Zhou Yaohe

Elimination of Fe in Al-Si cast alloy scrap by electromagnetic filtration

Fe in Al-Si cast alloy scrap melt was eliminated by electromagnetic filtration of primary iron-rich phases, which were formed by adding Mn in the melt. The principle of electromagnetic filtration is that the electromagnetic force scarcely acts on the primary iron-rich phases due to its low electric conductivity as compared to the melt. As a result, a repulsive force exerts on the primary iron-rich phases to move them in the direction opposite to that of the electromagnetic force. It has been found that the forming temperature of primary iron-rich phase increases gradually with the increment of ratio of Mn to Fe (Mn/Fe), and that the iron-rich phases are formed as primary phases, they appear as massive particles with size of 30–80 μm. Experimental results show that the primary iron-rich phases are separated from Al-Si alloy scrap melt and are collected in the electromagnetic separation chamber. Fe content in the cast ingot decreases from 1.20% to 0.41% by electromagnetic filtration, which can meet the demand for casting. This new technique is highly efficient and available for continuous processing compared with natural settling and filtration methods. It offers a possibility for recycling high quality aluminum alloys.

An in situ surface composite produced by electromagnetic force

Because of the different conductivities between the primary phase (low electric conductivity) and the metal melt, electromagnetic force (EMF) scarcely acts on the primary phase. Thus, the primary phase is moved in the direction opposite to that of the EMF when the metal melt with primary phase solidifies under an electromagnetic field. Based on this, a new method for production of in situ surface composites by EMF is proposed. This method has the advantages of being simple and inexpensive, and therefore, has bright prospects for application.

Formation mechanism of anomalous eutectics in highly undercooled Ag-39.9 at%Cu alloys

This paper investigates the solidification behaviour of the Ag–Cu eutectic alloy melt undercooled up to 100 K. It is revealed that lamellar eutectics grow in a dendritic form in the Ag–Cu eutectic melt with undercooling equal to or greater than 76 K. As undercooling increases, the remelted fraction of the primary eutectics during recalescence rises. The severe remelting and the subsequent ripening of the primary eutectic dendrites lead to the formation of anomalous eutectics.

Effect of interface kinetics on the eutectic growth

The atom-attachment kinetics at the solid-liquid interface was incorporated into the eutectic growth theory. The dependence of kinetic undercooling on the structure of the eutectic phases was investigated. Due to the introduction of the kinetic effect, the coupled eutectic growth can proceed in a wider undercooling range, but the growth velocity decreases while the minimum eutectic lamellar spacing remains unchanged. The proportion of kinetic undercooling to the total undercooling is dependent not only on the growth velocity, but also on the phase diagram. Calculation indicated that the proportion decreases as the crystallization temperature range of single eutectic phase at the eutectic composition enlarges.

Free-volume evolution of glassy Zr65Al7.5Ni10Cu17.5 during inhomogeneous deformation

Free-volume evolutions of the as-cast and pre-annealed Zr65Al7.5Ni10Cu17.5 metallic glasses during cold-rolling were investigated using differential scanning calorimetry. As deformation degree increases, free volume in the glasses always increases first and then saturates above a critical strain, while the structure remains completely amorphous. The glass with less initial free volume possesses a higher increase rate of free-volume content during deformation, and as a result the free-volume contents of all the glasses approach each other at higher strains. Coalescence of free volume in shear bands into nanovoids is proposed to be responsible for the saturation of free-volume content at high strains.

Effect of the repeated melting of mother ingot on the stability of icosahedral phase precipitated from Zr-Al-Ni-Cu-Ag glass

Differential scanning calorimetry (DSC) shows that repeated melting of mother ingot improves the stability of icosahedral phase (I-phase) precipitated from Zr65Al7.5Ni10Cu12.5Ag5 glass. The Kissinger analysis of crystallization implies that the effective activation energies for the precipitation of I-phase and its decomposition considerably increases due to the repeated melting of mother ingot. Repeated melting of mother ingot refines ingot microstructure. Because of structure heredity, the size of the short-range orders (SROs) in the glassy alloy produced from the mother ingot with finer microstructure becomes smaller, which makes the rearrangement of atoms more clifficult, and the I-phase more stable.

Glass Forming Ability of Metallic Glasses Evaluated by a New Criterion

The glass-forming ability (GFA) of Cu–Zr binary alloys is evaluated using the existing criteria based on calori-metric parameters, and poor relations are found. Therefore, another parameter Trk defined as Tk/Tl, in which Tk is the Kauzmann temperature and Tl the equilibrium liquidus temperature, is proposed. It exhibits good agreements with the experimental data of the Cu–Zr system and other representative bulk metallic glass formers so long as classifying them into strong or fragile category. It is suggested that kinetic effects are irrelevantly incorporated in the GFA analysis in the previous work.

Magnetohydrodynamic study of electromagnetic separation of nonmetallic inclusions from aluminum melt

AbstractMagnetohydrodynamic flow around the nonmetallic inclusions in aluminum melt and the force exerted on the inclusions were explored by dimensional analysis and numerical calculations. Dimensional analysis shows that the invariant

Purification technology of molten aluminum

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