TEM microstructure of rapidly solidified Mg-6Zn-1Y-1Ce alloy

Rapidly solidified（RS） Mg-6Zn-1Y-1Ce ribbons were prepared by single roller melt-spinning technique.Transmission electron microscopy and energy dispersive X-ray spectroscopy were employed to characterize the microstructure of RS ribbons.The results show that there is high density of particles distributed within grains and at grain boundaries in the region near wheel side.The particle density is decreased in the middle region and free surface region.The alloy is predominantly composed of supersaturated--Mg solid solution,T phase and W phase;meanwhile,a few icosahedral quasicrystalline and Mg4Zn7 particles are also observed.The T phase is confirmed having a body-centered orthorhombic structure that is transformed from the body-centered tetragonal structure Mg12Ce phase due to the partial substitution of Mg atoms by Zn.

Effects of deformation parameters on microstructure and texture of Mg−Zn−Ce alloy

Compression tests were performed on the Mg−6Zn−0.5Ce(wt.%)alloy using a Gleeble−1500 thermomechanical simulator testing system at temperatures of 250,300,350℃ and strain rates of 0.001,0.01,0.1 s^−1.The microstructure and texture evolution of the Mg−6Zn−0.5Ce alloy during hot compression were investigated by optical microscopy(OM)and electron backscattered diffraction(EBSD).The results showed that Zener−Hollomon parameters obtained from the deformation processes had a significant effect on the dynamic recrystallization and texture of the Mg−6Zn−0.5Ce alloy.The fraction of undynamically recrystallized(unDRXed)regions increased,and the dynamically recrystallized(DRXed)grain size decreased with increasing the Zener−Hollomon parameters.The texture intensity of the DRXed regions was weaker compared with that in the unDRXed regions,which resulted in a sharper texture intensity in the samples deformed with higher Zener−Hollomon parameters.The increase in recrystallized texture intensity was related to preferred grain growth.

Design and preparation of Al-Fe-Ce ternary aluminum alloys with high thermal conductivity

Ce element was introduced to modify Al−2%Fe(mass fraction)binary alloy.The microstructures,crystallization behavior,electrical/thermal conductivities and mechanical properties of these alloys were systematically investigated.The results indicated that the appropriate Ce addition decreased the recalescence temperature and growth temperature of Al−Fe eutectic structure,improved the morphology and distribution of Fe-containing phase,and simultaneously increased the conductivity and mechanical properties.The annealed treatment improved the thermal conductivity of these alloys due to the decreasing concentration of point defects.Rolling process further broke up the coarser Fe-containing phases into finer particles and made the secondary phases uniformly distributed in theα(Al)matrix.After subsequent annealing treatment and rolling deformation,the thermal conductivity,ultimate tensile strength and hardness of the Al−2%Fe−0.3%Ce(mass fraction)alloy reached 226 W/(m·K),(182±1.4)MPa and HBW(49.5±1.7),respectively.

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.

Effect of Ca content and rheo-squeeze casting parameters on microstructure and mechanical properties of AZ91−1Ce−xCa alloys

The microstructure,mechanical properties and flame resistance behavior of the AZ91−1Ce alloys with different Ca additions were firstly investigated.Then,the effect of processing parameters,including applied pressures and rotation speeds,on the microstructure and mechanical properties of the rheo-squeeze casting AZ91−1Ce−2Ca alloy was studied.The results indicate that with the increase of Ca content,the microstructure is refined and the flame resistance of the AZ91−1Ce−xCa alloys increases.But when the Ca content exceeds 1 wt.%,with the Ca content increasing,the mechanical properties of the AZ91−1Ce−xCa alloys reduce rapidly.For rheo-squeeze casting process,the increase of applied pressure and rotation speed can both bring about significant refinement in the microstructure of the AZ91−1Ce−2Ca alloy and reduction of the porosity,so the mechanical properties increase.Compared to conventional casting,the AZ91−1Ce alloy with the addition of 2 wt.%Ca by rheo-squeeze casting not only guarantees the oxidation resistance(801℃),but also improves mechanical properties.

Mechanical properties and microstructure of as-cast and extruded Mg-(Ce, Nd)-Zn-Zr alloys

Studies on the mechanical properties and microstructures of as-cast and extruded Mg-Ce-Zn-Zr and Mg-Nd-Zn-Zr alloys have been made before and after heat treatment. The results show that the mechanical properties of as-cast Mg-Ce and Mg-Nd alloys are as good as those of typical die cast AZ91 alloy and the heat resistant WE43 alloy. In Nd-containing alloys, the precipitated phase Mg_ 12Nd contributes significantly to age hardening. The mechanical properties of extruded alloys are improved obviously compared with those of as-cast alloys. The ultimate strength is 257.8MPa for extruded Mg-Ce alloy and 265.6MPa for extruded Mg-Nd alloy. Extrusion is a useful method to improve both the strengths and elongations of the two experimental alloys at both ambient and elevated temperatures. The grain refinement and precipitation strengthening are the main strengthening mechanisms in the alloys. Tensile fracture surfaces show a dimple pattern after extruding and therefore reflect an improved elongation.

Influence of Rare Earth(Ce and La) Addition on the Performance of Al-3.0 wt%Mg Alloy

The influences of rare earth elements（cerium and lanthanum） on the microstructure and phases of Al-3.0 wt%Mg alloys used for electromagnetic shielding wire were characterized by scanning electron microscopy（SEM）, energy-dispersive spectroscopy（EDS）, X-ray diffraction（XRD） and differential scanning calorimetry（DSC）. The mechanical properties and electrical resistivity were also investigated. The results indicated that a certain content of rare earth could improve the purification of the aluminum molten, enhance the strength, and reduce the electrical resistivity of Al-3.0 wt%Mg alloys. The strength reached the top value when RE content was 0.3 wt% while the alloy with 0.2 wt% RE addition had the smallest electrical resistivity. The elongation varied little when RE addition was no more than 0.2 wt%. But the excessive addition of rare earth would be harmful to the microstructure and properties of Al-3.0 wt%Mg alloys.

Effect of cobalt content on electrochemical performance of La-Mg-Ni system (Ce_2Ni_7-type) electrode alloys

In order to improve the cyclic stability of La-Mg-Ni system （Ce2Ni7-type） alloy electrode, small amount of Co was added in La0.75Mg0.25Ni3.5 alloy. The effect of Co on electrochemical performance and microstructure of the alloys were investigated in detail. XRD results showed that the alloys had multiphase structure composed of （La, Mg）2Ni7, LaNi5 and small amount of LaNi2 phases. The discharge capacity of the alloys first increased and then decreased with increasing Co content. At a discharge current density of 900 mA/g, the HRD of the alloy electrodes increased from 81.3% （x=0） to 89.2 % （x=0.2）, and then reduced to 87.8 % （x=0.6）. After 60 charge/discharge cycles, the capacity retention rate of the alloys enhanced from 52.67% to 61.32%, and the capacity decay rate of the alloys decreased from 2.60 to 2.05 mAh/g per cycle with increasing Co content. The obtained results by XPS and XRD showed that the fundamental reasons for the capacity decay of the La-Mg-Ni system （Ce2Ni7-type） alloy electrodes were corrosion and oxidation as well as passivation of Mg and Lain alkaline solution.

Study on Microstructure and Thermal Stability Behavior of Rapidly Solidified Al-Fe-Ce Alloy

Rapidly solidified Al 8Fe 4Ce alloy was prepared by melt spinning.As quenched and as annealed microstructures were studied by TEM and energy dispersive spectrum analysis.The microhardness of the alloy at different annealing temperature was measured.The results obtained indicated that as quenched microstructure varied with different cooling rates.The microstructure annealed at 300℃ was much the same as that of the as quenched.The dispersed phases at grain boundary of the microstructure annealed at 400℃ became coarsening.After annealing at 450℃ for 2 hours,the primary phase and the intercellular dispersed phases,metastable phase Al 6Fe and Al 20 Fe 5Ce respectively,coarsened further.The soften temperature was deduced at over 300℃ by measuring microhardness.

Damping Property of Supersaturated ZnA127Ce Alloy during Natural Aging

The microstructures and damping property of supersaturated ZnA127Ce alloy during natural aging have been investigated. H-800 TEM was mainly used to research the microstructures. The relationship between microstructure and damping property was primarily studied. The results showed that solution plus natural aging was the best heat treatment, which could improve the damping property. Both continuous precipitation and cellular reaction occurred during the aging. Continuous precipitation follows the sequence: β→spherical GP zones→elliptical GP zones→intermediate phase R→n. The cellular reaction can be written as follows:β→a+n+ε.

DISTRIBUTION OF Ce AND S IN Fe-C-Si ALLOY AND THEIR INFLUENCE ON MORPHOLOGY OF GRAPHITE

Electrolytic extraction-radiometry and microradioautography techniques were used to study the distribution of nodulizing element Ce and anti-nodulizing element S in phases of high purity Fe-C-Si alloy.The results show that,besides forming inclusions,most of Ce atoms concentrate in graphite firstly.As the Ce content increases,the concentration of Ce in graphite tends to saturate,relatively large amount of Ce dissolves in the alloy.Usually,the sulphur also concentrates in graphite.However,it may exist in the form of FeS at the eutectic colony boundaries,if the concentration of S is at a quite high level.Very little amount of S dissolves in the alloy.The morphology of graphite depends upon the degree of saturation of Ce.It appears as nodular when Ce was saturated and,as vermicular while it was semi-saturated.

INFLUENCES OF SMALL AMOUNTS OF Y AND Ce ON HIGH TEMPERATURE CORROSION PROPERTIES OF M38 ALLOY

High temperature corrosion properties of M38 alloy with and without 0.04 wt-%Y and 0.05 wt-%Ce additions were studied in equilibrated S0_(2)+0_(2)gas mixtures at 850℃and 900℃.It was found that adding Y or Ce decreased the corrosion rate of M38 and changed considerably the surface morphologies and composition of corrosion products on M38.The effectiveness of Y and Ce were also discussed.

Study on structure and magnetic entropy changes of Ce_(2-x)Pr_xFe_(16.5)Co_(0.5) alloys

A series of Ce2-xPrxFe16.5Co0.5 alloys were prepared by arc melting under purified argon atmosphere. The structure and magnetic entropy changes in Ce2-xPrxFe16.5Co0.5 alloys were investigated by means of X-ray diffraction pattern and MPMS XL-7 magnetometer. The experimental results show that the crystal structure of Ce2-xPrxFe16.5Co0.5 alloys keeps in Th2Zn17-type rhombohedral, and the Curie temperature of Ce2-xPrxFe16.5Co0.5 alloys can be shifted to room temperature around by a composition adjustment. The magnetic entropy changes (-ΔSM) in Ce2-xPrxFe16.5Co0.5 alloys are relatively large, and a platform of magnetic entropy changes appears near the temperature TC. Ce2-xPrxFe16.5Co0.5 alloys are the potential working media for magnetic refrigeration with their stable chemical properties and especially low price.

Thermodynamic prediction of thermal diffusivity and thermal conductivity in Mg–Zn–La/Ce system

Basic thermal properties and mechanical properties are critical parameters for the structural magnesium alloys.Solute atoms and second phases can improve mechanical properties,but are deteriorating the heat dissipation performance.Through experimental determination of alloys,it is found that REMg12 phases have fewer negative impacts on thermal diffusivities thanτ;phases.With the same intermetallic compound,the solute atom Zn have more negative influences on thermal diffusivities of Mg-Zn-La/Ce alloys than the content of second phases.In order to quantitatively evaluate thermal conductivities and further design Mg alloys with both high strength and high thermal conductivity,a calculated method is provided to describe the thermal diffusivity of alloys as a function of alloy composition and phase constitution.A set of parameters for expression of thermal diffusivity of Mg-Zn-La/Ce alloys were obtained through assessing the experimental data.The thermal conductivities of Mg-Zn-La/Ce system were predicted and agreed well with experimental values with calculation error of 1.6%and standard error of±3.0 W/(m K).The calculation method considering thermal diffusivity resistivity improves the calculation accuracy and would be physically significant.

Enhanced Damping Capacities of Mg–Ce Alloy by the Special Microstructure with Parallel Second Phase

Microstructure evolution and damping capacities of Mg–Ce binary alloys with three different Ce contents（0.5, 1, or 2 wt%） have been systematically investigated in this work. Numerous fine parallel second phases in Mg–2Ce alloy are obtained, as well as a large number of dislocations around them, but few dislocations appear around the reticular second phase in the Mg–1Ce alloy. Among the three alloys, two internal friction peaks（P;and P;） are detected at about 78 and 167?C in both the Mg–0.5Ce and Mg–1Ce alloys.In addition, the alloy with special parallel second phase structure exhibits excellent damping capacity in both strain amplitude and temperature-dependent regions. These results may be ascribed to the stress concentration and the formation of abundant parallel and uniform dislocation configurations in the ?-Mg matrix without the influence of crystal orientation. The obtained results may provide a novel idea to prepare high-damping magnesium alloys by tailoring their microstructure.

Electrochemical extraction of cerium and formation of Al–Ce alloy from CeO_2 assisted by AlCl_3 in LiCl–KCl melts

This work presents an electrochemical extraction of cerium and synthesization of Al–Ce alloy in LiCl–KCl melts on Mo and Al electrodes by chlorination of CeO2 using AlCl3 at 873 K. The cyclic voltammogram on Mo electrodes in LiCl–KCl–CeO2 melt showed no obvious reduction wave other than the reduction of Li(I). After the addition of AlCl3, the signals of the reaction of Ce(ⅡI)/Ce(0) and the synthesization of Al–Ce and Al–Li alloys were investigated by cyclic voltammetry, square-wave voltammetry, open-circuit chronopotentiometry and chronopotentiometry. These results indicated that AlCl3 can chloridize CeO2 and that it is possible to extract cerium and form Al–Ce and Al–Li–Ce alloys in LiCl–KCl–CeO2–AlCl3 melts. According to potentiostatic electrolysis, only the Al4 Ce layer coated the Al electrodes. According to galvanostatic electrolysis, Al–Ce(Al4Ce, Al3 Ce, and Al92Ce8), Al2Li3, and Al phases were formed on Mo electrodes, and the content of cerium in the Al–Li–Ce alloys was more than 17 wt%.

Research and development of Ce-containing Nd2Fe14B-type alloys and permanent magnetic materials

Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of Nd Fe B-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech industries, and emerging cutting-age frontiers. The balance and efficient use of rare-earth resources comes into being the national strategy, national defense, and border safety for many major countries and regions in the world.（Nd,Ce）Fe B-based permanent magnetic materials, which can not only reduce cost but also offer a feasible way for integrated and effective utilization of rare earth resources,have received much attention in recent years. The existence of CeFe2 and the mixed valence state of Ce in Ce Fe B compound, the different metallurgy behavior and the particular processing as well as potential various magnetic-hardening mechanisms, however, make it quite different from Nd-based alloys.For instance, the coercivity of Ce-containing magnets in some certain composition range, is even higher than that of the counterpart pure Nd-based magnets though the Ce-containing magnets possess inferior intrinsic properties. Consequently, it is very important to design proper composition and structure, optimize processing, and analyze the mechanisms in depth for this kind of magnet. High performance and cost-effective magnets can be fabricated if we can make full use of the composition＇s inhomogeneous and abnormal coercivity variation of the Ce-containing permanent magnets. In this paper, we have summarized the phase structures, magnetic properties and microstructures of（Nd,Ce）Fe B-based permanent magnetic materials to shed light on further research and development of this type of so-called ＂gap magnet＂.

Microstructure and corrosion properties of Mg-0.5Zn-0.2Ca-0.2Ce alloy with different processing conditions

The microstructure and corrosion resistance of Mg-0.5 Zn-0.2 Ca-0.2 Ce alloy with different processing conditions were investigated.The composition was detected by X-ray fluorescence(XRF),and the microstructure was analyzed by optical microscopy(OM)and scanning electron microscope(SEM)equipped with energy-dispersive spectroscopy(EDS).The corrosion behavior was investigated by hydrogen evolution tests,weight loss tests and electrochemical measurements.The Mg-0.5 Zn-0.2 Ca-0.2 Ce alloy has much better corrosion resistance compared with the commercial AZ31 sheet,which can be attributed to its dispersive second phases and protective corrosion products film on the alloy surface.Moreover,the as-rolled Mg-0.5 Zn-0.2 Ca-0.2 Ce alloy shows much better corrosion resistance compared with the as-extruded Mg-0.5 Zn-0.2 Ca-0.2 Ce alloy.This can be due to three aspects:The as-rolled alloy has smaller grain size;the as-rolled alloy has lower(1010)/(1120)texture intensity;the residual stress of the as-rolled alloy is eliminated during the annealing process,but large residual stress exists in the asextruded alloy produced by the extrusion process.

Effect of Zener–Hollomon Parameter on High-Temperature Deformation Behaviors of Mg–6Zn–1.5Y–0.5Ce–0.4Zr Alloy

High-temperature compressive deformation behaviors of Mg–6Zn–1.5Y–0.5Ce–0.4Zr alloy were investigated at temperatures and strain rates ranging from 523 to 673 K and from 0.001 to 1 s~(-1),respectively.The studied alloy was mainly composed ofα-Mg,Mg_(3)Zn_(6)Y(I phase),Mg–Zn–Ce and Mg_(3)Zn_(3)Y_(2)(W phase).The constitutive equation of Mg alloy was obtained,and the apparent activation energy(Q)was determined as 200.44 k J/mol,indicating that rare earth phase increases the difficulty of deformation.The work hardening involves three stages:(1)linear hardening stage;(2)strain hardening stage;and(3)softening and steady-state stage.During these three stages,the dislocation aggregation and tangling,dynamic recovery and recrystallization occur sequentially.To characterize the dynamic recrystallization(DRX)volume fraction,the DRX kinetics was investigated using the Avrami-type equation.The deformation mechanism of magnesium alloy under different Zener–Hollomon parameter(Z)value conditions was also studied.At high Z values and intermediate conditions,dislocations rapidly generate and pile up in the alloy.Recrystallization is hardly seen at this time.At low Z condition,the DRX occurs in the alloy.