In vitro performance of a biodegradable zinc alloy adjustable-loop cortical suspension fixation for anterior cruciate ligament reconstruction

Anterior cruciate ligament(ACL)injuries of the knee are one of the most common and serious athletic injuries.The widely used cortical suspension fixation buttons for ligament reconstruction are permanent implants,particularly those made from conventional steel or titanium alloys.In this study,a biodegradable Zn-0.45Mn-0.2Mg(ZMM42)alloy with the yield strength of 300.4 MPa and tensile strength of 329.8 MPa was prepared through hot extrusion.The use of zinc alloys in the preparation of cortical suspension fixation buttons was proposed for the first time.After 35 d of immersion in simulated body fluids,the ZMM42 alloy fixation buttons were degraded at a rate of 44μm/a,and the fixation strength was retained(379.55 N)in the traction loops.Simultaneously,the ZMM42 alloy fixation buttons exhibited an increase in MC3T3-E1 cell viability and high antibacterial activity against Escherichia coli and Staphylococcus aureus.These results reveal the potential of biodegradable zinc alloys for use as ligament reconstruction materials and for developing diverse zinc alloy cortical suspension fixation devices.

Effectiveness Evaluation Study of Self-made Zinc Alloy Sacrificial Anode under Chloride Salt Erosion Environment

To investigate the effectiveness of self-made zinc alloy sacrificial anode material for the protection of reinforcement in concrete under chlorine salt erosion environment,salt solution immersion corrosion and electromigration accelerated corrosion tests were used to evaluate the effectiveness of self-made zinc alloy anode with the help of relevant cathodic protection guidelines and evaluation criteria for the corrosion of reinforcement in concrete.The results showed that the protection was effective because the potential of the zinc alloy anode protection steel bar in the salt solution satis?ed the“-780 mV(SCE)”validity criterion.The self-corrosion potential(E_(corr))of the sacri?cial anode protection steel in concrete was greater than-276 mV,and the protective current density of the zinc alloy anode was 1-3μA·cm^(-2),which met the standards of EN12696-2000,further indicating that the self-made zinc alloy sacri?cial anode had a good protection combining with the polarization resistance and the appearance of the corroded surface of the steel in concrete.The microscopic morphology of the corroded surface and the composition of the corrosion products indicates that the mortar of the self-made zinc alloy anode has a lower pH than the imported anodes,so the long-term protection of the selfmade zinc alloy sacri?cial anode needs to be further improved.

Novel zinc alloys for biodegradable surgical staples

BACKGROUND The development of biodegradable surgical staples is desirable as non-biodegradable Ti alloy staples reside in the human body long after wound healing, which can cause allergic/foreign-body reactions, adhesion, or other adverse effects. In order to develop a biodegradable alloy suitable for the fabrication of surgical staples, we hypothesized that Zn, a known biodegradable metal, could be alloyed with various elements to improve the mechanical properties while retaining biodegradability and biocompatibility. Considering their biocompatibility, Mg, Ca, Mn, and Cu were selected as candidate alloying elements, alongside Ti, the main material of clinically available surgical staples.AIM To investigate the in vitro mechanical properties and degradation behavior and in vivo safety and feasibility of biodegradable Zn alloy staples.METHODS Tensile and bending tests were conducted to evaluate the mechanical properties of binary Zn alloys with 0.1–6 wt.% Mg, Ca, Mn, Cu, or Ti. Based on the results,three promising Zn alloy compositions were devised for staple applications(wt.%): Zn-1.0Cu-0.2Mn-0.1Ti(Zn alloy 1), Zn-1.0Mn-0.1Ti(Zn alloy 2), and Zn-1.0Cu-0.1Ti(Zn alloy 3). Immersion tests were performed at 37℃ for 4 wk using fed-state simulated intestinal fluid(Fe SSIF) and Hank’s balanced salt solution(HBSS). The corrosion rate was estimated from the weight loss of staples during immersion. Nine rabbits were subjected to gastric resection using each Zn alloy staple, and a clinically available Ti staple was used for another group of nine rabbits. Three in each group were sacrificed at 1, 4, and 12 wk post-operation.RESULTS Additions of ≤1 wt.% Mn or Cu and 0.1 wt.% Ti improved the yield strength without excessive deterioration of elongation or bendability. Immersion tests revealed no gas evolution or staple fracture in any of the Zn alloy staples. The corrosion rates of Zn alloy staples 1, 2, and 3 were 0.02 mm/year in HBSS and 0.12, 0.11, and 0.13 mm/year, respectively, in Fe SSIF. These degradation times are sufficient for wound healing. The degradation rate is notably increased under low pH conditions. Scanning electron microscopy and energy dispersive spectrometry surface analyses of the staples after immersion indicated that the component elements eluted as ions in Fe SSIF, whereas corrosion products were produced in HBSS, inhibiting Zn dissolution. In the animal study, none of the Zn alloy staples caused technical failure, and all rabbits survived without complications. Histopathological analysis revealed no severe inflammatory reaction around the Zn alloy staples.CONCLUSION Staples made of Zn-1.0Cu-0.2Mn-0.1Ti, Zn-1.0Mn-0.1Ti, and Zn-1.0Cu-0.1Ti exhibit acceptable in vitro mechanical properties, proper degradation behavior,and in vivo safety and feasibility. They are promising candidates for biodegradable staples.

Effect of Yttrium on Aging Resistance of Zinc Alloy ZA-27

By metalloscopy,scanning electron microscope,X-ray diffraction,electron probe,salt water erosion and hot steam erosion,the microstructures and the aging resistance of zinc alloy ZA-27 with different contents of yttrium were studied. The results show that with optimum addition of yttrium in the alloy ZA-27 the fine YAl_3 phase forms. The fine YAl_3 granules can act as the condensation nuclei of α phase and the number of the α phase′s nuclei increases greatly and the growth of the nuclei comes in for restrict during the crystallization and the alloy′s grains become fine and the segregation reduces. In addition,yttrium also combines with zinc and the fine dispersion Y-Zn phase forms which improves grain boundary conditions and the alloy′s aging resistance. But when the content of yttrium is overmuch some YAl_3 granules grow to be lumpy,so the fine and close texture of the alloy′s boundaries is damaged and the proportion of the interface among the phases increase which brings a decline in the alloy′s resistance to corrosion.

Microstructure and Eutectic Transformation of Squeeze Casting Alumina/Zinc Alloy Composites

Alumina fiber-reinforced zinc alloy composites were manufactured by squeeze casting, and the eutectic transformation in the zinc alloy composites was studied. The results indicate that there is a fine and close interface between the fiber and the matrix, and the alloy elements can improve the combination between the fibers and the matrix in the composites. The fibers can serve as the sites of heterogeneous nucleation of the eutectic in the zinc alloy during the solidification of the composites, and the silicon on the interface between the fibers and the matrix plays a leading role during the coupled growth of the eutectic so that the eutectic transformation of the composites consists of Al-Si eutectic transformation and Zn-AI eutectic transformation.

Effect of Cu addition on microstructure and properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy

To improve the strength,hardness and heat resistance of Mg-Zn based alloys,the effects of Cu addition on the as-cast microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy were investigated by means of Brinell hardness measurement,scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),XRD and tensile tests at room and elevated temperatures.The results show that the microstructure of as-cast Mg-10Zn-5Al-0.1Sb alloy is composed of α-Mg,t-Mg32(Al,Zn)49,φ-Al2Mg5Zn2 and Mg3Sb2 phases.The morphologies of these phases in the Cu-containing alloys change from semi-continuous long strip to black herringbone as well as particle-like shapes with increasing Cu content.When the addition of Cu is over 1.0wt.%,the formation of a new thermally-stable Mg2Cu phase can be observed.The Brinell hardness,room temperature and elevated temperature strengths firstly increase and then decrease as the Cu content increases.Among the Cu-containing alloys,the alloy with the addition of 2.0wt.% Cu exhibits the optimum mechanical properties.Its hardness and strengths at room and elevated temperatures are 79.35 HB,190MPa and 160MPa,which are increased by 9.65%,21.1% and 14.3%,respectively compared with those of the Cu-free one.After T6 heat treatment,the strengths at room and elevated temperatures are improved by 20% and 10%,respectively compared with those of the as-cast alloy.This research results provide a new way for strengthening of magnesium alloys at room and elevated temperatures,and a method of producing thermally-stable Mg-10Zn-5Al based high zinc magnesium alloys.

Effect of magnesium on the aluminothermic reduction rate of zinc oxide obtained from spent alkaline battery anodes for the preparation of Al–Zn–Mg alloys

The aluminothermic reduction of zinc oxide（ZnO） from alkaline battery anodes using molten Al may be a good option for the elaboration of secondary 7000-series alloys. This process is affected by the initial content of Mg within molten Al, which decreases the surface tension of the molten metal and conversely increases the wettability of ZnO particles. The effect of initial Mg concentration on the aluminothermic reduction rate of ZnO was analyzed at the following values： 0.90wt%, 1.20wt%, 4.00t%, 4.25wt%, and 4.40wt%. The ZnO particles were incorporated by mechanical agitation using a graphite paddle inside a bath of molten Al maintained at a constant temperature of 1123 K and at a constant agitation speed of 250 r/min, the treatment time was 240 min and the ZnO particle size was 450？500 mesh. The results show an increase in Zn concentration in the prepared alloys up to 5.43wt% for the highest initial concentration of Mg. The reaction products obtained were characterized by scanning electron microscopy and X-ray diffraction, and the efficiency of the reaction was measured on the basis of the different concentrations of Mg studied.

STUDIES OF LOW-CONCENTRATION CHROMATE PASSIVE FILM FOR ZINC-BASED ALLOY COATED STEEL WIRES

The corrosion resistance of a low concentration chromate passive film for zinc based alloy coated steel wires was assessed by salt spray and electrochemical corrosion tests. XPS and AES analyses showed that the composition of such chromate passive film was S 5 5, Na 3 4, C 11 8, Ti 7 9, O 41 6, Cr 13 7, Zn 16 0.

Catalytic Effect of SCN^- on Electrodeposition of Zinc-Nickle Alloy

The electrodeposition of zinc nickle alloy was obtained on a copper cathode of 1×1cm 2. The deposited alloys are quantitatively analyzed by atomic absorption spectrometry. The morphology of the deposits was observed by means of scanning electron microscopy(SEM).We observed that the electrodeposition of zinc nickle alloy is an anomalous codeposition. The catalytic effects of SCN - on the electrochemical behavior of Ni deposition and hydrogen discharge are obvious. SEM analysis shows that the surface morphology of the coating appears to be more compact and homogeneous with the increase of SCN - concentration.

TENSILE PROPERTIES AND CREEP RESISTANCE OF AZ91 ALLOY CONTAINING ANTIMONY

Small amount of antimony addition to the Mg-9Al-0.8Zn-0.2Mn(AZ91) alloy results in the obvious increase of tensile strength at both ambient and elevated temperatures. The creep resistance at the temperatures up to 200°C is also improved significantly by antimony addition. Microstructural observations revealed that the addition of antimony modifies morphology of the β(Mg17Al12) phase and causes the formation of some rod-shaped precipitates Mg3Sb2 at grain boundaries. These precipitates have high thermal stability and play an important role for strengthening grain boundaries at elevated temperatures.

QUANTITATIVE CHARACTERIZATION OF STRESS-STRAIN HYSTERESIS LOOPS OF Cu-Zn-Al SHAPE MEMORY ALLOY

A six-parameter mathematical model was introduced to simulate the stress-strain hysteresis and the sinner hysteresis of polycrystalline shape memory alloys (SMAs). By the comparison with experiments of Cu-Zn-Al SMA, it was shown that the model could be used to calculate the stress-strain relations with rather good accuracy. Moreover, it was found that the six parameters introduced in this paper represented the characteristics of the stress-strain hysteresis of polycrystalline SMAs and could be used to characterize the hysteresis quantitatively.

ON THE A/D TYPE TWIN BOUNDARY IN 18R MARTENSITE OF A Cu-Zn-Al ALLOY

The A/D type twin boundary in a Cu-Zn-Al shape memory alloy appears curved under TEM and shows irregularly serrated steps under HREM. Crystallographic analysis shows that the macroscopic curve results from non-self-accommodation of the boundary, the deviation from exact twin orientation and a preferential orientation for lower boundary energy.

Second phase refining induced optimization of Fe alloying in Zn:Significantly enhanced strengthening effect and corrosion uniformity

Many non-toxic alloying elements,such as Fe,Ca,and Sr,have negligible solid solubilities in Zn matrix,leading to formation of coarse second phase particles.They exhibit low strengthening effects but highly detrimental to ductility.So refining second phase is a common pursuit for Zn alloys.The present paper takes Zn-0.3Fe alloy suffered from coarse FeZn_(13) second phase particles as a touchstone to testify microstructure refining effect through solidification with an accelerated speed and multi-pass rolling.FeZn_(13) particles are refined from 24 to 2μm,and Zn grains are refined to 5μm.As a result,the strengthening effect of Fe is enhanced significantly,with yield strength and the ultimate tensile strength of the alloy increased from 132 to 218 MPa and from 159 to 264 MPa,respectively.Furthermore,corrosion non-uniformity and penetration are much alleviated.These results show that microstructure refinement,especially on coarse intermetallic second phases,has a great potential to improve mechanical and degradation properties of biodegradable Zn alloys.

Effect of Cerium on Mechanical Properties and Morphology of ZZn4-1 Alloy

Effect of the addition of cerium in appropriate amount on the mechanical properties and morphology of ZZn4-1 alloy was investigated. In the case of samples collected from metal mould, the results show that the addition of cerium in appropriate amount can increase tensile strength and HE hardness, and can refine the microstructure of ZZn4-1 alloy considerably. In the case of samples collected from pressure die-casting, the addition of cerium in appropriate amount can refine the primary eta-phase and the eutectic structure of pressure die-casting and improve mechanical and processing properties of the alloy.

Effects of solidification and melt treatment on microstructure and mechanical properties of cast ZA27 alloy

The effects of solidification rate, modifications and pouring temperature on the microstructure and mechanical properties of casting zinc aluminum alloy ZA27 have been investigated. The results show that the number and distribution of pores are the key factors affecting the mechanical properties of ZA27. A slow solidification rate is beneficial to the ductility, while a rapid solidification rate improves the tensile strength of alloy basically. Among the modification agents RE, Sb Te, Sb Te RE and Sb Te Ti B, the addition of Sb Te to melt results in the best modified microstructure. The optimum pouring temperature for ZA27 is approximately 550?℃.

Influence of La and RE on the Underside Shrinkage of ZA27 Alloy

The effect of pure La and mischmetal(RE) on underside shrinkage of ZA27 alloy with cooling rate of 32 min-1 was investigated. The results show that the volumes of the underside shrinkage and the total shrinkage(underside shrinkage plus internal shrinkage) of the alloy decrease as the content of La or RE increases. When the contents of La and RE exceed 03%04%(mass fraction) respectively, the underside shrinkage is eliminated and the internal shrinkage moves upwards gradually. The mechanism that the underside shrinkage is eliminated is the falling of La and RE compounds and their accumulation on the bottom of the ZA27 alloy sample. Since La and RE can not effectively prevent phases(Al base solid solution) in the alloy from rising, the internal shrinkage is still close to the bottom of the ZA27 sample.

Microstructure and mechanical properties of the micrograined hypoeutectic Zn–Mg alloy

A biodegradable Zn alloy, Zn-1.6Mg, with the potential medical applications as a promising coating material for steel components was studied in this work. The alloy was prepared by three different procedures： gravity casting, hot extrusion, and a combination of rapid solidification and hot extrusion. The samples prepared were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. Vickers hardness, tensile, and compressive tests were performed to determine the samples＇ mechanical properties. Structural examination reveals that the average grain sizes of samples prepared by gravity casting, hot extrusion, and rapid solidification followed by hot extrusion are 35.0, 9.7, and 2.1 μm, respectively. The micrograined sample with the finest grain size exhibits the highest hardness（Hv = 122 MPa）, compressive yield strength（382 MPa）, tensile yield strength（332 MPa）, ultimate tensile strength（370 MPa）, and elongation（9%）. This sample also demonstrates the lowest work hardening in tension and temporary softening in compression among the prepared samples. The mechanical behavior of the samples is discussed in relation to the structural characteristics, Hall-Petch relationship, and deformation mechanisms in fine-grained hexagonal-close-packed metals.

Improved strength and ductility of high alloy containing Al–12Zn–3Mg–2.5Cu alloy by combining non-isothermal step rolling and cold rolling

Al-12Zn-3Mg-2.5Cu alloy was prepared using a liquid metallurgy route under the optimized conditions. A sample cut from the ingot was rolled non-isothermally from 400℃ to 100℃ in 100℃ steps, with 15% reduction in thickness; it was then cold rolled isothermally at room temperature for 85% reduction. The cold-rolled alloys were characterized by electron microscopy, hardness test, and tensile test to elucidate their structural evolution and evaluate their mechanical behavior. In the results, the cast alloy consists of a-aluminum and various intermetallic compounds. These compounds are segregated along the grain boundaries, which makes the alloy difficult to roll at room tem- perature. The combined effect of non-isothermal step rolling and cold rolling results in the nano/microsized compounds distributed uniformly in the matrix. The hardness is substantially increased after rolling. This increase in hardness is attributed to the ultra-fine grain size, fine-scale intermetallic compounds, and structural defects （e.g., dislocations, stacking faults, and sub-grains）. The ultimate tensile strength of the rolled alloy is approximately 628 MPa with 7% ductility.

Effect of homogenization process on the hardness of Zn-Al-Cu alloys

The effect of a homogenizing treatment on the hardness of as-cast Zn–Al–Cu alloys was investigated. Eight alloy compositions were prepared and homogenized at 350 °C for 180 h, and their Rockwell 'B' hardness was subsequently measured. All the specimens were analyzed by X-ray diffraction and metallographically prepared for observation by optical microscopy and scanning electron microscopy. The results of the present work indicated that the hardness of both alloys(as-cast and homogenized) increased with increasing Al and Cu contents; this increased hardness is likely related to the presence of the θ and τ′ phases. A regression equation was obtained to determine the hardness of the homogenized alloys as a function of their chemical composition and processing parameters, such as homogenization time and temperature, used in their preparation.

APPLICATION OF GENETIC NEURAL NETWORK IN Zn-27 % Al-Mg ALLOY

A genetic neural net work m odel about design of Mg content in the alloy , based on tested databetw een Mg and tensile intensity or elongation in Zn 27 % Al alloy , has been established . Theresult has sho w n that the genetic neural netw ork is a better an d m ore applied method for m a terials design than the regress analysis .