Na partitioning during thermomechanical processing of an Mg-Sn-Zn-Na alloy

Microstructural characterization was used to examine the changes that occur in an Mg-6Sn-5Zn-0.3Na alloy from casting to extrusion at either 623 K or 723 K (350 _C or 450 _C) followed by artificial aging at 473 K (200 _C). In particular, the partitioning of Na was examined at each step using STEM-EDS mapping. Na atoms were found to preferentially partition to the Mg-Zn phase when present. After extrusion, when no Mg-Zn was observed, the spherical Mg2Sn particles were found to be enriched in Na, particularly at the higher extrusion temperature. Artificial aging following extrusion resulted in a change in Na partitioning, and a coarse distribution of Mg-Zn precipitate rods. Na microadditions led to a high as-extruded hardness, but a significant tension–compression yield asymmetry was still observed at room temperature. The compressive yield strength was found to decrease significantly after 1000 hours of aging.

Collagen type-I leads to in vivo matrix mineralization and secondary stabilization of Mg-Zr-Ca alloy implants

Biodegradable magnesium-zirconia-calcium (Mg-Zr-Ca) alloy implants were coated with Collagen type-I (Coll-I) and assessed for their rate and efficacy of bone mineralization and implant stabilization. The phases, microstructure and mechanical properties of these alloys were analyzed using X-ray diffraction (XRD), optical microscopy and compression test, respectively, and the corrosion behavior was established by their hydrogen production rate in simulated body fluid (SBF). Coll-I extracted from rat tail, and characterized using fourier transform infrared (FT-IR) spectroscopy, was used for dip-coating the Mg-based alloys. The coated alloys were implanted into the femur bones of male New Zealand white rabbits. In vivo bone formation around the implants was quantified by measuring the bone mineral content/density (BMC/BMD) using dual-energy X-ray absorptiometry (DXA). Osseointegration of the implant and new bone mineralization was visualized by histological and immunohistochemical analysis. Upon surface coating with Coll-I, these alloys demonstrated high surface energy showing enhanced performance as an implant material that is suitable for rapid and efficient new bone tissue induction with optimal mineral content and cellular properties. The results demonstrate that Coll-I coated Mg-Zr-Ca alloys have a tendency to form superior trabecular bone structure with better osteoinduction around the implants and higher implant secondary stabilization, through the phenomenon of contact osteogenesis, compared to the control and uncoated ones in shorter periods of implantation. Hence, Coll-I surface coating of Mg-Zr-Ca alloys is a promising method for expediting new bone formation in vivo and enhancing osseointegration in load bearing implant applications.

Structure and mechanical property variations in Mg-Gd-Y-Zn-Zr alloy depending on its composition and processing conditions

An effect of alloying element content on mechanical properties and precipitate formation in Mg-RE alloys was studied for Mg-8Gd-4Y- 1Zn-0.4Zr (wt%) and Mg-10Gd-5Y-1.8Zn-0.4Zr (wt%). It is shown that small variations in the alloying element concentration can be used to manipulate the alloy microstructure and precipitate formation towards eliminating the asymmetry (tension/compression) and anisotropy of yield stress.

The effect of ageing on the compressive deformation of Mg-Sn-Zn-Na alloy

The influence of ageing on deformation twinning in an extruded Mg-6Sn-3Zn-0.04Na alloy is investigated. In-situ compression tests have been carried out using high resolution synchrotron X-Ray Diffraction (XRD) to measure the influence of precipitates on twining activity. Synchrotron experiments revealed the increase in the critical resolved shear stress of twinning with ageing. The compressive yield strength (along the extrusion direction) of the aged sample increased by ∼ 150% over the non-aged specimen. To obtain statistical insight into the twinning activity, the microstructure of the non-aged and aged samples (200°C, 24 hours) deformed up to ∼1% plastic strain was studied using optical microscopy. A higher number of thinner twins were observed in the microstructure of the aged sample compared to the non-aged sample.

Evaluation of coatings for mg alloys for biomedical applications

The aim of this work was to assess a number of coatings developed for Mg for biomedical applications. The Mg substrates were high-purity (HP) Mg and ME10, an alloy recently developed for improved extrudability. The research utilized the new fishing-line specimen configuration to allow direct comparison to our recent in vivo and in vitro measurements. The in vitro measurements were immersion tests of fishing-line specimens immersed in Nor's solution at 37 °C. Tests of substantial duration are needed because the corrosion rates of uncoated samples are low. Nor's solution is the designation given to Hank's solution through which CO2 is bubbled at a partial pressure of 0.009 atm. In this solution, pH is maintained constant by the interaction of CO2 and the bicarbonate ions in the solution. This is the same buffer as that which maintains the pH of blood. Coatings examined were: (i) an anodization using a bio-friendly alkaline electrolyte consisting of phosphate, borate, and metasilicate, (ii) octyltrimethoxysilane (OSi), (iii) 1,2-bis[triethoxysilyl]ethane (BTSE), (iv) anodization+OSi, and (v) anodization + BTSE. The performance of coated samples was comparable to or better than that of the uncoated samples, and there was a substantially better performance for the ME10 samples after anodization+OSi. Reasons for the various performances are discussed.

Microstructures, mechanical and corrosion properties and biocompatibility of as extruded Mg-Mn-Zn-Nd alloys for biomedical applications

Extruded Mg-1Mn-2Zn-xNd alloys (x=0.5, 1.0, 1.5 mass %) have been developed for their potential use as biomaterials. The extrusion on the alloys was performed at temperature of 623K with an extrusion ratio of 14.7 under an average extrusion speed of 4mm/s. The microstructure, mechanical property, corrosion behavior and biocompatibility of the extruded Mg-Mn-Zn-Nd alloys have been investigated in this study. The microstructure was examined using X-ray diffraction analysis and optical microscopy. The mechanical properties were determined from uniaxial tensile and compressive tests. The corrosion behavior was investigated using electrochemical measurement. The biocompatibility was evaluated using osteoblast-like SaOS2 cells. The experimental results indicate that all extruded Mg-1Mn-2Zn-xNd alloys are composed of both α phase of Mg and a compound of Mg7Zn3 with very fine microstructures, and show good ductility and much higher mechanical strength than that of cast pure Mg and natural bone. The tensile strength and elongation of the extruded alloys increase with an increase in neodymium content. Their compressive strength does not change significantly with an increase in neodymium content. The extruded alloys show good biocompatibility and much higher corrosion resistance than that of cast pure Mg. The extruded Mg-1Mn-2Zn-1.0Nd alloy shows a great potential for biomedical applications due to the combination of enhanced mechanical properties, high corrosion resistance and good biocompatibility.

Biodegradable Mg-Ca and Mg-Ca-Y alloys for regenerative medicine

In this study, Mg-xCa (x = 0.5, 1.0, 2.0, 5.0, 10.0, 15.0 and 20.0 %, wt.%, hereafter) and Mg-1Ca-1Y alloys were investigated as new biodegradable bone implant materials. The compressive strength, ultimate strength and hardness of the Mg-Ca alloys increased, whilst the corrosion rate and biocompatibility decreased, with the increase of the Ca content in the Mg-Ca alloys; higher Ca content caused the Mg-Ca alloy to become brittle. Solutions of simulated body fluid (SBF) and modified minimum essential media (MMEM) with the immersion of Mg-xCa and Mg-1Ca-1Y alloys showed strong alkalisation. The yttrium addition to the Mg-Ca alloys does not improve the corrosion resistance of the Mg-1Ca-1Y alloy as expected compared to the Mg-1Ca alloy. It is suggested that Mg-Ca alloys with Ca additions less than 1.0 wt.% exhibited good biocompatibility and low corrosion rate.

Microstructural characterization and mechanical properties of Mg-Zr-Ca alloys prepared by hot-extrusion for biomedical applications

This paper investigated the microstructural characterization and mechanical properties of Mg-Zr-Ca alloys prepared by hot-extrusion for potential use in biomedical applications. Mg-Zr-Ca alloys were fabricated by commercial pure Mg (99.9%), Ca (99.9%), and master Mg-33% Zr alloy (mass%). The microstructural characterization of the hot-extruded Mg-Zr-Ca alloys was examined by X-ray diffraction analysis and optical microscopy, and the mechanical properties were determined from tensile tests. The experimental results indicate that the hot-extruded Mg-Zr-Ca alloys with 1 mass% Ca are composed of one single phase and those alloys with 2 mass% Ca consist of both Mg2Ca and α phase. The hot-extruded Mg-Zr-Ca alloys exhibit equiaxed granular microstructures and the hot-extrusion process can effectively increase both the tensile strength and ductility of Mg-Zr-Ca alloys. The hot-extruded Mg-1Zr-1Ca alloy (mass%) exhibits the highest strength and best ductility among all the alloys, and has much higher strength than the human bone, suggesting that it has a great potential to be a good candidate for biomedical application.

Biodegradable Mg-Zr-Ca alloys for bone implant materials

Mg–Zr–Ca alloys were developed for new biodegradable bone implant materials. The microstructure and mechanical property of the Mg–xZr–yCa [x=0·5, 1·0% and y=1·0, 2·0% (wt-% hereafter)] alloys were characterised by optical microscopy, compressive and hardness tests. The in vitro cytotoxicity of the alloys was assessed using osteoblast-like SaOS₂ cells. The corrosion behaviour of these alloys was evaluated by soaking the alloys in simulated body fluid (SBF) and modified minimum essential medium (MMEM). Results indicated that the mechanical properties of the Mg–Zr–Ca are in the range of the mechanical properties of natural bone. The corrosion rate and biocompatibility decreases with the increase in the Ca content in the Mg–Zr–Ca alloys. The solutions of SBF and MMEM with the immersion of the Mg–Zr–Ca alloys show strong alkalisation. The Zr addition to the Mg–Zr–Ca alloys leads to an increase in the corrosion resistance, compressive strength and the ductility of the alloys, and a decrease in the elastic modulus of the Mg–Zr–Ca alloys.

Compressive properties of hot-rolled Mg-Zr-Ca alloys for biomedical applications

This paper investigated the microstructures and compressive properties of hot-rolled Mg-Zr-Ca alloys for biomedical applications. The microstructures of the Mg-Zr-Ca alloys were examined by X-ray diffraction analysis and optical microscopy, and the compressive properties were determined from compressive tests. The experimental results indicate that the hot-rolled Mg-Zr-Ca alloys with 1% Ca are composed of one single α phase and those alloys with 2% Ca consist of both Mg2Ca and α phase. The hot-rolled Mg-Zr-Ca alloys exhibit typical elongated microstructures with obvious fibrous stripe, and have much higher compressive strength and lower compressive modulus than pure Mg. All the studied alloys have much higher compressive yield strength than the human bone (90~140 MPa) and comparable modulus with the human bone, suggesting that they have a great potential to be good candidates for biomedical applications.

Effects of alloying elements on the corrosion behavior and biocompatibility of biodegradable magnesium alloys: a review

Magnesium (Mg) based alloys have been extensively considered for their use as biodegradable implant materials. However, controlling their corrosion rate in the physiological environment of the human body is still a significant challenge. One of the most effective approaches to address this challenge is to carefully select alloying compositions with enhanced corrosion resistance and mechanical properties when designing the Mg alloys. This paper comprehensively reviews research progress on the development of Mg alloys as biodegradable implant materials, highlighting the effects of alloying elements including aluminum (Al), calcium (Ca), lithium (Li), manganese (Mn), zinc (Zn), zirconium (Zr), strontium (Sr) and rare earth elements (REEs) on the corrosion resistance and biocompatibility of Mg alloys, from the viewpoint of the design and utilization of Mg biomaterials. The REEs covered in this review include cerium (Ce), erbium (Er), lanthanum (La), gadolinium (Gd), neodymium (Nd) and yttrium (Y). The effects of alloying elements on the microstructure, corrosion behavior and biocompatibility of Mg alloys have been critically summarized based on specific aspects of the physiological environment, namely the electrochemical effect and the biological behavior. This journal is © the Partner Organisations 2014.

Corrosion behavior of Mg-5Al-xZn alloys in 3.5 wt.% NaCl solution

Five types of Mg-5Al alloys with different weight percentages of Zn ranging from 0 to 4 wt.% were examined using electrochemical techniques and surface analysis. The electrochemical results indicated that the Mg-5Al alloys containing Zn have a lower corrosion and hydrogen evolution rates than the Mg-5Al based specimens with a decrease of value being observed with the decrease in Zn content. Zn addition induced the precipitation of Mg-Al and Mg-Zn phases in the Mg matrix along with grain refinement and increased an interaction of Zn oxide with Mg and Al products serving as a corrosion barrier. © 2014 Elsevier B.V. All rights reserved.