Solidification of Al alloys under electromagnetic pulses and characterization of the 3D microstructures under synchrotron x-ray tomography

A novel programmable electromagnetic pulse device was developed and used to study the solidification of Al-15 pct Cu and Al-35 pct Cu alloys. The pulsed magnetic fluxes and Lorentz forces generated inside the solidifying melts were simulated using finite element methods, and their effects on the solidification microstructures were characterized using electron microscopy and synchrotron X-ray tomography. Using a discharging voltage of 120 V, a pulsed magnetic field with the peak Lorentz force of ~1.6 N was generated inside the solidifying Al-Cu melts which were showed sufficiently enough to disrupt the growth of the primary Al dendrites and the Al2Cu intermetallic phases. The microstructures exhibit a strong correlation to the characteristics of the applied pulse, forming a periodical pattern that resonates the frequency of the applied electromagnetic field

SURFACE TENSION OF LIQUID TI, V AND THEIR BINARY ALLOYS MEASURED BY ELECTROMAGNETIC LEVITATION

Ti-based alloys are prime candidates for construction materials used for applications in extreme conditions and environments, due to the combination of light weight with high strength, high temperature stability, large corrosion resistance as well as their bio-compatibility. Alongside this rising industrial demand comes an increasing need for precise knowledge of the thermophysical properties of Ti-based alloys, as input for process optimization, phase calculation and atomic modelling. The Ti-Al-V system is currently the most relevant alloy system when it comes to industrial application. While, now, there are some data regarding the thermophysical properties of the Ti-Al [1] side of the system, reliable and systematic data for the Ti-V system are still sparse. One of the major reasons for this is the difficult processability of liquid Ti-V at elevated temperatures, due to the high chemical reactivity of the system. Electromagnetic levitation offers a container-less measurement method for density as well as surface tension without the risk of contamination of the sample by container walls. Density is hereby measured in a shadow graph technique where an expanded laser is directed onto the levitating sample. The molar volume is subsequently obtained from integration over the profile edge curve of the sample shadow captured by a camera on the other side of the sample. Surface tension is measured by means of the oscillating drop technique. Here a high-speed camera records the surface oscillations of the molten droplet and the frequency spectra are evaluated according to the sum formula of Cummings and Blackburn. The obtained density and surface tension data are analyzed by means of different thermodynamic models. In case of the density, it is found that Ti-V obeys the ideal solution model, so no excess volume needs to be considered [2]. The surface tension data can be evaluated using Butler’s thermodynamic model. Again, near perfect agreement is found only with the ideal solution model. Even while utilizing the levitation method, contact between the melt and the surrounding atmosphere cannot completely be prevented. Oxygen, plays a crucial role for metallic melts in most applications, since already small oxygen contents can greatly influence the thermophysical properties of liquid alloys [3]. Therefore, in a second step, the influence of oxygen on the before studied thermophysical properties of the Ti-V system will be reviewed

Electrophysical properties of immiscible liquid conducting alloys

Electroconductivity measurements for liquid In-Te alloys were earned out under high excess pressure through the entire miscibility gap region. On the base of obtained data. 1) Behaviour of the surface dividing fluid phases, so-called meniscus, was investigated for temperature-concentration regions of liquid-liquid coexistence. It is shown that temperature dependency of averaged system properties reflects directly the meniscus appearance and its further displacement; 2) Temperature-time regimes of homogenization are discussed; 3) The liquid-liquid coexistence curve on the phase diagram of the In-Te system and the critical point data are determined from the measurements. The critical indices and amplitudes are evaluated

Thermophysical properties of some liquid binary Mg-based alloys

In this study, some structure-sensitive thermophysical properties, namely, electrical conductivity, thermal conductivity and thermoelectric power of liquid binary alloys Al33.3Mg66.7, Mg47.6Zn52.4 and Mg33.3Zn66.7 (all in wt.%), as the most promising cast alloys to fabricate components for cars, aircraft and other complex engineering products, were investigated. The electrical conductivity and thermoelectric power were measured in a wide temperature range by the four-point contact method. The thermal conductivity was measured by the steady-state concentric cylinder method. The obtained results are compared with literature experimental and calculated data

Density and atomic volume in liquid Al-Fe and Al-Ni binary alloys

Abstract The density of liquid Al – Fe and Al – Ni binary alloys have been determined over a wide temperature range by a non-contact technique combining electromagnetic levitation and optical dilatometry. The temperature and composition dependences of the density are analysed. A negative excess volume correlates with the negative enthalpy of mixing, compound forming ability and chemical short-range ordering in liquid Al – Fe and Al – Ni alloys.</jats:p

Investigation of the miscibility gap region in liquid Ga-Pb alloys

The miscibility gap of the Ga-Pb system has been investigated by different experimental methods and techniques. Viscosity, acoustic and electrical conductivity measurements were carried out through the entire immiscibility region. Possible reasons of revealed discrepancies in the absolute values of the phase separation temperatures are discussed in relation with peculiarities of the experimental methods employed. The shape of the miscibility gap has been analysed

Investigation of the miscibility gap region in liquid Ga-Pb alloys

The miscibility gap of the Ga-Pb system has been investigated by different experimental methods and techniques. Viscosity, acoustic and electrical conductivity measurements were carried out through the entire immiscibility region. Possible reasons of revealed discrepancies in the absolute values of the phase separation temperatures are discussed in relation with peculiarities of the experimental methods employed. The shape of the miscibility gap has been analysed