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This work produced a MgAl-layered double hydroxide by hydrothermal treatment of a plasma electrolytic oxidation (PEO) coating on magnesium alloy AZ31 in an phosphate electrolyte, followed by an ion-exchange reaction in 0.1 M phosphate solution. The coated specimens were scratched. Characterization, including utilization of the localized technique SIET, measured the pH and pMg distributions and optical morphologies around the artificial defects during immersion in 0.05 M NaCl solution. In contrast with phosphate loaded PEO/LDHs, a stronger alkalinization area (with pH 11.4∼12.3) appeared in the passive PEO specimens. Due to formation of insoluble Mg(OH)2 products, the pMg map showed depletion of Mg2+ in this high pH area. Combined with optical morphologies and SEM images, the better self-healing ability toward defects for phosphate loaded PEO/LDHs was confirmed.

In general, different extrusion conditions will affect the microstructure of magnesium alloys and further determine the mechanical properties. The effects of extrusion parameters and heat treatment processes such as extrusion speed, pre-forging, annealing time, extrusion ratio and cooling rate on the microstructure, texture evolution and tensile properties of Mg-2Gd-0.3Zr alloys were investigated in this study. Compared with the as-cast alloy, the extrusion process significantly refines the grains and exhibit the rare earth texture. With the increase of extrusion speed and annealing time, the growth of recrystallized grains is accelerated, leading to the increase of elongation. Large pre-forging deformation achieves to refine the grains by promoting recrystallization nucleation, resulting in increased strength of Mg-2Gd-0.3Zr alloy. Decreasing the extrusion ratio or increasing the cooling rate will introduce coarse un-DRXed grains, which transformed the texture into the basal texture. In particular, the effect of rapid cooling on refining the recrystallized grains is also obvious. Different extrusion conditions influence the mechanical properties of the Mg-2Gd-0.3Zr alloy through the grain size, proportion of non-recrystallization region and texture type.

This research studied the mechanisms of Ca and Zn microalloying on the enhancement of ductility of extruded Mg-Gd sheet by combing electron backscattered diffraction and slip trace analysis. The ductility and microstructure of extruded Mg-0.6Gd and Mg-0.6Gd-0.3Ca-0.2Zn (wt%) sheets were investigated. Basal slip was the main deformation mode under investigation. Ca and Zn microalloying increased the frequency of grain boundaries (GBs) with misorientation angles (θs)

A doublely-doped layered double hydroxide (LDH) film was produced on an anodized magnesium alloy AZ31. The Ce-doped Mg-Al LDH film was prepared by in-situ hydrothermal treatment method, and the intercalation of vanadate was realized by ion-exchange reaction. The structure, morphology and composition of as-prepared LDH film were investigated by X-ray diffractometer, field-emission scanning electronic microscope and energy dispersive spectrometry. Results indicated that a uniform and compact LDH film was formed and the intercalation of Ce3+ and vanadate would change the crystal structure of LDHs. The results of the potentiodynamic polarization, electrochemical impedance spectra, hydrogen evolution and corrosion weight loss tests showed the Ce3+ and vanadate anions significantly improve the impedance of LDH film, and the active double-doped LDH film could effectively protect the magnesium substrate from corrosion.

On-line heating rolling mill which could efficiently preheat sheet and apply tensile force on both ends of the sheet along rolling direction (RD) was used to investigate the effect of tension on mechanical behavior and shape quality of magnesium sheets. For revealing the influence mechanism, many analysis techniques including optical microscope, electron backscattered diffraction, macrotexture and transmission electron microscope were performed. The shape defect, edge wave, could be eliminated under higher tension along RD, which was attributed to more uniform distribution of microstructure and microstrain. Nevertheless, it is undesirable that the forward tensile force exceeds 3 kN in present work because the strength decreased for high recrystallization level when the tensile force is beyond this value. Furthermore, the main deformation mode was still slip during rolling process despite of accompanying twining, e.g., double twins, but more prismatic slip activated when tensile force exceeds 3 kN. The distribution of shear bands was affected by the applied tensile force that they appear as “V” shape along RD at a low forward or backward tensile force, while they appear as reticulate shape under applied tensile force of 5 kN.

The microstructure distribution, tensile anisotropy and fracture behaviors in the dissimilar friction stir welded joint of AM60/AZ31 alloys were investigated. Experimental results showed that a significant grain refinement and an orientation fluctuation occurred in the weld. The grain size of AZ31 side in joint was obviously smaller than that of AM60 side. There was a higher percentage of low angle grain boundaries (LAGBs) and a lower degree of recrystallization in AZ31 side compared with those in AM60 side, especially for the thermo-mechanically affected zone in AZ31 side. The discrepancies of grain size distribution, recrystallization behavior and LAGBs in joint depended on the different initial state of two metals and the inhomogeneous temperature distribution in joint. In addition, the (0001) basal plane in weld was roughly parallel to the surface of the pin, showing the symmetrically distributed texture characteristics. The joint showed an obvious tensile anisotropy due to the special texture distribution. The comprehensive tensile properties of joint along the three directions decreased in the order: welding direction, 45° direction and transverse direction. The maximum ultimate tensile strength, yield strength and elongation of the joint were 242 MPa, 116 MPa and 21.2%, respectively. The fluctuations of grain size and texture in joint affected the fracture behavior of samples in the three directions.

The Mg–9Al–5Sn−xSb (x = 0.0, 0.3, 0.6, 1.0, 1.5 wt%) alloys were prepared by a simple alloying process followed by hot extrusion with an extrusion ratio of 28.2. The effects of Sb additions on the microstructure and mechanical properties of the Mg–9Al–5Sn alloys were investigated by optical microscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer. The results indicated that the phases α-Mg matrix, Mg2Sn, Mg3Sb2 and Mg17Al12 exist in the as-cast Sb-containing alloys. Sb addition results in the precipitation of Mg3Sb2. The dendritic size of these alloys decreases with the addition of Sb. Both their ultimate tensile strength and yield strength of extruded alloys increase, and their elongation decreases gradually with increasing the content of Sb. The better mechanical properties of the as-extruded alloys were achieved due to the refined grains and the formation of dispersive second phases Mg3Sb2.

The effect of Al addition on microstructure and mechanical properties of hot extruded Mg–1Mn alloy sheet was investigated. The results revealed that the dynamic recrystallization was promoted by increasing Al content. The ultimate tensile strength and yield strength of the alloy increased with the increase of Al content. The Mg–9Al–1Mn alloy exhibited the highest strength, with tensile strength of 308 MPa, 307 MPa, 319 MPa, yield strength of 199 MPa, 207 MPa, 220 MPa and the elongation of 20.9%, 20.1%, 19.2% in 0°, 45°, 90°, respectively. The high strength was mainly attributed to the formation of fine dynamically recrystallized grains and large amounts of the second phase. The strengthening mechanism of the alloys was explained.

The development of Mg-Al-Zn-Mn-Ca series alloys provides a potential prospect to achieve high strength and formability at room temperature (RT). The formation of elliptical annular texture is treated as a crucial factor for the enhanced RT formability. However, the origin of such an elliptical annular texture formation has been rarely reported. Herein, we unveiled the formation and evolution of elliptical annular texture in the hot-rolled Mg-1.6Al-0.8Zn-0.4Mn-0.5Ca (AZMX1100, wt.%) alloy after annealing at different temperatures for 1 h, and its static recrystallization (SRX) kinetics in given annealing temperature for different time. The results revealed that the formation of elliptical annular texture in the hot-rolled AZMX1100 alloy after annealing was derived from nucleation-oriented SRX mechanism, which took place in 200−300 °C, induced by cracked chain-shaped Al2Ca phases, contraction twins, intersections of double twins, intersections of double twins and grain boundaries and non-basal slips. On further annealing from 300−450 °C, the grains with 45°–70° transverse direction (TD) preferentially grew, which made elliptical annular texture extended along the TD. Based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, Avrami exponent n value was estimated to be 0.68–1.02, attributed to non-random SRX nucleation, giving rise to the lower activation energy QR of nucleation of ∼74.24 kJ/mol. Since the co-segregation of Al, Zn and Ca atoms in grain boundaries created a strong interaction of solutes and grain boundaries, the hot-rolled AZMX1100 alloy exhibited the higher activation energy Qg (∼115.48 kJ/mol) of grain growth.

The mechanical behavior of hot-rolled Mg-xZn-0.2Ca-0.2Ce (x = 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, 2.0 wt.%) was studied by the uniaxial tension test. Meanwhile, the microstructure and texture were analyzed using an optical microscope, x-ray diffraction and scanning electron microscope. The sheets exhibited a bimodal basal texture along the transverse direction (TD). Zn addition led to an increase of the TD tilted texture component and a reduction of the rolling direction tilted texture component. However, the yield strengths were not always increasing when the amount of Zn increased, which was related to the solid solution softening and unique texture distribution. The best ductility and formability were obtained in Mg-1.5Zn-0.2Ca-0.2Ce alloy with fracture elongation of ~ 42.1% and Erichsen value of 7.7 mm. The enhanced plasticity and formability were owing to the modified texture, non-basal slips and enhanced grain boundary cohesion.

The influence of Mn on the microstructure and mechanical properties of as-cast and as-solution Mg–Mn alloys was investigated in the present work. X-ray diffraction patterns revealed that the dominant phases of the experimental alloys were the α-Mg matrix and Mn precipitates. The average grain sizes of the as-cast Mg–Mn alloys decreased monotonically with increasing Mn content, although Mn addition showed a negative grain refinement effect on the as-cast Mg alloys. Increasing the Mn content enhanced the tensile yield strength of the as-cast alloys from 17.6 to 35.1 MPa. The improved mechanical properties are mainly attributed to precipitation hardening; a large number of Mn precipitates were located within the matrix and along the grain boundaries. Meanwhile, the lower tensile strength and Vickers hardness of the as-solution alloys is explained by the coarsened microstructure and poor solid-solution strengthening behaviour.

A modified global Schmid factor under different stress states was developed by introducing the stress intensity to normalize the stress tensor. The new method offers an efficient way to compare the activation of one deformation mode under different stress states. The distributions of global Schmid factors for deformation modes in Mg alloys were also studied using this new method. The results indicated that stress state dominated the distributions of global Schmid factors for different deformation modes in a similar way. Additionally, the deformation compatibilities among deformation modes were also influenced by the stress state, especially under a biaxial stress state.

Super-hydrophobic films were synthesized on the Mg alloy AZ31 by modifying in-situ grown Mg-Al layered double hydroxide (LDH) films with stearic acid (SA), sodium laurate (SL), myristic acid (MA) and 1H, 1H, 2H, 2H–perfluorodecyltrimethoxysilane (PFDTMS). These films exhibited a static water contact angle of 150.6°, 153.7°, 152° and 145.5°, respectively. Mg-Al LDH-SA, Mg-Al LDH-SL and Mg-Al LDH-MA films were produced by the neutralization reaction of the fatty acid and Mg(OH)2 whereas the Mg-Al LDH-PFDTMS film was produced by the hydrolysis reaction of PFDTMS along with the condensation polymerization reaction. The electrochemical impedance spectroscopy (EIS), the hydrogen evolution data as well as long-term immersion tests indicated that Mg-Al LDH-PFDTMS provided better barrier protection to improve the corrosion resistance of AZ31 Mg compared with the Mg-Al LDH-SA, Mg-Al LDH-SL and Mg-Al LDH-MA films, because the Si OH groups and the hydroxyl groups on the surface of the film were combined to form CF3(CF2)7(CH2)2Si(O-Surface)3, which decreased the surface energy and improved the corrosion resistance.

The microstructure evolutions of cascade annealing in α-Zr crystals at T=300K, 400 K, and 500 K for energy of 2, 6 and 10 keV with initially driving directions ⟨0001⟩ and ⟨011¯0⟩ of the pri...

A one-step electrodeposition method was used to construct a superhydrophobic coating on the surface of magnesium alloy. Using magnesium nitrate and ethanol solution of stearic acid as electrolyte, four groups of electrolytes with different ratios of stearic acid and magnesium nitrate were designed to explore the influence of electrolyte to the process. The contact angles of the four coating samples were 136.4 ± 5.8°, 152.7 ± 2.8°, 156.2 ± 4.9° and 155.1 ± 4.4° The addition of magnesium nitrate in the solution increased the hydrogen evolution reaction in the electrodeposition process, which was not conducive to electrodeposition process. During the deposition process, the sample prepared in a molar ratio of stearic acid to magnesium nitrate of 10:1 had the best corrosion resistance, and its corrosion circuit density was 3.74 × 10−8 A/cm2, far lower than the corrosion current density of the magnesium alloy substrate. Keywords: Magnesium alloy, Superhydrophobicity, Corrosion resistance

Two types of material positions, with AZ31 or AM60 in retreating side, were used for dissimilar friction stir welding in this study. The appearance, microstructure evolution, mechanical properties and fracture mechanism of the joints were investigated. The results showed that significant microstructure evolution occurred in the joint under the intense stirring and thermal cycling. Furthermore, the material positions had little influence on the appearance, tensile properties and failure locations of the joints. It is interesting that all the tensile joints fractured at the boundary of thermo-mechanically affected zone (TMAZ)/nugget zone (NZ) near the AZ31 side. In order to explore the fracture mechanism of the joints, the relationship of failure locations, microstructure and texture evolution of joints were analyzed. The analysis on EBSD demonstrated that the texture evolution in both TMAZ and NZ, as well as a certain extent of dislocation density and strain existing adjacent to TMAZ/NZ interface, was the main factor leading to the fracture at the boundary of TMAZ/NZ. The tensile strength of AZ31 alloy was smaller than that of AM60, the grain gradient and the second phases size near the NZ/TMAZ interface of AZ31 side were larger than those of AM60, resulting in the fracture tending to AZ31 side.

Mg-Al layered double hydroxides (LDHs) were deposited on the anodized magnesium alloy AZ31 via an easy in-situ method, and the surfaces of MgAl-LDHs were modified with myristic acid (MA) and 1H, 1H, 2H, 2H-Perfluorodecyltrimethoxysilane (PFDTMS). The obtained results showed that LDHs with the biggest flakes were preferential sites for absorption of MA, while unfavorable for the adsorption of PFDTMS. All of films modified with MA were superhydrophobic. The corrosion behavior of the AZ31 with modified LDH films was evaluated using hydrogen collection, electrochemical impedance spectroscopy (EIS), polarization potentiodynamic curves and the immersion tests. The superhydrophobic films considerably improved the corrosion performance of the LDH films on the AZ31 substrate.

In this paper, in situ electron back scattered diffraction combined with scanning electron microscopy and digital image processing techniques were used to study the microscopic deformation compatibility of AZ31 Mg alloy rolled sheets with strong basal texture during biaxial tension at room temperature. The results firstly quantitatively showed that the distribution of microscopic strain in AZ31 rolled sheet was inhomogeneous during formation. Strain concentrations happened in some regions even at early stage of deformation. Short distorted bands also appeared in these regions and extended to connect each other with increasing macroscopic strain. The appearance of distorted bands play an important role in strain compatibility since the materials lack easy deformation modes at room temperature. Besides slips and twins, the grain distortion should also be an indispensable mechanism in accommodating plastic deformation in some parts in distorted bands. According to the analysis from the Schmid factor, the geometric compatibility factors and slip trace identification, the comprehensive effect of strong basal texture and biaxial tensile stress state not only led to the quite low SFs for prismatic , pyramidal slips and tensile twinning, but limited the compatibility between slip systems and tensile twins. This mechanism was the main reason for the lack of easy deformation modes and the appearance of distorted bands, which further led to the inhomogeneous strain distribution at room temperature. Therefore, the formability of Mg alloys rolled sheets with strong basal texture was weakened at room temperature.

A cast Mg–3Gd–0.6Zr alloy with microscale {101¯2} growth twins was designed successfully. After the alloy was annealed at 350°C for 1 h, the volume fraction of the growth twins was increased by approximately 120%. Gd solute atoms segregated on both sides of twin boundaries and facilitated their formation in the as–cast alloy. The formation mechanism of {101¯2} growth twins in the as–cast alloy was discussed in five aspects: the supersaturation of Gd solute atoms, the segregation ability of Gd, the composition of Gd, the nucleate sites of growth twins, and the total energy of the system. The growth twins elicited remarkable toughening effect but a moderate strengthening effect on the alloy.

Mg-Sn-Mn-based alloys exhibit great application prospect because of their high mechanical properties and good creep resistance. The content of Mn in Mg-Sn-based alloys is commonly less than 1 wt%. In this study, the effect of Mn addition on the microstructure, mechanical properties and work-hardening behavior of Mg-1Sn (wt%) alloys has been investigated. The as-extruded alloys are mainly composed of α-Mg and Mn precipitates, which exist in TM11 and TM12. The average grain size sharply decreases with Mn addition. In addition, with increase in Mn content, the basal texture of the alloys has strengthened. The experimental results show that Mn addition significantly increases the tensile and compressive yield strengths, ultimate tensile strengths, and elongation of the as-extruded Mg-Sn-Mn alloys because of the good microstructures. Moreover, the decrease of number of tensile twins in compress leads to the yield asymmetry reduces with Mn addition. With increasing Mn content, the value of work-hardening exponent and capacity decreases, the work-hardening behavior in stage III significantly improved. The variation in microstructures, mechanical properties and work-hardening of Mg-Sn-Mn alloys have been analyzed.

Ultrafine-grained aluminum processed by a new severe plastic deformation technique, accumulative extrusion bonding (AEB), was investigated. Microstructural characterization indicated good interfacial bonding and an average grain size of ∼440 nm was obtained after six passes. Tensile testing revealed that the strength reached the maximum value of 195 MPa and the total elongation exceeded 16% after five passes. The hardness was also significantly improved and almost reached saturation after the first pass. SEM fractography of AEB-processed specimens after tensile test showed that failure mode was shear ductile fracture with elongated shallow dimples. Comparison with conventional accumulative roll bonding indicates that this new AEB technique is more effective in refining grain and improving mechanical properties of the specimens.

All the time, it is difficult for magnesium alloys to equilibrate the relationship among strength, ductility and stretch formability at room temperature. Here, we added 0.6 wt% Zn into Mg-0.4Sn-0.7Y (TW00, wt%) alloy attempting to achieve a good combination among strength, ductility and stretch formability at room temperature. After extrusion, we found that Mg-0.4Sn-0.7Y-0.6Zn (TWZ000, wt%) alloy sheet exhibited a weak elliptical texture, accompanied with significant grain and second phase refinement. The formation of this weak elliptical texture was mainly originated from the joint contributions of multiple dynamic recrystallization (DRX) mechanisms consisted of twin-, compound- and dislocation slip-induced DRX behaviors. Grain boundary strengthening and second phase strengthening were mainly dedicated to the enhanced yield strength (~ 150.0 MPa) and ultimate tensile strength (~ 235.1 MPa), while non-basal slip, grain boundary cohesion, texture modification and twins commonly guaranteed the high ductility (~ 39.8%). Besides texture modification and non-basal slip, a large number of twins altered the initial microstructure along with the formation of new twinning textures during stretch forming. These new twinning texture facilitated the higher Schmid factor (SF) for basal slip beneficial to the enhancement in stretch formability (~ 7.0 mm). Therefore, TWZ000 alloy sheet provided an enormous potential to broaden magnesium alloys applications.

Corrosion inhibitors 2,5-pyridinedicarboxilate (PDC), sodium metavanadate (SMV) and 5-aminosalicylate (AS) were impregnated into porous PEO coatings respectively via vacuuming process, followed by fast sealing treatment in a Ce containing solution. After that layered double hydroxides (LDHs) based nanocontainers were respectively prepared on them via hydrothermal treatment. In frame of this work it was shown, that sealing effect for the pore was provided by formation of new phase CeO2 on the surface of PEO coatings. And, hydrothermal preparation for preparing LDHs leaded obvious changes in structure and thickness of the coatings. In addition, impregnation of inhibitors was in favor of improving LDHs content in final composite coatings. EIS result indicated that AS/Ce-HT specimen exhibited a best corrosion protection.

The effect of titanium on the microstructure, the texture, and the mechanical properties of as-extruded Mg–Sn alloy has been investigated in the present work. The result reveals that the alloy subjected to the optimized extrusion process shows an extremely refined microstructure with an average grain size of 1.7 μm. Meanwhile, the addition of titanium has an obvious effect on intensifying the basal texture where the basal slip cannot be easily activated during tensile testing. As a result, the alloy shows excellent mechanical properties where yield strength and elongation are 200 MPa and 30.2%, respectively. The enhanced yield strength of the alloy can be attributed to the extremely refined microstructure and the intensified basal texture, while the improved elongation of the alloy can be explained by the ultra-fine-grained microstructure through reducing the critical resolved shear stress that favors the prismatic slip activity to accommodate the basal slip.

Mg alloys usually deform under complex biaxial compressive stress states (e.g. during drawing, forging and extrusion). In order to better understand how the biaxial compressive stress state influences the evolution of the microstructure and the deformation compatibility, the uniaxial and biaxial compression tests of AZ31 rolled sheets were performed at room temperature. The new self-developed biaxial compression devices offered a possibility to obtain the evolution of the microstructures by in situ measurements via electron backscatter diffraction. The analysis of geometrically necessary dislocation and the simulation based on the visco-plastic self-consistent method were used to examine the microscopic behaviors in the sheets during the uniaxial and biaxial compression tests. The results indicated that the reorientation of the texture during the biaxial compression was different from that during the uniaxial compression. The simulated results based on the visco-plastic self-consistent model suggested that the equivalent yield strength under a biaxial compressive stress state was lower than that under a uniaxial stress state. This was due to the higher relative activity of extension twins under biaxial compressive stress state. This also led to a lower geometrically necessary dislocation density in the biaxial compressed sample. The geometrically necessary dislocations were also more homogeneously distributed with a biaxial compressive stress state. The analysis of the activation of all the deformation mechanisms proved that the appearance of extension twinning variants limited the activation of prismatic slip during the uniaxial compression while promoting prismatic slip during the biaxial compression. This changeable interaction between extension twinning and prismatic slip combining with the lower geometrically necessary dislocations, the lower flow stress inferred that the application of the biaxial compressive stress state during processing at room temperature was a way to improve the deformability of Mg alloys.

MgAl-LDH films were produced through hydrothermally chemical conversion of pre-prepared anodic films on Mg alloy AZ31. The growth behavior and corrosion performance of the LDH films were investigated. Results reveal that morphology, chemical compositions and structure of LDH films vary greatly as a function of the conversion treatment conditions. Internal sources of Mg2+ and Al3+ cations for the formation of LDH films were ascribed to: (i) degradation of the anodic films; and (ii) dissolution of the AZ31 substrate. Moreover, the Stranski-Krastanov (SK) growth mode, two-dimensional layer growth (2D) to three-dimensional (3D) growth, was proposed to explain the transformation process.

In order to develop new magnesium alloy sheets with a good balance between ductility and stretch formability at room temperature, here we designed an Mg alloy with dilute Sn and Y and investigated the microstructure, texture, mechanical properties and stretch formability of Mg-0.4Sn-0.7Y in wt% (TW00) alloy compared with AZ31 alloy under extrusion and hot rolling-annealing conditions. We found that, after extrusion, the extruded TW00 (TW00-E) sheet exhibited a more homogeneous complete dynamic recrystallized microstructure and a splitting texture character with ~ ± 20° tilted to the extrusion direction, compared with the extruded AZ31 (AZ31-E) sheet. After hot rolling-annealing at 400 °C, both the hot rolled annealed TW00 (TW00-RA-400) and AZ31 (AZ31-RA-400) sheets presented similar complete static recrystallized microstructures. However, significant texture weakening occurred in the TW00-RA-400 sheet rather than the AZ31-RA-400 sheet, due to static recrystallization induced by twins and grain boundaries. Tensile tests revealed that the TW00-E and TW00-RA-400 sheets with high Schmid factor (SF) for basal slip exhibited high ductility (~ 33% and ~ 32%). Simultaneously, prismatic slip and texture weakening played a significant role on decreasing r-values for the TW00-E and TW00-RA-400 sheets, respectively, which contributed to the improvement in stretch formability (~ 6.2 mm and ~ 5.4 mm) at room temperature. Therefore, we concluded that the TW00 alloy provided a bright prospect to achieve a good balance between the ductility and stretch formability at room temperature via extrusion or hot rolling-annealing.

Here, Mg-0.4 wt%Sn based alloys containing different Y contents, Mg-0.4Sn-xY (x = 0, 0.7 and 2.0 wt%) alloys, were extruded into the sheets to systemically investigate the role of Y element on the microstructure, texture and mechanical properties of extruded Mg-0.4Sn alloy. We found that, with the Y addition, the average grain size gradually was reduced and the typical basal texture was transformed into the splitting one tilted to the extrusion direction. Moreover, the evidence of low number density and rough grain boundary cracks after tension indicated the strengthening in grain boundary cohesion with the Y addition. Besides more basal slips, the activation of prismatic slip and high intergranular strain propagation capacity were observed, which efficiently accommodated the sheet strain at room temperature. Those mentioned key factors contributed to the high room-temperature ductility of Mg-0.4Sn-0.7Y sheet. However, the formation and coarsening of Sn3Y5 and MgSnY phases were increasingly severe with increasing the Y addition to 2.0%. Those coarse secondary phases served as crack sources during tension deteriorating the ductility of Mg-0.4Sn-2.0Y sheet at room temperature. Therefore, we concluded that Y micro-alloying provided a new insight to achieve a superior room-temperature ductility of Mg-0.4Sn sheet.

This study presented a novel intense plastic straining process called on-line twist extrusion (OLTE). An on-line torsional strain was applied on magnesium extruded rod during extrusion. After OLTE, the grains are refined from the periphery to the center of the bar, and the refined extent can be promoted with increased torsion speed. A fully recrystallized ultrafine grained structures and spiral shaped basal texture with the average grain size of 1.2 μm are successfully achieved with increased torsion speed. The microstructure evolution and strengthening mechanism were also discussed. Keywords: Metals and alloys, Magnesium, Ultrafine grain, Mechanical property

A composite coating was produced via (i) plasma electrolytic oxidation (PEO) with Ce salt sealing, on which layered double hydroxides (LDHs) were deposited via a hydrothermal treatment, and (ii) then modified by phytic acid (PA) via an ion-exchange reaction. The final coating (characterized using XRD, XPS, FT-IR, SEM, EDS and GDOES) consisted of LDHs/Mg(OH)2/CeO2/Ce(OH)3 with a non-uniform Ce distribution. The corrosion protection and self-healing ability were investigated using polarization curves, EIS, immersion tests and SVET. The composite coating modified with PA showed the most superior corrosion protection and self-healing ability, attributed to the synergistic effect between Ce species and phosphate.

In this work, Mg-3Al-1Zn/Mg-0.3Y (AZ31/W0) laminated composite sheet was successfully fabricated by porthole die extrusion. Herein, microstructures, textures and stretch formability at room temperature of the AZ31 sheet, the W0 sheet and AZ31/W0 laminated composite sheet were systematically investigated and compared. The results showed that a tiny diffusion zone of ~ 0.35 µm and crystallographic interface were observed in the AZ31/W0 interface, indicating that the AZ31/W0 laminated composite sheet had a well bonding interface. The stretch formability at room temperature of the AZ31/W0 laminated composite sheet was apparently improved by ~ 71% and ~ 20%, respectively, as compared with the AZ31 sheet and W0 sheet. The activation of more basal slip in the W0 layer of the AZ31/W0 laminated composite sheet and the formation of extensive tensile twins in the AZ31 layer, which could effectively accommodate through-thickness strain during stretch forming, were assumed to be the main contribution to the stretch formability enhancement. Therefore, the bimetal laminated composite sheet provided a new thought to achieve high stretch formability Mg alloys via the porthole die extrusion.

In order to improve the strength and ductility of AZ31 magnesium alloy thin sheet with thickness of 1.5 mm, an accumulated extrusion bonding (AEB) process was conducted for 1 and 2 passes at 473 K. Microstructure evolution and mechanical properties were subsequently investigated. The results showed that the interface bonded successfully with a good bonding quality due to the large strain induced by AEB process. {10–12} tensile twinning dominated the deformation at the initial stage of extrusion. As the strain increasing, dynamic recrystallization (DRX) occurred and dominated the further deformation. A fully DRXed microstructure was observed in the sizing band and the average grain size was significantly reduced to ∼1.4 μm. Grain growth occurred after the extruded sheet exited from extrusion die. AZ31 alloy sheet after by 1 pass AEB process exhibited a double-peak texture with the basal poles inclined from normal direction (ND) towards extrusion direction (ED) and showed a similar texture intensity to as-received sample. Due to the grain refinement strengthening, the AEB processed sample exhibited better comprehensive mechanical properties with a higher yield strength (169 MPa vs. 145 MPa), ultimate tensile strength (336 MPa vs. 385 MPa) and fracture elongation (24.9% vs. 28.0%) at room temperature. However, for the 2 passes extruded sample, the microstructure evolution and mechanical properties showed a similar characteristic to that of first pass sample. This indicated that increase in the number of AEB pass had no more effect on the grain refining and improving the mechanical properties.

Nano-titanium (Nano-Ti) was prepared by high-energy ball milling from pure Ti power and grinding agents (Epoxy resin) at room temperature. The effect of milling time on structure and properties of Nano-Ti polymer were investigated systematically. The results show that high-energy ball milling is an effective way to produce Nano-Ti polymer. The dispersion stability and compatibility between Ti power and grinding agents are improved by prolonging the milling time at a certain degree, that is to say, the optimization milling time is 240 min. The particle size of Ti powder and the diffraction peaks intensity of Ti decrease obviously as the milling time increases due to the compression stress, shear friction and other mechanical forces are formed during ball milling. FT-IR result displays that the wavenumber of all the bands move to lower wavenumber after ball milling, and the epoxy ring is open. The system internal energy rises owing to the broken epoxy group and much more Nano-Ti is formed to promote the grafting reaction between Nano-Ti and epoxy resin. The results from TEM and XPS also prove that. And the grafting ration is maximum as the milling time is 240 min, the mass loss ratio is 17.53%.

This paper provided an effective plastic deformation technique, asymmetric porthole die extrusion, for fabricating AZ31 magnesium alloy sheets. Three kinds of asymmetric porthole extrusion dies were designed and entitled as APE-45, APE-60 and APE-90 die in terms of asymmetric porthole die angle, respectively. The effect of different APE processes on the microstructures, texture evolutions and mechanical properties of AZ31 sheets was investigated at room temperature. For comparison, conventional extrusion (CE) and symmetric porthole die extrusion (PE) were also conducted on processing AZ31 sheets. Shear deformation induced by APE declined the grain size and promoted a broad angular distribution of basal planes in the APE sheets compared with the CE and PE sheets. Especially, the APE-90 sheet obtained finest grain size of 5.2 µm and made basal planes tilted towards the extrusion direction by ~ 21° rotation in the sheet plane. With increasing asymmetric porthole die angle, the volume fraction of recrystallized grains gradually increased, resulting in the decrease of basal pole intensity. Due to the increased activity of basal slip, APE sheets exhibited the decrease in yield strength and r-value and increase in elongation to failure, especially for the APE-90 sheet. The improved formability of the APE sheets was attributed mainly to texture weakening. The APE-90 sheet exhibited the highest index Erichsen value and improved by ~ 74% and ~ 94% compared to the CE and PE sheets, respectively. Consequently, microstructure-texture control induced by APE could enhance the room-temperature stretch formability of AZ31 sheets.

In the present investigation, microstructure, texture and mechanical properties of Mg-3Mn alloys fabricated by hot extrusion process with the extrusion temperatures of 250 °C and 300 °C were investigated. The results revealed that the samples exhibited the refined microstructure and weakened basal texture. Refined microstructure of the samples was attributed to the dynamic precipitates suppressing the recrystallization grain growth during extrusion process. Weakened basal texture of the samples was explained as a result of particle stimulated nucleation (PSN) promoted by coarsened Mn precipitates altering the texture of extruded profiles during recrystallization by orienting the c-axis of grains at an angle that favors basal slip activity. As a result, the samples exhibited the high tensile elongation and good yield strength at room temperature.

Highly oriented Mg-M layered double hydroxide (LDH) films were firstly fabricated by a facile in-situ growth method on anodized magnesium alloy AZ31. It is proved to be an effective method to seal the porous anodic oxide film. M presents metal cations, such as Al3+, Cr3+ and Fe3+. The characteristic structure, morphology and composition of the LDH films were investigated via field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), fourier transform infrared spectrometer (FT-IR) and energy dispersive spectrometer (EDS) respectively. Besides, the corrosion resistance of the LDH films on magnesium alloy was investigated by using potentiodynamic polarization and electrochemical impedance spectroscopy. The result demonstrates that anodic oxide film can be sealed by the formation of LDHs with nano-container structures. The corrosion resistance of anodized magnesium alloy is remarkably improved by Mg-M LDHs, especially by Mg-Al LDHs. Finally, the protection mechanism of Mg-M LDHs was proposed.

In the present work, for the first time micro-arc oxidation (MAO) coatings were produced at different voltages on the magnesium alloy AZ31, leading to the formation ofMAO coatings with different properties (e.g. composition, structure and morphology). Then, we studied MgAl layered double hydroxides (LDHs) grown in-situ on MAO coatings. The properties of final composite coatings were largely determined by the dissolution of the MAO coating, and the final composite coatings significantly increased in thickness with the thickest one being 18.0 mu m. The corrosion protection was investigated using EIS, hydrogen evolution tests and immersion tests. Due to a synergistic effect of LDHs and spinel, MAO coating formed at the highest production voltage, modified with LDHs, provided the better corrosion protection.

Mg–3Al–1Zn alloy sheets have been deformed by continuous bending (CB) to investigate the effects of processing parameters (bending angle and repetitive passes) on the texture and formability. The samples exhibited a bimodal microstructure with abnormal growth grains in the surface region and fine grains distributed in the center after CB process followed by annealing. The texture evolution measured by XRD indicated that the basal poles were rotated from ND toward RD, and the texture intensity decreased with the bending angle decreasing and repetitive passes increasing. Compared with the as-received sample, the yield strength of CBA-120-2 sample significantly decreased from 183 to 112 MPa, and a smaller r-value and a larger n-value were obtained. The formability of CB processed samples in annealing condition was significantly enhanced with the highest of Erichsen value of 5.4 mm, increased by about 135%. The improvement of formability was likely attributed to the weakened and RD-tilt basal texture and coarse grains in the surface part.

Diffusion behaviour of Zn in primary Mg phase (α (Mg)) was investigated using Glow Discharge Optical Emission Spectroscopy (GD-OES) characterization on semi-infinite diffusion-couples employing quantitive chemical analysis method under the eroding mode. The obtained composition profiles along the diffusion area were continuous without obvious steps in the phase boundary. Self-consistent diffusion coefficients were obtained as 6.3 × 10−17, 1.2 × 10−16, and 2.5 × 10−16 at 498, 548 and 573 K respectively, which follow the Arrhenius relationship. The currently applied method is suitable for studying systems in which the second element shows only limited solubility in the primary element phase.

Diffusion behaviour of Mg–Gd intermetallic compounds (IMCs) were studied in the temperature range of 713–793 K using the diffusion couple method. Measured growth constants and integral interdiffusion coefficients of formed IMCs showed inverse-correlation to melting temperatures, excluding metastable phase Mg7Gd. Mechanical properties of obtained IMCs were studied using nanoindentation characterization technique and first-principles calculations. The experimental measured nano-hardness of Mg5Gd, Mg3Gd and Mg2Gd are 4.11 GPa, 4.05 GPa and 4.72 GPa, respectively, nearly twice of that of α (Mg). The obtained kinetic and mechanical information of Mg–Gd system is the basis for the development of high-strength Mg–Gd based Mg alloys.

In this work, a facile in situ method to prepare the Mg-Al layered double hydroxide (LDH) films on an anodised AZ31 substrate was proposed. The morphology, structure and composition of the LDH films produced within a range of pH values were studied by scanning electronic microscopy, X-ray diffractometer, energy-dispersive spectrum and Fourier transform infrared. The corrosion behaviours of the LDH films were further investigated using electrochemical impedance spectroscopy and potentiodynamic polarisation. The influence of pH on the LDH films was also studied. The results revealed that the pH of solution is important in the formation of the LDH. The films, which formed within the pH range from 10.72 to 11.72, possessed higher crystallinity and denser layered structure. These LDH films could effectively seal the anodic oxide films and enhance the corrosion resistance of the AZ31 substrate.

TiO2 films were grown onto unheated 5083 aluminum alloy substrates by reactive magnetron sputtering from a pure Ti target in Ar-O2 gas mixture in different power, bias voltage, Ar/O2 ratio and deposition time at room temperature. The effects of different deposition parameters on the structure and properties of TiO2 films were investigated systematically by field emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), nanoindentation tests, electrochemical tests and antibacterial tests. The results show that power and bias voltage are two main factors to affect the structure and properties of TiO2 films during the sputtering process. XRD results show that anatase phase is the main phase of the film, and the enhanced content of anatase phase with the increase of sputtering power and bias voltage. Nanoindentation tests exhibit that higher H/E (Hardness/Modulus) ratio can be achieved by depositing TiO2 film. And the corrosion resistance and antifouling property are all improved after depositing TiO2 film. 2# sample shows the optimal corrosion resistance, Ecorr and Icorr are −0.27388 V and 3.7232 μA/cm2, respectively. 1# sample exhibits excellent antibacterial property, the d ensity of bacteria is only 217 cell / mm2, which is 484% higher than that of uncoated matrix.

Mg-x Zn-0.2Ca-0.2Ce (x = 0.5, 1.0, 1.5 and 2.0, wt%) alloys were subject to hot extrusion, for the purpose of evaluating the effects of Zn addition on the mechanical properties and texture characteristics in this current paper. A spread of basal poles in extrusion direction (ED) was found in all four extruded alloys, beyond that, the rare earth texture component existed in the alloys. It is interesting that both the ED-split texture and rare earth texture components reduced with the increasing Zn addition; furthermore, the increasing Zn addition leaded to a broader spread of basal poles toward transverse direction (TD). Both the strength and plasticity were improved with the increasing Zn addition, by solid solution hardening, solid solution softening, and the enhanced cohesion of grain boundaries; while further Zn addition deteriorated the plasticity, because of the dominant solid solution hardening. Mg-Zn-Ca-Ce magnesium alloys received the best comprehensive mechanical properties when Zn addition reached 1.5 wt%, with tension yield strength (TYS) and tension fracture elongation (TFE) about 131.0 MPa and 42.4%, respectively, in ED.

In this paper, the effect of aluminium on microstructure and mechanical properties of as-cast magnesium–manganese alloy has been investigated by means of X-ray diffraction, optical microscopy and scanning electron microscopy. The results reveal that various Al–Mn intermetallic compounds form with an increase of Al content. As a result, microstructure of AM11 alloy has been effectively refined due to the formation of Al8Mn5 phase along the grain boundary, while Al addition is explained as the main reason on refining the microstructure of AM91 alloy due to its higher grain growth restriction factor value of ∼4.32. The tensile yield strength (TYS) has been improved steadily from 27.4 to 122.9 MPa with increasing Al content, because of the combined effects of grain boundary strengthening, solid solution strengthening and precipitation hardening behaviours.

AZ31 magnesium alloy sheet was fabricated by two different approaches, namely conventional extrusion (CE) and differential speed extrusion (DSE), under the same process conditions and extrusion ratio. The microstructures, textures and mechanical properties of AZ31e magnesium alloy sheets processed by the CE and DSE processes were investigated. It was found that with the DSE process more uniform and finer microstructures were obtained. The DSE sheet exhibited the lower yield strength and yield ratio, but the larger n value combined with the lower r value, which made the DSE sheet achieve an excellent formability. Those results were mainly attributed to a tilted weak texture resulted from the differential flow speed of alloy at the severe deformation zone.

A precipitation hardenable Mg–3Gd–3Nd–0.6Zr alloy was designed by thermodynamic calculations firstly and then investigated by experiment. In the as–cast alloy, the solution of Nd atoms into equilibrium Mg5Gd phase facilitated its formation and increased its lattice constant. After a two–step solution and a two–step aging treatment, the alloy showed remarkable age–hardening response, which was caused by the formation of massive fine β1 precipitates. It is quite possible that the β1 phase is a continuous solid solution with metastable Mg3Nd and Mg3Gd phases.

In this study, as-extruded Mg-Sr alloys were studied for orthopedic application, and the microstructure, mechanical properties, bio-corrosion properties and cytotoxicity of as-extruded Mg-Sr alloys were investigated by optical microscopy, scanning electron microscopy with an energy dispersive X-ray spectroscopy, X-ray diffraction, tensile and compressive tests, immersion test, electrochemical test and cytotoxicity test. The results showed that as-extruded Mg-Sr alloys were composed of α-Mg and Mg 17 Sr 2 phases, and the content of Mg 17 Sr 2 phases increased with increasing Sr content. As-extruded Mg-Sr alloy with 0.5 wt.% Sr was equiaxed grains, while the one with a higher Sr content was long elongated grains and the grain size of the long elongated grains decreased with increasing Sr content. Tensile and compressive tests showed an increase of both tensile and compressive strength and a decrease of elongation with increasing Sr content. Immersion and electrochemical tests showed that as-extruded Mg-0.5Sr alloy exhibited the best anti-corrosion property, and the anti-corrosion property of as-extruded Mg-Sr alloys deteriorated with increasing Sr content, which was greatly associated with galvanic couple effect. The cytotoxicity test revealed that as-extruded Mg-0.5Sr alloy did not induce toxicity to cells. These results indicated that as-extruded Mg-0.5Sr alloy with suitable mechanical properties, corrosion resistance and good cytocompatibility was potential as a biodegradable implant for orthopedic application.

Mg–Zn–Mn-based alloys have received considerable attention because of their high creep resistance, strength, and good corrosion resistance. The alloying element Mn in Mg–Zn-based alloys is commonly less than 1 wt%. In the present study, the effect of high Mn content (1 wt% and 2 wt%) on the microstructures and mechanical properties of Mg–2Zn–0.3Sr extruded alloy was investigated. The results revealed that the high Mn content significantly increased the ultimate tensile strength, tensile yield strength, compress yield strength, and yield asymmetry of the alloy without affecting its ductility. The dynamically recrystallized (DRXed) grains of Mg–2Zn–0.3Sr were remarkably refined because of the large amount of fine Mn precipitates in the homogenized alloy. The improved strengths were mainly attributed to the fine DRXed grains according to the Hall–Petch effect and to the large amount of spherical and Mn precipitates through the precipitation and dispersion strengthening. The fine DRXed grains and numerous Mn precipitates effectively suppressed the extension twining, substantially enhanced the compress yield strength, and resulted in improved anisotropy.

Mg-Al-Sn magnesium alloys have bright future in application because of good properties without rare earth elements. To study the effects of rotation rate on microstructures and mechanical properties of Mg-5Al-1Sn alloy after friction stir welding (FSW), extruded plates were butt welded by FSW with various rotation rates at constant other parameters. The results showed that after FSW, Mg17Al12 phase with poor thermal stability was dissolved, while Mg2Sn phase remained due to high dissolution point and good thermal stability. The hole-type defects were observed at 600 rpm, and the weld joint was with no defects at 800~1100 rpm. The weld joint at 800 rpm gave a maximum ultimate tensile strength (UTS), which was 91% of the base material (BM). After FSW, both UTS and elongation of weld joints decreased compared with the BM, caused by the soften region between nugget zone (NZ) and thermo-mechanically affected zone (TMAZ), the dissolution of Mg17Al12 phases, the residual stress and dislocation content in the TMAZ, and the textural variation. With increasing rotation rate from 600 to 1100 rpm, the UTS of weld joints first increased and then decreased, while the elongation kept mostly unchangeable due to the common action of multifactors.

Mg-Al-Sn alloys are being developed as a new series of magnesium alloys due to good properties without any rare earth components. In order to investigate the effects of friction stir welding (FSW) on microstructures and mechanical properties of Mg-5Al-3Sn magnesium alloy, the hot-extruded alloy plates were butt welded by FSW at various welding speeds. The results showed that the alloy was jointed without defects. After FSW, β-Mg17Al12 phase was dissolved into α-Mg matrix while Mg2Sn phase with high dissolution point and good thermal stability remained in the nugget zone (NZ). With increasing welding speed, the maximum (0002) pole intensity in the NZ first decreased and then increased, and grain size of α-Mg matrix decreased arising from lower heat input while some intermetallic particles coarsened at higher welding speed due to solid state diffusion and less applied stress. In all cases the tensile properties of the alloy after FSW decreased due to the softened region at the heat-affected zone (HAZ), the dissolution of β-Mg17Al12 phase, the residual stress and dislocation content in the TMAZ, the textural variation and the secondary phase changes. The elastic behavior of weld joints was different from the BM due to the dissolution of β-Mg17Al12 particles. Keywords: Friction stir welding, Mg-5Al-3Sn magnesium alloy, Texture, Mechanical properties, Welding speed