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In recent years, more attention to unique and complex structures, such as nature-inspired and porous structures for medical applications, has been strongly developed. Open-cell porous metal-based ones display more benefits than rigid ones since they facilitate the transformation of load between the bone and the implants and avoid the phenomenon of stress shielding and bone resorption. By being biodegradable and non-toxic, as well as having lower density and mechanical properties close to those of natural bone, Mg and its alloys are considered promising materials for porous scaffolds. However, a high corrosion rate is the main drawback of Mg alloys. The porosity of porous structures can also worsen it as it enhances the surface area exposed to the corrosive solution and negatively impacts the performance of porous structures, that these issues have not been addressed in detail so far. Since fabrication methods of Mg-based scaffolds can significantly affect the porosity-related properties (e.g., porosity percentage, type, size, and geometry) and, consequently, scaffolds' mechanical behavior and corrosion resistance, this paper reviews and compares the fabrication methods of porous structures and how they affect the resultant properties. However, among different methods, due to the expansion of additive manufacturing as a novel and exciting manufacturing technique, the paper's central focus is on using additive manufacturing in biomedical applications, discussing its advantages over other techniques. The effect of geometrical parameters on mechanical properties and corrosion rate, which strongly affects bio-application, are also given. Moreover, different strategies are briefly introduced for tailoring the high corrosion rate of Mg and its alloys, such as alloying elements and coatings. However, there is still less information regarding the additive manufacturing of porous Mg scaffolds and the optimum way of controlling the corrosion rate of Mg-based parts. [ABSTRACT FROM AUTHOR]

AA6101 Al alloy is widely used as a high-strength conductive aluminum alloy, and the contents and existence of Mg and Si can influence its electrical conductivity and mechanical properties obviously. In this paper, experiments were conducted to find the optimal Mg, Si additions and Mg/Si ratio and then combined with heat treatment to improve the EC and mechanical properties at the same time. Firstly, considering the proper Mg/Si ratio, two optimal Mg and Si additions were determined: Al–0.7Mg–0.5Si and Al–0.4Mg–0.7Si with EC of 51.5%IACS and 51.4%IACS, and through homogenization treatment, their EC improved to 57.0%IACS and 55.7%IACS, respectively. Then, appropriate Fe was added to further control Si to achieve the balance of EC and mechanical properties. Results showed that for AA6101 Al alloy the ideal Mg/Si mass ratio was 1.4 and high Mg and low Si can obtain good EC and mechanical properties. Besides, it can be found that at low Mg/Si ratio, the alloy conductivity takes longer to reach its peak hardness. So the best performance Al–0.7Mg–0.5Si–0.2Fe alloy was obtained within the range of AA6101 national standard. The EC of Al–0.7Mg–0.5Si–0.2Fe can reach 56.3%IACS, and hardness is 91.3 Hv. Based on the study, a schematic diagram was drawn to analyze the influence mechanisms of Mg, Si and Fe on EC and hardness of AA6101 Al alloy. [ABSTRACT FROM AUTHOR]

The microstructure, compressive properties and in vitro degradation behavior of as-cast Mg alloys with high Zn or Ca content were investigated. The results showed that the addition of Ca (1 wt%) to Mg–5Zn or Zn (1 wt%) to Mg–5Ca changed the shape, distribution, volume fraction and the type of second phase. When 1 wt% Ca was added to Mg–5Zn alloy, the second phase changed from Mg7Zn3 to Ca2Mg6Zn3 phase and it was distributed from granular formation to a continuous network structure. While the second phase was changed from Mg2Ca in Mg–5Ca alloy to the coexistence of Mg2Ca(Zn) and slight Ca2Mg6Zn3 phase in Mg–5Ca–1Zn alloy. The second phase exhibited a continuous network distribution in both of Mg–5Ca and Mg–5Ca–1Zn alloys, but the width of Mg2Ca(Zn) phase was reduced obviously after adding 1 wt% Zn to Mg–5Ca alloy. The compressive test revealed that Zn element was contributed to the promotion of ultimate compressive strength and fracture elongation, while Ca element was beneficial for improving the yield strength of Mg alloys. The immersion test proved that the weight loss of Mg–5Zn–1Ca was the highest, followed by Mg–5Zn, Mg–5Ca and Mg–5Ca–1Zn alloy. The Mg–5Zn-based alloys suffered severe pitting, while Mg–5Ca-based alloy exhibited a relatively uniform corrosion. The Ca addition accelerated the corrosion of Mg–5Zn alloy due to the expansion of potential difference between second phase and Mg matrix, while Zn addition reduced the micro-galvanic corrosion of Mg–5Ca alloy due to the lowest potential difference between Mg2Ca(Zn) phase and Mg matrix. [ABSTRACT FROM AUTHOR]

Introducing of thermodynamically stable strengthening phases is an important means enhancing the properties of magnesium alloys. To introduce a stable Al2Nd strengthening phase, the Mg-Al-Nd alloys were prepared with a fixed atomic ratio of 2:1 for Al and Nd. The total content of Al and Nd was varied at 1%, 3%, 5%, and 7%, respectively. The effects of Al2Nd phase on the microstructure and mechanical properties of the Mg-Al-Nd alloys were systematically studied in this work. The experimental results indicated that the as-cast alloy primarily consisted of the acicular Al11Nd3 phase as a secondary phase. After undergoing a homogenization treatment at 500 °C for 12 h, the secondary phase underwent a transformation, resulting in the formation of short rod shape Al2Nd structures. Simultaneously, layered Al2Nd precipitated within the α-Mg matrix. The formation of twinning was inhibited, while the Al2Nd phase promoted recrystallization and refined the microstructure through the mechanism of particles stimulated nucleation (PSN), as the Al and Nd contents increased during thermal deformation. At the same time, the increases of Al2Nd phase can enhance the strength and the plasticity of the alloy. The mechanical properties of extruded Mg-1.36Al-3.64Nd (AE5) alloy were excellent with yield strength of 175 MPa, ultimate tensile strength of 249 MPa, and the elongation of 15.4%. The enhanced performance can be primarily attributed to the refined microstructure and the presence of Al2Nd precipitates with small size, which contributed to effective fine grain strengthening and secondary phase strengthening. [ABSTRACT FROM AUTHOR]

Data-driven methodology has become a key tool in computationally predicting material properties. Currently, these techniques are priced high due to computational requirements for generating sufficient training data for high-precision machine learning models. In this study, we present a support vector regression (SVR)-based machine learning model to predict the stability of silicon (Si)–alkaline metal alloys, with a strong emphasis on the transferability of the model to new silicon alloys with different electronic configurations and structures. We elaborate on the role of the structural descriptor in imparting transferability to the model that is trained on limited data (~ 750 Si alloys) derived from the Material Project database. Three popular descriptors, namely X-ray diffraction (XRD), sine coulomb matrix (SCM), and orbital field matrix (OFM), are evaluated for representing Si alloys. The material structures are represented by descriptors in the SVR model, coupled with hyperparameter tuning techniques like Grid Search CV and Bayesian optimization, to find the best performing model for predicting total energy, formation energy and packing fraction of the Si alloy systems. The models are trained on Si alloys with lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and aluminum (Al) metals, where Si–Na and Si–Al systems are used as test structures. Our results show that XRD, an experimentally derived characterization of structures, performs most reliably as a descriptor for total energy prediction of new Si alloys. The study demonstrates that by qualitatively selection of training data, using hyperparameter tuning methods, and employing appropriate structural descriptors, the data requirements for robust and accurate ML models can be reduced. [ABSTRACT FROM AUTHOR]

The effects of pre-twinning on the microstructure and dynamic compression properties of non-aged and artificially aged Mg–Y–Nd–Gd–Zr alloys were investigated in this study. Previous studies have shown that in the pre-deformed T3 alloy, precompression along the extrusion direction (ED) generates high-density < a > and < c + a > dislocations and deformation twins, such as the 10 1 ¯ 2 < 10 1 ¯ 1 ¯ > extension, the 10 1 ¯ 1 - 10 1 ¯ 2 double, and 10 1 ¯ 1 < 10 1 ¯ 2 ¯ > compression twins at 86°, 38°, and 56°, respectively. In the pre-deformed T8 alloy artificially aged at 200 °C for 12 h, the dislocation density was found to decrease, with β″ (Mg3Y0.85Nd0.15) and β′ (Mg12NdY) precipitates appearing at both ends of the twin boundary. Subsequently, the precipitates extended toward [0001]Mg and [0001]T in the matrix region and the twin, respectively. The orientation relationships (ORs) between the β″ and β′ precipitates and the matrix/twin were determined to be 01 1 ¯ 0 β ″ / / 0001 Mg / T , 2 1 ¯ 1 ¯ 0 β ″ / / 2 1 ¯ 1 ¯ 0 Mg / T and (001)β′//(0001)Mg/T, 2 1 ¯ 1 ¯ 0 β ′ / / 2 1 ¯ 1 ¯ 0 Mg / T , respectively, in contrast to the counterpart ORs between the β″ and β′ precipitates and the matrix/twin in the non-deformed T61 alloy. Evaluation of the dynamic compression properties showed that compared with the compressive yield strength (CYS) of the T61 alloy, that of the T8 alloy considerably increased from 220 to 339 MPa. However, their ultimate compressive strengths (UCSs) of 363 and 360 MPa, respectively, were similar owing to the synergistic effect between the dislocations, the twin boundaries, and the precipitates. These results suggest that the pre-twinning approach should be adopted to improve the strengths of magnesium alloys. [ABSTRACT FROM AUTHOR]

The present study aims to collect data, compare results and assess techniques used for improving corrosion resistance and mechanical properties of biodegradable Mg alloys for fixation elements and orthopedic applications. A general description of biomaterials used for orthopedic implants is performed, including non-bioabsorbable materials. Different methods for reducing the corrosion rate in Mg alloys are researched, and the efficiencies are assessed. After evaluating different techniques, surface modification is found to be the most promising technique to reduce the corrosion rate with an efficiency of 85%. Regarding the Mg alloying agents, Zn is considered as the best candidate to improve the corrosion response and biocompatibility of the Mg. [ABSTRACT FROM AUTHOR]

In order to obtain compact epoxy-based organic coatings with superior corrosion resistance and self-healing performance, a novel Ti3C2Tx/LDH-epoxy hybrid coating was prepared on AZ31 magnesium alloy in this work. The layered double hydroxide (LDH) adopted here is MgAl-LDH intercalated by the cysteine acid (Cys), an environmentally friendly organic acid anions, as corrosion inhibitors, and the MXene (Ti3C2Tx)/MgAl-LDH (TML) heterostructure nanosheets were grown by a facile in situ assembled method. The morphology, composition, structure and the corrosion protection of the Ti3C2Tx/MgAl-LDH-epoxy (EP-TML) composite coatings were systematically investigated and compared with the other three epoxy-based coatings: bare waterborne epoxy resin (EP), Ti3C2Tx pigmented in EP (EP-T), MgAl-LDH in EP (EP-ML). It is found that the TML heterostructure has good dispersion and compatibility with the epoxy resin. The corrosion current density and the impedance value at low frequency (|Z|0.01 Hz) of the EP-TML composite coating are 1.4 × 10–9 A/cm2 and 1.66 × 107 Ω cm2, which is 4 orders of magnitude lower than that of the uncoated Mg substrate and 1–2 orders of magnitude higher than that of EP (8.7 × 105 Ω cm2), respectively, indicating its excellent corrosion resistance. And the self-healing efficiency of EP-TML composite coating is found to be higher as 56.17% after 6 days immersion in a corrosive environment. The significant improvement of the anti-corrosion and self-healing performance of the EP-TML composite coating are mainly ascribed to the synergistic effect of "barrier effect" of TML and the corrosion inhibition effect of the cysteine acid encapsulated in MgAl-LDH. This work provides some valuable insights to widen the functional application of Ti3C2Tx and the design of highly corrosion-resistant and self-healing organic coatings for Mg alloys. [ABSTRACT FROM AUTHOR]

Mg–8.7Gd–4.18Y–0.42Zr magnesium alloys are subjected to hot compressive tests at a strain rate of 0.002–2 s−1 and a compression temperature of 300–450 °C. Compared with strain rate, compression temperature appears to have a greater impact on dynamic precipitation. By virtue of the pinning effect, precipitates located immediately adjacent to the dynamic recrystallized (DRX) grain boundaries may greatly affect grain growth. As the compression temperature increases, DRX grains multiply rapidly. Nevertheless, the number of DRX grains is decreased owing to the increase in strain rate. However, further increasing the strain rate to 2 s−1, the increased energy stored generates stronger driving forces, causing dislocations to move, thereby raising the number of DRX grains by a considerable amount. With an increase in compression temperature and a decrease in strain rate, substructure development has been described as high-density dislocation → VLAGBs (sub-GBs) → LAGBs → HAGBs → DRX grains. It is DRX that is responsible for the predominant softening mechanism in this studied alloy, accompanied by a continuous dynamic recrystallization (CDRX) process characterized by transforming low-angle grain boundaries into high-angle grain boundaries, as well as discontinuous dynamic recrystallization (DDRX), which is characterized by bulging grain boundaries. [ABSTRACT FROM AUTHOR]

Potential industrial applications of high-performance cast Al−Li−Cu−(Mg) alloys micro-alloyed with Sc have been strongly limited due to the extremely high production cost and scarcity of Sc. This work aimed at evaluating the effect of substituting Yb for Sc on the microstructure characteristics, age-hardening response and mechanical performances of cast Al−2Li−2Cu−0.5 Mg−0.2Zr alloy. Varied Yb additions were tried (0%, 0.1wt%, 0.2wt%) and results indicated that no appreciable grain refinement was achieved in alloys modified with Yb, accompanied with the absence of coarse primary phases. Dissolution of Cu-rich secondary phases during solution treatment was markedly retarded as the Yb addition increased to 0.2wt%. Nucleation of Al3Li on Al3(Yb, Zr) led to the significant reduction in the strain energy change (ΔGS) and interfacial energy. The addition of 0.1wt% Yb resulted in the accelerated age-hardening response and promoted precipitation of L12-structured nanometric core–shell Al3Li/Al3(Yb, Zr) precipitates, which acted as preferential nucleation sites for T1 and S′ phases. As a result, a better mechanical characteristics and microstructural stability was obtained in alloy with 0.1Yb addition compared with the base alloy. Moreover, as compared to the Sc-modified alloy, a small reduction in mechanical properties was achieved in 0.1Yb alloy accompanied with significant reduction in production cost, revealing the feasibility of substituting Yb for Sc. [ABSTRACT FROM AUTHOR]

The microstructure, corrosion behavior and corrosive film formation of as-extruded Mg–2Zn–0.4Mn–0.1Sr–xGd alloys (x = 0, 0.5, 1 and 2 wt%) in Hank's solution were studied. Microstructure was investigated by scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM), X-ray photoelectron spectroscopy (XPS). Corrosion behavior was evaluated by immersion and electrochemical tests. The microstructural observations indicated that the addition of 0.5–2 wt% Gd led to the formation of Mg3Zn3Gd2 phase and grain refinement. SKPFM results showed that the Gd-rich (Mg3Zn3Gd2) phase was nobler than the α-Mg matrix in Gd-containing alloys and formed micro-galvanic corrosion. The alloy with 0.5–1 wt% Gd addition had better corrosion resistance and displayed uniform corrosion behavior than that Gd-free alloy. However, excessive Gd addition (2 wt%) decreased the corrosion rate and caused severe localized corrosion due to massive cathode Gd-rich particles. Combined with mechanical properties and corrosion resistance, the alloy with 1 wt% Gd exhibited a potential for degradable implant applications. The obtained superior corrosion resistance was due to the refined microstructure and the compactness of Gd-containing corrosion products film. In addition, a systematic discussion of corrosion behavior and corrosion film formation was provided by means of schematic illustration. [ABSTRACT FROM AUTHOR]

The present study was designed to investigate the role of 11 2 ¯ 1 extension twinning on deformation and subsequent recrystallization behavior of binary Mg-Y alloys (Mg-5wt.%Y and Mg-10wt.%Y). The selected alloys in solution-treated condition were uniaxially deformed at room temperature and then annealed. Increasing the Y content switches the dominant twinning mode from 10 1 ¯ 2 extension twins and 10 1 ¯ 1 - 10 1 ¯ 2 double twins, to less commonly observed 11 2 ¯ 1 extension twins. The former was found to assist recrystallization, while the contribution of latter in the formation of new grains was minimal. Moreover, the concurrent precipitation in the Mg-10Y alloy pins the grain boundaries and twin boundaries and thereby suppresses the recrystallization of the alloy despite holding for a longer duration. Finally, the weakening of the annealing texture was only observed in the Mg-5Y alloy as compared to the Mg-10Y alloy. This was attributed to the grain boundary bulging as the prominent mechanism of recrystallization in the Mg-10Y alloy. [ABSTRACT FROM AUTHOR]

The corrosion mechanism of as-cast, heat-treated (H400) and extruded (E30, E60, E90) Mg-3Zn-1Mn-1Y alloys with different microstructure is investigated by scan electron microscope (SEM), scan Kelvin probe force microscope (SKPFM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance analysis and immersion experiments equipped with a dynamic corrosion device. The relevant results are as follows: continuously strip-like I-phase (Mg3Zn6Y) in as-cast alloy distributed along the grain boundary played a significant obstacle impact during corrosion, whereas this capability is weakened after heat treatment and large plastic extrusion deformation. However, extrusion deformation significantly improved alloy corrosion performance, the extruded E30 alloy performed superior anti-corrosion behavior among the three extruded alloys owing to the smaller potential difference between I-phase (2.59 V) and DRXed (2.51 V) or un-DRXed (2.54 V) grains. In addition, the corrosion obstacle effect of grains boundaries (the grain boundary has higher potential than the Mg substrate), dense corrosion products film protection (isolate the substrate from contact with SBF) and typical basal texture (lower reactivity of base atoms) have great influence on corrosion behavior. [ABSTRACT FROM AUTHOR]

Al-Sc-Zr alloy contains precipitate Al(Sc,Zr) shows good coarsening resistance due to the small diffusivities of Sc and Zr. Two supersaturated Al-0.4Sc-0.4Zr at% alloys were produced using melt-spinning and following extrusion. The coarsening behavior of supersaturated Al-0.4Sc-0.4Zr at% alloys was investigated using scanning transmission electron microscopy (STEM). Accelerated coarsening was observed in the extruded melt-spun ribbon with larger precipitate size and higher precipitate volume fraction than in melt-spun ribbon. The accelerated effective diffusivity after extrusion was explicitly linked to the initially refined extruded microstructure. Precipitate volume fraction and chemical composition in both melt-spun ribbon and extruded rod during annealing were quantified with the help of STEM and energy-dispersive x-ray spectroscopy. Precipitate size and number density were predicted using Umantsev-Olson-Kuehman-Voorhees model for ternary alloys, and the predictions showed good agreement with experimental results by considering changes in diffusivity and precipitate volume fraction. [ABSTRACT FROM AUTHOR]

This work studied the high-temperature oxidation resistance properties of Mg alloys with Gd and Ca. The oxidation property of Mg-3.5Gd-xCa (x = 0, 0.5, 1.0 and 3.0 wt%) alloys followed parabolic oxidation kinetics at 500 °C. A stable oxide film was formed on the alloy surface and limited further oxidation. The oxide film was composed of Gd2O3, MgO and MgCO3 for Mg-3.5Gd and was mainly CaO and CaCO3 with increasing Ca content for Mg-3.5Gd-xCa alloys. The high oxidation affinity of Ca caused it to be oxidized preferentially and the fast diffusion of Ca in Mg alloys provided a source for the continuous oxidation of Ca at the surface. The parabolic rate constant, grains size and surface roughness of the oxide film increased with the increasing Ca content in Mg-3.5Gd-xCa alloy. The understanding of multi-element alloying on the oxidation behavior of Mg alloy is helpful for the design of multi-element oxidation-resistant Mg alloys. [ABSTRACT FROM AUTHOR]

The relationship between microstructure evolution and mechanical performance of Al–Zn–Mg–Cu alloys with varying Cu/Mg ratios was discussed in detail under different two-step aging (T7X). The results showed that the undissolved second-phase particles including σ-Al7Cu2Fe and T-Al2Mg3Zn occurred in the quenched Al–Zn–Mg–Cu alloys. When the Cu/Mg ratio approaches 1.64, the S-Al2CuMg phase was also observed. Although the Cu/Mg ratio did not change the precipitation sequence of the Al–Zn–Mg–Cu alloys, it changed the coarsening rate and precipitate size distribution during aging process. The Al–Zn–Mg–Cu alloy with the lowest Cu/Mg ratio has the slowest coarsening rate and the highest strength (655 MPa). The fracture morphology of Al–Zn–Mg–Cu alloys changes from the typical brittle fracture to the intergranular-dominated mixed fracture mode or ductile fracture when the Cu/Mg ratios increases. Besides, the T79-aged alloys with varying Cu/Mg ratios have similar grain boundary precipitates (GBPs) and precipitate-free zones (PFZs). The T74-aged alloys with higher Cu/Mg ratio have more coarser GBPs and wider PFZs. [ABSTRACT FROM AUTHOR]

This study investigated the microstructure, mechanical properties, corrosion behavior of as-cast Mg–1.8Zn–0.4Zr–1.74Gd–xY (x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 wt%) biodegradable magnesium alloys. Microstructures of the alloys were characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results showed that the alloys were mainly composed of α-Mg matrix (Mg, Zn)3(Gd, Y) phase, Mg3Zn3(Gd, Y)2 phase and Mg12Zn(Gd, Y) phase. It was found that 0–1.25 wt% Y addition led to significant grain refinement of the alloys from 111.5 to 57.3 μm. Moderate amount of Y resulted in improved strength. However, the strength and elongation decreased when the Y content exceeded 0.5 wt%. With 0.5 wt% of Y, the corrosion rate and corrosion current density were 0.721 ± 0.042 mm y−1 and 4.76 μA cm−2, respectively, which were lower than the other investigated alloys. Among all the tested samples, Mg–1.8Zn–0.4Zr–1.74Gd–0.5Y alloy has the moderate corrosion rate and mechanical properties, making it promising for the future optimization of the biodegradable Mg–Zn–Zr–Gd–Y alloys. [ABSTRACT FROM AUTHOR]

Magnesium-based alloys presented great potential for biodegradable implant materials. However, the poor mechanical properties and high corrosion rate blocked its extensive application. In this study, a new biodegradable Mg–Zn–Y–Gd–Zr alloy was fabricated and extruded. The microstructure, corrosion morphologies and corrosion products film of the as-cast, homogenized and as-extruded alloys were characterized by optical micrographs, scanning electron microscopy, X-ray diffraction and laser scanning confocal microscopy. Moreover, the corrosion mechanisms of the as-cast and as-extruded alloys were proposed, and the influencing factors of corrosion properties were discussed. The electrochemical test, immersion tests and corrosion morphologies demonstrated that the as-extruded alloy exhibited favorable corrosion properties. The as-cast and homogenized alloys displayed localized corrosion mode, and the as-extruded alloy displayed uniform corrosion mode. The Volta potential of the Mg3(Y,Gd)2Zn3 phase relative to Mg matrix was measured by using Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]