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Mg–3Nd–0.2Zn–0.4Zr (NZ30K, wt.%) alloy is a new kind of high-performance metallic biomaterial. The combination of the NZ30K Magnesium (Mg) alloy and selective laser melting (SLM) process seems to be an ideal solution to produce porous Mg degradable implants. However, the microstructure evolution and mechanical properties of the SLMed NZ30K Mg alloy were not yet studied systematically. Therefore, the fabrication defects, microstructure, and mechanical properties of the SLMed NZ30K alloy under different processing parameters were investigated. The results show that there are two types of fabrication defects in the SLMed NZ30K alloy, gas pores and unfused defects. With the increase of the laser energy density, the porosity sharply decreases to the minimum first and then slightly increases. The minimum porosity is 0.49 ± 0.18%. While the microstructure varies from the large grains with lamellar structure inside under low laser energy density, to the large grains with lamellar structure inside & the equiaxed grains & the columnar grains under middle laser energy density, and further to the fine equiaxed grains & the columnar grains under high laser energy density. The lamellar structure in the large grain is a newly observed microstructure for the NZ30K Mg alloy. Higher laser energy density leads to finer grains, which enhance all the yield strength (YS), ultimate tensile strength (UTS) and elongation, and the best comprehensive mechanical properties obtained are YS of 266 ± 2.1 MPa, UTS of 296 ± 5.2 MPa, with an elongation of 4.9 ± 0.68%. The SLMed NZ30K Mg alloy with a bimodal-grained structure consisting of fine equiaxed grains and coarser columnar grains has better elongation and a yield drop phenomenon.

In this work, FeCrB-based composites modified by in-situ ceramic particles (TiB2 and TiC) were synthesized, and the effects of ceramic particles on their microstructure evolution and the corrosion-resistant behavior in liquid aluminum were systematically investigated. Results indicate that the introduction of in-situ ceramic particles can significantly improve the size, morphology and distribution of borides, thus leading to a remarkable enhancement of the corrosion resistance. Based on the growth-dissolution kinetic relationship of intermetallic compounds (IMCs) at the corrosion interface, a theoretical numerical model was established to quantitatively describe the corrosion behavior of ferrous alloys in liquid aluminum, and the multi-scale corrosion-resistance mechanism is proposed to elucidate the excellent performance of FeCrB-based composites in liquid aluminum.

Highlights Graphene-like 2D V2O5 nanosheets rich in oxygen vacancies are designed as multi-functional catalysts to fabricate MgH2-H-V2O5 composites. Hydrogen release starts from 185 °C and capacity retention is as high as 99% after 100 cycles at 275 °C. The composites present rapid kinetics and impressive hydrogen absorption capability at near room temperature. The oxygen vacancies could directly enhance kinetics of MgH2 while indirectly exciting “hydrogen pump” effect of VH2/V.

Effect of in-situ nanoparticles (NPs) induced by Ti addition on the microstructure and tribological properties of FeCrB alloys has been investigated systematically by various advanced techniques. The results reveal that the TiC and TiB2 nanoparticles can be in-situ formed when adding Ti into the FeCrB alloys and they show great contribution to the microstructure refinement and tribological performance improvement of FerCrB alloys. With the gradual addition of Ti, the improvement effect of in-situ NPs increases initially and subsequently decreases. The JDF2 alloy (refers to FeCrB alloy containing 1.17 wt % Ti) shows the finest microstructure and the exceptional wear resistance. The average size and fracture toughness of primary borides are only 11.8 % of that in FeCrB matrix alloy (without Ti addition) and increase to 22.7 MPa∙m1/2, respectively. Moreover, the wear rate measures at 3.38 × 10−5 mm3/N·m, which is only 48.8% compared to that of FeCrB matrix alloy. The underlying wear mechanisms of FeCrB alloys have been discussed by unraveling the role of in-situ nanoparticles in the microstructure evolution, which belongs to adhesive wear and abrasive wear.

Molecule hydrogen (H2) has been used to suppress tumor growth. To employ the H2 therapy, it is necessary to use a proper agent for continuous generation of H2. As a biodegradable metal, magnesium (Mg) generates H2 in an aqueous environment, but the H2 release rate is still too low. Here, we design a Mg-Al-Ca (AX) alloy that degrades very rapidly due to the presence of a secondary phase Al2Ca. Having a reduction potential much higher than Mg and any other Mg-based secondary phases, Al2Ca accelerates the corrosion of the Mg matrix by a micro-galvanic process. Al2Ca also enhances the strength and ductility of the AX alloy. AX alloy rods show better anti-tumor efficacy than pure Mg rods in vivo. Moreover, implanted AX alloy rods can be heated under an alternating magnetic field to suppress large-size tumors. This work suggests that the H2 therapy using highly degradable Mg alloys may provide an effective cancer treatment.

High-performance cast magnesium rare-earth (Mg-RE) alloys are one of the most important materials among all developed Mg alloy families, and have shown great potential in military and weapons, aerospace and aviation, orthopedic implants, etc. Controlling grain size and distribution of it is key to the promising mechanical performance of Mg-RE alloy casting components. During the casting of a real component, nearly every procedure in the fabrication process will influence the grain refinement effect. The procedure may include and may not be limited to the chemical inoculations, possibly applied physical fields, the interfere between grain refiner and purifications, and the casting techniques with different processing parameters. This paper reviews the recent advances and proposed future developments in these categories on grain refinement of cast Mg-RE alloys. The review will provide insights for the future design of grain refinement techniques, the choosing of processing parameters, and coping strategies for the failure of coarsening for cast Mg-RE components with high quality and good performance.

Mathematical models were proposed to clarify the effect of alloying on corrosion of magnesium alloys based on film-free and film-covered status. The models are applicable to explain the “barrier effect” by cathodes and the “analogous Hall-Petch relationship” between corrosion rates and grain size. The slope of corrosion rates versus alloying content is determined by the dissolution ability of film-free substrate and the hindering effects by corrosion product film. Designing strategy for corrosion-resistant Mg alloys is established.

Highlights A comprehensive discussion of the recent advances in the nanostructure engineering of Mg-based hydrogen storage materials is presented. The fundamental theories of hydrogen storage in nanostructured Mg-based hydrogen storage materials and their practical applications are reviewed. The challenges and recommendations of current nanostructured hydrogen storage materials are pointed out.

High-strength Mg alloys are often sought-after for automotive and aerospace applications, but they have an inferior corrosion resistance. Here, the authors develop a Mg-11Y-1Al (wt. %) alloy that shows both significantly improved mechanical properties and corrosion resistance.

Abstract Zingiber officinale Roscoe extract, Raphanus sativus L. extract, Rheum palmatum extract, Coptis chinensis extract, Glycyrrhiza uralensis extract (GUE), Potentilla discolor extract (PDE) and Taraxacum officinale extract (TOE) were screened for the green corrosion inhibitors of AZ91 alloy in saline environment. The experiment results demonstrated that GUE, PDE and TOE can significantly enhance the corrosion resistance of AZ91 alloy by 73.4, 87.6 and 84.6%, respectively. Surface characterization using FTIR, UV–Vis and XPS revealed that the organic compounds of GUE, PDE and TOE can interact with the alloy surface to form a protective physisorbed film, effectively mitigating the corrosion process of AZ91 alloy. The present results may be helpful to discover the new green inhibitors with high inhibition efficiency for AZ91 alloy.

The sand castings of Mg–Y–RE–Zr series alloys are widely utilized in the large scales and complex shapes in the aerospace industry, as a result of which there are always some cast defects in the products. In this study, the feasibility of repair welding of sand-cast Mg–4Y–3RE–0.5Zr alloy by tungsten inert gas (TIG) welding was scrutinized with different welding currents from 150 to 210 A. The results indicated that defect-free repaired joints with good appearance could be acquired at 170 and 190 A. Interestingly, the grain size of the fusion zone (FZ) was refined initially and then increased with the linear increment of welding current. Because at the higher heat inputs, although the cooling rate of the molten pool was reduced, substantial constitutional supercooling for the grain refinement was attained after the Zr particles were transformed into Zr solutes. The tensile strength of the repaired joint at 170 A was 195 MPa with the maximum joint efficiency of 87.8%, and the elongation reached to 124.4% of the sand-cast base material (BM). However, serious grain coarsening and continuous eutectic structures generated in heat-affected zone (HAZ) above 190 A resulted in the weakening of the joint due to the brittle intergranular fracture.

Isothermal uniaxial compression experiments were performed in the range of 300–450 °C and 0.001 to 10 s−1 to clarify the hot deformation behavior of homogenized Al–5Mg–3Zn–1Cu alloy. The results revealed that the flow curves exhibited typical characteristics of DRV/DRX accompanied by the work-hardening, and the existence of three distinct stages of work-hardening, transition, and steady-state in each flow curve. A strain-compensated constitutive model for determining flow stress in this alloy was established with highly acceptable predictability. The dominant deformation mechanism of the alloy is dislocation climbing. Also, dynamic-material-model-based processing maps at various strains were constructed, and the unstable and workable domains were distinguished. Instability generally occurred in high strain rates and low temperatures zone with prevalent instability forms such as cracking and flow localization. The workable domain was 375–450 °C and 0.001–0.1 s−1, in which the microstructure of the deformed alloy was characterized by dynamic recovery and multiple types of dynamic recrystallization. The dynamic precipitates were labeled as T-Mg32(AlZnCu)49 phase. These intermittently distributed precipitates along the grain boundaries were stable in all temperature ranges, while the intragranular precipitates were inhibited at 300 °C. Temperature increment to 400 °C led to a large number of dispersed intragranular precipitates which redissolved into the matrix as temperature exceeded 450 °C.

In this study, the tensile and high-cycle fatigue properties of as-cast, solid solution treated and as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy are investigated. The results show that the yield strength and ultimate tensile strength of as-cast alloy is 198.1 MPa and 222.5 MPa, which are improved to 274.7 MPa and 321.7 MPa, 282.4 MPa and 319.3 MPa after solid solution and extrusion treatment, respectively. The high-cycle fatigue strength (at 107 cycles, R = -1) of as-cast studied alloy is 65 MPa, which is improved to 90 MPa and 105 MPa after solid solution and extrusion treatment, respectively. The improvement of fatigue property of the solid solution treated alloy is mainly due to the lattice distortion caused by solid solution hindering the crack propagation. However, the improvement of fatigue property of the as-extruded alloy is mainly due to that the refined grains, stacked dislocations and dispersed secondary particles impede the crack propagation.

Background: /Objective: This study aimed to evaluate the effectiveness and safety of treating medial malleolar fractures using our patented Mg-Nd-Zn-Zr alloy (abbr. JDBM) screws with Ca–P coating, in order to provide a solid basis for their further clinical translation. Methods: Nine patients with medial malleolar fractures were treated using coated JDBM screws. All patients had closed injuries, and none had open fractures. Postoperative radiography was performed to evaluate fracture healing and degradation of the JDBM screws. The visual analogue scale (VAS) was used to evaluate the degree of postoperative pain perceived by the patients, and the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot scoring system was used to evaluate their postoperative ankle function. Postoperative complications, including infection, failure of internal fixation, and malunion, were carefully recorded during follow-up. Results: The mean follow-up time was 12.2 ​± ​4.9 months. After the operation, all patients achieved good medial malleolar fracture alignment, and none of them experienced breakage of the JDBM screws before fracture healing. Postoperative radiography indicated JDBM screws gradually degradated with implantation time, and obvious degradation could be observed 12 months, postoperatively. At the final follow-up, the patients’ mean VAS score was 2.3 ​± ​1.9. The mean AOFAS score was 90.4 ​± ​8.9, with excellent or good rates of 88.9%. None of the patients experienced infection, failure of internal fixation, malunion, or other complications. Conclusion: Coated biodegradable JDBM screws are effective for the treatment of medial malleolar fractures, and have good prospects for further clinical translation in the future. Translational potential statement: The results of this study indicates coated biodegradable JDBM screw is an alternative internal fixation instrument for fracture treatment and has excellent prospects for clinical translation.

During the past decades, with the increasing demands in lightweight structural materials, Mg alloys with low density and high performance have been extensively investigated and partly applied in some industries. Especially when rare earth (RE) elements are added as major alloying elements to Mg alloys, the alloy strength and creep resistance are greatly improved, which have promoted several series of Mg-RE alloys. This paper reviews the progress and developments of high-performance Mg-RE alloys in recent years with emphasis on cast alloys. The main contents include the alloy design, melt purification, grain refinement, castability, novel liquid casting and semisolid forming approaches, and the industrial applications or trials made of Mg-RE alloys. The review will provide insights for future developments of new alloys, techniques and applications of Mg alloys.

Abstract The time‐consuming and laborious heat treatment is indispensable for preparing seed layer in solvothermal synthesis of WO3 film. Herein, WO3 film is prepared composed of single crystal WO3 nanowires on indium tin oxide (ITO) glass assisted with simple and energy‐saving electrodeposited seed layer for the first time. The catalyst Pt is sputtered on it for 30 s after WO3 film is synthesized to form the hydrogen gasochromic film. The film structure is redesigned to improve its hydrogen gasochromic properties further. Before WO3 film is solvothermally synthesized, Pt is sputtered on seed layer for 15 s, then it is sputtered for 15 s again after WO3 film is prepared. The Pt sputtered on seed layer greatly changes the morphology of nanowires, making them sparse, slender, and cross‐linked like a bird's nest. Moderate 37% HCl is added during the solvothermal process to promote the growth of WO3 nanowires. The variation of transmittance (wavelength: 1000 nm), coloring rate (4% H2/Ar) and bleaching rate (air) of WO3 hydrogen gasochromic film with new structure at room temperature are 69.1%, 3.1%/s (increases 19.6%) and 0.85%/s (increases 193%), respectively. This study offers a new strategy for seed layer technology of WO3 film and structural design of WO3 hydrogen gasochromic film.

Due to their capability of fabricating geometrically complex structures, additive manufacturing (AM) techniques have provided unprecedented opportunities to produce biodegradable metallic implants—especially using Mg alloys, which exhibit appropriate mechanical properties and outstanding biocompatibility. However, many challenges hinder the fabrication of AM-processed biodegradable Mg-based implants, such as the difficulty of Mg powder preparation, powder splash, and crack formation during the AM process. In the present work, the challenges of AM-processed Mg components are analyzed and solutions to these challenges are proposed. A novel Mg-based alloy (Mg–Nd–Zn–Zr alloy, JDBM) powder with a smooth surface and good roundness was first synthesized successfully, and the AM parameters for Mg-based alloys were optimized. Based on the optimized parameters, porous JDBM scaffolds with three different architectures (biomimetic, diamond, and gyroid) were then fabricated by selective laser melting (SLM), and their mechanical properties and degradation behavior were evaluated. Finally, the gyroid scaffolds with the best performance were selected for dicalcium phosphate dihydrate (DCPD) coating treatment, which greatly suppressed the degradation rate and increased the cytocompatibility, indicating a promising prospect for clinical application as bone tissue engineering scaffolds.

This work studied the interface morphology, microstructure behavior, and mechanical properties of the fabricated trilayered Cu/Al8011/Al1060 composite. In this regard, the roll-casted Cu/Al8011 bimetal was subjected to the hot-roll-bonding process with Al1060 at a thickness reduction of 47%. As a result, the hot-roll-bonding broke the produced nonuniform continuous interface within the copper and aluminum during the roll-casting process. The corresponding interface from the copper side includes Al4Cu9, AlCu, and Al2Cu, respectively. Additionally, SEM-based in-situ tensile deformation revealed that the initiated cracks at the Cu/Al8011 interface propagated into the copper layer that led to its fracture before the aluminum. Based on the FEM results, the effective stress distribution of the Cu strip is not homogeneous at the deformation zone. Moreover, the thickness reduction of the Cu and Al layers was respectively lower and slightly higher than that of the trilayered composite, indicating that plastic deformation mainly occurred at the aluminum matrix due to its large plasticity amount.

Few studies were reported on the phases’ relationships of AE44 (Mg-4.0Al-4.1RE-0.3Mn, wt.%) and its composites. In this work, AE44 alloy and Saffil (δ-Al2O3)/AE44 Metal matrix composite (MMC) were both prepared by slow shot high pressure die casting (SS-HPDC) technology and their phase constitutions were all studied in detail using experimental techniques combined with CALPHAD (Calculation of Phase Diagram) modeling. The results revealed that the alloy consists of the α-Mg matrix, Al11RE3 intermetallic phase, and one trace phase Al3RE, while the composite contains five major phases: α-Mg, δ-Al2O3, Al3RE, MgO and Mg2Si, and two trace phases of Al2RE and Al11RE3, respectively. Al11RE3 is partly derived from Al2RE, while Al3RE is a product of the peritectoid reaction between the two precipitates. The presence of MgO and Mg2Si is due to the interfacial reaction between the SiO2 binder in the fiber preforms and the molten magnesium during infiltration. The use of SiO2 binder in the preform manufacturing was limited/minimized to reduce the MgO formation in the MMC casting process, which can be detrimental to the fatigue performance of the MMC materials.

The influence of trace As content (0.04, 0.05, 0.06 wt%) on the microstructure and corrosion behavior of AZ91 alloy in different metallurgical conditions (as-cast, as-quenched, peak-aged) was firstly investigated. It is found that the corrosion resistance of AZ91 alloy in all conditions is significantly enhanced by As addition, mainly due to cathodic toxication, melt purification and incidence reduction of local corrosion. As alloying leads to the formation of Mg3As2 and makes the β-Mg17Al12 phase less continuous in the as-cast alloys. The alloy containing 0.06 wt% As obtains a higher corrosion rate than those of the alloy containing 0.05 wt% As owing to a more discontinuity of β phase. The β phase is dissolved into the matrix in the as-quenched alloys and reprecipitates along the grain boundaries after aging. The more continuous β phase distribution in the peak-aged alloys contributes to corrosion resistance. The corrosion rates are in the order of as-quenched>as-cast>peak-aged. The lowest corrosion rate (0.67 mm/y) in 3.5 wt% NaCl solution is obtained in the peak-aged AZ91-0.05As alloy, which is over 70% lower than that of as-cast AZ91 alloy (2.22 mm/y). Keywords: Magnesium alloy, AZ91, Microstructure, Corrosion behavior

In the application of WE43, it is found that Y2O3 inclusion formed in the process of casting seriously reduced the mechanical properties of the products. The reduction of the mechanical properties is even more distinct when it comes to the application in the thin walled complex-precision castings. In order to decrease the Y2O3 inclusions, Gd element was used to replace part of the Y element in Mg-Y-RE series alloys. The effect of Y content (Mg-xY-1Gd-2Nd-0.5Zn-0.5Zr) and Y/Gd ratio (Mg-xY-(5-x)Gd-2Nd-0.5Zn-0.5Zr) on the microstructure and mechanical properties of Mg–Y–RE alloys were investigated in this paper. With decreasing Y content, the grain size of the alloys increased, both ultimate tensile strength (UTS) and yield strength (YS) of alloys decreased monotonically. Replacing part of Y content with Gd and keeping the total rare earth content unchanged, the low Y content Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy showed the same mechanical properties as the high Y content Mg-4Y-1Gd-2Nd-0.5Zn-0.5Zr alloy at both room and elevated temperatures. After solution treatment at 525 °C for 8 h and aging treatment at 225 °C for 10 h, the UTS, YS and elongation (ε) of Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy reached 281.7 MPa, 198 MPa and 11.1% at room temperature, and 216.7 MPa, 171.6 MPa and 16.1% at 250 °C. The new low Y content Mg-2Y-2Nd-3Gd-0.5Zn-0.5Zr alloy is expected to replace the high Y content WE43 alloys, which can be used in the complex thin-walled parts of aviation products. Keywords: Mg–Y–RE alloy, Microstructure, Mechanical property, Y/Gd ratio, Heat treatment

The effects of different Zn addition (0, 0.2, 0.5, 1.0 wt%) on the microstructure and mechanical properties of cast Mg–1Nd–1Ce–Zr alloy in as-cast, solution-treated and 200 °C peak-aged conditions were studied. Precipitates in cast Mg–1Nd–1Ce–Zr alloy are significantly modified by the Zn addition. In the Zn-free alloy, the disk-shaped prismatic precipitates and the point-like precipitates are the main strengthening phases. When 0.2 Zn is added, the disk-shaped precipitates are refined and very fine basal precipitates form additionally. When 0.5 Zn is added, the basal precipitates become the main strengthening phase. Further increasing the Zn addition to 1.0%, only spare basal precipitates and point-like precipitates exist. The 0.5 Zn addition alloy has the highest strength at room temperature, whose yield strength, ultimate tensile strength and elongation in T6 condition are 136 MPa, 237 MPa and 9%, respectively. Keywords: Mg alloy, Precipitate, Rare earth, Zn addition, Mechanical properties, Mg wheel

Magnesium hydride (MgH2) is a promising solid-state hydrogen source with high storage capacity (7.6 wt%). Although it is recently established that MgH2 has potential applications in medicine because it sustainably supplies hydrogen gas (H2), the biological functions of MgH2 in plants have not been observed yet. Also, the slow reaction kinetics restricts its practical applications. In this report, MgH2 (98% purity; 0.5–25 μm size) was firstly used as a hydrogen generation source for postharvest preservation of flowers. Compared with the direct hydrolysis of MgH2 in water, the efficiency of hydrogen production from MgH2 hydrolysis could be greatly improved when the citrate buffer solution is introduced. These results were further confirmed in the flower vase experiment by showing higher efficiency in increasing the production and the residence time of H2 in solution, compared with hydrogen-rich water. Mimicking the response of hydrogen-rich water and sodium hydrosulfide (a hydrogen sulfide donor), subsequent experiments discovered that MgH2-citrate buffer solution not only stimulated hydrogen sulfide (H2S) synthesis but also significantly prolonged the vase life of cut carnation flowers. Meanwhile, redox homeostasis was reestablished, and the increased transcripts of representative senescence-associated genes, including DcbGal and DcGST1, were partly abolished. By contrast, the discussed responses were obviously blocked by the inhibition of endogenous H2S with hypotaurine, an H2S scavenger. These results clearly revealed that MgH2-supplying H2 could prolong the vase life of cut carnation flowers via H2S signaling, and our results, therefore, open a new window for the possible application of hydrogen-releasing materials in agriculture.

Nanoscale precipitations in deformed dilute alloying Mg-Zn-RE alloys usually play critical positive roles in mechanical properties, while characterizing them still poses a significant challenge due to their small size and low volume fraction. Here, we conduct a systematic structural analysis of the nanoscale secondary phase particles, including W phase, a small amount of I phase and a handful of Mg3Gd phase, in hot deformed dilute alloying Mg-Zn-Gd alloy by combining atomic-resolution transmission electron microscopy with first-principles calculations. The investigation of atomic structure of nanoscale W phase reveals that the stoichiometric composition of W phase is determined by the quantity of Mg atoms which are replaced by Zn at certain positions. Furthermore, nanoscale W phase, I phase and Mg3Gd phase particles could exhibit certain orientation relationships and coherent or semi-coherent interface with Mg matrix, which contributes to atomic bonding at their interfaces. We also identify a phase transition from Mg3Gd phase to W phase, which is further supported by first-principles calculations showing that Mg3Zn3Gd2 phase is energetically more favorable than Mg3Gd phase. The phase transition between W phase and I phase could also take place during hot deformation and is reversible by absorbing or releasing Zn atoms at the interfacial region.

Significant grain refinement of AZ91 alloys was achieved by ceramic nanoparticle(NP)-induced growth control. Advanced characterization techniques including 3D tomography and in-situ observation were carried out to examine the microstructure evolution. The results show that the NPs are distributed in matrix in three ways, i.e. along the grain boundaries, inside the α-Mg grains and within the interior of β phases. The intergranular NPs that are distributed along the grain boundaries can form a multilayer of NPs covering the surface of α-Mg, greatly restricting the grain growth. A numerical model is proposed to predict the grain size, in which the solute concentration gradient at dendrite tip and the impingement of grains are recognized as two pivotal factors in modelling. It is demonstrated from the model prediction that a reduced growing rate of α-Mg can be obtained upon NP addition due to the lowered solute concentration gradient at dendrite tip, which could increase the nucleation events, accelerate the grain impingement and thus induce significant grain refinement. Given the chemically and thermally stability of ceramic NPs, which can avoid the intrinsic drawbacks of conventional inoculation, e.g. element poisoning, NP-induced growth control (NIGC) may provide a new avenue for grain refinement in magnesium alloys.

A reflection upon the recent developments of semisolid rheoforming techniques of magnesium (Mg) alloys is vital for successfully shaping the future landscape of lightweight and high-performance metal materials. In our paper, formation mechanisms of non-dendritic structure were firstly reviewed, and slurry preparation methods as well as rheoforming processes of Mg alloys were then summarized. Afterwards, microstructures and mechanical properties of semisolid Mg alloys were elaborated. The various formation mechanisms of non-dendritic structures provide theoretical bases for understanding the microstructure evolution of semisolid metal slurries. Despite the abundant slurry preparation methods to date, inexpensive industrial solutions for producing high-quality Mg alloy slurries are still scarce, which is constituting one of many key challenges in the future. In the case of rheoforming processes, high pressure die casting (HPDC) and squeeze casting are the most promising processes for mass production of semisolid Mg alloys. At present, researches on semisolid Mg alloys are mainly focused on AZ and AM series alloys. To develop high-performance semisolid Mg alloys, the slurry preparation and rheoforming technology of Mg-RE alloys are worthy of further investigation.

Inspired by the process of bone reconstruction, porous scaffolds with robust osteogenesis and biodegradability would provide an ideal bone substitute for clinical practice. In this study, a novel porous Mg–Nd–Zn–Zr (JDBM) alloy scaffold coated with brushite (i.e., DCPD), denoted as JDBM-DCPD, is fabricated using a special patent template technique, which forms the main spherical pores (400–450 μm) and smaller pores (150–250 μm) interconnected between the adjacent main pores, facilitating nutrient penetration and cell in-growth, exhibiting sufficient mechanical properties. In vitro results demonstrate that JDBM-DCPD scaffolds promote cell in-growth and osteogenic differentiation, which significantly enhance mineralization, osteogenesis and angiogenesis-related genes expression when cultured with bone marrow mesenchymal stem cells. After implanting in vivo, JDBM-DCPD scaffolds effectively stimulate angiogenesis, osteogenesis, and remodeling with the degradation of JDBM-DCPD, and perfectly repair large bone defect in rat and rabbit models. Results from the present study provide the solid evidence that porous biodegradable Mg-based scaffolds whose pore structure can be precisely regulated by a spacer-selection technique may be a promising tissue engineering scaffolds for large bone defect repair clinically, free from any extra growth factors and live cells, such advances will make scaffold-based bone tissue repair safer, more convenient and more cost-effective. Keywords: Biodegradable Mg–Nd–Zn–Zr alloy scaffold, DCPD coating, Osteogenesis, Angiogenesis, Bone tissue engineering

We prepare a new type of patented biodegradable biomedical Mg–Nd–Zn–Zr (JDBM) alloy system and impose double continuously extrusion (DCE) processing. The lowest processing temperature is 250 °C for JDBM-2.1Nd and 310 °C for JDBM-2.8Nd, which increases with the Nd concentration. The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250 °C and the elongation is about 3.7%. Moreover, the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing. However, when extruded under the same conditions, the alloy with a higher alloying contents exhibits better tensile properties. Keywords: Magnesium alloys, Microstructure, Mechanical properties, Double continuously extrusion

A method of forming an Mg/Al intermetallic compound coating enriched with Mg17Al12 and Mg2Al3 was developed by heat treatment of electrodeposition Al coatings on Mg alloy at 350 °C. The composition of the Mg/Al intermetallic compounds could be tuned by changing the thickness of the Zn immersion layer. The morphology and composition of the Mg/Al intermetallic compound coatings were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). Nanomechanical properties were investigated via nano-hardness (nHV) and the elastic modulus (EIT), and the corrosion behavior was studied through hydrogen evolution and potentiodynamic (PD) polarization. The compact and uniform Al coating was electrodeposited on the Zn-immersed AZ91D substrate. After heat treatment, Mg2Al3 and Mg17Al12 phases formed, and as the thickness of the Zn layer increased from 0.2 to 1.8 μm, the ratio of Mg2Al3 and Mg17Al12 varied from 1:1 to 4:1. The nano-hardness increased to 2.4 ± 0.5 GPa and further improved to 3.5 ± 0.1 GPa. The Mg/Al intermetallic compound coating exhibited excellent corrosion resistance and had a prominent effect on the protection of the Mg alloy matrix. The control over the ratio of intermetallic compounds by varying the thickness of the Zn immersion layer can be an effective approach to achieve the optimal comprehensive performance. As the Zn immersion time was 4 min, the obtained intermetallic compounds had relatively excellent comprehensive properties.

The Al coatings achieved via electrodeposition on a Cu electrode from AlCl3-NaCl-KCl (80–10–10 wt.%) molten salts electrolyte with Tetramethylammonium Chloride (TMACl) and Sodium Iodide (NaI) additives is reported. The effect of the two additives on electrodeposition were investigated by cyclic voltammetry (CV), chronopotentiometry (CP), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results reveal that compact and smooth Al coatings are obtained at 150 °C by the electrodeposition process from the electrolyte with 1% TMACl and 10% NaI. The Al coatings exhibit great corrosion resistance close to that of pure Al plate, with a corrosion current of 3.625 μA. The average particle size is approximately 2 ± 1 μm and the average thickness of the Al layer is approximately 7 ± 2 μm. The nucleation/growth process exhibits irrelevance with TMACl or NaI during the electrodeposition of Al. TMACl cannot affect and improve the electrodeposition effectively. However, the addition of TMACl and NaI can intensify the cathodic polarization, producing an inhibition of Al deposition, and contribute to form uniform Al deposits. This can increase the conductivity and facilitate in refining the size of Al particles, contributing to forming a continuous, dense and uniform layer of Al coating, which can be used as effective additives in molten salts electrolyte.

Previous studies have proved that the zirconium (Zr) alloying and grain refining performance of a Mg–Zr master alloy on Mg alloy is closely related to the distribution of Zr particle size, and a Mg–Zr master alloy with more Zr particles in size range of 1–5 μm exhibits a better refining efficiency. In this paper, friction stir processing (FSP) was used to modify the Zr particles size distribution of a commercially available Mg–30 wt.%Zr master alloy, and the subsequent grain refinement ability was studied by trials on a typical Mg–3Nd–0.2Zn–0.6Zr (wt.%, NZ30K) alloy. It is found that plenty of large Zr particles in the as-received Mg–30%Zr master alloy are broken by FSP. Grain refinement tests reveal that the refining efficiency of Mg–30%Zr alloy is significantly improved by FSP, which is attributed to the better distribution of Zr particles. The refinement effect by adding 0.6% FSP-ed Mg–30%Zr is approximately equivalent to that by adding 1.0% as-received Mg–30%Zr. Due to the easy and convenient operation of FSP, this study provides a new method to develop a more efficient Mg–Zr refiner.

The microstructure and mechanical properties of cast Mg–9Al–2Sn–xMn (x = 0, 0.1, 0.3 wt.%) alloys in as-cast, solution treated and aged conditions are investigated. The results reveal that Mn addition into Mg–9Al–2Sn alloy leads to the formation of Al8(Mn,Fe)5 phases, the grain refinement and the increase of discontinuous Mg17Al12 precipitates along the grain boundaries. 0.1 wt.% Mn addition has an obvious effect on accelerating the aging behavior of Mg–9Al–2Sn alloy at the early aging period up to 8 h, while 0.3 wt.% Mn addition alloy has an comparable aging behavior with the Mn-free alloy. Mn addition has less influence on the fracture behavior of Mg–9Al–2Sn alloy, while the fracture pattern is mainly determined by the thermal conditions. Mg–9Al–2Sn–0.1Mn alloy has the best combination of strength and elongation when aged at 200 °C for 8 h and the yield strength, ultimate tensile strength and elongation are 154 MPa, 292MPa and 5%, respectively.

The effect of various Sn contents (1⁻2 wt. %) on the microstructure, age hardening response, and tensile and casting properties of the high-pressure die cast Mg-6Zn-4Al alloy were studied. All as-cast alloys consisted of α-Mg and icosahedral quasi-crystalline phase; and the addition of 2% Sn caused the formation of Mg2Sn phases. Dendrite structure and eutectic phases were observably refined by Sn addition. The hot tearing susceptibility of the die cast Mg-6Zn-4Al alloy prominently decreased with increasing Sn addition. During T6 heat treatment, Sn addition did not obviously affect the time to reach peak hardness, but significantly enhanced the age hardening response and improved the strength of alloys under peak-aged conditions. Compared to single aging, double aging resulted in the higher density of finer β1′ and β2′ precipitates. The double aged Mg-6Zn-4Al-1Sn alloy offered the optimum tensile properties among all conditions. The yield strength, ultimate tensile strength, and elongation were 209 MPa, 305 MPa, and 4.3%, respectively.

The microstructure, high-temperature tensile properties and fracture behavior of the Mg-10Gd-5Y-0.5Zr alloy after thermo-mechanical processing (pre-tension between solution and aging treatment) were investigated. The pre-deformed alloy shows the accelerated aging kinetics compared to the un-deformed alloy. Microstructure of pre-deformed samples showed not only the homogeneous nucleation of the precipitate but also heterogeneous nucleation of precipitates on the dislocation and twin boundaries. Tensile results show that the pre-deformation enhanced the strength of the alloy, while it deteriorates the ductility of the alloy. The ultimate tensile strength (UTS) of the T6 treated un-deformed and pre-deformed alloy at room temperature are 331 MPa and 366 MPa, respectively. Tensile strength of the T6 treated alloy in both un-deformed and deformed conditions was enhanced by raising the test temperature and then reduced by further raising the test temperature. The higher strength of the pre-deformed alloy could be related to the higher density of the precipitates, which grow on the twin boundaries and can hinder the dislocation movement and strengthen the alloy. The results shows that thermo-mechanical processing can significantly improve the room- and high-temperature mechanical properties and enhance the formation of precipitates in Mg-10Gd-5Y-0.5Zr alloy, which can lead to wider application of the alloy in industries such as aerospace or powertrains that need better room- and high-temperature mechanical properties.