Effect of Interdendritic Precipitations on the Mechanical Properties of GBF or EMS Processed Al-Zn-Mg-Cu Alloys

The effects of nanoprecipitations on the mechanical properties of Al-Zn-Mg-Cu alloys after GBF (gas bubbling filtration) and EMS (electromagnetic stirring) casting were investigated. Dendritic cell structures were formed after GBF processing, while globular dendritic structures were nucleated after EMS processing. Equiaxed cell sizes were smaller in the EMS-processed specimens compared to the GBF-processed specimens, confirmed by EBSD (electron backscatter diffraction) analysis. Nanoprecipitations of η′ phases inside of dendrites were observed by TEM (transmission electron microscope), and other Fe-bearing compounds were located in the dendritic boundaries. The yield strength of the T4 and T6 heat-treated specimens was close to 400 MPa and 500 MPa, respectively. Fractographic analysis was performed to investigate the effect of precipitations on tensile fracture.

Modeling of inclusion removal in a tundish by gas bubbling

Inclusion removal from liquid steel by attachment to rising gas bubbles has been reviewed. A mathematical model of inclusion removal by gas bubbling in a tundish has been developed and it is found that minimization of bubble size is critical to enhance removal. However, small bubble formation in a tundish may be problematic as bubble size is controlled by high contact angles between liquid metal and bubble orifice materials. A physical modeling technique has been developed to simulate inclusion removal by tundish bubbling. The influence of a floating particle sink, a flow pattern modifying impact pad, and a bubbler, on particle separation was examined. The influence of gas flow rate, tundish residence time, particle size and bubble size was also examined. Physical modeling confirms that particle separation by gas bubbling in a tundish can be efficient at enhancing inclusion removal. It was also confirmed that relatively small bubbles (<1mm in diameter) are required for maximum separation efficiency.

Modeling of inclusion removal in a tundish by gas bubbling

Inclusion removal from liquid steel by attachment to rising gas bubbles has been reviewed. A mathematical model of inclusion removal by gas bubbling in a tundish has been developed and it is found that minimization of bubble size is critical to enhance removal. However, small bubble formation in a tundish may be problematic as bubble size is controlled by high contact angles between liquid metal and bubble orifice materials. A physical modeling technique has been developed to simulate inclusion removal by tundish bubbling. The influence of a floating particle sink, a flow pattern modifying impact pad, and a bubbler, on particle separation was examined. The influence of gas flow rate, tundish residence time, particle size and bubble size was also examined. Physical modeling confirms that particle separation by gas bubbling in a tundish can be efficient at enhancing inclusion removal. It was also confirmed that relatively small bubbles (<1mm in diameter) are required for maximum separation efficiency.

Effect of Gas Bubbling Filtration Treatment Conditions on Melt Quality of AlSiMgCu Alloy

In this study, the optimal conditions of gas bubbling filtration (GBF) treatment for securing highly-clean molten Al-Si-Mg-Cu alloy were identified. The effects of GBF treatment time and stabilization time on the degree of molten metal cleanliness were examined by measuring melt quality parameters such as density index, bifilm index, porosity, and the amount of dissolved hydrogen [H]. A high melt quality was achieved when GBF treatment was performed on 10 kg melt for more than 10 min (i.e., 1 L gas/kg melt). However, as the stabilization holding time after GBF treatment increased to 10, 20, and 30 min, the melt quality degraded. GBF treatment for 30 min had a similar effect to treatment for 10 min, and the degree of deterioration of melt quality during the stabilization time was also similar. Considering the economics, 10 min GBF treatment and short holding time are required. Observations of the shape and volume of the largest pore suggested the cause of defect formation and confirmed that the volume of the largest pore can be used as an index of the melt quality.

Estimating Inert Gas Bubbling from Simple SCUBA Diving Parameters

Inert gas bubbles frequently occur in SCUBA divers’ vascular systems, eventually leading to decompression accidents. Only in professional settings, dive profiles can be adjusted on individual basis depending on bubble grades detected through ultrasonography. A total of 342 open-circuit air dives following sports diving profiles were assessed using echocardiography. Subsequently, (Eftedal-Brubakk) bubble grades were correlated with dive and individual parameters. Post-dive cardiac bubbles were observed in 47% of all dives and bubble grades were significantly correlated with depth (r=0.46), air consumption (r=0.41), age (r=0.25), dive time (r=0.23), decompression diving (r=0.19), surface time (r=− 0.12). Eftedal-Brubakk categorical bubble grades for sports diving with compressed air can be approximated by bubble grade = (age*50−1 – surface time*150−1+maximum depth*45−1+air consumption*4500−1)2 (units in years, hours, meter, and bar*liter; R2=0.31). Thus, simple dive and individual parameters allow reasonable estimation of especially relevant medium to higher bubble grades for information on relevant decompression stress after ascent. Echo bubble grade 0 is overestimated by the formula derived. However, echo might fail to detect minor bubbling only. The categorical prediction of individual decompression stress with simple bio and dive data should be evaluated further to be developed towards dive computer included automatic ex-post information for decision-making on individual safety measures.

Thermodynamic Modeling of Iron and Nickel Reduction from B2O3-CaO-FeO-NiO Melts

At present, during solving theoretical and applied problems of metallurgical technologies improving, thermodynamic modeling (TDM) methods are widely used to calculate multicomponent and multiphase systems. However, existing methodology TДM are intended for the balance analysis in the ”closed” systems. The authors of [9] proposed a technique that allows, using TDMs, to describe metal reduction processes during gas bubbling of multicomponent oxide melts in approximation to “open” real systems. The applicability of the methods is estimated using the example of joint Nickel and Iron reduction modeling in the B2O3-CaO-FeO-NiO system by Carbon monoxide for ”open” and ”closed” systems. The data obtained comparison for ”open” and ”closed” systems show that the consecutive output of products (gas and metal) from working medium promotes achievement of the best parameters for Nickel extraction to alloy and to its residual content in oxide melt. Using this technique, the TДM process of joint reduction of Nickel and Iron in system B2O3-CaO-FeO-NiO by Carbon monoxide in ”open” system was undertaken at various temperatures in the 1273-1773K interval. Keywords: thermodynamic modeling, ”closed” system, ”open” system, joint reduction, Carbon monoxide, oxide melt, gas bubbling