Structural,mechanical and electronic properties of precipitates in Mg−Zn alloys

To accelerate the development and design of magnesium(Mg)alloys,the structural and mechanical properties of important precipitates in Mg−Zn alloys were studied by experiments and density functional theory.The nano-indentation tests revealed that the hardness of the precipitates initially increased and then decreased with increasing Zn content,and was significantly higher than that of pure Mg and Zn.The calculation results revealed that the precipitates stability initially increased and then decreased with increasing Zn concentration.The bulk moduli of the precipitates increased,whereas their shear and Young’s moduli initially increased and then decreased with increasing Zn content.The decreasing order of ductility for these compounds is MgZn_(2)>Mg_(21)Zn_(25)>Mg_(2)Zn_(11)>Mg_(4)Zn_(7).The surface profiles of the compounds revealed that they are obvious anisotropy.Both the degree of covalency and bond length of covalent bonds initially increased and then decreased with increasing Zn content.

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.

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.

Machine learning design of 400 MPa grade biodegradable Zn-Mn based alloys with appropriate corrosion rates

The commonly used trial-and-error method of biodegradable Zn alloys is costly and blindness.In this study,based on the self-built database of biodegradable Zn alloys,two machine learning models are established by the first time to predict the ultimate tensile strength(UTS)and immersion corrosion rate(CR)of biodegradable Zn alloys.A real-time visualization interface has been established to design Zn-Mn based alloys;a representative alloy is Zn-0.4Mn-0.4Li-0.05Mg.Through tensile mechanical properties and immersion corrosion rate tests,its UTS reaches 420 MPa,and the prediction error is only 0.95%.CR is 73μm/a and the prediction error is 5.5%,which elevates 50 MPa grade of UTS and owns appropriate corrosion rate.Finally,influences of the selected features on UTS and CR are discussed in detail.The combined application of UTS and CR model provides a new strategy for synergistically regulating comprehens-ive properties of biodegradable Zn alloys.

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.

Effect of cold rolling deformation on microstructure evolution and mechanical properties of spray formed Al−Zn−Mg−Cu−Cr alloys

The impact of cold rolling deformation,which was introduced after solid solution and before aging treatment,on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu−0.13Cr(wt.%)alloy,was investigated.SEM,TEM,and EBSD were used to analyze the microstructures,and tensile tests were conducted to assess mechanical properties.The results indicate that the D1-T6 sample,subjected to 25%cold rolling deformation,exhibits finer grains(3.35μm)compared to the D0-T6 sample(grain size of 4.23μm)without cold rolling.Cold rolling refines the grains that grow in solution treatment.Due to the combined effects of finer and more dispersed precipitates,higher dislocation density and smaller grains,the yield strength and ultimate tensile strength of the D1-T6 sample can reach 663 and 737 MPa,respectively.In comparison to the as-extruded and D0-T6 samples,the yield strength of the D1-T6 sample increases by 415 and 92 MPa,respectively.

Improvement of microstructure and mechanical properties of Al−Cu−Li−Mg−Zn alloys through water-cooling centrifugal casting technique

The microstructure and mechanical properties of as-cast Al−Cu−Li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated.Experimental results demonstrated that compared with the gravity casting technique,the water-cooling centrifugal casting technique significantly reduces porosity,refinesα(Al)grains and secondary phases,modifies the morphology of secondary phases,and mitigates both macro-and micro-segregation.These improvements arise from the synergistic effects of the vigorous backflow,centrifugal field,vibration and rapid solidification.Porosity and coarse plate-like Al13Fe4/Al7Cu2Fe phase result in the fracture before the gravity-cast alloy reaches the yield point.The centrifugal-cast alloy,however,exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%.This high yield strength is attributed to solid solution strengthening(SSS)of 225.3 MPa,and grain boundary strengthening(GBS)of 35.7 MPa.Li contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^(-1).The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior,refining the microstructure and changing the morphology of secondary phases.

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.

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.

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.

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al Zn Mg Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al Zn Mg Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.

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. [

Effects of high-pressure heat treatment on the solid-state phase transformation and microstructures of Cu_(61.13)Zn_(33.94)Al_(4.93) alloys

The phase transformation activation energy of the Cu61.13Zn33.94A14.93 alloys, which were treated at 4 GPa and 700 ℃ for 15 minutes, was calculated by means of differential scanning calorimetry curves obtained at various heating and cooling rates. Then, the effects of high-pressure heat treatments on the solid-state phase transformation and the microstructures of Cu61.13Zn33.94A14.93 alloys were investigated. The results show that high-pressure heat treatments can refine the grains and can change the preferred orientation from （111） to （200） of α phase. Compared with the as-cast alloy, the sample with high-pressure heat treatment has finer grains, lower β＇→β and/β→β＇ transformation temperature and activation energy. Furthermore, we found that high cooling rate favours the formation of fine needle-like α phase in the range of 5-20℃/min.

Quench sensitivity and microstructures of high-Zn-content Al−Zn−Mg−Cu alloys with different Cu contents and Sc addition

The Zn,Cu,and Sc contents of 7xxx Al alloys were adjusted according to the chemical composition of a 7085 Al alloy,and the effects of Zn and Cu contents and Sc addition on the microstructures,hardness,and quench sensitivity of the 7xxx Al alloys were studied.The alloys with high Zn content and Sc addition exhibited higher hardness than the 7085 alloy at the position 3 mm away from the quenching end.The density ofηand T phases increased with the increase in Zn and Cu contents,and the Sc addition led to the formation of the Y phase and moreηphases at the position 120 mm away from the quenching end.Compared with the 7085 alloy,the high Zn−high Cu and Sc-added alloys exhibited higher quench sensitivity,while the simultaneous increase in Zn content and decrease in Cu content could enhance the hardness and reduce the quench sensitivity of the 7085 alloy.

Theoretical design and distribution control of precipitates and solute elements in Al−Zn−Mg−Cu alloys with heterostructure

In order to simultaneously improve strength and formability,an analytical model for the concentration distribution of precipitates and solute elements is established and used to theoretically design and control the heterogeneous microstructure of Al−Zn−Mg−Cu alloys.The results show that the dissolution of precipitates is mainly affected by particle size and heat treatment temperature,the heterogeneous distribution level of solute elements diffused in the alloy matrix mainly depends on the grain size,while the heat treatment temperature only has an obvious effect on the concentration distribution in the larger grains,and the experimental results of Al−Zn−Mg−Cu alloy are in good agreement with the theoretical model predictions of precipitates and solute element concentration distribution.Controlling the concentration distribution of precipitates and solute elements in Al−Zn−Mg−Cu alloys is the premise of accurately constructing heterogeneous microstructure in micro-domains,which can be used to significantly improve the formability of Al−Zn−Mg−Cu alloys with a heterostructure.

Investigation on microstructures and mechanical properties of Mg-6Zn-0.5Ce-xMn(x=0 and 1)wrought magnesium alloys

The microstructure evolution and mechanical properties of Mg–6Zn–0.5Ce–xMn(x=0 and 1 wt.%)wrought magnesium alloys were researched,and the morphologies and role of Mn element in the experimental alloys were analyzed.The research shows that all of Mn elements form theα-Mn pure phases,which do not participate in the formation of other phases,such as theτ-phases.The mechanical properties of Mn-containing alloys in as-extruded and aged states are superior to Mn-free alloys.During the hot extrusion process,the dispersed fineα-Mn particle phase hinders the migration of grain boundaries and inhibits dynamic recrystallization,which mainly takes effect of grain refining and dispersion hardening.During the aging treatments,the dispersed fineα-Mn particle phase not only hinders the growth of the solution-treated grains,but also becomes the nucleation cores ofβ1 rod-like precipitate phase,which is conducive to increasing the nucleation rate of the precipitate phase.For the aged alloy,the Mn addition mainly takes effect of grain refining and promoting aging strengthening.

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.

Microstructure and mechanical properties of squeeze-cast Al−5.0Mg−3.0Zn−1.0Cu alloys in solution-treated and aged conditions

The microstructure and mechanical properties at different depths of squeeze-cast,solution-treated and aged Al−5.0Mg−3.0Zn−1.0Cu alloy were investigated.For squeeze-cast alloy,from casting surface to interior,the grain size ofα(Al)matrix and width of T-Mg32(AlZnCu)49 phase increase significantly,while the volume fraction of T phase decreases.The related mechanical properties including ultimate tensile strength(UTS)and elongation decrease from 243.7 MPa and 2.3%to 217.9 MPa and 1.4%,respectively.After solution treatment at 470℃ for 36 h,T phase is dissolved into matrix,and the grain size increases so that the UTS and elongation from surface to interior are respectively reduced from 387.8 MPa and 18.6%to 348.9 MPa and 13.9%.After further peak-aging at 120℃ for 24 h,numerous G.P.II zone andη′phase precipitate in matrix.Consequently,UTS values of the surface and interior increase to 449.5 and 421.4 MPa,while elongation values decrease to 12.5%and 8.1%,respectively.

Effect of non-isothermal aging on microstructure and properties of Al−5.87Zn−2.07Mg−2.42Cu alloys

The evolution of microstructure and properties of Al−5.87Zn−2.07Mg−2.42Cu alloys during non-isothermal aging was studied.The mechanical properties of the alloy were tested by stretching at room temperature.The results show that in the non-isothermal aging process,when the alloy is cooled to 140℃,the ultimate tensile strength of the alloy reaches a maximum value of 582 MPa and the elongation is 11.9%.The microstructure was tested through a transmission electron microscope,and the experimental results show that the GP zones andη'phases are the main strengthening precipitates.At the cooling stage,when the temperature dropped to 180℃,the GP zones were precipitated again.Besides,the experimental results show that the main strengthening phase during non-isothermal aging isη'phases.

Influence of cobalt content on microstructure and corrosionperformance of extruded Sn-9Zn solder alloys

The Pb-free solders have attracted a great deal of attention recently due to the environmental concerns.The present work focuses on the effect of cobalt content(0,0.5 and 3.0)on the microstructural characteristics,melting point and corrosion performance of extruded Sn-9Zn solder alloys.The results reveal that the Zn-rich precipitates with spherical or needle-like shape in the Sn-9Zn-xCo alloys are refined remarkably by forming the γ-Co5Zn21 and Co2Sn2Zn Co-contained intermetallic compounds,though the melting point and eutectic reaction temperature decrease slightly.It is suggested that the corrosion property of the extruded Sn-9Zn-xCo alloys is improved significantly by adding the cobalt element,while the content should be controlled reasonably.Combining the corrosion morphology,the influence of cobalt content on the corrosion behavior of the Sn-9Zn-xCo alloys is analyzed in terms of the refined microstructure and the enhanced passive film stability.