As-cast Phase Research Articles

Investigating Metal Solidification with X-ray Imaging

In the last two decades, X-ray imaging techniques have been used increasingly to study metal solidification in real-time as, thanks to advances in X-ray sources (synchrotron and laboratory-based) and detector technology, images can now be obtained with spatio-temporal resolutions sufficient to record key phenomena and extract quantitative information, primarily relating to crystal growth. This paper presents an overview of the research conducted at the University of Oxford over the last 6 years as a partner in the UK’s Future Liquid Metal Engineering (LiME) Manufacturing Hub. The focus is on in situ X-ray radiography to investigate the solidification of Al alloys, including the formation of primary α-Al crystals, and the formation and growth of secondary intermetallic phases. Technologically, the thrust is to understand how to control as-cast phases, structures and element distributions, particularly elements associated with recycling, as a means to facilitate greater recirculation of aluminium alloys. We first present studies on refinement of primary α-Al, including extrinsic grain refinement using inoculation and intrinsic refinement based on dendrite fragmentation. Second, we describe studies on intermetallic phase formation and growth, because intermetallic fraction, morphology and distribution are frequently a limiting factor of alloy mechanical properties and recyclability. Then we present some of the latest progress in studying liquid flow during solidification and associated hot tear formation. Finally, future research directions are described.

Effects of Nd and Homogenizing on As-cast Phase of ZM21 Alloy

In this paper, by adding different amounts of magnesium in ZM21 alloy we look into the influence that Trace Nd has on the microstructure and mechanical properties of magnesium alloy cast ZM21 and how homogenizing effects the mechanism of its organization and performance. The results showed Mg-Zn-Nd ternary phase forms in ZM21and the reducing of solute concentration in the solid-liquid interface Zn atomic frontier. As a result, the component avoids being too cold and the nucleation rate declines. That is why the grains become larger.

Al<sub>2</sub>Ca를 함유한 A356 합금에서의 다양한 열처리 조건에 따른 공정 Si 개량화 거동

This study is focused on the effect of Al2Ca as a modifier on eutectic Si modification of A356 alloy. Microstructural observation was carried out for as-cast, as-solution treated and as-aged samples. Solution treatment and aging were performed for 2, 4, 6 and 10 hrs at 540oC and 170oC, respectively. Although A356 alloy, which Al2Ca was added, has no significant difference in as-cast phases with normal A356 alloys, it shows much more modified eutectic Si, grain refinement and improved tensile property both in as-cast and as-heat treated conditions. TGA result shows that Al2Ca added A356 alloy has a certain improvement in oxidation resistance.

Optimization of the technological conditions of producing thin sheets and strips from corrosion-resistant VNS9-Sh steel

The technological conditions of producing thin sheets and strips from corrosion-resistant VNS9-Sh steel are optimized at the stages of casting, deformation, and heat treatment. The effect of the as-cast phase composition of VNS9-Sh steel on the ductility of the metal during cold rolling and on the mechanical properties of the end products in the form of thin sheets and strips is studied. It is shown that, for the required level of the mechanical properties of sheets and strips to be achieved, the magnetization of as-cast steel samples should be J = 3–10 mV on the scale of an IFSS (MKL) device, which corresponds to 1.5–5% martensite in the as-cast steel. It is also shown that the required level of mechanical properties (σu ≥ 1470 MPa, δ ≥ 12%) is achieved after work hardening of 17–35% and that 40–50% deformation martensite and 50–60% cold-worked austenite exist in a ready strip if the magnetization of as-cast steel samples is 3–10 mV and the strip is subjected to work hardening. The effect of tempering temperature in the range 100–450°C is studied to increase the yield strength of the steel in the form of a ready strip at low degrees of cold deformation (17–25%). The increase in the yield strength without a decrease in the ultimate tensile strength is maximal after tempering at 125°C for 1 h due to strain aging processes.

Microstructural Aspects of Second Phases in As-cast and Homogenized 7055 Aluminum Alloy with Different Impurity Contents

The microstructural factors such as type, area fraction, morphology, distribution, and size of second phases in as-cast and homogenized 7055 aluminum alloy and the influence of impurity content variations have been investigated by using optical microscope (OM), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS), and X-ray diffraction (XRD). In as-cast microstructures, the dominant second phases of η [Mg(Al, Cu, Zn)2] with extended solubility of Cu and Al, a small amount of impurity phases of Al7Cu2Fe and Al3Fe with a little solubility of Cu and Si, and trace Mg2Si are identified. The variations of Fe and Si contents have no significant influence on the area fraction of η phases, but the area fraction of Fe-rich phase decreases from 0.231 to 0.102 pct with Fe content decreasing from 0.080 to 0.038 wt pct. Decreasing Fe contents reduces the size parameters of Fe-rich phases and refines their morphology correspondingly. After being homogenized at 753 K (480 °C) for 24 hours, η phases are largely dissolved, but the coarse impurity phases are insoluble. Compared with as-cast microstructures, the area fraction and composition of Fe-rich phases change a little but their morphologies are slightly coarsened.

Microstructure and Phases of As-Cast and Heat-Treated Al-Si-Mg/AlN Composites Prepared by Stir Casting

Al-Si-Mg/AlN composites were prepared by stir casting technique. The amount of AlN added to Al-Si-Mg alloy was from 2 to 10 wt%. As-cast composites were solutionised at 540 °C for 4 h, quenched in warm water, 60 °C then artificially aged at 180 °C for 4 h. The microstructure of Al-Si-Mg matrix alloy contained dendritic α-Al, needle-like Si and very little inter-metallic compounds. As-cast Al-Si-Mg/AlN composites have rounded α-Al phase and needle-like Si where AlN particles dispersed surrounding α-Al. Needle-like Si transformed to spheroid after artificial aging. The size of α-Al phases of heat-treated composites containing 2 and 5 wt% AlN was bigger than that of as-cast composites whereas the heat-treated Al-Si-Mg/10% AlN composite has thin and elongated dendritic α-Al phases, and larger AlN particles.

Structural Characterization of GdNi(1‐x)Cux Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structural characterization of GdNi (1− x) Cu x compounds

Phase transformations and crystal structures in the ternary compounds GdNi (1− x) Cu x were examined with x parameter variation from 0 to 0.2 using X-ray diffraction on powders and single crystals. Depending from the heat treatment two structures were characterized for x = 0.1 depending from the heat treatment: a monoclinic CrB variant for the as-cast phase (space group Pm, Z = 16 , a = 7.619 ( 1 ) , b = 8.543 ( 2 ) , c = 10.990 ( 7 ) Å , β = 112.8 ( 3 ) ° ) and a monoclinic βCaCu variant for the annealed phase (space group P-1, Z = 40 , a = 17.723 ( 9 ) , b = 4.270 ( 2 ) , c = 10.959 ( 3 ) Å , β = 95.22 ( 6 ) ° ).

Influences of hydrostatic pressure during casting and Pd contenton as-cast phase in Zr-Al-Ni-Cu-Pd bulk alloys

The influences of sample diameter (D), Pd content (x), and hydrostatic pressure (P) in a chamber during casting on the structure of as cast Zr65Al7.5Ni10Cu17.5−xPdx(x=10,17.5at.%) bulk alloys were investigated. Zr65Al7.5Ni10Cu7.5Pd10 and Zr65Al7.5Ni10Pd17.5 alloys (D=3mm) cast in a vacuum chamber (P∼4.0×10−3Pa) were mainly of the tetragonal-Zr2Ni equilibrium phase and nanosize icosahedral primary phase, respectively, while the same alloys cast in inert argon gas at atmospheric pressure (P∼0.1MPa) were of the single glassy phase. Due to the higher cooling rate obtained by decreasing the sample diameter (D=2mm) even in the vacuum chamber, the Zr65Al7.5Ni10Pd17.5 alloy was still of the icosahedral phase, while the Zr65Al7.5Ni10Cu7.5Pd10 alloy froze into a single glassy phase. These results indicate that the temperature- and time- transformation curves for the icosahedral and subsequent equilibrium phase formations in the alloy system shifts to a shorter time side with decreasing P, and the pressure sensitivity of the icosahedral phase formation increases with x.

Hydrogen absorption and phase transitions in rapidly quenched LaNi alloys

Several LaNi binary alloys were rapidly quenched by melt spinning. A metastable phase and an uniform Laves phase were obtained. Differences in behaviour were observed between hydrogenation of quenched materials and of as-cast materials whose compositions were identical. The quenched materials, in contrast to the as-cast phases, had a tendency to form amorphous LaNiH alloys. The amorphous alloy was stable, in particular when the ratio La:Ni was 1:2.