Kinetics of Al Evaporation from Liquid U-Al Alloys in Vacuum Induction Melting

A research on kinetics of Al evaporation from liquid U—Al alloys was made in a vacuum induction melting（VIM） furnace at 1673—1843 K.The evaporation rate of Al was found to be first order with respect to Al content in the melt.The overall mass transfer coefficient of Al was determined and it was found that the evaporation rate of Al increased with increasing temperatures.The apparent activation energy of Al evaporation at 1673-1843 K was 171.5 kJ mol-1.The value of mass transfer coefficient of Al in the liquid phase was estimated to be 3.77 × 10-6,7.41×10-6,and 9.40 × 10-6m s-1at 1673,1753,and 1843 K,respectively.Meanwhile,rate determining steps were discussed and it was concluded that the evaporation rate of Al is mainly controlled by liquid phase mass transfer.

Correlation between liquid structure and γ_2-phase precipitation of Cu-Al-Ni shape memory alloys

Cu 71Al 25Ni 4 (mole fraction,%) shape memory alloy ribbons exhibit a good shape memory effect, which were prepared by melt-spinning technique. The microstructure of the as-spun ribbons was identified by D/Max-rA X-ray diffractometer. The order degree of martensite increases with decreasing liquid quenching temperature at the same quenching rate. The liquid structure of Cu 75Al 25 and Cu 71Al 25Ni 4 was investigated using X-ray diffraction method. The distinct pre-peaks have been found in front of main peaks of the structure factors. The pre-peak increases intensity with decreasing temperature or adding Ni. Gaussian peaks decomposing radial distribution function (RDF) indicated that Cu-Al distance is anomalously short. These results suggest that a strong interaction between Cu and Al is favorable to form β-phase-like clusters, which leads to chemical medium-range ordering in melt. This promotes formation of order martensite and suppresses γ 2-phase precipitation.

Surface pretreatment of Mg alloys prior to Al electroplating in TMPAC-AlCl_3 ionic liquids

It is difficult to directly electroplate Al on Mg alloys. The effects of pretreatment parameters on the corrosion resistance of films obtained on AZ31 Mg alloy surface were studied by using potentiodynamic polarization curves, to produce a compact interfacial layer as zinc-immersion deposition. After the substrate was pretreated under optimized conditions, aluminum was electrodeposited on AZ31 from TMPAC-AlCl3 room temperature ionic liquids. The depositions were characterized by scanning electron microscope equipped with energy dispersion X-ray. The results show that the traditional pretreatment of Mg alloys was successfully used for the Al-electroplating process from TMPAC-AlCl3 ionic liquids. The entire procedure includes alkaline cleaning, chemical pickling, surface activation （400 mL/L HF acid, 10 min）, zinc-immersion （20 min） and anhydrous treatment. A relatively compact zinc-immersion film was prepared on the substrate surface. A silvery-colored satin aluminum deposition was obtained on AZ31 from TMPAC-AlCl3 using direct current plating.

Electrodeposition of aluminium and aluminium-copper alloys from a room temperature ionic liquid electrolyte containing aluminium chloride and triethylamine hydrochloride

The electrodeposition of A1 and A1-Cu binary alloys on to gold substrates from a room temperature ionic liquid electrolyte containing A1C13-EtaNHC1 was studied. The electrochemical behavior of the electrolyte and the mechanism of deposition were investigated through cyclic voltammetry （CV）, and the properties of deposits obtained were assessed by scanning electron microscopy with energy dispersive X-ray spectroscopy （SEM-EDS） and X-ray diffraction （XRD）. A1 of 70μm in thickness and an A1-Cu alloy of 30μm in thickness with 8at% copper were deposited from the electrolyte. SEM images of the deposits indicate that the A1 deposit was smooth and uniform, whereas the Al-Cu deposit was nodular. The average crystalline size, as determined by XRD patterns, was found to be （30±5） and （29±5） nm, respectively, for A1 and A1-Cu alloys. Potentiodynamic polarization （Tafel plots） and electrochemical impedance spectroscopic （EIS） measurements showed that Al-Cu alloys are more corrosion resistant than Al.

Characterization of surface liquid segregation in SSM-HPDC aluminium alloys 7075,2024,6082 and A201

The surface liquid segregation(SLS) phenomenon in semi-solid metal-high pressure die casting(SSM-HPDC) plates of 7075,2024,6082 and A201 was investigated by different techniques.Depth profiles were determined by firstly measuring the chemical composition of the surface of the plates using a Thermo Quantris optical emission spectrometer(OES).Material was then removed by a grinding process followed by measurement of the amount of material removed and chemical analysis.Chemical profiles of the main alloying elements were plotted for the cross-section of the plates in the as-cast and T6(after solution treatment) temper conditions.Vickers hardness profiles from the surface to the centre of the plates were determined.Metallographic samples of cross-sections of the castings were prepared and evaluated using a scanning electron microscope.The results show that surface liquid segregation in SSM-HPDC alloys causes significant differences in properties between the surface and the bulk of these castings in both the F and T6 temper conditions.

Effect of Zn/Mg/Cu Additions on Hot Cracking Tendency and Performances of Al-Cu-Mg-Zn Alloys for Liquid Forging

During the process of liquid forging, a host of hot cracking defects were found in the Al-CuMg-Zn aluminum alloy. Therefore, mechanical tests and analyses by optical microscope, scanning electron microscope, and X-ray diffraction were performed to research the influences of zinc, magnesium, and copper(three main alloying elements) on hot cracking tendency and mechanical properties. It was concluded that all the three alloying elements exerted different effects on the performances of newly designed alloys. And the impact of microstructures on properties of alloys was stronger than that of solution strengthening. Among new alloys, Al-5 Cu-4.5 Mg-2.5 Zn alloy shows better properties as follows: σb=327 MPa, δ=2.7%, HB=107 N/mm^2, and HCS=40.

PREDICTION OF THE MIXING ENTHALPIES OF BINARY LIQUID ALLOYS BY MOLECULAR INTERACTION VOLUME MODEL

The mixing enthalpies of 23 binary liquid alloys are calculated by molecular interaction volume model （MIVM）, which is a two-parameter model with the partial molar infinite dilute mixing enthalpies. The predicted values are in agreement with the experimental data and then indicate that the model is reliable and convenient.

Effects of Ni addition on liquid phase separation and giant magnetoresistance of Cu-Co alloys

The effects of Ni addition on the liquid phase separation and giant magnetoresi stance (GMR) of Cu Co alloys were discussed. The results reveal that Ni additio n can partially restrain the liquid phase separation of Cu Co alloys, resultin g in a decrease of volume fraction for the Co rich particles separated from the liquid phase and in refined microstructures. The composition analyses indicate t hat Ni is dissolved in both the Co rich and the Cu rich phases, but Ni content in the Co rich phase is much higher than that in the Cu matrix. At the same ti me, Ni addition enhance the solubility between Cu and Co, especially Cu in Co s olid solution. Ni alloying into Cu Co alloys can fully prevent the liquid phase separation during melt spinning, which is very beneficial to improve GMR of Cu Co alloys.

Surface and transport properties of Cu-Sn-Ti liquid alloys

The lack of experimental data and / or limited experimental information concerning both surface and transport properties of liquid alloys often require the prediction of these quantities. An attempt has been made to link the thermophysical properties of a ternary Cu-Sn-Ti system and its binary Cu-Sn, Cu-Ti and SnoTi subsystems with the bulk through the study of the concentration dependence of various thermodynamic, structural, surface and dynamic properties in the frame of the statistical mechanical theory in conjunction with the quasi-lattice theory （QLT）. This formalism provides valuable qualitative insight into mixing processes that occur in molten alloys.

Enthalpy of Mixing of Liquid Al-Cr and Cr-Ni Alloys

The partial and the integral enthalpies of mixing of liquid Al-Cr and Ni-Cr binary alloys have been determined by high temperature isoperibolic calorimetry at 1723±5 K and 1729±5 K, respectively. The results were analytically described by the thermodynamically adapted power series (TAPS). The enthalpies of mixing values for both binary liquid melts are small and negative and in good agreement with the available literature data. Minima of the mixing enthalpies of liquid Al-Cr and Ni-Cr alloys are -7.0 kJ·mol-1 at 46 at. pct Cr and -3.0 kJ·mol-1 at 37 at. pct Cr, respectively.

INFLUENCES OF TRACE ADDITIONS OF STRONTIUM AND PHOSPHORUS ON ELECTRICAL RESISTIVITY AND VISCOSITY OF LIQUID Al-Si ALLOYS

The electrical resistivity and viscosity of liquid hypoeutectic Al 7%Si and hypereutectic Al 18%Si alloys, and the influences of trace strontium and phosphorus on them were investigated. The trace additions of the two elements increase the electrical resistivity. At the precipitation temperatures of primary phase, the electrical resistivity exhibits a discontinuity for all experimental Al Si alloys. In the discontinuity the electrical resistivity, respectively, decreases and increases abruptly for Al 7%Si alloys and Al 18%Si alloys. Phosphorus and strontium both have some effects on the discontinuity temperature and the jump value of electrical resistivity of Al 18%Si alloys, but strontium hardly has effect on them in Al 7%Si alloys. The trace additions of strontium and phosphorus increase the viscosity of the experimental alloy.

PREDICTION ON THE THERMODYNAMIC PROPERTIES OF TERNARY LIQUID ALLOYS BY MODIFIED COORDINATION EQUATION

The coordination numbers in the Molecular Interaction Volume Model can be calcu-lated from the common physical quantities of pure matters.A significant advantage ofthe model lies in its ability to predict the thermodynamic properties of ternary liqmdalloys using only the binary infinite dilute activity coefficients,and the predicted values are in good agreement with the experimental data of ternary liquid alloys,whichshows that the model is reliable,convenient and economic.

Liquid State Undercoolability and Crystal Growth Kinetics of Ternary Ni-Cu-Sn Alloys

The liquid state undercoolability and crystal growth kinetics of ternary Ni-5%Cu-5%Sn and Ni-10%Cu-10%Sn alloys are investigated by the glass fluxing method. In these two alloys, experimental maximum undercoolings of 304 K （0.18TL ） and 286K （0.17TL ） are achieved and the dendritic growth velocities attain 39.8 and 25.1 m/s, respectively. The transition of morphology from coarse dendrite into equiaxed structure occurs and the grain size of the a （Ni） phase decreases remarkably when the undercooling increases. Both the lattice constant and microhardness increase obviously with the enhancement of undercooling. The enrichment of Cu and Sn solute contents reduces the dendritic growth velocity, while enhances the lattice constant and microhardness of a （Ni） phase.

Application of the Embedded-atom Method to Liquid Binary Cu-Ni Alloys

A simple analytic embedded-atom model of monoatoms that includes more than nearest neighbours has been extended to study properties of binary liquid Cu-Ni alloys, here the two-body potential between different species of atoms is taken as a function of the two-body potential for the pure metals with a unique form which yields alloy models with the same invariance to electron density transformations as monoatomic models. Faber-Ziman structure factors have been computed by molecular dynamics simulation on the base of this model. The results are in good agreement with experimental data given by Waseda, thus supporting the overall validity of the approach, especially for cross potential of Cu-Ni pair. Further, a detailed description of structure of binary liquid Cu-Ni alloys with different compositions have been performed using pair analysis and bond orientational order method etc., and then the chemical short range order has also been examined to reveal the structural characterization.

Effect of liquid-liquid structure transition on solidification of Sn-Bi alloys

The effect of the liquid-liquid structure transition(L-LST) on the solidification behaviors and morphologies of Sn-Bi alloys was studied further. The results show that the undercooling of the primary and eutectic phase increases and the microstructure becomes finer after solidifying from the melt experiencing the L-LST. In the meantime, in hypoeutectic alloy, when solidifying from the melt experiencing the L-LST, the morphology of primary phase changes from the fir-tree crystal into the equiaxed crystal, and less primary phase and more eutectic structure are observed. Moreover, in eutectic alloy, the spacing of eutectic phase decreases markedly. These investigations would be beneficial to further exploration of the correlation between the melt structure and the micro mechanism of solidification.

Liquid phase separation of Cu-Cr alloys during rapid cooling

The ribbons of Cu-Cr alloys with high Cr content (15%- 35%, mass fraction) were prepared by rapid solidification. The microstructures of solidified samples were analyzed by scanning electron microscopy and transmission electron microscopy. The results reveal that a representative liquid phase separation microstructures are observed in Cu75Cr25 ribbons solidified at a cooling rate of about 104K/s. The liquid phase separation is not restrained when the cooling rate is enhanced to about 107K/s. However, the size of Cr particles solidified from Cr-rich liquid or Cr-rich regions in alloy melts could be refined by increasing the cooling rates. The size of Cr particles increases with increasing Cr contents when the ribbons contain 15% to 35%Cr.

Liquid-liquid phase separation in highly undercooled Ni-Pb hypermonotectic alloys

Liquid-liquid phase separation in the undercooled Ni-20%Pb(mole fraction, the same below if not mentioned) hypermonotectic melts was investigated by the observation of the water-quenched structure and DTA analysis. The results indicate that the number of spherical cells in the water-quenched microstructure increases with dropping temperature, and the cells gather and grow up obviously. The spherical cell origins from L1 phase separated from homogeneous melt, and is the product of monotectic reaction. Both results of the water-quenched structures and DTA analysis prove that liquid phase separation still occurs in the highly undercooled Ni-Pb hypermonotectic alloy melts, and liquid phase separation in the immiscible gap can not be fully inhibited by high undercooling and rapid solidification.

Prediction of Surface Tensions of Pure Liquid Metals and Alloys

The surface tensions of pure liquid metals were estimated by using the artificial neural network method. Based on Butler's equation the surface tensions of some liquid Sn-, Ag-, Cu-based binary alloys were calculated from surface tensions of pure components and thermodynamic parameters of liquid alloys using a well designed computer program with C++ language, named STCBE. The agreement between calculated values and experimental data was excellent. The surface tensions of binary liquid Cu-RE(RE: Ce, Pr, Nd) alloys at 1400 K were predicted therewith.

Experimental investigation of the normal spectral emissivity and other thermophysical properties of pulse-heated Ni-Ti and Au-Ni alloys into the liquid phase

In a previous paper it was shown that the normal spectral emissivity at 684.5 nm of a binary alloy can be lower than that of the pure constituent components. For the actual probes it was found that the observed values of normal spectral emissivity of the alloys are in between or higher than those of the pure constituent components. Experiments were conducted on the alloy systems Ni-Ti and Au-Ni. Their emissivity as well as electrical resistivity and enthalpy as a function of temperature is presented.

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.