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Mg-Gd alloys are candidates for degradable implants combining favorable mechanical and corrosion properties. Gd has a high solid solubility in Mg and an acceptable biocompatibility. The influence of different amount of Gd additions and solid solution (T4) treatment on mechanical properties and corrosion in 0.9 wt.% NaCl and cell culture medium (CCM) of magnesium was investigated systematically. The effects of Gd were clarified by microstructural characterizations as well as stress and degradation analysis. It was found that minor Gd additions to pure Mg led to Gd solid solution in Mg (α) and the formation of Mg5Gd IMPs (intermetallic particles), which increased the hardness, tensile and compressive strength. The GdH2 phase was found in low-alloyed Mg-Gd alloys. The corrosion rate (CR) was increased by the addition of more Gd due to the increased kinetics of the cathodic reaction. However, the resistance to degradation was effectively improved by T4 heat treatment due to the dissolution of IMPs. The reduced susceptibility to pitting can be achieved by a minor Gd addition and T4 heat treatment. The Mg-2Gd alloy is a potential candidate for implants due to its good combination of tailorable mechanical properties and low homogeneous in vitro degradation rate (DR).

Previous investigations demonstrated that rare-earth elements (REs) could improve their creep properties effectively. Herein, the influence of Y content on the creep properties of magnesium is investigated systematically with different amount of Y additions. The mechanisms responsible for creep deformation are clarified by the analysis of stress exponent and microstructural characterizations. It is found that the addition of Y in Mg can improve both the ambient strength and high temperature strength owing to its effective solid solution strengthening. At room temperature, the yield strength of Mg–Y alloys has a linear relation with the content of Y. When tested at high temperatures, the yield strength reduces. Compared with pure magnesium, Mg–Y alloys exhibit a high thermal stability even above 200 °C. Small amount of Y addition can improve the creep resistance of Mg largely. With further increasing its content, its contribution to the improvement of creep resistance is weakened for Mg. Under the applied stresses 60–100 MPa and at temperatures of 200–250 °C, the responsible creep mechanism is dislocation controlled. During creep deformation, the Y segregation regions play an important role in hindering the movement of dislocations.

Open-porous MAX phase skeletons from Ti3SiC2 were manufactured by Microwave-Assisted Self-propagating High-temperature Synthesis (MASHS) and subsequently subjected to squeeze casting infiltration with an Al-Si lightweight casting alloy (EN AC-44200). This alloy was chosen due to its high flowability, corrosion resistance and good machinability. The manufactured composites, together with a reference sample of the original alloy, underwent testing of thermal properties, including thermal conductivity and diffusivity, specific heat and thermal expansion in the temperature range 50-500 °C, which corresponds to the expected working temperatures of the material. The fabricated AlSi/Ti3SiC2 composites have significantly increased thermal stability, with coefficients of thermal expansion (approximately 10-11 × 10−6 °C−1) half that of the original alloy. As regards mechanical properties, the instrumental Young’s modulus and Vickers hardness of the composite materials are 170.8 and 8.5 GPa, respectively. Moreover, the microstructure and phase composition, structural defects and potential impacts between constituents of the manufactured composites were characterized using SEM, TEM and STEM microscopy and EDS and XRD analysis.

The microstructure and texture evolution during static recrystallization of Mg-Nd alloys were investigated. Depending on the third alloying element added into Mg-Nd alloy, either Al or Zn, diverse textures are formed during recrystallization annealing. The rolled Mg-2Nd-1Zn sheet shows a high activity of prismatic slip and the formation of a weak texture with basal pole spread in the sheet transverse direction. In contrast, a strong texture with a basal pole spread in the rolling direction was formed in the Mg-2Nd-1Al sheet. An equivalent growth of the recrystallized grains at the early annealing stage retains their orientations during grain growth.

Elektron21 (E21) and its composites with additions of 0.25 wt.%, 0.5 wt.%, and 1 wt.% AlN/Al nanoparticles (NPs) were fabricated by a high shear dispersion technology. Their creep properties were investigated over a stress range between 80 MPa and 140 MPa at 240°C. The grain size exhibits an obvious increase with the addition of AlN/Al NPs compared with the monolithic E21 alloy. Increasing the content of AlN/Al NPs leads to a pronounced improvement of creep resistance. Microstructural analysis shows that, with the addition of 1% AlN/Al NPs in E21, the distribution of the intermetallics Mg3RE becomes much more homogeneous and their size is reduced. Such Mg3RE particles can prevent the dislocation slip more efficiently during creep. Besides these Mg3RE particles, the additional formation of Al2RE and Al2Zr3 phases, which results from the reactions of AlN/Al NPs and the alloying elements Zr and REs, could act as thermal stable particles to improve the creep resistance. Finally, the remained AlN NPs without reactions are beneficial for the improvement of the creep resistance to some extent due to Orowan strengthening.

Materials characterization 175, 111044 (1-12) (2021). doi:10.1016/j.matchar.2021.111044, Texture modification during sheet rolling appears differently in binary Mg-RE (rare-earth) or Mg-Ca alloy, compared to their ternary counterparts containing Zn. The differences in texture development and the active deformation mechanisms under tensile loading were investigated in the binary alloys. These analyses are based on in-situ synchrotron experiments and electron backscatter diffraction measurements to reveal direct experimental evidence of the texture development and the active deformation mechanisms. Higher activations of nonbasal < a > and pyramidal < c+a > dislocations were found in the Nd or Ca containing Mg alloys, compared to the Mg-Zn alloy. The texture development shows an obvious feature, which is a broadening of the basal pole intensity distribution perpendicular to the loading direction and a strengthening of the pole at the loading direction in all examined sheets. This texture development relates to the higher activation of prismatic < a > slip. The addition of Zn in the Mg-RE or Mg-Ca alloys further promotes the activation of nonbasal < a > and pyramidal < c+a > dislocations. This enhanced prismatic < a > slip in the Zn containing ternary alloys is confirmed by EBSD misorientation analysis., Published by Science Direct, New York, NY

A novel high shear dispersion technique (HSDT) was used for the first time to effectively distribute AlN/Al nanoparticles (NPs) in Elektron21 (El21) Mg alloys. Different high shearing speeds were adopted to investigate the optimum shearing speed for optimum deagglomeration of NPs and enhancing the creep resistance of AlN/Al NPs reinforced El21 alloy. The results showed that the creep resistance of El21 + 0.5% AlN/Al nanocomposite increased with the increasing speed of HSDT. The individual/synergistic roles of AlN and Al were also systematically identified by comparing the microstructural evolutions and creep properties of El21, El21 + 0.25% Al, El21 + 0.75% AlN, and El21 + 1% AlN/Al. The creep results showed that the mixture additions of AlN and Al NPs gave a synergistic improvement on the creep resistance of El21 alloy compared to the single addition of Al or AlN NPs.

Acta biomaterialia 121, 695 - 712 (2021). doi:10.1016/j.actbio.2020.11.050, The influence of amount of intermetallics on the degradation of as-extruded Mg-Nd alloys with different contents of Nd was investigated via immersion testing in DMEM+10% FBS under cell culture conditions and subsequent microstructural characterizations. It is found that the presence of intermetallic particles Mg$_{41}$Nd$_5$ affects the corrosion of Mg-Nd alloys in two conflicting ways. One is their negative role that their existence enhances the micro-galvanic corrosion. Another is their positive role. Their existence favours the formation of a continuous and compact corrosion layer. At the early stage of immersion, their negative role predominated. The degradation rate of Mg-Nd alloys monotonously increases with increasing the amount of intermetallics. Mg-$_5$Nd alloy with maximum amount of intermetallics suffered from the most severe corrosion. With the immersion proceeding (≥7 days), then the positive role of these intermetallic particles Mg$_{41}$Nd$_5$ could not be neglected. Owing to the interaction between their positive and negative roles, at the later stage of immersion the corrosion rate of Mg-Nd alloys first increases with increasing the content of Nd, then reaches to the maximum at 2 wt. % Nd. With a further increase of Nd content, a decrease in corrosion rate occurs. The main corrosion products on the surfaces of Mg-Nd alloys include carbonates, calcium-phosphate, neodymium oxide and/or neodymium hydroxide. They are amorphous at the early stage of immersion. With the immersion proceeding, they are transformed to crystalline. The existence of undegradable Mg$_{41}$Nd$_5$ particles in the corrosion layer can enhance the crystallization of such amorphous corrosion products., Published by Elsevier, [Amsterdam]

The influence of intermetallic microstructure on the degradation of Mg-5Nd alloy with different heat treatments was investigated via immersion testing in DMEM + 10 pct FBS under cell culture conditions and subsequent microstructural characterizations. It was found that T4 heat-treated sample had the poorest corrosion resistance due to the lack of finely dispersed precipitates inside grains, continuous lamellar particles along grain boundaries and outer Ca-P layer, and to the formation of a loose corrosion product layer. In contrast, the aged samples exhibited a better corrosion resistance due to their presence and to the formation of a compact corrosion layer. Their degradation behavior largely depended on the intermetallic microstructure. Corrosion was initiated in the matrix around stable globular particles Mg41Nd5 at grain boundaries. In the sample aged at high temperature 245 °C, the coexistence of lamellar Mg41Nd5 particles and their nearby Nd-poor regions enhanced the corrosion. The corrosion first started in such regions. It was shown that those finely dispersed precipitates formed during aging had no influence on the corrosion initiation. However, they indeed affected the subsequent corrosion propagation with the immersion proceeding. They supplied barriers for corrosion propagation and hence were beneficial for improving the corrosion resistance. The continuously distributed lamellar Mg41Nd5 precipitates formed at grain boundaries during aging at 245 °C supplied an additional effective obstacle to corrosion propagation. This was especially beneficial for hindering the corrosion propagation at the later stage of corrosion.

Wires of magnesium alloys possess a high potential, e.g., as filler materials, for joining applications but also for biodegradable applications, such as suture materials. While the typical process of producing wires is based on a wire drawing process, direct extrusion by using adjusted dies to deal with high degrees of deformation allows a one-step manufacturing of wires to some extent. In this work, the extrusion of wires with a thickness of 1 mm and even lower is shown feasible for pure magnesium and three Al-containing magnesium alloys (AZ31, AZ80, AZ91). The surface quality and the mechanical properties are improved with increasing Al content. It is shown that, despite the large difference in the degrees of deformation, the properties and their development are similar to those of extruded round bars. Wrapping tests were carried out as an exemplary more complex forming procedure, and the behavior is correlated to the microstructure and texture of the extruded wires.

© 2020 The Authors. Materials and Corrosion published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim AZ91D and MRI153M alloys were produced by thixomolding. Their corrosion resistance is significantly higher than that of similar materials produced by ingot or die-casting. A corrosion rate smaller than 0.2 mm/year in 5 wt% NaCl solution is measured for the thixomolded AZ91D alloy. The corrosion behaviour was evaluated using immersion tests, electrochemical impedance spectroscopy, hydrogen evolution, glow discharge optical emission spectroscopy, and atomic emission spectroelectrochemistry. A bimodal microstructure is observed for both alloys, with the presence of coarse primary α-Mg grains, fine secondary α-Mg grains, β-phase, and other phases with a minor volume fraction. The amount of coarse primary α-Mg is significantly higher for the AZ91D compared with the MRI153M. The network of β-phase around the fine secondary α-Mg grains is better established in the thixomolded AZ91D alloy. A combination of several factors such as the ratio of primary to secondary α-Mg grains, localised corrosion or barrier effect due to other phases, as well as regions of preferential dissolution of the α-Mg due to chemical segregation, are thought to be responsible for the high corrosion resistance exhibited by the thixomolded AZ91D and MRI153M. German Ministry of Education and Research; Christian Doppler Society

The influence of particles with different melting points on the microstructure, phase composition and properties of plasma electrolytic oxidation (PEO) coatings was investigated. PEO coatings were produced on AM50 Mg alloy from an alkaline phosphate-based electrolyte (1 g/L KOH + 20 g/L Na3PO4) with and without addition of clay, SiO2, Si3Ni4 and SiC micro-sized particles. The incorporation mode of the particles primarily depends on their melting point. Particles with relatively low melting point can achieve fully reactive incorporation, while high melting point particles are mainly inertly incorporated into the coating. Reactive incorporation of clay particles contributes to formation of a dense layer and improvement of corrosion and wear resistance. Addition of SiO2 and Si3Ni4 particles can improve the wear resistance of PEO coating, while the corrosion performance and degradation process of the coating is marginally influenced by the inertly incorporated particles.

Plasma electrolytic oxidation (PEO) technology is widely used for coating of light metals and their alloys because of the excellent coating properties it provides and its non-line-of-sight treatment which allows forming coatings on substrates with complex geometry. However, non-uniform coating thickness and surface properties may be an issue at different locations on substrates with complex shapes. In order to understand the effect of substrate geometry on PEO coating formation and uniformity, AM50 magnesium alloy specimens with drill holes of various diameter to length ratios were coated. PEO coatings were applied on these substrates in an alkaline electrolyte at constant voltage. Phase composition, coating morphology, thickness and elements distribution were studied at different locations of the drill holes. Complementary, a 3D model describing the processing is built to simulate and to predict the effect of substrate geometry on the anodic current distribution and coating formation using finite element analyses. The model can provide useful information for predicting coating growth and uniformity towards optimized PEO process design.

Plasma electrolytic oxidation (PEO) is a well-known surface treatment for Mg alloys, while high porosity is an issue to achieve long-term corrosion protection. Nevertheless, the presence of inherent porosity can be turned into advantage while used as nano/micro-structured reservoir of corrosion inhibitors or functional agents next to Mg surface providing an active corrosion protection and multi-functionality. For the first time, we report here the 3D internal architecture of PEO coated Mg via synchrotron-based microtomography. The pore characteristics have been qualitatively and quantitatively investigated to unveil the formation of the coating porosity and potential incorporation of functional elements in the pores.

Plasma electrolytic oxidation (PEO) process is employed to coat AM50 magnesium alloy in an alkaline phosphate solution applying constant voltage. Effects of treatment time on the morphology, composition and thickness of the resulting coatings are investigated by XRD and SEM respectively. Based on the analysis of the experimental results, a mathematical model is developed to simulate PEO coating growth including porosity and coating thickness. It is assumed that the current density of electrical discharges generated at the bottom of the pores remains constant and the coating growth is determined by Faraday’s law. This model describes a 2D transient finite element approach including necessary physical system parameters in mathematically coupled conditions. It demonstrates how the coating thickness is affected by current density, phase composition and porosity. The model reproduces the PEO process reasonably well and simulation results are in good agreement with experimental results, especially for predicted coating thicknesses. Although the model has a drawback in describing the oxygen release and hydroxyl ion concentration due to an empirical kinetic description, it may still be a useful tool in explaining and predicting PEO coating growth on magnesium alloy under constant DC voltage.

Wrought magnesium alloys attract special interests as lightweight structural material due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys. In this contribution, recent research and developments on wrought magnesium alloys are reviewed from the viewpoint of the alloy design, focusing on Mg-Al, Mg-Zn and Mg-rare earth (RE) systems. The effects of different alloying elements on the microstructure and mechanical properties are described considering their strengthening mechanisms, e.g. grain refinement, precipitation and texture hardening effect. Finally, the new alloy design and also the future research of wrought magnesium alloys to improve their mechanical properties are discussed. Keywords: Wrought magnesium alloys, Alloy design, Mechanical properties

The influence of Nd contents and particles on the microstructure and mechanical properties of extruded Mg alloys are discussed. Pure Mg and binary Mg-xNd (x = 0.2 wt.%, 0.5 wt.%, 1 wt.%, 2 wt.%, 5 wt.%) alloys were cast and extruded. Hardness and tensile/compression tests were measured on those alloys. The results show that the addition of Nd to Mg leads to improvements in hardness, tensile/compression yield strengths and elongation. However, the Nd has little effect on ultimate strengths and compressibility of Mg alloys. The contributions of strengthening mechanisms to the tensile/compressive yield strength of extruded Mg-Nd alloys are investigated. Mg41Nd5 phase was distributed in Mg-2Nd and Mg-5Nd alloys after extrusion, which is the main reason that decreased the grain size of Mg-Nd. The tension-compressing yield asymmetry is decreased from 1.8 to 1 with the increased additions Nd in extruded alloys.

The creep properties of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (El21) alloys with additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al nanoparticles (NPs) were studied over a stress range from 80 to 140 MPa at 240 °C, respectively. The individual/synergistic roles of Al and AlN in the El21 alloy were investigated systematically to reveal their creep strengthening mechanisms. Creep results show that individually all three additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al could increase the creep resistance of El21 alloy apparently. However, the addition of mixed 1 wt% AlN/Al NPs shows the best strengthening effect on creep properties in El21 alloy. Microstructural characterizations reveal that the additions of Al and AlN increased the area fraction of intermetallic particles obviously. Blocky Al2Zr, Al2Zr3 particles and Al2(Nd, Gd) (Al2RE) particulates were observed in both El21 + 0.25% Al and El21 + 0.75%AlN. Nevertheless, when Al and AlN were simultaneously added into El21 alloy the formation of these blocky phases Al2Zr/Al2Zr3 was suppressed, and a larger amount of Al2RE phase was observed. This is attributed to the preferential reaction between AlN and Zr, which restricted the formation of Al–Zr phase and subsequently promoted the reaction of Al-RE phase. The dominant mechanism during creep at 240 °C was calculated to be viscous glide of dislocation. The simultaneous additions of Al and AlN NPs could lead to a more homogeneous distribution of intermetallic particles and increase the amount of Al2RE phase. Such kind of microstructures is beneficial for hindering the dislocation movement, transfer the load from matrix and alleviate the local stress concentration. Consequently, El21 + 1% AlN/Al exhibits the best creep properties among four alloys.

Three magnesium alloys with texture and microstructure modifying elements, binary M2, and the alloyed counterparts with Ca (MX21) and rare earth element (ME21) were extruded to flat bands under similar conditions. The microstructure and texture in extrusion significantly differ from those developed in rolled magnesium sheets. The influence on the mechanical properties and the forming behaviour, in terms of Erichsen values, with relation to microstructure, texture, and strain rate sensitivity was examined. A clear difference in texture development and strain rate sensitivity is shown in dependence on the alloying composition. In addition, not only the texture, but also the microstructure has a great influence on formability.

JOM 71(7), 2227 - 2234 (2019). doi:10.1007/s11837-019-03515-7, The effect of second phases on the creep behavior of Mg-Ca-Zr alloys was investigated. Casting and hot-extrusion processes were performed to prepare Mg-xCa-0.5Zr (x = 0 wt.%, 0.3 wt.% and 0.6 wt.%) alloys with different morphologies and distributions of second phases. The as-cast microstructures of Mg-Ca-Zr alloys consisted of an Mg matrix and coarse Mg$_2$Ca intermetallic compounds distributed at the grain boundaries. The hot-extruded microstructures exhibited finer Mg$_2$Ca spherical particles and precipitates distributed homogeneously inside the matrix and along the grain boundaries. The results of creep tests suggested that the viscous glide of dislocation and dislocation climb were the dominant creep mechanisms of Mg-Ca-Zr alloys crept at 200°C. The creep property was strongly related to the morphology and distribution of the Mg$_2$Ca phases. The finer and more homogeneously distributed particles showed a better strengthening effect than the coarser intermetallic compounds distributed along the grain boundaries., Published by TMS, [S.l.]

A homogeneous microstructure of as-cast magnesium alloys is desired to improve the formability during their subsequent thermomechanical processing. Owing to its similar crystal structure to Mg, the part of Zr formed by peritectic reaction during solidification was considered to be the most effective nucleants for alpha-Mg. However, regarding the Al-containing magnesium alloys, up to now no suitable and effective external nucleants were found for them. Recently, it was demonstrated that the additions of SiC worked in refining both the Mg-Al and Mg-Zn alloys. The SiC particles acted as nucleants in magnesium alloys are attracting more attentions. The present work investigated and compared the effects of external SiC particle additions on the grain refinements of Mg-Al and Al-free Mg-Zn (Mn) alloys. Their microstructures were characterized using XRD, SEM and TEM. It was found that the additions of SiC particles could refine the grains of both Mg-Al and Mg-Zn alloys. The SiC particles cannot act as a direct heterogeneous nucleant for the nucleation of alpha-Mg in both Mg-Al and Mg-Zn (Mn) alloys. The responsible mechanisms for their grain refinements are different. Regarding for Mg-Al alloys, the grain refinement caused by the addition of SiC particles is attributed to the formation of a ternary intermetallics Al2MgC2, which has a very similar crystal structure to that of Mg. As for Mg-Zn (Mn) alloys, the grain refinement is attributed to the formation of a (Mn, Si)-enriched intermetallics by the interactions between SiC and impurity Mn in alloys.

The sintering behavior of metal injection molded titanium aluminide alloys, their microstructure formation and resulting mechanical properties were investigated. As reference material, the alloy Ti-45Al-5Nb-0.2B-0.2C at.% (TNB-V5) was selected. Additionally, two other variations with Mo and Mo + Si additions were prepared: Ti-45Al-3Nb-1Mo-0.2B-0.2C at.% and Ti-45Al-3Nb-1Mo-1Si-0.2B-0.2C at.%. The results indicate that the optimum sintering temperature was slightly above the solidus line. With proper sintering parameters, very low porosities (

Plasma electrolytic oxidation (PEO) processing for light metals is known for decades and has been established as a well-known industrial surface treatment offering a reasonable wear and corrosion protection. However, long-term protection is compromised by the intrinsic porosity and limited range of composition in the PEO layer. A novel approach is to introduce particles to the electrolyte, aiming at their in-situ incorporation into PEO coatings during growth. The idea is that with the help of particles the defects can be sealed, and the composition range and the functionalities of produced coatings can be enhanced. So far, multifunctional coatings with anticorrosion, self lubrication, anti-wear, bioactive and photocatalytic properties were produced with the aid of particle addition. The properties of particle itself, together with electrical and electrolyte parameters during PEO processing determine the way and efficiency of particle uptake and incorporation into the coatings. Normally incorporation of the particles into the coating can range from fully inert to fully reactive. This paper reviews recent progress on particle-containing PEO coatings formed on Mg, Al and Ti alloy substrates. The main focus is given to the uptake mechanism of particle into PEO layers and the introduced microstructural and functional changes. (C) 2016 Elsevier B.V. All rights reserved.

The influence of electrode distance between anode and cathode during plasma electrolytic oxidation (PEO) process on the coating formation was investigated by combining experiments and simulation. Firstly a model was built to simulate the effect of electrode distance on the anodic current distribution using finite element analyses. Complementary, PEO coatings were fabricated on AM50 magnesium alloy in an alkaline electrolyte with different electrode distances applying constant voltage. Phase composition, coating morphology and thickness were studied for both the front and back sides of the PEO coating depending on the electrode distance. For paralleled plate-like electrodes, based on coating uniformity, an optimum electrode distance of 60–80 mm was identified under the chosen experimental conditions. Via correlation of simulation and experimental results, the influence of electrode distance on coating formation is explored. It is demonstrated that under constant voltage mode, PEO coating formation is affected by electrode distance on both front and back sides of magnesium substrates. This effect is ascribed to the influence of electrode distance on the current distribution in the bath and to the related average current density on the surfaces.

A new Mg-RE (rare earth) alloy was previously developed by micro-alloying method (RE< 0.4 wt.%), which achieves a high ductility and good corrosion resistance. In-situ tensile test via neutron and synchrotron diffraction were performed to investigate first the deformation behaviour; and second the texture evolution which can be related to the deformation mechanism, and finally to understand why the as-cast Mg-RE alloys show such a high tensile ductility.Preliminary results showed that a dominated basal fibre texture was gradually developed with the increase of tensile strain. However, before the sample was broken a (10.0) fibre texture showed a similar intensity to that in (00.2), which means more activations of the non-basal slip planes during tensile deformation. This could also contribute to a relatively high elongation of this new Mg-RE alloy at room temperature. Further discussion will be showed together with the microstructures.

The hourglass-shaped specimen, which is commonly used for axial fatigue testing, cannot be easily fabricated by metal injection moulding. Consequently, this work aimed at evaluating the performance...

Magnesium and its alloys are attractive for lightweight construction, but suffer often from poor corrosion resistance. Plasma electrolytic oxidation is a promising surface treatment to overcome these limitations. Recently, introduction of particles to the PEO electrolyte has been explored as new strategy to provide a wider range of compositions and new functionalities for PEO coatings. However, this surface treatment can have negative impact on the fatigue strength. In the present study, the influence of PEO coatings with and without particle addition on the corrosion fatigue behavior of AZ31 Mg alloy is investigated. The corrosion fatigue behavior is investigated in load increase tests and constant amplitude tests in 0.5% NaCl solutions. Results are correlated with the corrosion behavior evaluated in polarization and electrochemical impedance spectroscopy measurements. Corrosion tests show significant improvement of the corrosion resistances of PEO-coated specimens. However, the uncoated material exhibits the highest corrosion fatigue strength, whereas a reduction of 7% for the PEO-coated specimen without particles and 27% for the PEO-coated specimen with particles is found.

The growth of plasma electrolytic oxidation (PEO) coatings can be considered a complex process that includes discharge breakdown, sintering, and deposition process. In this work, inert SiO 2 and La 2 O 3 particles were used as tracers to investigate the formation mechanisms of PEO coatings on Mg alloy AM50. The growth direction and kinetics of the coating formation are primarily controlled by the intensity and the number of discharges. High-intensity discharges enable the inward growth of the PEO coating rapidly. Low-intensity discharges allow the outward growth of the coating at a slow speed. At the initial stage of a treatment, conversion products form locally around the intermetallics and disseminate gradually. Discharges appear after reaching the breakdown potential, leading to rapid growth of the coating. The outward growth of the layer is non-uniform because the protruding conversion products are the last locations converted by the discharges. Inward growth of the layer occurs preferentially around intermetallic phases and the formation of the inner layer is related to the inward growth.

The present study examines the influence of Ca or Nd on the microstructure and texture modification during indirect extrusion and after subsequent annealing of Mg–Zn based alloys. The addition of such elements influence the recrystallization processes, i.e. dynamic (DRX) and static recrystallization (SRX), and leads to distinctive texture changes of samples extruded at different extrusion speeds. In the binary Mg–Zn alloys, the resulting texture after extrusion is the classical basal type texture, where there is an alignment of basal planes along the arc between the and poles. This development is independent of the extrusion speed, as the resulting microstructures are almost completely recrystallized. In the case of the Mg–Zn–Ca, there is a distinctive component together with a pole, while in the Mg–Zn-Nd alloy the so-called rare-earth texture component and the pole intensity are observed as DRX dominates the microstructural development. It is found that this distinctive behavior can be changed if partially recrystallized microstructures are subsequently annealed. This leads to an increase of the importance of SRX and a different resulting texture while maintaining a similar grain structure. Both recrystallization processes lead to different mechanical properties, yielding behavior and toughness as a result of the different texture development.

In previously published research, creep resistance of commercial alloy Elektron21 (El21) and El21 + 1% AlN/Al nanocomposite were predominantly investigated in as-cast condition, little work focused on creep resistance following heat treatment. In this work, El21 and its nanocomposite with and without T6 treatment (520 °C for 8 h and 200 °C for 16 h) were prepared to reveal the influence of heat treatment on their microstructural evolutions and creep properties. Different intermetallic particles and precipitates that formed in El21 and El21 + 1% AlN/Al with different states were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Creep tests were performed over a stress range of 80–140 MPa at 240 °C. Creep results showed that the application of T6 treatment could improve the creep resistance of El21, but deteriorate that of El21 + 1% AlN/Al. This is attributed to the reduced amount of γ'' and β′ precipitates in El21 + 1% AlN/Al (T6) after ageing, resulting from the formation of plate-like Al2(Nd, Gd) (Al2RE) precipitates. It is also found that after T6 heat treatment, El21 (T6) had a lower minimum creep rate with a shorter duration of secondary creep stage than El21 + 1% AlN/Al (T6) at high creep temperatures due to the overageing of precipitates and the thermal stability of the Al2RE particles. El21 + 1% AlN/Al nanocomposites, either in the as-cast or T6 condition, show a much longer duration of secondary creep than NP-free El21. The responsible mechanism was attributed to the addition of AlN NPs and the formation of particulate/plate Al2RE phase.

A homogeneous microstructure of as-cast magnesium alloys is desired to improve their mechanical properties when achieving lightweighting. Recently, it was demonstrated that the addition of SiC refines both Mg–Al and Mg–Zn alloys. The present work investigates the effect of SiC particle additions on the grain refinement of Mg–Zn alloys, including their addition amount, particle size, addition temperature and holding time. The microstructures were characterized using XRD, SEM and EDS. It was found that the addition of SiC particles refines the grains of Mg–Zn alloys. With increasing their amount and reducing the addition temperature and holding time, the grain size decreases. The optimal SiC particle size for nucleation of alpha-Mg was found to be around 2 µm. The responsible refinement mechanism is attributed to the formation of (Mn, Si)-enriched intermetallics by the interactions between SiC and impurity Mn in alloys.

Materials science and engineering / A 761, 138053 (2019). doi:10.1016/j.msea.2019.138053, n situ hard X-ray diffraction experiments were carried out to investigate the dislocation slip activity of Mg-1 wt.% Zn-based alloys containing Nd or Ca during tensile loading. Diffraction patterns collected during tensile loading at 3 temperatures were analyzed using a convolutional multiple whole profile fitting procedure. High activation of nonbasal and pyramidal dislocations was found in the Nd- and Ca-containing alloys. The microstructure evolution after 10% deformation was examined by complementary EBSD measurements. The microstructure evolution was related to the differences in the initial texture and active deformation modes, according to the alloying and temperature. In-grain misorientation axes analysis obtained from the EBSD measurements confirms that the addition of Nd or Ca contributes to the higher activity of prismatic slip. The high activity of prismatic slip leads to a broadening of the basal poles perpendicular to the loading direction and a strengthening of the $< 10{\bar{1}0} >$ pole along the loading direction. The overall dislocation density evolution at elevated temperatures is controlled by dynamic recovery and dynamic recrystallization. These thermally activated mechanisms are retarded in the Nd- or Ca-containing alloys., Published by Elsevier, Amsterdam

The precipitation behavior of Mg-Al alloys during isothermal ageing has been investigated by dilatometry. Only continuous precipitation was observed in Mg-5.5Al during ageing at 175°C, 200°C, or 225°C, while both discontinuous and continuous precipitation occurred in Mg-8.9Al at the same ageing temperatures. Dilatometry curves showed that Mg-8.9Al expanded when aged at 225°C or 250°C. These results demonstrate that high content of Al is beneficial for discontinuous precipitation in binary Mg-Al alloys. Additional analyses indicated that the expansion of Mg-8.9Al during isothermal ageing can be attributed to the increment of the Mg cell lattice parameters. Moreover, continuous precipitation could suppress the discontinuous precipitation by reducing the driving force for growth of discontinuous precipitates.