Designing new low alloyed Mg-RE alloys with high strength and ductility via high-speed extrusion

Two new low-alloyed Mg-2RE-0.8Mn-0.6Ca-0.5Zn(wt%,RE=Sm or Y)alloys are developed,which can be produced on an in-dustrial scale via relatively high-speed extrusion.These two alloys are not only comparable to commercial AZ31 alloy in extrudability,but also have superior mechanical properties,especially in terms of yield strength(YS).The excellent extrudability is related to less coarse second-phase particles and high initial melting point of the two as-cast alloys.The high strength-ductility mainly comes from the formation of fine grains,nano-spaced submicron/nano precipitates,and weak texture.Moreover,it is worth noting that the YS of the two alloys can maintain above 160 MPa at elevated temperature of 250°C,significantly higher than that of AZ31 alloy(YS:45 MPa).The Zn/Ca solute segregation at grain boundaries,the improved heat resistance of matrix due to addition of RE,and the high melting points of strengthening particles(Mn,MgZn_(2),and Mg-Zn-RE/Mg-Zn-RE-Ca)are mainly responsible for the excellent high-temperature strength.

Effect of Initial Microstructure Prior to Extrusion on the Microstructure and Mechanical Properties of Extruded AZ80 Alloy with a Low Temperature and a Low Ratio

Magnesium(Mg)alloys are the lightest metal structural material for engineering applications and therefore have a wide market of applications.However,compared to steel and aluminum alloys,Mg alloys have lower mechanical properties,which greatly limits their application.Extrusion is one of the most important processing methods for Mg and its alloys.However,the effect of such a heterogeneous microstructure achieved at low temperatures on the mechanical properties is lacking investigation.In this work,commercial AZ80 alloys with different initial microstructures(as-cast and as-homogenized)were selected and extruded at a low extrusion temperature of 220℃and a low extrusion ratio of 4.The microstructure and mechanical properties of the two extruded AZ80 alloys were investigated.The results show that homogenized-extruded(HE)sample exhibits higher strength than the cast-extruded(CE)sample,which is mainly attributed to the high number density of fine dynamic precipitates and the high fraction of recrystallized ultrafine grains.Compared to the coarse compounds existing in CE sample,the fine dynamical precipitates of Mg17(Al,Zn)12form in the HE sample can effectively promote the dynamical recrystallization during extrusion,while they exhibit a similar effect on the size and orientation of the recrystallized grains.These results can facilitate the designing of high-strength wrought magnesium alloys by rational microstructure construction.

Developing new Mg alloy as potential bone repair material via constructing weak anode nano-lamellar structure

The mechanics-corrosion and strength-ductility tradeoffs of magnesium(Mg)alloys have limited their applications in fields such as orthopedic implants.Herein,a fine-grain structure consisting of weak anodic nano-lamellar solute-enriched stacking faults(SESFs)with the average thickness of 8 nm and spacing of 16 nm is constructed in an as-extruded Mg96.9Y1.2Ho1.2Zn0.6Zr0.1(at.%)alloy,obtaining a high yield strength(YS)of 370 MPa,an excellent elongation(EL)of 17%,and a low corrosion rate of 0.30 mm y−1(close to that of high-pure Mg)in a uniform corrosion mode.Through scanning Kelvin probe force microscopy(SKPFM),one-dimensional nanostructured SESFs are identified as the weak anode(∼24 mV)for the first time.The excellent corrosion resistance is mainly related to the weak anodic nature of SESFs and their nano-lamellar structure,leading to the more uniform potential distribution to weaken galvanic corrosion and the release of abundant Y^(3+)/Ho^(3+)from SESFs to form a more protective film with an outer Ca_(10)(PO_(4))_(6)(OH)_(2)/Y_(2)O_(3)/Ho_(2)O_(3) layer(thickness percentage of this layer:72.45%).For comparison,the as-cast alloy containing block 18R long period stacking ordered(LPSO)phase and the heat-treated alloy with fine lamellar 18R-LPSO phase(thickness:80 nm,spacing:120 nm)are also studied,and the characteristics of SESFs and 18R-LPSO phase,such as the weak anode nature of the former and the cathode nature of the latter(37-90 mV),are distinguished under the same alloy composition.Ultimately,we put forward the idea of designing Mg alloys with high mechanical and anti-corrosion properties by constructing"homogeneous potential strengthening microstructure",such as the weak anode nano-lamellar SESFs structure.

Recent developments in high-strength Mg-RE-based alloys:Focusing on Mg-Gd and Mg-Y systems

Higher strength is always the goal pursued by researchers for the structural materials,especially for the lightweight magnesium(Mg)alloys which generally have relatively low strength at present.From this aspect,the present paper reviews the recent reports of a kind of Mg alloys,i.e.Mg-RE(RE:rare earths,mainly Gd or Y)casting and wrought alloys,which have been able to achieve high strength compared with common or commercial Mg alloys,from the viewpoint and content of the alloy system,alloying constitution,preparation process,tensile strength and each of the main strengthening mechanisms.This review of recent research and developments in high-strength Mg-RE alloys is beneficial for the further design of Mg alloys with higher strength as well as excellent comprehensive performance.

Towards developing Mg alloys with simultaneously improved strength and corrosion resistance via RE alloying

Magnesium(Mg)alloys have received an increasing interest in the past two decades for their tremendous application potential.The strength and corrosion resistance levels of common Mg alloys are still relativity low,and especially they are to be improved simultaneously.The addition of rare earth(RE)to Mg alloys is believed to be beneficial for both the strength and corrosion resistance,and some RE-modified traditional Mg alloys have been studied and some new RE-containing Mg alloys have been developed by now.However,further simultaneous improvements in both strength and anti-corrosion require a better understanding of the behavior and mechanism of RE in Mg alloys.In this review,the common influence mechanisms of RE on mechanical and anti-corrosion properties of Mg alloys are summarized,and the latest research progress of RE-containing Mg alloys with simultaneously improved strength and corrosion resistance are introduced.It is demonstrated that the research on high-strength and high corrosion resistant RE-containing Mg alloys is still immature,and some opinions and suggestions are put forward for the synergetic improvement of the strength and corrosion resistance of Mg alloys,so as to contribute to the further development of Mg alloys with higher performance.

The transformation of LPSO type in Mg-4Y-2Er-2Zn-0.6Zr and its response to the mechanical properties and damping capacities

The transformation of LPSO type in Mg-4Y-2Er-2Zn-0.6Zr during heat treatment and its influence on damping and mechanical properties are reported in this work.Prior to heat treatment,the alloy consisted of a-Mg matrix and lamellar 14H LPSO phases.After 510℃heat treatment,lamellae shortened,and their content decreased.Upon 8h heat treatment,block 18R LPSO phases formed at the grain boundaries while 14H LPSO lamellae disappeared.Presence of block 18R LPSO phases improved mechanical and damping properties of the alloy.The corresponding mechanisms of the influence of LPSO type and morphology on mechanical and damping capacities are discussed.

Modifying microstructures and tensile properties of Mg-Sm based alloy via extrusion ratio

Microstructure and tensile properties of a Mg-Sm-Zn-Zr alloy with various extrusion ratios(ERs)of 6.9,10.4 and 17.6 were systematically investigated.It was identified that,greater ER increased dynamic recrystallization(DRX)fraction and coarsened DRX grains,which further suggests weakened basal fiber texture for the studied alloy.This is mainly due to the rising temperature from massive deformation heat when hot-extrusion.As a result,greater ER corresponds to a decreased strength but improved ductility.Finally,transmission electron microscopy(TEM)observations reveal that the dominant intermetallic phase,Mg_(3)Sm,is metastable,and it will transform into Mg_(41)Sm_(5)during extrusion with high-ER.This transformation leads to the accumulation of surplus Sm and Zn atoms,which induces the precipitation of Sm Zn_(3)phase at the surface of Mg_(41)Sm_(5)matrix.

Effect of carbonate additive on the microstructure and corrosion resistance of plasma electrolytic oxidation coating on Mg-9Li-3Al alloy

Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,structure,and phase composition of the coating were investigated by scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion resistance of the coating was evaluated by electrochemical experiment,hydrogen evolution,and immersion test.The results showed that the addition of carbonate resulted in a denser coating with increased hardness,and the corrosion-resistant Li_(2)CO_(3) phase was formed.Electrochemical experiments showed that compared with the coating without carbonate,the corrosion potential of the carbonate coating positively shifted(24 mV),and the corrosion current density was reduced by approximately an order of magnitude.The coating with carbonate addition possessed a high corrosion resistance and long-term protection capability.

Mathematical analysis and its experimental comparisons for the accumulative roll bonding(ARB)process with different superimposed layers

Based on the traditional two-layer accumulative roll bonding(TARB),the geometrical variations and mathematical relationship during the four-layer accumulative roll bonding(FARB)were derived and summarized.Furthermore,the multi-layer accumulative roll bonding(MARB)technology was proposed and the geometrical variations and mathematical relationship of MARB were simultaneously derived and summarized.Experimentally,Mg-14Li-3Al-2Gd(LAGd1432)sheets were fabricated by TARB and FARB,respectively.Compared with the TARB,the FARB has a higher accumulative efficiency in terms of accumulative layers,total number of interfaces,interface spacing,total deformation and equivalent strain.Therefore,the FARB-processed sheets in lower cycles have the similar microstructure and mechanical properties of the TARB-processed sheets in higher cycles.In addition,FARB process can further break through the deformation limit of TARB process in a single cycle through adopting two-step rolling in one cycle with 50%deformation in one pass and 75%accumulative deformation in one cycle,which can effectively solve the problem of poor interface bonding of the latest interface brought by the last cycle,and thus significantly improve the phenomenon of unstable performance of the ARB-processed sheets.

Influence of rolling directions on microstructure,mechanical properties and anisotropy of Mg-5Li-1Al-0.5Y alloy

Mg-5Li-1Al-0.5Y alloy was rolled with different directions.The microstructure,mechanical properties and texture of the specimens were investigated with optical microscope,tensile tester and X-ray diffraction.The results show that changing rolling directions can refine the grain size of as-rolled alloys.Meanwhile,rolling directions have an obvious influence on the mechanical properties and texture of Mg-5Li-1Al-0.5Y alloy,thus affecting the anisotropy of the alloy.The sheet,of which the RD(rolling direction)and ND(normal direction)are both changed between two passes,possesses the smallest anisotropy.From the texture results,changing rolling directions reduces the maximum pole density,making the highest point distribution region excursion and the highest point distributes more scatteredly.

Reform and Practice on Cultivation of Data Thinking oriented Course Construction of Introduction to Big Data

With rapidly increasing massive data,mankind is entering a new era of big data.This brings new opportunities and challenges to modern society,and big data techniques also play an important role in advancing techniques of computer science(CS)and software engineering(SE).To keep pace with developments in technology,more and more university universities are incorporating big data into their curriculum courses.However,it is distinguished from traditional CS/SE courses and big data courses.This paper attempts to think deeply about the course construction of introduction to big data from the cultivation of data thinking,and further explore the implementation result and existing problems of the course,so as to better carry out the teaching of big data course.

Simultaneously improving mechanical and anti-corrosion properties of extruded Mg-Al dilute alloy via trace Er addition

Simultaneously improving the mechanical properties and corrosion resistance of magnesium(Mg)alloys is a long-standing challenge to be solved in their engineering applications.In this work,we find that trace Er addition can improve the mechanical and anti-corrosion properties of Mg-1.4Al-0.4Mn-0.4Ca-0.3Er(wt%,AMXE)dilute alloy synergistically,especially reducing the corrosion rate(0.75 mm y-1)by one order of magnitude compared with the reference Mg-1.4Al-0.4Mn-0.4Ca(AMX)alloy and making it comparable to that of high-purity Mg.Adding trace Er reduces the dynamic recrystallization degree and increases the strengthening phase particles,which is mainly responsible for the increase of yield strength by 42 MPa.The addition of Er promotes the formation of much less noble Al8Mn4Er with effective Fe trapping ability and induces dislocation segregation,thus dramatically reducing micro-galvanic corrosion tendency.Meanwhile,Er addition promotes the formation of a more passivation and dense corrosion film.These two factors together lead to the extremely low corrosion rate of AMXE alloy.Our findings are expected to promote the development of low alloyed high performance Mg alloys.

Ultra-high strength Mg-Li alloy with B2 particles and spinodal decomposition zones

The bcc-structured Mg-Li alloy is currently the engineering metallic material with the lowest density,but it has not been widely used due to its low strength.In this paper,alloying Zn effectively improves the strength of the bcc-structured Mg-Li alloy.Due to the semi-coherent B2 structured nanoparticles,the compressive yield strength of the as-cast Mg-13Li-9Zn alloy reaches higher than 300 MPa.Due to the solid solution strengthening of Zn and the spinodal zone,the compressive yield strength of the as-quenched Mg-13Li-15Zn(LZ1315)alloy immediately increases to 400 MPa.In addition,the as-quenched LZ1315 alloy exhibits natural aging strengthening behavior.Due to the precipitation of B2 nanoparticles,the yield strength of the peak aged alloy is up to 495 MPa.

Corrosion mechanism of Mg alloys involving elongated long-period stacking ordered phase and intragranular lamellar structure

It is a long-term challenge to further improve the corrosion resistance while ensuring the strength of magnesium(Mg)alloys.Revealing the effect of potential fluctuation on the micro-galvanic corrosion and the subsequent film formation is important for understanding the corrosion mechanism of Mg alloys with multiple strengthening phases/structures.Here,we prepared the high-strength Mg-14.4Er-1.44Zn-0.3Zr(wt.%)alloys containing hybrid structures,i.e.,elongated long-period stacking ordered(LPSO)blocks+intragranular stacking faults(SFs)/LPSO lamellae.The Mg alloy with elongated LPSO blocks and intragranular LPSO lamellae(EZ-500 alloy)obtains good corrosion resistance(2.2 mm y^(–1)),while the Mg alloy containing elongated LPSO blocks and intragranular SFs(EZ-400 alloy)shows a significantly higher corrosion rate(6.9 mm y^(–1)).The results of scanning Kelvin probe force microscopy(SKPFM)show the elongated LPSO blocks act as cathode phase(87 mV in EZ-400 alloy),and the SFs serve as the weak anode(30 mV in EZ-400 alloy),resulting in high potential fluctuation in EZ-400 alloy.On the contrary,both elongated blocks and intragranular lamellae are cathodic LPSO phase(67–69 mV)in EZ-500 alloy,leading to a lower potential fluctuation.Quasi in-situ atomic force microscope(AFM)observation indicates that high potential fluctuation would cause strong micro-galvanic corrosion,and subsequently leads to the failure in rapid formation of corrosion film,finally forming a loose and porous film,while relatively low potential fluctuation could result in more uniform corrosion mode and facilitate the rapid formation of protective film.Therefore,we propose that it is an effective way to develop high-strength corrosionresistant Mg alloys by controlling the potential fluctuation to form a“uniform potential”strengthening microstructure。

Towards designing high mechanical performance low-alloyed wrought magnesium alloys via grain boundary segregation strategy:A review

Low-alloyed magnesium(Mg)alloys have emerged as one of the most promising candidates for lightweight materials.However,their further application potential has been hampered by limitations such as low strength,poor plasticity at room temperature,and unsatisfactory formability.To address these challenges,grain refinement and grain structure control have been identified as crucial factors to achieving high performance in low-alloyed Mg alloys.An effective way for regulating grain structure is through grain boundary(GB)segregation.This review presents a comprehensive summary of the distribution criteria of segregated atoms and the effects of solute segregation on grain size and growth in Mg alloys.The analysis encompasses both single element segregation and multi-element co-segregation behavior,considering coherent interfaces and incoherent interfaces.Furthermore,we introduce the high mechanical performance low-alloyed wrought Mg alloys that utilize GB segregation and analyze the potential impact mechanisms through which GB segregation influences materials properties.Drawing upon these studies,we propose strategies for the design of high mechanical performance Mg alloys with desirable properties,including high strength,excellent ductility,and good formability,achieved through the implementation of GB segregation.The findings of this review contribute to advancing the understanding of grain boundary engineering in Mg alloys and provide valuable insights for future alloy design and optimization.

Effect of Y and Ce on the microstructure, mechanical properties and anisotropy of as-rolled Mg-8Li-1Al alloy

The effects of combined addition of Y and Ce on the microstructure,mechanical properties and anisotropy of as-rolled Mg-8 Li-1 Al(LA81)alloy were studied.The combined addition of Y and Ce improves the mechanical properties with a low plasticity loss by solution strengthening,dispersion strengthening,grain refinement strengthening.Mg-8 Li-1 Al-0.6 Y-0.6 Ce(LA81-0.6 Y-0.6 Ce)has better mechanical properties and shows an almost isotropy.It possesses an ultimate tensile strength of 278.7 MPa and an elongation of 15.0%.Compared to LA81 alloy,the ultimate tensile strength increases by about 17.6%with an elongation reduction of only 3.5%,and a good isotropy of ultimate tensile strength and elongation(the value of ravg is near 1).

Enhanced Electromagnetic Interference Shielding in a Duplex-Phase Mg-9Li-3Al-1Zn Alloy Processed by Accumulative Roll Bonding

High electromagnetic shielding performance was achieved in the Mg-9Li-3Al-1Zn alloy processed by accumulative roll bonding(ARB).The microstructure,electromagnetic interference shielding effectiveness(SE) in the frequency of 30-1500 MHz and mechanical properties of the alloy were investigated.A model based on the shielding of the electromagnetic plane wave was used to theoretically discuss the EMI shielding mechanisms of ARB-processed alloy.Results indicate that the SE of the material increases gradually with the increase in the ARB pass.The enhanced SE can be attributed to the obvious microstructure orientation caused by ARB,and the alternative arrangement of alpha(Mg) phase and beta(Li)phase.In addition,with the increase in ARB pass,the number of interfaces between layers increases and the grain orientation of each layer tends to alignment along c-axis,which is beneficial to the reflection loss and multiple reflection loss of the incident electromagnetic wave.

Development of extruded Mg-6Er-3Y-1.5Zn-0.4Mn(wt.%) alloy with high strength at elevated temperature

A new Mg-6 Er-3 Y-1.5 Zn-0.4 Mn(wt.%) alloy with high strength at high temperature was designed and extruded at 350℃. The as-extruded alloy exhibits ultimate tensile strength of 301 MPa, yield strength(along ED) of 274 MPa and thermal conductivity of 73 W/m·K at 300℃. Such outstanding hightemperature strength is mainly attributed to the formation of nano-spaced solute-segregated basal plane stacking faults(SFs) with a large aspect ratio throughout the entire Mg matrix, fine dynamically recrystallized(DRXed) grains of 1–2μm and strongly textured un-DRXed grains with numerous sub-structures.Microstructural examination unveils that long period stacking ordered(LPSO) phases are formed in Mg matrix of the as-cast alloy when rational design of alloy composition was employed, i.e.(Er + Y): Zn = 3:1 and Er: Y = 1: 1(at.%). It is worth mentioning that it is the first report regarding the formation of nano-spaced basal plane SFs throughout both DRXed and un-DRXed grains in as-extruded alloy with well-designed compositions and processing parameters. The results provide new opportunities to the development of deformed Mg alloys with satisfactory mechanical performance for high-temperature services.

Development of high mechanical properties and moderate thermal conductivity cast Mg alloy with multiple RE via heat treatment

A new cast Mg-2Gd-2Nd-2Y-1Ho-1Er-0.5Zn-0.4Zr （wt%） alloy was prepared by direct-chill semicontinuous casting technology. The microstructure, mechanical properties and thermal conductivity of the alloy in as-cast, solid-solution treated and especially peak-aged conditions were investigated. The as-cast alloy mainly consists of α-Mg matrix, （Mg, Zn）3 RE phase and basal plane stacking faults. After proper solid-solution treatment, the microstructure becomes almost Mg-based single phase solid solution except just very few RE-riched particles. The as-cast and solid-solution treated alloys exhibit moderate tensile properties and thermal conductivity. It is noteworthy that the Mg alloy with 8 wt% multiple RE exhibits remarkable age-hardening response （AHV=35.7）, which demonstrates that the multiple RE （RE = Gd, Nd, Y, Ho, Er） alloying instead of single Gd can effectively improve the age-hardening response. The peak-aged alloy has a relatively good combination of high strength/hardness （UTS （ultimate tensile strength） 〉 300 MPa; TYS （tensile yield strength）〉210 MPa; 115.3 HV）, proper ductility （ε≈ 6%） and moderate thermal conductivity （52.5 W/（m K））. The relative mechanisms mainly involving aging precipitation of β″ and β＂ phases were discussed. The results provide a basis for development of high performance cast Mg alloys.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Coarsening kinetics and strengthening mechanisms of core-shell nanoscale precipitates in Al-Li-Yb-Er-Sc-Zr alloy

The tailored nanoparticles with a complex core/shell structure can satisfy a variety of demands, such as lattice misfit, shearability and coarsening resistance. In this research, core-shell nanoscale Al3(Yb, Er, Sc,Zr, Li) composite particles were precipitated in Al-2 Li-0.1 Yb-0.1 Er-0.1 Sc-0.1 Zr(wt%) alloy through the double-aging treatment, in which the core was(Yb, Er, Sc, Zr)-rich formed at 300°C and the shell was Li-rich formed at 150°C. The coarsening kinetics and precipitate size distributions(PSDs) of Al3(Yb, Er, Sc,Zr, Li) particles aged at 150°C previously aged at 300°C for 24 h showed a better fit to the relation of 2∝ kt and normal distribution, indicating that the coarsening of precipitates was controlled by interface reaction, not diffusion. The Orowan bypass strengthening was operative mechanism at 150°C.