Microstructure Evolution of Mg96.9Gd2.7Zn0.4 Alloy Containing Multiple Phases Prepared by Spark Plasma Sintering Method

The synergic strengthening of multiple phases is an essential way to achieve high-performance Mg alloys. Herein, Mg-Gd-Zn alloy containing four phases was prepared by rapid solidification (RS) ribbons and spark plasma sintering (SPS). The microstructure of the alloy consisted of α-Mg, nanosized β1 phase particles, lamellar long period stacking ordered (LPSO) phase, and β′ phase precipitates. The microstructural evolution was also investigated. The results show that the metastable β1 phase was formed in the as-cast solidification through rapid solidification, because both Zn atoms and the short holding-time at molten liquid facilitated the formation of the β1 phase. The β1 phase grew from 35.6 to 154 nm during the sintering process. Meanwhile, the fine lamellar LPSO phase was simultaneously formed after the Zn-Gd clusters were generated from the supersaturated solid solution, and the width of the LPSO phase was only in the range of 2–30 nm. The third strengthening phase, the metastable β′ phase, was obtained by aging treatment. The results of hardness testing implied that the hardness of the alloy containing the aforementioned three nanosized strengthening phases significantly improved about 47% to 126 HV compared with that of the as-cast ingot.

Mathematical Model of Melting of Solid Sulfur Particles when Loaded into a Melting Bath

The study solved the problem of determining the technological mode of operation of the device for loading solid lumpy and granulated sulfur into a melting bath with molten liquid sulfur. For this it is necessary to solve two main problems: to determine the method of loading solid sulfur into the melt, to calculate the main design and technological parameters to ensure the required performance of the smelting bath. As a result of experimental studies, the mode of operation of the loading device was obtained, during which the partial melting of the surface of sulfur particles in the surface layer of the melt occurred. This led to the adhesion of particles to each other, the formation of conglomerates having a size that is much larger compared with that of particles of the initial particle size distribution. As a result of this phenomenon, the melting rate and the melting bath were significantly reduced, filled with a solid phase. As a result of the study, a model was developed and the problem of calculating the limiting modes of the loading device operation was solved for preventing solid particles from sticking together.

The Effect of Ca Content on the Formation Behavior of Inclusions in the Heat Affected Zone of Thick High-Strength Low-Alloy Steel Plates after Large Heat Input Weldings

Ca deoxidation has been acknowledged recently as an effective oxide metallurgy technology that improves the toughness of the heat affected zone (HAZ) in high-strength low-alloy (HSLA) steel plates after large heat input welding. This paper describes the effect of Ca concentrations on the formation behavior of the non-metallic inclusions in the HAZs of a series of thick HSLA steel plates after large heat input welding at 400 kJ cm−1. The quantitative statistics on the inclusions show that the Ca addition significantly decreases the quantity of the pure MnS sulfide, but increases that of the complex oxysulfide. The pure MnS sulfide precipitates below the solidus temperature, while the complex oxysulfide forms in the molten liquid, leading to the core (oxide) and shell (sulfide) structure. The Ca addition proportionally improves the HAZ toughness of these thick HSLA steel plates, primarily owing to the positive effect of the complex oxysulfides on the refinement of the HAZ microstructure.

Fabrication of Light Weight Metal Matrix Nanocomposites Using Ultrasonic Cavitation Process: A State of Review

Fabrication of nanocomposites is a highly challenging task because of the particles need to be disseminated across the molten liquid due to broad surface area, poor wettability. Homogeneous dispersion is tough in traditional stirring methods leads to cluster and agglomeration formation in high viscous molten metals. In such attempts, the ultrasonic vibration process exhibits the better dispersion and distribution of nanocomposites with enhanced material properties as compared to other fabrication processes. This paper deals with the fabrication process, probe design and effective process parameters of sonication process to the uniform dispersion of nanoparticles.

Research and Development of a 3D Jet Printer for High-Viscosity Molten Liquids

Micro-droplet jetting manufacture is a new 3D printing technology developed in recent years. Presently, this new technology mainly aims at ejecting a low-viscosity medium. Therefore, a device for ejecting high-viscosity molten liquid is designed by analyzing the injection principle of high-viscosity molten liquid. Initially, the cooling mechanism is designed to overcome the defect that the piezoelectric stacks cannot operate in high-temperature conditions. Thereafter, the mathematical model of the liquid velocity in the nozzle is derived, and the factors influencing injection are verified by Fluent. Subsequently, a prototype of the jet printer is fabricated, and the needle velocity is tested by the laser micrometer; the relationship between voltage difference and the needle velocity is also obtained. The experimental results matched the theoretical model well, showing that the voltage difference, needle radius, nozzle diameter, and taper angle are closely related to the injection performance of the 3D jet printer. By using a needle with a radius of 0.4 mm, a nozzle with a diameter of 50 μm, a taper angle of 90°, a supply pressure of 0.05 Mpa, and a voltage difference of 98 V, a molten liquid with a viscosity of 8000 cps can be ejected with a minimum average diameter of 275 μm, and the variation of the droplet diameter is within ±3.8%.

Effect of Melt Temperature on the Effectiveness of the Grain Refining in Al-Si Castings

The results inferred from the present work show that Al3Ti phase has a strong affinity to react with silicon (Si) in the molten alloy leading to formation of (Al,Si)3Ti phase instead. This reaction is independent of the grain refiner type. The molten liquid temperature would change its morphology from platelets at 750°C into dendritic structure at 950°C. It has also been observed that (Al,Si)3Ti phase platelets precipitate within the α-aluminum dendrites, whereas TiB2 or AlB2 particles are released into the surrounding interdendritic regions. Introduction of the grain refiner, regardless its type, would cause change in the α-aluminum dendrite morphology from an elongated to a more rounded form. The results also reveal that addition of 100 ppm B will reduce the initial grain size by ∼85% which is more than the effect of addition of 0.2%Ti in the form of Al-10%Ti (about 65%). Elimination of undercooling is important to obtain the maximum grain refining effect.