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LZ91 Mg-Li alloy plates with three types of initial texture were rolled by 70% reduction at both room temperature and 200 °C to explore the rolling texture formation of α-Mg phase. The results showed that the rolling texture is largely affected by the initial texture. All the samples exhibited two main texture components as RD-split double peaks texture and TD-split double peaks texture after large strain rolling. The intensity of the two texture components was strongly influenced by the initial orientation and rolling temperature. Extension twinning altered the large-split non-basal orientation to a near basal one at low rolling strain. The basal orientation induced by twinning is unstable, which finally transmitted to the RD-split texture. The strong TD-split texture formed due to slip-induced orientation transition from its initial orientation. The competition between prismatic 〈a〉 and basal slip determined the intensity and tilt angle of the TD-split texture. By increasing the rolling temperature, the TD-split texture component was enhanced in all three samples. Limitation of extension twinning behavior and the promotion of prismatic slip at elevated temperature are the main reasons for the difference in hot and cold rolling texture.

In this work, preeminent bendability at room temperature is achieved by simultaneously introducing the gradient microstructure and texture along the normal direction (ND) of Mg-4.05Gd-0.57Zr alloy sheets prepared by turned bearing extrusion (TBE). The grain size of the VK-TBE sheet at the top, middle and bottom layers are 4.54 μm, 8.48 μm and 7.84 μm respectively. In addition, the fine-grained layer presents the highest texture deviation angle witch provides this layer with the highest Schmid factor (SF) for basal slip. When this layer is placed at the outer side, the bending angle is promoted by about 99.8% compared with the conventionally extruded sheet. The sample with a thickness of 3 mm is bent to 60° without cracking, revealing an excellent promotion in the bendability. During bending, the combination of high SF for basal slip and fine grains contributes to the elevated plasticity of the outer layer. Furthermore, at the inner region, a lot of twin bands appear in the relatively coarse grains with high SF for tensile twinning, which significantly regulates the strain distribution along the ND. Consequently, the VK-TBE-FG sample exhibits preeminent bendability owing to the cooperative effects of enhanced plasticity of the outer layer and regulated strain distribution.

On certain occasions, such as bending, a sheet with gradient microstructure may present higher formability compared to one with uniform microstructure. In this study, the formation of gradient microstructure in AZ31 alloy sheets extruded by the asymmetric die is comprehensively investigated. The results exhibit the microstructure evolution undergoes three stages, namely the initial dynamic recrystallization (DRX), abnormal grain growth (AGG), and the secondary DRX. After the initial DRX, the microstructure is fine and uniform, and the transverse direction (TD) preferred texture is formed due to the initiation of non-basal slip. Owing to the high extrusion temperature, AGG occurs after the initial DRX. The grains with basal texture are engulfed by the grains with TD-preferred texture. During the AGG, the grain size is coarsened from 11.4 μm to 382.1 μm. As the material flows through the die bearing, the secondary DRX occurs near the corner of the die. Ascribed to the gradient strain near the bearing, the grains near the bottom surface of the sheet are refined again, while those near the other side inherit the large sizes from grown grains. Ultimately, the extruded sheet exhibits gradient microstructure along the thickness direction, i.e. normal direction (ND). The gradient-distributed plastic strain and strain rate are the main causes of gradient microstructure.

The effects of extrusion temperatures (430, 450, 470 and 490 °C) on the microstructures and mechanical properties of Mg–11Gd–5Y–2Zn–0.7Zr (GW) alloys at room temperature (RT), 250, 300, 350 °C were systematically investigated. The dynamic precipitation of blocky and lamellar long period stacking ordered (LPSO) phases was taken place during hot extrusion. The dominant texture changed from //ED to //ED with increasing extrusion temperature. Tensile results indicated that the GW alloy extruded at 430 °C (GW430) exhibited the highest mechanical properties at both RT and elevated temperatures, which was ascribed to the fine dynamic recrystallized (DRXed) grains, un-DRXed grains with an orientation of //ED, and the LPSO phase strengthening. When tensile tested below 300 °C, slips on the blocky LPSO phase and kinks of lamellar LPSO phase were the primary deformation modes, followed by grain boundary crack. At 350 °C, grain boundaries became the vulnerable sites to be activated. For GW alloys extruded at 450, 470 and 490 °C, an abnormal increase of mechanical properties was observed at 300 °C. This was due to the occurrence of multiple-slip, which showed the intersection and entanglement of dislocations and thus improving the strength of Mg matrix.

Dual-phase Mg-Li alloys sheets were rolled at four different temperatures ranging from liquid nitrogen to 300 °C to explore effect of rolling temperature on texture and mechanical properties of the material. Crystal plasticity simulation was utilized to illustrate the influence of slip activity on rolling texture development. The results show that the rolling texture is largely depended on deformation temperature. Unlike commercial Mg alloys, the critical resolved shear stress of basal slip in α-Mg phase of Mg-Li alloy decreased more significantly by increasing temperature compared to that of pyramidal slip. Enhancement of basal slip by increasing temperature triggered a decrease of split angle of basal poles for the double-peak texture. Prismatic slip largely enhanced by increasing temperature upon 200 °C, which induced a wider orientation spread along the transverse direction. For the β-Li phase, the promotion of {110} slip system at elevated temperature triggered the enhancement of {211} and {111} texture components. The cryo-rolled sample exhibited the highest strength compared to the others due to a strong hardening behavior at this temperature. A two-stage hardening behavior was observed in these as-rolled dual-phase alloys. Strain transition at phase boundaries could be the reason for appearance of this two-stage hardening.

The microstructural features of long period stacking ordered (LPSO) phase in Mg–(11-x)Gd–xY–1Zn–0.3Zr (wt.%) alloys were optimized by adjusting Gd/Y ratios to10:1, 8:3, 6:5, 4:7 and 2:9, respectively. Superior high-temperature strength was successfully obtained in the extruded 6Gd–5Y alloy with ultimate tensile strength (UTS) values of 338 MPa and 286 MPa at 250 °C and 300 °C, respectively. In the as-cast alloys, with the decrease of Gd/Y ratio, the type of intermetallic compound gradually changed from (Mg, Zn)3(Gd, Y) (W) to LPSO phase. After homogenization, the W phase was completely converted to LPSO phase except for the 10Gd–1Y alloy. Importantly, the block-shaped LPSO phases with the smallest size and the abundant lamellar LPSO phases were formed in the 6Gd–5Y alloy, which significantly influenced the microstructures of the extruded alloy. Firstly, the small sized block-shaped LPSO phase before extrusion provided favorable conditions for the formation of thin plate-shaped LPSO phase at DRXed regions, which effectively hindered the grain boundary migration at high temperature due to superior thermal stability. Secondly, the profuse lamellar LPSO phases prior to extrusion contributed to the highest density of low angle grain boundaries (LAGBs) and residual dislocations in the extruded 6Gd–5Y alloy, which obstructed dislocation slip at elevated temperatures. In addition, the abundant lamellar LPSO phase also caused the fine DRXed grain size and strong basal texture to enhance the high-temperature strength of the extruded 6Gd–5Y alloy.

In this work, novel turned-bearing extrusions (TBE) conducted by using the dies with the single corner and double corner, named SC-TBE and DC-TBE respectively, are developed to introduce additional shear strain during the preparation of AZ31 alloy sheets, which is expected to improve the strengths of sheets. Numerical simulations are conducted to uncover the effect of additional shear deformation on the microstructure during the TBE. The results show that the high strain during the TBE leads to a high nucleation rate for dynamic recrystallization (DRX), resulting in grain refinement of the extruded Mg alloy sheet. However, the high strain also increases the temperature of the material due to the heat generated by plastic deformation, which provides a great driving force for grain growth and consumes dislocations. As these two effects compete with each other when increasing the strain near the die orifice, the SC-TBE sheet has finer grains and a higher residual dislocation density compared to the DC-TBE sheet or the sheet prepared by the conventional extrusion (CE). Fine-grain strengthening and substructure strengthening work together and enhance the tensile yield strength (TYS) of the SC-TBE sheet. The TYSs along extrusion direction (ED), transverse direction (TD) and 45° direction (the half angle between ED and TD) of the SC-TBE sheet are improved by 32 MPa, 65 MPa and 35 MPa respectively compared with the CE sheet. The findings of this research provide some new insights into the development of new preparation methods for Mg alloy sheets with higher strength.

The mechanical properties of the extruded and peak-aged Mg-12.8Gd-4.7Y-2.6Zn-0.9Zr (wt.%) (GWZ1352) alloys at room and high temperatures were systematically investigated with respect to their microstructures. The microstructural features were tailored through altering the cooling rates after homogenization by water-quenching, air-cooling and furnace-cooling, respectively. As the cooling rate reduced, the number of lamellar long period stacking ordered (LPSO) phase increased substantially and its spacing decreased gradually. Additionally, solute segregation at grain boundaries occurred after furnace-cooling. After extrusion, the quenching (QE) alloy exhibited nearly full dynamic recrystallized (DRXed) grains, whereas the air-cooling (AE) and furnace-cooling (FE) alloys displayed a typical bimodal structure consisting of fine DRXed and coarse un-DRXed grains. The nucleation and development of the DRXed grains were hampered by the nano-spaced lamellar LPSO phase and the solute segregation of grain boundary. The excellent high temperature mechanical properties of the FE alloy were mostly due to the abundant lamellar LPSO phase. After aging treatment, plentiful fine β′ phase was precipitated in the quenching and aged (QEA) alloy. In contrast, the β′ phase with a larger size and lower density, accompanied with a wide precipitation-free zone (PFZ) at grain boundaries was formed in the air-cooling and aged (AEA) and furnace-cooling and aged (FEA) alloys, which severely deteriorated their mechanical properties both at room and high temperatures.

In this work, pre-strain annealing strengthening (PSAS) effect was investigated in an extruded Mg-1.0Gd-1.5 Zn (wt.%) alloy with respect to different grain sizes. The evolution of microstructures was provided by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) under the initial state, pre-compression, intermediate annealing and re-compression conditions. The obtained results showed a grain size-dependent PSAS effect in the alloy. The sample with larger grain sizes corresponded to a higher strengthening effect, which mainly resulted from a more remarkable hindrance for the growth of existing twins and a larger proportion of activation for the nucleation of new twins. This was closely associated with the increase of back stress and friction stress for twin boundary motion impeded by the larger restraint of dislocations, the higher stress field surrounding solutes and the more Zn segregation. In addition to twinning behavior, Guinier Preston (G.P.) zones on basal 〈a〉 dislocations were found after intermediate annealing and provided an extra strengthening by inhibiting the motions of gilding pre-existing dislocations and newly formed ones, but it was independent on the grain size.

In this work, laminated composite sheets of Mg alloys AZ31 and Mg-xGd are fabricated through co-extrusion using a pothole die. The asymmetric deformation of the dissimilar Mg alloys during the extrusion is analyzed by combining the results of experiments and numerical simulations. The microstructure, tensile properties and bendability of the laminated composite sheets are comparatively investigated. The results show that the sheet AZ31/Mg-1.2Gd obtains a flat profile, uniform composite layers and high bonding strength of 131 MPa because of the relatively symmetric deformation of the Mg alloys AZ31 and Mg-1.2Gd during the co-extrusion. Compared with the sheet AZ31, the bendability of the laminated composite sheet AZ31/Mg-xGd is significantly improved. In addition, when the Mg-xGd alloys, instead of the AZ31 alloy, are placed in the outer layer of the specimens during bending experiments, the laminated composite sheets get higher bendability. With the actions of the weakened texture and activation of non-basal slip in the composite layer containing the Gd element, both the ductility and bendability of sheet AZ31/Mg-1.6Gd reach the highest levels among those of the laminated composite sheet, corresponding to the elongation of 29% and the ultimate bending angle of 101 °, respectively. The analysis of the asymmetric deformation of dissimilar Mg alloys during the extrusion and the discussion of the effects of Gd content on the microstructure, tensile properties, and bendability in this study provides a comprehensive insight into the fabrication of high-formability laminated composite sheets of Mg alloys.

Despite the laminated composite sheets of dissimilar magnesium (Mg) alloys have attracted great attention due to their excellent comprehensive mechanical properties as compared to the sheets of individual alloys, how the structural parameters, especially the layer thickness ratio (LTR), influence their formability is still left unstated in the previous researches. We investigate the effects of LTR on the bendability of the co-extruded laminated composite sheet of Mg alloys, Mg-Al-Zn/Mg-Gd, by combining the V-shaped bending experiments, quasi-in-situ electron backscattered diffraction (EBSD) measurement and finite element (FE) simulations. When the layer Mg-Gd is placed in the outer layer, the bendability of the laminated composite sheet first increases and then decreases, and it reaches the optimum at an LTR (AZ31:Mg-Gd) of 2:1, which goes against the intuition that the higher the volume fraction of the Mg-Gd alloy, the better the bendability. This phenomenon is explained by the competitive effect between the improved plasticity of the outer layer and the enhanced tensive-compressive asymmetry of the outer and inner layers with increasing the thickness of layer Mg-Gd. The neutral layer migrates from the geometrical central layer to the compressive zone due to the asymmetrical responses of the inner and outer layers. Both the shift of the neutral layer and the strain of the outer layer increased by reducing the LTR. It is believed that this research provides some new insights into the design and development of high-formability laminated composite sheets of Mg alloys.

In this work, we investigated the microstructure and the mechanical properties of extruded Mg-xGd-0.5Mn alloys (GMx0) with the variation of Gd content (0, 2, 4, 7 wt.%). For the GM00 alloys with no Gd content, the typical basal fiber texture (BFT) was formed, which led to similar mechanical properties to the pure Mg. However, with the dilute addition of the Gd element, the texture was transformed into ED-split texture, termed Rare Earth (RE)-texture, which improved the ductility significantly. As the Gd content increased, the texture was transformed from RE-texture to the BFT, decreasing the ductility and increasing the stretch yield strength. Furthermore, the electron backscattered diffraction (EBSD)-assisted slip trace analysis method and the Visco-Plastic Self-Consistent (VPSC) model were utilized to uncover the strain coordination mechanism variation. The results indicated that non-basal slip systems, including prismatic slip and the pyramidal slip, were activated more frequently with the increase of Gd content. The Gd addition has more excellent facilitation for the pyramidal slip than the prismatic slip. However, this promotion effect of non-basal slip systems was insufficient to compensate for the overall reduction in ductility owing to the texture change.

The demand for soluble magnesium alloys with high plasticity used for sealing tools in petroleum field is increasing. Here, the effects of Ni content (0.1, 0.2 and 0.5wt.%) on microstructure, mechanical properties and corrosion rate of Mg-2Gd alloy were studied. The volume fraction of LPSO phases and the average grain size (α-Mg) increased and decreased with the increase of Ni content, respectively. After adding Ni, the texture changed from the rare earth texture to the basal fiber texture, and the strength, hardness and corrosion rate were increased with an acceptable decrease in elongation: the ultimate tensile strength/elongation/corrosion rate of the Mg-2Gd alloy and Mg-2Gd-0.5Ni alloy were 191 MPa/23.1%/15.2 mm·y-1, 287 MPa/18.1%/499.9 mm·y-1, respectively. Therefore, the addition of Ni effectively improved the strength and degradation rate of the Mg-2Gd alloy, which was mainly due to the grain refinement, the enhancement of basal fiber texture and the appearance of LPSO phases.

To study the microstructural evolution of the as-extruded Mg–6Zn–1Mn alloy sheets with different initial microstructures during high strain rate tensile deformation, the interruptible tensile tests were performed at the strain rate of 1000 s−1, with controlled strain of 2.5%, 7.5% and 12.5%. The microstructure of the samples was characterized by electron backscatter diffraction and transmission electrical microscopy. The results demonstrate that the microstructural evolution of alloys during high strain rate tensile deformation is strongly influenced by the grain size and texture. Twins are suppressed during deformation in the fine-grained samples with strong basal texture, and only a few tension twins are observed at the large strain. Conversely, tension twins are activated greatly in the coarse-grained samples with the weaker basal texture. Twins are firstly activated at a small strain, and then more twins form and grow up as the strain increases. Regardless of the degree of twinning activity, the plastic deformation of the samples with different initial microstructures under high strain rate tensile loading is mainly provided by dislocation slip, and the dislocation density increases with the increase of strain. Moreover, the large grain size and relatively weak basal texture promote the formation of more dislocations.

In this paper, the effect of La addition on the Al-RE phase in Mg-Al-Zn-Ce magnesium alloy was studied. Melting method was used to prepare AZ80-Ce magnesium alloys with different La content, and the morphological transformation mechanism of Al-RE phase was proposed by XRD, SEM, EPMA, TEM and extraction. The results show that the Al11RE3 phase can be formed by adding RE (Ce/La) into AZ80 magnesium alloy. With the increase of La, the morphology of Al11RE3 phase in the alloy changes from acicular to tubular. La replaces part of Ce in the Al11Ce3 cell and the Al11Ce3 phase is transformed into Al11RE3 phase based on Al11RE3 cell when La is added. In the Al11RE3 phase, the doping of La will cause lattice distortion in the crystal, which increases the surface energy on the growth surface of the Al11RE3 phase and accelerates its growth rate in (001) direction, resulting in the formation of tubular Al11RE3 phase. After forming the tubular structure, the growing process of Al11RE3 phase is divided into three stages owing to different control factors.

The microstructure evolution and mechanical properties of Mg–6Zn–0.5Ce–xMn (x = 0 and 1 wt.%) wrought magnesium alloys were researched, and the morphologies and role of Mn element in the experimental alloys were analyzed. The research shows that all of Mn elements form the α-Mn pure phases, which do not participate in the formation of other phases, such as the τ-phases. The mechanical properties of Mn-containing alloys in as-extruded and aged states are superior to Mn-free alloys. During the hot extrusion process, the dispersed fine α-Mn particle phase hinders the migration of grain boundaries and inhibits dynamic recrystallization, which mainly takes effect of grain refining and dispersion hardening. During the aging treatments, the dispersed fine α-Mn particle phase not only hinders the growth of the solution-treated grains, but also becomes the nucleation cores of β1′ rod-like precipitate phase, which is conducive to increasing the nucleation rate of the precipitate phase. For the aged alloy, the Mn addition mainly takes effect of grain refining and promoting aging strengthening.

The effect of microalloyed Ca on the microstructure, mechanical properties and aging precipitation of Mg–6Zn–1Mn–4Sn (wt.%, ZMT614) alloy were investigated. The as-cast ZMT614 alloy was mainly composed of α-Mg, Mg–Zn and Mg2Sn phase, and a new CaMgSn phase with high melting point was formed with Ca addition. The CaMgSn phase was easier to form than Mg2Sn during solidification, so the formation of Mg2Sn was suppressed. Undissolved CaMgSn phases after solution treatment played an important role in pinning grain boundary migration and grain growth, and can act as nucleation sites promoting precipitation during aging process. CaMgSn particles also retarded the recovery process and the retained dislocations could act as additional heterogeneous nucleation sites for precipitation. β′ precipitates along [0001]α were finer and disc-like precipitates β'' on (0001)α were denser for Ca-containing alloys after aging treatment. The peak-aged ZMT614-0.5Ca alloy exhibited the optimum mechanical properties and its yield strength, ultimate tensile strength and elongation were 345 MPa, 378 MPa and 6.5%, respectively. The strengthening mechanism was mainly attributed to the grain refinement and precipitation strengthening.

The demand for magnesium (Mg) alloy with high elongation, certain strength and good degradation rate used in oil and gas exploitation filed is increasing. Based on Mg-2Gd alloy, effect of copper (Cu) addition (0.25, 0.5 and 0.75 wt.%) on microstructure, mechanical properties and degradation rate were investigated. It showed that more Mg2Cu second phases were precipitated and the grain size was refined with increasing Cu content, accompanied with texture changing from //ED to //ED. As a result, hardness, tensile strength, compressive strength and degradation rate were enhanced while the strain hardening rate and elongation decreased. Nevertheless, the elongation was still up to at least 20%. Overall, the comprehensive mechanical properties and degradation rate of Mg-2Gd alloy can be effectively coordinated by Cu addition.

This paper focused on the effect of angle α that the basal poles tilted from normal direction (ND) toward the extruded direction (ED) on the formability of as-extruded Mg-2Gd (wt.%) alloy sheets. The studied Mg-2Gd (wt%) alloy sheets with the angle α of 23°, 32° and 45°, respectively, were designed. The Erichsen test was carried out at the ambient temperature, in which the microstructure and texture evolution was characterized by the electron backscatter diffraction (EBSD) technique. The results showed that the strain coordination ability of the Mg-2Gd sheet along the thickness direction was enhanced with the increase of angle α, giving rise to a higher Index Erichsen (IE) value of 7.5 mm for the α of 45° due to a lower r-value. This superior high formability is not only closely associated with the lower r-value but also with the higher Schmid factors for basal slip (SF basal) in the large-angle α alloy sheets. Furthermore, the twinning induced a more random distribution along the transverse direction (TD) of basal texture in the early stage of the Erichsen test, which cancels out the SF basal reduction effect caused by the activation of basal slip. The TD-extended twinning texture provided a softer orientation for the TD strain during the Erichsen test, such that excellent formability was achieved in the alloy sheets with a larger angle α.

In the current work, we successfully prepared Mg-8Zn-1Mn-3Sn-1.2Gd-0.2Dy alloy with an excellent combination of ultimate tensile strength and ductility. The mechanism of the Dy-modified MgSnGd phase and its effect on the microstructure and mechanical properties of as-cast and as-extruded alloy were systematically investigated. Experimental results reveal that a new phase MgSn (Gd, Dy) is formed with Dy addition to Mg-8Zn-1Mn-3Sn-1.2Gd alloy, MgSn (Gd, Dy) phase can act as an effective heterogeneous nucleation site of MgSnGd phase. Meanwhile, the addition of Dy consumes Sn and Gd atoms, reducing the enrichment of solute atoms and inhibiting the MgSnGd phase's growth. The Dy addition can effectively promote the dynamic recrystallization process due to the combined effects of the refined grain structure of as-cast alloy and the particle-stimulated nucleation effect caused by dispersed MgSnGd phase. The alloy exhibits an excellent combination of high strength and ductility with the ultimate tensile strength of 384 MPa and an elongation of 14.5%. The fine-grained structure, the uniformly distributed MgSnGd particle, and MgSn (Gd, Dy) nanoparticles are mainly responsible for the ultra-high ultimate tensile strength. The high ductility is due to the fine-grained structure, appropriate decrease of dislocation density, and dynamic recrystallization.

AbstractTo ensure the safety of project construction and reduce development costs, it is necessary to obtain a reasonable design before project initiation and to analyze and study geological information from multiple perspectives to achieve intuitive and effective project planning. Therefore, it is proposed to integrate above- and underground information to realize integrated spatial information expression. Generally, geological body model construction is based on drilling data, but most geological bodies are not simple layered structures, and complex geological phenomena usually occur, such as faults, lenses, and fissures. It is difficult to construct a high-quality geological body model with only limited drilling data. To fully consider existing geological information in complex geological areas with limited geological data information available, profile maps are considered in the modeling process. This article focuses on the geological model construction of a primary school in Shuicheng County, Guizhou Province, using the GoCAD platform. The Structure and Stratigraphy Workflow is applied in three-dimensional geological body structure model establishment, the stratum rock mass is outlined, and the complex geological structure (karst cave) is embedded into the geological surface. The model can be sliced at any angle to accomplish integrated spatial information expression of above- and underground building information combined with the same platform’s geological body to obtain engineering information and analyze future construction problems.

The microstructure evolution and age hardening behavior of Mg-6Zn-1Mn-4Sn (wt.%, ZMT614) through various Gd addition were investigated. The as-cast ZMT614 alloy was mainly composed of Mg2Sn, Mg7Zn3 and α-Mg solid solution, and new MgSnGd phases were detected with Gd addition. The MgSnGd phase nucleated prior to Mg2Sn during solidification, resulting in consumption of Sn element and reduction of Mg2Sn phase. Owing to the pinning effect of MgSnGd phase, some dislocations were preserved during solution treatment. The retained dislocations could act as heterogeneous nucleation sites for the rod-like β1´ precipitates. A trace of Gd addition could enhance the peak hardness and shorten the peak aging time, while excessive Gd addition would weaken the age hardening response. The ZMT614-0.2Gd alloy exhibited the optimum mechanical properties with yield strength of 373 ± 4 MPa and ultimate tensile strength of 405 ± 6 MPa.

In this work, the effect of thermomechanical processing schedules on microstructure, texture and mechanical anisotropy of Mg-1.64Al-0.84Zn-0.38Mn-0.49Ca (AZMX1100, wt.%) alloy was investigated. Two hot rolling regimes: unidirectional and cross rolling (UR and CR, respectively), followed by subsequent annealing, were systematically studied using different reductions per pass (r. p. p.) from 10 to 30%. The findings showed that the CR samples developed more recrystallized grains and fine twins compared to the UR ones. At a low r. p. p. of 10%, the CR sample exhibited a close circular ring texture. With increasing the r. p. p., an elliptical ring texture along the rolling direction (RD) was observed. For the UR samples, the degree of transverse direction (TD)-split texture component was ascending as the r. p. p. increased. After annealing, the CR annealed samples inherited and expanded texture traits of the as-rolled samples. The UR samples after annealing showed stronger TD-oriented texture components and weakened RD-oriented components. The texture of the UR annealed samples gave rise to a continuous worsening of mechanical anisotropy as the r. p. p. increased. On the contrary, with the r. p. p. of 10%, the CR annealed sample emerged with near isotropic mechanical properties due to the symmetric texture. At the higher r. p. p., the mechanical anisotropy of the CR annealed samples was slightly deteriorated.

The effect of Gd addition on the microstructure and mechanical properties of as-aged Mg–6Zn-1Mn (ZM61) alloy were investigated. The results showed that coarse second phase particles containing both Zn and Gd elements were detected after the addition of Gd element, leading to reduce the amount of Zn available as solutes in the α-Mg matrix. Compared with ZM61, the peak aging hardness had a little difference and the peak aging time was shortened with micro amount of Gd addition, while the hardness decreased significantly for the alloys with high Gd addition. The age hardening response was mainly dictated to the precipitation of fine rod-like β1′ phase, and the number density of β1′ phase was related to the Zn content in the α-Mg matrix. Aging treatment could effectively improve the strength of alloys with minor Gd addition and it was of little significance for alloys with high Gd content. The as-aged ZMG61-0.2 exhibited optimal mechanical properties, and the yield tensile strength, ultimate tensile strength, elongation were 360 MPa, 390 MPa, 8.3%, respectively.

The contribution of recrystallization and grain growth to the texture evolution in AZ31 alloy and a modified version AZ31+0.5 wt.% Ca was investigated utilizing a multi-step annealing process. The results showed that the addition of Ca triggered a considerable texture modification by increasing the texture spread and decreasing the overall texture intensity. This effect was found to be temperature dependent. When the annealing temperature remained lower than 450 °C, a weak double peak texture with large basal pole tilt towards the RD was formed. This is correlated to microstructure observations of a large number of Ca-containing nano-sized particles that seemed to suppress grain growth below 450 °C, which stabilized the weak recrystallization texture. This favorable texture was lost upon annealing at higher temperatures. In AZ31, recrystallization nuclei were found to preserve the orientation of their deformed parents, which offered limited potential to optimize the texture via annealing treatments. Grain growth of recrystallized grains resulted in a distinct sheet texture transition from a double-peak to a single-peak basal texture. Aspects of grain boundary energy and grain topology are discussed to explain the growth advantage of the sharp basal component over other orientations. Keywords: Magnesium alloys, Microstructure, Texture, Recrystallization, Grain growth

The microstructures and mechanical properties of the composite extruded AZ31/AZ31 and AZ31/4047 Al sheets were investigated and made a comparison to the conventional extruded AZ31 sheet. Owing to the introduced intense shear deformation at the interface during the composite extrusion, grain refinement and tilted texture were detected in AZ31 layers of the AZ31/AZ31 and AZ31/4047 Al sheets, while the conventional extruded AZ31 sheet exhibited a relative coarse, inhomogeneous microstructure and strong basal texture. The compression-tension yield ratio was increased gradually from the AZ31 to the AZ31/AZ31 and AZ31/4047 Al sheets. Besides, the AZ31/4047 Al sheet could successfully accomplish the whole bending forming process at room temperature, while the AZ31 and AZ31/AZ31 sheets were both bend-formed to failure with significant cracks in the outer tensile region under the identical bending parameters. Moreover, under the same bending strain, both the outward offset degree of strain neutral layer and the sheet thickening were more serious in the AZ31/4047 Al composite sheet than those of the AZ31 and AZ31/AZ31 sheets. The foremost reason was the quite wide gap of material properties between Mg alloy AZ31 layer (tensile loading in the outer region) and Al 4047 layer (compressive loading in the inner region). Keywords: Mg alloy sheet, Composite extrusion, Tension–compression yield asymmetry, Bendability

The premature failure phenomenon that occurs in solid insulation under the application of repetitive impulse voltages is known as the accumulative effect of impulse voltages on a solid dielectric. The accumulative failure of winding insulation is considered to be a core problem resulting from this phenomenon. The main problems include the accumulative failure of motor winding insulation under pulse-width modulation impulses and the accumulative failure of transformer winding insulation under the application of overvoltages, and these problems represent new challenges in the safe and stable operation of power grids. With regards to the above problems, this study reviews the results of recent research on the accumulative failure characteristics and mechanisms of winding insulation when subjected to repetitive impulse voltages. The challenges faced are discussed at the end of this study.

Hot tears were frequently formed in Aluminum (Al) parts with complex structure. In this study, OM (optical microscope), SEM (scanning electron microscope), EDS (energy dispersive spectrometer), and FDM (finite difference method) were used to reveal the hot tears mechanisms in the casted AC4B Al engine. Shrinkage porosities with the size of 300–500 μm were found in casted specimens near the parts’ surface. Many cracked brittle Fe-bearing phase were also found in crack section. The secondary dendrite arm spacing observation in five typical positions showed that the cooling rate in position 5 was faster than that in position 1. The impropriety solidification sequence in position 5 and position 1 impeded the solidification feeding of position 1, and it might lead to casting defects or even casting cracks. Numerical simulation also showed that solidification sequence promoted casting defects, which was accordant with microstructure observation. Impurity may concentrate at position 5 during filling. It is concluded that large β-Fe intermetallics and improper solidification sequence together contributed to crack initiation in the engine.

Nano-modification is a prospective method for improving the electrical properties of transformer oil. In most situations, transformer oil combined with cellulose paper is used to construct an insulation system for power equipment, such as power transformers. However, the influence of nanoparticles on the electrical performance of oil-impregnated paper is still unclear. Therefore, in this paper, we identify the failure characteristics of both fresh and nano-modified oil/paper. Specifically, the accumulative failure characteristics of nano-oil-impregnated paper (NOIP) are experimentally determined. The space charge distribution and trap characteristics of fresh paper and NOIP were measured, and the effect of nanoparticles on the space charge behavior are then analyzed. Finally, we measure the microstructure of fresh paper and NOIP subjected to repeated impulses. The test results indicate that nano-titanium oxide (TiO2) particles have a limited effect on the breakdown voltage of NOIP. However, the particles can dramatically improve the resistant ability of NOIP against repeated impulses. For the NOIP with a nano-concentration of 0.25 g/L, the improvement reaches 62.5% compared with fresh paper. Under repeated applications of impulse voltages, the space charge density of NOIP is much lower than that of fresh paper. The deep trap density of NOIP is much higher than that of fresh OIP, whereas shallow trap density is relatively lower. Micropores are generated in paper insulation subjected to repeated impulses. The amount of the generated micropores in NOIP is lower than that in fresh paper. Nano-TiO2 particles suppress the accumulation of space charge in the oil paper insulation, which weakens the electric field distortion in the dielectric. However, nanoparticles reduce the accumulative damage caused by repeated impulses. The above two points are considered the main reasons to improve the resistant ability against repeated impulses.