Effects of Si alloying and T6 treatment on mechanical properties and wear resistance of ZA27 alloys

To improve the mechanical properties and wear resistance of ZA27 alloy, Si was introduced to the alloy, and the effect of Si alloying and T6 heat treatment on the microstructure, mechanical properties and wear resistance was investigated. The results show that with 0.55% Si, the microstructure of the alloy can be refined effectively, which leads to the increase of hardness. But the tensile strength and elongation decrease because Si undermines the integrity of the matrix. On the other hand, the dendrites are transformed into a desired α+η+(α+η)mixture with T6 heat treatment, which introduces a remarkable increase to the elongation and hardness of the alloy. The wear resistance of the ZA27 alloy with Si alloying is significantly better than that of the ZA27 alloy without Si. With the increase of Si addition, the wear resistance of the alloy firstly increases and then decreases.In the alloy without Si alloying, severe plastic deformation and large delamination were observed on the worn surface of the alloy. However, with the increase of Si, the main wear mechanism transformed to abrasive wear gradually. In addition, the T6 treatment can further improve the wear resistance of the alloy with Si alloying.

Nano silica aerogel-induced formation of an organic/alloy biphasic interfacial layer enables construction of stable high-energy lithium metal batteries

Lithium metal batteries represent promising candidates for high-energy-density batteries, however, many challenges must still be overcome,e.g., interface instability and dendrite growth. In this work, nano silica aerogel was employed to generate a hybrid film with high lithium ion conductivity(0.6 mS cm^(-1)at room temperature) via an in situ crosslinking reaction. TOF-SIMS profile analysis has revealed conversion mechanism of hybrid film to Li–Si alloy/Li F biphasic interface layer, suggesting that the Li–Si alloy and Li F-rich interface layer promoted rapid Li+transport and shielded the Li anodes from corrosive reactions with electrolyte-derived products. When coupled with nickel-cobalt-manganese-based cathodes, the batteries achieve outstanding capacity retention over 1000 cycles at 1 C. Additionally the developed film coated on Li enabled high coulombic efficiency(99.5%) after long-term cycling when coupled with S cathodes. Overall, the results presented herein confirm an effective strategy for the development of high-energy batteries.

Investigation of the Laser Powder Bed Fusion Process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy

Laser powder bed fusion(LPBF)is an advanced manufacturing technology;however,inappropriate LPBF process parameters may cause printing defects in materials.In the present work,the LPBF process of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was investigated by a two-step optimization approach.Subsequently,heat transfer and liquid flow behaviors during LPBF were simulated by a well-tested phenomenological model,and the defect formation mechanisms in the as-fabricated alloy were discussed.The optimized process parameters for LPBF were detected as laser power changed from 195 W to 210 W,with scanning speed of 1250 mm/s.The LPBF process was divided into a laser irradiation stage,a spreading flow stage,and a solidification stage.The morphologies and defects of deposited tracks were affected by liquid flow behavior caused by rapid cooling rates.The findings of this research can provide valuable support for printing defect-free metal components.

Effect of Ti on microstructure and properties of electromagnetic stirred Al-18wt.%Mg_(2)Si alloy

By adding different amounts of Ti into the electromagnetic stirred Al-18wt.%Mg_(2)Si alloy,the effect of Ti element on the microstructure and mechanical properties of the alloy was studied.The experimental results show that the microstructure is refined after modification with Ti,which is related to the heterogeneous nucleation of TiAl_(3) particles on theα-Al matrix.With the increase of Ti content and holding time after stirring,the primary Mg_(2)Si phase is refined firstly and then coarsened,and correspondingly,the mechanical properties of the alloy show a trend of increasing at first and then decreasing.When the addition of Ti is 0.5wt.%and the holding time is about 20 min,the refinement effect of primary Mg_(2)Si phase is the most significant and the mechanical properties of the alloy are optimal.

Microstructures and tensile properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements of Y,Bi,Sb and Sr

The microstructures and mechanical properties of as-cast Mg-5 Sn-1 Si magnesium alloy modified with trace elements Y,Bi,Sb and Sr were investigated and compared.Results show that the microstructure of the as-cast Mg-5 Sn-1 Si alloy consists ofα-Mg,Mg_(2) Si,Mg_(2) Sn and Mg_(2)(Si_xSn_(1-x))phases.After adding 0.8 wt.%Y,0.3 wt.%Bi,0.9 wt.%Sb and 0.9 wt.%Sr,respectively into the Mg-5 Sn-1 Si magnesium alloy,Mg_(24)Y_(5),Mg_(3) Bi_(2),Mg_(3) Sb_(2) and Mg_(2) Sr phases are precipitated accordingly.Trace elements can refineα-Mg grain and Chinese scriptshaped Mg_(2) Si phase.Refinement efficiency of different trace elements onα-Mg grain and Mg_(2) Si phase is varied.Sr element has the best refinement effect,followed by Sb and Bi,while Y has the least refinement effect.Mg-5 Sn-1 Si-0.9 Sr alloy has higher tensile properties than the other three modified alloys.The refinement mechanism of Y,Bi and Sr elements on Mg-5 Sn-1 Si magnesium alloy can be explained by the growth restriction factors and the solute undercooling.For Mg-5 Sn-1 Si-0.9 Sb alloy,the heterogeneous nuclei of Mg_(3) Sb_(2) phase is the main reason for the refinement of grains and second phases.

Microstructure evolution and mechanical properties of the Sip/Zn- Al composite joints by ultrasonic-assisted soldering in air

Hypereutectic Al -27Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn -5Al the filler alloys, and Si particulate-reinforced Zn - Al based composites filler joints were obtained. The ultrasonic vibration introduced into soldering could influence the migration of Si particles and the microstructure of solidified Zn - Al based alloys. Both the distribution of Si particles and microstructure of the solidified Zn - Al based alloys affected the shear strength of joints. The shear strength increased with the ultrasonic vibration time. The highest average shear strength of joints reached to -68.5 MPa. Transcrystalline rupture mode was observed on the fracture surface.

Isothermal corrosion Fe_3Si alloy in liquid zinc

The isothermal corrosion testing, microscopic examination and the performance of Fe3Si alloy as materials of construction for bath hardware in continuous hot-dipping lines were studied. The corrosion of Fe3Si alloy in molten zinc was controlled by attacking the grain boundaries preferentially. Aluminum reacted with iron of Fe3Si alloy firstly while the samples were immersed in molten zinc, although aluminum contents in the molten zinc were very low. The phase of reaction product was thought to be Fe2Al5. The corrosion rate of the Fe3Si alloy in molten zinc was determined to be approximately 2.9×10^-3 mm/h, therefore the liquid zinc corrosion resistance of Fe3Si alloy was very weak.

Effect of TiB2 and Al3Ti on the microstructure,mechanical properties and fracture behaviour of near eutectic Al−12.6Si alloy

A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were studied.The unmodified Al−12.6Si al-loy has an irregular needle and plate-like eutectic silicon(ESi)and coarse polygonal primary silicon(PSi)particles in the matrix-likeα-Al phase.The P_(Si),E_(Si),andα-Al morphology and volume fraction were changed due to the addition of the Al−5Ti−1B master alloy.The hardness,UTS,and elongation improved due to the microstructural modification.Nano-sized in-situ Al3Ti particles and ex-situ TiB_(2)particles caused the mi-crostructural modification.The fracture images of the developed alloys exhibit a ductile and brittle mode of fracture at the same time.The Al−5Ti−1B modified alloys have a more ductile mode of fracture and more dimples compared to the unmodified alloy.

Effects of Yttrium Ion on Formation Mechanism of ZrO_2-Y_2O_3 Ceramic Coatings Formed by Plasma Electrolytic Oxidation on Al-12Si Alloy

ZrO2-Y2O3 ceramic coating was produced by plasma electrolytic oxidation （PEO） on ZAlSil2Cu3Ni2 alloy. The microstructure and phase composition of the coating were investigated by SEM and XRD.： The results show that adding an appropriate amount of yttrium ion can improve the growing rate of ceramic coating at different oxidation stages and decrease arc voltage. The thickness of ZrO2-Y2O3 coating is 16 μn thicker than that of ZrO2 coating and the maximum oxidation rate improves by 0.6 μm/min. In addition, the arc voltage decreases from 227 to 172 V. It can be seen that the rate of oxidation firstly increases to some extent and then decreases with the content of yttrium ion increasing. The growth rate reaches the maximum while the content of yttrium ion is 0.05 g-L-1The maximum thickness is 90 μm.Compared to ZrO2 coating, the micropores of ZrO2-Y2O3 coating are less and the ceramic layer is repeatedly deposited by ZrO2 and Y2O3 ceramic particles. Meanwhile, the binding force between coating and substrate is better and the coating is uniform and compact. The ceramic layer is mainly composed of c-Y0.15Zr0.85O1.93□0.07, m-ZrO2, α-Al2O3, ,γ-Al2O3 and Y2O3. It is indicated that ZrO2 has beert fully stabilized by yttrium ion through the formation of solid solution.

Refinement and thermal analysis of hypereutectic Al-25%Si alloy

Refinement and thermal analysis of hypereutectic Al 25%Si alloy were investigated with scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that the average size of primary silicon in Al 25%Si alloy without and with phosphorus addition are 250 μm and 30 μm, respectively. But the primary and eutectic growth temperature is raised by about 17.3 ℃ and 4?℃ respectively due to phosphorus addition. The primary nucleation temperatures are 745.0 ℃ and 762.0 ℃ for untreated and treated samples and in addition, the enthalpy changes of primary and eutectic transformation are -261.0 J/g and -397.3 J/g without phosphorus addition, -294.2 J/g and -386.1 J/g with phosphorus addition, respectively. Otherwise the mechanisms of refinement and thermal transformation of Al 25%Si alloy in solidifying process are also discussed. [

Research on flow stress of spray formed 70Si30Al alloy under hot compression deformation

The flow stress of spray formed 70Si30Al alloy was studied by hot compression on a Gleeble- 1500 test machine. The experimental results indicated that the flow stress depends on the strain rate and the deformation temperature. The flow stress increases with an increase in strain rate at a given deformation temperature. The flow stress decreases with the deformation temperature increasing at a given strain rate. The relational expression among the flow stress, the swain rate, and the deformation temperature satisfies the Arrhenius equation. The deformation activation energy of 70Si30Al alloy during hot deformation is 866.27 kJ/mol from the Arrhenius equation.

Effect of P/M value on the preforms and microstructures of spray formed 70Si30Al alloy

A novel 70Si30Al alloy was prepared by the spray forming process for electronic packaging materials. The effect of the ratio of atomization pressure to metal melt mass flux rate （P/M） on the preforms and microstructures of the spray-deposited 70Si30Al alloy was studied. The results indicate that the PIM value has a considerable influence on the formation of the preforms and the optimal value is in the range of 0.209-0.231 MPa/（kg.min^-1）. The microstructure of the spray formed 70Si30AI alloy is fine and homogenous. The primary silicon phases distributing in the aluminum matrix evenly are fine and irregular. The aluminum matrix is divided into two groups： supersaturated α-Al phase or α-Al phase and Al-Si pseudoeutectic phase or Al-Si eutectic phase.

Optimization of processing parameters for preparation of Al-3Ti-1B grain refiner

Al-3Ti-1B master alloys were prepared at different processing parameters by the reaction of halide salts,and the grain refining response of Al-7Si alloy was investigated with Al-3Ti-B master alloy.The microstructure of master alloy and its grain refining effect on Al-7Si alloy were investigated by means of OM,XRD and SEM.Experimental results show that,the size of Al3Ti particles presented in Al-3Ti-1B master alloys increases with the increase of reaction temperature and decreases with the increase of cooling rate.The grain refining efficiency of Al-3Ti-1B master alloy on Al-7Si alloy is mainly attributed to heterogeneous nucleation of Al3Ti particles,and the morphology ofα(Al)changes from coarse dendritic to fine equiaxed.As a result,Al-3Ti-1B master alloy is prepared by permanent mold,and holding at 800 ℃for 30min,which has better grain refining performance on Al-7Si alloy.

Weldability and Microstructure of Nickel-Silicon Based Alloys

The NiSix based alloy typically has poor weldability due to its lower ductility. A limited amount of work has been performed on the weldability of NiSix based alloys. Therefore, the effect of heat treatment and welding parameters on weldability of the alloys, and the relationship between the weldability and microstructure were studied. The results show that the as-cast Ni-Si-Nb-B alloy （Ni 76. 5%, Si 20%, Nb 3%, and B 0. 5%） could be successfully welded after preheating at 600 ℃. The welding procedure should be performed on the alloys before any heat treatment and a preheating at 600 ℃ should be used. The fusion zone is harder than the matrix due to a large amount of 7 phase and a finer microstructure. The cracks are predominantly intergranular in heat affected zone and associated with the needle-like ）, phase. The heat treatment before welding increases the tendency of cracking in the fusion zone.

Deformation mechanism of the spray formed 70Si30Al alloy during hot compression

The deformation mechanism of the spray formed 70Si30Al alloy was studied by hot compression on a Gleeble-1500 test machine. It is shown that hot deformation of the spray formed 70Si30Al alloy is achieved by liquid flow due to isostatic pressure and movement of solid particles due to shear force. Deformation condition depends on the nucleation rate and closure rate of the cavities. The flow stress slightly varies when the difference between the nucleation rate and closure rate of the cavities is small; however, it decreases when the nucleation rate of the cavities is greater than the closure rate of the cavities.

Wettability of CuNi-Ti Alloys on Si_3N_4 and Interfacial Reaction Products

Based on the alloy Cu55Ni45 (at pct), holding the proportion of Cu to Ni in constant and in the temperature range of 1233~1573 K, the wetting angles of CuNi-0~56 at pct Ti alloys on Si3N4 have been measured by the sessile drop method. With the increase of Ti content, the wetting angles decreased. The equilibrium wetting angle was 5° when Ti content ≥32 at pct.In the case of same Ti content, the activity of Ti in CuNiTi alloy was weaker than that in CuTi alloy The cross-section of the CuNiTi-Si3N4 interface and the elements distribution were examined by scanning electron microscope with X-ray wave-dispersion spectrometer, and the reaction products formed at the interface were determined by X-ray diffiaction analysis method.

Efects of Al-Mn-Ti-P-Cu master alloy on microstructure and properties of Al-25Si alloy

To obtain a higher microstructural refining efficiency,and improve the properties and processing ability of hypereutectic Al-25Si alloy,a new environmentally friendly Al-20.6Mn-12Ti-0.9P-6.1Cu(by wt.%)master alloy was fabricated;and its modification and strengthening mechanisms on the Al-25Si alloy were studied.The mechanical properties of the unmodified,modified and heat treated alloys were investigated.Results show that the optimal addition amount of the Al-20.6Mn-12Ti-0.9P-6.1Cu master alloy is 4wt.%.In this case,primary Si and eutectic Si as well asα-Al phase were clearly refined,and this refining effect shows an excellent long residual action as it can be heat-retained for at least 5 h.After being T6 heat treated,the morphology of primary and eutectic Si in the Al-25Si alloys with the addition of 4wt.%Al-20.6Mn-12Ti-0.9P-6.1Cu alloy changes into particles and short rods.The average grain size of the primary and eutectic Si decreases from 250μm(unmodified)to 13.83μm and 35μm(unmodified)to 7μm;theα-Al becomes obviously finer and the distribution of Si phases tends to be uniform and dispersed.Meanwhile,the tensile properties are improved obviously;the tensile strengths at room temperature and 300 oC reach 241 MPa and127 MPa,increased by 153.7%and 67.1%,respectively.In addition,the tensile fracture mechanism changes from brittle fracture for the alloy without modification to ductile fracture after modification.Modifying the morphology of Si phase and strengthening the matrix can effectively block the initiation and propagation of cracks,thus improving the strength of the hypereutectic Al-25Si alloy.

DIFFUSION OF La IN LIQUID Al-Si ALLOY

The diffusion coefficients of lanthnum in liquid Al-Si alloy have been measured successfully by the anodic chronopotentiometry. At 973K, the diffusion coefficient of lanthanum (D_(La(Al-Si))) in liquid Al-5.2wt-%Si alloy equals (0.91±0.01)×10^(-5) cm^2 s^(-1) . In the range of temperatures 953-1053K, the relationship between the diffusion coefficient and the tem- perature is represented by 1gD_(La(Al-Si))=-1.78×10^(-3)-4909/T. The activation energy is Q=94.00kJ·mol^(-1). Using the diffusion data of lanthanum and strontium, the effect of the diffusion of the modifier on the incubation period of modification and cooling rate has been discussed.

Characteristics of Faigue Crack Initiation in Ti-5Al-4Sn-2Zr-1Mo-0.7Nd-0.25Si Alloy

The characteristics of fatigue crack initiation in Ti-5AI-4Sn-2Zr1Mo-O.7Nd-O.25Si alloy wereStudied. Two modes Of fatigue crack initiation were found. The Nd-rich phase particles displaybetter resistance to fatigue crack initiation than the matrix at lower stress.

Theoretical prediction of new C–Si alloys in C2/m-20 structure

We study structural,mechanical,and electronic properties of C_（20）,Si_（20） and their alloys（C_（16）Si_4,C_（12）Si_8,C_8Si_（12）,and C_4Si_（16）） in C2/m structure by using density functional theory（DFT） based on first-principles calculations.The obtained elastic constants and the phonon spectra reveal mechanical and dynamic stability.The calculated formation enthalpy shows that the C-Si alloys might exist at a specified high temperature scale.The ratio of BIG and Poisson＇s ratio indicate that these C-Si alloys in C2/m-20 structure are all brittle.The elastic anisotropic properties derived by bulk modulus and shear modulus show slight anisotropy.In addition,the band structures and density of states are also depicted,which reveal that C_（20）,C_（16）Si_4,and Si_（20） are indirect band gap semiconductors,while C_8Si_（12） and C_4Si_（16） are semi-metallic alloys.Notably,a direct band gap semiconductor（C_（12）Si_8） is obtained by doping two indirect band gap semiconductors（C_（20） and Si_（20））.