Zn Ca Alloy Research Articles

Microstructural refinement and mechanical properties improvement of Mg–Al–Mn–Zn–Ca alloy processed by rotary swaging at room temperature

Mg-4.1Al-0.6Mn-0.5Zn-0.4Ca alloy with high strength was prepared through hot extrusion at 330 °C followed by room temperature rotary swaging. The changes of microstructure and mechanical behaviors of extruded and swaged alloys after undergoing different rotary waging passes were investigated. The results reveal significant microstructural refinement, fragmentation of the Al8Mn5 phases, and precipitation of the Al2Ca phases after rotary swaging. With the increase of rotary swaging passes, a noticeable rise in the fraction of LAGBs and a more uniform distribution and refinement of second phases occurred. The texture with <10–10> parallel to processing direction was formed after rotary swaging. The rotary swaging largely improves the alloy's strength, with the ultimate tensile strength and yield strength increasing from 298 MPa to 198 MPa for the as-extruded alloy to 372 MPa and 359 MPa for the as-swaged alloy after 13 passes, respectively. The improvement of mechanical properties is a result of grain boundary strengthening, dislocation strengthening, and the strengthening of second phases. This result may provide valuable insights and guidance in the design of high-strength magnesium alloys as well as their plastic processing methods.

Quantitative Imaging of Magnesium Biodegradation by 3D X‐Ray Ptychography and Electron Microscopy

AbstractMagnesium‐based alloys are excellent materials for temporary medical implants, but understanding and controlling their corrosion performance is crucial. Most nanoscale corrosion studies focus on the surface, providing only 2D information. In contrast, macro‐ and microscale X‐ray tomography offers representative volume information, which is, however, comparatively low in resolution and rather qualitative. Here a new mesoscale approach overcomes these drawbacks and bridges the scale gap by combining 3D measurements using ptychographic X‐ray computed tomography (PXCT) with electron microscopy. This combination allows to observe the corrosion progress non‐destructively in 3D and provides high‐resolution chemical information on the corrosion products. A medical Mg–Zn–Ca alloy is used and compared the same sample in the pristine and corroded states. With PXCT an isotropic resolution of 85 and 123 nm is achieved for the pristine and corroded states respectively, which enables to distinguish nanoscale Mg2Ca precipitates from the matrix. The corroded state in best approximation to the in situ conditions is imaged and reveals the complexity of corrosion products. The results illustrate that the corrosion‐layer is dense and defect‐free, and the corrosion of the material is grain‐orientation sensitive. The developed workflow can advance research on bioactive materials and corrosion‐sensitive functional materials.

Mechanism study on improving the corrosion resistance of screw rolled Mg–Zn–Ca alloy by nano-MgO addition

To reduce the corrosion rate of biodegradable magnesium alloys, n-MgO/Mg–Zn–Ca composites (SR-3ZXM) were prepared using nano-MgO (n-MgO) reinforcement and screw rolling (SR). n-MgO addition and SR refined the grain size and improved the passivation ability and corrosion resistance of SR-3ZXM. After SR, adding n-MgO reduced the corrosion current density of SR-3ZXM to 20.99 μA/cm2. The corrosion rate calculated based on the material weight loss decreased to 0.88 mm/y, which is attributed to the grain size refinement and variation of secondary phase fraction. Thus, n-MgO addition and SR change the corrosion mechanism and improve the corrosion resistance of SR-3ZXM.

Tuning biomechanical behavior and biocompatibility of Mg–Zn–Ca alloys by Mn3O4 incorporated plasma electrolytic oxidation coatings

In this study, the mechanical behavior and biocompatibility of plasma electrolytic oxidation (PEO)-coated Mg–Zn–Ca alloy specimens were investigated. The coatings were synthesized by incorporating KMnO4 and Mn3O4 nanoparticles into an electrolytic solution. An indentation test revealed a significant increase in the reduced elastic modulus of the PEO coatings with incorporated Mn3O4 under various loads. This increase was attributed to the higher coating thickness and reduced porosity achieved by the addition of Mn-based additives to the electrolyte. The composite PEO coatings prepared with Mn3O4 nanoparticles exhibited a more pronounced reduction in elastic modulus under pressure. Wettability tests showed that the prepared coatings maintained their hydrophilic nature with water contact angles in the range of 25–63°. The presence of Mn3O4 in the PEO coatings provided a conducive environment for cell viability. The enhanced biocompatibility of the composite coatings achieved by incorporating KMnO4 into the electrolyte was particularly noteworthy. This improvement was attributed to the controlled release of Mn ions, which generates a microenvironment that favors cellular activities. The study showed that incorporating Mn3O4 into PEO coatings enhances mechanical properties, preserves hydrophilicity, and improves biocompatibility, thus indicating its potential for orthopedic implant applications.

Improving In-Vitro Corrosion and Degradation Performance of Mg–Zn–Ca Alloy for Biomedical Applications by Equal Channel Angular Pressing

Improving In-Vitro Corrosion and Degradation Performance of Mg–Zn–Ca Alloy for Biomedical Applications by Equal Channel Angular Pressing

Mechanical Integrity and In vitro Degradation Behavior of Mg–Zn–Ca Biodegradable Alloy Prepared by Different Casting Technologies

Mg–Zn–Ca alloys have been widely used as biodegradable orthopedic and cardiovascular scaffolds because of their non-cytotoxicity, remarkable biodegradability, good biocompatibility and excellent mechanical properties similar to human bone. However, degradation causes poor corrosion resistance and mechanical properties. In this study, Mg-6%Zn-0.6%Ca alloys were produced using three distinct methodologies: casting, casting via the ultrasonic vibration process (USV), and casting via the mechanical vibration process (MV). Surface characterization, mechanical characteristics and corrosion resistance of the as-cast (untreated) and treated species were studied. The morphology and microstructure showed that the grain size of the as-cast, MV and USV specimens all had average grain sizes of about 191, 93 and 82 µm, respectively. The ultrasonic vibration treated specimen has the greatest degree of grain refinement. Mechanical tests showed that microstructure refinement promotes the mechanical characteristics of Mg alloy, such as compression, ultimate tensile strength as well as elongation. It was observed that the USV-treated sample has exceptional mechanical properties (Compressive strength 360.64 MPa, ultimate tensile strength (UTS) 178.41 MPa and Elongation 3.45%). Corrosion tests revealed that the USV-treated specimen exhibited uniform corrosion and low corrosion rate due to uniform compact fine grains with higher oxide concentration of about 42.82 wt%. The results of electrochemical analyses revealed that the average corrosion rate obtained from Potentiodynamic polarization curves of the as-cast, MV and USV specimens was about 5.3144, 4.5311 and 4.1087 mm/year, respectively and the passive film resistance (Rf) that was obtained from the electrochemical impedance spectroscopy (EIS) model of the USV, MV-treated samples and as-cast sample was 457 Ω, 430 Ω and 204 Ω, respectively. The results of immersion tests revealed that the USV-treated sample lost less weight and exhibits a relatively low degradation rate than the as-cast and MV-treated samples. After two weeks the weight of the as-cast, MV and USV samples decreased by about 18.6%, 18.5%, 16.8%., and the degradation rates were 7.304, 7.097 and 6.78 mm/y, respectively, and then gradually declining over the course of the immersion period.

Enhanced strength-ductility synergy and activation of non-basal slip in as-extruded Mg–Zn–Ca alloy via heterostructure

The relationship between the heterogeneous grain structure and mechanical properties is an emerging aspect of the effort to expand the applications of Mg alloy. In this study, heterostructured Mg alloy, comprising elongated and fine equiaxed grains, was fabricated through a simple hot-extrusion process with extrusion temperature of 320 °C. This resulted in a yield strength (YS) of approximately 192 MPa and excellent elongation of approximately 20.4 %. When compared to the alloy extruded at 360 °C, which had a homogenized structure, the increased YS in the 320 °C extruded alloy was primarily attributed to hetero-deformation-induced (HDI) strengthening. The inclusion of Zn and Ca, along with stress concentration, promoted active <c+a> slips, thereby enhancing the ductility of the alloy extruded at 320 °C. This endeavour provides an inspiring strategy for improving the YS of Mg–Zn–Ca alloys without significantly compromising ductility.

Effect of Tip Content on the Work Hardening and Softening Behavior of Mg–Zn–Ca Alloy

Effect of Tip Content on the Work Hardening and Softening Behavior of Mg–Zn–Ca Alloy

Plastic deformation behavior of a Mg-1.5Zn-0.1Ca (mass%) alloy sheet under different strain paths

Mg–Zn–Ca alloy sheets with weak basal texture are expected to improve the room-temperature press formability of Mg-alloy sheets. The plastic deformation behavior of Mg–Zn–Ca alloy sheets should differ significantly from that of typical Mg-alloy sheets with strong basal texture. However, this has not yet been substantially studied. In this study, the plastic deformation behavior of a rolled Mg-1.5Zn-0.1Ca (mass%) alloy sheet with a thickness of 1 mm is studied experimentally. Tests of uniaxial tension, compression, reverse loadings from tension to compression, and from compression to tension are conducted in the rolling and transverse directions, and the work-hardening behavior and evolution of the Lankford value are investigated. Electron backscattered diffraction measurements are also conducted to examine the texture evolution. Under tension, the stress was less in the transverse direction than that in the rolling direction, and an apparent plateau region appeared only in the transverse direction. Under compression, the stress-strain curves exhibited plateau regions at the initial stage and were similar in the rolling and transverse directions. The Lankford values were less under compression than under tension in both directions. Under reverse loading from compression to tension, sigmoidal curves appeared, irrespective of the loading direction; however, they were more pronounced in the rolling direction than in the transverse direction. Under reverse loading from tension to compression, sigmoidal trends did not occur, irrespective of the loading direction, and the in-plane anisotropy in the work-hardening behavior was small. The mechanisms yielding these macroscopic deformation behaviors are discussed in terms of twinning and slip activities.

Synthesis of Magnesium-Based Alloys by Mechanical Alloying for Implant Applications

The biocompatibility and biodegradability of magnesium (Mg), along with its lightness, make magnesium-based materials promising for use in the biomedical industry. In this work, ternary Mg–Zn–Ca alloys were manufactured for biomedical applications using mechanical alloying (MA). The objective of this work was to study the effect of milling time on the produced ternary alloys Mg65–Zn30–Ca5 and Mg70–Zn25–Ca5 (percentages by weight), the degradation of the alloys in synthetic human fluids, and their generated cytotoxicity. The Mg-based alloys were synthesized in a planetary ball mill under an argon atmosphere using stainless-steel containers and balls with a milling regimen of 400 rpm for 2, 5, 10, 15, and 20 h. The powders obtained after MA were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), which verified that ternary Mg–Zn–Ca alloys can be obtained using MA. The XRD refinement analysis of the samples showed the presence of a MgZn intermetallic phase. Electrochemical tests showed that the corrosion resistance and corrosion current density of Mg65–Zn30–Ca5 and Mg70–Zn25–Ca5 alloys improved compared to those of pure Mg. Cytotoxicity testing was conducted using the Sulforhodamine B (SRB) assay, which revealed that the alloys did not exhibit cytotoxicity toward human fibroblast cells. Mg65–Zn30–Ca5 and Mg70–Zn25–Ca5 alloys show good potential to be used in biomedical applications.

Effects of MgO nano particles on the mechanical properties and corrosion behavior of Mg–Zn–Ca alloy

An as-extruded Mg–3Zn-0.2Ca-0.3MgO (wt.%, ZX0.3) composite with good mechanical properties and high corrosion resistance was designed and fabricated by hot extrusion based on the requirements of biodegradable Mg alloys. The results revealed that the average grain size was reduced about 50% to 1.9 μm and the yield stress was increased about 34%–269 MPa after adding MgO to Mg–3Zn-0.2Ca (wt.%, ZX) alloy. Theoretical calculation and experimental results showed that the grain boundary strengthening and Orowan strengthening were the main strengthening mechanisms (>95%) of the composite, while the addition of MgO NPs and the increasing of basal texture were harmful to the plastic of ZX0.3 composite. However, the activation of prismatic <a> dislocations and pyramidal <c> dislocations would reduce the negative impact of them. The corrosion test results revealed that in ZX0.3 composite, MgO nanoparticles (NPs) not only promoted the formation of the Mg(OH)2 layer, but also effectively barricaded the cracks extension in corrosion products layer, making the corrosion product layer much denser and durable. The corrosion rate of ZX0.3 composite was reduced by 30% to 0.79 mm/yr compared with that of ZX alloy. In addition, the reduced corrosion rate of matrix could provide a more suitable environment for cell adhesion and differentiation, which results in better cytocompatibility of the ZX0.3 compared with ZX alloy.

The effect of grain size on deformation modes and deformation heterogeneity in a rolled Mg–Zn–Ca alloy

Grain refinement could promote the activation of non-basal slip and enhance the strength and ductility of Mg alloy simultaneously. In this work, the grain size effect on deformation modes and deformation heterogeneity and its relations to crystallographic orientation in a rolled Mg–1.58Zn–0.1Ca alloy sheet with a weakened transverse direction (TD) spread texture were investigated via intragranular misorientation axis (IGMA) and high resolution-digital image correlation (HR-DIC) measurement. The results indicate that a decrease of the grain size from 55 to 13 μm increased the yield strength (YS) by 56.9%, from 72 MPa to 113 MPa, for the TD samples, but only by 8% for the rolling direction (RD) samples, from 125.7 to 135.7 MPa. Moreover, grain refinement enhanced the elongation by 76.4% for the TD samples, from 11% to 19.1%, and merely by 26.5% for the RD samples, from 16.6% to 21%. The transition in dominant deformation modes due to grain size decreasing can be summarized as: for the RD samples: basal slip → prismatic slip; for the TD samples: basal slip + tension twinning → prismatic slip. The enhanced activity of prismatic slip in the fine-grained (FG)-TD and FG-RD samples can be ascribed to the reduced ratio of critical resolved shear stress (CRSS)prismatic/CRSSbasal. For both the RD and TD samples, grain refinement facilitated deformation homogeneity, which could be related to the enhanced activity of basal slip and non-basal slip, as well as the resulting improved deformation compatibility across grain boundary.

Enhanced Corrosion Resistance and Biocompatibility of NaMgF3Coating on Mg–Zn–Ca Alloy: An In Vivo and In Vitro Study

The objective of the present work is to investigate the in vitro and in vivo performance of NaMgF3coating on Mg–3Zn–0.2Ca (MZC) alloy for bone applications. NaMgF3coating is developed on MZC alloy by using NaF solution, which prepares the F−containing coating while avoiding the use of hydrofluoric acid, which is of higher toxicity. The dense NaMgF3coating with a thickness of ≈20 μm contributes to reducing the corrosion rate of MZC exposed to Hanks’ solution by ≈43% from 0.7 to 0.4 mm y−1. The NaMgF3coating also depresses the corrosion rate of MZC in vivo, causing the residual volume of the implanted MZC rods to increase from below 70% to ≈90%. Besides, the toughness value of MZC rods coated with NaMgF3after implantation is 2780 MJ m−3, which demonstrates the continuous and sufficient mechanical support that is provided by it for bone repair. Importantly, osteoblasts can adhere and differentiate on the coating surface, and the NaMgF3coating enhanced the biocompatibility and osteogenesis of the MZC alloy. So, the NaMgF3‐coated MZC alloy could be used in bone repair applications.

Observation of morphology and compositional changes of magnesium alloy using liquid cell TEM

Liquid cell transmission electron microscopy (LCTEM) was developed for analyzing the liquid-phase samples and shows not only the in-situ morphological images of the sample, but also the in-situ material information such as selected area diffraction (SAD) and energy-dispersive X-ray spectroscopy (EDS). The researchers analyzed the corrosion behavior of Mg–Zn–Ca alloys using both polarization and immersion tests. However, these methods only provide macro scale corrosion characteristics. In this study, the corrosion behavior of the Mg–Zn–Ca alloy powders was analyzed using LCTEM. It provided the in-situ sub-micron scale images and time-dependent composition, thereby revealing evidence of selective corrosion of the α-Mg phase as well as the IM1 phase (Ca2Mg6Zn3).

Achieving exceptional improvement of yield strength in Mg–Zn–Ca alloy wire by nanoparticles induced by extreme plastic deformation

The size and distribution of second phase particles have an important influence on the mechanical properties of Mg alloys and further determine their application. In this study, extreme plastic deformation was employed to control the microstructure and tune the corresponding mechanical properties of Mg–Zn–Ca alloy. The uniformly dispersed nanoparticles (average diameter of ∼14.3 nm) could be successfully introduced into the Mg–Zn–Ca alloy wire after cold drawing with an area reduction of ∼99.8%, and the high yield strength of ∼285 MPa was obtained. When compared to the as-extruded alloy with yield strength of ∼171 MPa, the exceptional improvement in yield strength (∼114 MPa) for the Mg–Zn–Ca alloy wire is mainly attributed to the formation of nanoparticles. Moreover, the Mg wire also exhibited a good ductility of ∼11.8%. The results indicate that extreme plastic deformation can enable a refined microstructure to enhance the mechanical properties of Mg–Zn–Ca alloys.

Precipitation in lean Mg–Zn–Ca alloys

While lean Mg–Zn–Ca alloys are promising materials for temporary implants, questions remain on the impact of Zn and Ca on the microstructure. In this context, the precipitation of Zn and Ca in Mg-1.5Zn-0.25Ca (in wt.%), initially extruded at 330°C, towards Mg–Ca binary precipitates or Ca–Mg–Zn ternary precipitates was probed in a multiscale correlative approach using atom probe tomography (APT) and analytical transmission electron microscopy (TEM). Particular focus was set on the ternary precipitate phase whose structure is debated. In the as-extruded material, the binary precipitates are made of hexagonal C14 Mg2Ca containing up to about 3 at.% of Zn. The ternary ones are based on the hexagonal Ca2Mg5Zn5 prototype structure with a composition close to Ca3Mg11Zn4, as deduced from atomically resolved EDS mapping and scanning TEM imaging, supported by simulations. The precipitation sequence was scrutinized upon linear heating from room temperature to 375°C, starting from the solutionized material. Three exothermic differential scanning calorimetry (DSC) peaks were observed, at respectively 125, 250 and 320°C. Samples were taken after the peak decays, at respectively 205, 260 and 375°C for structural analysis. At 205°C, APT analysis revealed Ca-rich, Zn-rich and Zn‒Ca-rich clusters of about 3 nm in size and with a number density of 5.7 × 1023 m−3. At 260°C, APT and TEM showed mono-layered Zn‒Ca-rich Guinier‒Preston (GP) zones of about 8 nm in size and with a number density of 1.3 × 1023 m−3. At 375°C, larger and highly coherent elongated precipitates were found, with a size of about 50 nm. They occur as binary Mg–Ca precipitates or ternary Ca2Mg6Zn3 precipitates, as deduced from scanning TEM-based energy dispersive X-ray spectroscopy (EDS) and nanodiffraction in TEM. Here, the binary precipitates outnumber the ternary ones, while in the as-extruded material the ternary precipitates outnumber the binary ones, which corresponds well to the calculated phase diagram. We correlated the microstructure to hardness probed by Vickers testing. The largest hardening relates to the end of the 125°C DSC peak and thus to GP zones, which outperform the hardening induced by the nanometer-sized clusters and the larger intermetallic particles. The complexity of the precipitation sequence in lean Mg–Zn–Ca alloys is discussed.

Achieving superior mechanical properties in a low-alloyed magnesium alloy via low-temperature extrusion

A low-alloyed Mg-1.2Zn-0.1Ca (wt.%) alloy was extruded at low temperatures. The alloy extruded at 150 °C exhibits a yield strength (YS) of 374 MPa and an elongation of 14.2%. The YS is superior to most Mg–Zn–Ca alloys, and can compete with high-alloyed AZ91 and Mg-RE alloys.

Segregation-driven exceptional twin-boundary strengthening in lean Mg–Zn–Ca alloys

Twinning-mediated plasticity in hexagonal close-packed crystal structures offers great potential for achieving lean Mg-based alloys with high strength and extended ductility. Micropillars from a lean MgZn1 Ca0.3 (ZX10, in wt%) alloy and pure Mg, each comprising one or more pre-existing {101¯2}<1¯011> extension twin boundaries and a parent orientation with its c-axis perpendicular to the loading direction, were subjected to in situ micropillar compression. By means of correlative characterization using transmission electron backscattered diffraction, transmission electron microscopy and nanoscale energy-dispersive X-ray spectroscopy, we assesed the effects of Zn and Ca solutes on micropillar deformation and on the response of pre-existing twin-boundaries to applied stress. In ZX10, both Zn and Ca solutes periodically segregate at the pre-existing extension twin boundaries, giving rise to a strengthening increment by about 300% compared to pure Mg, along with ductility enhancement. Due to segregation, the twin boundaries remain immobile throughout the deformation process, playing a critical role both in non-basal slip and twin-nucleation events. The former is facilitated by the formation of stable I1 stacking faults, while the latter is stimulated by active <c+a> slip across the pinned twin interface. In contrast, the pure Mg micropillars respond by massive twin growth followed by higher-order twinning events and profuse basal slip. In the absence of non-basal slip, pure Mg exhibits an earlier onset to failure due to shear incompatibility at the twin interface. The findings provide new insights into the role of solute Zn and Ca in stabilizing twinned microstructures for achieving synergistic strength-ductility enhancement in lean Mg alloys.

Revealing the influence of crystallographic orientation on the electrochemical and discharge behaviors of extruded diluted Mg–Sn–Zn–Ca alloy as anode for Mg-air battery

In this work, in order to reveal the role of crystallographic orientation in the electrochemical and discharge behaviors of the extruded diluted Mg-0.5Sn-0.5Zn-0.5Ca (wt.%) alloy through investigating the longitude surface (LS) and transversal surface (TS). The results show that the LS sample is mainly consisted of (0001) orientated grains, while the TS one is composed of (10-10)/(11–20) orientated grains. Although the self-corrosion rate for TS sample is higher than that of the counterpart as a result of the non-basal planes possess lower surface energy and higher activation energy, the real-time self-discharge rates for both samples are similar at constant applied current density. Nevertheless, the TS sample exhibits a remarkably higher anodic efficiency than that of the LS one, which can be attributed to the uniform dissolution of the substrate along with the weakened chunk effect (CE). Additionally, the Mg-air battery with the TS sample as anode exhibits a more stable discharge course and higher cell voltage due to the loose discharge products as well as enhanced discharge activity.

Improving room-temperature ductility of a Mg–Zn–Ca alloy through friction stir processing

The effect of friction stir processing (FSP) on the microstructure evolution and mechanical properties of as-cast Mg–Zn–Ca (Mg-1.2wt%Zn-0.1wt%Ca) alloy was investigated. The result shows that the average grain size of the stir zone is greatly refined from ∼170 μm to ∼13 μm. Moreover, a basal texture is formed in the stir zone, and the c-axis of the grain is tilted to the normal direction about 42.6° away from the processing direction. Although the tensile strength has little improvement compared to the as-cast alloy, the elongation is increased from 24.6% to 45.4%. The excellent room-temperature ductility of the FSP alloy is mainly attributed to the fine grain size and the preferential orientation of the grains in the stir zone. The Schmid factor up to 0.44 means that basal slip is beneficial to be activated, resulting in a high elongation.