Simultaneously improving thermal conductivity,mechanical properties and metal fluidity through Cu alloying in Mg-Zn-based alloys

Mg-Zn-based alloys have been widely used in computer,communication,and consumer(3C)products due to excellent thermal conductivity.However,it is still a challenge to balance their mechanical performance and thermal conductivity.Here,we investigate microstructure,mechanical performance,thermal conductivity and metal fluidity of Mg-5Zn(wt.%)alloy after Cu alloying by experimental and simulation methods.First,Mg-5Zn alloy consist ofα-Mg matrix and interdendritic MgZn phases.As the Cu content increases,however,MgZn phases disappear but intragranular Mg_(2)Cu and interdendritic MgZnCu phases appear in Mg-5Zn-Cu alloys.Besides,the grain size ofα-Mg phase is refined and the volume fraction of MgZnCu phase increases as the Cu content increases.Second,Cu addition is found to improve thermal conductivity of Mg-5Zn alloy remarkably.Especially,Mg-5Zn-4Cu alloy exhibits the best thermal conductivity of 124 W/(m·K),which is mainly due to the significant reduction in both solid solubility of Zn in theα-Mg matrix and lattice distortion ofα-Mg matrix.Moreover,a stable crystal structure of MgZnCu phase also contributes to an increased thermal conductivity based on first principles and molecular dynamics simulations.Third,Cu addition simultaneously enhances strength and ductility of Mg-5Zn alloy.Tensile yield strength and elongation of Mg-5Zn-6Cu alloy reach 117 MPa and 18.0%,respectively,which is a combined result of refinement,solution,second phase,and dislocation strengthening.Finally,combined with a phase field simulation,we found that Cu addition enhances metal fluidity of Mg-5Zn alloy.On the one hand,Cu alloying not only delays dendrite growth but also prolongs solidification time.On the other hand,MgZnCu phase stabilizes the dendrite growth of theα-Mg phases by reducing energy consumption during solidification of liquid metal.This work demonstrates that Cu alloying is an ideal strategy for synergistically improving the thermal conductivity,mechanical performance and metal fluidity of Mg-based alloys.

Research progress in friction stir processing of magnesium alloys and their metal matrix surface composites: Evolution in the 21^(st )century

Rising concerns about climate change drive the demand for lightweight components.Magnesium(Mg)alloys are highly valued for their low weight,making them increasingly important in various industries.Researchers focusing on enhancing the characteristics of Mg alloys and developing their Metal Matrix Composites(MMCs)have gained significant attention worldwide over the past decade,driven by the global shift towards lightweight materials.Friction Stir Processing(FSP)has emerged as a promising technique to enhance the properties of Mg alloys and produce Mg-MMCs.Initially,FSP adapted to refine grain size from the micro to the nano level and accelerated the development of MMCs due to its solid-state nature and the synergistic effects of microstructure refinement and reinforcement,improving strength,hardness,ductility,wear resistance,corrosion resistance,and fatigue strength.However,producing defect-free and sound FSPed Mg and Mg-MMCs requires addressing several variables and their interdependencies,which opens up a broad range of practical applications.Despite existing reviews on individual FSP of Mg,its alloys,and MMCs,an attempt has been made to analyze the latest research on these three aspects collectively to enhance the understanding,application,and effectiveness of FSP for Mg and its derivatives.This review article discusses the literature,classifies the importance of Mg alloys,provides a historical background,and explores developments and potential applications of FSPed Mg alloys.It focuses on novel fabrication methods,reinforcement strategies,machine and tool design parameters,material characterization,and integration with other methods for enhanced properties.The influence of process parameters and the emergence of defects are examined,along with specific applications in mono and hybrid composites and their microstructure evolution.The study identifies promising reinforcement materials and highlights research gaps in FSP for Mg alloys and MMCs production.It concludes with significant recommendations for further exploration,reflecting ongoing advancements in this field.

Mitigated reaction kinetics between lithium metal anodes and electrolytes by alloying lithium metal with low-content magnesium

Lithium(Li)metal is regarded as a promising anode candidate for high-energy-density rechargeable batteries.Nevertheless,Li metal is highly reactive against electrolytes,leading to rapid decay of active Li metal reservoir.Here,alloying Li metal with low-content magnesium(Mg)is proposed to mitigate the reaction kinetics between Li metal anodes and electrolytes.Mg atoms enter the lattice of Li atoms,forming solid solution due to the low amount(5 wt%)of Mg.Mg atoms mainly concentrate near the surface of Mg-alloyed Li metal anodes.The reactivity of Mg-alloyed Li metal is mitigated kinetically,which results from the electron transfer from Li to Mg atoms due to the electronegativity difference.Based on quantitative experimental analysis,the consumption rate of active Li and electrolytes is decreased by using Mgalloyed Li metal anodes,which increases the cycle life of Li metal batteries under demanding conditions.Further,a pouch cell(1.25 Ah)with Mg-alloyed Li metal anodes delivers an energy density of 340 Wh kg^(-1)and a cycle life of 100 cycles.This work inspires the strategy of modifying Li metal anodes to kinetically mitigate the side reactions with electrolytes.

Microstructure and mechanical properties of Mg-Gd-Y-Zr alloy cast by metal mould and lost foam casting

The microstructure and mechanical properties of Mg-10.1Gd-3.74Y-0.25Zr （mass fraction, %） alloy （GW104 alloy） cast by metal mould casting （MMC） and lost foam casting （LFC） were evaluated, respectively. It is revealed that different forming modes do not influence the phase composition of as-cast alloy. In the as-cast specimens, the microstructures are similar and composed of α-Mg solid solution, eutectic compound of α-Mg＋Mg 24 （Gd, Y） 5 and cuboid-shaped Mg 5 （Gd, Y） phase; whereas the average grain size of the alloy produced by metal mould casting is smaller than that by lost foam casting. The eutectic compound of the alloy is completely dissolved after solution treatment at 525 ℃for 6 h, while the Mg 5 （Gd, Y） phase still exists after solution treatment. After peak-ageing, the lost foam cast alloy exhibits the maximum ultimate tensile strength of 285 MPa, and metal mould cast specimen 325 MPa at room temperature, while the tensile yield strengths of them are comparable. It can be concluded that GW104 alloy cast by lost foam casting possesses similar microstructure and evidently lower mechanical strength compared with metal mould cast alloy, due to slow solidification rate and proneness to form shrinkage porosities during lost foam casting process.

Microstructure and mechanical properties of AZ31B magnesium alloy gas metal arc weld

Wrought magnesium alloy sheets were butt welded with gas metal arc welding process. Pores in the weld were investigated under different welding parameters, the causes of pore formation were systematically disposed, and the effects of porosity on the microstructure and mechanical properties of the joint were analyzed. The microstructure examination shows that the pores mainly appear close to the top or bottom part of the weld, and could connect to each other and lead to the formation of cracks in the welds. However, the pores can be controlled with proper welding parameters. The tensile testing results reveal that the average joint strength is close to or higher than that of the base metal. The microhardness in the weld can be even higher than that in the base metal due to the second ohase strengthening of β-Mg17（A1, Zn）12 formed in the weld.

Effects of low melting point metals(Ga,In,Sn) on hydrolysis properties of aluminum alloys

Low melting point metals（Ga, In, Sn） as alloy elements were used to prepare Al-In-Sn and Al-Ga-In-Sn alloys through mechanical ball milling method. The effects of mass ratio of In to Sn and Ga content on the hydrolysis properties of aluminum alloys were investigated. X-ray diffraction（XRD） and scanning electron microscopy（SEM） with energy disperse spectroscopy（EDS） were used to analyze the compositions and morphologies of the obtained Al alloys. The results show that the phase compositions of Al-In-Sn ternary alloys are Al and two intermetallic compounds, In3 Sn and In Sn4. All Al-In-Sn ternary alloys exhibit poor hydrolysis activity at room temperature. Al-In-Sn alloy with the mass ratio of In to Sn equaling 1：4 has the highest hydrogen yield. After Ga is introduced to the ternary alloys, the hydrolysis activity of aluminum alloys at room temperature is greatly improved. It is speculated that the addition of Ga element promotes the formation of defects inside the Al alloys and Ga-In3Sn-In Sn4 eutectic alloys on the alloys surface. Al atoms can be dissolved in this eutectic phase and become the active spots during the hydrolysis process. The small size and uniform distribution of this eutectic phase may be responsible for the enhancement of hydrolysis activity.

Influences of different filler metals on electron beam welding of titanium alloy to stainless steel

Electron beam welding experiments of titanium alloy to stainless steel were carried out with different filler metals, such as Ni, V, and Cu. Microstructures of the joints were examined by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. As a result, influences of filler metals on microstructures and mechanical properties of electron beam welded titanium-stainless steel joints were discussed. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. For each type of the filler metal, the type of solid solution and interfacial intermetallics depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe2Ti＋Ni3Ti＋NiTi2, TiFe, and Cu2Ti＋CuTi＋CuTi2 in the joints welded with Ni, V, and Cu filler metals, respectively. The tensile strengths of the joints were dependent on the hardness of the interfacial intermetallics. The joint welded with Ag filler metal had the highest tensile strength, which is about 310 MPa.

Microstructures of brazing zone between titanium alloy and stainless steel using various filler metals

Titanium alloy (Ti-Al-V alloy) substrate was brazed with stainless steel (STS304) using filler metal.At an optimized brazing condition,various filler metals were used.Microstructures were observed at each condition.Filler metals were titanium based 40Ti-20Zr-20Cu-20Ni,silver based Ag 5Pd,and nickel based Ni-7Cr-3.1B-4.5Si-3Fe-0.06C (BNi2) and Ni-14Cr-10P-0.06C (BNi7).To select a good filler metal for brazing process,wetting test was performed at 880-1050 °C.It was not brazed using silver based filler metals,but at the conditions using titanium and nickel based filler metals had brazed zone between titanium alloy and stainless steel.However,titanium alloy was eroded during brazing using titanium based filler metals.Nickel based filler metal has a good brazed zone between titanium alloy and stainless steel among the filler metals.

Microstructures and properties analysis of dissimilar metal joint in the friction stir welded copper to aluminum alloy

This paper mainly concentrated on the feasibility of friction stir welding of dissimilar metal of aluminum alloy to copper （I2） and a preliminary analysis of welding parameters influencing on the microstructures and properties of joint was carried out. The results indicated that the thickness of workpiece played an important role in the welding parameters which could succeed in the friction stir welding of dissimilar metal of copper to aluminum alloy, and the parameters were proved to be a narrow choice. The interfacial region between copper and aluminum in the dissimilar joint was not uniformly mixed, constituted with part of incomplete mixing zone, complete mixing zone, dispersion zone and the most region＇ s boundary was obvious. Meantime a kind banded structure with inhomogeneous width was formed. The intermetallic compounds generated during friction stir welding in the interfacial region were mainly CugAl4, Al2Cu etc, and their hardness was higher than oihers.

Microstructural evolution and intermetallic formation in Al-8wt% Si-0.8wt% Fe alloy due to grain refiner and modifier additions

An alloy of A1-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstrucmral changes due to Ti-B refiner and Sr modifier additions were studied. Apart from usual refinement and modification of the microstructure, some mutual influences of the additives took place, and no mutual poisoning effects by these additives, in combined form, were observed. It was noticed that the dimensions of the iron-rich intermetallics were influenced by the additives causing them to become larger. The needle-shaped intermetallics that were obtained from refiner addition became thicker and longer when adding the modifier. It was also found that a-Al and eutectic silicon phases preferentially nucleate on different types of intermetallic compounds. The more iron content of the intermetallic compounds and the more changes in their dimensions occurred. Formation of the shrinkage porosities was also observed.

Brazing 6061 aluminum alloy with Al-Si-Zn filler metals containing Sr

Al-6.5Si-42Zn and Al-6.5Si-42Zn-0.09Sr filler metals were used for brazing 6061 aluminum alloy. Air cooling and water cooling were applied after brazing. Si phase morphologies in the brazing alloy and the brazed joints were investigated. It was found that zinc in the Al-Si filler metals could reduce the formation of eutectic Al-Si phase and lower the brazing temperature at about 520℃. Adding 0.09wt% Sr element into the Al-6.5Si-42Zn alloy caused a-Al phase refinement and transformed acicular Si phase into the finely fiber-like. After water cooling, Zn element dissolved into the Al-Si eutectic area, and η-Zn phase disappeared in the brazed joints. Tensile strength testing results showed that the Sr-modified filler metal could enhance the strength of the brazed joints by 13% than Al-12Si, while water-cooling further improved the strength at 144 MPa.

EAM APPROACH TO ENTHALPY OF FORMATION OF ALKALI METAL ALLOYS

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Effect of Mo on properties of the industrial Fe–B-alloy-derived Fe-based bulk metallic glasses

The experimental results concerning the effects of Mo on the glass-forming ability(GFA), thermal stability, and mechanical, anticorrosion, and magnetic properties of an(Fe_(71.2)B_(24)Y_(4.8))_(96)Nb_4 bulk metallic glass(BMG) were presented. An industrial Fe–B alloy was used as the raw material, and a series of Fe-based BMGs were synthesized. In BMGs with the Mo contents of approximately 1at%–2at%, the cast alloy reached a critical diameter of 6 mm. The hardness and fracture strength also reached their maximum values in this alloy system. However, the anticorrosion and magnetic properties of the BMGs were not substantially improved by the addition of Mo. The low cost, good GFA, high hardness, and high fracture strength of the Fe-based BMGs developed in this work suggest that they are potential candidates for commercial applications.

Light alloying element‐regulated noble metal catalysts for energy‐related applications

Noble metals have been widely used as heterogeneous catalysts because they exhibit high activity and selectivity for many reactions of both academic and industrial interest.The introduction of light atomic species(e.g.,H,B,C,and N)into noble metal lattices plays an important role in optimizing catalytic performance by modulating structural and electronic properties.In this review,we present a general overview of the recent advances in the modification of noble metals with light alloying elements for various catalytic reactions,particularly for energy‐related applications.We summarize the types,location,concentration,and ordering degree of light atoms as major factors in the performance of noble metal‐based catalysts,with emphasis on how they can be rationally controlled to promote activity and selectivity.We then summarize the synthetic strategies developed to incorporate light elements and highlight the theoretical and experimental methods for understanding the alloying effects.We further focus on the wide usage of noble metal‐based catalysts modified with different light alloying atoms and attempt to correlate the structural features with their catalytic performances.Finally,we discuss current challenges and future perspectives regarding the development of highly efficient noble metal‐based catalysts modified with light elements.

In situ laser deposition of NiTi intermetallics for corrosion improvement of Ti-6Al-4V alloy

NiTi intermetallic coatings were fabricated on the surface of Ti-6Al-4V alloy by melting Ni and Ti powders using laser metal deposition（LMD） process.The effects of NiTi reinforcement content on the microstructure,hardness and corrosion properties of the coatings were examined.The results show that the deposited coatings are characterized by NiTi,NiTi2 and NiTi3 intermetallic phases.An appreciable increase in corrosion resistance is obtained for all the coatings,and Ti55Ni45 coating shows the highest corrosion resistance;while coatings Ti50Ni50 and Ti45Ni55 follow in that succession.The reinforcement materials are proven to be corrosion resistant in the tested environment,and the effect of Ti is more dominant.

Wire and arc additive manufacturing of 4043 Al alloy using a cold metal transfer method

Cold metal transfer plus pulse(C+P)arc was applied in the additive manufacturing of 4043 Al alloy parts.Parameters in the manufacturing of the parts were investigated.The properties and microstructure of the parts were also characterized.Experimental results showed that welding at a speed of 8 mm/s and a wire feeding speed of 4.0 m/min was suitable to manufacture thin-walled parts,and the reciprocating scanning method could be adopted to manufacture thick-walled parts.The thin-walled parts of the C+P mode had fewer pores than those of the cold metal transfer(CMT)mode.The thin-and thick-walled parts of the C+P mode showed maximum tensile strengths of 172 and 178 MPa,respectively.Hardness decreased at the interface and in the coarse dendrite and increased in the refined grain area.

Theoretical investigations of half-metallic ferromagnetism in new Half-Heusler YCrSb and YMnSb alloys using first-principle calculations

Structural,electronic,and magnetic properties of new predicted half-Heusler YCrSb and YMnSb compounds within the ordered MgAgAs Clb-type structure are investigated by employing first-principal calculations based on density functional theory.Through the calculated total energies of three possible atomic placements,we find the most stable structures regarding YCrSb and YMnSb materials,where Y,Cr(Mn),and Sb atoms occupy the(0.5,0.5,0.5),(0.25,0.25,0.25),and(0,0,0) positions,respectively.Furthermore,structural properties are explored for the non-magnetic and ferromagnetic and anti-ferromagnetic states and it is found that both materials prefer ferromagnetic states.The electronic band structure shows that YCrSb has a direct band gap of 0.78 eV while YMnSb has an indirect band gap of 0.40 eV in the majority spin channel.Our findings show that YCrSb and YMnSb materials exhibit half-metallic characteristics at their optimized lattice constants of 6.67 and 6.56 ,respectively.The half-metallicities associated with YCrSb and YMnSb are found to be robust under large in-plane strains which make them potential contenders for spintronic applications.

Microstructure and properties of an Al–Ti–Cu–Si brazing alloy for SiC–metal joining

An Al–Ti–Cu–Si solid–liquid dual-phase alloy that exhibits good wettability and appropriate interfacial reaction with SiC at 500–600°C was designed for SiC–metal joining. The microstructure, phases, differential thermal curves, and high-temperature wetting behavior of the alloy were analyzed using scanning electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, and the sessile drop method. The experimental results show that the 76.5Al–8.5Ti–5Cu–10Si alloy is mainly composed of Al–Al2Cu and Al–Si hypoeutectic low-melting-point microstructures (493–586°C) and the high-melting-point intermetallic compound AlTiSi (840°C). The contact angle, determined by high-temperature wetting experiments, is approximately 54°. Furthermore, the wetting interface is smooth and contains no obvious defects. Metallurgical bonding at the interface is attributable to the reaction between Al and Si in the alloy and ceramic, respectively. The formation of the brittle Al4C3phase at the interface is suppressed by the addition of 10wt% Si to the alloy. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

The electrochemical characteristics of AB_(4)-type rare earth-Mg-Ni-based superlattice structure hydrogen storage alloys for nickel metal hydride battery

Rare earth-Mg-Ni-based alloys with superlattice structures are new generation negative electrode materials for the nickel metal hydride batteries.Among them,the novel AB_(4)-type superlattice structure alloy is supposed to have superior cycling stability and rate capability.Yet its preparation is hindered by the crucial requirement of temperature and the special composition which is close to the other superlattice structure.Here,we prepare rare earth-Mg-Ni-based alloy and study the phase transformation of alloys to make clear the formation of AB_(4)-type phase.It is found Pr_(5)Co_(19)-type phase is converted from Ce_(5)Co_(19)-type phase and shows good stability at higher temperature compared to the Ce_(5)Co_(19)-type phase in the range of 930-970℃.Afterwards,with further 5℃increasing,AB_(4)-type superlattice structure forms at a temperature of 975℃by consuming Pr_(5)Co_(19)-type phase.In contrast with A_(5)B_(19)-type alloy,AB_(4)-type alloy has superior rate capability owing to the dominant advantages of charge transfer and hydrogen diffusion.Besides,AB_(4)-type alloy shows long lifespan whose capacity retention rates are 89.2%at the 100;cycle and 82.8%at the 200;cycle,respectively.AB_(4)-type alloy delivers 1.53 wt.%hydrogen storage capacity at room temperature and exhibits higher plateau pressure than Pr_(5)Co_(19)-type alloy.The work provides novel AB_(4)-type alloy with preferable electrochemical performance as negative electrode material to inspire the development of nickel metal hydride batteries.

Vacuum brazing of Si/SiC ceramic composite and Invar alloy using TiSOCu-W filler metals

Si/SiC ceramic composite and lnvar alloy were successfidly joined by vacuum brazing using Ti5OCu-W filler metals into which W was added to release the thermal stress of the brazed joint. Microstructures of the brazed joints were irwestigated by scanning electron micrascope （SEM） and energy dispersive spectrometer （EDS）. The mechanical properties of the brazed joints were measured by shearing tests. The results showed that the brazed joints were composed of Ti-Cu phase, W phase and Ti-Si phase. W had no effect on the wettability and mobility of the .filler metals. The growth of Ti2 Cu phase was restrained, and the reaction between ceramic composite and filler metals was weakened. The specimen, brazed at 970°C for 5 rain, had the maximum shear strength of 108 MPa at room temperature.