热挤压对快速凝固Al-Si-Fe-Cu-Mg合金显微组织及性能的影响

采用单辊旋淬法制备了快速凝固Al-20Si-5Fe-Cu-Mg合金,采用了SEM对其进行观察分析。结果表明,快速凝固能够极大细化Al-20Si-5Fe-Cu-Mg合金组织,抑制Si相及β-Fe相的析出长大,且组织的细化程度呈梯度分布。对快速凝固Al-20Si-5Fe-Cu-Mg合金进行了不同工艺参数的热挤压实验。结果表明,粉末包套热挤压工艺能够使快速凝固Al-20Si-5Fe-Cu-Mg带材合金致密化,当挤压温度为400℃、挤压比为1∶16时,合金获得了较优异的力学性能,其屈服强度和抗拉强度分别达到了456 MPa和805 MPa,压缩率为9.3%。

Stable operation of highly loaded pure Si-Fe anode under ambient pressure via carboxy silane-directed robust solid electrolyte interphase

Incorporation of higher content Si anode material beyond 5 wt% to Li-ion batteries(LIBs)is challenging,owing to large volume change,swelling,and solid electrolyte interphase(SEI)instability issues.Herein,a strategy of diacetoxydimethylsilane(DAMS)additive-directed SEI stabilization is proposed for a stable operation of Si-0.33FeSi_(2)(named as Si-Fe)anode without graphite,which provides siloxane inorganics and organics enrichment that compensate insufficient passivation of fluoroethylene carbonate(FEC)additive and reduce a dependence on FEC.Unprecedented stable cycling performance of highly loaded(3.5 mA h cm^(-2))pure Si-Fe anode is achieved with 2 wt%DAMS combined with 9 wt%FEC additives under ambient pressure,yielding high capacity 1270 mA h g^(-1)at 0.5 C and significantly improved capacity retention of 81% after 100 cycles,whereas short circuit and rapid capacity fade occur with FEC only additive.DAMS-directed robust SEI layer dramatically suppresses swelling and particles crossover through separator,and therefore prevents short circuit,demonstrating a possible operation of pure Si or Sidominant anodes in the next-generation high-energy-density and safe LIBs.

Ti-Si-Fe添加量与氮气压强对BN/SiC/Si_(3)N_(4)复相陶瓷材料的影响

以BN粉、Si粉、SiC粉、Ti-Si-Fe合金、助烧剂B_(2)O_(3)及外加结合剂酚醛树脂(PFF)为原料,采用原位氮化反应烧结制备BN/SiC/Si_(3)N_(4)复相陶瓷材料。探讨了在氮气气氛中添加不同含量Ti-Si-Fe合金部分替代硅粉及不同的气压下制得试样的力学性能差异。结果表明,Ti-Si-Fe合金中的Fe、Mn等元素促进了硅粉的氮化和氮化硅晶须的生长,所有的氮化产物均可以更好地填充气孔并提高试样的致密化程度以及调控材料的力学性能。当Ti-Si-Fe合金添加量为1.5 wt.%时,常压下试样的显气孔率最低为25.3%、体积密度最高为1.97 g·cm^(-3),常温抗弯强度最高为33.8 MPa;气压下试样的显气孔率最低为20.8%,体积密度最高为2.15 g·cm^(-3),常温抗弯强度最高为43.4 MPa。与常压相比,2 MPa气氛压力烧成的试样,纤维状的Si_(3)N_(4)晶须明显偏少,柱状的Si_(3)N_(4)晶须明显偏多。

Ti-Si-Fe合金添加量对Si_(3)N_(4)结合SiC材料结构与性能的影响

为促进Si_(3)N_(4)结合SiC耐火材料的致密化,降低Si粉氮化温度,以SiC颗粒和细粉、Si粉为主要原料,利用从高钛型高炉渣提取的Ti-Si-Fe合金部分取代Si粉,在埋碳气氛下于1350℃反应烧结5 h,制备了Si_(3)N_(4)结合SiC耐火材料。研究了Ti-Si-Fe合金添加量(加入质量分数分别为0、1.8%、3.6%、5.4%、7.2%)对Si粉的氮化行为、材料力学性能和显微结构的影响,并探讨了氮化反应烧结机制。结果表明:1)随着Ti-Si-Fe合金添加量的增加,材料的常温力学性能和高温抗折强度明显改善,荷重软化温度均超过1700℃,Ti-Si-Fe合金添加量超过3.6%(w)后材料性能的增幅变缓;2)Ti-Si-Fe合金促进了Si粉在较低温度下的完全氮化和材料的反应烧结,Ti-Si-Fe合金中各物相及Si粉氮化反应的体积增加能够充填气孔,氮化产物改善骨料与基质、基质内部的结合状态,从而提高材料的致密化程度,改善力学性能;3)引入Ti-Si-Fe合金后,反应体系中形成了富含Ti、Si、N、Fe成分的液相,氮化物的形成除传统的VS、VLS机制外,溶解-沉淀机制在短柱状β-Si_(3)N_(4)、粒状TiN的形成中起到主导作用,交错连结的α-Si_(3)N_(4)晶须、短柱状β-Si_(3)N_(4)、粒状TiN对材料的力学性能起到增强作用。

微量Ce添加对Al-Si-Fe铝合金微观组织及导热性能的影响

随着汽车零部件、通讯和电子产品的发展,其对铝合金的导热性能提出更高的需求,因此急需开发新型高强韧高导热铝合金材料。通过金相显微镜、扫描电镜、涡流电导率仪和万能力学性能测试仪等研究了微量Ce添加对Al-Si-Fe铝合金的微观组织、导电导热性能以及力学性能的影响。结果表明,稀土Ce添加量少于0.05%时对组织没有明显细化,0.07%Ce可以细化铝合金的微观组织,减少二次枝晶臂间距,初生α-Al相由粗大的枝状晶转化成胞状晶。当Ce含量为0.07%时,合金中出现亮白色的块状Al11Ce3相和灰白色针片状β-Al5FeSi相。稀土Ce元素的添加能提高合金的导电和导热性能,当添加0.07%Ce时,合金的导电率和导热率达到最佳值,导电率为36.6%IACS,导热率为153.97 W/(m·K)。随着微量稀土Ce元素的添加,合金的抗拉强度与屈服强度整体变化不大,抗拉强度为144.5 MPa,屈服强度为89.7 MPa,但伸长率有所提升。当添加0.07%Ce时,合金伸长率为4.54%,比未添加Ce时提升26.1%,这是由于微量Ce没有对组织产生足够的细化效果来提高强度,而使共晶Si和富铁相变质与细化,故提高了合金的伸长率。

Modification ofβ-Al_5FeSi Compound in Recycled Al-Si-Fe Cast Alloy by Using Sr,Mg and Cr Additions

The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-likeβ-Al-5FeSi phases （β-compound） into the fibrousα-Al-8Fe-2Si （α-compound）.The additions of Sr and Sr/Mg were less effective to modify theβ-compound into theα-compound,while the eutectic Si was fully modified into the fibrous morphology.A small secondary dendrite arm spacing （DAS） was found in the Sr-added,Cr-added and Sr/Cr-added alloys,especially in a steel mold.The Sr,Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously.A sludge phase was found in the addition of Cr-added,Sr/Cr-added and Mg-added alloys,especially in the graphite mold casting.The volume fraction ofβ-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify theβ-compound for the recycled Al-Si-Fe based alloys.

Microstructure and compressive deformation of hypereutectic Al-Si-Fe based P/M alloys fabricated by spark plasma sintering

Al-Si-Fe based alloys are attractive light-weight structural materials for automotive engine components because of their high wear resistance, low density and low thermal expansion. Al-17Si 5Fe-2Cu-lMg-lNi-lZr alloys were produced in compact form by a spark plasma sintering （SPS） technique using gas atomized powders. The mean grain size of the compact was 530 nm, and fine equiaxed grains and uniformly distributed precipitates were observed in the compact. The compressive deformation behavior of the SPSed materials was examined at various temperatures and strain rates. All the true stress-true strain curves showed steady state flow after reaching peak stress. The peak stress decreased with increasing test temperature and decreasing strain rate. In the deformed specimens, the equiaxed grain morphology and the dislocation microstructure within the equiaxed grains were observed. These facts strongly indicated the occurrence of dynamic recrystallization during high temperature deformation of the present alloy.

Relationship between the unique microstructures and behaviors of high-entropy alloys

High-entropy alloys(HEAs),which were introduced as a pioneering concept in 2004,have captured the keen interest of nu-merous researchers.Entropy,in this context,can be perceived as representing disorder and randomness.By contrast,elemental composi-tions within alloy systems occupy specific structural sites in space,a concept referred to as structure.In accordance with Shannon entropy,structure is analogous to information.Generally,the arrangement of atoms within a material,termed its structure,plays a pivotal role in dictating its properties.In addition to expanding the array of options for alloy composites,HEAs afford ample opportunities for diverse structural designs.The profound influence of distinct structural features on the exceptional behaviors of alloys is underscored by numer-ous examples.These features include remarkably high fracture strength with excellent ductility,antiballistic capability,exceptional radi-ation resistance,and corrosion resistance.In this paper,we delve into various unique material structures and properties while elucidating the intricate relationship between structure and performance.

Microstructure and damping properties of LPSO phase dominant Mg-Ni-Y and Mg-Zn-Ni-Y alloys

This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.

High corrosion and wear resistant electroless Ni–P gradient coatings on aviation aluminum alloy parts

A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni–P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90°and was not corroded visually after 500 h of neutral salt spray test at 35℃. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.

Influence of heat treatment on microstructure,mechanical and corrosion behavior of WE43 alloy fabricated by laser-beam powder bed fusion

Magnesium(Mg)alloys are considered to be a new generation of revolutionary medical metals.Laser-beam powder bed fusion(PBF-LB)is suitable for fabricating metal implants withpersonalized and complicated structures.However,the as-built part usually exhibits undesirable microstructure and unsatisfactory performance.In this work,WE43 parts were firstly fabricated by PBF-LB and then subjected to heat treatment.Although a high densification rate of 99.91%was achieved using suitable processes,the as-built parts exhibited anisotropic and layeredmicrostructure with heterogeneously precipitated Nd-rich intermetallic.After heat treatment,fine and nano-scaled Mg24Y5particles were precipitated.Meanwhile,theα-Mg grainsunderwent recrystallization and turned coarsened slightly,which effectively weakened thetexture intensity and reduced the anisotropy.As a consequence,the yield strength and ultimate tensile strength were significantly improved to(250.2±3.5)MPa and(312±3.7)MPa,respectively,while the elongation was still maintained at a high level of 15.2%.Furthermore,the homogenized microstructure reduced the tendency of localized corrosion and favoredthe development of uniform passivation film.Thus,the degradation rate of WE43 parts was decreased by an order of magnitude.Besides,in-vitro cell experiments proved their favorable biocompatibility.

An ionic liquid-assisted strategy for enhanced anticorrosion of low-energy PEO coatings on magnesium–lithium alloy

A low-energy plasma electrolytic oxidation(LePEO)technique is developed to simultaneously improve energy efficiency and anti-corrosion.Ionic liquids(1-butyl-3-methylimidazole tetrafluoroborate(BmimBF_(4)))as sustainable corrosion inhibitors are chosen to investigate the corrosion inhibition behavior of ionic liquid(ILs)during the LePEO process for LA91 magnesium-lithium(Mg-Li)alloy.Results show that the ionic liquid BmimBF_(4)participates in the LePEO coating formation process,causing an increment in coating thickness and surface roughness.The low conductivity of the ionic liquid is responsible for the voltage and breakdown voltage increases during the LePEO with IL process(LePEO-IL).After adding BmimBF_(4),corrosion current density decreases from 1.159×10^(−4)A·cm^(−2)to 8.143×10^(−6)A·cm^(−2).The impedance modulus increases to 1.048×10^(4)Ω·cm^(−2)and neutral salt spray remains intact for 24 h.The superior corrosion resistance of the LePEO coating assisted by ionic liquid could be mainly attributed to its compact and thick barrier layer and physical absorption of ionic liquid.The ionic liquid-assisted LePEO technique provides a promising approach to reducing energy consumption and improving film performance.

Machine learning-assisted efficient design of Cu-based shape memory alloy with specific phase transition temperature

The martensitic transformation temperature is the basis for the application of shape memory alloys(SMAs),and the ability to quickly and accurately predict the transformation temperature of SMAs has very important practical significance.In this work,machine learning(ML)methods were utilized to accelerate the search for shape memory alloys with targeted properties(phase transition temperature).A group of component data was selected to design shape memory alloys using reverse design method from numerous unexplored data.Component modeling and feature modeling were used to predict the phase transition temperature of the shape memory alloys.The experimental results of the shape memory alloys were obtained to verify the effectiveness of the support vector regression(SVR)model.The results show that the machine learning model can obtain target materials more efficiently and pertinently,and realize the accurate and rapid design of shape memory alloys with specific target phase transition temperature.On this basis,the relationship between phase transition temperature and material descriptors is analyzed,and it is proved that the key factors affecting the phase transition temperature of shape memory alloys are based on the strength of the bond energy between atoms.This work provides new ideas for the controllable design and performance optimization of Cu-based shape memory alloys.

Microstructures,corrosion behavior and mechanical properties of as-cast Mg-6Zn-2X(Fe/Cu/Ni)alloys for plugging tool applications

Mg-6Zn-2X(Fe/Cu/Ni)alloys were prepared through semi-continuous casting,with the aim of identifying a degradable magnesium(Mg)alloy suitable for use in fracturing balls.A comparative analysis was conducted to assess the impacts of adding Cu and Ni,which result in finer grains and the formation of galvanic corrosion sites.Scanner electronic microscopy examination revealed that precipitated phases concentrated at grain boundaries,forming a semi-continuous network structure that facilitated corrosion penetration in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys.Pitting corrosion was observed in Mg-6Zn-2Fe,while galvanic corrosion was identified as the primary mechanism in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys.Among the tests,the Mg-6Zn-2Ni alloy exhibited the highest corrosion rate(approximately 932.9 mm/a)due to its significant potential difference.Mechanical testing showed that Mg-6Zn-2Ni alloy possessed suitable ultimate compressive strength,making it a potential candidate material for degradable fracturing balls,effectively addressing the challenges of balancing strength and degradation rate in fracturing applications.

Influence of layer thickness on formation quality,microstructure,mechanical properties,and corrosion resistance of WE43 magnesium alloy fabricated by laser powder bed fusion

Laser powder bed fusion(L-PBF)of Mg alloys has provided tremendous opportunities for customized production of aeronautical and medical parts.Layer thickness(LT)is of great significance to the L-PBF process but has not been studied for Mg alloys.In this study,WE43 Mg alloy bulk cubes,porous scaffolds,and thin walls with layer thicknesses of 10,20,30,and 40μm were fabricated.The required laser energy input increased with increasing layer thickness and was different for the bulk cubes and porous scaffolds.Porosity tended to occur at the connection joints in porous scaffolds for LT40 and could be eliminated by reducing the laser energy input.For thin wall parts,a large overhang angle or a small wall thickness resulted in porosity when a large layer thicknesses was used,and the porosity disappeared by reducing the layer thickness or laser energy input.A deeper keyhole penetration was found in all occasions with porosity,explaining the influence of layer thickness,geometrical structure,and laser energy input on the porosity.All the samples achieved a high fusion quality with a relative density of over 99.5%using the optimized laser energy input.The increased layer thickness resulted to more precipitation phases,finer grain sizes and decreased grain texture.With the similar high fusion quality,the tensile strength and elongation of bulk samples were significantly improved from 257 MPa and 1.41%with the 10μm layer to 287 MPa and 15.12%with the 40μm layer,in accordance with the microstructural change.The effect of layer thickness on the compressive properties of porous scaffolds was limited.However,the corrosion rate of bulk samples accelerated with increasing the layer thickness,mainly attributed to the increased number of precipitation phases.

Effect of icosahedral phase formation on the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li(in wt.%)based alloys

Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy was 47%,whilst the I_(SCC)of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%.Surface,cross-sectional and fractography observations indicated that for the Mg-8%Li alloy,theα-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process.With regard to the Mg-8%Li-6%Zn-1.2%Y alloy,the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li andα-Mg/β-Li,and the preferential propagation paths were the I-phase/β-Li andα-Mg/β-Li interfaces.Moreover,the SCC of the two alloys was concerned with hydrogen embrittlement(HE)mechanism.

Prediction of the thermal conductivity of Mg–Al–La alloys by CALPHAD method

Mg-Al alloys have excellent strength and ductility but relatively low thermal conductivity due to Al addition.The accurate prediction of thermal conductivity is a prerequisite for designing Mg-Al alloys with high thermal conductivity.Thus,databases for predicting temperature-and composition-dependent thermal conductivities must be established.In this study,Mg-Al-La alloys with different contents of Al2La,Al3La,and Al11La3phases and solid solubility of Al in the α-Mg phase were designed.The influence of the second phase(s) and Al solid solubility on thermal conductivity was investigated.Experimental results revealed a second phase transformation from Al_(2)La to Al_(3)La and further to Al_(11)La_(3)with the increasing Al content at a constant La amount.The degree of the negative effect of the second phase(s) on thermal diffusivity followed the sequence of Al2La>Al3La>Al_(11)La_(3).Compared with the second phase,an increase in the solid solubility of Al in α-Mg remarkably reduced the thermal conductivity.On the basis of the experimental data,a database of the reciprocal thermal diffusivity of the Mg-Al-La system was established by calculation of the phase diagram (CALPHAD)method.With a standard error of±1.2 W/(m·K),the predicted results were in good agreement with the experimental data.The established database can be used to design Mg-Al alloys with high thermal conductivity and provide valuable guidance for expanding their application prospects.

Effect of melt holding on morphological evolution and sedimentation behavior of iron-rich intermetallic phases in Al-Si-Fe-Mn-Mg alloy

The effect of the melt holding temperature on the morphological evolution and sedimentation behavior of iron-rich intermetallics in Al-7.0 Si-1.0 Fe-1.2 Mn-0.25 Mg alloy was investigated using an optical microscope,scanning electron microscope and differential thermal analyzer.The results show that as the holding temperature decreases,the morphologies of the primary iron-rich phase in matrix change from star-like to polygonal,and the number of the primary phases gradually decreases and disappears at 615°C.Finally,the Chinese script phases with small size,high compact and uniform distribution are obtained.In contrast,the primary iron-rich phases in slag transform into a coarser polygonal shape with lower roundness,and some of them have hollow structures.Furthermore,the area fraction of intermetallics and Fe content in the matrix decrease gradually due to the formation and growth of sludge and subsequent natural sedimentation during melt holding.With the decrease of holding temperature,the main factors hindering the settlement of the primary phases are morphology,size,and density in turn.

Alloy design for laser powder bed fusion additive manufacturing:a critical review

Metal additive manufacturing(AM)has been extensively studied in recent decades.Despite the significant progress achieved in manufacturing complex shapes and structures,challenges such as severe cracking when using existing alloys for laser powder bed fusion(L-PBF)AM have persisted.These challenges arise because commercial alloys are primarily designed for conventional casting or forging processes,overlooking the fast cooling rates,steep temperature gradients and multiple thermal cycles of L-PBF.To address this,there is an urgent need to develop novel alloys specifically tailored for L-PBF technologies.This review provides a comprehensive summary of the strategies employed in alloy design for L-PBF.It aims to guide future research on designing novel alloys dedicated to L-PBF instead of adapting existing alloys.The review begins by discussing the features of the L-PBF processes,focusing on rapid solidification and intrinsic heat treatment.Next,the printability of the four main existing alloys(Fe-,Ni-,Al-and Ti-based alloys)is critically assessed,with a comparison of their conventional weldability.It was found that the weldability criteria are not always applicable in estimating printability.Furthermore,the review presents recent advances in alloy development and associated strategies,categorizing them into crack mitigation-oriented,microstructure manipulation-oriented and machine learning-assisted approaches.Lastly,an outlook and suggestions are given to highlight the issues that need to be addressed in future work.

Microstructures and micromechanical behaviors of high -entropy alloys investigated by synchrotron X-ray and neutron diffraction techniques: A review

High-entropy alloys(HEAs)possess outstanding features such as corrosion resistance,irradiation resistance,and good mechan-ical properties.A few HEAs have found applications in the fields of aerospace and defense.Extensive studies on the deformation mech-anisms of HEAs can guide microstructure control and toughness design,which is vital for understanding and studying state-of-the-art structural materials.Synchrotron X-ray and neutron diffraction are necessary techniques for materials science research,especially for in situ coupling of physical/chemical fields and for resolving macro/microcrystallographic information on materials.Recently,several re-searchers have applied synchrotron X-ray and neutron diffraction methods to study the deformation mechanisms,phase transformations,stress behaviors,and in situ processes of HEAs,such as variable-temperature,high-pressure,and hydrogenation processes.In this review,the principles and development of synchrotron X-ray and neutron diffraction are presented,and their applications in the deformation mechanisms of HEAs are discussed.The factors that influence the deformation mechanisms of HEAs are also outlined.This review fo-cuses on the microstructures and micromechanical behaviors during tension/compression or creep/fatigue deformation and the application of synchrotron X-ray and neutron diffraction methods to the characterization of dislocations,stacking faults,twins,phases,and intergrain/interphase stress changes.Perspectives on future developments of synchrotron X-ray and neutron diffraction and on research directions on the deformation mechanisms of novel metals are discussed.