Fabrication and corrosion behavior of HA/Mg-Zn biocomposites

The thermal-treated hydroxyapatite (HA) particles, Mg and Zn powders were used to prepare the HA/Mg-Zn composites with different HA contents by means of powder metallurgy technology. The microstructures, formation phases, and corrosion behaviors in simulated body fluid (SBF) were studied in comparison with pure magnesium and HA/Mg composites fabricated by the same preparation technology. As a result, no evident reaction happened between HA particles and Mg matrix during sintering process, and Zn atoms diffused into Mg matrix to form a single phase Mg-Zn alloy matrix. The addition of HA particles changed the corrosion mechanism of Mg matrix. During the corrosion process, HA particles would adsorb and Ca²⁺ ions efficiently and induce the deposition of Ca-P compounds on the surface of composites. HA could improve the corrosion resistance of magnesium matrix composites in SBF and restrain the increase of pH of SBF. Furthermore, the addition of Zn was favorable to improve the corrosion resistance of HA/Mg composites due to the densification of composites and the formation of Mg-Zn alloy matrix.     

In vitro degradation,hemolysis and MC3T3-E1 cell adhesion of biodegradable Mg–Zn alloy

In this study a kind of patent binary Mg–6 wt.%Zn magnesium alloy was investigated as degradable biomedical material. The results of in vitro degradation including electrochemical measurements and immersion tests in simulated body fluid (SBF) revealed that zinc could elevate both the corrosion potential and Faraday charge transfer resistance of magnesium and thus improve the corrosion resistance. XRD and EDS analysis proved that the corrosion products on the surface of Mg–Zn contained hydroxyapatite (HA), Mg(OH)₂ and other Mg/Ca phosphates, which could reduce the degradation rate. The degradation process of magnesium alloy and the mechanism of corrosion layer formation were also discussed in this work, i.e. the byproducts of degradation of magnesium, Mg²⁺ and OH^?, reacted with the phosphate and Ca²⁺ in the SBF, thus the corrosion layer containing HA, Mg(OH)₂ and other magnesium-substituted apatite precipitated in corrosion pits and covered the surface of magnesium alloy.The hemolysis test found that the hemolysis rate of Mg–Zn was 3.4%, which is lower than the safe value of 5% according to ISO 10993-4. For the cell culture experiments, after 2 h incubation the pre-osteoblastic cell MC3T3-E1 was able to adhere and spread on the corrosion layer of Mg–Zn alloy, indicating that despite the fluctuation of pH value of DMEM culture solution, Mg–Zn alloy could still support the earlier adhesion of pre-osteoblastic cells on the surface. Hemolysis and adhesion of cells display good biocompatibility of Mg–Zn alloy in vitro.     

Phosphating treatment and corrosion properties of Mg–Mn–Zn alloy for biomedical application

A phosphating treatment was applied to Mg–Mn–Zn alloy in order to improve the corrosion resistance. Surface morphology and phase constitute were observed and identified by SEM, EDS, SAXS, XRD and XPS. SEM observation showed that a rough and crystalline reaction layer was formed on the surface of Mg alloy. With the increasing of phosphating time, the layer became thicker and denser. It has been showed that the reaction layer was mainly composed of brushite (CaHPO₄ · 2H₂O). Small amount of Zn²⁺ was also detected by XPS and EDS. The corrosion resistance of the phosphated samples was measured by the electrochemical polarization and the immersion test in comparison with the bare alloy. The results manifested that the corrosion resistance of Mg alloy was improved by the phosphating treatment, and the corrosion resistance increased with the increase of the phosphating time within 50 min. Immersion tests showed that the phosphate layer could protect magnesium alloy from fast corrosion. The brushite layer has been transformed into hydroxyapatite (HA) during the immersion in the simulated body fluid (SBF) solution, which suggested the brushite layer could provide good biocompatibility.     

Corrosion behavior of Al–60 vol.% SiCp composites in NaCl solution

In this study, corrosion behavior of pure Al and Al–4 wt.% Mg alloy matrix composites, comprising 60 vol.% SiC particles, has been investigated. Composites were produced by pressure infiltration technique at 750 °C. The corrosion tests were carried out in 3.5 wt.% NaCl environment up to 28 days. The weight loss of the composites increased with increasing duration time up to 3–5 days then remained constant. Scanning electron microscopy (SEM) analysis showed that Al–4 wt.% Mg alloyed matrix composite exhibited higher corrosion resistance than pure Al matrix composite although potentiodynamic polarisation measurements showed higher i_corr values of Al–4 wt.% Mg alloyed matrix composites than pure Al matrix composites. Experimental results revealed that precipitation of Mg₂Si as a result of reaction between Al–Mg alloy and SiC particle has a beneficial effect on corrosion resistance of Al–4Mg alloy matrix composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.     

Development and evaluation of a magnesium–zinc–strontium alloy for biomedical applications — Alloy processing,microstructure, mechanical properties,and biodegradation

A new biodegradable magnesium–zinc–strontium (Mg–Zn–Sr) alloy was developed and studied for medical implant applications. This first study investigated the alloy processing (casting, rolling, and heat treatment), microstructures, mechanical properties, and degradation properties in simulated body fluid (SBF). Aging treatment of the ZSr41 alloy at 175 °C for 8 h improved the mechanical properties when compared to those of the as-cast alloy. Specifically, the aged ZSr41 alloy had an ultimate tensile strength of 270 MPa, Vickers hardness of 71.5 HV, and elongation at failure of 12.8%. The mechanical properties of the ZSr41 alloy were superior as compared with those of pure magnesium and met the requirements for load-bearing medical implants. Furthermore, the immersion of the ZSr41 alloy in SBF showed a degradation mode that progressed cyclically, alternating between pitting and localized corrosion. The steady-state average degradation rate of the aged ZSr41 alloy in SBF was 0.96 g/(m²·hr), while the pH of SBF immersion solution increased. The corrosion current density of the ZSr41 alloy in SBF solution was 0.41 mA/mm², which was much lower than 1.67 mA/mm² for pure Mg under the same conditions. In summary, compared to pure Mg, the mechanical properties of the new ZSr41 alloy improved while the degradation rate decreased due to the addition of Zn and Sr alloying elements and specific processing conditions. The superior mechanical properties and corrosion resistance of the new ZSr41 alloy make it a promising alloy for next-generation implant applications.     

微波辅助法制备镁合金的植酸镁/羟基磷灰石复合涂层及其耐蚀性能

采用微波辅助法在AZ31镁合金表面制备了植酸镁/羟基磷灰石(PA/HA)复合涂层。利用FESEM、EDS、XRD和电化学性能测试等方法表征涂层的表面形貌、物相组成以及耐蚀性能,探究了植酸溶液的pH值对PA/HA复合涂层形貌及耐蚀性能的影响,并通过浸泡实验研究了镁合金及PA/HA复合涂层在模拟体液(SBF)中的降解矿化行为。结果表明:在植酸预处理中,植酸溶液的pH=5.0时制备得到的PA/HA复合涂层表面均匀、无裂纹,与镁合金基底的界面结合良好;并且在此pH值下PA/HA复合涂层包覆镁合金样品的交流阻抗最大,自腐蚀电流密度最小,说明其耐蚀性最好。在SBF中,PA/HA复合涂层能够快速诱导磷灰石的生成,并显著提高镁合金基底的耐蚀性能。     

Properties of ultrafine-grained Mg-based composites modified by addition of silver and hydroxyapatite

In this study, hydroxyapatite and silver were added to Mg–1Zn–1Mn–0.3Zr alloy to fabricate ultrafine-grained metal matrix composites. Grain sizes of approximately 85?nm were recorded by atomic force microscopy for the Mg–1Zn–1Mn–0.3Zr–5 wt-% HA–1 wt-% Ag composite. The contact angles in water and simulated body fluid on the ultrafine-grained Mg–1Zn–1Mn–0.3Zr-based composites were determined. Following a hydrofluoric acid treatment, the surface wettability changed from hydrophilicity to hydrophobicity. The electrochemical test showed that the corrosion resistance of the fluoride-treated specimens was higher, when compared with the untreated samples. The Mg–1Zn–1Mn–0.3Zr–5 wt-% HA and Mg–1Zn–1Mn–0.3Zr–5?wt-% of HA–1 wt-% Ag composites modified with MgF₂ have a higher degree of biocompatibility, which makes them potential candidates for medical applications     

Effect of trace HA on microstructure,mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy

Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites(x = 0, 0.1 and 0.3 wt%) were characterized by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy dispersion spectroscopy(EDS) and X-ray diffraction(XRD). Results of tensile tests at room temperature show that yield strength(YS) of Mg-2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength(UTS) and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential(Ecorr)of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from-1724 to-1660 m VSCE and the corrosion current density decreases from 479.8 to 280.8 μA cm~(-2) with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.5Sr/HA composites decreases from11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO_4 protective film due to the adsorption of Ca~(2+)on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.     

The influence of HF treatment on corrosion resistance and <Emphasis Type="Italic">in vitro</Emphasis> biocompatibility of Mg-Zn-Zr alloy

The samples made of a Mg-2.5wt.%Zn-0.5wt.%Zr alloy were immersed in the 20% hydrofluoric acid (HF) solution at room temperature for different time, with the aim of improving the properties of magnesium (Mg) alloy in applications as biomaterials. The corrosion resistance and in vitro biocompatibility of untreated and fluoride-coated samples were investigated. The results show that the optimum process is to immerse Mg alloys in the 20% HF solution for 6 h. After the immersion, a dense magnesium fluoride (MgF₂) coating of 0.5 μm was synthesized on the surface of Mg-Zn-Zr alloy. Polarization tests recorded a reduction in the corrosion current density from 2.10 to 0.05 μA/cm² due to the MgF₂ protective coating. Immersion tests in the simulated body fluid (SBF) also reveal a much milder corrosion on the fluoride-coated samples, and its corrosion rate was calculated to be 0.05 mm/yr. Hemolysis test suggests that the conversion coated Mg alloy has no obvious hemolysis reaction. The hemolysis ratio (HR) of the samples decreases from 11.34% to 1.86% with the HF treatment, which meets the requirements of biomaterials (HR < 5%). The coculture of 3T3 fibroblasts with Mg alloy results in the adhesion and proliferation of cells on the surface of fluoride-coated samples. All the results show that the MgF₂ conversion coating would markedly improve the corrosion resistance and in vitro biocompatibility of Mg-Zn-Zr alloy.     

Microstructure,mechanical properties and corrosion behaviour of Al–Si–Mg alloy matrix/zircon and alumina hybrid composite

In the present study, the effect of reinforcement on microstructure, mechanical properties and corrosion behaviour of aluminium–silicon–magnesium (Al–Si–Mg) alloy matrix hybrid composites reinforced with varying amounts of zircon and alumina has been investigated. Hardness and room temperature compressive tests were performed on Al–Si–Mg alloy as well as composites. Hardness and compressive strength was found to be higher for composites containing 3.75?% ZrSiO₄?+?11.25?% Al₂O₃. Similarly, Al–Si–Mg alloy and its composites were studied for corrosion behaviour in 1 N HCl corrosive media. The weight loss of all the composites was found to decrease with time due to the formation of passive oxide layer on the sample surface. The results obtained indicate that composites exhibit superior mechanical properties and corrosion resistance compared to unreinforced alloy.     

Microstructure,mechanical property,bio-corrosion and cytotoxicity evaluations of Mg/HA composites

Mg/HA (10 wt.%, 20 wt.% and 30 wt.%) composites were prepared by pure magnesium and hydroxyapatite (HA) powders using powder metallurgy (PM) method. The microstructure, mechanical property, corrosion and cytotoxicity of these Mg/HA composites were studied, with the bulk pure magnesium as control. The results showed that the main constitutional phases of Mg/HA composites were simply α-Mg and HA. The HA particulates distributed uniformly in Mg matrix for Mg/10HA composite, and few HA clustering occasionally spread over the Mg/20HA composite, whereas severe agglomeration of HA particulates could be seen for Mg/30HA composite. The yield tensile strength of Mg/10HA composite increased compared with that of the as-extruded bulk pure magnesium, yet the yield tensile strength, ultimate tensile strength and ductility of Mg/HA composites decreased with the further increase of HA content. The corrosion rate of Mg/HA composites increased with the increment of HA content. The cytotoxicity tests indicated that Mg/10HA extract showed no toxicity to L-929 cells, whereas Mg/20HA and Mg/30HA composite extracts induced significantly reduced cell viability.     

Microstructure and corrosion properties of as sub-rapid solidification Mg–Zn–Y–Nd alloy in dynamic simulated body fluid for vascular stent application

Magnesium alloy stent has been employed in animal and clinical experiment in recent years. It has been verified to be biocompatible and degradable due to corrosion after being implanted into blood vessel. Mg–Y–Gd–Nd alloy is usually used to construct an absorbable magnesium alloy stent. However, the corrosion resistant of as cast Mg–Y–Gd–Nd alloy is poor relatively and the control of corrosion rate is difficult. Aiming at the requirement of endovascular stent in clinic, a new biomedical Mg–Zn–Y–Nd alloy with low Zn and Y content (Zn/Y atom ratio 6) was designed, which exists quasicrystals to improve its corrosion resistance. Additionally, sub-rapid solidification processing was applied for preparation of corrosion-resisting Mg–Zn–Y–Nd and Mg–Y–Gd–Nd alloys. Compared with the as cast sample, the corrosion behavior of alloys in dynamic simulated body fluid (SBF) (the speed of body fluid: 16 ml/800 ml min⁻¹) was investigated. The results show that as sub-rapid solidification Mg–Zn–Y–Nd alloy has the better corrosion resistance in dynamic SBF due to grain refinement and fine dispersion distribution of the quasicrystals and intermetallic compounds in α-Mg matrix. In the as cast sample, both Mg–Zn–Y–Nd and Mg–Y–Gd–Nd alloys exhibit poor corrosion resistance. Mg–Zn–Y–Nd alloy by sub-rapid solidification processing provides excellent corrosion resistance in dynamic SBF, which open a new window for biomedical materials design, especially for vascular stent application.     

The influence of HF treatment on corrosion resistance and in vitro biocompatibility of Mg-Zn-Zr alloy

The samples made of a Mg-2.5wt.%Zn-0.5wt.%Zr alloy were immersed in the 20% hydrofluoric acid (HF) solution at room temperature for different time, with the aim of improving the properties of magnesium (Mg) alloy in applications as biomaterials. The corrosion resistance and in vitro biocompatibility of untreated and fluoride-coated samples were investigated. The results show that the optimum process is to immerse Mg alloys in the 20% HF solution for 6 h. After the immersion, a dense magnesium fluoride (MgF₂) coating of 0.5 μm was synthesized on the surface of Mg-Zn-Zr alloy. Polarization tests recorded a reduction in the corrosion current density from 2.10 to 0.05 μA/cm² due to the MgF₂ protective coating. Immersion tests in the simulated body fluid (SBF) also reveal a much milder corrosion on the fluoride-coated samples, and its corrosion rate was calculated to be 0.05 mm/yr. Hemolysis test suggests that the conversion coated Mg alloy has no obvious hemolysis reaction. The hemolysis ratio (HR) of the samples decreases from 11.34% to 1.86% with the HF treatment, which meets the requirements of biomaterials (HR < 5%). The coculture of 3T3 fibroblasts with Mg alloy results in the adhesion and proliferation of cells on the surface of fluoride-coated samples. All the results show that the MgF₂ conversion coating would markedly improve the corrosion resistance and in vitro biocompatibility of Mg-Zn-Zr alloy.     

Influence of Tris in simulated body fluid on degradation behavior of pure magnesium

In current paper, influence of tris-hydroxymethyl-aminomethane (tris) in simulated body fluid (SBF) on degradation behavior of pure magnesium is investigated using electrochemical tests as well as degradation measurement. Our results shows that tris mainly affects earlier degradation behavior of pure magnesium alloy. Tris and HCl used in preparation of SBF will form Tris–HCl which only lowers corrosion potential of magnesium slightly but accelerates degradation rates of pure magnesium by teens times. Consumption of OH^? generated during magnesium dissolution by Tris–HCl progressively promotes transformation from Mg to Mg²⁺, which is the main reason for quite high degradation rate of pure magnesium in SBF. Pure magnesium is also more sensitive to pitting corrosion due to inclusion of Tris–HCl in SBF. This study deepens the understanding on degradation mechanism of biomedical magnesium alloys.     

Blood triggered corrosion of magnesium alloys

Intravascular stents manufactured out of bioabsorbable magnesium (Mg) or Mg-alloys are considered as auspicious candidates for the next stent generation. However, before clinical application numerous physical and biological tests, especially to predict the clinically highly important degradation kinetics in vivo, have to be performed. In a Chandler-Loop model, the initial degradation of eight different magnesium alloys during 6 h in contact with human whole blood was investigated. The magnesium release varied between 0.91 ± 0.33 mg/cm² (MgAl9Zn1) and 2.57 ± 0.38 mg/cm² (MgZn1). No correlation could be found with Mg release data obtained after immersion in simulated body fluid (SBF). This pilot study showed that Mg corrosion is highly influenced by the biological test environment (SBF or blood, etc.) and that a modified Chandler-Loop model with human whole blood may be superior to predict corrosion of Mg alloys under clinical conditions than the SBF models presently used.     

Interface microstructure and mechanical properties of zinc–aluminum thermal diffusion coating on AZ31 magnesium alloy

The zinc–aluminum (Zn–Al) alloy coating with excellent wear and corrosion resistance was fabricated on the surface of magnesium substrate (AZ31) using thermal diffusion technique. The microstructure, phase constitution and chemical composition were investigated. The experimental observation exhibited that the interfacial microstructures were composed of network eutectic structures and lamellar eutectoid structures at heating temperature of 350 °C for holding time of 30 min under 0.1 MPa in a vacuum of 10⁻³ Pa. X-ray diffraction (XRD) pattern analysis identified that α-Mg, Mg₇Zn₃ and MgZn phases were formed in the diffusion layer. The interdiffusion of Mg and Al atoms were restricted by Mg–Zn intermetallic compounds (IMCs). The value of microhardness at the diffusion layer increased due to the formation of Mg–Zn eutectic phases. This technique is beneficial to improving poor wear and corrosion resistance of magnesium alloy.     

Quasicrystal-reinforced Mg alloys

The formation of the icosahedral phase (I-phase) as a secondary solidification phase in Mg–Zn–Y and Mg–Zn–Al base systems provides useful advantages in designing high performance wrought magnesium alloys. The strengthening in two-phase composites (I-phase + α-Mg) can be explained by dispersion hardening due to the presence of I-phase particles and by the strong bonding property at the I-phase/matrix interface. The presence of an additional secondary solidification phase can further enhance formability and mechanical properties. In Mg–Zn–Y alloys, the co-presence of I and Ca₂Mg₆Zn₃ phases by addition of Ca can significantly enhance formability, while in Mg–Zn–Al alloys, the co-presence of the I-phase and Mg₂Sn phase leads to the enhancement of mechanical properties. Dynamic and static recrystallization are significantly accelerated by addition of Ca in Mg–Zn–Y alloy, resulting in much smaller grain size and more random texture. The high strength of Mg–Zn–Al–Sn alloys is attributed to the presence of finely distributed Mg₂Sn and I-phase particles embedded in the α-Mg matrix.     

Effect of Y on the bio-corrosion behavior of extruded Mg–Zn–Mn alloy in Hank's solution

The bio-corrosion properties of Mg–Zn–Mn alloys with and without Y in Hank's solution at 37 °C were investigated by using electrochemical test and electrochemical impedance spectra (EIS). The results of open circuit potential (OCP) and polarization tests indicated that Y could reduce the cathodic current density. A passivative stage appeared in the Tafel curve of the Y containing magnesium alloy, indicating that a passivative film was formed on the surface of the Y containing magnesium alloy. EIS results showed that the Y containing alloy had higher charge transfer resistance and film resistance, but lower double layer capacity than the alloy without the Y element. The surface reaction product identification by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the surface corrosion products were hydroxide and phosphate (Mg₃Ca₃(PO₄)₄) for Mg–Zn–Mn alloy and phosphate (MgNaPO₄) for the Y containing Mg–Zn–Mn alloys. The XPS results also showed that a Y₂O₃ protective film was formed on the surface of the Y containing magnesium alloy which contributed mainly to the low cathodic current density and the high resistance.     

医用Mg-Zn-Ca-Mn合金在PBS模拟体液中的腐蚀行为

利用真空感应熔炼,采用金属模浇铸制备了Mg(100-x-y-z)-Znx-Cay-Mnz四元合金。使用光学显微镜、X射线衍射仪、扫描电镜及能谱仪对合金进行分析和表征。探讨了合金在PBS模拟体液中的腐蚀行为。结果表明,Ca、Zn及Mn原子的复合加入可显著细化合金的铸态显微组织;镁合金的腐蚀发生于晶粒内部,至晶界处终止;当加入2.0%的Zn和0.5%的Ca时,铸态合金的抗腐蚀性能最佳(平均腐蚀速率为0.77mm/a);当Zn、Ca含量均大于1%时,固溶时效态合金的腐蚀速率下降为铸态的1/2～1/4,表现出优异的耐蚀性;固溶时效处理可有效减少Mg2Ca相的体积分数,改善其分布,提高合金的耐蚀性能。     

Effect of solution heat treatment and hot extrusion on in vitro corrosion behavior of Mg−2Y−1Zn−0.4Zr−0.3Sr alloys as a potential biodegradable material

In this work, the influence of solution heat treatment and hot extrusion on the microstructure and corrosion behavior of as-cast Mg−2Y−1Zn−0.4Zr−0.3Sr alloys are systematically investigated via X-ray diffractometer, scanning electron microscope coupled with energy-dispersive X-ray spectroscopy, electrochemical testing, and mass loss testing. The as-cast alloy comprises α-Mg matrix and Mn₃Y₂Zn₃ (W-phase). Solution heat treatment and hot extrusion exert a conspicuous influence on the corrosion behavior of Mg−2Y−1Zn−0.4Zr−0.3Sr alloys through microstructure transformation. Both methods can remarkably improve corrosion resistance, and the as-extruded alloys exhibit an optimal corrosion resistance of 0.0432 mg ⋅ cm⁻² ⋅ h⁻¹ via mass loss testing. The three alloys exhibit a similar corrosion mechanism, which is based on galvanic corrosion. In the later stage of corrosion, a three-tier corrosion layer structure is formed. In combination with an array of analytical methods, the corrosion mechanisms of the three alloys are described in detail.