Recent advances using equal-channel angular pressing to improve the properties of biodegradable Mg-Zn alloys

Magnesium alloys are of considerable current interest for use as degradable implants due to their unique properties including biodegrad-ability,biocompatibility,low density and adequate mechanical properties.Nevertheless,there is a need to further improve these properties either by alloying or through the use of appropriate processing.Among the different biodegradable Mg alloys now in use,the Mg-Zn series are of special interest and have been the subject of many research investigations.This is primarily because Zn is an essential element for the human body in addition to its positive effects in improving the mechanical strength and lowering the degradation rate of the implant.The properties of Mg-Zn alloys may be further improved both through the addition of third and fourth alloying elements such as Ca,Ag,Sn or Sr and/or by thermo-mechanical processing where the latter is more environmentally and economically favorable.In practice,procedures based on the application of severe plastic deformation(SPD)are especially suited to produce fine-grained microstructures with improved mechanical,degradation and cell behavior.Equal-channel angular pressing(ECAP)is a popular SPD technique that has the capability of pro-ducing bulk materials that are sufficiently large for use as typical implants.Accordingly,this review is designed to provide a comprehensive summary of the research that has been undertaken on ECAP-processed biodegradable Mg-Zn alloys.

Corrosion characteristics of single-phase Mg-3Zn alloy thin film for biodegradable electronics

Biodegradable metals as electrodes, interconnectors, and device conductors are essential components in the emergence of transient electronics, either for passive implants or active electronic devices, especially in the fields of biomedical electronics. Magnesium and its alloys are strong candidates for biodegradable and implantable conducting materials because of their high conductivity and biocompatibility, in addition to their well-understood dissolution behavior. One critical drawback of Mg and its alloys is their considerably high dissolution rates originating from their low anodic potential, which disturbs the compatibility to biomedical applications. Herein, we introduce a single-phase thin film of a Mg-Zn binary alloy formed by sputtering, which enhances the corrosion resistance of the device electrode, and verify its applicability in biodegradable electronics. The formation of a homogeneous solid solution of single-phase Mg-3Zn was confirmed through X-ray diffraction and transmission electron microscopy. In addition, the dissolution behavior and chemistry was also investigated in various biological fluids by considering the effect of different ion species. Micro-tensile tests showed that the Mg-3Zn alloy electrode exhibited an enhanced yield strain and elongation in relation to a pure Mg electrode. Cell viability test revealed the high biocompatibility rate of the Mg-3Zn binary alloy thin film. Finally, the fabrication of a wireless heater demonstrated the integrability of biodegradable electrodes and highlighted the ability to prolong the lifecycle of thermotherapy-relevant electronics by enhancing the dissolution resistance of the Mg alloy.

Preparation of a single-phase Mg-6Zn alloy via ECAP-stimulated solution treatment

The solution of the intermetallic phase and the homogenization of composition are important for Mg alloy biomaterials.A single-phase Mg-6Zn alloy with the average grain size of about 20μm was prepared by ECAP processed for six passes at 320°C.It indicated that the ECAP could significantly promote the process of solid solution in Mg-Zn alloy.The results showed that complete dissolution of the intermetallic phase improved the corrosion resistance of Mg-6Zn alloy in 0.9%NaCl solution by turning the corrosion behavior into uniform corrosion and increased the hardness in combination with its smaller grain size.

Improved tensile properties of Mg-8Sn-1Zn alloy induced by minor Ti addition

In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and tensile tests. The results showed that Ti can decrease the secondary dendrite arm spacing(SDAS). The tensile strength of the Mg-8Sn-1Zn-Ti alloys is initially increased by increasing the Ti content up to 0.09 wt.%, but subsequently decreased for further increase of Ti content. The improved tensile properties are attributed to the decreased SDAS and refi ned Mg_2Sn phases, as well as the increased fraction of tin(Sn) segregated regions. The tensile fracture surface of the studied alloys shows mixed characteristics of cleavage and quasi-cleavage fracture. Adding Ti does not significantly change the fracture mode of the studied alloys.

Static and Dynamic Precipitation Behavior of the Al-20wt.% Zn Alloy

The static and dynamic precipitation behavior of solution-treated binary Al-20 wt.% Zn alloy is investigated via artificial aging, cold rolling and artificial aging combined with cold rolling. The solution-treated Al-Zn alloy exhibits high thermal stability during aging, and low densities of nano-sized Zn particles are precipitated along with AI grain boundaries after aging at 200℃ for 13 h. Compared with static precipitation, dynamic precipitation occurs more easily in the Al-Zn alloy. Zn clusters are obtained after cold rolling at an equivalent plastic strain of 0.6, and the size of the Zn phase reaches hundreds of nanometers when the strain is increased to 12.1. The results show that the speed of static precipitation can be significantly enhanced after the application of 2.9 rolling strain. Grain refinement and defects induced by cold rolling are considered to promote Zn precipitation. The hardness of Al-Zn alloy is also affected by static and dynamic precipitations.

Influence of Si Contents on the Microstructure Evolution and Mechanical Properties of Al-Mg-Si-Cu-Zn Alloys

The influence of different Si contents on the microstructure evolution and mechanical properties of Al⁃Mg⁃Si⁃Cu⁃Zn alloys was systematically studied using tensile testing,OM,SEM,EDS,and EBSD.The results indicate that the grain size of as⁃cast alloys was gradually reduced with the increase of the Si content,which mainly resulted from the formation of many iron⁃rich phases and precipitates during the casting process.During homogenization treatment,the plate⁃likeβ⁃AlFeSi phases in the alloy with a higher Si content easily transformed to the sphericalα⁃Al(FeMn)Si phases,which is helpful for improving the formability of alloys.The microstructure evolution of the alloys was also greatly dependent on the content of Si that the number density and homogeneous distribution level of precipitates in the final cold rolled alloys both increased with the increase of the Si content,which further provided a positive effect on the formation of fine recrystallization grains during the subsequent solution treatment.As a result,the yield strength,ultimate tensile strength,and elongation of the pre⁃aged alloys in the direction of 45°with respect to the rolling direction were all increased with increasing Si content.

In Vitro Evaluation of Effects of Mg-6Zn Alloy Extracts on Apoptosis of Intestinal Epithelial Cells

We assessed the in vitro cytotoxicity of Mg-6Zn alloy and analyzed the cell apoptosis rate and the expression of caspase-3 to evaluate the effects of Mg-6Zn alloy extracts on apoptosis of intestinal epithelial cells（IEC）-6. IEC-6 cells were cultured in different concentrations of Mg-6Zn alloy extracts（40%, 20%） and in the control group. The indirect effects of Mg-6Zn alloy on IEC-6 cells were studied by calculating the cell relative growth rate（RGR）, measuring the apoptosis of IEC-6 cells through flow cytometry, and investigating the expression of caspase-3 using real-time polymerase chain reaction. The experimental results show that the cytotoxicity of these extracts is Grade 0-1. The level of apoptosis in IEC-6 cells cultured in 40% Mg-6Zn alloy extracts is significantly higher than that in cells treated with 20% extract and the control group. The expression of caspase-3 is found to be up-regulated in the 40% extract as compared to 20% extract and the control group. Taken together, the data show that the Mg-6Zn alloy in 40% and 20% concentration extracts proves noncytotoxicity. But the 40% concentration of Mg-6Zn alloy extract can induce the apoptosis and the related caspase-3 expression in vitro.

Synergistic effect of gradient Zn content and multiscale particles on the mechanical properties of Al-Zn-Mg-Cu alloys with coupling distribution of coarse-fine grains

This study investigated the influence of graded Zn content on the evolution of precipitated and iron-rich phases and grain struc-ture of the alloys,designed and developed the Al–8.0Zn–1.5Mg–1.5Cu–0.2Fe(wt%)alloy with high strength and formability.With the increase of Zn content,forming the coupling distribution of multiscale precipitates and iron-rich phases with a reasonable matching ratio and dispersion distribution characteristics is easy.This phenomenon induces the formation of cell-like structures with alternate distribu-tion of coarse and fine grains,and the average plasticity–strain ratio(characterizing the formability)of the pre-aged alloy with a high strength is up to 0.708.Results reveal the evolution and influence mechanisms of multiscale second-phase particles and the corresponding high formability mechanism of the alloys.The developed coupling control process exhibits considerable potential,revealing remarkable improvements in the room temperature formability of high-strength Al–Zn–Mg–Cu alloys.

Improving the strength and SCC resistance of an Al-5Mg-3Zn alloy with low-angle grain boundary structure

The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.

Behavior and influence of Pband Biin Ag-Cu-Zn brazing alloy

The effects of trace content of Pb and Bi elements on the spreading property and the strength of brazed joints of Ag Cu Zn filler metal have been studied. The results show that Pb has little effect on both above properties, and Bi has remarkable influence on the spreading property but little effect on the strength of brazed joint. Pb and Bi dissolve into the Ag Cu Zn matrix and will melt and gather at lower temperature when that alloy is being heated. Therefore a liquid forms on the surface of the Ag Cu Zn alloy and overlays the melting alloy, then keeps the filler metal away from the materials being joined, and so decreases the spreading property.

Design biodegradable Zn alloys: Second phases and their significant influences on alloy properties

Alloying combined with plastic deformation processing is widely used to improve mechanical properties of pure Zn.As-cast Zn and its alloys are brittle.Beside plastic deformation processing,no effective method has yet been found to eliminate the brittleness and even endow room temperature super-ductility.Second phase,induced by alloying,not only largely determines the ability of plastic deformation,but also influences strength,corrosion rate and cytotoxicity.Controlling second phase is important for designing biodegradable Zn alloys.In this review,knowledge related to second phases in biodegradable Zn alloys has been analyzed and summarized,including characteristics of binary phase diagrams,volume fraction of second phase in function of atomic percentage of an alloying element,and so on.Controversies about second phases in Zn-Li,Zn-Cu and Zn-Fe systems have been settled down,which benefits future studies.The effects of alloying elements and second phases on microstructure,strength,ductility,corrosion rate and cytotoxicity have been neatly summarized.Mg,Mn,Li,Cu and Ag are recommended as the major alloying elements,owing to their prominent beneficial effects on at least one of the above properties.In future,synergistic effects of these elements should be more thoroughly investigated.For other nutritional elements,such as Fe and Ca,refining second phase is a matter of vital concern.

Production of high strength Al-Zn-Mg-Cu alloys by spray forming process

High strength Al Zn Mg Cu alloys were produced by spray forming process, and compacted by hot extrusion. The results show that the as deposited billets have fine grained microstructure and low porosity. After heat treatment, mechanical properties increase greatly: tensile strength up to 754 MPa, yield strength up to 722 MPa, fracture elongation up to 8%, and elastic modulus up to 72 GPa, respectively. [

Effect of crystal orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy

Microstructure and crystallographic orientation of directionally solidified Mg-4 wt% Zn alloy were characterized by X-ray computed tomography （XCT） and electron backscatter diffraction （EBSD） in this study. Results reveal that Mg-4 wt% Zn alloy with dendritic microstructure exhibits typical { 0002} basal texture along growth direction. Based on this, the effect of grain orientation on corrosion behavior of directionally solidified Mg-4 wt% Zn alloy in 0.9 wt% NaCl solution was investigated. Result shows that {0002} oriented planes have better corrosion resistance than {1120} and {1010 } ones, which is attributed to a synergistic effect of surface energy, atomic packing density and the stability of oxidation film,2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology,

In Vitro Evaluation of the Feasibility of Commercial Zn Alloys as Biodegradable Metals

In this work, three widely used commercial Zn alloys （ZA4-1, ZA4-3, ZA6-1 ） were purchased and pre- pared by hot extrusion at 200℃. The microstructure, mechanical properties, corrosion behaviors, biocompatibility and hemocompatibility of Zn alloys were studied with pure Zn as control, Commercial Zn alloys demonstrated increased strength and superb elongation compared with pure Zn. Accelerated corrosion rates and uniform corrosion morphologies were observed in terms of commercial Zn alloys due to galvanic effects between Zn matrix and α-Al phases. 100% extracts of ZA4-1 and ZA6-1 alloys showed mild cytotoxicity while 50% extracts of all samples displayed good biocompatibility. Retardant cell cycle and inhibited stress fibers expression were observed induced by high concentration of Zn^2＋ releasing during corrosion. The hemolysis ratios of Zn alloys were lower than 1% while the adhered platelets showed slightly activated morphologies. In general, commercial Zn alloys possess promising mechanical properties, appropriate corrosion rates, significantly improved biocompatibility and good hemocompatibility in comparison to pure Zn. It is feasible to develop biodegradable metals based on commercial Zn alloys.

Synchronously Improving the Thermal Conductivity and Mechanical Properties of Al–Si–Fe–Mg–Cu–Zn Alloy Die Castings Through Ultrasonic-Assisted Rheoforming

An ultrasonic vibration-assisted air-cooled stirring rod process(ACSR+UV)was used to efficiently prepare a large-volume semisolid slurry with a mass of more than 40 kg.A low-cost Al–Si–Fe–Mg–Cu–Zn die-casted alloy with high thermal conductivity,high plasticity and medium strength was developed.The alloy was used to manufacture large,thin-walled parts for 5 G base stations by using the ACSR+UV rheological die-casting(ACSR+UV R-DC)process.Investigations were performed on the microstructure,porosity,mechanical properties,fracture behaviour and thermal conductivity of the ACSR+UV R-DC alloy,which was then compared to traditionally die-casted(T-DC)and ACSR R-DC alloys.The mechanisms for the microstructural refinement and enhancement of the mechanical and thermal conductivity performances of the ACSR+UV R-DC alloy were also analysed.The results showed that the ACSR+UV process increased the nucleation rate of the melt due to the increase in the nucleation area and the generation of cavitation bubbles.A radial-and an axial-forced convection was also generated inside the melt under the combined effects of acoustic flow and mechanical stirring,thereby homogenising the melt composition field and the temperature field.Therefore,the ACSR+UV R-DC process not only refined the primaryα-Al(α_(1)-Al),the eutectic silicon and the secondaryα-Al(α_(2)-Al),but also greatly improved the morphology and the distribution of the β-Al5FeSi phase.The mechanical properties of the ACSR+UV R-DC alloy were higher than those of the T-DC and the ACSR R-DC alloys.Compared to the T-DC alloy,the ultimate tensile strength,elongation and yield strength of the ACSR+UV R-DC alloy were increased by 34%,122%and 19%,respectively.This was because the ACSR+UV R-DC technique gave the alloy the characteristics of high density,fine sphericalα1-Al grain and a fine and uniform β-phase,which improved the fracture behaviour of the alloy.The thermal conductivity of the ACSR+UV R-DC alloy was 184 W/(m K),which was 10.2%and 3.4%higher than that of T-DC and ACSR R-DC alloys,respectively.This was because the refined eutectic silicon and β phases in the ACSR+UV R-DC alloy facilitated an easier electron flow through the eutectic region,and the decrease in porosity increased the effective area of heat conduction.

Processing of a Novel Zn Alloy Micro-Tube for Biodegradable Vascular Stent Application

In recent years, zinc based alloys as a new biodegradable metal material aroused intensive interests. However, the processing of Zn alloys micro-tubes （named slender-diameter and thin-walled tubes） is very difficult due to their HCP crystal structure and unfavorable mechanical properties. This study aimed to develop a novel technique to produce micro-tube of Zn alloy with good performance for biodegrad- able vascular stent application. In the present work, a processing method that combined drilling, cold rolling and optimized drawing was proposed to produce the novel Zn-5Mg-1Fe （wt%） alloy micro- tubes. The micro-tube with outer diameter of 2.5 mm and thickness of 130 μm was fabricated by this method and its dimension errors are within 10 μm. The micro-tube exhibits a fine and homogeneous microstructure, and the ultimate tensile strength and ductility are more than 220 MPa and 20% respectively. In addition, the micro-tube and stents of Zn alloy exhibit superior in vitro corrosion and expansion performance. It could be concluded that the novel Zn alloy micro-tube fabricated by above method might be a promising candidate material for biodegradable stent.

Microstructures, mechanical properties and in vitro corrosion behavior of biodegradable Zn alloys microalloyed with Al, Mn, Cu, Ag and Li elements

In this work,Zn microalloyed with Al,Mn,Cu,Ag and Li was cast,annealed and extruded.The results showed that addition of multiple trace elements causes significant change in the microstructures,mechanical properties and corrosion behavior of Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag(^(1)ZM),Zn-0.1Al-0.1Mn-0.1Cu0.1Ag-0.1Li(^(2)ZM-0.1Li)and Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag-0.35Li(^(3)ZM-0.35Li)alloys.Two ternary phases with the approximate compositions of Al_(13)Mn_(3)Zn_(34) and Al_(10)MnZn_(89) phases are formed in the casting and annealing processes of these alloys,respectively.Wavyβ-LiZn_(4) lamellae that have not been extensively reported are precipitated from the primary Zn dendrites in the casting process of ZM-0.35Li alloy.Also,Zn laths are precipitated from the eutecticβ-LiZn_(4) phase in the annealing process of ZM-0.35Li alloy.The above-mentioned phases are crushed or elongated in the as-extruded alloys,which play an important role in improving the strength of the alloys.All the as-extruded alloys have typical(0001)basal texture,accompanied with relatively low{0001}<1120>slip and high{1012}<1011>twinning Schmid factors,which are advantageous and disadvantageous to the strength enhancement of the alloys,respectively.All the as-cast alloys exhibit poor mechanical properties,especially low ductility.The as-extruded ZM alloy exhibits ultrahigh ductility,with an elongation of up to 82.2%±2.94%.The as-extruded ZM0.35Li alloy shows the best comprehensive mechanical properties,with yield strength,ultimate tensile strength,elongation and hardness of 380±1.6 MPa,449±7.4 MPa,62.3%±4.63%and 98±1.4 HV,respectively.Electrochemical corrosion rates of the ZM,ZM-0.1Li and ZM-0.35Li alloys are 0.241±0.004,0.206±0.006 and 0.189±0.008 mm/year,respectively.In vitro immersion corrosion rates(after 26 d in SBF solution)of them are 0.134±0.005,0.125±0.004 and 0.121±0.003 mm/year,respectively.The as-extruded ZM-0.35Li alloy exhibits the best corrosion resistance.

Electrochemical and corrosion behaviors of the wrought Mg–Y–Zn based alloys with high Y/Zn mole ratios

The electrochemical behaviors and corrosion resistance of the wrought Mg–Y–Zn based alloys with high Y/Zn mole ratio have been investigated in details.The results show that the corrosion resistance of the investigated Mg–Y–Zn based alloys are dependent on the modified arrangement of LPSO phase by adjusting Y/Zn mole ratios.Increasing the Y/Zn mole ratio not only greatly decreases the size of LPSO phase plates,but also leads to the precipitation of Mg_(24)Y_(5) phase.The corrosion rate of Mg–Y–Zn based alloys greatly increases from 7.4 mg·cm^(−2)·day^(−1) to 11.3 mg·cm^(−2)·day^(−1) with increasing the Y/Zn mole ratio up to 3.It should be attributed to the decreasing size of LPSO phase plates as cathodes,further increasing the hydrogen evolution kinetics.The related corrosion mechanism is discussed in details.

Pseudo-copper Ni–Zn alloy catalysts for carbon dioxide reduction to C_(2) products

Electrocatalytic CO_(2) reduction reaction(CO_(2)RR)to obtain C_(2) products has drawn widespread attentions.Copper-based materials are the most reported catalysts for CO_(2) reduction to C_(2) products.Design of high-efficiency pseudo-copper catalysts according to the key characteristics of copper(Cu)is an important strategy to understand the reaction mechanism of C_(2) products.In this work,density function theory(DFT)calculations are used to predict nickel–zinc(NiZn)alloy catalysts with the criteria similar structure and intermediate adsorption property to Cu catalyst.The calculated tops of 3d states of NiZn3(001)catalysts are the same as Cu(100),which is the key parameter affecting the adsorption of intermediate products.As a result,NiZn3(001)exhibits similar adsorption properties with Cu(100)on the crucial intermediates*CO_(2),*CO and*H.Moreover,we further studied CO formation,CO hydrogenation and C–C coupling process on Ni–Zn alloys.The free energy profile of C_(2) products formation shows that the energy barrier of C_(2) products formation on NiZn3(001)is even lower than Cu(100).These results indicate that NiZn3 alloy as pseudo-copper catalyst can exhibit a higher catalytic activity and selectivity of C_(2) products during CO_(2)RR.This work proposes a feasible pseudo-copper catalyst and provides guidance to design high-efficiency catalysts for CO_(2)RR to C_(2) or multi-carbon products.

Enhancing Mechanical Properties of Mg–6Zn Alloy by Deformation-Induced Nanoprecipitation

We presented the solution of deformation-induced precipitation after homogenization to enhance the mechanical properties of Mg–6 Zn alloys.The results show that the improved strategy exhibits more effective strengthening role than grain refinement methods based on low-temperature severe plastic deformation under the same strain.The low-temperature deformation with larger extrusion ratio results in massive nano-sized precipitates and excellent mechanical properties with the yield strength of 355 MPa and the ultimate tensile strength of 405 MPa.The increased mechanical properties are strong and tough enough to resist the stress and not be worn away when the alloy nail penetrates through the pig thigh bone,potentially extending more orthopedic surgery applications for Mg–Zn alloys.