundary, this interfacial defect becomes the nucleation/formation site for twins. Stress required to form the twins is lower than that in a single crystal. Grain boundaries, which have a role in prevention of dislocation slips, create high stress fields; as a result, they lead to nucleation of a twin embryo. While twin nucleation is a probabilistic event, stress required to form the twins shows size effect.

Effect of pre-induced {1012} twin boundaries on tensile response at low temperatures of 77 K similar to 293 K is examined in the Mg-Al-Zn alloys. Irrespective of temperatures, the specimens containing twins exhibit lower yield strength than those of specimens without twins, due to detwinning behavior. However, the ductility and absorption properties are significantly enhanced by the presence of these twins. This is owing to existences of dislocations with (c) component, which are generated by dislocation transformation through twin boundary migration. The pre-induced twin boundaries with (c) and/or (c + a) dislocations play a role in relaxation of strain accumulation as well as compensation of slip systems; thus, leading to retardation of localized necking. The twin boundaries with control of interfacial structures break a negative notion that twins are harmful for mechanical properties relating to ductility. This strategy can open a door for new microstructural design of Mg alloys.

Effect of pre-induced {10 (1) over bar2} twin fraction on plastic response in tension at strain rates of 10(-5) /s similar to 1 /s is examined in three Mg-3Al-1Zn (AZ31) alloys having different average grain sizes. The pre-induced {10 (1) over bar2} twin volume fraction affects tensile behavior, regardless of the grain size and strain rate. Decrease in yield strength and large strain hardening are observed in the specimens with twin volume fraction of greater than 10 %. Quasi in-situ microstructural observations during tensile tests reveal that such unusual behavior is due to detwinning. Microstructure evolution after complete detwinning is changed by twin volume fraction. The {10 (1) over bar1} type twins newly form in the specimens with low volume fraction of twins, instead of retwining of existing {10 (1) over bar2} twins. On the other hand, in the specimens with high volume fraction of twins, an ideal crystallographic relationship occurs for dislocation slip on basal and pyramidal planes; thus, there is high contribution of intragranular deformation.

This study investigates the effect of loading direction on the compression behaviour of extruded pure magnesium with different grain-sizes and at different strain-rate. At the same grain-size level, samples compressed at 45 degrees to the extrusion direction have lower yield stress than samples compressed parallel to the extrusion direction. However, the loading direction has a negligible effect on the dominant deformation modes in the studied conditions.

The effect of p-block elements (Ga, Ge and In) addition on grain boundary structures and room temperature mechanical responses was investigated on extruded Mg binary alloys with fine-grained structures. Grain boundary segregation was confirmed in the Mg–Ga and Mg–In alloys, whereas the Mg–Ge alloy did not show such microstructures associated with solubility. Grain boundary segregation affected the plastic deformation of the Mg–Ga and Mg–In alloys. In particular, the Mg–In alloy had a large strain rate dependency and exhibited good deformability at low strain rate regimens. First-principles calculations indicated that p-block elements produce a bond-weakening effect at grain boundaries, and atomistic distances at grain boundaries varies according to the element. Solute atom which brings about both bond-weakening and bond-expansion effects to Mg atoms is effective in enhancing the contribution of grain boundary sliding in deformation.

Static annealing process of 423 K for 2.5 h is adequate to segregate alloying elements at {101¯2} twin boundaries in various Mg binary alloys. These segregated twin boundaries play a role in obstruction of dislocation slips; thus, they contribute to increase in hardness. Internal friction tests reveal that, irrespective of the solute elements, induced twin boundaries are effective in enhancing damping capacity, owing to their reversible motion, i.e., growth and shrinkage. In contrast, by comparison of the loss factor of specimens with/without twin boundary segregation, segregation leads to a decrease in damping capacity. The energy barrier required for twin boundary sliding to occur is closely related to the loss factor. When solute element having a characteristic of high (or low) energy barrier exists at twin boundaries, such an alloying element prevents (or enhances) the occurrence of twin boundary motion; as a result, shows a low (or high) loss factor.

This study investigates the effect of Sc addition on the deformation behaviour of near-<0001>-oriented Mg via micropillar compression. The Sc addition significantly increases the yield stress and promotes activation of non- dislocation while suppressing dislocation.

In-situ observations obtaining mechanical response reveal that no twins form even at the maximum stress of similar to 1.4 GPa during loading; nucleation of {10 (1) over bar2} twins occur during unloading. The source of twin nucleation is due to interaction between activated dislocations through slips and pre-existed dislocation, which causes a high stress concentration.

This study demonstrated the possibility of dynamic recovery by forming a kink boundary in the long-period stacking ordered phase of the Mg85Y9Zn6 (at%) alloy. The compressive deformation at 1 % strain on the double-notched directionally solidified specimen produced three regions; undeformed, deformed, and kinkdeformed regions. A nanoindenter was applied to three different regions. The deformed region sufficiently far from the kink boundary exhibited a 26 % higher nanoindentation hardness than the undeformed region owing to work-hardening, whereas the hardness decreased when approaching the kink boundary. At 1 mu m or less from the kink boundary, the magnitude of hardness recovered to the same level as the undeformed region. This observation implies a "recovery kink zone" because of the dynamic recovery associated with kink boundary formation.

Complex physical and mathematical concepts of quasicrystals have been applied, for the first time, to an engineering processing of an alloy containing a quasicrystalline phase. Icosahedral quasicrystals (i-phase), which are quasiperiodic and possess fivefold symmetry, are often found as stable phase in aluminum and magnesium alloys. They are known to be hard and brittle at room temperature, therefore their deformation behavior at lower temperatures is not well understood yet. High pressure torsion (HPT) gives an opportunity to study deformation of brittle materials due to confinement of the dies. Here, we report on deformation behavior of 27 vol α -Mg phase deformed by twinning and dislocation slip, leading to full recrystallization. Consequently, diffraction peaks showed broadening, followed by sharpening. The peaks of i-phase continued to broaden. Fivefold symmetry diffraction peaks broadened disproportionately to the others. Peak broadening analysis showed that deformation occurs predominantly by changes in fivefold symmetry planes, as observed to be by twinning and formation of narrow planar faults. No evidence of new random phason strains was detected. Introduction of localized phonon strain was detected at high strains, which could be correlated with creation of interfaces and surfaces by fragmentation of i-phase into nanoparticles and dispersion into the matrix. Vickers microhardness of the alloy increased from 118 Hv to over 175 Hv after N = 40.

Effect of twin boundary with/without segregation of solute atoms on deformation behavior in tension is examined in Mg-3Al-1Zn (AZ31) alloys from low strain rates to high strain rates. Solute atoms (Al and/or Zn atoms) are segregated at {10 1 2} twin boundaries by static annealing at a temperature of 423 K with a holding time of 150 min. The room-temperature tensile mechanical response of the specimens, which have pre-induced twin boundaries, shows detwinning behavior, regardless of the strain rate between 10-5/s and 100/s. The yield strength of these specimens is also unlikely to be affected by strain rate, because twin boundary mobility, i.e., the shrinkage, is an athermal process. On the other hand, the specimen with segregating of solute atoms at twin boundaries exhibits an increased strength and a decreased strain hardening as compared with those in the specimen having non-segregated twin boundaries. Newly formed deformation twins of several types, i.e., the {10 1 2} twins, {101 1} twins and {101 2}-{101 1} double twins, are the origin of fracture in these specimens.

AZ31 magnesium alloys were deformed by five wrought processes (forging, rolling, extrusion, equal-channel-angular-extrusion (ECAE), and caliber rolling) under the condition of an introduced equivalent plastic strain of approximately 1.5 at 573 K. The strain components induced by these wrought processes were computed using the finite element method (FEM). By combining the calculation results with the microstructure observations, the texture and microstructure evolution were discussed from the viewpoint of the strain state. The FEM showed that approximately the same equivalent strain was induced at the center of the alloys where observations were performed. Therefore, as the values of the equivalent plastic strain were fixed in all wrought processes, the effect of the strain component could be compared. The forged and rolled alloys had an intensive basal texture perpendicular to the compression and normal directions, respectively. In the others, a basal fiber texture parallel to the material flow direction was observed. These basal textures were oriented perpendicular to the compressive strain, and their intensities strengthened with an increase in the strain component. The microstructure became more refined and homogenized as the magnitude of the minimum principal strain decreased. This decrease corresponds to the transition of the deformation mode from the uniaxial compression mode to the multidirectional deformation mode as long as the same equivalent strain is induced. This result demonstrates that the microstructure obtained through dynamic recrystallization depends on the deformation mode, separately from the effect of the conventionally reported equivalent plastic strain.

The tribological properties are evaluated using several types of Mg/SiC composites, which SiC powders with particle sizes of 20∼30 nm, 130 nm and 2∼3 μm are dispersed in up to 25 % by volume fraction. Sound and bulky Mg/SiC composites are successfully fabricated by powder-metallurgy combining extrusion process. The initial SiC particle size and their dispersed volume fraction affect the wear and friction properties. The specific wear rate increases with increasing contents of SiC particles, regardless of the initial SiC particle size. However, when the SiC particle size is larger than a certain size and its content is greater than 10 %, the friction coefficient suddenly decreases. In the surface observations after friction tested specimens, the element map shows the Mg ratio relative to Si ratio (= SiC) increases with reducing friction coefficient. This indicates that good wear resistance is due to the formation of self-formed SiC layers during the friction process.

To improve the cycle performance of Mg metal batteries, a spinel-type MgMn2O4 (MMO) as the active material of the cathode was coated with a poly(styrene-4-sulfonyl trifluoromethylsulfonyl)imide Mg salt (PSTFSI-Mg) on the MMO surface. Coating was performed by spray drying, freeze drying, simple mixing, and one-pot spray drying. Transmission electron microscopy measurements of the resulting polymer-coated MMO were undertaken to verify the surface and the inner morphology. The results of charge-discharge measurements suggest that the polymer coating on the MMO surface promotes electron transfer between the particles. These results are interested in terms of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the modified polymers obtained from density functional theory (DFT), confirming that the polymer reduces the gap between the valence band maximum of MMO and the HOMO level of the electrolyte solution, suppressing the degradation of the electrolyte.