Quasicrystalline Phase in As-cast Mg-Zn-Y-Zr Alloy

An icosahedral phase in as-cast Mg 5. 78Zn-0.89Y-0.48Zr (wt-%) alloy has been identified with transmission electron microscope (TPM) The selected area diffraction patterns (SADP) from the phase show a five-fold symmetry of a quasicrystalline structure. The energy dispersive X-ray spectra (EDXS) indicate that the quaternary phase has a chemical composition of 67.6Zn-1 9.4Mg-8,1 Y-4 9Zr in at -%

Microstructures and Phase Transition Points of As-Cast Mg-Zn-Y System Alloys

As-east mierostruetures and their distribution of Mg-Zn-Y ternary alloy with high magnesium, low zinc and yttrium were examined using Nikon Epiphot optical microscopy （OM）, RigakuD/max-3C X- ray diffraetion （XRD）, and JEOL JSM-6700F scanning electron microscopy （SEM） equipped with an energydispersive X-ray spectroscopy （EDS）. In the as-east mierostructures, Yttrium and zinc tend to segregate at grain boundaries,

Effects of Zn content on the microstructure and the mechanical and corrosion properties of as-cast low-alloyed Mg–Zn–Ca alloys

The effects of Zn content on the microstxucture and the mechanical and corrosion properties of as-cast low-alloyed Mg-xZn~.2Ca alloys （x = 0.6wt%, 2.0wt%, 2.5wt%, hereafter denoted as 0.6Zn, 2.0Zn, and 2.5Zn alloys, respectively） axe investigated. The results show that the Zn content not only influences grain refinement but also induces different phase precipitation behaviors. The as-cast microstxucture of the 0.6Zn alloy is composed of ct-Mg, Mg2Ca, and Ca2Mg6Zn3 phases, whereas 2.0Zn and 2.5Zn alloys only contain ct-Mg and Ca2Mg6Zn3 phases, as revealed by X-ray diffraction （XRD） and txonsmission electron microscopy （TEM） analyses. Moreover, with in- creasing Zn content, both the ultimate tensile strength （UTS） and the elongation to fracture first increase and then decrease. Among the three investigated alloys, the largest UTS （178 MPa） and the highest elongation to fracture （6.5%） are obtained for the 2.0Zn alloy. In addition, the corrosion rate increases with increasing Zn content. This paper provides on updated investigation of the alloy composi- tion-microstxucture-property relationships of different Zn-containing Mg-Zn-Ca alloys.

A comparative study of the role of solute,potent particles and ultrasonic treatment during solidification of pure Mg,Mg-Zn and Mg-Zr alloys

Ultrasonic treatment(UST)applied during the solidification of pure Mg,eutectic(Mg-Zn)and peritectic(Mg-Zr)alloys was investigated in order to explore the grain refinement mechanisms.Temperature dependent grain refinement is observed in pure Mg where decreasing the superheat temperature(at which UST is applied from above the melting temperature,TM)from 100℃to 40℃produces significant refinement with a uniform grain structure.The presence of solute reduces the temperature dependence of the UST refinement and excellent grain refinement is obtained regardless of the superheat temperature(100℃or 40℃)and even with the use of preheated sonotrode in the Mg-6 wt.%Zn alloy.A further improvement in grain refinement is achieved when the alloy contains potent particles that introduce additional nucleation of grains in Mg-0.5 and 1.0 wt.%Zr alloys(producing an average grain size of≤100μm).At 40℃superheat,UST of Mg-Zn alloys produces excellent refinement(average grain size<200μm)with non-dendritic grains,which is normally achieved only with the addition of grain refining master alloy in the as-cast condition.The enhanced refinement observed in the eutectic alloy is explained through the undercooling imposed by a relatively cold sonotrode combined with high frequency vibrations and acoustic streaming.The advantages of using a cold sonotrode,a low superheat and solute are demonstrated for achieving significant refinement during solidification of Mg alloys under UST without or with a lower addition of grain refining master alloys.

Research on microstructure in as-cast 7A55 aluminum alloy and its evolution during homogenization

The microstructure of the as-cast 7A55 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and differential scanning calorimetry （DSC） analysis. The results indicate that the microstructure of the as-cast 7A55 aluminum alloy mainly consists of the dendritic network of aluminum solid solution, Al/AIZnMgCu eutectic phases, and intermetaUic compounds MgZn2, Al2CuMg, Al7Cu2Fe, and Al23CuFe4. After homogenization at 470℃ for 48 h, Al/AlZnMgCu eutectic phases are dissolved into the matrix, and a small amount of high melting-point secondary phases were formed, which results in an increasing of the starting melting temperature of 7A55 aluminum alloy The high melting-point secondary phases were eliminated mostly when the homogenization time achieved to 72 h. Therefore, the reasonable homogenization heat treatment process for 7A55 aluminum alloy ingots was chosen as 470℃/72 h.

Effect of Neodymium on As-Cast Microstructure and Mechanical Properties of AZ31 Wrought Alloy

Nd in the form of powder or intermediate alloy was added to AZ31 wrought alloy. The as-obtained alloy was characterized and tested with respect to its microstructure and mechanical properties. The relationship between the microstructure,mechanical properties and tensile fracture mechanism were discussed, with relevant alloys as reference for comparison. Experimental results show that the same quantity of Nd was added into AZ31 in powder form or in intermediate alloy, the absorption rate of Nd reached only 10.8% for the former case and as high as 95% for the later case. Pure Nd powder was added, no new compound was detected, but it served as reductant and purified alloy melt, resulting in improving the tensile strength while Nd was added into AZ31 as Mg-Nd intermediate alloy. The compound Al2Nd and Mg12Nd were formed in magnesium alloy, which were distributed in the matrix in the shapes of strip and particle, evidently refined the as-cast structure. The as-cast tensile strength (228 MPa) of adding pure Nd powder approximated to the figure (245 MPa) of adding Mg-Nd intermediate alloy. The tensile fracture mechanism of as-cast AZ31 transformed from cleavage fracture into quasi-cleavage fracture.

Influence of alloying elements on hot tearing susceptibility of Mg-Zn alloys based on thermodynamic calculation and experimental

Based on the hot tearing index|△T/△(fs)^(0.5)|recently proposed by Kou and the thermodynamic calculations of Pandat software,Al,Cu,and Mn elements were picked up and their influence on hot tearing susceptibility of Mg-x Zn(x=6,8,10,wt%)alloys was studied by experiments.The results indicate that Al addition can significantly reduce the hot tearing susceptibility of Mg-Zn alloys.Either 0.5Cu or 0.3Mn addition individually can reduce the HTS of the Mg-6Zn-(1,4)Al alloys,while adding together increases the susceptibility.The addition of 0.5Cu and 0.3Mn both individually and together increases the HTS of Mg-8/10Zn-1Al alloys.Based on the experimental and calculation results,the index can be modified to|△T/△(fs)^(0.5)|(d)^(2)for more accurate prediction on the hot tearing resistance of Mg-Zn based alloys.Grain refinement significantly improves the hot tearing resistance of Mg-Zn based alloys.

A comparison study of Ce/La and Ca microalloying on the bio-corrosion behaviors of extruded Mg-Zn alloys

The influences of Ca and Ce/La microalloying on the microstructure evolution and bio-corrosion resistances of extruded Mg-Zn alloys have been systematically investigated in the current study.Compared with single Ca or Ce/La addition,the Ca-Ce/La cooperative microalloying results in an outstanding grain refinement,because the fine secondary phase particles effectively hinder the recrystallized grain growth.The coarse Ca2Mg6Zn3 phases promote the formation of Ca3(PO4)2 or hydroxyapatite particles during the immersion process and accelerate the dissolution of the corrosion product film,which destroys its integrity and results in the deterioration of anti-corrosive performance.The Ce/La elements can be dispersed within the conventional Mg7Zn3 phases,which reduce the internal galvanic corrosion between Mg matrix and the secondary phases,leading to an obvious improvement of corrosion resistance.Therefore,the Ca-Ce/La cooperative microalloying achieves a homogenous fine-grained microstructure and improves the protective ability of surface film,which will pave a new avenue for the design of biomedical Mg alloys in the coming future.

Effects of Cu addition on microstructureand mechanical properties of as-cast Mg-6Znmagnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.

Creep resistance of as-cast Mg-5Al-5Ca-2Sn alloy

In the present study, creep properties of as-cast Mg-5Al-5Ca-2Sn(AXT552) alloy were investigated by means of a GWT304 creep testing machine at temperatures of 175 °C and 200 °C in the stress range of 35-90 MPa. Results show that creep rates increase with applied stress at an identical temperature. Creep strain at 100 hours is 0.0518% and 0.083% at creep conditions of 175°C/75 MPa and 200°C/60 MPa, respectively, which is comparable to MRI230 D and much lower than most of AX series alloys. By the observation and analysis for samples before and after creep tests using a Shimadzu XRD-7000 type X-ray diffractometer(XRD) and a Hitachi S-3400 N type scanning electron microscope(SEM), it was found that Al_2Ca(C15) phase precipitated out of C36 phase or matrix. The cavity formation and connection at the interface of soft matrix and hard intermetallics caused the propagation of cracking along the eutectic phase during creep process and dislocation accommodated grain/phase boundary sliding is expected to be the dominant creep mechanism.

Investigation of dry sliding wear properties of multi-directional forged Mg-Zn alloys

Effect of multi-directional forging(MDF)on wear properties of Mg-Zn alloys(with 2,4,and 6wt%Zn)is investigated.Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples.Wear behavior of samples was analyzed at loads of ION and 20 N,with sliding distances of 2000m and 4000m,at a sliding velocity of 3m/s.Microstructures of worn samples were observed under scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and x-ray diffraction(XRD)and the results were analyzed.Mechanical properties were evaluated using microhardness test.After 5 passes of MDF,the average grain size was found to be 30±4p m,22±3 pm,and 18±3 pm,in Mg-2%Zn,Mg-4%Zn,and Mg-6%Zn alloys,respectively,with significant improvement in hardness in all cases.Wear resistance was improved after MDF processing,as well as,with increment in Zn content in Mg alloy.However,it decreased when the load and the sliding distance increased.Worn surface exhibited ploughing,delamination,plastic deformation,and wear debris along sliding direction,and abrasive wear was found to be the main mechanism.

As-cast structure of DC casting 7075 aluminum alloy obtained under dual-frequency electromagnetic field

We have experimentally determined the as-cast structures of semi-continuous casting 7075 aluminum alloy obtained in the pres-ence of dual-frequency electromagnetic field. Results suggest that the use of dual-frequency electromagnetic field during the semi-continuous casting process of 7075 aluminum alloy ingots reduces the thickness of the surface segregation layer, increases the height of the melt menis-cus, enhances the surface quality of the ingot, and changes the surface morphology of the melt pool. Moreover, low-frequency electromag-netic field was found to show the most obvious influence on improving the as-cast structure because of its high permeability in conductors.

AS-CAST STRUCTURE OF Fe-Mo-C ALLOY

The structure and morphology of as-cast Fe-13wt-% Mo-0.8wt-% C alloy have been ob- served under SEM and TEM.Few δ-eutectoid but certain minor eutectics appear in the core of dendrites of the alloy.The eutectic carbide is found as skeleton M_6C while the eutectoid carbide as rodlet M_6C.

Predictability of Al-Mn Alloy Exposure Time Based on Its As-Cast Weight and Corrosion Rate in Sea Water Environment

This paper presents the predictability of aluminium-manganese alloy exposure time based on its as-cast weight and corrosion rate in sea water environment. The validity of the derived model: α = 26.67γ + 0.55β?- 0.29 is rooted on the core expression: 0.0375α = γ + 0.0206β?- 0.0109 where both sides of the expression are correspondingly approximately equal. Statistical analysis of model-predicted and experimentally evaluated exposure time for each value of as-cast weight and alloy corrosion rate considered shows a standard error of 0.0017% & 0.0044% and 0.0140% & 0.0150% respectively. The depths of corrosion penetration (at increasing corrosion rate: 0.0104 - 0.0157 mm/yr) as predicted by derived model and obtained from experiment are 0.7208 × 10-4 & 1.0123 × 10-4 mm and 2.5460 × 10-4 & 1.8240 × 10-4 mm (at decreasing corrosion rate: 0.0157 - 0.0062 mm/yr) respectively. Deviational analysis indicates that the maxi- mum deviation of the model-predicted alloy exposure time from the corresponding experimental value is less than 10%.

(Y,Gd)H_(2) phase formation in as-cast Mg-6Gd-3Y-0.5Zr alloy

In this work,a new(Y,Gd)H_(2) precipitate was identified and systematically investigated in the as-cast Mg-6Gd-3Y-0.5Zr alloy by XRD,SEM with EDS,TEM with EDS techniques and thermodynamics analysis.Results show that the as-cast alloy contains α-Mg,Mg_(24)(Gd,Y)_(5),and(Y,Gd)H_(2) phase.The(Y,Gd)H_(2) phase usually forms near the eutectic phase Mg_(24)(Gd,Y)_(5) or in the α-Mg grains,displaying a rectangle-shape.The Mg_(24)(Gd,Y)_(5) and(Y,Gd)H_(2) phases crystalize in bcc and fcc structure,respectively,and the(Y,Gd)H_(2) phase has a semi-coherent relationship with α-Mg matrix.The thermodynamics calculation results reveal that the hydrogen dissolved in the melt leads to the formation of hydrides.It is also found that the(Y,Gd)H_(2) hydride can form directly from the liquid phase during solidification.Additionally,it can precipitate by the decomposition of Mg_(24)(Gd,Y)_(5) phase due to absorbing hydrogen from the remaining melt.

Influence of the M and M’Metals on the Carbides Population in As-Cast M’-based Alloys Designed to be MC-Strengthened

High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals and reinforced by MC carbides stay in good place and their metallurgy merits to be well known.This work consists in a general exploration of the as-cast microstructures which can be obtained after solidification and solid state cooling down to ambient temperature for a wide series of alloys for which the base element and the MC-former element both vary.For fixed contents in chromium and carbon contents,the compositions of a total of nineteen alloys were considered.These alloys are based on Ni,Co,Fe or Nb and the M content was each time chosen to favor the appearance of TiC,TaC,NbC,HfC or ZrC,as single carbide in a given alloy.After elaboration,metallographic samples were observed by electron microscopy to investigate the obtained microstructures.The obtained results show first that the MC carbides were in many cases successfully obtained at the expense of other possible carbides(for all Co-based alloys for example)but there are also several exceptions(notably for some Nibased alloys).Second,the obtained monocarbides have a eutectic origin and they are script-liked shaped.However they are here too some exceptions,as the rare HfC obtained in a Nb-base).In general,the results obtained in this work show that the principle of dendritic matrix combined with MC carbides with a script-like morphology is not necessarily obtained:the nature of the{base element,MC-former element}combination governs the microstructure of the alloy in its as-cast state for these particular compositions in chromium and carbon.In some cases other carbides may appear and the microstructures may be even of another type.

As-Cast Microstructures of High Entropy Alloys Designed to Be TaC-Strengthened

In this work two new alloys were obtained by extrapolation from a well-known high entropy alloy,the equimolar CoNiFeMnCr one.This was done by the addition of carbon and of tantalum,Ta being one of the strongest MC-former elements.They were produced by conventional casting under inert atmosphere.The obtained microstructures were characterized by X-ray diffraction,metallography,electron microscopy,and energy dispersion spectrometry.Their hardness was also measured by hardness indentation.In parallel,the original CoNiFeMnCr alloy was also synthesized and characterized for comparison.The reference HEA alloy is single-phased with an austenitic structure,while the two{Ta,C}-added alloys are double-phased,with an austenitic matrix and interdendritic script-like TaC carbides.The matrixes of these HEA/TaC alloy are equivalent to an equimolar CoNiFeMnCr alloy to which 2 wt.%Ta is present in solid solution.The presence of the TaC carbides caused a significant increase in hardness which suggests that the HEA/TaC alloys may be mechanically stronger than the HEA reference alloy at high temperature.

Effects of Alloying Elements on the Microstructures and Mechanical Properties of Heavy Section Ductile Cast Iron

The effects of alloying elements on the as-cast microstructures and mechanical properties of heavy section ductile cast iron were investigated to develop press die material having high strength and high ductility. Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of alloy amounts within 0.25 to 0.75 wt pct range. Hardness is measured on the broken tensile specimens. The small additions of Mo, Cu, Ni and Cr changed the as-cast mechanical properties owing to the different as-cast matrix microstructures. The ferrite matrix of Mo and Ni alloyed cast iron exhibits low strength and hardness as well as high elongation and impact energy. The increase in Mo and Ni contents developed some fractions of pearlite structures near the austenite eutectic cell boundaries, which caused the elongation and impact energy to drop in a small range. Adding Cu and Cr elements rapidly changed the ferrite matrix into pearlite matrix, so strength and hardness were significantly increased. As more Mo and Cr were added, the size and fraction of primary carbides in the eutectic cell boundaries increased through the segregation of these elements into the intercellular boundaries.

Effect of texture and twinning on mechanical properties and corrosion behavior of an extruded biodegradable Mg-4Zn alloy

Microstructure,texture,mechanical properties and corrosion behavior of the extruded Mg-4Zn alloy,as a biodegradable material,were investigated.A refined microstructure caused by dynamic recrystallization(DRX),and a general fiber texture were achieved after extrusion.Mechanical properties along different directions of the extruded samples were investigated using shear punch test(SPT).The shear yield stress(SYS)of 113.8 MPa obtained in the transverse direction(TD)was higher than the 106 MPa achieved for the extruded direction(ED)and 45˚samples.This was attributed to the higher amounts of twins and also lower Schmid factor(SF)in the TD.On the other hand,encouraged activation of the basal slip system in the 45˚samples resulted in improved room temperature formability,as indicated by the normalized displacement in the SPT diagram.Electron back scattered diffraction(EBSD)analysis of the surfaces corroded in the phosphate buffered saline(PBS)solution,showed that despite having similar grain sizes and second phase particles shape and volume fractions,surfaces containing grains near(0001)orientations and extension twins<10¯12>(TD and 45˚samples)have lower corrosion rates,as compared to the ED specimens.

Effects of Cobalt Content and Preparation on Electrochemical Capacity of AB_5-Type Hydrogen Storage Alloys at Different Temperature

The effects of Co as a substituent for Ni on microstructure and electrochemical capacity of hydrogen storage alloys MI（NiCoMnAl）5.4 at -30- ＋80 ℃, in which the content of Co was 0, 1.31%, 2.63%, 3.94%, 5.25%, and 6.56% （mass fraction）, respectively, were reported. All of the alloys were prepared by vacuum induction melting followed by melt-spinning. It is found that the electrochemical capacity of alloys at different temperature depends upon the compositions and preparation methods. The electrochemical capacity of alloys increases at higher temperature （40 - 80 ℃ ） and decreases at lower temperature （ - 30 - 0 ℃ ） with an increasing cobalt content. With an increasing temperature, melt-spinning is more favorable for improved capacity of the alloys than casting. Analyses of the charging/discharging potential curves illustrate that higher cobalt content and melt-spinning techniques are more effective to increase the capacity at higher temperature because of the higher hydrogen evolution potential. On the contrary, the capacity of alloys at lower temperature can be increased by decreasing cobalt content and casting, which is ascribed to higher hydrogen evolution potential and delayed hydrogen evolution reaction, as well as reduced potential drop in the charging/discharging process. XRD patterns confirm that all of the specimens present a single hexagonal CaCu5-type structure and an increased lattice parameters with increasing Co content. The FWHM of the main peak of melt-spun ribbons reduces because of more homogeneous composition and less lattice strain defects.