Effect of the Mg3N2 Sub-Micron Particle on the Grain Refinement of AZ80 Alloy

AZ80 alloy has been widely used to produce high performance Mg casting and wrought parts for high-end applications due to its high mechanical properties and deformation ability. However, at least two important issues still need to be solved in order to further improve its mechanical properties and deformation ability. Firstly, the grain size of α-Mg in AZ80 alloy is relatively large (more than 1000 µm) due to a lack of efficient grain refinement methodologies. Secondly, the size of the eutectic Mg17Al12 phase is also large and the distribution of the eutectic Mg17Al12 phase is continuous, which is very harmful for the mechanical properties, in particular to elongation. In this paper, these two important issues are investigated by adding Mg3N2 sub-micron particle into AZ80 alloy and thereby refining the α-Mg and the eutectic Mg17Al12 phase. Firstly, the Mg3N2 sub-micron particle was directly added into AZ80 alloy by using mechanically stirring in the semi-solid state, subsequently the melting temperature was increased above the liquidous temperature, and finally the melting was casted in the liquid state. It was found that the grain size of α-Mg can be refined from 883.8 µm to 169.9 µm. More importantly, the eutectic Mg17Al12 phase was also refined and the distribution became discontinuous. It should be noted that directly adding the Mg3N2 sub-micron particle into AZ80 alloy leads to a great loss of the Mg3N2 sub-micron particle due to the weak wetting behavior between the Mg3N2 sub-micron particle and Mg melt. The second methodology through mixing Mg3N2 sub-micron particles with AZ91 chips using a twin extruder was also used to prepare AZ91 master alloy with 3wt.% Mg3N2 sub-micron particle, which was subsequently added into AZ80 alloy in the liquid state. In this way, a significant grain refinement of α-Mg and a simultaneous refinement of the eutectic Mg17Al12 phase in AZ80 alloy was also achieved. The grain size of α-Mg can be refined from 883.8 µm to 325.9 µm. However, no significant grain refinement by using UST was observed. Instead, the grain size increases from 325.9 µm to 448.6 µm, indicating that the Mg3N2 sub-micron particle may lose its grain refinement potency due to possible aggregation and clustering. This paper provides an efficient and simple methodology for the grain refinement of α-Mg and the simultaneous refinement of the eutectic Mg17Al12 phase in AZ80 alloy.

Preparation of Semi-Solid 357.0 Slurries with Different α-Al Phase Features by Solidification from Full Liquid State and Remelting

The characteristics of the solid phase, namely the volume fraction, particle size, and morphology, are dominant variables that can determine the viscosity of the semi-solid slurry. However, particle size and morphology were always being ignored and the solid fraction was simply determined using the temperature in the conventional power-law viscosity, resulting in a disagreement in the viscosity values in different researches. To make the power-law viscosity model more accurate for predicting the filling process of semi-solid die casting, it is essential to modify this viscosity model based on particle characteristics. Therefore, there is a fundamental demand to prepare semi-solid slurries with different α-Al phase features at first. This is achieved in this study by two kinds of heat history controlling methods: remelting and solidification, which can get slurries with spherical structure and dendric structure, respectively. The semi-solid 357.0 slurries with 0.11-0.43 solid fraction, 137-182μm particle size, and 0.81-0.90 shape factor were prepared in the remelting process, while dendritic structures (shape factor<0.5) with 0.1 and 0.3 solid fractions were obtained by solidification controlling from the full liquid state. Besides, the effect of parameters on the evolution of the α-Al phase has been discussed. These slurries with different solid features will be further used to quantify the influence of primary phase characteristics on rheological behavior and make the power-law viscosity model more accurate for simulation.

Porosity Formation in Thin Welded Joints of Al–MG–LI Alloys

This work is about the study of the correlation of pore formation in welded joints of Al–MG–LI alloy with zirconium additives with the state of the base metal, thermal vacuum treatment, and welding technologies MIG and EBW. Metallographic analysis has been carried out, the phase composition of the alloy and weld metal has been investigated, and thermal cycles of welding have been calculated, allowing to estimate the residence time of metal in the alloying zone and weld metal in the liquid state. The nature of the allocation of strengthening fine-dispersed phases in the welded joints of the alloy has been determined. The regularity and character of pore formation in welded joints depending on the applicable thermal vacuum treatment (TVT) and welding technology have been revealed. It was established that TVT with subsequent hardening and aging has no effect on the phase composition of the alloy. However, this type of treatment contributes to the formation of a more homogeneous and uniform nature of the separation of fine-dispersed strengthening phases. It was revealed that the MIG technology (metal with and without TVT) is characterized by a large length of the fusion zone, the high residence time of metal in the fusion zone and weld metal in the liquid state, and the formation of pores. Phase formation in the temperature range of the beginning and end of the alloy crystallization occurs not only in the weld at the final stage of crystallization but also in the fusion zone, which may induce pore formation, whereas EBW welding shows the opposite trend and no pores. It was found that EBW technology prevents pore formation and makes it possible to obtain welded joints of 1420 Al alloys of the required quality.

Liquid-State Volumetric Properties of a Set of Alcohols with Up to Five Carbon Atoms

This work provides density data (~1300 values) of 14 alcohols with up to five carbon atoms at p ∈ [0.1–40] MPa and T ∈ [278–358] K. The information obtained is modeled with a convenient reformulation of the Tait equation from which the volumetric coefficients, α and β, are derived both analytically and numerically. The general EoS containing α and β is also used for checking the consistency of the hypothesis on the invariability of the cited thermophysic parameters. The results obtained can be considered reliable because of the low estimated errors between the experimental data and those of the literature, which are below 0.4% for volume, while for the volumetric coefficients there is always a reference diverging 10%, or less, from the proposed model estimations. By including the averages of α and β into the general state of equation the errors increase, being <15%, compared to those based on the Tait equation. Hence, the assumption on the stability of the volumetric coefficients in this working interval is sufficient to make rough estimations of the molar volume of the selected alcohols.

J-driven Dynamic Nuclear Polarization for sensitizing high field solution state NMR

Dynamic nuclear polarization (DNP) is widely used to enhance solid state nuclear magnetic resonance (NMR) sensitivity. Its efficiency as a generic signal-enhancing approach for liquid state NMR, however, decays rapidly...

Rheological characteristics of steel in continuous roll casting-rolling

Problems. In the process of obtaining a strip in a casting and rolling device, the question arises of combining the process of hot rolling of the solidified material and the process of crystallization of the liquid melt. This makes it possible to implement an efficient technology for producing thin-sheet products. Purpose of the study. Determination of rational parameters for performing mathematical modeling of material behavior during roll casting requires clearly defined recommendations. The material for the rolling process is steel. The starting material was used in solid, solid-liquid and liquid states. Implementation technique. The analysis of the properties of steel was carried out on the basis of the results of experiments obtained at the Physico-Technological Institute of Metals and Alloys of the National Academy of Sciences of Ukraine. To analyze the rheological properties of steel, the dependences of the yield stress for alloyed and carbon steels were used in a certain temperature range. The selected temperature range includes solidus and solid-liquid state of steel, located above 0.8 melting point. Research results. Based on the research results, the analysis of the rheological properties of steel in solid, solid-liquid and liquid states during continuous casting-rolling on rolls was carried out. The use of the obtained dependencies makes it possible to perform mathematical modeling of the deformation and hydrodynamics of the material during continuous casting-rolling of steel strips using roll casting-rolling devices. Conclusions. The constructed dependences, together with studies of the viscosity of steel in the liquid state and the resistance of steel to deformation in the solid state, most fully describe the rheological properties of steels during casting-deformation processes. The obtained dependences will make it possible to implement an ultra-efficient technology for producing thin-sheet rolled products.

Methods of manufacture and innovations in steel aerosol cans’ production

The production of aerosols has had a significant position in the industry for many years. We use aerosol products almost every day for very different purposes. The aerosol industry growth very dynamically, the shapes and the materials of the containers are changing, but the main principle remains the same – “aerosol dispenser shall mean any non-reusable container made of metal, glass or plastic and containing a gas compressed, liquefied or dissolved under pressure, with or without a liquid, paste or powder, and fitted with a release device allowing the contents to be ejected as solid or liquid particles in suspension in a gas, as a foam, paste or powder or in a liquid state”. The purpose of this article is to present the methods of aerosols’ steel can manufacture together with the changes that have been made over the last century. Since the beginning of aerosol industry metal is the main material from which aerosol containers are made of, and steel is one of the most popular raw materials, the main law requirements regarding aerosol containers made of steel will be analysed. As the consequence of these analyses, the future possible development directions will be shown.